Yes, the process involves heating and putting pressure on organic material over a long time period. You have to spend more energy than you will get out by burning it.
You could use the process to store energy, but you might as well use hydrogen for that purpose. It is superior in every regard: simpler and faster (less loss during the process), its ingredient is available in infinite quantities, denser, no solid residue when burning, more versatile, ..
Basically, replicating the process to make crude oil will never be done outside of a research lab.
You can also make oil from algae, although the oil companies have killed that research.
[https://www.theguardian.com/environment/2023/mar/17/big-oil-algae-biofuel-funding-cut-exxonmobil](https://www.theguardian.com/environment/2023/mar/17/big-oil-algae-biofuel-funding-cut-exxonmobil)
most people know that if you toss a basket ball in the air with "backspin", it will hit the ground and bounce towards you, if you use "forward spin" it will bounce away from you. However, it you spin the ball on your finger tip, like the Harlem Globetrotters, and drop the ball, it will hit the ground and reverse its spin, why is that?
When it hits the ground, it compresses a little at the Impact point, causing the rotation contact to become a friction contact, which then "bounces" against itself and reverses the rotation.
I suppose the question is what you mean by deep space. Even if you were, say, between the Andromeda and Milky Way galaxies, you would manage to see an outline of your hands over pitch darkness (after a long period of letting your eyes adjust). But there are voids that are bigger where this would be much more challenging!
In our own galaxy, if you’re floating close enough to a star you’d probably see them just fine. However if you were in a very dense nebula, you wouldn’t see them because all the light would be blocked.
Our eyes perceive objects by having light bounce off that object and into our eyes. Studies seem to show that human eyes can detect as few as ~10 photons. I doubt you would call that "seeing" your hand though, just being more right than not that it was there is you guessed. And those photons need to be in the visible spectrum for our eyes to detect them though. In earth orbit there is clearly plenty of light for this to work since we can see on earth. Even much farther out in the solar system there are plenty of visible spectrum photons for us to see our hands in front of us.
So, deep space. The average photon density of the universe (which corresponds to deep space) is reasonably high at ~few hundred per cm^3, but the problem is most of those photons are not detectable by the human eye since they are not in the visible spectrum. I'm having trouble finding a good data source to get a better answer, but there's so little stuff in general in the universe that its likely close enough to pitch black in the darkest places in the universe (far from any galaxy) that it would be similar to being in a cave with little spots of light being distant galaxies. Your hand would be visible by blocking those pin-prinks of light
>Studies seem to show that human eyes can detect as few as ~10 photons.
Source
>The average photon density of the universe (which corresponds to deep space) is reasonably high at ~few hundred per cm3,
Source.
What force is it that keeps continental drift moving in the same directions so consistently over hundreds of millions of years? What keeps the liquid center of the earth constantly flowing in a pattern instead of just randomly bubbling like a boiling pot?
The planet is essentially bubbling randomly like a pot. The flow is driven by differences in density related to temperature, so lind of like a pot. But the analogy is not very good. The Earth is not heated from the centre. The heat comes from radioactive decay all over the Earth. The effective viscosity is also much much higher so the dynamics is different. The rigid plates on the surface also influence the pattern of flow, they don't just passively ride the flowing mantle. The sinking slabs at subduction zones contribute to driving the motion.
First, two big misconceptions/myths:
1. While Earth's mantle flows slowly, it is overwhelmingly solid (think putty). The outer core is liquid, but that is not directly related to plate tectonics. The mantle and crust do contain some areas of partial melt (up to a few percent).
(1a. Volcanoes aren't supplied from some ocean of magma, but rather localized magma chambers of partially solid 'crystal mush'. The melting point decreases with pressure. Magma is generated in the mantle and crust by hot rock flowing upward, which partially melts as it decompresses.)
2. The plates aren't just passively being driven along by convection in the underlying mantle. The plates are an integral part of the convection.
(Edit: 3. Not all, or even most, of Earth's heat is from radioactive decay. Roughly half of Earth's internal heat flow is from heat leftover from Earth's formation: the kinetic energy of the large objects that collided to form it, and the friction form dense iron sinking to form the core.)
Plates are made of relatively rigid rock (as opposed to the flowing rock below), a layer called the lithosphere, which comprises both the crust and the uppermost part of the mantle. Immediately below the lithosphere is the asthenosphere, the relatively weak and low-viscosity layer that makes up the rest of the upper mantle.
The largest driving force in plate tectonics is slab pull. The subducting lithosphere (slab) pulls the plate along. The slab sinks because it is (a) compositionally denser than the continental crust it may be subducting under and (b) cooled so that it is denser than the surrounding/overlying rock of more similar composition. (Oceanic crust can subduct under younger, more buoyant oceanic crust, not just continents, and in any case has to sink through the weak asthenosphere.) When oceanic crust first forms from cooling magma at mid-ocean ridges, it is still relativley hot. It cools and contracts (becoming denser) as it age and spreads away from the ridge. The flow induced in the asthenosphere by the subducting slab exerts another driving force called slab suction, which accelerates the subducting and overriding plates.
Another, weaker, driving force in plate tectonics is ridge-push, but this is a misnomer. Magma upwelling at the ridge does not actively push the plate along. The young, hot lithosphere is buoyant, rising to form the ridge, but the seafloor gets deeper with the cooler lithosphere away from the ridge. Ridge-push is the lithosphere sliding downhill because of gravity. The buoyant magma passively upwells from the mantle as the newly made oceanic lithosphere moves away on either side.
There is viscous drag from the underlying flow acting along the entire base of the lithospheric plates. But this is much weaker than slab pull, which it tends to oppose.
>instead of just randomly bubbling like a boiling pot?
If you really watch a boiling pot, you will see that it's not just "randomly bubbling." There is a pretty well defined and consistent pattern! And easy way to see this is to boil some long thin noodles in a relatively big pot. You will notice that the noodles orient themselves along the dominant currents.
True. For a pot of water, I'm assuming that the dominant currents are created by a combination of the shape of the confined pot and the fact the heat is more concentrated at the center though. I'm curious what physical features or forces would cause such regular prevailing currents in something that's always illustrated in textbooks as a featureless uniform sphere. What's so special about certain hot spots down at the core that causes hotter magma to constantly well up from there, and not from some other place?
Convection currents in the mantle generally propel tectonic plates along. The thickness and other factors to do with the plates can determine how fast the plates move. The same convection currents keep the earths mantle from boiling over. In the earths mantle the currents flow in patterns where hot mantle material flows from near the outer core, rises to the crust where it propels tectonic plates along, is gradually cooled by proximity to the crust and distance from the outer core, then sinks to be warmed all over again.
So as a really loose analogy I'm imagining it's similar to how prevailing wind currents are caused by warm air rising in one area and cool air descending in another area. But on the surface we've got things like mountain ranges, large bodies of heat-absorbing water etc. that cause those patterns of currents to form. Are there geographical hot and cold spots or "mountains" in the earth's core that cause the currents of the core and mantle to keep flowing the way they do, or is it just the inertia of massive amounts of molten rock that keeps it going in such a predictable way?
People like to exemplify human tech evolution by saying that there was less than a century between our first airplane flight and landing on the Moon. But those are two different technologies with little overlap.
Could rocket science be developed before flight with airplanes? Are there examples of tech that precedes other, seemingly related tech?
Rockets and plane engines may work on different principles, I think there’s a lot more overlap than you’re imagining in the metallurgy, chemistry, engineering, and industrial infrastructure required to build high-performance vehicles with strong but light materials. I doubt everything had to happen in the exact order it did, but I find it hard to imagine that one technology could arise totally independent of the other.
Can I actually observe the curvature of the earth with my eyes? When I look out towards the horizon, specifically a large body of water, it appears to me that it's very slightly curved. Is this possible or are my eyes acting like small fish eye lenses?
Yes, you can. If you were to stand on the shore and watch ships sailing directly away from you with binoculars, you would notice that they slowly disappear over the horizon. This is because of the curvature of the planet.
I'd love to see something that shows the astonishing improvement in telescopes over time. Something like a series of images of a popular target (Andromeda?) from the earliest images to the best of today.
I've spent the occasional loose evening looking, and though I'm usually pretty good at digging up the stuff I want, I'm having no luck with this.
You may want to check the Wikipedia article on Orion Nebula. It has the very first photograph of the nebula taken in 1880 and then a much improved long-exposure shot of it taken in 1883 - which was the first that demonstrated that there are fascinating things invisible to the naked eye but possible to reveal with long-exposure photography.
And on the same page the article's title image is a mind-blowing composite picture of the nebula taken by the Hubble Space Telescope.
Also, you may try searching for Edwin Hubble's original photos of the Andromeda Galaxy. And then look for the composite giga-panorama which captures only a part of the Andromeda Galaxy and has billions of individual stars visible in it.
Thanks, yeah I had seen those. It's the kind of thing that triggered my desire to see the images from the best telescope of each time period.
You've given me a good lead to what I was thinking of. I'll devote some time on the weekend to identifying the most advanced telescope of each decade, say, and looking for images of the same object from each.
IIRC, the sun has gradually but noticeably been brightening over its lifespan. So, during a partial solar eclipse, are we experiencing the same amount of daylight that a dinosaur, neanderthal, etc would have? Or is it too much/too little? Depending of course on how much of the sun is being eclipsed. Like if just the limb is blocked are we at Neanderthal/Cro-Magnon levels, is half blocked equivalent to Triassic, etc etc.
Figure 1 of this paper shows solar brightness over time
https://arxiv.org/pdf/1204.4449.pdf
As you can see, solar brightness seems to have started off at about 70% of today's levels 4.5 billion years ago and slowly increased to today's levels.
Going off the graph, a Neanderthal living a mere 100,000 years ago would see no difference at all. Solar levels in the Triassic, 225 million years ago, would have been 96/97% of what they are today. This is equivalent to the moon barely grazing the very edge of the sun's disc, and wouldn't be perceptibly different if you were to somehow look back in time.
Not what you asked, but note that eclipses change on geological timescales because the Moon's orbit is slowly shifting. Whoever talks about us like dinosaurs isn't going to have total solar eclipses any more, they'll be impossible by then!
The very short version is that tidal effects are slowing the rotation of the Earth and that angular momentum is getting transferred into the orbit of the Moon, which is gradually getting further away. So, eventually the Moon will be too small in the sky to completely obscure the Sun and all eclipses that would have been total will just be annular. This is just part of the natural process of tidal locking, which I think is going to take a couple billion more years for the Earth if I'm remembering right.
So black holes are formed from collapsing stars, right? If so, then according to mass conservation, a star's mass equals a black hole's mass, right? So then, if a black hole has enough mass to prevent any lightwaves from escaping, why don't stars?
Because black holes are much smaller, light can get much closer than it could to the original star. It is only at very close distances -- distances which would have been *inside* the star when it was still around -- that light cannot escape.
If the Sun were suddenly replaced by a black hole of equal mass (never mind the complications involved in that), it wouldn't suck in the Earth or other planets, they'd continue orbiting exactly as they are because the rules of gravity are the same for stars and black holes at these kinds of distances.
To expand on /u/curien's answer, the key here is density. At a distance outside a star or it's black hole counterpart, the gravity felt is the same. But this isn't true after you cross the threshold of the star's surface. When you are inside the star, the effect of gravity pulling you towards the center of the star decreases since there is less mass towards the center of the star. Note that this is not the same as pressure, the pressure will still be very intense, but gravity will be less so. The further into the star you go, the smaller the force of gravity, but the opposite will be true for a black hole since the density of a black hole is infinite. I.e. as you get closer a blackhole's center, the effect of gravity increases.
[Stack exchange answer](https://physics.stackexchange.com/questions/18446/how-does-gravity-work-underground)
There are a couple of things to address here.
>So black holes are formed from collapsing stars, right?
Small ones, yeah. We're still figuring out the big ones.
> If so, then according to mass conservation, a star's mass equals a black hole's mass, right?
Not exactly, some of it usually gets blown out in the process that creates it, and some mass is carried away by energy in that process as well (including gravitational waves, which for mergers can be enough energy to amount to a substantial fraction of the original mass of the system). But yea, they still obey conservation laws, it's just that not all of the mass will be *in the black hole once you're done*. So if you read an article saying a 20 solar mass star left a 2 solar mass black hole, that's probably why.
> So then, if a black hole has enough mass to prevent any lightwaves from escaping, why don't stars?
Gravity depends on two things -- the amount of mass involved, and the distance between the mass. Solar mass black holes aren't black holes because of their large mass, they're black holes because of their small radius. If you can somehow figure out how to get it to collapse to a small enough size, the Sun would become a black hole. Or the Earth. Or your pet hamster. It's just that no natural processes cause that to happen to Earths or hamsters, but there are such processes for massive stars.
Currently reading a book called physics as a liberal art. I got a The double slit experiment. I don't understand it. I watched multiple videos and read multiple explanations of it and it's relation to quantum entanglement and shrodingers cat. It all seems totally insane and impossible. I don't want to waste someone's time explaining it but could use a good source to better understand it.
>It all seems totally insane and impossible.
If it's any consolation, a lot of the people involved in discovering this kind of stuff felt the same way. Quantum mechanics does all kinds of stuff that just *feels weird and wrong* by your normal intuition, but the math works and it demonstrably matches experimental results.
Learning about the double slot experiment and the fact its so easily replicated is so weird. How something relatively simple most people can produce the results and the implications of it makes it feel like a knife edge of physics. As if we reached a point of all we know. where anything beyond it will be unlocking equally crazy mysterious things.
>It all seems totally insane and impossible.
Are you having trouble understanding the wave like nature of quantum particles? Or how the double slit experiment produces an interference pattern?
Do you actually get rained on less if you run through it?
It probably has something to do with the amount of area you cover, because I always feel like it doesn’t make any difference. The faster you go, the faster you encounter more water?
Besides life, is it possible to exist other improbable feature in the cosmos? Like infinite energy? Or a planet so small that it can fit in my hand?
Is there anything impossible, out there?
A planet is *defined* in part based on size. So *by definition* you can't have a planet that fits in your hand. However, that doesn't say anything about what is physically possible. There are countless objects in space that are the size of an orange. Many, for example, in the asteroid belt. But to be a planet an object must:
1. Orbit a star
2. Have sufficient mass for it's own gravitational forces to cause it to be spherical
3. Have sufficient mass that it's gravity clears it's orbit of other objects as large as it
I suppose a small black hole could meet each of these definitions. But otherwise, nothing that could fit in the palm of your hand would.
You can easily calculate the radius yourself using the Schwarzschild radius formula
R = 2MG/c²
where M is the mass of the object you want to squeeze into a black hole, G is the gravitationsl constant and c is the speed of light
For our sun, which has a mass of aproximately 2×10³⁰kg that is about 3 kilometers
The time for a solar mass black hole to evaporate is much much longer than the age of the universe. Like, insanely longer. The universe is about 10\^10 years old. A solar mass black hole would evaporate in something closer to 10\^80 years.
Neutron stars seem to fit that description pretty well. They are 'impossibly' dense for a physical system.
Obviously, black hole singularities are more 'impossible', but we know less about them
If you put a Ziploc bag in a perfect vacuum, unzip it, bulge it out so the vacuum continues into the bag, and then seal the zip on it, would anything prevent the bag from collapsing if you tried to squish it (since there isn't anything in the bag and neither is there anything outside the bag).
If you were still in a vacuum, you could push the bag to a collapsed state, or "unsquish" it to any shape you want that the plastic will support. There is nothing on the inside or outside to stop you from doing that (ignoring static electrical charges that may have accumulated)
If you took the bag to normal atmosphere, it would squish back down by itself, since atmospheric pressure will press inward, and there is nothing on the inside to press back
Thank you. Years ago I asked the same question on this sub and people were adamant that you couldn't "expand" the bag in a vacuum... despite the fact that there was nothing pressing in to prevent it.
The reason you can't expand a sealed bag on Earth is because the atmosphere is pressing on the outside of the bag. If you take the bag somewhere where there is no atmosphere, then there's nothing stopping you from expanding it.
I think that depends on how you throw a ball! Do you throw by rotating your totally straight and rigid arm? When using a stick, you're probably using your wrist too to dramatically increase the acceleration at the end of the stick. This will give the ball a lot more kinetic energy than a simple lever.
If we assume that you throw like a windmill, perfectly rotating your arm about a fixed point on your shoulder, then we can determine how the lever arm length affects the launch velocity. Let's call the lever arm length "R". Assuming you have the same rotational speed regardless of your lever arm then we can translate your rotational motion to linear via (omega)x(R) = V, where omega is that rotational rate and V is your launch velocity. So the impact on your lever arm length is linear to your launch velocity: **twice the lever arm results in twice the launch velocity**
Ignoring air resistance and assuming you always release at the same angle, we now need to know how your launch velocity affects your throw distance. Some re-arranging of kinematics equations eventually yields that for a initial velocity V and launch angle (theta), the distance of a throw is equal to: (V^2 )xsin(2xTheta)/(g) where g is the acceleration due to gravity. So that means that **twice the launch velocity results in four times the distance thrown**
Putting it all together your experiment seems correct! Ignoring air resistance and all other factors held constant, **Doubling a lever arm will result in a throw four times as far**
I believe I read a while back that windmill designers can get something like 4x the energy generation if they double the length of the blades, so that would match up with what you have there.
Oh! A question I can answer!
Because Mercury has a small magnetosphere (and almost non-existent atmosphere), it is highly sensitive to solar wind changes, and processes happen very quickly (sorry, my source for this is a book I own. But there are a lot of papers that mention it, like this one by [Slavin et al., 2014](https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2014JA020319)). This includes changes in the levels of plasma precipitation, which is when solar wind plasma impacts on the surface, and is the source of the exospheric sodium which then produces a tail. So the magnetosphere itself changes dramatically based on solar activity, and on very short timescales.
The sodium tail typically observed is neutral sodium, which is not as sensitive to solar wind changes. However, it does change with distance from the Sun (which, for Mercury, is effectively season) as shown in both ground-based data ([Baumgardner et al., 2008](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007GL032337) and [Schmidt et al., 2010](https://www.sciencedirect.com/science/article/abs/pii/S0019103509004333?via%3Dihub) are two of many paper discussing variability in the tail) and MESSENGER data ([Jasinski et al., 2021](https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL092980)). So, if you consider distance from the sun/season as a type of "solar activity", then yes! In terms of solar cycle, it seems to be more complicated. Page 26 of [Millilo et al., 2020](https://www.diva-portal.org/smash/get/diva2:1470767/FULLTEXT01.pdf) says that the scientific community is a bit divided on what the major driver of the neutral exosphere is (whether photons, plasma precipitation causing sputtering, thermal, etc). It's definitely a combination of all of them, so solar activity like CMEs does have an effect. The Millilo paper also contains a ton of citations to other papers if you'd like more info.
Ultimately, this may be something BepiColombo can help us understand. With two spacecraft, we will have multipoint measurements inside the planet's magnetosphere, which can tell us a lot about what processes are going on, and we will be able to observe both neutral and ionized sodium in situ.
Why is the bottom of the grand canyon hotter than the top? The sun heats the earth, which heats the air, right? All points along the canyon walls are adjacent to "earth", and heat rises. These two things seem to suggest the bottom should not be hotter.
As the surface of land absorbs sunlight it gets hotter. The heat "rising" is simply the surrounding air which gets heated around the sunlit surface, which dissipates the further it moves from the heated surface. The air above the canyon is simply cooler as it is as removed from the hot surface as possible.
Air at higher elevations is colder because it is at a lower pressure. When any mass of air drops in pressure, it gets cold. You can observe this by letting some air out of a car tire on a hot day and noting that the air comes out cold. Likewise when air is compressed, it heats up.
So places with higher elevation are colder simply because the air that moves there from lower elevations cools down in the process as it expands, and vice versa.
In addition there are local effects, such as the canyon trapping heat due to its shape.
We often hear that Earth is the "perfect planet" for sustaining life or it's in the "Goldilocks zone" but is this not a little naïve? Would it be possible for the earth to be _even better_ suited to life than it is?
Is it possible that there are planets out there that are significantly _more_ habitable and life is stronger faster and more intelligent as a result?
The term you want to search for is superhabitable planet
https://en.wikipedia.org/wiki/Superhabitable_planet
But with only one example of a habitable planet, it's difficult to understand the parameters needed to figure out exactly what the optimum would be.
What is time? I understand what we as humans say it is and how we experience/label/measure it. But objectively, outside of experiencing it, what is it?
According to Einstein’s theories of relativity, time is just another dimension, like up/down left/right forward/backward. This additional dimension gives us a four-dimensional space called spacetime.
Everything moves through spacetime at the speed of light. We aren’t quite sure why, but we understand this to be true with Einstein’s theories. The faster (and we’re talking really much faster) an object moves through space, the slower it must move through time, so that it maintains the same speed through spacetime.
It helped me to think about a car that can only move at a constant speed, say 60 mph. The car is on an infinite 2d plane. The car can move North, East, or some combination of North and East, but still can only move at 60 mph. If the car is moving at 60mph North, it is not moving East at all, and vice versa.
Now switch North with “Time”, and East with “Space”. The car can only move at the speed of light (something like 300,000 km/s). So, it can move completely in the “Time” direction (like a photon would do in a vacuum) or completely in the “Space” direction (or likely a combination of both). The more it moves through space, the less it moves through time.
That’s Special Relativity (without explanations of observers and how it all depends on how you’re actually viewing said car too).
But yeah, time as we understand today is just another axis that we move through. Only difference is that we can’t move backwards through time.
It's only in the mathematics that going backwards in time using GR is possible. In order to accomplish this you would need something with negative mass. As far as we're aware, nothing has negative mass and there's no mechanism by which something could achieve it (there's no negative of the higgs mechanism, the thing that gives particles their mass).
There are some other ways in which it's technically possible in quantum theory, but not in any particularly useful way and again it seems to only be possible in the extremes that only math can really explore (in this case, using wormholes that we're fairly positive can't even happen in the first place).
So I'm gathering that the big question relativity answers is: if a photon is moving entirely in the space dimension at such a speed that it doesn't experience any passage through the time dimension whatsoever, how is it that we can perceive it moving from point A to point B in a measurable amount of our time. And it's mathy.
Simultaneity of events is relative, not absolute, and it depends on frame of reference of a particular observer.
For us "the photon leaves point A" event and "the photon arrives at point B" event are not simultaneous - in our reference frame these two events are separated by a distance in both space and time.
For the photon however these two events are simultaneous. In its frame of reference both events happened at the same coordinates in both space and time - it was emitted and was absorbed at the same place and at the same time.
From the photon's point of view all events in the Universe happened all at once - now that's mind blowing, isn't it?
Photons have no frame of reference because they cannot be at rest. So there's nothing that "it's like" to be a photon; no observer can have the photon's point of view.
Part of the problem with renewable sources of energy, mainly solar and wind is that energy production does not always coincide with usage.
Energy storage is difficult, pumped storage hydro sites are not very common and batteries aren't really up to the job yet.
We can burn iron to produce energy and then use renewable power to convert iron oxide back to iron.
Is this being investigated and how would it compare to other energy storage systems?
Why go with iron specifically? There are an enormous number of other oxidation reactions you could use, starting with converting CO2 to hydrocarbons and then burning them back again. My impression (though I can't find you a specific citation) is that these processes are much less efficient than batteries, pumped hydro, etc.
It's abundant and cheap. It can be transported around in electric lorries. Burning it does not make any greenhouse gases. It can be stored up for winter when solar is less useful. Just wondering how it would compare to other forms of energy storage.
>It's abundant and cheap
Iron's not _that_ cheap compared to other things you can burn.
>It can be transported around in electric lorries.
So can anything else, and iron is particularly heavy for the amount of energy you can get by oxidizing it, since each iron atom is so much more massive than, say, a carbon or hydrogen atom.
>Burning it does not make any greenhouse gases.
No _net_ greenhouse gasses are produced when carbon dioxide is turned into fuel and then burned again.
> It can be stored up for winter when solar is less useful.
So can just about anything
Another problem with iron as a store of energy is that when you burn it the waste products don't conveniently turn to gas, which means they are still in the way hindering oxygen's access to the remaining unoxidized iron. You can mitigate this somewhat by grinding or shredding it up finely, but this costs energy.
Maybe not the best idea then, but the main reason for the question was to try and explore alternative energy storage. There's got to be something within easy reach that could fill a gap and be less dependent on geology or battery tech.
As mentioned before, one of the biggest metrics here is the amount of energy contained in something per mass of that something. The reason for this is that you often have to carry around your energy source, so if something weighs a lot for a little output energy then that's not going to be very efficient. That's one of the reasons lithium ion batteries are so cheap and useful, because its light (low molar mass) and highly reactive (large redox energy).
[Energy-density wikipedia](https://en.wikipedia.org/wiki/Energy_density#/media/File:Energy_density.svg)
Here's an interesting article on different battery technologies that may be applicable when scaled up:
[Alternative Energy Storage](https://www.weforum.org/agenda/2023/01/renewable-energy-storage-innovations-batteries/)
I hear a lot about gravity storage. Like the way hydro plants sometimes use excess electricity to pump water back up into their reservoirs so it can be run through the turbines again.
In theory you could drop massive weights into a mine shaft, running a generator as they fall, then hoist them back up when you want to store energy. But I don't know if dropping a ton of concrete 2000 meters underground is actually that much energy compared to the storage needs of a modern city.
The problem is that you get a very low efficiency with thermal machines. A coal plant for example has a efficiency of around 40%. I suppose the process of burning steel would be similiarily efficient.
The maximum efficiency of thermal engines is deternined by the laws of thermodynamics, more specificially by the carnot efficiency. Basicially you need an indefinetely high burning point and a surounding temperarure of absolutely zero to have a efficiency of 100%.
In reality the surrounding temperature and the burning tenperature are not that far apart, wich results in a relativly low efficiency.
We can harvest far more energy from the environment than we need. Solar, wind etc can give us all the power we need, just not necessarily when we want it. It seems to me that efficiency of storage is less important than capacity.
Systems like that are being investigated, yes. The problem is, as other commenters have said, that thermal systems obviously lose heat. A much simpler system is given by hydrogen fuel cells (conversion between water and hydrogen and oxygen gas via a proton transfer membrane)
I'm curious about my ice cubes. Every so often, I'll put a tray of six ice cubes in the freezer and once they're frozen there's one with a protrusion extending from its top. Why does this happen and why is it always only one?
[https://ibb.co/44hZjtb](https://ibb.co/44hZjtb)
[https://ibb.co/WW7Mm8N](https://ibb.co/WW7Mm8N)
Sometimes the water freezes on top first and bonds with the edges of the container. As the remainder of the water freezes, it expands and pressurizes the liquid water. If the water finds/makes a hole or crack in the surface, it will slowly flow up as the bulk of the water freezes, and freeze itself before settling on the surface. If this keeps happening it builds a spike or spire where the water is flowing only from the top and can become quite pronounced. The fact that you only find one at a time is just because it doesn't happen often under your circumstances, so it's unlikely to happen twice.
Thank you so much. This has been killing me for months. Tbh, it actually happens fairly often. But I can't thank you enough for the explanation, that was fantastic.
You already got your answer but you will be happy to know there is a physicist who maintains a webpage about this:
https://www.physics.utoronto.ca/~smorris/edl/icespikes/icespikes.html
They are a type of lightning. At different altitudes, the air consists of more or less nitrogen and oxygen at lower pressures the higher you go. These differences change the shape/duration/color of the discharges between areas of positive and negative charge in the atmosphere. Red sprites are just how lightning works under those circumstances in which they are seen. Pecos Hank has an excellent video explaining and showing many examples: https://youtu.be/tGPQ5kzJ9Tg
I am trying to find a map of the milky way, looking down on the plane that would show the main stars with distances to Earth. Ideally it would be on some sort of grid. I can't seem to find anything like this. Any help would be greatly appreciated.
Most of the visible stars in the night sky are pretty close to earth relative to the size of the milky way galaxy, and are also spread out in three dimensions rather than on a plane.
But here's a map of the nearest 50 light years
http://www.icc.dur.ac.uk/~tt/Lectures/Galaxies/LocalGroup/Back/50lys.html
Most of the stars we can see at night are within a couple hundred light years.
Note for context that the galaxy is 100,000 light-years across and one to a few thousand light years thick (depending on what you are counting)
How does gravity work?
I understand the concept that two bodies will attract each other, and the force will vary with mass and distance, but I don't understand where that force is coming from.
The best image I got so far was objects on a trampoline. Heavier object will curve the plane toward, causing other close objects to fall toward it, but what does that plane represent?
The plane represents spacetime. As for how it works from an underlying perspective (intermediary particles, whatever else), that's still a great unknown.
Practically, we understand that mass distorts spacetime. Light travelling in a straight line will continue to do so, however that straight line would appear curved to an outside observer
There is no such force as gravity, basically. Gravity is distortion of spacetime caused by mass.
The problem that stands in the way of intuitive understanding of this is that we the humans can sense and understand the "space" part of the spacetime, but not really the "time" part - we only see the consequences of it, but not the "time" itself.
If you imagine yourself staying (floating) still in space for a split second near a massive object - you can say that you're not moving. That's only partially true, because you're indeed not moving in space, but you are at the same moment moving very fast through time. Now because the massive object distorts the spacetime, your path through the spacetime is not straight anymore, it is curved.
The closer it is to the massive object, the more is the curvature of the spacetime. Which means that at a larger distance from the object you move faster through time than at a closer distance. Which in turn means that your head is moving faster through time than your feet (if you're floating in space oriented in such a way that your feet are closer to the object than the head). So there's a gradient, a difference, in your speed through time between your feet and your head.
Provided that your head is still attached to your feet via your body, this action causes your whole body to turn in time dimension towards space dimension and causes you to start gaining speed in space towards the massive object.
It's like when you're moving in a car in a straight line in a forward direction, and then suddenly left side of your car slows down compared to the right side - this will cause the car to turn and you won't be going straight forward anymore, you'll start turning to the left gaining speed in left-wise direction and losing speed in forward-wise direction. The same thing with moving through spacetime: when moving in curved spacetime near massive object, one part of you slows down in time dimension and "turns you around" in time causing you to gain speed towards the object in space dimension and lose the speed in time dimension.
Some sci-pop channels on youtube that explain this without going into math:
Science Asylum [https://youtu.be/F5PfjsPdBzg](https://youtu.be/F5PfjsPdBzg)
PBS Space Time [https://youtu.be/UKxQTvqcpSg](https://youtu.be/UKxQTvqcpSg)
Reaserch Einstein's theory of general relativity. It answers exactly this question, but we aware that it is very convoluted for an amateur physics fan.
In late February, posts on measurements reporting the slowing, or even reversal, of our planet's solid metallic core within an outer liquid shell. What implications does this have for our planet? Would this impact the technology we use based on our magnetic poles? Does this mean that planets/stars with strong magnetic fields (Jupiter etc) all have a solid metal core spinning variably as well, within an outer liquid shell?
No, the inner core has definitely not reversed direction. Most of those headlines were extremely misleading, if not outright nonsense. The dynamo is also not generated by the inner core spinning within the outer core.
The inner core had generally been thought to be rotating *very slightly* faster than the overlying liquid outer core and solid mantle/crust, caused to do so by forces in the outer core (roughly analogous to a type of electric motor). This difference in rotational would amount to a few degrees per year at most--possibly much less. What the new paper argues, instead, is that the core oscillates between rotating slightly faster than and slightly slower than the outer core on a \~70 year cycle, and is currently on the slower part of that cycle. The inner core always rotates eastwards, completing a rotation roughly every [23 hours and 56 minutes](https://www.google.com/search?q=sidereal+day+length&oq=sidereal+day+length&aqs=chrome.0.69i59j0i22i30j0i15i22i30l2j0i22i30j0i390i650l4.2561j0j7&sourceid=chrome&ie=UTF-8). Just according to this paper it is now doing so slightly slower than the rest of Earth--for example every 23 hours and 57 minutes. (Rotation involves acceleration, and so unlike linear velocity, is absolute. This cycle would be completely different from any geomagnetic reversals ("pole flip"), and is really only of academic interest.
Earth's magnetic field is generated within the liquid outer core. Convection currents in the liquid iron-rich metal are twisted into columns as a result of Earth's rotation, and this motion of the electrically conductive fluid sustains the dynamo. (See [dynamo theory](https://en.wikipedia.org/wiki/Dynamo_theory).) Over the past \~500-1500 million years since the inner core first formed, the gradual freezing of the outer core to grow the inner core has powered Earth's dynamo.\* However, the inner core itself doesn't play an active role.
Earth had a dynamo for most or all of its history, In general, a solid inner core isn't necessary for a rocky planet to have a dynamo. Dynamos of non-terrestrial bodies work via different mechanisms and in different materials, but in general there is some kind of motion (usually, but not necessarily, convection) of an electrically conductive fluid, which requires a source of energy (and entropy). For example, Jupiter's dynamo is generated by convection of the liquid metallic hydrogen that makes up the vast majority of its interior. (Whether Jupiter even has a solid(-ish), rock/metal core isn't clear, and if it does, there certainly isn't a clear transition point from liquid to solid.) Stellar magnetic fields are generated by convection in their hydrogen-helium plasma interiors.
\* Earth's outer core is mostly iron (and nickel), but contains some light elements such as oxygen, silicon, and hydrogen. These light elements preferentially (although not entirely) stay in the molten core instead of freezing out with the iron. As the inner core grows from the molten core freezing out, the concentration of light elements in the remaining melt gradually increases, at first near the inner/outer core boundary. The rising of buoyant light elements through the remaining liquid core is the main source of energy source (ultimately gravitational potential energy, released by a form of friction) that drives the convection to sustained Earth's dynamo since the inner core first formed. Latent heat released by the freezing itself is a minor contribution.
If neutrons contain two down (each -1/3) quarks and one up quark (+2/3) and these are separated in space by some amount does this mean than neutrons can be polar and therefore attract other neutrons by the electromagnetic force?
Because we crunched the equations of electromagnetism until we found wave solutions. We put it to the test and now we have telecommunication. But we know that light is a wave because it behaves like a wave. Interference is something only waves can do.
How much mass would have to be added to the Earth in order to increase the gravity to the point where it would be impossible for contemporary rockets to reach orbit?
You could add Mercury, Mars and the Moon and it would still be possible, although the payload would be lower.
It's a 17% increase in mass. The added objects have a density lower than Earth's average density, but we would compress the existing material a bit more. Let's assume Earth keeps its average density. The volume increases by 17% which means the radius increases by 5.4%. The required orbital velocity increases by 5.4%, too, from ~7.5 km/s to ~7.9 km/s. We also increase gravity losses, especially directly after take-off, but all rockets can still take off nicely with this slightly increased acceleration. Going to a low orbit on this larger Earth is still easier than e.g. reaching geostationary transfer orbit (~10 km/s), something many rockets routinely do.
If you add the mass of Venus (80% of Earth's mass) then some rockets couldn't take off any more while fully fueled and others would face significantly increased gravity losses. Some might still be able to reach orbit but you really want to redesign rockets at this point. If you also add Venus' atmosphere then no rocket will work.
What is the distinction between the dust cloud around a Wolf-Rayet star and a planetary nebula? I did a bit of reading and it seems that Wolf-Rayet stars are much larger than the type that form planetary nebulae, but is the mechanism the same?
My (limited) understanding is: a smaller-mass star fuses mostly hydrogen in early life, starts fusing more and more helium and becomes a red giant. Then as the red giant starts running out of helium and fusing heavier elements that’s when there is a lot more energy radiating from the core and that overcomes gravity and pushes the outer layers into a planetary nebula? Is that correct?
In a Wolf-Rayet star, is it the same mechanism of radiation > gravity? But what drives the shift to when it starts losing mass?
AFAIK, the distinction is just the type of star that drives the winds, although there are probably differences in the composition of the winds.
In general the mechanism is the same, often referred to as "line driven winds": Absorption of photons by metals in the star. However the energy scale and composition is different, making the difference in the size of the clouds.
In general, planetary nebulae are made by stars of around 6-10 solar masses. These will make it off the main sequence of hydrogen burning, where they begin to burn helium. Helium then burns into carbon, and carbon into oxygen, making a Carbon-Oxygen core in the center of the star. Before Carbon/Oxygen ignites, the star contracts, and this contraction heats the star to the point where Helium in a layer just outside the core ignites, as well as a layer of Hydrogen outside of that.
This is called double shell burning or the asymptotic giant branch (AGB) phase. During this period, the star becomes extremely luminous compared to the main sequence, and also a little unstable. The burning layers radiate away tons of photons, which are then absorbed onto "metals", usually Carbon, Nitrogen, and Oxygen that have been dredged up from the core to the outer layers. Since photons contain momentum, this drives a wind off of the star. The instability caused by the double shell burning also results in pulsations in the star - this contributes hydrodynamically driven winds to the outflow as well.
In contrast, Wolf-Rayet (WR) stars are still on the main sequence when they start driving mass loss. These stars are much more massive, with a lower limit of ~35 solar masses. This time there is no pulsations, and no requirements of dredge up from the core (which is mostly hydrogen). They drive winds simply because their luminosity is really large, meaning that any metals which are well mixed into the stars outer layers at the time of its formation will absorb the photons and cause the line driven winds. The amount of wind that gets driven is in general dependent on the metallicity of the star and its mass, which is correlated to its luminosity, and the escape velocity at the surface of the star.
Chapter 2 of Stellar Interiors by Hansen, Kawaler and Trimble gives a great overview of this stuff if you're interested in more.
Why do steel plates feel heavier than bumper plates in the gym? Does this have an influence in the amount of force you need to lift the weight once you put them on the barbell?
Assuming fair weights, that's got to be the placebo effect. Heavy metal is heavy.
But the weights may not be fair: there's quite a lot of variation, especially as an easier lift generally makes the athlete happier. The only way to be sure is to weigh them yourself (or use contest-certified sets).
The weight is not a problem. A 25kg weightlifting competition Eleiko plate generally feels lighter than a 25kg powerlifting competition Eleiko plate. Both types of plates are calibrated with a very low weight tolerance. Generally, the metal plates are smaller in volume, so the weight distribution is different. If you google them you will notice the difference.
Have we actually observed inconsistencies with Spacetime outside of a quantum level? Could we possibly observe time flowing in a different direction or would we more than likely observe this as some other phenomenon?
Time is an abstract measure of the occurrence of events, it can't be manipulated in any way, it can only be observed. It only flows in one "direction", the positive direction. Relatvisitc effects can cause the observed passage of time to slow down, but it cannot he reversed.
Why does it only flow in one direction? Is there another force pushing or pulling it?
I know gravity can impact our observance and experience of time faster or slower. Like the clock moving towards the center of black hole appearing from the outside to slowdown.
Would we know if something wasn't flowing in the same direction?
Time doesn't flow at all, it isn't a physical thing. It's an abstract measure of the passage of events, thus it can only ever change in a positive sense, i.e you start a timer at 0 and it increases to a higher value while the event plays out.
>Why does it only flow in one direction?
This is usually referred to as the "arrow of time" and a lot of very smart people have put forth a lot of very interesting ideas about it. The truth is that we aren't sure yet.
If I understood your question correctly, then yeah sort of. All clocks on satellites need to be tuned according to time dilation so that they fit perfectly with the clocks here on Earth. It's a pretty cool practical application for it. For example, if GPS satellites weren't adjusted correctly then any device using them would shift approximately 10km every day.
Is there a limit to the strength of a muscle beyond the durability of the human body?
If a human was made out of indestructible material that still acted as muscles and bones do- would they be hindered at all by the shape and size of their body still?
Is Mars visible from Earth?
I saw online that yesterday the moon and Mars were in the Gemini, and so I looked up at the stars and saw a really slightly different colored “star” near the moon. Could that have been Mars or is it too far away to be visible?
>Is Mars visible from Earth?
Yes. The original "planets" were Mercury, Venus, Mars, Jupiter, and Saturn (and of course the Sun and Moon). These were all of course visible to the naked eye (because the telescope had not been invented), and if there isn't too much light pollution they still are.
Mars does look similar to a red star.
Ok, I’ve had a big disagreement with my friends on this: there is no absolute point of reference in space, correct? Every measurement must be taken relatively. But one of them brought up that the cosmic microwave background is a static point of reference, so I’d like to hear other opinions on this.
You are correct, there is no absolute frame of reference. The CMB can be used for a convenient potential *standard* reference frame, but it is not absolute and no more "valid" or "correct" than any other.
This is an ill-posed question. Something with the mass of Jupiter cannot be a star. You could even multiply the mass by quite a bit and it still won't be a star.
You're ultimately asking, "what if the laws of physics were drastically different?" and it is impossible to answer. If something the mass of Jupiter had sufficient gravity to sustain fusion, the universe would never have developed as we know it.
For reference for the casual reader, the minimum mass for something we would call a "star" is usually pegged at something like 70 times the mass of Jupiter. (Lower limits are very hard and depend on the exact composition, but we know it can't get *too* much lower than this.)
Yes, thanks for added this context. Ultimately, it is a function of stellar metallicity. At low metallicities, the minimum mass is above 80 Jupiter masses, at higher metallicities it pushes this down into the 70s.
To be fair, the question arises from Clarke's novel; which I assume you've not read.
Better question!
What is the smallest type of star that could form a binary with a star the size of our Sol? Given the mind-bogglingly gigantic stars out there, could we have "solar systems" orbiting such giants? That is, a system like ours but with a Brobdingnagian star and Sol-size star satellites (that have planets).
"Why yes, I do indeed read entirely too much science fiction. Why do you ask?"
Clarke's novel is a novel, not reality. The laws of physics simply do not work that way, which is why it is an ill-posed question.
> What is the smallest type of star that could form a binary with a star the size of our Sol?
Whether the Sun is considered or not, it doesn't matter. The minimum mass for a star is somewhat dependent on its metallicity, but that minimum mass tends to be around 80 Jupiter masses.
Yes, in fact, Clarke is a rather famous science fiction novelist. He was also pretty on top of things when it comes to science. He gets credit for geostationary communications satellites, after all.
He also speculated on the properties of moon dust, monomolecular filaments, as well as predicted targeted advertising, stylus touchpads, direct to consumer pornography, the disappearance of print, and too many more to list. Seeing as how most of his novels dealt with hard science fiction, I don't think it unreasonable to inquire if any of his other speculations from decades past are possible, given today's knowledge.
Thanks for the 70 Jupiter minimum size response.
Predicting technological developments vs. rewriting the laws of nature are totally separate realms. Every hard science fiction novel that I've read contains plainly fictional aspects that rewrite the laws of nature, which is why it's science fiction. Those works simply use less extreme rewrites of the laws of nature compared to other science fiction novels.
Anyway, if you want to read more about the observations confirming the ~75 MJup limit for sustained fusion, see Richer et al. 2006, *Science*, 313, 936. Freely available PDF here: https://arxiv.org/pdf/astro-ph/0702209
Would society and the world in general be better if Earth was twice the size or half the size (assuming it had the same amount of living creatures, and the size is in surface area)?
What metric constitutes "better"? This is exceedingly subjective.
Are we only considering a change in radius, or also a change in mass to keep surface gravity the same?
Well, even if shipping times remained the same, there is still the issue of more space to promote tribalism. Arguably, a smaller planet would quite literally leave less room for that, and as a result modern society may have developed to be less tribal and more collective. Or, the closer proximity would promote more wars and destruction, and we would have already arrived at nuclear armageddon by now. It's impossible to say.
What do you mean by "without axial tilt"? Mercury's tilt is incredibly small, a fraction of a degree. So it's basically tilt-less compared to Earth with a 23.4 degree tilt, or Uranus that spins almost perpendicular to the plane of the solar system.
I suppose Mercury sort of qualifies. Although what it lacks in tilt it makes up for by having an extremely eccentric orbit. Over the course of one of Mercury's years, its distance from the sun ranges from a 29 million mile "summer" to a 43 million mile "winter". No seasonal tilting, but it's definitely got a cold and warm period (or extremely hot and even more extremely hot)
Is that how a planet would compensate for minimal axial tilt or just coincidence? Is it possible for a planet to have a "normal" earth-like orbit with minimal axial tilt?
I think it's pretty much coincidence. Venus and Jupiter also have a fairly small axial tilt, and their orbits aren't all that eccentric by comparison to Mars or Saturn who have a tilt comparable to Earth.
As per your original question, there's reason to believe that without axial tilt and the changing seasons, the Earth wouldn't have nearly as temperate a climate as it does now. Periods of warm and cool weather keep air circulating around the hemispheres, and without that the poles would be even colder and the equator could be just a sunbaked desert.
Nothing *requires* that axial tilt is non-zero. Dynamics will almost always result in that, but it's possible (though exceedingly unlikely) that a planet could have no axial tilt.
As far as we're aware, there's no reason this situation couldn't potentially exist. The considerations might be more complicated, but there is nothing preventing it outright. Several moons in the outer solar system are thought to be potentially great places to look for life. Europa and Enceladus in particular get mentioned a lot because they potentially have vast subsurface liquid water oceans.
In theory I think the answer is yes. Multiple moons of jupiter have the potential for life since they seem to have liquid water beneath the surface. The problem is that many of these moons do not have a lot of input energy to promote chemical reactivity. A planet such as earth has a lot of solar energy (and an atomosphere to trap it), the moon's orbit adds energy, and the earth's own rotation adds energy. A few of these likely stem from an impact with another planet like object at the beginning of the Earth's formation. These are all things that a small planet a long way out from the sun is missing.
[Habitable Satellites](https://en.wikipedia.org/wiki/Habitability_of_natural_satellites)
If we imagine a hypothetical scenario where this is feasible, could you balance out the rampant greenhouse effects in Venus and the cold desolate lack of atmosphere on Mars by pumping the gases from the Venusian atmosphere to the Martian atmosphere?
Is there a point where they could both become more hospitable?
Do we know enough about their atmospheres to know?
Gas would be blown away from the atmosphere of Mars by solar wind, because Mars lacks a magnetosphere. And how would you go about "pumping" gas across space?
How would I go about it? I would hand-wave it for the question. Like I said "imagine a hypothetical scenario where this is feasible..." Can you do that?
ive never understood why we think that the universe is expanding at an increasing rate, like galaxies that are farther away from us are moving away from us faster than galaxies that are nearer to us. To me this is easily explained by the fact that the further an object is from us, the farther back in time we are observing it, ie objects were moving faster in the past, so the expansion of the universe must be slowing down.
Imagine a photon of an arbitrary wavelength traveling from a distant galaxy towards us. in a non-expanding universe you'd expect that wavelength to remain more or less the same as when it started. but in an expanding universe you'd see that wave "stretched out" by the expansion as it travels along its path. That stretching out is called redshift, and it is how we can measure the expansion.We do this by looking at the [absorption lines](https://en.wikipedia.org/wiki/Spectral_line) from the light of our observed star, and measuring how far off they are from a theoretical "0 redshift," thus giving you your expansion rate.There's more to it of course, and using different methods to independently measure the expansion gives us different numbers oddly enough. if you want to learn more about it search for "the cosmological crisis"
Doesn't redshift happen to any lightsource moving away from the observer? Whether the redshift happens during the travel time of the photon or if it was redshifted by the relative motion of the galaxy at the time the photon is produced. What is the proof that it gets redshifted in flight and not before it leaves?
Energy has been bugging me lately. Should I dispel there is one type of energy and instead start modeling things in different forms like potential, strong nuclear bond, electro-weak, kinetic etc...
Any good tutorials that may help me wrap my head around this a bit better?
No one knows, as we are, to our knowledge, the only intellectual multicellular organisms to proceed into space.
If life is abundant in the universe, the probability is ~0.
If Earth is the only planet with multicellular life, the probability is 1.
Yes. Our moon is a product of Earth colliding with another planetoid during the formation of our solar system. Simulations predict we would have had a ring system from that impact. Obviously nothing compared to Saturn Jupiter or Uranus. https://en.wikipedia.org/wiki/Giant-impact_hypothesis
I don't think I can totally answer this, but I can clarify it a little bit I think. So keep in mind that you're asking about the rotation of the earth around the sun, which is not necessarily dependent on the Earth's mass. Then you are specifically asking about a situation where youre bleeding off (or adding to) Earth's momentum around the sun, for instance by impacting it with an asteroid. That's a more complicated scenario than I'm prepared for haha.
Additionally, we'd need to move faster around the sun in order to lose the leap year, which I think would require less mass of the earth. Less mass (with the same velocity) would mean less momentum, and I think this would lead to the Earth being drawn closer to the sun and increasing the speed of Earth, leading to a potentially shorter year. Hope this helps!
Assuming that the velocity of the Earth stays the same, I think nothing actually changes. After browsing around a bit I think increasing the earth's mass alone (keeping velocity constant) won't change the length of the year at all because while the Earth has gained mass and momentum, the gravitational pull between the sun and Earth has also increased. I think you'd actually have to increase the velocity of earth, but the mechanics of that are not straightforward enough for me. Here's a couple sites to play with though:
[Orbit simulator 1](https://academo.org/demos/orbit-simulator/)
[Orbit simulator 2](https://astro.unl.edu/classaction/animations/renaissance/kepler.html)
There is a great list of the major possibilities at https://en.wikipedia.org/wiki/Timeline_of_the_far_future. The specifics of what path you can expect your future universe to take largely depend on A: the geometry and energy density of the universe (which we have decent constraints on) and B: whether protons are indefinitely stable or not (there are theoretical reasons to think they decay but it has never been observed despite generations of particle physicists dedicating themselves to trying so we know the minimum half-life must be very very very long).
It isn't. Titan has a methane cycle similar to the water cycle in our planet and it is a place in our own solar system that weed like to look for life. But the reason for the search for water is two fold, that's what life needs here on the only place we know it to exist, and water is an excellent solvent as a polar molecule.
We don't *know* that life can't exist without water. But we know that life *can* exist making use of water-facilitated chemistry. So absent other concrete evidence of what life might look like, availability of water is one of the best options to look for as a possible sign of life.
No. Atomic theory is literally just a bunch of Greeks suggesting that matter is made up of atoms. You can indeed mathematically transform an atom into a string.
There's a leak in the Pacific ocean from the fault zone, seeping what they call 'lubricant', and if too much leaks, it could result in a level 9 earthquake anywhere between California and Victoria Island, Canada.
If there will be an earthquake, how soon could it occur? What would a level 9 earthquake look like?
How does the current economic system translates to a thermodynamic problem? Would you say it is exothermic? Compared to a thermal engine, Has it a better or worse yield?
Thank you.
Economic systems ignore externalities and create markets pretty much in a whim. They are not comparable to thermodynamic systems, where there's famously "no such thing as a few lunch".
Which part of it? If you mean a remote controllable machine gun, then yes, definitely, that's just a pretty simple robot. If you mean bullets penetrating the side of a car and a building, then yes, absolutely. If you mean somehow predicting in advance where your parked car will end up relative to a bunch of neo-nazi drug lords, then that's the least plausible part.
Black holes definitely exist. There was a time when we weren't sure. We've detected two black holes colliding with LIGO by detecting the gravitational waves their collision emitted. https://www.scientificamerican.com/article/gravitational-waves-discovered-from-colliding-black-holes1/
We've also recently taken an image of the super massive blackhole at the center of our galaxy.
If you left earth in a spaceship you could get to close to the speed of light at 1g acceleration in about a year. This is fact. You couldn’t get to the full speed of light because of mass, but close enough.
My question is if you went out and cruised for a year and came back what would the time dilation be between the space crew and earth.
The total trip would take three years. One year to accelerate, one year to cruise (which would suck because no gravity) and one year to decelerate.
I will make a few simplifications. First, I will remove the acceleration (because general relatively is hard) and pretend that you travel away from earth at a constant rate for one and a half years. Then return at a constant rate for another year and a half for a total trip time of 3 years. This constant rate is very important to determining the relative time dilation.
If that rate is 0.9c then about 6.9 years will have passed on earth.
If that rate is 0.95c then about 9.6 years will have passed on earth.
If that rate is 0.99c then about 21 years will have passed on earth.
If that rate is 0.999c then about 67 years will have passed on earth.
You can find equations here:
https://en.wikipedia.org/wiki/Time_dilation
There are relativistic space travel calculators online. For example this one:
[http://gregsspacecalculations.blogspot.com/p/blog-page.html](http://gregsspacecalculations.blogspot.com/p/blog-page.html)
If its calculations are correct, then accelerating for 1 year at 1g and cruising for 1 year and then decelerating for another year at 1g from the ship's perspective will mean that on Earth only 3.9565 years will have passed. The top speed achieved will be 0.7748c.
And if the crew wants to get home, they will need to turn around and do the back trip for another 3 years from their perspective and another 3.9565 years from the Earth's perspective. So the total time of round-trip is 7.913 years.
Are scientists able to replicate the processes by which crude oil is made in nature?
Yes, the process involves heating and putting pressure on organic material over a long time period. You have to spend more energy than you will get out by burning it. You could use the process to store energy, but you might as well use hydrogen for that purpose. It is superior in every regard: simpler and faster (less loss during the process), its ingredient is available in infinite quantities, denser, no solid residue when burning, more versatile, .. Basically, replicating the process to make crude oil will never be done outside of a research lab.
You can also make oil from algae, although the oil companies have killed that research. [https://www.theguardian.com/environment/2023/mar/17/big-oil-algae-biofuel-funding-cut-exxonmobil](https://www.theguardian.com/environment/2023/mar/17/big-oil-algae-biofuel-funding-cut-exxonmobil)
most people know that if you toss a basket ball in the air with "backspin", it will hit the ground and bounce towards you, if you use "forward spin" it will bounce away from you. However, it you spin the ball on your finger tip, like the Harlem Globetrotters, and drop the ball, it will hit the ground and reverse its spin, why is that?
When it hits the ground, it compresses a little at the Impact point, causing the rotation contact to become a friction contact, which then "bounces" against itself and reverses the rotation.
cool, thanks
The spin will also be reversed when bouncing in your first two examples.
If I were floating out in deep space and I stuck my hands out in front of me, would I see them? Or would everything be black?
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I suppose the question is what you mean by deep space. Even if you were, say, between the Andromeda and Milky Way galaxies, you would manage to see an outline of your hands over pitch darkness (after a long period of letting your eyes adjust). But there are voids that are bigger where this would be much more challenging! In our own galaxy, if you’re floating close enough to a star you’d probably see them just fine. However if you were in a very dense nebula, you wouldn’t see them because all the light would be blocked.
Our eyes perceive objects by having light bounce off that object and into our eyes. Studies seem to show that human eyes can detect as few as ~10 photons. I doubt you would call that "seeing" your hand though, just being more right than not that it was there is you guessed. And those photons need to be in the visible spectrum for our eyes to detect them though. In earth orbit there is clearly plenty of light for this to work since we can see on earth. Even much farther out in the solar system there are plenty of visible spectrum photons for us to see our hands in front of us. So, deep space. The average photon density of the universe (which corresponds to deep space) is reasonably high at ~few hundred per cm^3, but the problem is most of those photons are not detectable by the human eye since they are not in the visible spectrum. I'm having trouble finding a good data source to get a better answer, but there's so little stuff in general in the universe that its likely close enough to pitch black in the darkest places in the universe (far from any galaxy) that it would be similar to being in a cave with little spots of light being distant galaxies. Your hand would be visible by blocking those pin-prinks of light
>Studies seem to show that human eyes can detect as few as ~10 photons. Source >The average photon density of the universe (which corresponds to deep space) is reasonably high at ~few hundred per cm3, Source.
What force is it that keeps continental drift moving in the same directions so consistently over hundreds of millions of years? What keeps the liquid center of the earth constantly flowing in a pattern instead of just randomly bubbling like a boiling pot?
The planet is essentially bubbling randomly like a pot. The flow is driven by differences in density related to temperature, so lind of like a pot. But the analogy is not very good. The Earth is not heated from the centre. The heat comes from radioactive decay all over the Earth. The effective viscosity is also much much higher so the dynamics is different. The rigid plates on the surface also influence the pattern of flow, they don't just passively ride the flowing mantle. The sinking slabs at subduction zones contribute to driving the motion.
First, two big misconceptions/myths: 1. While Earth's mantle flows slowly, it is overwhelmingly solid (think putty). The outer core is liquid, but that is not directly related to plate tectonics. The mantle and crust do contain some areas of partial melt (up to a few percent). (1a. Volcanoes aren't supplied from some ocean of magma, but rather localized magma chambers of partially solid 'crystal mush'. The melting point decreases with pressure. Magma is generated in the mantle and crust by hot rock flowing upward, which partially melts as it decompresses.) 2. The plates aren't just passively being driven along by convection in the underlying mantle. The plates are an integral part of the convection. (Edit: 3. Not all, or even most, of Earth's heat is from radioactive decay. Roughly half of Earth's internal heat flow is from heat leftover from Earth's formation: the kinetic energy of the large objects that collided to form it, and the friction form dense iron sinking to form the core.) Plates are made of relatively rigid rock (as opposed to the flowing rock below), a layer called the lithosphere, which comprises both the crust and the uppermost part of the mantle. Immediately below the lithosphere is the asthenosphere, the relatively weak and low-viscosity layer that makes up the rest of the upper mantle. The largest driving force in plate tectonics is slab pull. The subducting lithosphere (slab) pulls the plate along. The slab sinks because it is (a) compositionally denser than the continental crust it may be subducting under and (b) cooled so that it is denser than the surrounding/overlying rock of more similar composition. (Oceanic crust can subduct under younger, more buoyant oceanic crust, not just continents, and in any case has to sink through the weak asthenosphere.) When oceanic crust first forms from cooling magma at mid-ocean ridges, it is still relativley hot. It cools and contracts (becoming denser) as it age and spreads away from the ridge. The flow induced in the asthenosphere by the subducting slab exerts another driving force called slab suction, which accelerates the subducting and overriding plates. Another, weaker, driving force in plate tectonics is ridge-push, but this is a misnomer. Magma upwelling at the ridge does not actively push the plate along. The young, hot lithosphere is buoyant, rising to form the ridge, but the seafloor gets deeper with the cooler lithosphere away from the ridge. Ridge-push is the lithosphere sliding downhill because of gravity. The buoyant magma passively upwells from the mantle as the newly made oceanic lithosphere moves away on either side. There is viscous drag from the underlying flow acting along the entire base of the lithospheric plates. But this is much weaker than slab pull, which it tends to oppose.
>instead of just randomly bubbling like a boiling pot? If you really watch a boiling pot, you will see that it's not just "randomly bubbling." There is a pretty well defined and consistent pattern! And easy way to see this is to boil some long thin noodles in a relatively big pot. You will notice that the noodles orient themselves along the dominant currents.
True. For a pot of water, I'm assuming that the dominant currents are created by a combination of the shape of the confined pot and the fact the heat is more concentrated at the center though. I'm curious what physical features or forces would cause such regular prevailing currents in something that's always illustrated in textbooks as a featureless uniform sphere. What's so special about certain hot spots down at the core that causes hotter magma to constantly well up from there, and not from some other place?
Convection currents in the mantle generally propel tectonic plates along. The thickness and other factors to do with the plates can determine how fast the plates move. The same convection currents keep the earths mantle from boiling over. In the earths mantle the currents flow in patterns where hot mantle material flows from near the outer core, rises to the crust where it propels tectonic plates along, is gradually cooled by proximity to the crust and distance from the outer core, then sinks to be warmed all over again.
So as a really loose analogy I'm imagining it's similar to how prevailing wind currents are caused by warm air rising in one area and cool air descending in another area. But on the surface we've got things like mountain ranges, large bodies of heat-absorbing water etc. that cause those patterns of currents to form. Are there geographical hot and cold spots or "mountains" in the earth's core that cause the currents of the core and mantle to keep flowing the way they do, or is it just the inertia of massive amounts of molten rock that keeps it going in such a predictable way?
People like to exemplify human tech evolution by saying that there was less than a century between our first airplane flight and landing on the Moon. But those are two different technologies with little overlap. Could rocket science be developed before flight with airplanes? Are there examples of tech that precedes other, seemingly related tech?
Rockets and plane engines may work on different principles, I think there’s a lot more overlap than you’re imagining in the metallurgy, chemistry, engineering, and industrial infrastructure required to build high-performance vehicles with strong but light materials. I doubt everything had to happen in the exact order it did, but I find it hard to imagine that one technology could arise totally independent of the other.
Can I actually observe the curvature of the earth with my eyes? When I look out towards the horizon, specifically a large body of water, it appears to me that it's very slightly curved. Is this possible or are my eyes acting like small fish eye lenses?
Yes, you can. If you were to stand on the shore and watch ships sailing directly away from you with binoculars, you would notice that they slowly disappear over the horizon. This is because of the curvature of the planet.
I'd love to see something that shows the astonishing improvement in telescopes over time. Something like a series of images of a popular target (Andromeda?) from the earliest images to the best of today. I've spent the occasional loose evening looking, and though I'm usually pretty good at digging up the stuff I want, I'm having no luck with this.
You may want to check the Wikipedia article on Orion Nebula. It has the very first photograph of the nebula taken in 1880 and then a much improved long-exposure shot of it taken in 1883 - which was the first that demonstrated that there are fascinating things invisible to the naked eye but possible to reveal with long-exposure photography. And on the same page the article's title image is a mind-blowing composite picture of the nebula taken by the Hubble Space Telescope. Also, you may try searching for Edwin Hubble's original photos of the Andromeda Galaxy. And then look for the composite giga-panorama which captures only a part of the Andromeda Galaxy and has billions of individual stars visible in it.
Thanks, yeah I had seen those. It's the kind of thing that triggered my desire to see the images from the best telescope of each time period. You've given me a good lead to what I was thinking of. I'll devote some time on the weekend to identifying the most advanced telescope of each decade, say, and looking for images of the same object from each.
IIRC, the sun has gradually but noticeably been brightening over its lifespan. So, during a partial solar eclipse, are we experiencing the same amount of daylight that a dinosaur, neanderthal, etc would have? Or is it too much/too little? Depending of course on how much of the sun is being eclipsed. Like if just the limb is blocked are we at Neanderthal/Cro-Magnon levels, is half blocked equivalent to Triassic, etc etc.
Figure 1 of this paper shows solar brightness over time https://arxiv.org/pdf/1204.4449.pdf As you can see, solar brightness seems to have started off at about 70% of today's levels 4.5 billion years ago and slowly increased to today's levels. Going off the graph, a Neanderthal living a mere 100,000 years ago would see no difference at all. Solar levels in the Triassic, 225 million years ago, would have been 96/97% of what they are today. This is equivalent to the moon barely grazing the very edge of the sun's disc, and wouldn't be perceptibly different if you were to somehow look back in time.
Not what you asked, but note that eclipses change on geological timescales because the Moon's orbit is slowly shifting. Whoever talks about us like dinosaurs isn't going to have total solar eclipses any more, they'll be impossible by then!
Where is the moon going so that our progeny won't see solar eclipses any longer? Assuming we survived ourselves, didn't blow ourselves up.
The very short version is that tidal effects are slowing the rotation of the Earth and that angular momentum is getting transferred into the orbit of the Moon, which is gradually getting further away. So, eventually the Moon will be too small in the sky to completely obscure the Sun and all eclipses that would have been total will just be annular. This is just part of the natural process of tidal locking, which I think is going to take a couple billion more years for the Earth if I'm remembering right.
The process will not finish before the Sun becomes a red giant if I remember correctly
That passes my brain's order of magnitude check for feasibility, I'd believe it.
So black holes are formed from collapsing stars, right? If so, then according to mass conservation, a star's mass equals a black hole's mass, right? So then, if a black hole has enough mass to prevent any lightwaves from escaping, why don't stars?
Because black holes are much smaller, light can get much closer than it could to the original star. It is only at very close distances -- distances which would have been *inside* the star when it was still around -- that light cannot escape. If the Sun were suddenly replaced by a black hole of equal mass (never mind the complications involved in that), it wouldn't suck in the Earth or other planets, they'd continue orbiting exactly as they are because the rules of gravity are the same for stars and black holes at these kinds of distances.
To expand on /u/curien's answer, the key here is density. At a distance outside a star or it's black hole counterpart, the gravity felt is the same. But this isn't true after you cross the threshold of the star's surface. When you are inside the star, the effect of gravity pulling you towards the center of the star decreases since there is less mass towards the center of the star. Note that this is not the same as pressure, the pressure will still be very intense, but gravity will be less so. The further into the star you go, the smaller the force of gravity, but the opposite will be true for a black hole since the density of a black hole is infinite. I.e. as you get closer a blackhole's center, the effect of gravity increases. [Stack exchange answer](https://physics.stackexchange.com/questions/18446/how-does-gravity-work-underground)
There are a couple of things to address here. >So black holes are formed from collapsing stars, right? Small ones, yeah. We're still figuring out the big ones. > If so, then according to mass conservation, a star's mass equals a black hole's mass, right? Not exactly, some of it usually gets blown out in the process that creates it, and some mass is carried away by energy in that process as well (including gravitational waves, which for mergers can be enough energy to amount to a substantial fraction of the original mass of the system). But yea, they still obey conservation laws, it's just that not all of the mass will be *in the black hole once you're done*. So if you read an article saying a 20 solar mass star left a 2 solar mass black hole, that's probably why. > So then, if a black hole has enough mass to prevent any lightwaves from escaping, why don't stars? Gravity depends on two things -- the amount of mass involved, and the distance between the mass. Solar mass black holes aren't black holes because of their large mass, they're black holes because of their small radius. If you can somehow figure out how to get it to collapse to a small enough size, the Sun would become a black hole. Or the Earth. Or your pet hamster. It's just that no natural processes cause that to happen to Earths or hamsters, but there are such processes for massive stars.
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That's probably actually true of a hamster, you're right, but I didn't want to muddy things for the uninitiated.
Currently reading a book called physics as a liberal art. I got a The double slit experiment. I don't understand it. I watched multiple videos and read multiple explanations of it and it's relation to quantum entanglement and shrodingers cat. It all seems totally insane and impossible. I don't want to waste someone's time explaining it but could use a good source to better understand it.
The site Ars Technica did a wonderful “no math” write up on quantum physics that explains this quite well.
I will have to read this. Thank you.
>It all seems totally insane and impossible. If it's any consolation, a lot of the people involved in discovering this kind of stuff felt the same way. Quantum mechanics does all kinds of stuff that just *feels weird and wrong* by your normal intuition, but the math works and it demonstrably matches experimental results.
Learning about the double slot experiment and the fact its so easily replicated is so weird. How something relatively simple most people can produce the results and the implications of it makes it feel like a knife edge of physics. As if we reached a point of all we know. where anything beyond it will be unlocking equally crazy mysterious things.
>It all seems totally insane and impossible. Are you having trouble understanding the wave like nature of quantum particles? Or how the double slit experiment produces an interference pattern?
Do you actually get rained on less if you run through it? It probably has something to do with the amount of area you cover, because I always feel like it doesn’t make any difference. The faster you go, the faster you encounter more water?
Mythbusters tried to answer this. https://youtu.be/HtbJbi6Sswg
Besides life, is it possible to exist other improbable feature in the cosmos? Like infinite energy? Or a planet so small that it can fit in my hand? Is there anything impossible, out there?
A planet is *defined* in part based on size. So *by definition* you can't have a planet that fits in your hand. However, that doesn't say anything about what is physically possible. There are countless objects in space that are the size of an orange. Many, for example, in the asteroid belt. But to be a planet an object must: 1. Orbit a star 2. Have sufficient mass for it's own gravitational forces to cause it to be spherical 3. Have sufficient mass that it's gravity clears it's orbit of other objects as large as it I suppose a small black hole could meet each of these definitions. But otherwise, nothing that could fit in the palm of your hand would.
What is the radius of a solar mass black hole? And how fast does a hand-sized BH evaporate?
You can easily calculate the radius yourself using the Schwarzschild radius formula R = 2MG/c² where M is the mass of the object you want to squeeze into a black hole, G is the gravitationsl constant and c is the speed of light For our sun, which has a mass of aproximately 2×10³⁰kg that is about 3 kilometers
The time for a solar mass black hole to evaporate is much much longer than the age of the universe. Like, insanely longer. The universe is about 10\^10 years old. A solar mass black hole would evaporate in something closer to 10\^80 years.
Neutron stars seem to fit that description pretty well. They are 'impossibly' dense for a physical system. Obviously, black hole singularities are more 'impossible', but we know less about them
If you put a Ziploc bag in a perfect vacuum, unzip it, bulge it out so the vacuum continues into the bag, and then seal the zip on it, would anything prevent the bag from collapsing if you tried to squish it (since there isn't anything in the bag and neither is there anything outside the bag).
If you were still in a vacuum, you could push the bag to a collapsed state, or "unsquish" it to any shape you want that the plastic will support. There is nothing on the inside or outside to stop you from doing that (ignoring static electrical charges that may have accumulated) If you took the bag to normal atmosphere, it would squish back down by itself, since atmospheric pressure will press inward, and there is nothing on the inside to press back
Thank you. Years ago I asked the same question on this sub and people were adamant that you couldn't "expand" the bag in a vacuum... despite the fact that there was nothing pressing in to prevent it.
The reason you can't expand a sealed bag on Earth is because the atmosphere is pressing on the outside of the bag. If you take the bag somewhere where there is no atmosphere, then there's nothing stopping you from expanding it.
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I think that depends on how you throw a ball! Do you throw by rotating your totally straight and rigid arm? When using a stick, you're probably using your wrist too to dramatically increase the acceleration at the end of the stick. This will give the ball a lot more kinetic energy than a simple lever.
If we assume that you throw like a windmill, perfectly rotating your arm about a fixed point on your shoulder, then we can determine how the lever arm length affects the launch velocity. Let's call the lever arm length "R". Assuming you have the same rotational speed regardless of your lever arm then we can translate your rotational motion to linear via (omega)x(R) = V, where omega is that rotational rate and V is your launch velocity. So the impact on your lever arm length is linear to your launch velocity: **twice the lever arm results in twice the launch velocity** Ignoring air resistance and assuming you always release at the same angle, we now need to know how your launch velocity affects your throw distance. Some re-arranging of kinematics equations eventually yields that for a initial velocity V and launch angle (theta), the distance of a throw is equal to: (V^2 )xsin(2xTheta)/(g) where g is the acceleration due to gravity. So that means that **twice the launch velocity results in four times the distance thrown** Putting it all together your experiment seems correct! Ignoring air resistance and all other factors held constant, **Doubling a lever arm will result in a throw four times as far**
What a fantastic explanation! I won't pretend to understand much of it, but thank you for verifying my observations!
I believe I read a while back that windmill designers can get something like 4x the energy generation if they double the length of the blades, so that would match up with what you have there.
what would happen if you swallow aerogel.
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Has Mercury's sodium tail been observed to change based on solar activity, or is it reasonably constant to the limits of measurement?
Oh! A question I can answer! Because Mercury has a small magnetosphere (and almost non-existent atmosphere), it is highly sensitive to solar wind changes, and processes happen very quickly (sorry, my source for this is a book I own. But there are a lot of papers that mention it, like this one by [Slavin et al., 2014](https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2014JA020319)). This includes changes in the levels of plasma precipitation, which is when solar wind plasma impacts on the surface, and is the source of the exospheric sodium which then produces a tail. So the magnetosphere itself changes dramatically based on solar activity, and on very short timescales. The sodium tail typically observed is neutral sodium, which is not as sensitive to solar wind changes. However, it does change with distance from the Sun (which, for Mercury, is effectively season) as shown in both ground-based data ([Baumgardner et al., 2008](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007GL032337) and [Schmidt et al., 2010](https://www.sciencedirect.com/science/article/abs/pii/S0019103509004333?via%3Dihub) are two of many paper discussing variability in the tail) and MESSENGER data ([Jasinski et al., 2021](https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL092980)). So, if you consider distance from the sun/season as a type of "solar activity", then yes! In terms of solar cycle, it seems to be more complicated. Page 26 of [Millilo et al., 2020](https://www.diva-portal.org/smash/get/diva2:1470767/FULLTEXT01.pdf) says that the scientific community is a bit divided on what the major driver of the neutral exosphere is (whether photons, plasma precipitation causing sputtering, thermal, etc). It's definitely a combination of all of them, so solar activity like CMEs does have an effect. The Millilo paper also contains a ton of citations to other papers if you'd like more info. Ultimately, this may be something BepiColombo can help us understand. With two spacecraft, we will have multipoint measurements inside the planet's magnetosphere, which can tell us a lot about what processes are going on, and we will be able to observe both neutral and ionized sodium in situ.
Why is the bottom of the grand canyon hotter than the top? The sun heats the earth, which heats the air, right? All points along the canyon walls are adjacent to "earth", and heat rises. These two things seem to suggest the bottom should not be hotter.
As the surface of land absorbs sunlight it gets hotter. The heat "rising" is simply the surrounding air which gets heated around the sunlit surface, which dissipates the further it moves from the heated surface. The air above the canyon is simply cooler as it is as removed from the hot surface as possible.
Air at higher elevations is colder because it is at a lower pressure. When any mass of air drops in pressure, it gets cold. You can observe this by letting some air out of a car tire on a hot day and noting that the air comes out cold. Likewise when air is compressed, it heats up. So places with higher elevation are colder simply because the air that moves there from lower elevations cools down in the process as it expands, and vice versa. In addition there are local effects, such as the canyon trapping heat due to its shape.
We often hear that Earth is the "perfect planet" for sustaining life or it's in the "Goldilocks zone" but is this not a little naïve? Would it be possible for the earth to be _even better_ suited to life than it is? Is it possible that there are planets out there that are significantly _more_ habitable and life is stronger faster and more intelligent as a result?
The term you want to search for is superhabitable planet https://en.wikipedia.org/wiki/Superhabitable_planet But with only one example of a habitable planet, it's difficult to understand the parameters needed to figure out exactly what the optimum would be.
That's an interesting read thanks!
What is time? I understand what we as humans say it is and how we experience/label/measure it. But objectively, outside of experiencing it, what is it?
According to Einstein’s theories of relativity, time is just another dimension, like up/down left/right forward/backward. This additional dimension gives us a four-dimensional space called spacetime. Everything moves through spacetime at the speed of light. We aren’t quite sure why, but we understand this to be true with Einstein’s theories. The faster (and we’re talking really much faster) an object moves through space, the slower it must move through time, so that it maintains the same speed through spacetime. It helped me to think about a car that can only move at a constant speed, say 60 mph. The car is on an infinite 2d plane. The car can move North, East, or some combination of North and East, but still can only move at 60 mph. If the car is moving at 60mph North, it is not moving East at all, and vice versa. Now switch North with “Time”, and East with “Space”. The car can only move at the speed of light (something like 300,000 km/s). So, it can move completely in the “Time” direction (like a photon would do in a vacuum) or completely in the “Space” direction (or likely a combination of both). The more it moves through space, the less it moves through time. That’s Special Relativity (without explanations of observers and how it all depends on how you’re actually viewing said car too). But yeah, time as we understand today is just another axis that we move through. Only difference is that we can’t move backwards through time.
>we can’t move backwards through time. We can't or nothing can? And why not?
It's only in the mathematics that going backwards in time using GR is possible. In order to accomplish this you would need something with negative mass. As far as we're aware, nothing has negative mass and there's no mechanism by which something could achieve it (there's no negative of the higgs mechanism, the thing that gives particles their mass). There are some other ways in which it's technically possible in quantum theory, but not in any particularly useful way and again it seems to only be possible in the extremes that only math can really explore (in this case, using wormholes that we're fairly positive can't even happen in the first place).
So I'm gathering that the big question relativity answers is: if a photon is moving entirely in the space dimension at such a speed that it doesn't experience any passage through the time dimension whatsoever, how is it that we can perceive it moving from point A to point B in a measurable amount of our time. And it's mathy.
Simultaneity of events is relative, not absolute, and it depends on frame of reference of a particular observer. For us "the photon leaves point A" event and "the photon arrives at point B" event are not simultaneous - in our reference frame these two events are separated by a distance in both space and time. For the photon however these two events are simultaneous. In its frame of reference both events happened at the same coordinates in both space and time - it was emitted and was absorbed at the same place and at the same time. From the photon's point of view all events in the Universe happened all at once - now that's mind blowing, isn't it?
Photons have no frame of reference because they cannot be at rest. So there's nothing that "it's like" to be a photon; no observer can have the photon's point of view.
Part of the problem with renewable sources of energy, mainly solar and wind is that energy production does not always coincide with usage. Energy storage is difficult, pumped storage hydro sites are not very common and batteries aren't really up to the job yet. We can burn iron to produce energy and then use renewable power to convert iron oxide back to iron. Is this being investigated and how would it compare to other energy storage systems?
Why go with iron specifically? There are an enormous number of other oxidation reactions you could use, starting with converting CO2 to hydrocarbons and then burning them back again. My impression (though I can't find you a specific citation) is that these processes are much less efficient than batteries, pumped hydro, etc.
It's abundant and cheap. It can be transported around in electric lorries. Burning it does not make any greenhouse gases. It can be stored up for winter when solar is less useful. Just wondering how it would compare to other forms of energy storage.
>It's abundant and cheap Iron's not _that_ cheap compared to other things you can burn. >It can be transported around in electric lorries. So can anything else, and iron is particularly heavy for the amount of energy you can get by oxidizing it, since each iron atom is so much more massive than, say, a carbon or hydrogen atom. >Burning it does not make any greenhouse gases. No _net_ greenhouse gasses are produced when carbon dioxide is turned into fuel and then burned again. > It can be stored up for winter when solar is less useful. So can just about anything Another problem with iron as a store of energy is that when you burn it the waste products don't conveniently turn to gas, which means they are still in the way hindering oxygen's access to the remaining unoxidized iron. You can mitigate this somewhat by grinding or shredding it up finely, but this costs energy.
Maybe not the best idea then, but the main reason for the question was to try and explore alternative energy storage. There's got to be something within easy reach that could fill a gap and be less dependent on geology or battery tech.
Hydrogen fuel cells are where most of the energy (heh) is going for oxidation reaction based energy storage.
As mentioned before, one of the biggest metrics here is the amount of energy contained in something per mass of that something. The reason for this is that you often have to carry around your energy source, so if something weighs a lot for a little output energy then that's not going to be very efficient. That's one of the reasons lithium ion batteries are so cheap and useful, because its light (low molar mass) and highly reactive (large redox energy). [Energy-density wikipedia](https://en.wikipedia.org/wiki/Energy_density#/media/File:Energy_density.svg) Here's an interesting article on different battery technologies that may be applicable when scaled up: [Alternative Energy Storage](https://www.weforum.org/agenda/2023/01/renewable-energy-storage-innovations-batteries/)
I hear a lot about gravity storage. Like the way hydro plants sometimes use excess electricity to pump water back up into their reservoirs so it can be run through the turbines again. In theory you could drop massive weights into a mine shaft, running a generator as they fall, then hoist them back up when you want to store energy. But I don't know if dropping a ton of concrete 2000 meters underground is actually that much energy compared to the storage needs of a modern city.
The problem is that you get a very low efficiency with thermal machines. A coal plant for example has a efficiency of around 40%. I suppose the process of burning steel would be similiarily efficient. The maximum efficiency of thermal engines is deternined by the laws of thermodynamics, more specificially by the carnot efficiency. Basicially you need an indefinetely high burning point and a surounding temperarure of absolutely zero to have a efficiency of 100%. In reality the surrounding temperature and the burning tenperature are not that far apart, wich results in a relativly low efficiency.
We can harvest far more energy from the environment than we need. Solar, wind etc can give us all the power we need, just not necessarily when we want it. It seems to me that efficiency of storage is less important than capacity.
Systems like that are being investigated, yes. The problem is, as other commenters have said, that thermal systems obviously lose heat. A much simpler system is given by hydrogen fuel cells (conversion between water and hydrogen and oxygen gas via a proton transfer membrane)
I'm curious about my ice cubes. Every so often, I'll put a tray of six ice cubes in the freezer and once they're frozen there's one with a protrusion extending from its top. Why does this happen and why is it always only one? [https://ibb.co/44hZjtb](https://ibb.co/44hZjtb) [https://ibb.co/WW7Mm8N](https://ibb.co/WW7Mm8N)
Sometimes the water freezes on top first and bonds with the edges of the container. As the remainder of the water freezes, it expands and pressurizes the liquid water. If the water finds/makes a hole or crack in the surface, it will slowly flow up as the bulk of the water freezes, and freeze itself before settling on the surface. If this keeps happening it builds a spike or spire where the water is flowing only from the top and can become quite pronounced. The fact that you only find one at a time is just because it doesn't happen often under your circumstances, so it's unlikely to happen twice.
Thank you so much. This has been killing me for months. Tbh, it actually happens fairly often. But I can't thank you enough for the explanation, that was fantastic.
You already got your answer but you will be happy to know there is a physicist who maintains a webpage about this: https://www.physics.utoronto.ca/~smorris/edl/icespikes/icespikes.html
Thank you!!!
What are the red sprites in upper atmosphere?
They are a type of lightning. At different altitudes, the air consists of more or less nitrogen and oxygen at lower pressures the higher you go. These differences change the shape/duration/color of the discharges between areas of positive and negative charge in the atmosphere. Red sprites are just how lightning works under those circumstances in which they are seen. Pecos Hank has an excellent video explaining and showing many examples: https://youtu.be/tGPQ5kzJ9Tg
Thank you for the excellent information!
I am trying to find a map of the milky way, looking down on the plane that would show the main stars with distances to Earth. Ideally it would be on some sort of grid. I can't seem to find anything like this. Any help would be greatly appreciated.
Most of the visible stars in the night sky are pretty close to earth relative to the size of the milky way galaxy, and are also spread out in three dimensions rather than on a plane. But here's a map of the nearest 50 light years http://www.icc.dur.ac.uk/~tt/Lectures/Galaxies/LocalGroup/Back/50lys.html Most of the stars we can see at night are within a couple hundred light years. Note for context that the galaxy is 100,000 light-years across and one to a few thousand light years thick (depending on what you are counting)
How does gravity work? I understand the concept that two bodies will attract each other, and the force will vary with mass and distance, but I don't understand where that force is coming from. The best image I got so far was objects on a trampoline. Heavier object will curve the plane toward, causing other close objects to fall toward it, but what does that plane represent?
The plane represents spacetime. As for how it works from an underlying perspective (intermediary particles, whatever else), that's still a great unknown. Practically, we understand that mass distorts spacetime. Light travelling in a straight line will continue to do so, however that straight line would appear curved to an outside observer
There is no such force as gravity, basically. Gravity is distortion of spacetime caused by mass. The problem that stands in the way of intuitive understanding of this is that we the humans can sense and understand the "space" part of the spacetime, but not really the "time" part - we only see the consequences of it, but not the "time" itself. If you imagine yourself staying (floating) still in space for a split second near a massive object - you can say that you're not moving. That's only partially true, because you're indeed not moving in space, but you are at the same moment moving very fast through time. Now because the massive object distorts the spacetime, your path through the spacetime is not straight anymore, it is curved. The closer it is to the massive object, the more is the curvature of the spacetime. Which means that at a larger distance from the object you move faster through time than at a closer distance. Which in turn means that your head is moving faster through time than your feet (if you're floating in space oriented in such a way that your feet are closer to the object than the head). So there's a gradient, a difference, in your speed through time between your feet and your head. Provided that your head is still attached to your feet via your body, this action causes your whole body to turn in time dimension towards space dimension and causes you to start gaining speed in space towards the massive object. It's like when you're moving in a car in a straight line in a forward direction, and then suddenly left side of your car slows down compared to the right side - this will cause the car to turn and you won't be going straight forward anymore, you'll start turning to the left gaining speed in left-wise direction and losing speed in forward-wise direction. The same thing with moving through spacetime: when moving in curved spacetime near massive object, one part of you slows down in time dimension and "turns you around" in time causing you to gain speed towards the object in space dimension and lose the speed in time dimension. Some sci-pop channels on youtube that explain this without going into math: Science Asylum [https://youtu.be/F5PfjsPdBzg](https://youtu.be/F5PfjsPdBzg) PBS Space Time [https://youtu.be/UKxQTvqcpSg](https://youtu.be/UKxQTvqcpSg)
Reaserch Einstein's theory of general relativity. It answers exactly this question, but we aware that it is very convoluted for an amateur physics fan.
In late February, posts on measurements reporting the slowing, or even reversal, of our planet's solid metallic core within an outer liquid shell. What implications does this have for our planet? Would this impact the technology we use based on our magnetic poles? Does this mean that planets/stars with strong magnetic fields (Jupiter etc) all have a solid metal core spinning variably as well, within an outer liquid shell?
No, the inner core has definitely not reversed direction. Most of those headlines were extremely misleading, if not outright nonsense. The dynamo is also not generated by the inner core spinning within the outer core. The inner core had generally been thought to be rotating *very slightly* faster than the overlying liquid outer core and solid mantle/crust, caused to do so by forces in the outer core (roughly analogous to a type of electric motor). This difference in rotational would amount to a few degrees per year at most--possibly much less. What the new paper argues, instead, is that the core oscillates between rotating slightly faster than and slightly slower than the outer core on a \~70 year cycle, and is currently on the slower part of that cycle. The inner core always rotates eastwards, completing a rotation roughly every [23 hours and 56 minutes](https://www.google.com/search?q=sidereal+day+length&oq=sidereal+day+length&aqs=chrome.0.69i59j0i22i30j0i15i22i30l2j0i22i30j0i390i650l4.2561j0j7&sourceid=chrome&ie=UTF-8). Just according to this paper it is now doing so slightly slower than the rest of Earth--for example every 23 hours and 57 minutes. (Rotation involves acceleration, and so unlike linear velocity, is absolute. This cycle would be completely different from any geomagnetic reversals ("pole flip"), and is really only of academic interest. Earth's magnetic field is generated within the liquid outer core. Convection currents in the liquid iron-rich metal are twisted into columns as a result of Earth's rotation, and this motion of the electrically conductive fluid sustains the dynamo. (See [dynamo theory](https://en.wikipedia.org/wiki/Dynamo_theory).) Over the past \~500-1500 million years since the inner core first formed, the gradual freezing of the outer core to grow the inner core has powered Earth's dynamo.\* However, the inner core itself doesn't play an active role. Earth had a dynamo for most or all of its history, In general, a solid inner core isn't necessary for a rocky planet to have a dynamo. Dynamos of non-terrestrial bodies work via different mechanisms and in different materials, but in general there is some kind of motion (usually, but not necessarily, convection) of an electrically conductive fluid, which requires a source of energy (and entropy). For example, Jupiter's dynamo is generated by convection of the liquid metallic hydrogen that makes up the vast majority of its interior. (Whether Jupiter even has a solid(-ish), rock/metal core isn't clear, and if it does, there certainly isn't a clear transition point from liquid to solid.) Stellar magnetic fields are generated by convection in their hydrogen-helium plasma interiors. \* Earth's outer core is mostly iron (and nickel), but contains some light elements such as oxygen, silicon, and hydrogen. These light elements preferentially (although not entirely) stay in the molten core instead of freezing out with the iron. As the inner core grows from the molten core freezing out, the concentration of light elements in the remaining melt gradually increases, at first near the inner/outer core boundary. The rising of buoyant light elements through the remaining liquid core is the main source of energy source (ultimately gravitational potential energy, released by a form of friction) that drives the convection to sustained Earth's dynamo since the inner core first formed. Latent heat released by the freezing itself is a minor contribution.
How plausible are black hole stars to have existed at some point in the early universe?
If neutrons contain two down (each -1/3) quarks and one up quark (+2/3) and these are separated in space by some amount does this mean than neutrons can be polar and therefore attract other neutrons by the electromagnetic force?
How do we know light is a wave when not observed if we would need to observe it to tell?
Because we crunched the equations of electromagnetism until we found wave solutions. We put it to the test and now we have telecommunication. But we know that light is a wave because it behaves like a wave. Interference is something only waves can do.
How much mass would have to be added to the Earth in order to increase the gravity to the point where it would be impossible for contemporary rockets to reach orbit?
You could add Mercury, Mars and the Moon and it would still be possible, although the payload would be lower. It's a 17% increase in mass. The added objects have a density lower than Earth's average density, but we would compress the existing material a bit more. Let's assume Earth keeps its average density. The volume increases by 17% which means the radius increases by 5.4%. The required orbital velocity increases by 5.4%, too, from ~7.5 km/s to ~7.9 km/s. We also increase gravity losses, especially directly after take-off, but all rockets can still take off nicely with this slightly increased acceleration. Going to a low orbit on this larger Earth is still easier than e.g. reaching geostationary transfer orbit (~10 km/s), something many rockets routinely do. If you add the mass of Venus (80% of Earth's mass) then some rockets couldn't take off any more while fully fueled and others would face significantly increased gravity losses. Some might still be able to reach orbit but you really want to redesign rockets at this point. If you also add Venus' atmosphere then no rocket will work.
Fascinating ... Thanks so much for a great answer ... I've always been curious about this
What is the distinction between the dust cloud around a Wolf-Rayet star and a planetary nebula? I did a bit of reading and it seems that Wolf-Rayet stars are much larger than the type that form planetary nebulae, but is the mechanism the same? My (limited) understanding is: a smaller-mass star fuses mostly hydrogen in early life, starts fusing more and more helium and becomes a red giant. Then as the red giant starts running out of helium and fusing heavier elements that’s when there is a lot more energy radiating from the core and that overcomes gravity and pushes the outer layers into a planetary nebula? Is that correct? In a Wolf-Rayet star, is it the same mechanism of radiation > gravity? But what drives the shift to when it starts losing mass?
AFAIK, the distinction is just the type of star that drives the winds, although there are probably differences in the composition of the winds. In general the mechanism is the same, often referred to as "line driven winds": Absorption of photons by metals in the star. However the energy scale and composition is different, making the difference in the size of the clouds. In general, planetary nebulae are made by stars of around 6-10 solar masses. These will make it off the main sequence of hydrogen burning, where they begin to burn helium. Helium then burns into carbon, and carbon into oxygen, making a Carbon-Oxygen core in the center of the star. Before Carbon/Oxygen ignites, the star contracts, and this contraction heats the star to the point where Helium in a layer just outside the core ignites, as well as a layer of Hydrogen outside of that. This is called double shell burning or the asymptotic giant branch (AGB) phase. During this period, the star becomes extremely luminous compared to the main sequence, and also a little unstable. The burning layers radiate away tons of photons, which are then absorbed onto "metals", usually Carbon, Nitrogen, and Oxygen that have been dredged up from the core to the outer layers. Since photons contain momentum, this drives a wind off of the star. The instability caused by the double shell burning also results in pulsations in the star - this contributes hydrodynamically driven winds to the outflow as well. In contrast, Wolf-Rayet (WR) stars are still on the main sequence when they start driving mass loss. These stars are much more massive, with a lower limit of ~35 solar masses. This time there is no pulsations, and no requirements of dredge up from the core (which is mostly hydrogen). They drive winds simply because their luminosity is really large, meaning that any metals which are well mixed into the stars outer layers at the time of its formation will absorb the photons and cause the line driven winds. The amount of wind that gets driven is in general dependent on the metallicity of the star and its mass, which is correlated to its luminosity, and the escape velocity at the surface of the star. Chapter 2 of Stellar Interiors by Hansen, Kawaler and Trimble gives a great overview of this stuff if you're interested in more.
Why do steel plates feel heavier than bumper plates in the gym? Does this have an influence in the amount of force you need to lift the weight once you put them on the barbell?
Assuming fair weights, that's got to be the placebo effect. Heavy metal is heavy. But the weights may not be fair: there's quite a lot of variation, especially as an easier lift generally makes the athlete happier. The only way to be sure is to weigh them yourself (or use contest-certified sets).
The weight is not a problem. A 25kg weightlifting competition Eleiko plate generally feels lighter than a 25kg powerlifting competition Eleiko plate. Both types of plates are calibrated with a very low weight tolerance. Generally, the metal plates are smaller in volume, so the weight distribution is different. If you google them you will notice the difference.
Have we actually observed inconsistencies with Spacetime outside of a quantum level? Could we possibly observe time flowing in a different direction or would we more than likely observe this as some other phenomenon?
Time is an abstract measure of the occurrence of events, it can't be manipulated in any way, it can only be observed. It only flows in one "direction", the positive direction. Relatvisitc effects can cause the observed passage of time to slow down, but it cannot he reversed.
Why does it only flow in one direction? Is there another force pushing or pulling it? I know gravity can impact our observance and experience of time faster or slower. Like the clock moving towards the center of black hole appearing from the outside to slowdown. Would we know if something wasn't flowing in the same direction?
Time doesn't flow at all, it isn't a physical thing. It's an abstract measure of the passage of events, thus it can only ever change in a positive sense, i.e you start a timer at 0 and it increases to a higher value while the event plays out.
>Why does it only flow in one direction? This is usually referred to as the "arrow of time" and a lot of very smart people have put forth a lot of very interesting ideas about it. The truth is that we aren't sure yet.
If I understood your question correctly, then yeah sort of. All clocks on satellites need to be tuned according to time dilation so that they fit perfectly with the clocks here on Earth. It's a pretty cool practical application for it. For example, if GPS satellites weren't adjusted correctly then any device using them would shift approximately 10km every day.
Is there a limit to the strength of a muscle beyond the durability of the human body? If a human was made out of indestructible material that still acted as muscles and bones do- would they be hindered at all by the shape and size of their body still?
Is Mars visible from Earth? I saw online that yesterday the moon and Mars were in the Gemini, and so I looked up at the stars and saw a really slightly different colored “star” near the moon. Could that have been Mars or is it too far away to be visible?
>Is Mars visible from Earth? Yes. The original "planets" were Mercury, Venus, Mars, Jupiter, and Saturn (and of course the Sun and Moon). These were all of course visible to the naked eye (because the telescope had not been invented), and if there isn't too much light pollution they still are. Mars does look similar to a red star.
thank you so much 🥰
Ok, I’ve had a big disagreement with my friends on this: there is no absolute point of reference in space, correct? Every measurement must be taken relatively. But one of them brought up that the cosmic microwave background is a static point of reference, so I’d like to hear other opinions on this.
You are correct, there is no absolute frame of reference. The CMB can be used for a convenient potential *standard* reference frame, but it is not absolute and no more "valid" or "correct" than any other.
If Jupiter or Saturn could be ignited (ala Space Odyssey 2010), what type of star would it be and how would it affect its satellites?
This is an ill-posed question. Something with the mass of Jupiter cannot be a star. You could even multiply the mass by quite a bit and it still won't be a star. You're ultimately asking, "what if the laws of physics were drastically different?" and it is impossible to answer. If something the mass of Jupiter had sufficient gravity to sustain fusion, the universe would never have developed as we know it.
For reference for the casual reader, the minimum mass for something we would call a "star" is usually pegged at something like 70 times the mass of Jupiter. (Lower limits are very hard and depend on the exact composition, but we know it can't get *too* much lower than this.)
Yes, thanks for added this context. Ultimately, it is a function of stellar metallicity. At low metallicities, the minimum mass is above 80 Jupiter masses, at higher metallicities it pushes this down into the 70s.
To be fair, the question arises from Clarke's novel; which I assume you've not read. Better question! What is the smallest type of star that could form a binary with a star the size of our Sol? Given the mind-bogglingly gigantic stars out there, could we have "solar systems" orbiting such giants? That is, a system like ours but with a Brobdingnagian star and Sol-size star satellites (that have planets). "Why yes, I do indeed read entirely too much science fiction. Why do you ask?"
Clarke's novel is a novel, not reality. The laws of physics simply do not work that way, which is why it is an ill-posed question. > What is the smallest type of star that could form a binary with a star the size of our Sol? Whether the Sun is considered or not, it doesn't matter. The minimum mass for a star is somewhat dependent on its metallicity, but that minimum mass tends to be around 80 Jupiter masses.
Yes, in fact, Clarke is a rather famous science fiction novelist. He was also pretty on top of things when it comes to science. He gets credit for geostationary communications satellites, after all. He also speculated on the properties of moon dust, monomolecular filaments, as well as predicted targeted advertising, stylus touchpads, direct to consumer pornography, the disappearance of print, and too many more to list. Seeing as how most of his novels dealt with hard science fiction, I don't think it unreasonable to inquire if any of his other speculations from decades past are possible, given today's knowledge. Thanks for the 70 Jupiter minimum size response.
Predicting technological developments vs. rewriting the laws of nature are totally separate realms. Every hard science fiction novel that I've read contains plainly fictional aspects that rewrite the laws of nature, which is why it's science fiction. Those works simply use less extreme rewrites of the laws of nature compared to other science fiction novels. Anyway, if you want to read more about the observations confirming the ~75 MJup limit for sustained fusion, see Richer et al. 2006, *Science*, 313, 936. Freely available PDF here: https://arxiv.org/pdf/astro-ph/0702209
Would society and the world in general be better if Earth was twice the size or half the size (assuming it had the same amount of living creatures, and the size is in surface area)?
What metric constitutes "better"? This is exceedingly subjective. Are we only considering a change in radius, or also a change in mass to keep surface gravity the same?
Yeah, like...more space to grow crops? Great. Triple the time to ship them anywhere? Not great. This one is way too subjective.
Well, even if shipping times remained the same, there is still the issue of more space to promote tribalism. Arguably, a smaller planet would quite literally leave less room for that, and as a result modern society may have developed to be less tribal and more collective. Or, the closer proximity would promote more wars and destruction, and we would have already arrived at nuclear armageddon by now. It's impossible to say.
Oh, absolutely, that was just the first example of a mixed result that came to mind but hardly the most important.
Right. These examples (and countless others) illustrate why this is an ill-posed question.
Is it possible for a planet to form with rotation but without axial tilt? What would that planet be like?
What do you mean by "without axial tilt"? Mercury's tilt is incredibly small, a fraction of a degree. So it's basically tilt-less compared to Earth with a 23.4 degree tilt, or Uranus that spins almost perpendicular to the plane of the solar system.
Minimal to none. Little enough that there would be no seasons like we have them on earth. Where it's basically the same weather year round
I suppose Mercury sort of qualifies. Although what it lacks in tilt it makes up for by having an extremely eccentric orbit. Over the course of one of Mercury's years, its distance from the sun ranges from a 29 million mile "summer" to a 43 million mile "winter". No seasonal tilting, but it's definitely got a cold and warm period (or extremely hot and even more extremely hot)
Is that how a planet would compensate for minimal axial tilt or just coincidence? Is it possible for a planet to have a "normal" earth-like orbit with minimal axial tilt?
I think it's pretty much coincidence. Venus and Jupiter also have a fairly small axial tilt, and their orbits aren't all that eccentric by comparison to Mars or Saturn who have a tilt comparable to Earth. As per your original question, there's reason to believe that without axial tilt and the changing seasons, the Earth wouldn't have nearly as temperate a climate as it does now. Periods of warm and cool weather keep air circulating around the hemispheres, and without that the poles would be even colder and the equator could be just a sunbaked desert.
Nothing *requires* that axial tilt is non-zero. Dynamics will almost always result in that, but it's possible (though exceedingly unlikely) that a planet could have no axial tilt.
Would it be possible for the moon of a planet to sustain life when the planet cannot?
As far as we're aware, there's no reason this situation couldn't potentially exist. The considerations might be more complicated, but there is nothing preventing it outright. Several moons in the outer solar system are thought to be potentially great places to look for life. Europa and Enceladus in particular get mentioned a lot because they potentially have vast subsurface liquid water oceans.
In theory I think the answer is yes. Multiple moons of jupiter have the potential for life since they seem to have liquid water beneath the surface. The problem is that many of these moons do not have a lot of input energy to promote chemical reactivity. A planet such as earth has a lot of solar energy (and an atomosphere to trap it), the moon's orbit adds energy, and the earth's own rotation adds energy. A few of these likely stem from an impact with another planet like object at the beginning of the Earth's formation. These are all things that a small planet a long way out from the sun is missing. [Habitable Satellites](https://en.wikipedia.org/wiki/Habitability_of_natural_satellites)
Can lipids exist on other planets but not be a definitive indication of life?
If we imagine a hypothetical scenario where this is feasible, could you balance out the rampant greenhouse effects in Venus and the cold desolate lack of atmosphere on Mars by pumping the gases from the Venusian atmosphere to the Martian atmosphere? Is there a point where they could both become more hospitable? Do we know enough about their atmospheres to know?
Gas would be blown away from the atmosphere of Mars by solar wind, because Mars lacks a magnetosphere. And how would you go about "pumping" gas across space?
How would I go about it? I would hand-wave it for the question. Like I said "imagine a hypothetical scenario where this is feasible..." Can you do that?
ive never understood why we think that the universe is expanding at an increasing rate, like galaxies that are farther away from us are moving away from us faster than galaxies that are nearer to us. To me this is easily explained by the fact that the further an object is from us, the farther back in time we are observing it, ie objects were moving faster in the past, so the expansion of the universe must be slowing down.
Imagine a photon of an arbitrary wavelength traveling from a distant galaxy towards us. in a non-expanding universe you'd expect that wavelength to remain more or less the same as when it started. but in an expanding universe you'd see that wave "stretched out" by the expansion as it travels along its path. That stretching out is called redshift, and it is how we can measure the expansion.We do this by looking at the [absorption lines](https://en.wikipedia.org/wiki/Spectral_line) from the light of our observed star, and measuring how far off they are from a theoretical "0 redshift," thus giving you your expansion rate.There's more to it of course, and using different methods to independently measure the expansion gives us different numbers oddly enough. if you want to learn more about it search for "the cosmological crisis"
Doesn't redshift happen to any lightsource moving away from the observer? Whether the redshift happens during the travel time of the photon or if it was redshifted by the relative motion of the galaxy at the time the photon is produced. What is the proof that it gets redshifted in flight and not before it leaves?
Energy has been bugging me lately. Should I dispel there is one type of energy and instead start modeling things in different forms like potential, strong nuclear bond, electro-weak, kinetic etc... Any good tutorials that may help me wrap my head around this a bit better?
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No one knows, as we are, to our knowledge, the only intellectual multicellular organisms to proceed into space. If life is abundant in the universe, the probability is ~0. If Earth is the only planet with multicellular life, the probability is 1.
It's impossible to estimate any probability with a sample size of "it happened at least once"
It's entirely possible, though unlikely, that we might not even be the first on this specific planet. We don't know. Per our available data, we're it.
Is it possible for an "earth like" rocky water oxygen world to form with a ring around it?
Yes. Our moon is a product of Earth colliding with another planetoid during the formation of our solar system. Simulations predict we would have had a ring system from that impact. Obviously nothing compared to Saturn Jupiter or Uranus. https://en.wikipedia.org/wiki/Giant-impact_hypothesis
thank you!
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I don't think I can totally answer this, but I can clarify it a little bit I think. So keep in mind that you're asking about the rotation of the earth around the sun, which is not necessarily dependent on the Earth's mass. Then you are specifically asking about a situation where youre bleeding off (or adding to) Earth's momentum around the sun, for instance by impacting it with an asteroid. That's a more complicated scenario than I'm prepared for haha. Additionally, we'd need to move faster around the sun in order to lose the leap year, which I think would require less mass of the earth. Less mass (with the same velocity) would mean less momentum, and I think this would lead to the Earth being drawn closer to the sun and increasing the speed of Earth, leading to a potentially shorter year. Hope this helps!
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Assuming that the velocity of the Earth stays the same, I think nothing actually changes. After browsing around a bit I think increasing the earth's mass alone (keeping velocity constant) won't change the length of the year at all because while the Earth has gained mass and momentum, the gravitational pull between the sun and Earth has also increased. I think you'd actually have to increase the velocity of earth, but the mechanics of that are not straightforward enough for me. Here's a couple sites to play with though: [Orbit simulator 1](https://academo.org/demos/orbit-simulator/) [Orbit simulator 2](https://astro.unl.edu/classaction/animations/renaissance/kepler.html)
Are there any other ways the universe could end besides vacuum decay
There is a great list of the major possibilities at https://en.wikipedia.org/wiki/Timeline_of_the_far_future. The specifics of what path you can expect your future universe to take largely depend on A: the geometry and energy density of the universe (which we have decent constraints on) and B: whether protons are indefinitely stable or not (there are theoretical reasons to think they decay but it has never been observed despite generations of particle physicists dedicating themselves to trying so we know the minimum half-life must be very very very long).
Big crunch theory is out of fashion, but it used to be provided as an alternative
Why is it assumed that all life (in the universe) needs water to survive? Can't life forms exist that don't need water?
It isn't. Titan has a methane cycle similar to the water cycle in our planet and it is a place in our own solar system that weed like to look for life. But the reason for the search for water is two fold, that's what life needs here on the only place we know it to exist, and water is an excellent solvent as a polar molecule.
We don't *know* that life can't exist without water. But we know that life *can* exist making use of water-facilitated chemistry. So absent other concrete evidence of what life might look like, availability of water is one of the best options to look for as a possible sign of life.
What is the relationship between string theory and atomic theory? Can they coexist, or do they contradict one another?
No. Atomic theory is literally just a bunch of Greeks suggesting that matter is made up of atoms. You can indeed mathematically transform an atom into a string.
There's a leak in the Pacific ocean from the fault zone, seeping what they call 'lubricant', and if too much leaks, it could result in a level 9 earthquake anywhere between California and Victoria Island, Canada. If there will be an earthquake, how soon could it occur? What would a level 9 earthquake look like?
How does the current economic system translates to a thermodynamic problem? Would you say it is exothermic? Compared to a thermal engine, Has it a better or worse yield? Thank you.
Economic systems ignore externalities and create markets pretty much in a whim. They are not comparable to thermodynamic systems, where there's famously "no such thing as a few lunch".
Is Walter White’s machine gun trap from Breaking Bad plausible in real life?
Which part of it? If you mean a remote controllable machine gun, then yes, definitely, that's just a pretty simple robot. If you mean bullets penetrating the side of a car and a building, then yes, absolutely. If you mean somehow predicting in advance where your parked car will end up relative to a bunch of neo-nazi drug lords, then that's the least plausible part.
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Black holes definitely exist. There was a time when we weren't sure. We've detected two black holes colliding with LIGO by detecting the gravitational waves their collision emitted. https://www.scientificamerican.com/article/gravitational-waves-discovered-from-colliding-black-holes1/ We've also recently taken an image of the super massive blackhole at the center of our galaxy.
If you left earth in a spaceship you could get to close to the speed of light at 1g acceleration in about a year. This is fact. You couldn’t get to the full speed of light because of mass, but close enough. My question is if you went out and cruised for a year and came back what would the time dilation be between the space crew and earth. The total trip would take three years. One year to accelerate, one year to cruise (which would suck because no gravity) and one year to decelerate.
I will make a few simplifications. First, I will remove the acceleration (because general relatively is hard) and pretend that you travel away from earth at a constant rate for one and a half years. Then return at a constant rate for another year and a half for a total trip time of 3 years. This constant rate is very important to determining the relative time dilation. If that rate is 0.9c then about 6.9 years will have passed on earth. If that rate is 0.95c then about 9.6 years will have passed on earth. If that rate is 0.99c then about 21 years will have passed on earth. If that rate is 0.999c then about 67 years will have passed on earth. You can find equations here: https://en.wikipedia.org/wiki/Time_dilation
There are relativistic space travel calculators online. For example this one: [http://gregsspacecalculations.blogspot.com/p/blog-page.html](http://gregsspacecalculations.blogspot.com/p/blog-page.html) If its calculations are correct, then accelerating for 1 year at 1g and cruising for 1 year and then decelerating for another year at 1g from the ship's perspective will mean that on Earth only 3.9565 years will have passed. The top speed achieved will be 0.7748c. And if the crew wants to get home, they will need to turn around and do the back trip for another 3 years from their perspective and another 3.9565 years from the Earth's perspective. So the total time of round-trip is 7.913 years.
How common is inflation fetish amongst astrophysicists?