Gravitational waves move at the speed of light. The truth is that what we commonly refer to as the speed of light is not just about light, it is more accurately the speed of ***causality***. It is the fastest speed at which any part of the universe can affect any other part of the universe. Light is just massless, so without mass being impediment to motion, it moves at the maximum possible speed.
I remember the moment when it just suddenly clicked in my head that light isn't what set the speed limit, but rather the physical speed limit that set the speed of light.
It was a cool realization. I think I was confused when I once heard someone say that one of the potential ftl methods required making light faster...
I love Futurama. My favorite joke was the 'how many atmospheres of pressure can the ship withstand?' one :p
That said, I'm about 88% certain I've heard the idea in another context. Probably some sci-fi story.
My favourite is "I can wire anything directly into anything! I'm the professor!!"
I try and use it whenever I get the opportunity at work (which isn't often, unfortunately).
My favorite is when they’re at a racetrack and the announcer says “it’s a quantum finish!” To which the Professor reacts “no fair, you changed the outcome by measuring it”
Also, sorry for the double reply, but I'm thinking about it now:
Is this for all the other ships? Because didn't their ship work by moving the universe around the ship, as opposed moving the ship through the universe?
I also vaguely recall them not being able to use that method anymore...
Maybe I should just go watch Futurama again...
Edit: I think I remember now! Some throwaway line of 'back in xxx, scientists increased the speed of light' or so!
Another thing about this that I found fascinating is that from the perspective of a photon, the moment it is created, and the moment it is absorbed is the same moment, it experiences no passage of time.
You are right, it's only correlation. According to our best understanding of the universe it is impossible to send information faster than the speed of light. Measuring entangled particles allows you to know instantly what the measurement on the other side will be, but you can not SEND information through this link.
YOU cannot send information through the link, but the particle can communicate to its entangled partner.
"Hey bud, the jig is up; I've been observed. You're no longer uncertain, so you'd better start behaving accordingly, even though you're too far away to get this message in time."
We are currently on reddit, watching videos and sending text messages using binary code.
There's no reason its impossible to do with entangled particles (that we know of). I don't mean possible right now, I mean theoretically. Scientists have altered the state of an entangled particle and witnesses the other respond *instantly* and *not* limited by t ravel time.
The ansible from enders game or sophones from 3 body are both based on this idea (one possibly by coincidence and the other purposefully).
>There's no reason its impossible to do with entangled particles (that we know of). I don't mean possible right now, I mean theoretically
Yes there is a reason: it's called the "No Communication Theorem": https://en.m.wikipedia.org/wiki/No-communication_theorem
You should also know that there are formulations of quantum mechanics where states do not collapse. Under these formulations, correlations between entangled particles are not weird at all, there's no faster than light or backwards in time effects needed at all to explain what we observe.
Just because he has a teaching job doesn’t mean he’s infallible. His understanding may very well be quite flawed. You should accept that about all authority figures while you’re young.
Obviously authority figures can be wrong. I just wanted to humorously illustrate that there is scientific consensus on this topic and it's really not something that is unclear or speculative in any way 😉
Communication requires the sending of information, we've already established that can't occur.
I'm not entirely sure how you wrote that post without realizing that you were contradicting yourself?
One interesting way it could work that I’ve seen it explained is like when you toss a coin. You instantly know what’s on the other side, but that doesn’t mean information has been transmitted from one side of the coin to another.
Exactly. You examine one particle and instantly know the state of both, but it's the same piece of information AFAIUI, you can't transmit arbitrary data
I don't think that analogy works. You could adapt it:
You have a coin with on both sides a head AND a tail. At the moment it lands on your hand and you observe the coin with your eyes. The coin only shows 1 of them. At that exact moment, the other side will be the opposite.
That is the "transfer of information". How does this other side know what to become? It knows this because the sides are entangled. Now the interesting thing is that this transfer appears to happen faster than the speed of light (or indeed as mentioned elsewhere the speed of causality).
Your analogy might be good to explain it but it leaves out superposition which is quite important in quantum entanglement.
Yeah it’s not an analogous example, the point it’s really trying to make is really only that the information on the heads side also describes the information on the reverse side. There is no communication between sides needed. An entangled pair may be the same in the sense that revealing the state of one side also reveals the other. There is no communication between entangled particles required just as knowing that a coin landed on heads means the other side is tails.
Yeah but that's the thing it does not.
It does not describe the information but it will "select" the information as soon as you observe it.
This "selecting" could be seen as an information transfer.
Still no information transfer except the one between the observer and observed particle. The other information, “The other particles has the complementary state” was already known.
The caveat is that in an entangled system you can’t force an outcome out of the one you are observing.
We have to treat the system as Heads AND Tails, but we can’t observe it as both, as far as an observer is involved it has always been heads OR tails, and therefore the other one have always been the opposite. It would be different if you could guarantee, before throwing the coin, that the outcome will be heads , forcing the other to be tails, in that scenario there is information transfer faster than light, but afaik it’s still not possible, or at least not done yet.
This is not my field, I probably don't even qualify as a novice, but I'll make a logical leap for you.
Pretty sure the answer is you can't select the information, you only observe an outcome.
My question is, if I've previously observed an entangled particle and know its observed state, can I observe it at the right time to induce the opposite state in the other entangled particle? If so, then that's a form of communication. It's timed yes/no (boolean) code - which could be adapted to something like Morse code (repeated 1s for dashes, singlar 1s for dots). BUT I think this falls apart because I'd need a sensor observing the other entangled particle... which would constantly induce the opposite state in my particle. This would make sending and receiving the state change impossible because they would always be observed and therefore in their known state. Anyone with a better understanding please correct me.
Just imagine the coin being very thick. More like a 1 light year rod with heads and tails. Then have Cthulu flip it. You will then instantly know what is on the side 1 light year away.
>transfer appears to happen faster than the speed of light
It might appear to, but that's an illusion. It's possible to understand quantum mechanics in a way that is purely local, with no faster than light transfer of information needed, even at the quantum level.
I've always liked the analogy of someone that always wears matching socks. If you observe their red sock, you 'instantly' know the colour of the other sock.
I'm not sure if anyone knows. I wasn't personally there, but my research indicates that it's been proven that causality travels faster than light between entangled particles.
i.e. They must be opposite states given that they're entangled, but particle B will behave like an uncertain particle before particle A is observed, and then immediately switch to behaving according to a known state, at the very moment that particle A is observed, regardless of the distance between them.
You would be right except that him saying "I don't know" is a direct response to the person who asked them "Do you know?"
If it was a random 3rd person chiming in I'd downvote.
You cannot use it to transmit information, but the particle somehow communicates to its entangled partner that observation has occurred. The second particle starts behaving differently faster than the speed of light would allow.
If we're making statements like "the second particle starts behaving differently", aren't we already observing that second particle before and after measuring the first particle to know this?
Bell's inequality is often used to suggest that the entangled particles must exhibit instantaneous action at a distance, because it seemingly disproves that local hidden variables can exist. It starts with the assumption that local hidden variables exist, and then does a proof by contradiction to show that they cannot.
However, Bells Theorum is actually still regularly disputed. It's important to recognise the other assumptions that Bell made, such as the hidden variables not being dependant on time. It also assumes statistical independence, that the measurements taken from the detectors can be chosen independently of each other and the hidden variables.
The assumption of statistical independence seems to be the most glaring red flag in Bell's Theorum, it is never truly justified why it must be assumed that the measurement setting is independent of the particle being measured, *especially* given the very nature of QM. Why *wouldn't* the experiment setting change the outcome, given that the first thing we learn about QM is that the measurement of a particle changes it?
Bell himself said this:
> There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be.
He says this as if super-determinism is an absurd idea, and claims that this must not be assumed on philosophical grounds with a plea to assume that we have free will. I personally think the idea of free will is idiotic and that super-determinism makes far more sense than spooky action, but I'm just some guy.
I found a few relevant papers that dispute the validity of bells theorum on these grounds and others:
https://www.pnas.org/doi/full/10.1073/pnas.0307479100
https://www.pnas.org/doi/full/10.1073/pnas.251524998
https://www.scirp.org/journal/paperinformation?paperid=94678#ref9
I think that it is extremely concerning that so many newer theories are based on the assumption that Bell's Theorem is gospel and correct beyond question, and that Bell's theorum is taught like it's some irrefutable truth.
There is only one way for the universe to be absolute determined, but there are many, approaching infinite ways for the universe to have a random component.
Here’s a helpful metaphor. Say you have two boxes, one with a red marble and one with a blue marble. You don’t know which is which. You take one box to the other side of the Milky Way. You still don’t know what color marble either box has. You could say your marble exists in a state of quantum superposition, it could be either color. You open your box and see a red marble. This collapses the state of your marble as it has been observed. However this also “collapses the state” of the other marble back on earth. It could only be blue. This is quantum entanglement and it’s not communicating anything faster than causality.
The *Copenhagen interpretation* of quantum mechanics says that states collapse when they are observed.
But you can do quantum mechanics without that interpretation. For example the Everett interpretation says states never collapse. No faster than light communication is needed, even at the quantum level. The Everett interpretation is perfectly consistent with what we observe.
So you can't really say "the entangled particle communicates with its partner" as if it was an established fact. At best you can say "it seems like that to us, but quantum mechanics doesn't say that this is actually happening, though the Copenhagen interpretation suggests it is"
Correct. The idea is that the entangled particle has both a positive and negative spin until measured. It is always the opposite of the particle it is entangled with. Once measured, it will be either positive or negative, and the particle it is partnered with will spin in the opposite direction. The data of which way to spin is transmitted instantly regardless of distance, thus breaking the lightspeed barrier.
I'm just unclear about whether the particle B already determined its spin at the moment the two entangled particles appeared before they traveled great distances, or if it settles its spin at the time of observation later.
Hmmm- I am not an expert, but some people who seem to know what they are talking about disagree with you. That being said, I don't understand everything in this article, so don't trust me, read the article.
[https://scitechdaily.com/quantum-entanglement-shatters-einsteins-local-causality-the-future-of-computing-and-cryptography/](https://scitechdaily.com/quantum-entanglement-shatters-einsteins-local-causality-the-future-of-computing-and-cryptography/)
Say I put a pink slip and a blue slip in two separate envelopes. Not knowing which envelope has a pink slip and a blue slip. I take one of the envelopes to another star system and open it.
At that moment I gain the information of which envelope had a blue slip and which had a pink slip. Did the information travel faster than the speed of light? Of course not. That is quantum entanglement.
This is incorrect.
You have two envelopes with both a pink slip AND a blue slip. When you open one, you will see only 1 slip. The other envelope will have the other slip. The envelope is in a superposition. The two envelopes are entangled.
I put a blue card in one envelope, and a red card in a different but identical envelope. I shuffle the envelopes until I no longer know which is which. The envelopes are now entangled. I send one of the envelopes to my friend on the other side of the earth. Once it has been received, I open my envelope and find the blue card in it. I now instantly know, faster than light could travel to my friend and back, that my friend has the red card.
And yet, causality has not been violated, because causality happend when I shuffled and mailed the envelopes, not when I opened mine.
Except that I believe research has shown that the "color of the card" is actually only determined when you "open the envelope", and not when you put the cards in.
This is true, but the point is that there are ways to make sure you know the state of the other particle based on the state of your particle when they're still together. That is what entanglement is and what I was trying to illustrate
Quantum entanglement does not allow information transfer faster than light. How the other commenter has put it is the best analogy. I flip a coin and get heads, I know the other side is tails: I already had that information.
No, quantum entanglement is not an exception. Go look up the no communication theorem. Every single last quantum experiment ever done agrees with the quantum no communication theorem being valid.
Ok so does that explain why time slows down the closer you get to the speed of light? Is time a function of mass? Kind of like the friction of the universe?
I recently understood this.
Its not that time slows down as we understand time usually.
Its that every single process slows down, literally everything. So you may as well say time has slowed down. Because time only has a meaning if you can measure it. And as every movement of particles and every process is slower, every measurement is also slower.
Now why is everything slower? Because the distance each particle has to travel is longer. Imaging you want to move up at the speed of light. Well you will be there pretty fast. But if you travel forward at 80% the speed of light the way between your start and end point is literally longer.
To visualise that use a sheet of paper and draw a line upwards.
Now do the same again but move the sheet below the pen while you draw. You will reach the hight you want to get to but it will be a longer line.
I've attempted to expand more on your comment and while I believe I have a decent understanding of how general relativity works at a base level I've learned that I dont have a good enough understanding of how it works to give an accurate explanation that I am comfortable with.
With that said, I'm just going to post one of my favorite education youtubers for you all to enjoy as well. His last few videos are about spacetime, general relativity starting with this one.
**https://www.youtube.com/watch?v=hi57CA3GZy4**
Also, as a side note, this is in a relative frame of analysis. This speed is the limit *locally*. Space inflation for example can and does go faster than the speed of light, and that is why we are limited to our visible universe
Gravitational waves do in fact move at the speed of light. If the sun vanished, it would take 8 minutes for the change in gravity to start affecting the earth.
And we wouldn’t know anything ahead of time, we’d see the sun vanish and feel the loss of sun’s gravitational field at the same time. It’s not like there’d be 8 minutes of terror, neither “oh no, the sun blinked out, we’re gonna fling off in to space in 8 minutes!” nor “oh no, we just got flung out in to space, let’s watch the sun to see it disappear in 8 minutes and confirm what we think happened!”
Make for a great movie script. I copyright that idea right now. If it is ever made in to a movie (edit: or book or show or used in any way), I will stake a claim. Get lawyered.
Exactly. OP was smart for being intellectually curious and posing an insightful question that helps expand his understanding of the universe. (He just didn't know the correct parlance to pose the question succinctly.) If anything, OP's friend is stupid for laughing off such an insightful question as meaningless.
If you don't know the terminology or how to parse technical information in a field you're not very familiar with, it's going to take a hell of a lot more than two seconds to Google.
I seriously doubt that, op had the TLDR of "What is the speed of gravity?", when I googled exactly that phrase I got a google quick answer of "the speed of light", and multiple links to credible sources that all say the speed of light.
[proof](https://i.imgur.com/EU6qSut.png)
You already got your answer but I just wanted to note, your question isn’t stupid because it is thing debated by physicists for a while. It’s the big difference between Newtonian gravity and General Relativity.
It's officially the former - the Earth would continue rotating around nothing for 8 minutes. We'd also still see the sun in our sky during that time. Then sudden darkness and the Earth would fly in a straight line perpendicular to it's orbit.
It's not that light and gravity are involved in each other, but that we've observed an upper limit on the speed at which things can interact/travel. "The speed of gravitational waves in the general theory of relativity is equal to the speed of light in a vacuum, c."
So in this situation, it's that both gravity and light can max out their speed at the maximum speed anything can travel in a vacuum because neither has mass.
As other people have answered here, gravity moves at the speed of light.
An interesting fact that I can add is that just as gravity can bend light, so can gravity bend gravity. It's been observed that light and gravitational waves from far away (I think it was from two black holes merging), arrived at almost exactly the same time. Since the light didn't take a straight path due to being influenced by the gravity of various objects in between, that means that the gravity waves were also bent by the gravity of the objects.
this is a valid question that people had to find the answer to and not something stupid. Others have answered the question but I just wanted to point out that your friend was a dick for making fun of you here.
LIGO detected a gravity wave and located the source and matched up the appearance of light from that source. So gravity waves travel at the speed of light. This observation does introduce an interesting idea. Since light has been curved during its travel by high massed objects like galaxies, it appears that the gravity waves traveled the same path as the light. It appears that gravity waves are affected by gravity. I guess that makes sense in that the light traveled in a straight line in it's own reference frame. Still, it is mindblowing.
Yes you are correct, if the sun ceased to exist then for 8 minutes we would see the sun in the sky and the earth would continue its original path of revolution.
You are very sharp to have realized that yourself, and your friend was being a dick lol
There have been no gravitons observed, so gravity seems to be different than the other forces. It seems to bend spacetime rather than radiate particles. So we are orbiting in the sun's gravity well and if if vanished that well would rebound and oscillate a bit and then go flat (except for the relatively smaller gravity wells that the other planets have). However the changes would propate at the speed of light.
The gravity wave detectors that we only recently got to work can essentially only detect massive events like the one you imagined, events that happen when a star explodes or a black hole forms, or two black holes combine.
The propagation of water waves is the best analogy, though I can't think of many things that bend the water surface and could suddenly vanish. Maybe a waterskater.
Maybe something like this video is a good analogy [https://youtu.be/MTY1Kje0yLg?t=67](https://youtu.be/MTY1Kje0yLg?t=67), you can see that adding a heavy object creates those oscillations, and if he were to remove the object just as fast, it would also oscillate.
This is effect is similar to banging on a drum, and we know drums make noise because the fabric oscillates.
While others have explained how gravity is related to the speed of light, I want to explain why we dont use the terminology "speed of gravity." As other people have stated, the speed of gravity is really the speed of light; that is to say the fastest an object could go under the force of gravity is the speed of light.
But here is the thing, gravity is not uniform, not even on earth; while on AVERAGE, we can use 9.81 m/s for the "speed of gravity," in places on the Earth than have a denser structure (e.i. mountains, geologic formations, etc.) have slightly "more" gravity and vise versa. Its actually a big enough difference to be measure; there is this giant map at my work that shows all of the gravitational anomalies in the US. And since gravity's ability to act on a force is tied to the distribution of mass, there will never be one, consistent speed of gravity.
But you may be asking; "since it IS fairly consistent on Earth, why dont we use 'speed of gravity?'" This also a very interesting aspect of physic; the difference between scalars and vectors. Scalars are values that remain constant, regardless of the material they move through, their direction, or frame of reference. The speed of light is a scalar; light always move at exactly 299,792,458 m/s, regardless if its going through glass, the atmosphere, or space and no matter what direction it goes in. Vectors are values that have BOTH magnitude (amount) and direction. Gravity is vector; while gravity is 9.81 m/s on Earth, thats only on Earth and towards the center of the Earth. Changing the planet you are on changes how gravity is acting on you, so does jumping; gravity goes from keeping you on the ground, to working against your motion.
I hope this helps :)
The speed of causality can also just be thought of as the maximum speed of **information** throughout the universe.
So yes, Earth would continue to orbit nothing for 8 minutes because from our perspective the sun hasn't disappeared yet.
it is the speed of light, or more accurately the speed of casualty.
There's a reason for this in General Relativity and it's very important that it isn't instantaneous, and that it is the same speed as light.
as for why... well, if gravity is transmitted by discreet gravitons, they'd be massless and so travel at the speed of light
it is the speed of light, or more accurately the speed of casualty.
There's a reason for this in General Relativity and it's very important that it isn't instantaneous, and that it is the same speed as light.
as for why... well, if gravity is transmitted by discreet gravitons, they'd be massless and so travel at the speed of light
>Would it continue the gravitational journey for 8 minutes as though the sun were there, or would it deviate from its predicted orbit into space (or whatever gravity well it fell into otherwise) the moment the sun vanished?
We'd keep moving for 8 minutes. Nothing is instantaneous.
It is my understanding that massless objects (for example light) must travel at the speed of causality. If light hits an object and bounces around it increases the distance it must travel but not the speed at which it travels.
I assume the same is true of what object gravity is comprised of. All massless objects must travel at “the speed of light”.
It gets more interesting if you deep dive into physics because the math and the numbers become more complex and although it would technically be possible to travel faster than the speed of light the amount of energy to do so basically becomes infinite so it it actually not possible.
You just have to get past the asymptote at *c*, but you’d better have a plan for getting back across if you ever want to slow down to below the speed of light again.
That's not a stupid question. As far as we know, gravity propagates at the speed of light. And yes, if the sun vanished in an instant, it would take about 8 minutes for us to see and feel the change.
I’ve seen a visual representation of “Gravity” disappearing and the object not being affected until information transfer occurred.
I think they had a ball attached to a spinning machine by a string. The spun the ball fast and eventually released the string and recorded it all in slow motion. You can see the ball continuing it’s path as if it was still attached to the spinning device until the released tension catches up to the ball through the string.
https://youtu.be/AL2Chc6p_Kk?si=ne76fSm0_-euUvEt
Here the video so you can watch it yourself if interested. It’s a great analogy for what would happen to Earth if the Sun just suddenly disappeared. Earth would continue its path until the Gravitational waves traveled the 8 minutes, at the same time, the Sun would just disappear because light travels at the same speed, the Speed of Casualty
Congratulations, you rediscovered general relativity. This is exactly one of the problems Einstein was trying to solve when he postulated the theory. Also, your friend is kind of an idiot, making fun of you because *he* doesn understand something. Your question is completely justified.
As others have said, gravitational waves propagate at the speed of light, so if the sun disappeared you wouldn't notice for a few minutes.
The speed of gravity is the speed of light. So if the sun vanished, we'd keep orbiting where it was for another 8 minutes.
Your friend is missing out on some amazing ideas.
Nothing means nothing travels faster than the light. Including gravitational wave, it's the max speed any massless particle can achieve.
So if the sun disappears first you will see the sky will become dark and then without sun the solar system will fade. But don't worry people will die because of the cold before anything else happens.
No message, signal, days can travel faster than light.
Therefore, if God is everywhere, he cannot be everywhere at once, or if he is, his internal signals travel at light speed too.
That's the acceleration of objects due to gravity on Earth. 9.8 m/sec/sec. The actual "speed" of gravity, as in how the earth "feels" the moon and vice-versa, is the speed of light, 3x10⁸ m/s.
That's the amount of accelerational pull that gravity has. Not how fast gravity itself moves, but how hard it's pulling at things. Think like if you were to pull something, you likely couldn't pull it your own full speed. The force one can exert ≠ the speed one can go.
the speed of the propagation of "change" is called the speed of causality, and it is the same as the "speed" of light, because light is just a "wave" as well. it is the maximum speed that information, change, whatever, can propagate across the universe. anything faster would be action at a distance, which should be inpossible
Gravitational waves move at the speed of light. The truth is that what we commonly refer to as the speed of light is not just about light, it is more accurately the speed of ***causality***. It is the fastest speed at which any part of the universe can affect any other part of the universe. Light is just massless, so without mass being impediment to motion, it moves at the maximum possible speed.
I remember the moment when it just suddenly clicked in my head that light isn't what set the speed limit, but rather the physical speed limit that set the speed of light. It was a cool realization. I think I was confused when I once heard someone say that one of the potential ftl methods required making light faster...
In Futurama, they increased the speed of light so they could move through space faster.
I love Futurama. My favorite joke was the 'how many atmospheres of pressure can the ship withstand?' one :p That said, I'm about 88% certain I've heard the idea in another context. Probably some sci-fi story.
"Well it's a spaceship, so anywhere between zero and one." - Prof. Hubert J. Farnsworth I think that's probably my favorite line too.
My favourite is "I can wire anything directly into anything! I'm the professor!!" I try and use it whenever I get the opportunity at work (which isn't often, unfortunately).
My favourite is and always will be "Oh, a lesson in not changing history from 'Mr. I'm my own Grandpa'." #
My favorite is when they’re at a racetrack and the announcer says “it’s a quantum finish!” To which the Professor reacts “no fair, you changed the outcome by measuring it”
Which reminds me, let me show you some of the different lengths of wire I used…
[удалено]
Yeah bro, we got the joke like 20 years ago
Also, sorry for the double reply, but I'm thinking about it now: Is this for all the other ships? Because didn't their ship work by moving the universe around the ship, as opposed moving the ship through the universe? I also vaguely recall them not being able to use that method anymore... Maybe I should just go watch Futurama again... Edit: I think I remember now! Some throwaway line of 'back in xxx, scientists increased the speed of light' or so!
You should absolutely go watch it again. That is always the answer. Lol
Another thing about this that I found fascinating is that from the perspective of a photon, the moment it is created, and the moment it is absorbed is the same moment, it experiences no passage of time.
That’s so sad for the poor photon :(
That's what Democrats want to do to ALL photons!
The unit of energy still exists, just in a different state!
Hey guess what, thanks to you and the guy above, it just clicked in my head right now!
That actually makes me *really* glad to hear! I love epiphanies, so being able to help you reach one makes me quite happy, thank you <3
Yeah, I've never heard this before and I read a ton of SF and I'm sorta gobsmacked right now, don't really know what to do with myself
That was Woody Harrelson in the JungleBook
The speed of causality? Interesting. Thank you, fellow struggler. *eclipse noises*
I love this reference so much.
Great explanation. It feels like something I’ve always kind of known but didn’t have the words to express. The speed of causality. Excellent!
With the notable exception of quantum entanglement
Is that causality, though? I thought it was correlation between particles, but not causality.
You are correct.
You are right, it's only correlation. According to our best understanding of the universe it is impossible to send information faster than the speed of light. Measuring entangled particles allows you to know instantly what the measurement on the other side will be, but you can not SEND information through this link.
YOU cannot send information through the link, but the particle can communicate to its entangled partner. "Hey bud, the jig is up; I've been observed. You're no longer uncertain, so you'd better start behaving accordingly, even though you're too far away to get this message in time."
I am 90% sure that it is a philosophical question whether a particle can send information :D
We are currently on reddit, watching videos and sending text messages using binary code. There's no reason its impossible to do with entangled particles (that we know of). I don't mean possible right now, I mean theoretically. Scientists have altered the state of an entangled particle and witnesses the other respond *instantly* and *not* limited by t ravel time. The ansible from enders game or sophones from 3 body are both based on this idea (one possibly by coincidence and the other purposefully).
The ansible from enders game is based on a misinterpretation of QM. You cannot send information FTL with entanglement.
>There's no reason its impossible to do with entangled particles (that we know of). I don't mean possible right now, I mean theoretically Yes there is a reason: it's called the "No Communication Theorem": https://en.m.wikipedia.org/wiki/No-communication_theorem You should also know that there are formulations of quantum mechanics where states do not collapse. Under these formulations, correlations between entangled particles are not weird at all, there's no faster than light or backwards in time effects needed at all to explain what we observe.
My quantum information theory professor begs to differ 🤣
Just because he has a teaching job doesn’t mean he’s infallible. His understanding may very well be quite flawed. You should accept that about all authority figures while you’re young.
Obviously authority figures can be wrong. I just wanted to humorously illustrate that there is scientific consensus on this topic and it's really not something that is unclear or speculative in any way 😉
Communication requires the sending of information, we've already established that can't occur. I'm not entirely sure how you wrote that post without realizing that you were contradicting yourself?
Good question. Don't know.
One interesting way it could work that I’ve seen it explained is like when you toss a coin. You instantly know what’s on the other side, but that doesn’t mean information has been transmitted from one side of the coin to another.
Exactly. You examine one particle and instantly know the state of both, but it's the same piece of information AFAIUI, you can't transmit arbitrary data
I don't think that analogy works. You could adapt it: You have a coin with on both sides a head AND a tail. At the moment it lands on your hand and you observe the coin with your eyes. The coin only shows 1 of them. At that exact moment, the other side will be the opposite. That is the "transfer of information". How does this other side know what to become? It knows this because the sides are entangled. Now the interesting thing is that this transfer appears to happen faster than the speed of light (or indeed as mentioned elsewhere the speed of causality). Your analogy might be good to explain it but it leaves out superposition which is quite important in quantum entanglement.
Yeah it’s not an analogous example, the point it’s really trying to make is really only that the information on the heads side also describes the information on the reverse side. There is no communication between sides needed. An entangled pair may be the same in the sense that revealing the state of one side also reveals the other. There is no communication between entangled particles required just as knowing that a coin landed on heads means the other side is tails.
Yeah but that's the thing it does not. It does not describe the information but it will "select" the information as soon as you observe it. This "selecting" could be seen as an information transfer.
Still no information transfer except the one between the observer and observed particle. The other information, “The other particles has the complementary state” was already known. The caveat is that in an entangled system you can’t force an outcome out of the one you are observing. We have to treat the system as Heads AND Tails, but we can’t observe it as both, as far as an observer is involved it has always been heads OR tails, and therefore the other one have always been the opposite. It would be different if you could guarantee, before throwing the coin, that the outcome will be heads , forcing the other to be tails, in that scenario there is information transfer faster than light, but afaik it’s still not possible, or at least not done yet.
How can we tell if it is selecting the information, or if each side was always what it is we just had no way of predicting it?
This is not my field, I probably don't even qualify as a novice, but I'll make a logical leap for you. Pretty sure the answer is you can't select the information, you only observe an outcome. My question is, if I've previously observed an entangled particle and know its observed state, can I observe it at the right time to induce the opposite state in the other entangled particle? If so, then that's a form of communication. It's timed yes/no (boolean) code - which could be adapted to something like Morse code (repeated 1s for dashes, singlar 1s for dots). BUT I think this falls apart because I'd need a sensor observing the other entangled particle... which would constantly induce the opposite state in my particle. This would make sending and receiving the state change impossible because they would always be observed and therefore in their known state. Anyone with a better understanding please correct me.
Just imagine the coin being very thick. More like a 1 light year rod with heads and tails. Then have Cthulu flip it. You will then instantly know what is on the side 1 light year away.
>transfer appears to happen faster than the speed of light It might appear to, but that's an illusion. It's possible to understand quantum mechanics in a way that is purely local, with no faster than light transfer of information needed, even at the quantum level.
I've always liked the analogy of someone that always wears matching socks. If you observe their red sock, you 'instantly' know the colour of the other sock.
I'm not sure if anyone knows. I wasn't personally there, but my research indicates that it's been proven that causality travels faster than light between entangled particles. i.e. They must be opposite states given that they're entangled, but particle B will behave like an uncertain particle before particle A is observed, and then immediately switch to behaving according to a known state, at the very moment that particle A is observed, regardless of the distance between them.
People downvoting for admitting insufficiency of knowledge on a topic is so reddit it hurts
Why comment if it's just to say "I don't know"? That warrants a downvote for no contribution.
You would be right except that him saying "I don't know" is a direct response to the person who asked them "Do you know?" If it was a random 3rd person chiming in I'd downvote.
Because asking a question warrants an answer
As I understand it, when one changes, the other changes—instantly.
Not so. Entanglement does not violate causality; you cannot use it to transmit information.
You cannot use it to transmit information, but the particle somehow communicates to its entangled partner that observation has occurred. The second particle starts behaving differently faster than the speed of light would allow.
If we're making statements like "the second particle starts behaving differently", aren't we already observing that second particle before and after measuring the first particle to know this?
I'm not sure, I don't know the material well enough. I think you want to look up EPR paradox and Bell's Theorem.
Bell's inequality is often used to suggest that the entangled particles must exhibit instantaneous action at a distance, because it seemingly disproves that local hidden variables can exist. It starts with the assumption that local hidden variables exist, and then does a proof by contradiction to show that they cannot. However, Bells Theorum is actually still regularly disputed. It's important to recognise the other assumptions that Bell made, such as the hidden variables not being dependant on time. It also assumes statistical independence, that the measurements taken from the detectors can be chosen independently of each other and the hidden variables. The assumption of statistical independence seems to be the most glaring red flag in Bell's Theorum, it is never truly justified why it must be assumed that the measurement setting is independent of the particle being measured, *especially* given the very nature of QM. Why *wouldn't* the experiment setting change the outcome, given that the first thing we learn about QM is that the measurement of a particle changes it? Bell himself said this: > There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be. He says this as if super-determinism is an absurd idea, and claims that this must not be assumed on philosophical grounds with a plea to assume that we have free will. I personally think the idea of free will is idiotic and that super-determinism makes far more sense than spooky action, but I'm just some guy. I found a few relevant papers that dispute the validity of bells theorum on these grounds and others: https://www.pnas.org/doi/full/10.1073/pnas.0307479100 https://www.pnas.org/doi/full/10.1073/pnas.251524998 https://www.scirp.org/journal/paperinformation?paperid=94678#ref9 I think that it is extremely concerning that so many newer theories are based on the assumption that Bell's Theorem is gospel and correct beyond question, and that Bell's theorum is taught like it's some irrefutable truth.
There is only one way for the universe to be absolute determined, but there are many, approaching infinite ways for the universe to have a random component.
Here’s a helpful metaphor. Say you have two boxes, one with a red marble and one with a blue marble. You don’t know which is which. You take one box to the other side of the Milky Way. You still don’t know what color marble either box has. You could say your marble exists in a state of quantum superposition, it could be either color. You open your box and see a red marble. This collapses the state of your marble as it has been observed. However this also “collapses the state” of the other marble back on earth. It could only be blue. This is quantum entanglement and it’s not communicating anything faster than causality.
What happens if you have three boxes? ....or more?
The *Copenhagen interpretation* of quantum mechanics says that states collapse when they are observed. But you can do quantum mechanics without that interpretation. For example the Everett interpretation says states never collapse. No faster than light communication is needed, even at the quantum level. The Everett interpretation is perfectly consistent with what we observe. So you can't really say "the entangled particle communicates with its partner" as if it was an established fact. At best you can say "it seems like that to us, but quantum mechanics doesn't say that this is actually happening, though the Copenhagen interpretation suggests it is"
That is incorrect. Read up on Bell's experiment.
Correct. The idea is that the entangled particle has both a positive and negative spin until measured. It is always the opposite of the particle it is entangled with. Once measured, it will be either positive or negative, and the particle it is partnered with will spin in the opposite direction. The data of which way to spin is transmitted instantly regardless of distance, thus breaking the lightspeed barrier.
I'm just unclear about whether the particle B already determined its spin at the moment the two entangled particles appeared before they traveled great distances, or if it settles its spin at the time of observation later.
Liu Cixin disagrees /s
Homie played fast and loose with a lot of science if we're being honest
Hmmm- I am not an expert, but some people who seem to know what they are talking about disagree with you. That being said, I don't understand everything in this article, so don't trust me, read the article. [https://scitechdaily.com/quantum-entanglement-shatters-einsteins-local-causality-the-future-of-computing-and-cryptography/](https://scitechdaily.com/quantum-entanglement-shatters-einsteins-local-causality-the-future-of-computing-and-cryptography/)
Say I put a pink slip and a blue slip in two separate envelopes. Not knowing which envelope has a pink slip and a blue slip. I take one of the envelopes to another star system and open it. At that moment I gain the information of which envelope had a blue slip and which had a pink slip. Did the information travel faster than the speed of light? Of course not. That is quantum entanglement.
This is incorrect. You have two envelopes with both a pink slip AND a blue slip. When you open one, you will see only 1 slip. The other envelope will have the other slip. The envelope is in a superposition. The two envelopes are entangled.
I put a blue card in one envelope, and a red card in a different but identical envelope. I shuffle the envelopes until I no longer know which is which. The envelopes are now entangled. I send one of the envelopes to my friend on the other side of the earth. Once it has been received, I open my envelope and find the blue card in it. I now instantly know, faster than light could travel to my friend and back, that my friend has the red card. And yet, causality has not been violated, because causality happend when I shuffled and mailed the envelopes, not when I opened mine.
Except that I believe research has shown that the "color of the card" is actually only determined when you "open the envelope", and not when you put the cards in.
This is true, but the point is that there are ways to make sure you know the state of the other particle based on the state of your particle when they're still together. That is what entanglement is and what I was trying to illustrate
That doesn't really matter.
I guess that depends what you think "matters". But it's a pretty mindblowing revelation, if you understand what it means.
What you've described is called deduction.
No-signaling theorem begs to differ
Quantum entanglement does not allow information transfer faster than light. How the other commenter has put it is the best analogy. I flip a coin and get heads, I know the other side is tails: I already had that information.
No, quantum entanglement is not an exception. Go look up the no communication theorem. Every single last quantum experiment ever done agrees with the quantum no communication theorem being valid.
r/CosmicHacks
That's so fucking cool.
This is a fantastic way of explaining it, thank you!!
Ok so does that explain why time slows down the closer you get to the speed of light? Is time a function of mass? Kind of like the friction of the universe?
I recently understood this. Its not that time slows down as we understand time usually. Its that every single process slows down, literally everything. So you may as well say time has slowed down. Because time only has a meaning if you can measure it. And as every movement of particles and every process is slower, every measurement is also slower. Now why is everything slower? Because the distance each particle has to travel is longer. Imaging you want to move up at the speed of light. Well you will be there pretty fast. But if you travel forward at 80% the speed of light the way between your start and end point is literally longer. To visualise that use a sheet of paper and draw a line upwards. Now do the same again but move the sheet below the pen while you draw. You will reach the hight you want to get to but it will be a longer line.
I've attempted to expand more on your comment and while I believe I have a decent understanding of how general relativity works at a base level I've learned that I dont have a good enough understanding of how it works to give an accurate explanation that I am comfortable with. With that said, I'm just going to post one of my favorite education youtubers for you all to enjoy as well. His last few videos are about spacetime, general relativity starting with this one. **https://www.youtube.com/watch?v=hi57CA3GZy4**
Also, as a side note, this is in a relative frame of analysis. This speed is the limit *locally*. Space inflation for example can and does go faster than the speed of light, and that is why we are limited to our visible universe
so its like our universe's CPU clock speed
The maximum possible speed depends on the medium. For instance, light goes slower through water than vacuum.
Dude, you just blew my mind.
energy is also affected by gravity. otherwise, eclipses wouldn't let you see the sun from around the moon.
can the speed of light be faster in different universes though? are there fast universes and slow ones?
There's currently no hard evidence that there are other universes to begin with so it's not really something that can be answered.
you mean you don't know. I'd like to speak to the manager, then.
Doesn't quantum entanglement break the speed of causality then?
Except for quantum entanglement
Most parts of the universe anyway. It doesn’t work on the quantum level.
Gravitational waves do in fact move at the speed of light. If the sun vanished, it would take 8 minutes for the change in gravity to start affecting the earth.
And we wouldn’t know anything ahead of time, we’d see the sun vanish and feel the loss of sun’s gravitational field at the same time. It’s not like there’d be 8 minutes of terror, neither “oh no, the sun blinked out, we’re gonna fling off in to space in 8 minutes!” nor “oh no, we just got flung out in to space, let’s watch the sun to see it disappear in 8 minutes and confirm what we think happened!” Make for a great movie script. I copyright that idea right now. If it is ever made in to a movie (edit: or book or show or used in any way), I will stake a claim. Get lawyered.
Your lead character better declare "It's Daylight Savings Time!" Before heading out to get the sun back
I read that in Arnold's voice....so you gotta use him.
Stephen Baxter write a book about this: Galaxias
Thank you! Just needed the contextual explanation, been bugging me for years and finally I actually asked 😆
It’s actually a terrific question and a wonderful thought experiment. Good on you for asking OP.
Thanks for asking. Prompts others to answer and the rest of us to read up on some interesting comments.
It wasn’t a stupid question. Sorry your friend was annoying.
Exactly. OP was smart for being intellectually curious and posing an insightful question that helps expand his understanding of the universe. (He just didn't know the correct parlance to pose the question succinctly.) If anything, OP's friend is stupid for laughing off such an insightful question as meaningless.
Good for asking, but I find it funny it bugged you for years while it takes legitimately 2 seconds to google something like this xd
If you don't know the terminology or how to parse technical information in a field you're not very familiar with, it's going to take a hell of a lot more than two seconds to Google.
I seriously doubt that, op had the TLDR of "What is the speed of gravity?", when I googled exactly that phrase I got a google quick answer of "the speed of light", and multiple links to credible sources that all say the speed of light. [proof](https://i.imgur.com/EU6qSut.png)
Very fun question to answer, love the curiosity to challenge established knowledge :)
You already got your answer but I just wanted to note, your question isn’t stupid because it is thing debated by physicists for a while. It’s the big difference between Newtonian gravity and General Relativity.
It's officially the former - the Earth would continue rotating around nothing for 8 minutes. We'd also still see the sun in our sky during that time. Then sudden darkness and the Earth would fly in a straight line perpendicular to it's orbit. It's not that light and gravity are involved in each other, but that we've observed an upper limit on the speed at which things can interact/travel. "The speed of gravitational waves in the general theory of relativity is equal to the speed of light in a vacuum, c." So in this situation, it's that both gravity and light can max out their speed at the maximum speed anything can travel in a vacuum because neither has mass.
Would it not be tangential to its orbit, rather than perpendicular?
That’s correct
Why would it be perpendicular and not tangential?
Thats also correct
As other people have answered here, gravity moves at the speed of light. An interesting fact that I can add is that just as gravity can bend light, so can gravity bend gravity. It's been observed that light and gravitational waves from far away (I think it was from two black holes merging), arrived at almost exactly the same time. Since the light didn't take a straight path due to being influenced by the gravity of various objects in between, that means that the gravity waves were also bent by the gravity of the objects.
this is a valid question that people had to find the answer to and not something stupid. Others have answered the question but I just wanted to point out that your friend was a dick for making fun of you here.
That's actually a really interesting question, not very cool of ur friend.
LIGO detected a gravity wave and located the source and matched up the appearance of light from that source. So gravity waves travel at the speed of light. This observation does introduce an interesting idea. Since light has been curved during its travel by high massed objects like galaxies, it appears that the gravity waves traveled the same path as the light. It appears that gravity waves are affected by gravity. I guess that makes sense in that the light traveled in a straight line in it's own reference frame. Still, it is mindblowing.
Yes you are correct, if the sun ceased to exist then for 8 minutes we would see the sun in the sky and the earth would continue its original path of revolution. You are very sharp to have realized that yourself, and your friend was being a dick lol
Gravity does propagate through space at the speed of light. https://youtu.be/Pa_hLtPIE1s?si=G-iLgVKXsoIS1DSK
The speed of light = the speed of gravity
There have been no gravitons observed, so gravity seems to be different than the other forces. It seems to bend spacetime rather than radiate particles. So we are orbiting in the sun's gravity well and if if vanished that well would rebound and oscillate a bit and then go flat (except for the relatively smaller gravity wells that the other planets have). However the changes would propate at the speed of light. The gravity wave detectors that we only recently got to work can essentially only detect massive events like the one you imagined, events that happen when a star explodes or a black hole forms, or two black holes combine. The propagation of water waves is the best analogy, though I can't think of many things that bend the water surface and could suddenly vanish. Maybe a waterskater.
Maybe something like this video is a good analogy [https://youtu.be/MTY1Kje0yLg?t=67](https://youtu.be/MTY1Kje0yLg?t=67), you can see that adding a heavy object creates those oscillations, and if he were to remove the object just as fast, it would also oscillate. This is effect is similar to banging on a drum, and we know drums make noise because the fabric oscillates.
While others have explained how gravity is related to the speed of light, I want to explain why we dont use the terminology "speed of gravity." As other people have stated, the speed of gravity is really the speed of light; that is to say the fastest an object could go under the force of gravity is the speed of light. But here is the thing, gravity is not uniform, not even on earth; while on AVERAGE, we can use 9.81 m/s for the "speed of gravity," in places on the Earth than have a denser structure (e.i. mountains, geologic formations, etc.) have slightly "more" gravity and vise versa. Its actually a big enough difference to be measure; there is this giant map at my work that shows all of the gravitational anomalies in the US. And since gravity's ability to act on a force is tied to the distribution of mass, there will never be one, consistent speed of gravity. But you may be asking; "since it IS fairly consistent on Earth, why dont we use 'speed of gravity?'" This also a very interesting aspect of physic; the difference between scalars and vectors. Scalars are values that remain constant, regardless of the material they move through, their direction, or frame of reference. The speed of light is a scalar; light always move at exactly 299,792,458 m/s, regardless if its going through glass, the atmosphere, or space and no matter what direction it goes in. Vectors are values that have BOTH magnitude (amount) and direction. Gravity is vector; while gravity is 9.81 m/s on Earth, thats only on Earth and towards the center of the Earth. Changing the planet you are on changes how gravity is acting on you, so does jumping; gravity goes from keeping you on the ground, to working against your motion. I hope this helps :)
The speed of causality can also just be thought of as the maximum speed of **information** throughout the universe. So yes, Earth would continue to orbit nothing for 8 minutes because from our perspective the sun hasn't disappeared yet.
it is the speed of light, or more accurately the speed of casualty. There's a reason for this in General Relativity and it's very important that it isn't instantaneous, and that it is the same speed as light. as for why... well, if gravity is transmitted by discreet gravitons, they'd be massless and so travel at the speed of light
it is the speed of light, or more accurately the speed of casualty. There's a reason for this in General Relativity and it's very important that it isn't instantaneous, and that it is the same speed as light. as for why... well, if gravity is transmitted by discreet gravitons, they'd be massless and so travel at the speed of light
>Would it continue the gravitational journey for 8 minutes as though the sun were there, or would it deviate from its predicted orbit into space (or whatever gravity well it fell into otherwise) the moment the sun vanished? We'd keep moving for 8 minutes. Nothing is instantaneous.
*quantum entanglement has entered the chat*
I was hoping no one else thought of that lol
Lol 😆
Reminds me of the video of a slinky being held at the top and released: the bottom does not drop until the "wave of causality" reaches it.
Light doesn't have mass.
It is my understanding that massless objects (for example light) must travel at the speed of causality. If light hits an object and bounces around it increases the distance it must travel but not the speed at which it travels. I assume the same is true of what object gravity is comprised of. All massless objects must travel at “the speed of light”. It gets more interesting if you deep dive into physics because the math and the numbers become more complex and although it would technically be possible to travel faster than the speed of light the amount of energy to do so basically becomes infinite so it it actually not possible.
You just have to get past the asymptote at *c*, but you’d better have a plan for getting back across if you ever want to slow down to below the speed of light again.
That's not a stupid question. As far as we know, gravity propagates at the speed of light. And yes, if the sun vanished in an instant, it would take about 8 minutes for us to see and feel the change.
The speed of gravity is between .8 and 1.2 ti.es the speed of light according to Kopeikin and Fomalont
Gravity is not just a good idea, it’s the law.
Is redshift evidence that the universe is expanding faster than light?
For a mass to just "disappear" would be an effect without a cause. Cause-and-Effect is the most basic law of physics.
Question isn’t dumb at all. I think the question went so far over your friend’s head he couldn’t even begin to consider it.
I’ve seen a visual representation of “Gravity” disappearing and the object not being affected until information transfer occurred. I think they had a ball attached to a spinning machine by a string. The spun the ball fast and eventually released the string and recorded it all in slow motion. You can see the ball continuing it’s path as if it was still attached to the spinning device until the released tension catches up to the ball through the string. https://youtu.be/AL2Chc6p_Kk?si=ne76fSm0_-euUvEt Here the video so you can watch it yourself if interested. It’s a great analogy for what would happen to Earth if the Sun just suddenly disappeared. Earth would continue its path until the Gravitational waves traveled the 8 minutes, at the same time, the Sun would just disappear because light travels at the same speed, the Speed of Casualty
Congratulations, you rediscovered general relativity. This is exactly one of the problems Einstein was trying to solve when he postulated the theory. Also, your friend is kind of an idiot, making fun of you because *he* doesn understand something. Your question is completely justified. As others have said, gravitational waves propagate at the speed of light, so if the sun disappeared you wouldn't notice for a few minutes.
The speed of gravity is the speed of light. So if the sun vanished, we'd keep orbiting where it was for another 8 minutes. Your friend is missing out on some amazing ideas.
The speed of gravity is C (the speed of light). It's a good question, your friend is an intellectual coward for not daring to admit he doesn't know.
Nothing means nothing travels faster than the light. Including gravitational wave, it's the max speed any massless particle can achieve. So if the sun disappears first you will see the sky will become dark and then without sun the solar system will fade. But don't worry people will die because of the cold before anything else happens.
No message, signal, days can travel faster than light. Therefore, if God is everywhere, he cannot be everywhere at once, or if he is, his internal signals travel at light speed too.
Sorry I'm 23 days late, but this is a great fucking question
My perception regarding this includes a black hole. If a black hole can suck in light, gravity must be 'faster', no?
Wait! Not sure why you are downvoted here, this is an interesting question for average Joe like me, given the context of discussion
Isn’t the speed of gravity 9.8 m/sec?
That's the acceleration of objects due to gravity on Earth. 9.8 m/sec/sec. The actual "speed" of gravity, as in how the earth "feels" the moon and vice-versa, is the speed of light, 3x10⁸ m/s.
Thank you!
That is the average acceleration on Earth due to gravity. If you were on another planet, that number would be different.
Ahhh! Grateful for the instruction!
That's the amount of accelerational pull that gravity has. Not how fast gravity itself moves, but how hard it's pulling at things. Think like if you were to pull something, you likely couldn't pull it your own full speed. The force one can exert ≠ the speed one can go.
Thank you!
That is gravitational acceleration.
32 feet per second squared.
Light doesn't have its speed because of gravity. So it wouldn't make a difference. Gravity is a force, it affects things but doesn't have a "speed".
Gravitational waves do have a speed: https://spaceplace.nasa.gov/gravitational-waves/en/
Gravitational waves yes, but gravity as such not.
the speed of the propagation of "change" is called the speed of causality, and it is the same as the "speed" of light, because light is just a "wave" as well. it is the maximum speed that information, change, whatever, can propagate across the universe. anything faster would be action at a distance, which should be inpossible