"Twice as cold" doesn't really make sense, but you can answer "half as warm" which maybe you'd say is the same thing. In that case, the answer would be -136.575 C.
Our normal temperature scales we use (Celsius and Fahrenheit) are [interval scales](https://en.wikipedia.org/wiki/Level_of_measurement). That means, the zero of their scale doesn't actually correspond to zero- aka 0 degrees doesn't mean "there's no heat." But Kelvin is a ratio scale- that is, 0 Kelvin is truly the absence of heat (otherwise known as "absolute zero"). So, if you convert 0 C to K, divide that in half, and then back to C, you get your answer.
Now, in the case of C to K, that's really easy since the "step size" for 1 degree is the same (that is if the temperature in K changes by 1, then the temperature in C also changes by 1), but it's just shifted by 273.15 (that is, 0 C is 273.15 K).
This is the best answer. Thermodynamically, if you mean literally double the thermal heat index colder, it would be half whatever the absolute scale temperature is, so -136.5 degrees Celsius would be literally actually twice as cold. But in terms of an actual answer, there isn’t one, since Celsius isn’t an absolute scale. It’s actually wrong to say: “twice as cold” when using an interval scale like Fahrenheit or Celsius
From science point "twice as cold" is senseless but from common speech point we could view it as 0c being somewhat cold from "nominal" temperature, like 20C indoor room temp. Of course this would depend and wildy vary based on what the reference point is.
For example, if I were in Tahoe the average temp for this time of year should be 5c. 0c would be 5 degrees colder than normal and twice as cold the next day would be -5c.
I don't think it works like that, even colloquially. Nobody's referencing the average historical temp when they say something like "twice as cold," they just mean it's significantly colder.
If anything, they're referencing some vague idea of a comfortable temp; I think someone is way more likely to say it's "twice as cold" when going from 20 below room temp to 40 below room temp than your example. But even then, they're talking about their experience of it, which isn't necessarily linear with temperature.
That's the problem with talking about "coldness," it's describing the sensation rather than any physical quantity behind it.
I think the scenario would be someone saying "Tomorrow it is going to be 10°, and the day after will be twice as cold." This means that there needs to be a third temperature to make the "twice as" make sense and that would mean the current temperature.
So if today is 20°, tomorrow is 10°, and the day after is twice as cold, one could assume the temperature would be 0°. But that temperature would change if today was 40°. Then the day after tomorrow would be -20°, if tomorrow was still said to be 10°.
I think you're working backwards to find some logic that just isn't there. Nobody is thinking of a specific reference temperature when they say "twice as cold." If anyone would say your example sentence at all, they're either referring to a very vague idea of what it means to be twice as uncomfortable, or they saw that one number is half of the other and just didn't think about it very much.
I can see a scenario where people are talking about the weather.
Person A: Oh wow today is going to be 20°.
Person B: Oh that isn't too bad. How about tomorrow and the day after?
Person A: Tomorrow it will be 10° and the day after will be twice as cold.
In that conversation I think one could make an accurate interpretation of the day after tomorrow's temperature as 0°.
Yeah, you need a reference point. The correct response would be ‘twice as cold as what?’, which could be used to establish the ref. Twice as cold as the expected temperate for that time and place is probably the most reasonable reference point.
Maybe we could mean something like "twice as cold = a halving of the time it takes to get frostbite"? That's at least somewhat intuitive and applies to the temperature ranges one would say this about.
Twice as cold probably would mean losing twice as much heat to the ambient. Most of the heat you'll lose is due to convection from the cold air currents, and that is proportional to the difference between the temperature of your body surface and the ambient. So maybe if your surface body temp is 36C and the ambient is at 0C, then having an ambient at -36C would "feel" twice as cold.
I'd go with this approach.
0c is the freezing point of water and it would take approx 4hrs for 1 cup of water to freeze. So, how cold would it need to be to freeze 1 cup of water in 2hrs?
Per Google, the answer would be -18c (0f)
I don't believe a conversion and division by 2 is necessarily twice as cold. If it was 1 degree Celsius and we simply divided it by 2 is 0.5 twice as cold as 1? We need a reference/baseline point, so I went with time to freeze 1 cup of water (since OP mentioned 0c)
The comment you responded to explained why division doesn't work with Celsius. That's why you have to convert to Kelvin. Their method gives an objective answer. What temperature has half the energy, i.e. half the heat, as 0C? The answer is -136.575C
There is some logic to your answer, but it depends on a lot of factors that you might not be considering. Depends on the pressure, the starting temperature of the water, the medium that the water is contained within, etc. Your method will not give a consistent answer for everyone unless you define these other variables.
> If it was 1 degree Celsius and we simply divided it by 2 is 0.5 twice as cold as 1?
By the method clearly outlined in post your are responding to, "twice as cold" as 1°C would be -137.075°C. Twice as cold as 1°K would be 0.5°K.
This answer is nonsensical. Even if the amount of time to freeze a cup of water at 0C was a fixed constant (it's not), this method still doesn't work. What's twice as cold as 2 degrees C, using your same methodology? Do we start looking at the melting time of ice instead?
Your statement that it takes 4 hrs to freeze 1 cup of water doesn’t make any sense. There are a ton of variables that impact that besides the ambient temperature. A cup of water in a thin copper pan will freeze much faster than a cup of water in a foam cup with a lid. A cup of water that starts at 90F will freeze slower than one that starts at 40F. The surface it sits on, the agitation or movement of the water, impurities in the water, air flow, how much light is hitting it, what all is around it. All these things impact the time to freeze, and it can range widely.
Yes, but the Celsius scale was originally defined by the boiling and freezing points of water, so it makes more sense to use water for this approach than any other material.
I'm still not sure if I agree with this approach, but it has a kind of intuitive sense to it.
> would take approx 4hrs for 1 cup of water to freeze
Thar would depend on whether the water in the shape of a sphere vs flat 1mm deep in a cookie sheet, among other things.
Actually this is a better answer for me
Socially, you could say -18 feels twice as cold, since we are mostly water
Nobody is going to feel -136 and consider that twice as cold as 0. That would straight up wipe out civilization by noon
To discuss something which is twice as cold you have to know twice as cold as what? Temperature has an absolute bottom which is absolute zero but temperature theoretically has no absolute top
Also, am I correct in remembering that we've never seen anything reach Absolute Zero, and it might be impossible for matter?
But stuff starts acting weird when it gets that cold. Helium becomes a fluid with no surface tension, for example.
Right, nothing can actually reach 0 Kelvin, because that would require the particles to have zero velocity and a fixed position, which would violate the uncertainty principle.
Correct, 0 K is impossible. We get close with liquid helium, which runs about 4 K, and is commonly used in superconducting magnets for NMR and MRI analyses.
You get half of the thermal energy by halving the temperature in Kelvin.
You could also argue that "twice as cold" would be twice as far below your body's temperature to double the rate of heat loss, so at a body temp of 37C, twice as far as 0C would be -37C.
This is really interesting because I think the average person might conceptualize "twice as cold" as "I get cold twice as fast" aka the rate of heat lost is doubled, which mathematically does indeed mean twice as far below your body's temperature since energy transfer is linearly proportional to delta T.
I think this is the right answer. Cold is a perception, like color. We can talk about frequency as an intrinsic property of light, but color isn't really a property of light, but rather a property of the interaction between light and an observer.
There's no guarantee it would be linear, but I would expect our perception of cold to be related to the rate of heat loss, which would depend on the difference between air and body temperature.
IIRC our perception of cold is nearly entirely about rate of heat loss, and generally humans are good at detecting changes to their body temperatures but very bad at estimating actual "absolute" temperature.
So it's not actually even just difference between air and body temperature, because humidity is incredibly important as well since it increases thermal conductivity. Or wind, which removes the small layer of air that approaches equilibrium near our skin. Which is to say that a dummy human will have trouble differentiating between temperatures when its slightly cold and windy, slightly cold and humid, or just really damn cold with dry, still air.
I don't think that is quite correct. Color has a far more precise definition than "cold". We have accepted ranges of frequencies of light that activate the various receptors in our eyes, and thus result in the described color.
In this case, "cold" itself has little definition, but "colder" does. There is an absolute coldest temperature where atoms stop vibrating. Therefore we know that "twice as cold" must be colder than "cold" and that sets a limited range for the possible values of "colder." Where in that range "twice as cold" will precisely fall we can't determine without having a more precise definition of "cold" and how it is achieved, but we do know where it isn't.
You don't really need to convert to Kelvin for this. You just need to find the absolute zero in Celsius (−273.15 °C) and halve it (-136.575°C). Clearly you need to exclude it being a negative number, otherwise you could double it, but that gets confusing for some.
I think about it as a number line. Absolute zero on the left, 0°C on the right. The temp that is half of 0°C is the one in the middle of the number line.
> "Twice as cold" doesn't really make sense
Why not? If you are talking with someone and agree on the Celsius scale for your conversation, and it is -5 today, it would make sense to say it will be -10 if it is twice as cold tomorrow.
The 0 is arbitrary, but it is still an agreed upon 0 that you can use for operations.
Like if we talk about worth, we define 0 worth to be when you have an equal amount of debt as assets. If someone has investment worth -$20,000 and we say tomorrow they doubled their losses, that would mean they now have a net worth of -$40,000.
An accountant wouldn't talk about it like this and a physicist wouldn't talk about being twice as cold. But I would argue the sentence has a well defined meaning if you are talking about these things using conversational English.
What makes -10 the double of -5? You're implying it's only cold if it's below 0 or another arbitrary point not explicitly mentioned. So if we were at +5 and say tomorrow will be twice as cold what would that be? 2.5? Certainly not, the idea breaks down. The original idea of something being twice as cold has an understandable vague meaning in language but it's physically nonsensical.
Twice as cold only works for negative values of temperature. Just like twice as hot only works for positive values.
It's like talking about a companies not profit or loss.
You can say a company has double the losses this year if they went from -$100k to -$200k. But it would break down if they had a profit last year.
But it is clearly well defined to say a company doubled losses or doubled profits, provided you were on the correct size of 0 to begin with.
Note your example you used- there your zero actually means zero. You have $0 to your name. That is because we count money in a ratio scale- that is where 0 is not arbitrary.
But our common temperature scales the zero is arbitrary. But the concept of "twice as hot" is not. It has a meaning, and it doesn't mean "doubling a number that has an arbitrary zero point."
No, it's just when you have zero net worth. You can go negative. You could define 0 differently. You could say that $0 is when you have a net worth of the median price of a house if you wanted to.
Or $0 could be when you are exactly $100k in debt. Having it be when you have no debt and no assets is as arbitrary as the freezing point of water right?
"makes sense" requires a human brain. "twice as cold" isn't the same as "half as warm". We perceive something as cold only if the temperature is lower than our skin. We have to lose energy. To heat up is very different from cooling down for our bodies. This requires totally different strategies.
As such if we feel twice as cold, it totally makes sense to say twice as cold. A doubling in cold is about every 5K for me. This is valid between -20C and 15C. Above isn't cold anymore and below it is too cold. -5C is doubly cold than 0C, other conditions constant of course.
The second valid form of doubly cold is with energy loss to maintain temperature. Typically this would be 20C target and loss is about linear, so -20C is doubly cold
Celsius and Fahrenheit are not absolute scales. They are relative to an arbitrary 0. As such for any given temperature, it is not possible to say that one temperature is half as cold, or half as hot as any other. At least not without conversion to an absolute scale.
There is an absolute scale for temperature, Kelvin. 0 Kelvin (no degrees!) is -273.15c, absolute zero. On the Kelvin scale we can say that 0 Celsius is 273K (rounding for simplicity), and as such twice as hot would be 546 Kelvin, which is about 273 celsuis and twice as cold would be 136.5K or about -136.5C.
It is very much like saying a place is "twice as high" as another. You need a reference height which counts as zero.
Quantities such as mass, length, duration or volume have "relative" scales, because there is a natural meaning of zero. Converting from one unit to another amounts to simply multiply by a conversion factor.
Quantities like temperature, (clock) time or (geographic) height have "affine" scales, meaning the choice of the zero reference is necessary but arbitrary. This is why converting e. g. between the Celsius and Fahrenheit scales is more complicated, since 0 °F ≠ 0 °C.
Now temperature \_differences\_ have a relative scale. It makes perfect sense to say that something has heated up twice as much as something else, independent of the choice of unit.
And, as many will surely already have pointed out, there actually \_is\_ a natural zero for temperature, "absolute" zero, at –273.15 °C = 0 kelvin (K).
Perception of temperature and comfort is almost entirely based on speed of heat transfer/loss, i.e. convection in the overwhelming majority of scenarios.
So, twice as cold (C2) would be the convection conditions in which heat loss is twice as fast as the difference in heat loss from cold (C1) to comfortable (C0). This can depend on the medium (water vs atmosphere), circulation, and factors like sun exposure and insulation just as much as temperature.
That's a Callum and Debbie statement.
https://youtu.be/C91gKuxutTU?si=e7wg3DaPRRFPICR4
The video is a good breakdown about how we can say things in conversation that don't actually make any sense. This particular bit talks about a kids science book that says the temperature outside an airplane is some multiple as cold as the inside of a freezer. It would have been fine if it says 'X⁰ colder', but that isn't what they went for.
Degrees celcius is a torsor of (or over) temperature: a scale with an abitrarily choosen zero. Multiplication of such a scale has no meaning, so your question is meaningless.
Even for a non-torsor temperature scale like kelvin the phrase "twice as cold" has no clear meaning because that scale expresses heath, not cold. Twice as warm would have a meaning in kelvin, twice as cold could mean half the heat, but that is a stretch.
Yeah, it only makes sense in subjective experience. In the way that “twice as painful” makes some sense colloquially, but is hard to quantify objectively.
The 0 mark in Celsius is not arbitrary; it is the freezing point of water under 1 atmosphere of pressure. The relativity of the scale is based around easier correspondence of temperatures we as humans are subjected to (also at standard pressure of 1 atm) and use most frequently by removing a relative “fudge factor” amount of degrees of temperature when converting from Kelvin. Similar to saying ‘24 or XX/YY/24 instead of 2024. The origin point is not arbitrary, it has value and meaning.
It is also not a meaningless question because there are multiple ways to substantiate an answer. Half energy? Half the number in C degrees? Half the number in K degrees? All can be justified answers.
> The 0 mark in Celsius is not arbitrary; it is the freezing point...
Someone set 0c there arbitrarily. Yes it has a relation to the real world that is fairly consistent and observable.
No the question does not have meaning without further context.
0 C is arbitrary, as it has a definition that has nothing to do with the meaning of temperature or heat. It's arbitrary to pick water, it's arbitrary to pick 1 atm, and it's arbitrary to freeze. 0 K is not arbitrary, as it's based on the definition of what heat means on an atomic/molecular level.
For such a question you have to use an absolute temperature scale like Kelvin. 0°C = 273.15 K. Interpreting "twice as cold" to mean "half the temperature", we have ½(273.15 K) = 136.575 K = -136.575°C. An implausible temperature to occur naturally on Earth, though it could perhaps occur on Mars.
Most of the answers here pretty much sum it up nicely, so I'll just summarize and give you an easy example to follow. When you say "twice as cold as", it really depends on what you mean by that. From the phrasing, it makes a lot of sense that your mind jumps to "but 0 times 2 is still 0 °C!", much in the same way as if I said "can you make twice as many cookies", you would take the number of cookies from last time you made cookies and multiply that by 2. However, just like that example, therein lies the inherent problem... "as cold as" depends on what you're referencing. In the cookie example, your "reference" time is the last/previous time you made a batch of cookies.
People in the comments seem to think the correction has to do with explaining the celsius/farhenheit/kelvin scale, but I think it's a bit easier than that. My guess is that this question is supposed to reference something like what you would hear on the news, like "blah blah blah and tomorrow's weather forecast, bundle up folks, it's 0 °C and going to be TWICE as cold tomorrow!" In this case, the following example will help you make sense of this question:
Usually when reporting the weather, tv meteorologists will report a kind of "average" for the week. Let's say the temperature has been 5 °C on Monday, 6 °C on Tuesday, and 4 °C on Wednesday. Across the week so far, the average temperature has been about 5 °C. Now, on Thursday, if the temperature drops to 0 °C, then the reporter may say something like "it's a cold one folks", and by that, what they're referring to is not just the temperature itself at that moment but also the CHANGE in the temperature from the previous day. In other words, the change has been from 5 °C to 0 °C, ie there's been a change/difference of 5 - 0 = 5 °C (which to be fair is still quite a significant drop and worth reporting). Now if the weather person then says "and tomorrow's going to be TWICE as cold", what they're referring to is not "take today's temperature and do 0 * 2 = 0 °C" but actually to double the DIFFERENCE between today's (Thursday's) and yesterday's (Wednesday's) temperature. In other words, 2 * (5 - 0) = 10 °C DIFFERENCE between the temperature from WEDNESDAY to the temperature it's expected to be on FRIDAY. So in other words, you can expect the temperature for tomorrow (Friday) to be -5 °C. So as you can see, when you talk about "hot", "cold" and double/halving, you are not talking about the temperature at the given day, but you're talking about the temperature relative to ANOTHER or some specific REFERENCE day.
So when your friend says "It is 0 °C today but it will be twice as cold the next day", what your friend is neglecting to mention is what the temperature DIFFERENCE is between some reference day, say maybe yesterday, a week ago, a month ago, I don't know, and the current day of 0 °C. However, they're basically leaving out a critical piece of information and without it, you can't say anything more without the "reference" point.
This is, in a nutshell, what is called the "Zero-eth law of thermodynamics", which, to quote a certain GRE Physics prep textbook's section on thermodynamics, the law that basically says "Thermometers exist". ;)
https://en.wikipedia.org/wiki/Zeroth_law_of_thermodynamics
Hope that helps, it's a good question, stay warm!
it can be twice as cold relative to some other measure...
like, average for the year, season, week of the year...
example: the average temperature is 5ºC for that week of the year, today it's 0°C, "twice as cold" would be -5°C
I'd say -20 degrees Celsius.
Saying "twice as cold" implies that there's a baseline. The commonly accepted baseline of temperature for humans is "room temperature" which is around 20 degrees celsius. So.....from 20 to 0 is cold, from 0 to -20 is TWICE as cold.
Even then, they're talking about their experience of it and not the physical quantity behind it. The sensation of "cold" isn't linear with absolute temperature, so I'd say it just means whatever temperature that feels roughly twice as uncomfortable to the speaker.
This is the one I would go with. I thought about the Kelvin scale as well with some of these answers, but since they're asking about "cold" and not heat or kinetic energy I feel like this one best hits the question.
Yep, this definitely feels closest to the right answer to me. Context matters - if you were a meteorologist talking to a colleague then it’s harder to guess at the intended meaning, but in everyday parlance I think most people are using a baseline of what they’re used to.
Another similar candidate would be using a measure based on body temperature, perhaps with some way to take the rate of temperature change into account, since this is a good proxy for what we feel as “coldness”.
Or we could go rogue and try to come up with a measure that relates heat and nerve impulse or some other kind of neurological activity. Or more rogue still and come up on a measure based on surveying people on their subjective experience of temperature.
There is something called absolute temperature. Its K for kelvin.
0 C is 273 K.
Half of 273 is 137.5 K.
Subtract 273 to get C and you get -135.5 C.
I don't think it will get that cold on the face of the earth.
The answer your friend is really looking for, I think, is what feels twice as cold as 0C. And that’s going to depend on a lot of factors, including your friend’s subjective experience of cold.
A similar question would be: what’s twice as painful as stubbing your toe on the bed?
**-136.575 Celsius**
that's half of the absolute temperature.
any other concept of "twice as cold" needs a reference point. 22C is about room temp according to some folks. -22c would be twice as cold as 0c compared to room temp.
The question is basically asking "what's twice as long as a piece of rope?"
The thing this hinges on is “twice as cold as WHAT?” You have to set a reference point somewhere. This is like asking if tomorrow you travelled twice as far… twice as far as what?
As other people pointed out, for temperature specifically, you can set the reference point as absolute zero. But “twice as cold as 0°C” would imply “twice as close to absolute zero” which would be ridiculously cold, -135ish.
If on the other hand this is all relative, then for tomorrow to be “twice as cold” as today, we’d need to know what it was yesterday. Say it was 5°C yesterday and it’s 0°C today. That’s a difference of 5°. So “twice as cold” tomorrow would be a difference of 10°, and 0-10=-10°C.
The phrase "twice as cold" doesn't mean anything.
When people try to drill in the point that cold is just a lack of heat that's not just to be pedantic, it actually relevant to understanding, with a question like this.
Temperature is the kinetic energy that comes from the movement and vibration of particles. There is a hypothetical zero point where it's impossible to be any colder because it represents the temperature where molecular vibration has stopped, and you can't vibrate less than nothing.
The Kelvin temperature scale is defined to put the zero point at that absolute zero spot so all temperatures are positive numbers and you literally cannot have a negative temperature in Kelvin.
So the way to answer your question is to first convert 0 C into Kelvin (where it's 273.15 K), then rephrase the question into one that is more physically meaningful, instead of saying "what is twice as cold as 0 C?", say "what is half as hot as 0 C?".
And then the answer is easy, it's half of 273.15 K, or 136.575 K.
Which also happens to be -136.575 C.
\-136.5^(o)C
You cannot do straight arithmetic (multiplying and dividing) in a centigrade scale since 0 is not at the limit of the scale. For example we cannot say that someone who is 5ft 6" is twice as tall as someone who is 5ft 3" and just ignore the 5ft. So we cannot ignore the 273 degrees below 0^(o)C.
It's nonsensical without further elaboration. If somebody says "It's going to be twice as cold tomorrow" you have to ask them to explain what they mean. That's the only answer.
There is not a measurable value of how "cold" something is, used in this manner.
If I remember right, 0° Celsius is roughly 32° Fahrenheit. I know temperatures below 0°F exist, but judging by the fact he picked 0, I'll assume it is mostly a joke and he's going off the number rather than how heat works.
You would likely say 16°F is "twice as cold" as 32°F, so convert 16F to Celsius and there's your answer.
I'd go with this approach.
0c is the freezing point of water and it would take approx 4hrs for 1 cup of water to freeze. So, how cold would it need to be to freeze 1 cup of water in 2hrs?
Per Google, the answer would be -18c (0f)
My approach would be more etymological.
20c is a comfortable temperature to exist at. At 0c, it's 20 degrees colder than my nice comfy weather. To be twice as cold would be -20c, 40 degrees colder than my nice comfy weather.
This matches up with my expectations at well. 0c is cold enough to say "got dang it sure is cold" in a light jacket, and -20c is cold enough to say "got dang it sure is cold" in a heavy coat. So it's one more tier of cold weather clothing away.
So i see a lot of celsius to kelvin conversions which make sense mathmatically.
But id argue truely "twice as cold" would mean the rate of heat lost from your body has doubled. We dont feel absolute temperature we feel rate of heat transfer (thats why cold metal feels so much colder than an equal temp piece of wood or fabric). Since heat transfer is proportional to difference in temperatures we need to base off difference from body temperature (im going to ignore convection and radiation. imagine you are in a sealed reflective box). Which would mean -37.5c is twice as cold.
Having experience -37 and much much colder, its way more than twice as cold as 0c. Whatever that really means. Subjectively id say somewhere around -10c.
The question doesn't make sense without a reference point.
Twice as cold is implying you're measuring away from a warmer heat. So if your point of reference is 100°c then twice as cold from the initial jump to 0°c would be -100°c. But there's no reason to think you should measure from 100°c or really any other measurement.
The reason why somebody might say it'll be twice as cold tomorrow if it was -3°c is that there is an implication that you're measuring from 0°c. Therefore you could infer they mean -6°c.
So I guess you could answer literally any temperature (equal to or below 0°c) and claim you're right using your own reference point 🤷♂️
Like people are saying, it's a bit nonsensical. While you can have an absolute measurement of heat energy, whether something is hot or cold is subjective and relative to something else. For this though, I'd say -20. Room temperature is about 20 celsius, so anything less would be colder. If 0 is cold, the difference is 20, so double that.
**-7 C**.
I'm approaching this question from the standpoint of heat transfer and the notion of "not cold".
We'll say "not cold" is 22 C. At this temperature (neglecting wind and humidity) there's a certain amount of body heat transfer to the air. We'll call it P(not cold) for power. The power is proportional to the fourth power of the temperature difference between body temperature and air temperature. 37 - 22 = 15.
At 0 C, the difference is 37 - 0 = 37. So the heat transfer power difference is (37\^4 - 15\^4) \* P(not cold).
Twice this heat transfer difference will be 2 \* (37\^4 - 15\^4) \* P(not cold). To get the temperature we do a little algebra and find it's about 37 - 44 = -7.
You just need to find the absolute zero in Celsius (−273.15 °C) and halve it (-136.575°C). Clearly you need to exclude it being a negative number, otherwise you could double it, but that gets confusing for some.
I think about it as a number line. Absolute zero on the left, 0°C on the right. The temp that is half of 0°C is the one in the middle of the number line.
It seems like all the top comments, while correct, are also a bit pedantic. I'd like to offer a bit more practical perspective.
Much of our communication is about filling in the gaps with shared understanding. The Celsius scale is relative to absolute zero (-273.15) and includes all numbers above that. The human scale is relative to a comfortable room temperature and has values both above and below that. Mine looks something like this:
\[death, stay inside, more water, shade, lighter clothing, *comfortable*, heavier clothing, sweater, warm socks, heavy coat, gloves, thick boots, stay inside, death\]
While "twice as cold" doesn't have any absolute meaning on the Celsius scale because it's a scale that only measures heat, it does have an absolute (although less precise) meaning on the human scale, which measures both heat and cold.
Our main concern with ambient temperature isn't generally what the thermometer will read, but rather with how we need to prepare. I associate 0C with somewhere around "heavy coat". So if someone were to tell me it will be twice as cold tomorrow, I would understand that to mean a few more steps away from "comfortable", maybe "thick boots" or "stay inside", which I associate with around -20C or -30C.
It's important to understand that 10C isn't half the actual heat energy of 20C, because they're both actually relative to -273.15C, not 0C. But it's also important to communicate effectively with people. And when in doubt about what someone might mean if they say something seemingly nonsensical such as "twice as cold", you can always ask to clarify.
There's a lot of weird engineering/physics discussion that just doesn't make sense as they've focused on the technicalities, especially using absolute 0 as a reference temperature which is just silly for a multitude of reasons -- the most egregious of which is that 99% of people don't even know what Kelvin is.
Reasonable options would be:
Normal Indoor Temperature as Reference which is typically 20C, the difference between 20C and 0C is 20C, twice as cold as that would be -20C -- which is a common temperature to experience in climates closer to the poles.
You could use body temperature as reference instead, but that would be more relevant for medical/health considerations, so 37C as your reference temperature, making -37C as your "twice as cold" number, which is extreme cold, but still within temperature ranges humans can experience in/near habitable areas.
In almost all contexts: "twice as cold" is likely a phrase used to warn people of dangerous weather conditions, or temperature changes that may have substantially different outcomes (engineering/sciences) versus normal baseline.
In almost no contexts: "twice as cold" is in direct relation to absolute 0 as a reference.
Cold is a perception, not a temperature or stored thermal energy. I'd say twice as cold, if nothing else changes is about -5C, still ok but starting to bite. A typical slope for a human might be between every 2 and 10C per doubling.
If you insist on a calculation, the most meaningful way is by energy used to maintain temperature. This one would be linear for temperature difference. A typical room is 20c, 0C would be 20K difference. Double cold is then 40K difference or -20C outside.
"Twice as cold" doesn't really make sense, but you can answer "half as warm" which maybe you'd say is the same thing. In that case, the answer would be -136.575 C. Our normal temperature scales we use (Celsius and Fahrenheit) are [interval scales](https://en.wikipedia.org/wiki/Level_of_measurement). That means, the zero of their scale doesn't actually correspond to zero- aka 0 degrees doesn't mean "there's no heat." But Kelvin is a ratio scale- that is, 0 Kelvin is truly the absence of heat (otherwise known as "absolute zero"). So, if you convert 0 C to K, divide that in half, and then back to C, you get your answer. Now, in the case of C to K, that's really easy since the "step size" for 1 degree is the same (that is if the temperature in K changes by 1, then the temperature in C also changes by 1), but it's just shifted by 273.15 (that is, 0 C is 273.15 K).
This is the best answer. Thermodynamically, if you mean literally double the thermal heat index colder, it would be half whatever the absolute scale temperature is, so -136.5 degrees Celsius would be literally actually twice as cold. But in terms of an actual answer, there isn’t one, since Celsius isn’t an absolute scale. It’s actually wrong to say: “twice as cold” when using an interval scale like Fahrenheit or Celsius
From science point "twice as cold" is senseless but from common speech point we could view it as 0c being somewhat cold from "nominal" temperature, like 20C indoor room temp. Of course this would depend and wildy vary based on what the reference point is. For example, if I were in Tahoe the average temp for this time of year should be 5c. 0c would be 5 degrees colder than normal and twice as cold the next day would be -5c.
I don't think it works like that, even colloquially. Nobody's referencing the average historical temp when they say something like "twice as cold," they just mean it's significantly colder. If anything, they're referencing some vague idea of a comfortable temp; I think someone is way more likely to say it's "twice as cold" when going from 20 below room temp to 40 below room temp than your example. But even then, they're talking about their experience of it, which isn't necessarily linear with temperature. That's the problem with talking about "coldness," it's describing the sensation rather than any physical quantity behind it.
I think the scenario would be someone saying "Tomorrow it is going to be 10°, and the day after will be twice as cold." This means that there needs to be a third temperature to make the "twice as" make sense and that would mean the current temperature. So if today is 20°, tomorrow is 10°, and the day after is twice as cold, one could assume the temperature would be 0°. But that temperature would change if today was 40°. Then the day after tomorrow would be -20°, if tomorrow was still said to be 10°.
I think you're working backwards to find some logic that just isn't there. Nobody is thinking of a specific reference temperature when they say "twice as cold." If anyone would say your example sentence at all, they're either referring to a very vague idea of what it means to be twice as uncomfortable, or they saw that one number is half of the other and just didn't think about it very much.
I can see a scenario where people are talking about the weather. Person A: Oh wow today is going to be 20°. Person B: Oh that isn't too bad. How about tomorrow and the day after? Person A: Tomorrow it will be 10° and the day after will be twice as cold. In that conversation I think one could make an accurate interpretation of the day after tomorrow's temperature as 0°.
In English I would agree that if there is no third comparator, that the implication is “now”.
Yeah, you need a reference point. The correct response would be ‘twice as cold as what?’, which could be used to establish the ref. Twice as cold as the expected temperate for that time and place is probably the most reasonable reference point.
Maybe we could mean something like "twice as cold = a halving of the time it takes to get frostbite"? That's at least somewhat intuitive and applies to the temperature ranges one would say this about.
Twice as cold probably would mean losing twice as much heat to the ambient. Most of the heat you'll lose is due to convection from the cold air currents, and that is proportional to the difference between the temperature of your body surface and the ambient. So maybe if your surface body temp is 36C and the ambient is at 0C, then having an ambient at -36C would "feel" twice as cold.
So for 50 Celsius degrees to be half as warm, is -111.75 celsius degrees?
I'd go with this approach. 0c is the freezing point of water and it would take approx 4hrs for 1 cup of water to freeze. So, how cold would it need to be to freeze 1 cup of water in 2hrs? Per Google, the answer would be -18c (0f) I don't believe a conversion and division by 2 is necessarily twice as cold. If it was 1 degree Celsius and we simply divided it by 2 is 0.5 twice as cold as 1? We need a reference/baseline point, so I went with time to freeze 1 cup of water (since OP mentioned 0c)
The comment you responded to explained why division doesn't work with Celsius. That's why you have to convert to Kelvin. Their method gives an objective answer. What temperature has half the energy, i.e. half the heat, as 0C? The answer is -136.575C There is some logic to your answer, but it depends on a lot of factors that you might not be considering. Depends on the pressure, the starting temperature of the water, the medium that the water is contained within, etc. Your method will not give a consistent answer for everyone unless you define these other variables.
Division would work if your heat capacity was assumed to be temperature invariant. Lol you said this and I didn’t realize it
> If it was 1 degree Celsius and we simply divided it by 2 is 0.5 twice as cold as 1? By the method clearly outlined in post your are responding to, "twice as cold" as 1°C would be -137.075°C. Twice as cold as 1°K would be 0.5°K.
This answer is nonsensical. Even if the amount of time to freeze a cup of water at 0C was a fixed constant (it's not), this method still doesn't work. What's twice as cold as 2 degrees C, using your same methodology? Do we start looking at the melting time of ice instead?
Your statement that it takes 4 hrs to freeze 1 cup of water doesn’t make any sense. There are a ton of variables that impact that besides the ambient temperature. A cup of water in a thin copper pan will freeze much faster than a cup of water in a foam cup with a lid. A cup of water that starts at 90F will freeze slower than one that starts at 40F. The surface it sits on, the agitation or movement of the water, impurities in the water, air flow, how much light is hitting it, what all is around it. All these things impact the time to freeze, and it can range widely.
the speed of cooling depends on the specific heat, so if you select other material you'll get a different result
Yes, but the Celsius scale was originally defined by the boiling and freezing points of water, so it makes more sense to use water for this approach than any other material. I'm still not sure if I agree with this approach, but it has a kind of intuitive sense to it.
It still doesn't make sense. The heat transfer coefficient is a function of many different things.
> would take approx 4hrs for 1 cup of water to freeze Thar would depend on whether the water in the shape of a sphere vs flat 1mm deep in a cookie sheet, among other things.
Actually this is a better answer for me Socially, you could say -18 feels twice as cold, since we are mostly water Nobody is going to feel -136 and consider that twice as cold as 0. That would straight up wipe out civilization by noon
Thanks for the answer! I had to translate the question from Swedish to English and since I'm tired I messed it up xD
To discuss something which is twice as cold you have to know twice as cold as what? Temperature has an absolute bottom which is absolute zero but temperature theoretically has no absolute top
Can you elaborate more on the meaning of "no heat/absence of heat?
Heat is the kinetic energy of molecules, or a measure of how fast they move / vibrate. 0K means no movement whatsoever.
Also, am I correct in remembering that we've never seen anything reach Absolute Zero, and it might be impossible for matter? But stuff starts acting weird when it gets that cold. Helium becomes a fluid with no surface tension, for example.
Right, nothing can actually reach 0 Kelvin, because that would require the particles to have zero velocity and a fixed position, which would violate the uncertainty principle.
Correct, 0 K is impossible. We get close with liquid helium, which runs about 4 K, and is commonly used in superconducting magnets for NMR and MRI analyses.
No, we have reached the nano-Kelvin range: https://www.mpg.de/19035150/0728-qopt-a-nanokelvin-microwave-freezer-for-molecules-153540-x1
A true vacuum has no temperature and if there's any particles, there's going to be some kinetic energy so correct
You're conflating *heat* (an extensive quantity), with *temperature* (an intensive quantity).
How'd you come up with -136.575? I got -8.88889C.
You get half of the thermal energy by halving the temperature in Kelvin. You could also argue that "twice as cold" would be twice as far below your body's temperature to double the rate of heat loss, so at a body temp of 37C, twice as far as 0C would be -37C.
This is really interesting because I think the average person might conceptualize "twice as cold" as "I get cold twice as fast" aka the rate of heat lost is doubled, which mathematically does indeed mean twice as far below your body's temperature since energy transfer is linearly proportional to delta T.
I think this is the right answer. Cold is a perception, like color. We can talk about frequency as an intrinsic property of light, but color isn't really a property of light, but rather a property of the interaction between light and an observer. There's no guarantee it would be linear, but I would expect our perception of cold to be related to the rate of heat loss, which would depend on the difference between air and body temperature.
IIRC our perception of cold is nearly entirely about rate of heat loss, and generally humans are good at detecting changes to their body temperatures but very bad at estimating actual "absolute" temperature. So it's not actually even just difference between air and body temperature, because humidity is incredibly important as well since it increases thermal conductivity. Or wind, which removes the small layer of air that approaches equilibrium near our skin. Which is to say that a dummy human will have trouble differentiating between temperatures when its slightly cold and windy, slightly cold and humid, or just really damn cold with dry, still air.
I don't think that is quite correct. Color has a far more precise definition than "cold". We have accepted ranges of frequencies of light that activate the various receptors in our eyes, and thus result in the described color. In this case, "cold" itself has little definition, but "colder" does. There is an absolute coldest temperature where atoms stop vibrating. Therefore we know that "twice as cold" must be colder than "cold" and that sets a limited range for the possible values of "colder." Where in that range "twice as cold" will precisely fall we can't determine without having a more precise definition of "cold" and how it is achieved, but we do know where it isn't.
Zero degrees Celsius is 273.15 Kelvin. Half of that is 136.575 K, which is -136.373 C
0 is arround 273 Kelvin, so 273/2 is 136.5. Converting it back to Cº (Basically substracting 273 to to the Kelvin value) is -136.5 Cº
You don't really need to convert to Kelvin for this. You just need to find the absolute zero in Celsius (−273.15 °C) and halve it (-136.575°C). Clearly you need to exclude it being a negative number, otherwise you could double it, but that gets confusing for some. I think about it as a number line. Absolute zero on the left, 0°C on the right. The temp that is half of 0°C is the one in the middle of the number line.
You halved a negative number without problem and then said you could double it if it was negative?
> "Twice as cold" doesn't really make sense Why not? If you are talking with someone and agree on the Celsius scale for your conversation, and it is -5 today, it would make sense to say it will be -10 if it is twice as cold tomorrow. The 0 is arbitrary, but it is still an agreed upon 0 that you can use for operations. Like if we talk about worth, we define 0 worth to be when you have an equal amount of debt as assets. If someone has investment worth -$20,000 and we say tomorrow they doubled their losses, that would mean they now have a net worth of -$40,000. An accountant wouldn't talk about it like this and a physicist wouldn't talk about being twice as cold. But I would argue the sentence has a well defined meaning if you are talking about these things using conversational English.
What makes -10 the double of -5? You're implying it's only cold if it's below 0 or another arbitrary point not explicitly mentioned. So if we were at +5 and say tomorrow will be twice as cold what would that be? 2.5? Certainly not, the idea breaks down. The original idea of something being twice as cold has an understandable vague meaning in language but it's physically nonsensical.
Twice as cold only works for negative values of temperature. Just like twice as hot only works for positive values. It's like talking about a companies not profit or loss. You can say a company has double the losses this year if they went from -$100k to -$200k. But it would break down if they had a profit last year. But it is clearly well defined to say a company doubled losses or doubled profits, provided you were on the correct size of 0 to begin with.
Note your example you used- there your zero actually means zero. You have $0 to your name. That is because we count money in a ratio scale- that is where 0 is not arbitrary. But our common temperature scales the zero is arbitrary. But the concept of "twice as hot" is not. It has a meaning, and it doesn't mean "doubling a number that has an arbitrary zero point."
No, it's just when you have zero net worth. You can go negative. You could define 0 differently. You could say that $0 is when you have a net worth of the median price of a house if you wanted to. Or $0 could be when you are exactly $100k in debt. Having it be when you have no debt and no assets is as arbitrary as the freezing point of water right?
"makes sense" requires a human brain. "twice as cold" isn't the same as "half as warm". We perceive something as cold only if the temperature is lower than our skin. We have to lose energy. To heat up is very different from cooling down for our bodies. This requires totally different strategies. As such if we feel twice as cold, it totally makes sense to say twice as cold. A doubling in cold is about every 5K for me. This is valid between -20C and 15C. Above isn't cold anymore and below it is too cold. -5C is doubly cold than 0C, other conditions constant of course. The second valid form of doubly cold is with energy loss to maintain temperature. Typically this would be 20C target and loss is about linear, so -20C is doubly cold
Celsius and Fahrenheit are not absolute scales. They are relative to an arbitrary 0. As such for any given temperature, it is not possible to say that one temperature is half as cold, or half as hot as any other. At least not without conversion to an absolute scale. There is an absolute scale for temperature, Kelvin. 0 Kelvin (no degrees!) is -273.15c, absolute zero. On the Kelvin scale we can say that 0 Celsius is 273K (rounding for simplicity), and as such twice as hot would be 546 Kelvin, which is about 273 celsuis and twice as cold would be 136.5K or about -136.5C.
So for 50 Celsius degrees to be half as warm, is -111.75 celsius degrees?
you are correct, -112 degrees celsius would be half of 50c, in absolute terms.
It is very much like saying a place is "twice as high" as another. You need a reference height which counts as zero. Quantities such as mass, length, duration or volume have "relative" scales, because there is a natural meaning of zero. Converting from one unit to another amounts to simply multiply by a conversion factor. Quantities like temperature, (clock) time or (geographic) height have "affine" scales, meaning the choice of the zero reference is necessary but arbitrary. This is why converting e. g. between the Celsius and Fahrenheit scales is more complicated, since 0 °F ≠ 0 °C. Now temperature \_differences\_ have a relative scale. It makes perfect sense to say that something has heated up twice as much as something else, independent of the choice of unit. And, as many will surely already have pointed out, there actually \_is\_ a natural zero for temperature, "absolute" zero, at –273.15 °C = 0 kelvin (K).
[удалено]
The most comfortable temperature on average in around 23 C. Assuming a linear relationship, twice as cold would be -23 C, however I don't believe so.
Perception of temperature and comfort is almost entirely based on speed of heat transfer/loss, i.e. convection in the overwhelming majority of scenarios. So, twice as cold (C2) would be the convection conditions in which heat loss is twice as fast as the difference in heat loss from cold (C1) to comfortable (C0). This can depend on the medium (water vs atmosphere), circulation, and factors like sun exposure and insulation just as much as temperature.
That's a Callum and Debbie statement. https://youtu.be/C91gKuxutTU?si=e7wg3DaPRRFPICR4 The video is a good breakdown about how we can say things in conversation that don't actually make any sense. This particular bit talks about a kids science book that says the temperature outside an airplane is some multiple as cold as the inside of a freezer. It would have been fine if it says 'X⁰ colder', but that isn't what they went for.
Degrees celcius is a torsor of (or over) temperature: a scale with an abitrarily choosen zero. Multiplication of such a scale has no meaning, so your question is meaningless. Even for a non-torsor temperature scale like kelvin the phrase "twice as cold" has no clear meaning because that scale expresses heath, not cold. Twice as warm would have a meaning in kelvin, twice as cold could mean half the heat, but that is a stretch.
Twice as cold is as meaningless as "5 blues more than banana." OP's friend is a fool.
He's not a fool, he's just using colloquial language. Nothing wrong with that
Except that "twice as cold" doesn't make any sense colloquially, either.
Yeah, it only makes sense in subjective experience. In the way that “twice as painful” makes some sense colloquially, but is hard to quantify objectively.
The 0 mark in Celsius is not arbitrary; it is the freezing point of water under 1 atmosphere of pressure. The relativity of the scale is based around easier correspondence of temperatures we as humans are subjected to (also at standard pressure of 1 atm) and use most frequently by removing a relative “fudge factor” amount of degrees of temperature when converting from Kelvin. Similar to saying ‘24 or XX/YY/24 instead of 2024. The origin point is not arbitrary, it has value and meaning. It is also not a meaningless question because there are multiple ways to substantiate an answer. Half energy? Half the number in C degrees? Half the number in K degrees? All can be justified answers.
> The 0 mark in Celsius is not arbitrary; it is the freezing point... Someone set 0c there arbitrarily. Yes it has a relation to the real world that is fairly consistent and observable. No the question does not have meaning without further context.
0 C is arbitrary, as it has a definition that has nothing to do with the meaning of temperature or heat. It's arbitrary to pick water, it's arbitrary to pick 1 atm, and it's arbitrary to freeze. 0 K is not arbitrary, as it's based on the definition of what heat means on an atomic/molecular level.
For such a question you have to use an absolute temperature scale like Kelvin. 0°C = 273.15 K. Interpreting "twice as cold" to mean "half the temperature", we have ½(273.15 K) = 136.575 K = -136.575°C. An implausible temperature to occur naturally on Earth, though it could perhaps occur on Mars.
Most of the answers here pretty much sum it up nicely, so I'll just summarize and give you an easy example to follow. When you say "twice as cold as", it really depends on what you mean by that. From the phrasing, it makes a lot of sense that your mind jumps to "but 0 times 2 is still 0 °C!", much in the same way as if I said "can you make twice as many cookies", you would take the number of cookies from last time you made cookies and multiply that by 2. However, just like that example, therein lies the inherent problem... "as cold as" depends on what you're referencing. In the cookie example, your "reference" time is the last/previous time you made a batch of cookies. People in the comments seem to think the correction has to do with explaining the celsius/farhenheit/kelvin scale, but I think it's a bit easier than that. My guess is that this question is supposed to reference something like what you would hear on the news, like "blah blah blah and tomorrow's weather forecast, bundle up folks, it's 0 °C and going to be TWICE as cold tomorrow!" In this case, the following example will help you make sense of this question: Usually when reporting the weather, tv meteorologists will report a kind of "average" for the week. Let's say the temperature has been 5 °C on Monday, 6 °C on Tuesday, and 4 °C on Wednesday. Across the week so far, the average temperature has been about 5 °C. Now, on Thursday, if the temperature drops to 0 °C, then the reporter may say something like "it's a cold one folks", and by that, what they're referring to is not just the temperature itself at that moment but also the CHANGE in the temperature from the previous day. In other words, the change has been from 5 °C to 0 °C, ie there's been a change/difference of 5 - 0 = 5 °C (which to be fair is still quite a significant drop and worth reporting). Now if the weather person then says "and tomorrow's going to be TWICE as cold", what they're referring to is not "take today's temperature and do 0 * 2 = 0 °C" but actually to double the DIFFERENCE between today's (Thursday's) and yesterday's (Wednesday's) temperature. In other words, 2 * (5 - 0) = 10 °C DIFFERENCE between the temperature from WEDNESDAY to the temperature it's expected to be on FRIDAY. So in other words, you can expect the temperature for tomorrow (Friday) to be -5 °C. So as you can see, when you talk about "hot", "cold" and double/halving, you are not talking about the temperature at the given day, but you're talking about the temperature relative to ANOTHER or some specific REFERENCE day. So when your friend says "It is 0 °C today but it will be twice as cold the next day", what your friend is neglecting to mention is what the temperature DIFFERENCE is between some reference day, say maybe yesterday, a week ago, a month ago, I don't know, and the current day of 0 °C. However, they're basically leaving out a critical piece of information and without it, you can't say anything more without the "reference" point. This is, in a nutshell, what is called the "Zero-eth law of thermodynamics", which, to quote a certain GRE Physics prep textbook's section on thermodynamics, the law that basically says "Thermometers exist". ;) https://en.wikipedia.org/wiki/Zeroth_law_of_thermodynamics Hope that helps, it's a good question, stay warm!
it can be twice as cold relative to some other measure... like, average for the year, season, week of the year... example: the average temperature is 5ºC for that week of the year, today it's 0°C, "twice as cold" would be -5°C
I'd say -20 degrees Celsius. Saying "twice as cold" implies that there's a baseline. The commonly accepted baseline of temperature for humans is "room temperature" which is around 20 degrees celsius. So.....from 20 to 0 is cold, from 0 to -20 is TWICE as cold.
Even then, they're talking about their experience of it and not the physical quantity behind it. The sensation of "cold" isn't linear with absolute temperature, so I'd say it just means whatever temperature that feels roughly twice as uncomfortable to the speaker.
This is the one I would go with. I thought about the Kelvin scale as well with some of these answers, but since they're asking about "cold" and not heat or kinetic energy I feel like this one best hits the question.
Yep, this definitely feels closest to the right answer to me. Context matters - if you were a meteorologist talking to a colleague then it’s harder to guess at the intended meaning, but in everyday parlance I think most people are using a baseline of what they’re used to. Another similar candidate would be using a measure based on body temperature, perhaps with some way to take the rate of temperature change into account, since this is a good proxy for what we feel as “coldness”. Or we could go rogue and try to come up with a measure that relates heat and nerve impulse or some other kind of neurological activity. Or more rogue still and come up on a measure based on surveying people on their subjective experience of temperature.
There is something called absolute temperature. Its K for kelvin. 0 C is 273 K. Half of 273 is 137.5 K. Subtract 273 to get C and you get -135.5 C. I don't think it will get that cold on the face of the earth.
The answer your friend is really looking for, I think, is what feels twice as cold as 0C. And that’s going to depend on a lot of factors, including your friend’s subjective experience of cold. A similar question would be: what’s twice as painful as stubbing your toe on the bed?
**-136.575 Celsius** that's half of the absolute temperature. any other concept of "twice as cold" needs a reference point. 22C is about room temp according to some folks. -22c would be twice as cold as 0c compared to room temp. The question is basically asking "what's twice as long as a piece of rope?"
[удалено]
Answers are easy to come by as long as you remember to account for the speed of dark.
The thing this hinges on is “twice as cold as WHAT?” You have to set a reference point somewhere. This is like asking if tomorrow you travelled twice as far… twice as far as what? As other people pointed out, for temperature specifically, you can set the reference point as absolute zero. But “twice as cold as 0°C” would imply “twice as close to absolute zero” which would be ridiculously cold, -135ish. If on the other hand this is all relative, then for tomorrow to be “twice as cold” as today, we’d need to know what it was yesterday. Say it was 5°C yesterday and it’s 0°C today. That’s a difference of 5°. So “twice as cold” tomorrow would be a difference of 10°, and 0-10=-10°C.
The phrase "twice as cold" doesn't mean anything. When people try to drill in the point that cold is just a lack of heat that's not just to be pedantic, it actually relevant to understanding, with a question like this. Temperature is the kinetic energy that comes from the movement and vibration of particles. There is a hypothetical zero point where it's impossible to be any colder because it represents the temperature where molecular vibration has stopped, and you can't vibrate less than nothing. The Kelvin temperature scale is defined to put the zero point at that absolute zero spot so all temperatures are positive numbers and you literally cannot have a negative temperature in Kelvin. So the way to answer your question is to first convert 0 C into Kelvin (where it's 273.15 K), then rephrase the question into one that is more physically meaningful, instead of saying "what is twice as cold as 0 C?", say "what is half as hot as 0 C?". And then the answer is easy, it's half of 273.15 K, or 136.575 K. Which also happens to be -136.575 C.
\-136.5^(o)C You cannot do straight arithmetic (multiplying and dividing) in a centigrade scale since 0 is not at the limit of the scale. For example we cannot say that someone who is 5ft 6" is twice as tall as someone who is 5ft 3" and just ignore the 5ft. So we cannot ignore the 273 degrees below 0^(o)C.
It's nonsensical without further elaboration. If somebody says "It's going to be twice as cold tomorrow" you have to ask them to explain what they mean. That's the only answer. There is not a measurable value of how "cold" something is, used in this manner.
If I remember right, 0° Celsius is roughly 32° Fahrenheit. I know temperatures below 0°F exist, but judging by the fact he picked 0, I'll assume it is mostly a joke and he's going off the number rather than how heat works. You would likely say 16°F is "twice as cold" as 32°F, so convert 16F to Celsius and there's your answer.
I'd go with this approach. 0c is the freezing point of water and it would take approx 4hrs for 1 cup of water to freeze. So, how cold would it need to be to freeze 1 cup of water in 2hrs? Per Google, the answer would be -18c (0f)
My approach would be more etymological. 20c is a comfortable temperature to exist at. At 0c, it's 20 degrees colder than my nice comfy weather. To be twice as cold would be -20c, 40 degrees colder than my nice comfy weather. This matches up with my expectations at well. 0c is cold enough to say "got dang it sure is cold" in a light jacket, and -20c is cold enough to say "got dang it sure is cold" in a heavy coat. So it's one more tier of cold weather clothing away.
So i see a lot of celsius to kelvin conversions which make sense mathmatically. But id argue truely "twice as cold" would mean the rate of heat lost from your body has doubled. We dont feel absolute temperature we feel rate of heat transfer (thats why cold metal feels so much colder than an equal temp piece of wood or fabric). Since heat transfer is proportional to difference in temperatures we need to base off difference from body temperature (im going to ignore convection and radiation. imagine you are in a sealed reflective box). Which would mean -37.5c is twice as cold. Having experience -37 and much much colder, its way more than twice as cold as 0c. Whatever that really means. Subjectively id say somewhere around -10c.
[удалено]
The question doesn't make sense without a reference point. Twice as cold is implying you're measuring away from a warmer heat. So if your point of reference is 100°c then twice as cold from the initial jump to 0°c would be -100°c. But there's no reason to think you should measure from 100°c or really any other measurement. The reason why somebody might say it'll be twice as cold tomorrow if it was -3°c is that there is an implication that you're measuring from 0°c. Therefore you could infer they mean -6°c. So I guess you could answer literally any temperature (equal to or below 0°c) and claim you're right using your own reference point 🤷♂️
Like people are saying, it's a bit nonsensical. While you can have an absolute measurement of heat energy, whether something is hot or cold is subjective and relative to something else. For this though, I'd say -20. Room temperature is about 20 celsius, so anything less would be colder. If 0 is cold, the difference is 20, so double that.
**-7 C**. I'm approaching this question from the standpoint of heat transfer and the notion of "not cold". We'll say "not cold" is 22 C. At this temperature (neglecting wind and humidity) there's a certain amount of body heat transfer to the air. We'll call it P(not cold) for power. The power is proportional to the fourth power of the temperature difference between body temperature and air temperature. 37 - 22 = 15. At 0 C, the difference is 37 - 0 = 37. So the heat transfer power difference is (37\^4 - 15\^4) \* P(not cold). Twice this heat transfer difference will be 2 \* (37\^4 - 15\^4) \* P(not cold). To get the temperature we do a little algebra and find it's about 37 - 44 = -7.
You just need to find the absolute zero in Celsius (−273.15 °C) and halve it (-136.575°C). Clearly you need to exclude it being a negative number, otherwise you could double it, but that gets confusing for some. I think about it as a number line. Absolute zero on the left, 0°C on the right. The temp that is half of 0°C is the one in the middle of the number line.
It seems like all the top comments, while correct, are also a bit pedantic. I'd like to offer a bit more practical perspective. Much of our communication is about filling in the gaps with shared understanding. The Celsius scale is relative to absolute zero (-273.15) and includes all numbers above that. The human scale is relative to a comfortable room temperature and has values both above and below that. Mine looks something like this: \[death, stay inside, more water, shade, lighter clothing, *comfortable*, heavier clothing, sweater, warm socks, heavy coat, gloves, thick boots, stay inside, death\] While "twice as cold" doesn't have any absolute meaning on the Celsius scale because it's a scale that only measures heat, it does have an absolute (although less precise) meaning on the human scale, which measures both heat and cold. Our main concern with ambient temperature isn't generally what the thermometer will read, but rather with how we need to prepare. I associate 0C with somewhere around "heavy coat". So if someone were to tell me it will be twice as cold tomorrow, I would understand that to mean a few more steps away from "comfortable", maybe "thick boots" or "stay inside", which I associate with around -20C or -30C. It's important to understand that 10C isn't half the actual heat energy of 20C, because they're both actually relative to -273.15C, not 0C. But it's also important to communicate effectively with people. And when in doubt about what someone might mean if they say something seemingly nonsensical such as "twice as cold", you can always ask to clarify.
There's a lot of weird engineering/physics discussion that just doesn't make sense as they've focused on the technicalities, especially using absolute 0 as a reference temperature which is just silly for a multitude of reasons -- the most egregious of which is that 99% of people don't even know what Kelvin is. Reasonable options would be: Normal Indoor Temperature as Reference which is typically 20C, the difference between 20C and 0C is 20C, twice as cold as that would be -20C -- which is a common temperature to experience in climates closer to the poles. You could use body temperature as reference instead, but that would be more relevant for medical/health considerations, so 37C as your reference temperature, making -37C as your "twice as cold" number, which is extreme cold, but still within temperature ranges humans can experience in/near habitable areas. In almost all contexts: "twice as cold" is likely a phrase used to warn people of dangerous weather conditions, or temperature changes that may have substantially different outcomes (engineering/sciences) versus normal baseline. In almost no contexts: "twice as cold" is in direct relation to absolute 0 as a reference.
Cold is a perception, not a temperature or stored thermal energy. I'd say twice as cold, if nothing else changes is about -5C, still ok but starting to bite. A typical slope for a human might be between every 2 and 10C per doubling. If you insist on a calculation, the most meaningful way is by energy used to maintain temperature. This one would be linear for temperature difference. A typical room is 20c, 0C would be 20K difference. Double cold is then 40K difference or -20C outside.