If you want to talk about coldness being conceptual, I think IMHO is the place to discuss vibes…
An easy way to understand this is that heat is a measure of how much energy some stuff has in it. If it has more energy in it, it’s hot. If it has less energy in it, the stuff is cold.
Space doesn’t have any stuff in it (basically - technically there are tiny bits of dust and atoms here and there, but so little that you can think of space as basically an empty vacuum). So how much energy is in the stuff if you don’t have any stuff? You can’t really say whether the stuff is hot or cold because there isn’t any stuff.
With no disrespect to the OP, all of us are guessing at what he was trying to ask, and the farther we get, the less clear my own conception of his question is.
Right now we’ve got 20 posters spilling electrons shotgunning all over the place. And my bet is the OP is becoming more, not less confused about whatever thing is confusing them. Or more discomfited at how their point is being misunderstood. Or both.
I think the thread could usefully use the OP trying to set out his beliefs, or a straw man, or something in greater detail for us to grapple with.
But right now it’s not clear to me whether this is about strict English, colloquial English, physics, or some philosophical metaphysics thing. A great discussion can be had on any of those aspects of the question “What is cold? / What does ‘cold’ even mean?” But it’s hard to have a meaningful coherent non-confusing discussion about all 5 ideas at once.
I know we all mean well, but I’d like to invite @Peter_Morris to lay out his ideas and questions in a bit more detail. What is, and perhaps more importantly what is not, the topic of conversation?
YMMV of course. I may be well off the mark here.
I’m not fighting the answers here but in the case of two black holes colliding, the subsequent waves sent out at c are bending something aren’t they?
I am not a physicist, but is this accurate?
Heat is a real thing. Coldness isn’t.
Do physicists actually talk about the coldness in a system? When a liquid freezes, is it from gaining coldness?
I thought I had.
Okay, natural language is inexact and full of ambiguities. The word “cold” like so many words is open to interpretation.
I think that according to some common usage of the word, space can be described as cold.
Sure, people talk about the “coldness of space” all the time.
Here’s a good page on heat vs temperature:
If “coldness” isn’t a real thing, then “hotness” isn’t a real thing, either. “Heat” and “hot” are not the same thing. (See my previous link.)
When humans say something is hot or cold, what they are really referring to is the rate of heat transfer of the object, not the object’s absolute temperature. For instance, if a piece of wood and piece of iron are both at 200-degrees, the piece of iron will feel much hotter than the piece of wood. This is because iron can transfer heat very quickly while wood transfers heat very slowly. A person would say that the iron is much hotter than the wood even though they are actually at the same temperature. What they are really saying with the word “hot” is that the quantity of heat energy transferred by the object is high. Part of the confusion comes from using the human concept of hot and cold (e.g. rate of heat transfer) to the words hot and cold used by science to describe space.
Darren_Garrison’s link sums up the OP’s concern pretty well in the opening paragraph:
“Heat measures how energy moves or flows. An object can gain heat or lose heat, but it cannot have heat. Heat is a measure of change, never a property possessed by an object or system.”
“Cold is just the absence of heat,” is a bit like saying “East is just the absence of west.” It’s not a property an object has, it’s a direction the object is moving in.
I imagine the few particles in any given volume of space are quite energetic, so maybe their average kinetic energy is high, meaning space is hot!
Thank you for indulging me.
Yes, I agree completely that in colloquial usage, people who know little of space or physics use the word “cold” to describe the nature of space.
And because lots of people are in that condition, lots of them use the word “cold” in that way. Which has the effect of permitting them to use that word to communicate between them the idea that the other one thinks space is cold and they are of like mind.
And folks who know more or are thinking more technically can deliberately use “cold” in that way because they know their audience. Or can use it as a sloppy mental shorthand, much as we say “the soup is cold” when we strictly mean the soup is warm to hot, but not hot enough to be satisfying to eat.
In a more scientific sense you can say that “space is not hot” in that you cannot extract heat from it. Because it has none. And in a simple-minded extrapolation from that true physics fact one might say “if space is not hot, it must be cold. Cold and hot are opposites. Therefore space is cold”.
But that’s logically fallacious. There are three kinds of environments. Those which are hot, those which are cold, and those for which the concepts of hot and cold are (nearly) meaningless. In the meaningless case of space asserting that it’s not hot and therefore must be cold is just as (non-)sensible as asserting that it’s not cold and therefore must be hot.
Logically this is akin to the math jokes that “prove” that 2=1 by somehow slipping an unnoticed divide by zero operation into the algebra. Every number divided by zero is equal to, and simultaneously not equal to, every other number. The fix is to not divide by zero.
And in the case of “cold” (or “hot”) applied to space, the fix is to recognize that conventional notions simply don’t apply and colloquial use is actually inapplicable, not wrong. But when they all agree to apply it anyhow, and mostly agree on what the wrong meaning means, they can communicate something to one another by saying “space is cold”. What is that something? Beats me. But I think what it amounts to practically is “You can’t extract heat from space.”
As noted a couple posts up, there is a lot of confusion among non-technical users of the ideas of heat and temperature and how they are different. This stuff is genuinely kinda deep. But many uses of both “hot” and “cold” fudge the distinction, talking in one breath about temperature and the next about heat or heat flux without even noticing the transition.
Lotta room for fuzzy thinking and therefore fuzzy communication when jumping around concepts like that unwittingly.
ISTM, looking at the question perhaps too simplistically, one can take two views of the temperature of space. In the classical view, temperature is the measure of the average kinetic energy of the molecules within a system. Since for practical purposes there are virtually no molecules in empty space, one can say that “temperature of space” is undefined and meaningless in this classical sense.
But at a quantum level, the Cosmic Microwave Background (CMB) that permeates all of space does have a temperature, currently estimated as 2.7 K. This temperature takes the form of photon energy left over from the Big Bang, and can be conceptualized as a kind of photon cloud. It’s literally the thermal energy from the Big Bang that cooled as space expanded.
A very common misconception. But when you carry a bucket of ice into a room, you’re actually increasing the thermal energy content of the room… and yet, you’re also clearly adding coldness to the room.
But back to space… The corona of the Sun is not a vacuum; it’s made up of plasma. And it has a temperature. It is, in fact, quite hot, millions of degrees (the reason for this isn’t entirely understood, but it has to do with the Sun’s changing magnetic field). And yet, if you were in the corona, but shadowed from the direct light from the Sun, you’d freeze, not cook. Because while the corona isn’t a vacuum, it’s very, very close to one, so close that there would be almost no thermal coupling to it.
Language is always slippery. I’d posit that the most frequent use of “hot” and “cold” is in conveying temperature in an absolute sense. “How hot is it outside?” “Super hot today, 95 degrees F.” “How cold is the freezer?” “Is the engine running too hot?” “How do you keep your CPU from getting too hot?” “Will it be cold enough to freeze the lake this weekend?” All absolute temperature messages, where “hot” and “cold” are meaningfully connected to numerical temperatures given the context. Other usage can require additional context clues. “You can pick that up; it won’t feel too hot,” could mean that given the thermal conductivity of that material, the temperature isn’t high enough to cause trouble, although some other object at that same absolute temperature might be called hot (or “feels hot”) if it can give off its heat better.
I’m not sure any of this matters, though, for the question in the thread title.
Space is cold. If you stick something in deep space, far away from stars or whatever, it will cool down to 2.7 K. This is no different than sticking a brick in an infinite pool of 300-kelvin water. The brick will reach 300 K, heating up or cooling down as needed based on its starting temperature. The pool was and, due to its largeness, still is at 300 K, and the brick is also now at 300 K, and they are in thermal equilibrium.
The technical term for such a fixed-temperature thermal “bath” is, well, “thermal bath” – an effectively infinite source or sink of heat that maintains its temperature. If we stick a thermometer instead of a brick into our water-based thermal bath, we’d soon see a steady “300 K” on the dial.
A thermometer in deep space will eventually read “2.7 K”. That’s the temperature of space. I would call that cold.
For space, the thermal bath consists of photons rather than water molecules in a pool, but that doesn’t make the temperature any less real.
If you were naked and suddenly exposed to deep space, your body would lose heat into space at 800 watts or more, and you’d definitely say that deep space felt very cold.
On the definition of temperature:
The bedrock definition of temperature is technical and related to how the entropy of a system changes when its energy changes. I’m happy to expand on that.
For now, note that temperature isn’t defined as the average kinetic energy of molecules or whatnot. The latter is linearly related to temperature in some situations, but not others.
(Barring one nitpick that I won’t bother with here, a not-actually-a-joke definition of temperature that is equivalent to the entropy-energy one is “The temperature of X is defined as the reading on a thermometer that has reached thermal equilibrium with X.”)
For the kinetic energy misconception: this conception best works when considering the translational kinetic energy of negligibly interacting molecules that aren’t too hot or too cold, as in a regular gas at room temperature. In this case, the temperature is in fact a fixed multiple of the molecular translational kinetic energy. If the system gets cold enough, interactions or quantum mechanics will break this. If the gas gets hot enough, relativity will break this. If you count other kinetic energy, like rotational or vibrational energy, that would break this (and whether it does, and by how much, depends on temperature).
A few (out of many) mundane examples where the “kinetic energy as temperature” view is very bad:
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Everyday solids can have rather high “Debye temperatures”, which is the rough temperature below which the quantum nature of the lattice and its chemical bonds are relevant. Aluminum has corrections to the simple KE-to-temperature relationship below 400 K. Silicon, below 600 K. Diamond, below even the extreme 2000 K. This is not a rare thing, but in fact a routine feature of crystaline solids. The average KE of the atoms or molecules varies non-linearly with temperature below these cutoffs. Further, the atomic KE sits well above zero as T approaches absolute zero. (If that bothers you, consider how the electron in a hydrogen atom has non-zero kinetic energy even in the atom’s ground state. You can’t extract that energy, but there is real kinetic energy there all the same.)
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Next: conduction electrons in a metal (copper or whatever) at room temperature. Those electrons are unable to all have a kinetic energy as low as the temperature would “suggest” because there are not enough quantum states available for all the electrons. They instead form a Fermi gas. If you take the average kinetic energy of the conduction electons in copper and calculated what a “normal” material’s temperature would have to be for the particles to reach those KEs, you get 30,000 K or so. Yet, the electrons are just at room temperature, 300 K, even with all that kinetic energy.
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As in the deep space scenario, a thermally equilibrated photon gas has a well-defined and not weird temperature. While the relation between the average energy of the photons and the temperature is linear, the numerical factor differs from what you’d find for a physical gas.
So, KE is not trivially connected to temperature, even in plenty of normal stuff.
In all cases, energy will flow from a higher temp thing to a lower temp thing when those things come into thermal contact. And that’s what temperature is at its heart. (The nitpick mentioned at the top actually breaks even this, but sanity can be restored with a slight nudge to how temperature is labeled, so it’s not really a fundamental breakage.)
Let’s simplify this with a thought experiment. Say I’m in a space capsule far from the sun or any other star. I have a thermometer with me that says the ambient temperature is 65F. If I then eject it into space, what temperature will it eventually read?
2.7 K. That’s the temperature it will read eventually.
(This assumes the thought experiment’s thermometer is capable of functioning at both 65 F and 2.7 K; that your toasty heated capsule isn’t too close by; etc.)
It’ll eventually read lower than that.
Nice.
(So as not to sow confusion for others, at the cost of maybe ruining the joke: the 2.7 K number itself is dropping slowly with time as the universe expands. In hundreds of millions of years, we’ll see 2.6 K.)