# What Does General Relativity say About Absolute Zero? **URL:** \ **Category:** Factual Questions\ **Created:** [September 11, 2015, 3:01pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675 "2015-09-11T15:01:18Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [September 11, 2015, 3:01pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/1 "2015-09-11T15:01:18Z")
I have often wondered about this-because Absolute Zero means the cessation of time. We have a clue about this, because helium 3 (which is a superfluid with no friction) is close to absolute zero-its electrons have collapse into a zero energy state. So, at a state of zero energy, does the “time” dimension exist at all? Perhaps this explains the whole dark matter thing? ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [September 11, 2015, 3:10pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/2 "2015-09-11T15:10:35Z")
> [@ralph124c](#): > > …because Absolute Zero means the cessation of time. It does? You sure about that? ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [September 11, 2015, 3:22pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/3 "2015-09-11T15:22:54Z")
There is a vacuum solution to the General Relativity equations. In a vacuum the temperature is either undefined or zero I’d think. Quantum Mechanics might differ on this point, but then QM and GR aren’t on speaking terms. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [September 11, 2015, 5:01pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/4 "2015-09-11T17:01:28Z")
> [@ralph124c](#): > > I have often wondered about this-because Absolute Zero means the cessation of time. We have a clue about this, because helium 3 (which is a superfluid with no friction) is close to absolute zero-its electrons have collapse into a zero energy state. So, at a state of zero energy, does the “time” dimension exist at all? Perhaps this explains the whole dark matter thing? Absolute zero does not mean cessation of time. It has nothing really to do with time. It also does not mean zero energy but lowest internal energy. SDMB has some folks who are real experts at this stuff, hopefully they will be along soon. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [September 11, 2015, 5:10pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/5 "2015-09-11T17:10:13Z")
> [@CurtC](#): > > It does? You sure about that? I believe we’ve sent a watch into orbit and observed that when it comes back the time is behind where our time is. Proving that time dilates as we get closer to the speed of light. I’ll bet if you bring a watch near absolute zero it would stop as well. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [September 11, 2015, 5:13pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/6 "2015-09-11T17:13:12Z")
> [@Joey\_P](#): > > I’ll bet if you bring a watch near absolute zero it would stop as well. Yes but that is a purely mechanical effect if I understand what you’re saying. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [September 11, 2015, 5:14pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/7 "2015-09-11T17:14:22Z")
> [@OldGuy](#): > > Yes but that is a purely mechanical effect if I understand what you’re saying. whoosh ---
**Author:** ![Atamasama](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/atamasama/32/12961_2.png) [@Atamasama](https://boards.straightdope.com/u/Atamasama)\ **Post date:** [September 11, 2015, 5:14pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/8 "2015-09-11T17:14:46Z")
> [@Joey\_P](#): > > I believe we’ve sent a watch into orbit and observed that when it comes back the time is behind where our time is. Proving that time dilates as we get closer to the speed of light. > I’ll bet if you bring a watch near absolute zero it would stop as well. I left an old watch in a drawer for a few months, forgetting it was there. When I found it again it was a few minutes behind. I think that just proves it was a cheap watch. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [September 11, 2015, 5:18pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/9 "2015-09-11T17:18:53Z")
Joke y’all ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [September 11, 2015, 5:19pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/10 "2015-09-11T17:19:02Z")
> [@Joey\_P](#): > > I believe we’ve sent a watch into orbit and observed that when it comes back the time is behind where our time is. Proving that time dilates as we get closer to the speed of light. > I’ll bet if you bring a watch near absolute zero it would stop as well. If you send a Rolls-Royce into space, you won’t have to listen to the damned clock. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [September 11, 2015, 5:20pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/11 "2015-09-11T17:20:04Z")
> [@ralph124c](#): > > I have often wondered about this-because Absolute Zero means the cessation of time. We have a clue about this, because helium 3 (which is a superfluid with no friction) is close to absolute zero-its electrons have collapse into a zero energy state. So, at a state of zero energy, does the “time” dimension exist at all? Perhaps this explains the whole dark matter thing? If particles were to cease motion altogether you could simultaneously know their position and their momentum, which Quantum Mechanics (not General Rel) prohibits. The Uncertainty Principle guarantees that if you know the region particles are confined it, you must not be able to know their momentum to some limiting value inversely proportional to the confinement. So they won’t be without motion – they’ll be vibrating around some potential minimum. This is one reason absolute zero remains an elusive goal. Last June, MIT researchers got down to 500 nanoKelvins, which is (you should pardon the expression) pretty cool. > **[MIT team creates ultracold molecules](https://news.mit.edu/2015/ultracold-molecules-0610)** > > Physicists at MIT have cooled molecules in a gas of sodium potassium to a temperature of 500 nanokelvins — just a hair above absolute zero, and over a million times colder than interstellar space. These temperatures are nearly cool enough to observe... ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [September 11, 2015, 5:51pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/12 "2015-09-11T17:51:58Z")
Cal provides the explanation. We can never reach absolute zero, according to our current understanding of the laws of physics. Absolute zero means no motion at all. And that means we know the position of a particle exactly, and the momentum of the particle exactly, which can’t happen. And even beyond that, particles decay, virtual particles appear out of the ether, and so on. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 11, 2015, 7:35pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/13 "2015-09-11T19:35:03Z")
Even without quantum mechanical peskiness, the laws of thermodynamics are by themselves enough to guarantee that absolute zero is unattainable. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [September 12, 2015, 2:43am UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/14 "2015-09-12T02:43:49Z")
> [@Lemur866](#): > > Cal provides the explanation. We can never reach absolute zero, according to our current understanding of the laws of physics. Absolute zero means no motion at all. And that means we know the position of a particle exactly, and the momentum of the particle exactly, which can’t happen. > > And even beyond that, particles decay, virtual particles appear out of the ether, and so on. How does absolute zero mean you know the position of a particle exactly? ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [September 12, 2015, 2:58am UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/15 "2015-09-12T02:58:34Z")
> [@Napier](#): > > How does absolute zero mean you know the position of a particle exactly? IANA physicist, but my suspicion is that at absolute zero, ALL atomic and sub-atomic motion stops, and you could just look and see where everything is. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [September 12, 2015, 4:23am UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/16 "2015-09-12T04:23:11Z")
> [@bump](#): > > IANA physicist, but my suspicion is that at absolute zero, ALL atomic and sub-atomic motion stops, and you could just look and see where everything is. Looking and seeing requires you to send and receive energy from the system, no? ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [September 12, 2015, 5:47am UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/17 "2015-09-12T05:47:32Z")
> [@Telemark](#): > > Looking and seeing requires you to send and receive energy from the system, no? Not really. The uncertainty principle basically requires that he more certain you are of the of the location of a particle, the less certain you can be of its momentum. Now imagine you have a single hydrogen nucleus in your fridge, and you get the temperature of the fridge down to absolute zero. Now you can say with absolute certainty that the momentum of that hydrogen nucleus is zero degrees. But you can also say with absolute certainty that the hydrogen particle is within the area of 2 cubic metres defined by the walls of your fridge. You may not be certain \*exactly \*where it is in your fridge, but you know that it must \*be \*in your fridge So you are certain of the particle’s location to within 2 cubic metres. That should be mean that you are concomitantly uncertain if it momentum. But you aren’t at all uncertain. You are absolutely certain its momentum is zero. But that means that you have to be infinitely uncertain about its position. But you know its position to to within 2 cubic metres, which is pretty small in comparison to an infinite universe. Which means you have to be highly uncertain of its momentum. But you aren’t. And in case you’re thinking that the particle could have teleported or tunneled out of the fridge, all you need to do is weight the fridge really carefully. No need to actually look and see where it is exactly. you just need to know that it’s inside the fridge. ---
**Author:** ![Carl\_Pham](https://avatars.discourse-cdn.com/v4/letter/c/e9a140/32.png) [@Carl\_Pham](https://boards.straightdope.com/u/Carl_Pham)\ **Post date:** [September 12, 2015, 10:06am UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/18 "2015-09-12T10:06:19Z")
I don’t think GR says anything about absolute zero, or at least anything very interesting. GR is a classical theory, and from a classical point of view absolute zero isn’t a very remarkable state. It just means when all degrees of freedom in a collection of them cease motion entirely. Now \*technically \* temperature is only defined in the limit of an infinite number of degrees of freedom (the so-called “thermodynamic limit”), and it is plainly impossible to get an infinite number of degrees of freedom to cease motion entirely (as long as it is connected to an “outside world” – and let us not get into the metaphysics of what is “outside” an infinite system, save to note it is possible). Any ordinary macroscopic system will have 10^23 degrees of freedom, which is close enough to “infinity” for government work, so it would be practically (albeit not theoretically) impossible (if we lived in a classical universe) to get even small (but visible) systems to cease all motion, that is, to be at “absolute zero” (if you’re willing to define temperature for a finite system, and we usually are, through various arguments and waving of hands). Certainly if it’s small enough – a few classical particles – it would be possible, if not very illuminating. The only thing I can imagine GR saying about all this is that, since curvature of space implies energy, zero motion can only occur in a region of spacetime that is perfectly uniformly curved – if it were not, then there would be energy in one place but not another, and it would flow, which implies motion. None of this really matters, however, since absolute zero is the domain of quantum mechanics, and most of what classical theories say about it is wrong. This is not to say there is no interesting connection between thermodynamics and GR. In fact, there is a very rich field exploring the connections that can be deduced from general principles, many of them having to do with the properties of black holes. ---
**Author:** ![Nancarrow](https://avatars.discourse-cdn.com/v4/letter/n/c37758/32.png) [@Nancarrow](https://boards.straightdope.com/u/Nancarrow)\ **Post date:** [September 12, 2015, 11:03am UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/19 "2015-09-12T11:03:20Z")
> [@Chronos](#): > > Even without quantum mechanical peskiness, the laws of thermodynamics are by themselves enough to guarantee that absolute zero is unattainable. You sure? My understanding was that, firstly, it’s only the _third_ law that guarantees absolute zero is unattainable, not the first two. And secondly, that the third law is a necessary consequence of quantum mechanics, in a way that the first two are not. That is, ‘even without quantum mechanical peskiness’, the first two laws would still be true, but the third would not. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 12, 2015, 1:56pm UTC](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675/20 "2015-09-12T13:56:59Z")
A consequence of the Third Law is still a consequence of the laws. Though depending on exactly how you formulate the Third Law, you might need to incorporate the other two as well. And really, _everything_ is a consequence of quantum mechanics. But you can still observe, derive, and use the Third Law in contexts where quantum mechanics has little relevance or is poorly understood. The laws of black hole thermodynamics, for instance, are surprisingly well-understood, even though we don’t understand how quantum mechanics works for black holes. [Next page](https://boards.straightdope.com/t/what-does-general-relativity-say-about-absolute-zero/730675.md?page=2)