# Absolute zero and gravity

1. Oct 7, 2008

### GoneTroppo

Today in my physics class we got into a discussion about Absolute Zero and gravity. The argument was that if Absolute Zero was achieved, would it still be affected by gravity? Because gravity is a force and would make whatever that was at Absolute Zero move, but to have motion there would be resistance (friction, air resistance ect.) and that would make it not Absolute Zero. This is confusing to explain and hope you understand, but what I guess I'm asking is ... is it possiable to have something at Absolute Zero? and if so, can it be moved? and what if it is in deep space with near 0 gravity?

Thanks for reading and any relpies!

2. Oct 7, 2008

### Mapes

Since absolute zero can't be achieved, there seems little point in asking the question. Yes, no, what's the difference? However, we can say that gravity is theorized to be independent of temperature, and gravity is not known to change as we approach arbitrarily close to absolute zero.

Motion does not require resistance; I don't know where that claim comes from.

3. Oct 7, 2008

### gendou2

Temperature is a measure of random internal kinetic energy.
A volume of gas in deep space may have nearly zero temperature.
If, however, some potential energy is being converted into kinetic energy (we sometimes call this "falling") in the presence of a gravitational field, that kinetic energy would indeed manifest its self partially as heat.

Similarly, and attempt to "move" a body of gas measured to be nearly absolute zero in temperature will disturb it, no matter how delicate and careful you are. This will inevitably raise it's temperature.

Absolute zero is mathematical concept, not a real-life phenomena. There has, to my knowledge, never been an experiment that showed the temperature of an object to be exactly absolute zero. I find it unlikely such an experiment can be performed. One reason is the fact that the act of observing alters the experiment.

Last edited by a moderator: May 3, 2017
4. Oct 7, 2008

### gendou2

How have you concluded this? I don't suspect you are mistaken, but I worry about unsupported claims.

5. Oct 7, 2008

### mgb_phys

You can't reach absolute zero, but you can get within a few billionths of a degree of it.
However as mapes said, there is no experimental evidence or theoretical reason why temperature should affect gravity.

6. Oct 7, 2008

### davidelete

Most likely a misunderstanding of Newton's third law.

7. Oct 8, 2008

### atyy

Wald states that the temperature of a classical black hole is absolute zero, so it seems that within classical physics, gravity does not prevent absolute zero from being reached.

According to Chavanis et al, some classical self-gravitating systems can come to an equilibrium state of finite density only far above absolute zero.

The third law of thermodynamics is usually stated: a system at zero absolute has zero entropy. It is equivalent to a quantum mechanical system having a unique state of lowest energy. The third law does not hold for classical systems. My impression was that the third law implies that absolute zero cannot be reached in a finite number of steps. But Wald makes some very disparaging remarks about this idea.

Black Holes and Thermodynamics
Robert M. Wald
http://lanl.arxiv.org/abs/gr-qc/9702022

Thermodynamics of self-gravitating systems
P.H. Chavanis, C. Rosier, C. Sire
http://arxiv.org/abs/cond-mat/0107345

Last edited: Oct 8, 2008
8. Oct 10, 2008

### Minte

Absolute Zero is a tricky concept. You can get close, but never there. It's asymptotic and theoretical.

...But if you -could-, then I don't see why gravity would affect it.

9. Oct 10, 2008

### met4t

Well, absolute zero means no objects and particles are moving.
But gravity still independently acts on the particles and objects. That can only happen at some well equilibrated state.

10. Oct 14, 2008

### Naty1

Hawking proved black holes radiate...via Hawking radiation...tunneling....and get hotter as they disippate (shrink).....hence are not at absolute zero...hence have entropy and information within....who do you want to believe???

11. Oct 14, 2008

### f95toli

This is a common misconception. Particles would move due to quantum fluctuations even at absolute zero; although the effect is tiny.
See e.g. Gardiner's book "Quantum Noise"

12. Oct 14, 2008

### mgb_phys

Postulated that black holes radiate - it hasn't been proved, or even observed.
Additionally a classic black hole could have zero temperature, a classic black hole doesn't exist - it's like a smooth plane or a massless spring, just a mathematical convenience.

13. Oct 14, 2008

### HallsofIvy

Staff Emeritus
An object does not have to be moving, or even able to move, to be affected by gravity. I can feel my own weight as I sit in this chair. (And, in fact, now that I think of it, I should get out of this chair and exercise more so I don't feel it so much!)

14. Oct 14, 2008

### met4t

To be clear: zero temperature can be a relative concept. For example, when an object is not moving, it could be thought classically of as having zero temperature but this is not true as you know that your body temperature is about 37 degrees C.
Absolute zero should mean all particles including elementary particles have zero motion.
This can only possibly happen in a potential field (gravity as an example) if the system is at some well equilibriated state.
But also we know that this is not going to be in accordance with quantum laws of physics: an elementary particle cannot have a fixed position.
Only if the dynamic elementary particle is massless could it be given zero temperature according to the equipartion theorem.
The subject of "absolute zero and gravity" is more of a discussion topic rather than a real situation.

15. Dec 16, 2011

### Avi8tor857

I know this is an old topic but came across it searching.

If absolute Zero is an unreachable state requiring zero entropy and traveling at the speed of light is a state that takes infinite energy for a particle with mass (also an unreachable state) can these two points be considered the two boundaries in which mass can exist? If so one would think that the two items speed and temperature are some how related at the extreme boundaries. Then my mind goes to relativity, if one could achieve Absolute Zero what would the effect be on Time, and time is effected by gravity....

It all comes down to the source of gravity and since we are not positive that the higgs boson particle exists, and we don't understand how gravity is produced it is irresponsible to discount that at Absolute Zero Gravity might be effected if you consider Absolute Zero the state at which all particles cease to move or even vibrate who is to say that might cause the particle to no longer have a source of gravitational mass. If the particle no longer has a gravitational mass nor velocity at a subatomic level how does time proceed within this frame of reference compared to ours?

I know these states are not achievable but many theoretical states are used in particle physics in order to make the math work.

Of course this is just the pondering of a software engineer, but I do think that both time and gravity effects at or approaching Absolute Zero should be researched. And I do understand that what I postulate here isn't consistent with many popular theories, but that is just it they are theories and are unproven.

16. Dec 17, 2011

### Dal902

Wouldn't reaching absolute zero be impossible because of quantum mechanics? With heisenberg's uncertainty principle in mind it is impossible to get the momentum to actually equal zero even though it can come infinitely close. Since absolute zero to be achieve there must be a momentum equal to zero. This says to me that it is impossible. Sort of like traveling faster than c.

17. Dec 17, 2011

### Naty1

I think Beckenstein and especially Hawking pretty much proved that theoretically for black holes.