Quantum effects near 0 Kelvin

[nomadreid]

TL;DR Summary

Do quantum effects as well as thermodynamic laws forbid zero Kelvin? Is there a non-zero greatest lower bound?

In https://phys.org/news/2016-09-cold-black-holes.html it is stated that a supermassive black hole interior could be 10^-14 degrees Kelvin. Is there a limit, perhaps due to quantum effects, below which a temperature (in a black hole or elsewhere) can go? Or do the possibilities approach 0 asymptotically, with only 0 being the theoretical minimum?

Putting it slightly differently: Usually the laws of thermodynamics are invoked to forbid absolute zero; in https://en.wikipedia.org/wiki/Absolute_zero, it is stated that one cannot reach absolute zero by thermodynamic means. Are there other means besides thermodynamic that could subtract energy, or are there quantum effects that would forbid it as well?

 

[PeterDonis]

In https://phys.org/news/2016-09-cold-black-holes.html it is stated that a supermassive black hole interior could be 10^-14 degrees Kelvin.

This would be true (assuming our current beliefs about Hawking radiation are correct) if the hole was alone in the universe, but it's not. In our actual universe, the hole would be, even if no other matter fell in, continually absorbing CMBR radiation at 2.7 K, so (a) its mass would be increasing, not decreasing, and (b) the Hawking temperature is not a good description of its actual conditions.

As usual, phys.org does not bother to mention all of the relevant items.

Is there a limit, perhaps due to quantum effects, below which a temperature (in a black hole or elsewhere) can go? Or do the possibilities approach 0 asymptotically, with only 0 being the theoretical minimum?

As far as I know, theoretically, there is no minimum and absolute zero can in principle be approached asymptotically. The practical issue is that the colder something is, the harder it gets to remove any more heat from it, with the difficulty increasing without bound as absolute zero is approached. I don't know of any quantum effects that change that.

 

[nomadreid]

Thanks for the very helpful reply, PeterDonis.

 

[PeterDonis]

Thanks for the very helpful reply, PeterDonis.

You're welcome!