**[Skip to comment(s)]**

**from the**

**under-pressure**dept.Physicists discover black holes exert a pressure in serendipitous scientific first:

The University of Sussex scientists have shown that [black holes] are in fact even more complex thermodynamic systems, with not only a temperature but also a pressure.

The serendipitous discovery was made by Professor Xavier Calmet and Folkert Kuipers in the Department of Physics and Astronomy at the University of Sussex, and is published today in Physical Review D.

Calmet and Kuipers were perplexed by an extra figure that was presenting in equations that they were running on quantum gravitational corrections to the entropy of a black hole.

[...] Xavier Calmet, Professor of Physics at the University of Sussex, said: "Our finding that Schwarzschild black holes have a pressure as well as a temperature is even more exciting given that it was a total surprise. I'm delighted that the research that we are undertaking at the University of Sussex into quantum gravity has furthered the scientific communities' wider understanding of the nature of black holes.

"Hawking's landmark intuition that black holes are not black but have a radiation spectrum that is very similar to that of a black body makes black holes an ideal laboratory to investigate the interplay between quantum mechanics, gravity and thermodynamics.

"If you consider black holes within only general relativity, one can show that they have a singularity in their centres where the laws of physics as we know them must breakdown. It is hoped that when quantum field theory is incorporated into general relativity, we might be able to find a new description of black holes.

**Journal Reference**:

Xavier Calmet, Folkert Kuipers. **Quantum gravitational corrections to the entropy of a Schwarzschild black hole**, Physical Review D (DOI: 10.1103/PhysRevD.104.066012)

**12**comments | Search Discussion

**The Fine Print:**The following comments are owned by whoever posted them. We are not responsible for them in any way.

**(1)**

**(1)**

## (Score: 3, Insightful) by bradley13 on Monday September 13, @05:45PM (9 children)

TFA is utterly unclear as to what

kindof pressure they're talking about. I assume it must be more than radiation pressure from the black-body spectrum (because that's obvious). But I'm not finding a link to any sort of actual, technical paper.Everyone is somebody else's weirdo.

Reply to This## (Score: 1, Funny) by Anonymous Coward on Monday September 13, @06:00PM (2 children)

>> TFA is utterly unclear as to what kind of pressure they're talking about.

Peer pressure. The other more woke celestial bodies are trying to pressure it to stop referring to itself as "black" and it's pushing back (as Newton tells us must happen).

Reply to ThisParent## (Score: 0) by Anonymous Coward on Monday September 13, @08:42PM

Most of these type of comments are not very funny and are rather tiresome, but this one I found to be fairly clever.

Reply to ThisParent## (Score: 0) by Anonymous Coward on Tuesday September 14, @03:53AM

Fortunately the White Dwarves are the Protectors of Newtonian Physics (not that Einstenian jew crap) so the Universe is safe.

Reply to ThisParent## (Score: 2) by HiThere on Monday September 13, @06:14PM (3 children)

I think they're actually unclear as to what kind of pressure. If I read correctly they aren't even sure whether it has a positive or negative value. (Well, that was a different report of the same finding. And I don't even know what "Wald Entropy" is.)

Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.

Reply to ThisParent## (Score: 3, Interesting) by legont on Tuesday September 14, @03:59AM

It looks like they found out that event horizon radius and temperature have to be "adjusted" which could be described by pressure applied to the beast itself; similar to any usual body which is smaller and hotter under pressure.

"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.

Reply to ThisParent## (Score: 0) by Anonymous Coward on Tuesday September 14, @04:50AM (1 child)

You can find the description of Wald entropy here :

https://arxiv.org/abs/gr-qc/9307038 [arxiv.org]

It might not be especially easy to read, but basically it shows that the entropy of a black hole is proportional to the area of its event horizon (which is surprising, because the entropy of everyday things is proportional to their volume).

I don't entirely understand this new paper. Basically what it seems to be saying is that the traditional calculation of entropy is accurate for massive black holes, but it isn't accurate for extremely small black holes. The radius and temperature don't change, so a notion of pressure is created which allows for the entropy to be slightly different. This "pressure" is similar to the "spin" of an electron, it's not pressure as you would find in a gas, for example. The property has a physical meaning but the name comes from mathematical analogy.

This has absolutely no bearing yet on anything outside of theoretical physics, but it is a step toward determining whether Planck particles (tiny black holes with radius equal to the Planck length) can exist, which is relevant because they are a dark matter candidate.

Reply to ThisParent## (Score: 0) by Anonymous Coward on Tuesday September 14, @04:53AM

I actually did find what seems to be a similar paper :

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.88.104024 [aps.org]

It seems like the idea of adjusting the Wald entropy based on quantum effects isn't new, but they may have approached the problem from a different angle. (Does a perfectly smooth ideal black hole have angles?)

Reply to ThisParent## (Score: 1, Informative) by Anonymous Coward on Monday September 13, @06:29PM

https://arxiv.org/abs/2108.06824 [arxiv.org]

Reply to ThisParent## (Score: 2) by mhajicek on Monday September 13, @09:27PM

It seems this is just another fudge factor.

Reply to ThisParent## (Score: 0) by Anonymous Coward on Tuesday September 14, @03:48AM (1 child)

So quantum mechanics, right? Square well potential and all that. Why can't shit tunnel out of the black hole? It's not infinite, it's finite.

Reply to This## (Score: 3, Informative) by maxwell demon on Tuesday September 14, @08:32PM

Because even in quantum field theory, information travel is limited by the speed of light (and no, quantum entanglement is not a counter example; you can't use it to transmit information faster than light).

The Tao of math: The numbers you can count are not the real numbers.

Reply to ThisParent