Physicists observationally confirm Hawking’s black hole theorem for first time

[eximius]

Alright, I'm confused. How does this square with Hawking radiation? How can a black hole shrink without shrinking?

The article mentions both in the context that they are reconciled but not how they are reconciled.

[jleahy]

They're not reconciled, it's just garbage reporting.

The 'area theorem' they are referring to was by Bekenstein and others, not Hawking. It's basically the equivalent of the second law of thermodynamics for black holes (dA/dt>=0 instead of dS/dt>=0). Hawking's insight was that this formula was wrong and the area could decrease due to radiation.

[morebortplates]

Yes, black holes shrink because of Hawking radiation, but in reality this doesn't really happen because black holes are much colder than their surrounding space. Actually they are the coldest objects in nature. Stellar black holes have a temperature of a few Nanokelvins and the average temperature of space is 2.7 K so there's a net gain of energy/mass from absorbed photons from CMB radiation vs emitted photons via Hawking radiation. In order to have a higher temperature than the CMB a black hole would have to be really small with a mass about half of that of the moon.

[rakkhi]

Exactly what I came here to ask. Is Hawking's theory that the area never decreases or that it does not decrease in a black hole merger as was tested here. "central law for black holes predicts that the area of their event horizons — the boundary beyond which nothing can ever escape — should never shrink" this seems to imply the former to me.

Does that mean with Hawking radiation the black hole effectively evaporates by loosing mass (?) from the inside without the boundary area never shrinking?

[streamofdigits]

This might help https://physics.stackexchange.com/questions/169886/black-hol...

A black hole merger of this size is unlikely to have any significant quantum aspect

[edem]

If you drain your bathwater while also running the bath you can have a bathtub that's slowly filling up.

[edem]

Note that by the time black hole evaporation would be significant the CMB will be long gone because of dark energy (universe expanding). All this means that evaporation is delayed till there is nothing else left apart from black holes (because of the faster than light recession of space itself).

[Ankaios]

Here's the paper:

https://journals.aps.org/prl/accepted/36074Y8aM291c462a4e264...

https://arxiv.org/abs/2012.04486

[louloulou]

Thank you! It drives me crazy that news articles about a paper never link to the actual damn paper.

[lennoff]

So black holes can't evaporate? How does Hawking radiation works if the back hole are has to stay the same?

[jfengel]

Black holes can't evaporate now because the cosmic background radiation is too hot. The black holes are colder the CMBR, so they absorb heat and grow (albeit very, very slightly).

Eventually the CMBR will cool down and the holes will be able to evaporate, but not for an insanely long time.

[SiempreViernes]

I think it's more a case of the press release people wanting to call it a unqualified "law", as far as we know black holes do evaporate slowly.

But there remains is a statement about how the final area relates to the area of the two merging black holes.

[edem]

They _do_ evaporate, but they also absorb CMB, and right now CMB > evaporation. Later, when CMB fully dissipated they can evaporate in practice.

[ordu]

> There are certain rules that even the most extreme objects in the universe must obey.

A strange way to put it. The more object is extreme the harder it would be for it to disobey laws. If we try to imagine what forces are involved, all we'll find is that our imagination has it's limits. I'd be less surprised if some quark disobeyed laws, because it small, forces are minuscule and... who is to notice? Maybe they disobey laws all the time, just scientists fail to catch them red handed.

[justinboogaard]

I don’t think the quote is saying objects have to obey laws because they are extreme (and therefore easy to notice) I think it’s saying all objects have to follow the established rules of physics, regardless of how unusual they are. It’s an interesting idea though! Known, “extreme” objects may be less fruitful places to study unknown forces because they have qualities that overwhelming drown out smaller less known forces.

[notorandit]

If you have BH evaporation you cannot keep the horizon surface constant.

[867-5309]

so they're 95% sure.. how do they even come up with a figure like that? they didn't bother saying. might be equivalent to 'give or take a few trillion tonnes'

[Cthulhu_]

https://www.zmescience.com/science/what-5-sigma-means-042342... 95% means 2-sigma, when it comes things like the Higgs boson, they announced the results with 5-sigma certainty, which is a very good indication of statistical significance and confidence.

[mhh__]

It will say in the paper how they went about the error analysis.

These estimates are however, subjective. There is a good paper on this called "Bayesian methods in particle physics" (something like that).

[realYitzi]

Anyone can think of any practical effect this might have or is this something that at the moment seems to have only scientific relevance.

[eru]

Well, if the result had turned out the other way, we might have seen some practical effects, because it would overturn some well-established theories that we also use for predicting more practical things.