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View Full Version : How is entropy linked with blackholes?



WaxRubiks
2018-Jul-27, 06:58 PM
I guess for a naked singularity the entropy would be zero...?

So I wondered if someone had worked out an equivalent to the Schwarzchild radius based upon entropy...?

grant hutchison
2018-Jul-27, 07:38 PM
Use your favorite search engine on "black hole thermodynamics", the "Bekenstein Bound" and "Bekenstein-Hawking entropy".

Grant Hutchison

Ken G
2018-Jul-28, 07:57 AM
Yes, the idea is, if information falls across an event horizon, it exits from our universe. So that would mean entropy drop in our universe, if information leaves it (imagine the extreme case where everything falls into the black hole so our remaining universe contains nothing and no entropy). To allow entropy to always increase, we need to have the area of the event horizon count as a form of entropy, so information falling into the black hole increases the size of the event horizon.

Cougar
2018-Jul-28, 05:58 PM
....To allow entropy to always increase, we need to have the area of the event horizon count as a form of entropy, so information falling into the black hole increases the size of the event horizon.

Oh. I wondered why they assigned entropy to the black hole surface area. Problem is, if and when a black hole evaporates, the Hawking radiation emission is thermal, and the quantum state of the item falling in is apparently lost.

Ken G
2018-Jul-29, 02:19 PM
Oh. I wondered why they assigned entropy to the black hole surface area. Problem is, if and when a black hole evaporates, the Hawking radiation emission is thermal, and the quantum state of the item falling in is apparently lost.Ergo the famous bet, which still inspires controversy. (Hawking decided that true event horizons don't form because the environment is too chaotic, and Preskill believes that quantum mechanics trumps the whole idea of an event horizon, so both agree that information can leak back and forth, but Thorne believes that information is simply lost and the second law of thermodynamics does not survive GR nor does quantum mechanics trump GR.) Sadly, the current state of affairs on this topic is highly unscientific, because it comes down to "who do think has the better argument," and that's never what science looks like.