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

news.mit.edu

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

#51

Post by __MatrixMan__ »

jfengel wrote: post #42
lennoff wrote: post #2

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

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.

I imagine this holds only for black holes that are massive enough to be stable?

All those itsy bitsy ones created by the LHC, they've evaporated, yes?

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

#52

Post by kstrauser »

edem wrote: post #33
lennoff wrote: post #2

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

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

> Later, when CMB fully dissipated

That's one of the most understated uses of "later" I've heard.

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

#53

Post by wruza »

__MatrixMan__ wrote: post #51
jfengel wrote: post #42

Earlier quoted context omitted.

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.

I imagine this holds only for black holes that are massive enough to be stable? All those itsy bitsy ones created by the LHC, they've evaporated, yes?

I believe that LHC has no chance ever to harvest enough energy to create a sensible-sized black hole. It’s still mc-squared (give or take an order of magnitude and my layman mistakes), so 1g BH takes about 1e14 joules or 5 minutes of average EU electricity output. Also, there is no sea nearby to cool it off afterwards. Also, a planck-sized BH weighs 1e-5 g.

A mass similar to Mount Everest[13][note 1] has a Schwarzschild radius much smaller than a nanometre.[note 2] Its average density at that size would be so high that no known mechanism could form such extremely compact objects

It seems that at energies available to us they are basically either virtual or non-existent. This contradicts the common notion that cosmic rays create microbhs occasionally, but I guess we have to wait for a physicist to clarify this.

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

#54

Post by jfengel »

__MatrixMan__ wrote: post #51
jfengel wrote: post #42

Earlier quoted context omitted.

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.

I imagine this holds only for black holes that are massive enough to be stable? All those itsy bitsy ones created by the LHC, they've evaporated, yes?

Correct. It's not so much that the small ones are unstable, but just that there's a continuous curve of lifetimes that's a function of mass.

For the LHC, the lifetime of a black hole it could conceivably create would be 10^-86 seconds. It didn't even do that, but if it had, it would have evaporated before it moved the diameter of an electron. There's no functional difference between that black hole and a vastly bigger one besides the mass... but it's a difference of many, many, many orders of magnitude.

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

#55

Post by jfengel »

wruza wrote: post #53
__MatrixMan__ wrote: post #51

Earlier quoted context omitted.

I imagine this holds only for black holes that are massive enough to be stable? All those itsy bitsy ones created by the LHC, they've evaporated, yes?

I believe that LHC has no chance ever to harvest enough energy to create a sensible-sized black hole. It’s still mc-squared (give or take an order of magnitude and my layman mistakes), so 1g BH takes about 1e14 joules or 5 minutes of average EU electricity output. Also, there is no sea nearby to cool it off afterwards. Also, a planck-sized BH weighs 1e-5 g. A mass similar to Mount Everest[13][note 1] has a Schwarzsch…

In theory, it might have made a black hole. It would have lasted a ridiculously small period of time, but be quite recognizable by the energy it gave off. Instead of the usual decay patterns, it would give off a spray just of photons, like a black body at a recognizable (and very high) temperature.

We didn't see that, and in fact theory predicted that it was insanely unlikely that we would. But there's nothing wrong with the possibility of a black hole much, much, much smaller than a gram, with a radius smaller than the Planck length.

If we had seen it, it would have been insanely informative. But it wasn't ever gonna happen.

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

#56

Post by Florin_Andrei »

jleahy wrote: post #4
eximius wrote: post #3

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.

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.

I think what they really meant in the article is that it can never decrease through processes other than the radiation. E.g., BH mergers and so on, the area always increases.

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

#57

Post by nine_k »

lanerobertlane wrote: post #41
Cthulhu_ wrote: post #11

Earlier quoted context omitted.

I'm amazed - to the point of skepticism - that with such minute forces they can extrapolate so much information and prove theories. I mean I'm no astrophysicist, I like the "pop sci" bits, but when I look closer I'm seeing a lot of small numbers and statistics that imply something - e.g. exoplanets based on minute wobbles and brightness variations, water on said exoplanets based on spectrography. It's theories based…

The problem is the 'pop sci' reporting. "Earth-like" or "second earth" could easily be swapped for "Venus-like" or "second venus" in 99% of cases where pop-sci uses "Earth like" and still be factually correct. However, Wobbles and Transit photometry are done over time and plot trends which definitively show that something with a certain mass is orbiting with a certain period around the star. There isn't really anythi…

I suppose Venus has a different enough thermal spectrum due to surface temperatures being 3x Earth's, roughly 900K vs 300K.

Also, Venus must have a big enough sulfur line in the atmosphere, which is absent in Earth atmosphere.

Probably Mars and Earth could be considered close, save for the oxygen line, but not Venus and Earth,

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

#58

Post by nine_k »

DSingularity wrote: post #39
eru wrote: post #13

Earlier quoted context omitted.

It's fascinating what's possible. For example, we know more about the chemical composition of other galaxies than we know about the centre of the earth. Just because we can infer so much from their light spectrum. (For empirical information about the centre of the earth, we are basically limited to seismic data and perhaps the magnetic field and bumps in gravity?)

Why not launch a probe and point its sensors at earth?

We hardly resolve any individual stars in other galaxies (maybe some giant stars inside Andromeda?), so our idea of chemical composition of other galaxies is very... averaged.

We barely can resolve largest and closest exoplanets into a few pixels.

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

#59

Post by 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.

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

#60

Post by louloulou »

Ankaios wrote: post #35

Here's the paper: https://journals.aps.org/prl/accepted/36074Y8aM291c462a4e264... https://arxiv.org/abs/2012.04486

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