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

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

#41

Post by lanerobertlane »

Cthulhu_ wrote: post #11
aliasEli wrote: post #9

Earlier quoted context omitted.

It is a pity about the reporting. But it is a fascinating area of research. I never expected that we could measure gravitational waves in our life time.

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 anything else it could be except an exoplanet, unless our understanding of how physics works was way off, which we know it isn't.

as for Spectrography brabel sums it up in their comment very well.

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

#42

Post by jfengel »

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.

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

#43

Post by jfengel »

morebortplates wrote: post #23
phkahler wrote: post #18

Earlier quoted context omitted.

From the outside they must look cold since they can't radiate heat any more than light. That doesnt imply anything about the inside.

What's "inside" of a black hole, meaning behind the event horizon is forever causally cut off from our universe. The Hawking radiation comes from the space around the event horizon. In theory black holes can become very hot if their mass is small. This happens at the end of their life which is in the order of 10^80 years for stellar black holes. Here is a calculator to play with some values. https://www.vttoth.com/CM…

Note that this evaporation time assumes a universe at absolute zero. That 10^80 years can't even begin until the CMBR cools enough, perhaps 10^40 years.

Admittedly that's an eyeblink compared to the evaporation time scale, but it does mean that we won't observe any evaporation until many orders of magnitude longer than the universe has existed.

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

#44

Post by db48x »

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?

The Earth is opaque. I don’t have a source to cite for this, but I think you can check it easily enough.

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

#45

Post by db48x »

jfengel wrote: post #43
morebortplates wrote: post #23

Earlier quoted context omitted.

What's "inside" of a black hole, meaning behind the event horizon is forever causally cut off from our universe. The Hawking radiation comes from the space around the event horizon. In theory black holes can become very hot if their mass is small. This happens at the end of their life which is in the order of 10^80 years for stellar black holes. Here is a calculator to play with some values. https://www.vttoth.com/CM…

Note that this evaporation time assumes a universe at absolute zero. That 10^80 years can't even begin until the CMBR cools enough, perhaps 10^40 years. Admittedly that's an eyeblink compared to the evaporation time scale, but it does mean that we won't observe any evaporation until many orders of magnitude longer than the universe has existed.

Or unless you manufacture or discover a low–mass black hole

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

#47

Post by meowface »

Cthulhu_ wrote: post #11
aliasEli wrote: post #9

Earlier quoted context omitted.

It is a pity about the reporting. But it is a fascinating area of research. I never expected that we could measure gravitational waves in our life time.

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…

>water on said exoplanets based on spectrography

Even though from a theoretical perspective it should be way easier and more reasonable to detect particular molecules on distant planets via spectroscopy compared than to detect things on the mind-blowingly minuscule scale of gravitational waves, I think distant spectroscopy might actually be more prone to error, or at least more prone to false positives.

Just speculating since I have zero expertise in this area, but part of it may be because light from all sorts of sources is reaching us all the time, while gravitational waves significant enough to be feasibly detected pretty much only come from the top percentile of the most energetic events in the universe.

I think if you can discern a gravitational wave-induced spacetime wobble at least once and infer the motion that could've caused it (e.g. black holes/neutron stars merging) and see it matches theoretical expectations, you may continue to have a lot of false negatives, but you probably aren't at high risk of future false positives.

Whereas with spectroscopy, there seem to be a lot of things that can cause both false positives and false negatives even if you do have many prior detections that you believe are accurate. For spectroscopy, both error rates should go down over time as technology and techniques improve, but it seems like it may potentially be an inherently more "murky" observation technique, even if it's far simpler and far less expensive than gravitational wave detection.

(Someone please correct me if I'm wrong about any of this, because there's a pretty good chance I am.)

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

#48

Post by mhh__ »

867-5309 wrote: post #8

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'

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).

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

#49

Post by jfengel »

db48x wrote: post #45
jfengel wrote: post #43

Earlier quoted context omitted.

Note that this evaporation time assumes a universe at absolute zero. That 10^80 years can't even begin until the CMBR cools enough, perhaps 10^40 years. Admittedly that's an eyeblink compared to the evaporation time scale, but it does mean that we won't observe any evaporation until many orders of magnitude longer than the universe has existed.

Or unless you manufacture or discover a low–mass black hole

That's right. If we could create one in a supercollider, it would would be so small that it would be hot enough to evaporate instantly.

There might also be a range of primordial black holes formed directly out of pre-CMBR energy. They'd have to be small enough to be hotter than the CMBR, but not so hot that they'd already have evaporated in the last 14 billion years. That's a relatively narrow range, all things considered, but if primordial black holes exist at all then they could exist at any range.

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

#50

Post by untoxicness »

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.

While I agree that the article should have mentioned black hole evaporation, I would like to point out that "dA/dt > 0" is commonly referred to as "Hawking's area theorem" as a quick online search can verify and Stephen Hawking certainly did publish on this topic.
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