Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

news.mit.edu

Post reply on HN
Print view View original

31–40 of 73 posts

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

#31

Post by wyager »

Cthulhu_ wrote: post #12
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'

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.

It’s more that p-value is a bad indication of anything (since it’s vulnerable to p-hacking and all kinds of other issues), so physics just picks a really extreme publication threshold to avoid getting inundated with spurious developments.

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

#32

Post by wyager »

tibbetts wrote: post #24
eru wrote: post #16

Earlier quoted context omitted.

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.

I’m waiting for a Greg Egan short story to explain this better.

Looks like he already has one on BH boundaries: https://www.gregegan.net/PLANCK/Planck.html

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

#33

Post by edem »

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.

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

#34

Post by edem »

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.

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

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

#36

Post by colechristensen »

Yajirobe wrote: post #25
morebortplates wrote: post #10

Earlier quoted context omitted.

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 Ha…

how can the temperature of a black hole make sense? Is it the temperature of the singularity point? Is it the temperature of the space inside the event horizon (but it can't be, as that space is empty)?

it is a phenomenon at the event horizon at with radiation is emitted in a way comparable to the radiation produced by every object according to temperature

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

#37

Post by zaarn »

ttul wrote: post #21
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.

The inside is empty space.

The inside is empty time, space waved you a goodbye at the event horizon.

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

#38

Post by sandworm101 »

eru wrote: post #14
morebortplates wrote: post #10

Earlier quoted context omitted.

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 Ha…

> 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. Either that, or you just wait a couple eternities for the CMB to cool down enough.

Or you make a smaller one and watch it shrink. It is theoretically possible to construct a smaller black hole by cramming the necessary mass/energy into a small enough space. (Plug a death star into the LHC's big brother.) Such a hole would be very hot and short-lived.

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

#39

Post by DSingularity »

eru wrote: post #13
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…

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?

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

#40

Post by morebortplates »

edem wrote: post #29
morebortplates wrote: post #10

Earlier quoted context omitted.

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 Ha…

It _will_ happen, but first dark energy needs to be strong enough to expand the universe fast enough (faster than light) so that CMB wouldn't be able to reach anything.

Well there are already portions of space that are expanding faster than the speed of light relative to our position. (see cosmic horizon). The CMB is not just a glowing heat somewhere far away, it's everywhere in the universe in every volume of space. The moment when every point in space (on a Planck-lenght-scale i guess) will be expanding faster than the speed of light relative to one another, than space-time itself will rip apart and that's the end of our universe - at least that is what the Big-Rip theory proposes.
Post reply on HN