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.
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 on tiny but statistically significant data.
The pop sci then comes in and makes statements like "second Earth found!11", which is like, whoa hold on, when you look closer all they found is a wobble or dimness variation that kind of implies there might be a planet at a certain distance from its host star.
Anyway I don't dispute the findings or that there are exoplanets or whatever, I'm just impressed that they are able to make confident claims on what little information we can receive from here.
> e.g. exoplanets based on minute wobbles and brightness variations, water on said exoplanets based on spectrography.
The minute wobbles may be tiny, but they can plot a curve of those wobbles and see very clearly that it changes in a certain way that can only be caused by a planet (or something spherical and with a certain mass). If there was a competing theory of how you can get this exact curve in some other way, I am sure we would consider them as alternative possibilities and not be able to tell them apart, but as far as I know, there isn't any competing theories at all... so we can have very high confidence there's a planet there.
Regarding water detection: yeah, spectrography is just mind blowing, but again, given what we know, there's just nothing that could justify believing that when you detect radiation that fit exactly what you would expect from water molecules, that it could be something else instead... unless you come up with a convincing "something else", your only option is to conclude that the detection is accurate, otherwise you would need to stay open to the possibility of absolutely everything possibly having alternative explanations we haven't thought of yet (though every now and then, that indeed can happen and we need to adjust all our theories that are based on the changed body of knowledge), and progress would not be possible in any area (you need to accept something before you can build on top of it).
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.
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?)
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.
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.)
It is not just gravitational waves, they look at light, with telescopes (visible, infra and ultra), spectrographs, interferometers, radio signals, gamma rays...
Then they combine all that info to come up with cohesive theories. LIGO just by itself would be almost useless.
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.
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.
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.
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)?
"Temperature" in this case refers to the amount of energy they emit due to hawking radiation.
By comparing to a black-body curve, you can define a temperature for the hole. Obviously it's not a real object with a real temperature -- if it were, I believe the temperature might be infinite -- but this still works for the purposes of deciding whether it'll grow or shrink.
Temperature has several definitions that produce the same number under normal circumstances but may or may not be applicable in extreme circumstances. In this case, I imagine they could be using the thermodynamic definition (dE/dS, the marginal change in energy per marginal change in entropy - I’m not sure if a BH has well-defined entropy) or something to do with the emission curve of space around the black hole. I vaguely recall something about empty space behaving like a blackbody under a gravitational gradient, so maybe they can use that. You could also use amount of Hawking radiation per surface area. It’s possible that some of those produce the same number.
My understanding is it's the temperature of the event horizon: because it doesn't emit any blackbody radiation, other than the tiny amount from Hawking radiation, any heat measurement from it would be approximately 0k.
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
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.
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.
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.
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.
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?
The article mentions both in the context that they are reconciled but not how they are reconciled.