(November 5, 2014 at 10:20 pm)Heywood Wrote:

(November 5, 2014 at 10:12 pm)Parkers Tan Wrote: X-rays are physical evidence, aren't they?

X-rays are evidence of super heated gas. The reason it is superheated is because its believed to be circulating around a black hole. X-rays are indirect evidence.

You know, I was all set to agree with you until I realized that you shifted the goalposts from physical evidence to direct evidence.

X-ray emissions are indirect *physical* evidence, as are the gravitational effects on nearby objects and gravitational lensing on distant objects.

That indirect physical evidence tells us that there's an unseen mass. Theoretical physics tells us that mass is a black hole, to our best understanding.

(November 5, 2014 at 10:59 pm)Cthulhu Dreaming Wrote:

(November 5, 2014 at 10:20 pm)Heywood Wrote: X-rays are evidence of super heated gas. The reason it is superheated is because its believed to be circulating around a black hole. X-rays are indirect evidence.

You know, I was all set to agree with you until I realized that you shifted the goalposts from physical evidence to direct evidence.

X-ray emissions are indirect *physical* evidence, as are the gravitational effects on nearby objects and gravitational lensing on distant objects.

That indirect physical evidence tells us that there's an unseen mass. Theoretical physics tells us that mass is a black hole, to our best understanding.

Physical evidence for a dog is an observation of a dog. A coil left on your lawn is not physical evidence of a dog as that can be Minimalist's doing.

But I know what you're saying and think we are basically in agreement. Maybe I was nit picking a bit.

(November 5, 2014 at 11:04 pm)Heywood Wrote:

(November 5, 2014 at 10:59 pm)Cthulhu Dreaming Wrote: You know, I was all set to agree with you until I realized that you shifted the goalposts from physical evidence to direct evidence.

X-ray emissions are indirect *physical* evidence, as are the gravitational effects on nearby objects and gravitational lensing on distant objects.

That indirect physical evidence tells us that there's an unseen mass. Theoretical physics tells us that mass is a black hole, to our best understanding.

Physical evidence for a dog is an observation of a dog. A coil left on your lawn is not physical evidence of a dog as that can be Minimalist's doing.

Dog shit on my lawn is evidence of a dog, X-rays are direct evidence of an X-ray source.

Quote:But I know what you're saying and think we are basically in agreement. Maybe I was nit picking a bit.

You think?

Hawking radiation is on pretty firm ground, even if (gasp) black holes don't exist. Hawking was even able to cogently explain the spectrum of the radiation over time (long wavelength early on and increasingly shorter wavelength radiation as the mass of the black hole decreases).

It's just the timescale of all of this that is so daunting. In the current era of our universe, no black hole is actually getting less massive. Even a black hole totally isolated in the depths of intergalactic space and deprived of all matter to ingest will still absorb the current 2.73K degree cosmic background radiation faster than it will emit Hawking radiation, so no black holes are shrinking now, and it will be an extremely distant epoch of our universe before they can start doing so. EXTREMELY distant.

(I'm assuming 'mini primordial black holes' don't exist, if they do, a few might be emitting enough radiation now to be shrinking, but don't hold your breath on them existing)

(November 5, 2014 at 11:48 pm)vorlon13 Wrote: In the current era of our universe, no black hole is actually getting less massive. Even a black hole totally isolated in the depths of intergalactic space and deprived of all matter to ingest will still absorb the current 2.73K degree cosmic background radiation faster than it will emit Hawking radiation, so no black holes are shrinking now, and it will be an extremely distant epoch of our universe before they can start doing so. EXTREMELY distant.

I don't recall the source, and its been more than a few years since I read it, but IIRC, we're talking about timescales on the order of a hundred billion to a trillion years.

Way more than that.

Way, way, way more than that.

And to clarify, black holes will start evaporating once most/all the matter in the universe is in them and the cosmic background radiation peak decays below the emission peak of the black holes. This is in an extremely distant era.

And once the evaporation starts, it is an exceedingly slow process. Taking your car apart, 1 atom per year will be quick by comparison.

These timescales are only inconvenient to us btw, the universe has eternity to look forward to.

(November 5, 2014 at 10:20 pm)Heywood Wrote:

(November 5, 2014 at 10:12 pm)Parkers Tan Wrote: X-rays are physical evidence, aren't they?

X-rays are evidence of super heated gas. The reason it is superheated is because its believed to be circulating around a black hole. X-rays are indirect evidence.

Indeed. Indirect, physical, evidence.

(November 5, 2014 at 11:48 pm)vorlon13 Wrote: Hawking radiation is on pretty firm ground, even if (gasp) black holes don't exist. Hawking was even able to cogently explain the spectrum of the radiation over time (long wavelength early on and increasingly shorter wavelength radiation as the mass of the black hole decreases).

It's just the timescale of all of this that is so daunting. In the current era of our universe, no black hole is actually getting less massive. Even a black hole totally isolated in the depths of intergalactic space and deprived of all matter to ingest will still absorb the current 2.73K degree cosmic background radiation faster than it will emit Hawking radiation, so no black holes are shrinking now, and it will be an extremely distant epoch of our universe before they can start doing so. EXTREMELY distant.

(I'm assuming 'mini primordial black holes' don't exist, if they do, a few might be emitting enough radiation now to be shrinking, but don't hold your breath on them existing)

No need to assume primordial black hole. It would not be too distant in the future before subatomic black holes can be made in particle accelerators. That will get you some hot instantaneously evaporating black holes.

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At one time, quasars are theorized to be the other ends of wormholes that are connected to black holes. Ie material and radiation sucked in by black holes traverse wormholes to emerge as radiation from quasars.

Since then it has been found the quasars can be more economically and satisfactorily explained as a being the radiation powered by gravitational potential energy of Infalling material around black holes, rather than the actual Infalling matter themselves totally converted to radiation after traversing a wormhole.

(November 5, 2014 at 9:24 pm)vorlon13 Wrote: Hawking radiation is what (eventually) disperses black holes so we don't need white holes.

BTW, when I typed eventually, I really meant it. the process takes a VERY long time. But everything in a black hole someday dribbles out.

Do you mind explaining Hawking radiation a bit further? I'm a high school student, and I'm independently studying physics, so I'm really interested; I'm especially interested in the cosmos.

(November 6, 2014 at 2:15 am)JaceDeanLove Wrote:

(November 5, 2014 at 9:24 pm)vorlon13 Wrote: Hawking radiation is what (eventually) disperses black holes so we don't need white holes.

BTW, when I typed eventually, I really meant it. the process takes a VERY long time. But everything in a black hole someday dribbles out.

Do you mind explaining Hawking radiation a bit further? I'm a high school student, and I'm independently studying physics, so I'm really interested; I'm especially interested in the cosmos.

Well... There are several ways one can approach this. The usual picture is as follows: the event horizon of a black hole, which is the sphere around it within which gravity becomes so strong that light cannot escape any more, has some peculiar properties. For example, pairs of virtual particles pop out of the vacuum all the time. Under normal circumstances, one only notices their effect when other particles are there which interact with them, i.e. in the lamb shift in atoms. If there is an event horizon, and thw virtual pair is created near it, it can happen that one of the two escapes, while the other gets trapped in the black hole. For somewhat complicated reasons, it can carry negative energy into the black hole, this decreasing its mass. The guy who escapes carries this energy away. These particles are called hawking radiation. A related effect, the Unruh radiation, is theoretically seen by accelerated observers. In this case, there is a kind of fake event horizon seen by the accelerated observer without there being a black hole.