Hawking radiation

[Fubaruk]

So from what I've been told Hawking Radiation is when a partical and it's antipartical emerge from the quantum foam just at the event horizon of a black hole, normally when this happens elswhere they destroy each other and that's it, but at the event horizon there's a chance that 1 partical is absorbed and the other does not, making it look as though the black hole is radiating the partical.

I have heard this described as though the black hole is evaporating, but surely no matter or energy is actually leaving the singularity at all in fact more energy/matter is entering it.

Is this the case or have I either misunderstood or have been told incorrectly?

[DrWho]

I have heard this described as though the black hole is evaporating, but surely no matter or energy is actually leaving the singularity at all in fact more energy/matter is entering it.

Not exactly. The BH loses mass by contributing gravitational energy to the two virtual particles which form outside the event horizon, but only one of the two makes into the BH.

[Fubaruk]

Not exactly. The BH loses mass by contributing gravitational energy to the two virtual particles which form outside the event horizon, but only one of the two makes into the BH.

Sorry can you clarify, does this presume the existance of the graviton or are you saying that due to the effect of gravity has on the partical which I can pesume would be to speed up the partical thus increasing its mass and through e=mc^2 and the conservation of energy, energy increases which come from the singularity. Or something like that.

[JohnD]

Does Hawking's own explanation, from his "Brief History" help?

"A real particle [as opposed to it's twin antiparticle] close to a massive body has less energy than if it were far away, because it would take energy to lift it far away against the gravitational attaction of the body"
He then gets a bit obscure, but I think means that this process can cause an antiparticle to appear a positive one! Because he then says,
"The smaller the black hole, the shorter the distance the particle with negative energy will have to go before it becomes a real particle."
"To an observer at a distance, it will appear to have been emitted by the black hole,"
"The positive energy of the outgoing radition would be balanced by the flow of negative energy particles into the black hole"

John

[ShinAce]

Positive and negative energy is just a way to visualize who loses and who gains mass.

Another way to think of it is the following:
1-Without the black hole, no real particles would emerge from the quantum foam
2-The energy needed to 'create' the particle pair comes from the black hole's gravitational energy. The BH has therefore lost the mass of both particles
3-Both particles can't escape into the universe. One must fall in, giving back the energy used to create it. The other particle escapes, carrying away its energy from the black hole

So, you can either say that both particles have positive energy and the black hole gets reimbursed for 50% of the loan. Or, you can say that one particle has positive energy, balanced by the negative energy that falls into the black hole. No loan to cover the cost of two particles, just a straight withdrawal of one particle.

You pick. The end result is that the black hole loses 'mass' equivalent to the particle that escapes. How it actually happens does not matter(pun intended).

[Weakly Interacting MP]

Actually, Hawking proposes that the radiation we would see from a non-accreting black hole would be the evaporation of the black hole. Hawking Radiation is the creation of particle-antiparticle pairs near the Schwarchild radius which may result in one of the pairing falling into the black hole istead of almost instantly annihilating its partner. The infalling particle would then annihilate a particle within the black hole, resulting in a loss of mass. The particle which escapes is the radiation that we would see emanating from the black hole.

So yes, in essence, the black hole evaporates.

[DrWho]

The infalling particle would then annihilate a particle within the black hole, resulting in a loss of mass.

This is not reason for the loss of mass. Any energy produced through annihilation inside the EH stays inside. The BH mass loss is down to the escape of the partner particle.

[Weakly Interacting MP]

You know, even as I wrote that, I new it was mostly wrong, but I didn't want to go into a long explanation of Hawking Radiation wrt quantum fluctuations, energy/mass equalities, thermal radiative effects, etc etc.

So, yes I understand your correction, however for the purpose of the op, I don't think it changes my basic premise that, yes it appears that non-accreting black holes may evaporate.

[DrWho]

You know, even as I wrote that, I new it was mostly wrong, but I didn't want to go into a long explanation of Hawking Radiation wrt quantum fluctuations, energy/mass equalities, thermal radiative effects, etc etc.

So, yes I understand your correction, however for the purpose of the op, I don't think it changes my basic premise that, yes it appears that non-accreting black holes may evaporate.

Thing is, the OP didn't bring up accretion but did talk about quantum foam and virtual particles, so the discussion of virtual particles and mass/energy loss if quite pertinent.

[mugaliens]

To add, a solar mass BH would take about 10⁹⁹ to evaporate by Hawking radiation.

However, that's assuming no infalling matter/energy. As it is, the CMBR overpowers Hawking radiation for BH with a mass greater than our Moon! Thus, until the CMBR subsides, we're not going to see any BH's of any significant size evaporating out of existence anytime soon.

[Fubaruk]

Positive and negative energy is just a way to visualize who loses and who gains mass.

Another way to think of it is the following:
1-Without the black hole, no real particles would emerge from the quantum foam
2-The energy needed to 'create' the particle pair comes from the black hole's gravitational energy. The BH has therefore lost the mass of both particles
3-Both particles can't escape into the universe. One must fall in, giving back the energy used to create it. The other particle escapes, carrying away its energy from the black hole

So, you can either say that both particles have positive energy and the black hole gets reimbursed for 50% of the loan. Or, you can say that one particle has positive energy, balanced by the negative energy that falls into the black hole. No loan to cover the cost of two particles, just a straight withdrawal of one particle.

You pick. The end result is that the black hole loses 'mass' equivalent to the particle that escapes. How it actually happens does not matter(pun intended).

So you saying that virtual particals require/use gravitational energy to be created? I thought virtual particals could be created anywhere.

[ShinAce]

The energy used to split the particles, or prevent annihilation, makes the particles real instead of virtual.

You can also say the particle pair is created just inside the horizon, and then that energy makes the EH shrink by a tiny tiny amount, therefore allowing one particle to tunnel out(positive bookkeeping).

Or you can say they are created just outside the horizon, and one particle tunnels into the black hole. This particle falling in has negative energy and experiences time backwards(negative bookkeeping).

However you look at it, just make sure the particle that escapes is the amount of mass-energy lost by the BH.

[Cougar]

2-The energy needed to 'create' the particle pair comes from the black hole's gravitational energy. The BH has therefore lost the mass of both particles
3-Both particles can't escape into the universe. One must fall in, giving back the energy used to create it. The other particle escapes, carrying away its energy from the black hole

This is pretty much the way Kip Thorne explains it. (Also remember, Fubaruk, Hawking radiation is theoretical - never been observed - though it gets talked about a lot.)

To clarify a little, as the theory goes, the virtual particles appear, as they always do in the vacuum, but find themselves in this massively strong gravitational field of the black hole (but still outside it), which pulls the two virtual particles far apart, just like if you were to fall close to a black hole, your feet and head would be pulled apart due to the difference in gravity between them ("spaghettified"). I'm not quite sure if the virtual particles are considered real at this point or after one falls in and the other escapes, but in any case, the conversion from virtual to real is accomplished by this draw of energy from the hole's gravitational field. A bit less energy means a tiny bit less mass. And I mean tiny. As Mugs pointed out, the theory predicts that it takes a ridiculously long time for a hole to evaporate from this hypothesized mechanism.

I know Hawking is a genius and all, but........ how remote can you get?

[Coldcreation]

”I’m not a genius like Einstein was.”
(S. Hawking, EuroNews, April 16, 2005)



CC

[Hernalt]

Hawking Radiation is the creation of particle-antiparticle pairs near the Schwarchild radius which may result in one of the pairing falling into the black hole instead of almost instantly annihilating its partner. The infalling particle would then annihilate a particle within the black hole, resulting in a loss of mass. The particle which escapes is the radiation that we would see emanating from the black hole.

I naively expect that the gravitational energy consumed in the formation of particle-antiparticle pair will not in and of itself have some specific bias that will CAUSE the antiparticle to form _nearest_ the BH so as to be gravitationally drawn into the BH _rather than_ the (positive) particle. I naively expect that the axis of formation of particle-antiparticle pairs will be non-oriented with the same distribution as the spin orientations of all galaxies (no net orientation).

If it could be explained how the gravitational energy biases the particle-antiparticle pair so as to make the negative one conveniently form within gravity's quicker grasp, that would make Hawking Radiation (TM) a little more apprehensible for me.

OOOORRRR. Is it utterly irrelevant which particle, the negative or the positive, falls into the EH? If an antiparticle falls in and annihilates with a particle, then is the annihilation energy utterly contained still within the EH? And does that annihilation energy retain the absolutely identical mass to the sum of the previous constituents, no matter their baryon charge?

Thank you. I know nothing - please correct, inform, or insult entertainingly.

[Cougar]

Hey, Hernalt, welcome to the board.

I naively expect that the gravitational energy consumed in the formation of particle-antiparticle pair will not in and of itself have some specific bias that will CAUSE the antiparticle to form _nearest_ the BH so as to be gravitationally drawn into the BH _rather than_ the (positive) particle.

Not so naive. Your expectation is correct.

OOOORRRR. Is it utterly irrelevant which particle, the negative or the positive, falls into the EH?

Correct.

If an antiparticle falls in and annihilates with a particle, then is the annihilation energy utterly contained still within the EH?

Yep. The point is, one or the other particle escapes with half the (originally gravitational) energy that went into making the virtual pair real.

Thank you. I know nothing - please correct, inform, or insult entertainingly.

LOL! Sorry, no clever insults at the moment.

[zerocold]

I understand the virtual particle-antiparticle is some sort of explanation for the potential energy of the force fields (electrostatic-gravity), but how the particle escapes from the black hole?, ok one of them is absorbed, but why not both?

Or one of these virtual particles is acting over the black hole and the other is acting on the mass or object affected by the gravity field?

[Cougar]

I understand the virtual particle-antiparticle is some sort of explanation for the potential energy of the force fields...

Well, virtual particles are said to occur out of the vacuum everywhere (for very brief periods), not just in high gravity fields.

...but how the particle escapes from the black hole?

You mean from near the black hole. I don't know. I guess it popped into existence with a very large momentum.

ok one of them is absorbed, but why not both?

I imagine both are frequently absorbed, but that's a guess.

[Arnold Layne]

To add, a solar mass BH would take about 10⁹⁹ to evaporate by Hawking radiation.

However, that's assuming no infalling matter/energy. As it is, the CMBR overpowers Hawking radiation for BH with a mass greater than our Moon! Thus, until the CMBR subsides, we're not going to see any BH's of any significant size evaporating out of existence anytime soon.

Not that it makes such a huge difference, but would that be 10⁹⁹ seconds, years, or something else?

[01101001]

”I’m not a genius like Einstein was.”
(S. Hawking, EuroNews, April 16, 2005)

Part of his genius is that sort of self-effacement.

[BigDon]

LOL! Sorry, no clever insults at the moment.

Oh! Oh! Oh! Me! Me! Me!

*Ahem*

Is that your nose or did your pants fall down?


Thank you.


Welcome aboard Hernalt!

[Coldcreation]

Part of his genius is that sort of self-effacement.

I would have agreed had I found other examples of self-effacement.

The usual portrait Hawking paints of himself actually resembles Einstein, Newton, and Galileo (or even God). In fact, by acknowledging them as his masters he seems to imagine himself as their equal, but he has only one idea to his name (Hawking radiation) and he knows how to sell it. After all, theory is theory, and the market is the market.

His style seems to besiege a natural strain of ludicrous drollness. “If a two-dimensional creature ate something it could not digest completely, it would have to bring up the remains the same way it swallowed them, because if there were a passage right through its body, it would divide the creature into two separate halves…” Sounds like Tate Modern to be honest. Or try this one: “I had no desire to share the fate of Galileo, with whom I feel a strong sense of identity, partly because of the coincidence of having been born exactly 300 years after his death!” He knows a thing or two about clowning around cleverly. That is where his genius resides.

(See Hawking, S.W. 1988, A Brief History of Time, From the Big Bang to Black Holes, 177 - 182)



CC

[peter eldergill]

Welcome back, Coldcreation. It's been awhile since you've posted!

Pete

[Coldcreation]

Welcome back, Coldcreation. It's been awhile since you've posted!

Pete

Thank you Pete. It's good to be back. Hope all is well.

...(Hawking radiation) and he knows how to sell it. After all, theory is theory, and the market is the market.

...He knows a thing or two about clowning around cleverly. That is where his genius resides.

Hawking needed to spiritualize cosmology (to expand his market). It was both a personal and political response. He worked through a conflict that was his own, but also that of our civilization, its calamity and catastrophes, with the help of a little divine finger pointing. He is one of the only new-visionaries to have been illuminated by radiating particles from within, the temperatures of which are inversely proportional to the mass of the hole known quasi-pictorially as the Hawking effect or Hawking radiation, introduced ad hoc into black hole physics to avoid violating the second law of thermodynamics. Hawking radiation is a vestige from the Christ-antichrist asymmetry.

I don't believe Hawking radiation truly exists in the natural world.



CC


The views expressed in the contents above are personal and do not necessarily reflect the views of other BAUT users.

[DrWho]

I don't believe Hawking radiation truly exists in the natural world.

Why do you not believe it?

[Hornblower]

I don't believe Hawking radiation truly exists in the natural world.



CC


The views expressed in the contents above are personal and do not necessarily reflect the views of other BAUT users.

Absence of observable evidence is not necessarily evidence of absence.

[Coldcreation]

Why do you not believe it?

Good question.

Stephen Hawking himself begins to answer that question.

To quote, again, from A Brief History of Time:

This was a form of insurance policy for me. I have done a lot of work on black holes, and it would all be wasted if it turned out that black holes do not exist. But in that case, I would have the consolation of winning my bet, which would win me four years of the magazine Private Eye. If black holes do exist, Kip will get one year of Penthouse. When we made the bet in 1975, we were 80% certain that Cygnus was a black hole. By now, I would say that we are about 95% certain, but the bet has yet to be settled.

Source

Indeed, if BH's do not exist, then neither does Hawking radiation.


CC

[DrWho]

Stephen Hawking himself begins to answer that question.
...
Indeed, if BH's do not exist, then neither does Hawking radiation.

Even in '75 it was 80% certain that black holes existed and by now it would be much more than 95% (whether it's Cygnus X-1, or other). Besides, Hawking conceded the bet in 1990. You can deny anything being 100% certain or the minute mechanics of a phenomenon not being 100% understood, but the preponderance of evidence for black holes is overwhelming.

[Coldcreation]

Even in '75 it was 80% certain that black holes existed and by now it would be much more than 95% (whether it's Cygnus X-1, or other). Besides, Hawking conceded the bet in 1990. You can deny anything being 100% certain or the minute mechanics of a phenomenon not being 100% understood, but the preponderance of evidence for black holes is overwhelming.

The bet has yet to be settled.


CC

[BigDon]

CC,

that sounds a little bit like the "N'uh!" defense.

BD