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Offline Eric A. Taylor

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How do virtual particles evaporate black holes?
« on: 02/01/2011 06:36:21 »
If I understand correctly, at every point in space virtual particles are coming into existence then vanishing. What happens is you get a bit of energy that turns into two particles, one negative and one positive. Normally the get back together very quickly becoming energy again.

But in the region of a black hole one of the particles can cross the event horizon and it's partner escapes.

Statically half the the particles falling into the black hole would be negative, reducing the black hole's mass by the negative mass of the particle. However the other half should be positive particles which will ADD mass to the black hole. The net should be zero, thus the black hole will not lose mass over time. Am I wrong here? Must be because Steven Hawking is a lot smarter than me. I'd just like to know WHY I'm wrong.


 

Offline Fortran

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How do virtual particles evaporate black holes?
« Reply #1 on: 02/01/2011 15:51:55 »
I have heard of this being called a theory, yet a theory usually has some supporting evidence often obtained by experimentation. My gut feeling is that the science community is being nice to Mr Hawking due to his particular circumstances. I have no doubt that after his eventual demise this 'theory' will simply e lost.  How convenient to form a 'theory' that cannot be supported until after a googleplex of years has demised.
 

Offline lightarrow

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How do virtual particles evaporate black holes?
« Reply #2 on: 02/01/2011 17:48:53 »
If I understand correctly, at every point in space virtual particles are coming into existence then vanishing. What happens is you get a bit of energy that turns into two particles, one negative and one positive. Normally the get back together very quickly becoming energy again.

But in the region of a black hole one of the particles can cross the event horizon and it's partner escapes.

Statically half the the particles falling into the black hole would be negative, reducing the black hole's mass by the negative mass of the particle.
Negative mass? No, no, negative mass doesn't exist. If it's a couple electron/positron, for example, one of them is negatively charged (electron) and the other (positron) positively. So it's "charge" not mass. Both have *positive* mass and positive energy.
 

Offline graham.d

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How do virtual particles evaporate black holes?
« Reply #3 on: 02/01/2011 17:50:33 »
Many of the ideas involving quantum gravity are probably wrong. I think even the authors will admit this. But I wouldn't "diss" Hawking's ideas as much as Fortran. I think there is a consensus that small Black Holes probably do evaporate through radiation. It may be as Hawking described, or a variation of it, or possibly through thermal radiation. The jury may be out for some time yet.
 

Offline graham.d

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How do virtual particles evaporate black holes?
« Reply #4 on: 02/01/2011 17:57:02 »
Lightarrow, I think Hawking's idea can be interpreted that the particle falling into the hole has negative energy as observed from infinity (or at least a long way off).
 

Offline Soul Surfer

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How do virtual particles evaporate black holes?
« Reply #5 on: 02/01/2011 20:45:21 »
Virtual particles are effectively energy borrowed from the  Quantum mechanical vacuum.  If this happens across the event horizon of a black hole the black hole has to pay the energy debt.
 

Offline QuantumClue

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How do virtual particles evaporate black holes?
« Reply #6 on: 02/01/2011 22:30:45 »
I have heard of this being called a theory, yet a theory usually has some supporting evidence often obtained by experimentation. My gut feeling is that the science community is being nice to Mr Hawking due to his particular circumstances. I have no doubt that after his eventual demise this 'theory' will simply e lost.  How convenient to form a 'theory' that cannot be supported until after a googleplex of years has demised.

No need to sound patronizing. Prof. Hawking according some should have deserved a nobel prize at one point or another. What Haking has done is expand the quantum model sufficiently to explain the exotic phenomenon of black holes which are a direct prediction of GR. His work does not suggest he gets his attention merely because of some disability which he has; when he speaks, the scientific community listen, and this is not for any false reason.
 

Offline yor_on

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How do virtual particles evaporate black holes?
« Reply #7 on: 02/01/2011 22:58:08 »
Hawking radiation as described by Professor Steve Carlip
 

===Quote

There are a number of ways of describing the mechanism responsible for Hawking radiation. Here's one:

The vacuum in quantum field theory is not really empty; it's filled with "virtual pairs" of particles and antiparticles that pop in and out of existence, with lifetimes determined by the Heisenberg uncertainty principle. When such pairs forms near the event horizon of a black hole, though, they are pulled apart by the tidal forces of gravity. Sometimes one member of a pair crosses the horizon, and can no longer recombine with its partner. The partner can then escape to infinity, and since it carries off positive energy, the energy (and thus the mass) of the black hole must decrease.

There is something a bit mysterious about this explanation: it requires that the particle that falls into the black hole have negative energy. Here's one way to understand what's going on. (This argument is based roughly on section 11.4 of Schutz's book, A first course in general relativity.)

To start, since we're talking about quantum field theory, let's understand what "energy" means in this context. The basic answer is that energy is determined by Planck's relation, E=hf, where f is frequency. Of course, a classical configuration of a field typically does not have a single frequency, but it can be Fourier decomposed into modes with fixed frequencies. In quantum field theory, modes with positive frequencies correspond to particles, and those with negative frequencies correspond to antiparticles.

Now, here's the key observation: frequency depends on time, and in particular on the choice of a time coordinate. We know this from special relativity, of course -- two observers in relative motion will see different frequencies for the same source. In special relativity, though, while Lorentz transformations can change the magnitude of frequency, they can't change the sign, so observers moving relative to each other with constant velocities will at least agree on the difference between particles and antiparticles.

For accelerated motion this is no longer true, even in a flat spacetime. A state that looks like a vacuum to an unaccelerated observer will be seen by an accelerated observer as a thermal bath of particle-antiparticle pairs. This predicted effect, the Unruh effect, is unfortunately too small to see with presently achievable accelerations, though some physicists, most notably Schwinger, have speculated that it might have something to do with thermoluminescence. (Most physicists are unconvinced.)

The next ingredient in the mix is the observation that, as it is sometimes put, "space and time change roles inside a black hole horizon." That is, the timelike direction inside the horizon is the radial direction; motion "forward in time" is motion "radially inward" toward the singularity, and has nothing to do with what happens relative to the Schwarzschild time coordinate t.

The final ingredient is a description of vacuum fluctuations. One useful way to look at these is to say that when a virtual particle- antiparticle pair is created in the vacuum, the total energy remains zero, but one of the particles has positive energy while the other has negative energy. (For clarity: either the particle or the antiparticle can have negative energy; there's no preference for one over the other.) Now, negative-energy particles are classically forbidden, but as long as the virtual pair annihilates in a time less than h/E, the uncertainty principle allows such fluctuations.

Now, finally, here's a way to understand Hawking radiation. Picture a virtual pair created outside a black hole event horizon. One of the particles will have a positive energy E, the other a negative energy -E, with energy defined in terms of a time coordinate outside the horizon. As long as both particles stay outside the horizon, they have to recombine in a time less than h/E. Suppose, though, that in this time the negative-energy particle crosses the horizon. The criterion for it to continue to exist as a real particle is now that it must have positive energy relative to the timelike coordinate inside the horizon, i.e., that it must be moving radially inward. This can occur regardless of its energy relative to an external time coordinate.

So the black hole can absorb the negative-energy particle from a vacuum fluctuation without violating the uncertainty principle, leaving its positive-energy partner free to escape to infinity. The effect on the energy of the black hole, as seen from the outside (that is, relative to an external timelike coordinate) is that it decreases by an amount equal to the energy carried off to infinity by the positive-energy particle. Total energy is conserved, because it always was, throughout the process -- the net energy of the particle-antiparticle pair was zero.

Note that this doesn't work in the other direction -- you can't have the positive-energy particle cross the horizon and leaves the negative- energy particle stranded outside, since a negative-energy particle can't continue to exist outside the horizon for a time longer than h/E. So the black hole can lose energy to vacuum fluctuations, but it can't gain energy.

===End of quote

E= is energy (joules, often converted to electron volts)
h= is Planck's constant=6.626x10^-34 Joule x second == 6.63x10^-34
f= is frequency of the object, also described as 1/wavelength

so E(energy) is =h(Plank constant) times f( the frequency)

In terms of 'shaking a electron lose' you need 'photons' to hit whatever matter containing those electrons.
When you just apply enough force to get one electron free then that's called the 'Work force'.
Giving it more than the Work force is called delivering 'kinetic energy' to the atom containing the electron, and the photons 'energy' is regulated by this equation.

h times f = is the work function and so the 'threshold level' for releasing 'photoelectrons' and any energy over that will appear as kinetic energy in that photoelectron.


« Last Edit: 02/01/2011 23:38:29 by yor_on »
 

Offline yor_on

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How do virtual particles evaporate black holes?
« Reply #8 on: 02/01/2011 23:41:23 »
Anyone more than me that find this surprising?

"Now, here's the key observation: frequency depends on time, and in particular on the choice of a time coordinate. We know this from special relativity, of course -- two observers in relative motion will see different frequencies for the same source. In special relativity, though, while Lorentz transformations can change the magnitude of frequency, they can't change the sign, so observers moving relative to each other with constant velocities will at least agree on the difference between particles and antiparticles.

For accelerated motion this is no longer true, even in a flat spacetime. A state that looks like a vacuum to an unaccelerated observer will be seen by an accelerated observer as a thermal bath of particle-antiparticle pairs. This predicted effect, the Unruh effect, is unfortunately too small to see with presently achievable accelerations, though some physicists, most notably Schwinger, have speculated that it might have something to do with thermoluminescence. (Most physicists are unconvinced.)"
 

Offline yor_on

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How do virtual particles evaporate black holes?
« Reply #9 on: 03/01/2011 00:51:53 »
Then we can look at the one following too. "The next ingredient in the mix is the observation that, as it is sometimes put, "space and time change roles inside a black hole horizon." That is, the timelike direction inside the horizon is the radial direction; motion "forward in time" is motion "radially inward" toward the singularity, and has nothing to do with what happens relative to the Schwarzschild time coordinate t."

Here is how NASA defines how space and time change roles inside a black hole.

"Q. How is it possible for time to change inside a black hole?

A. In general relativity, time and space are a set of variables that can be used to parameterize the geometry of space-time and the kinds of geodesics that are possible. But they are not the only kinds of variables that form a set of four coordinates that "span" the dimensionality of space-time. In probing the mathematics of black holes, physicists have discovered other sets of coordinates that are even better. For example, the event horizon appears in the mathematics as a "coordinate singularity" if you use the coordinate set (x, y, z, t) or (t, r, theta, phi), but if you use the "Kruskal-Szekeres" coordinates, it vanishes completely.

There is only one true singularity in a non-rotating Schwartzschild black hole solution, and that is the one at r=0, at the event horizon, the curvature of space is non-infinite. That means that coordinate singularities are not real singularities and can be mathematically transformed away. Now, if you study what happens to the Kruskal-Szekeres coordinate system as you pass inside the black hole event horizon, nothing unusual happens. But in the conventional Newtonian (x, y, z, t) system, if you look at the formula for the so-called "metric," you see that the space and time parts reverse themselves. This means that just inside the horizon, space becomes time-like and time becomes space-like. What we call time does change to something with the mathematical properties we have normally associated with space.

This sounds pretty bizarre, but consider that we are using a non-proper coordinate system in the first place. It is possible that time changes somehow inside a black hole, but that is an experiment we will never be able to test because we can never receive information from inside a black hole. "
 

Offline yor_on

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How do virtual particles evaporate black holes?
« Reply #10 on: 03/01/2011 01:16:54 »
Now to some really weird statements.

"The vacuum is defined to have zero energy. Therefore yes, the virtual particles violate the law of energy preservation. But the particles disappear again directly after (e. g. eighty attoseconds for a photon of orange light) and give the energy back to the vacuum."

From Hawking radiation. Otherwise it seems very good, but that statement made me very surprised.

eighty huh?
Ok.

10^−44 is 1 "Plank time"
10^−18 is 1 "attosecond"
From orders of magnitude.

Notice the difference. Then we wonder, what is the lowest value of time ever measured? Well, 12 attoseconds seems to be the shortest period of time measured that I've found the world record for shortest controllable time With me so far?

So suddenly we should be having measurable 'virtual photons'?
Well, you're welcome to search for it?

I did as it would blow one of my ideas out of the water. That Planck time and under is where virtual photons should be, as they are expected to be able to 'tunnel' out of a Black Hole. Now, I didn't find anyone having 'measured' a virtual photon, yet, that is? So I will continue to have my view for a while longer :) To me that has to be a theoretical definition, unsupported by experiments. But if you know me wrong here just link me to the experiment showing how long one single 'virtual photon' is measured.
==

What is truly fascinating, if that (80) statement would be shown to be true, is that we then would have 'real photons' of a shorter measurable duration than a 'virtual'? Where would that place 'virtuality'?
« Last Edit: 03/01/2011 03:02:18 by yor_on »
 

Offline graham.d

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How do virtual particles evaporate black holes?
« Reply #11 on: 03/01/2011 10:13:11 »
That's interesting, yor_on. I have come across some of the concepts before (timelike space inside a BH for example) though don't have a very thorough appreciation of them because I have never found the time to dig deep enough and then go through the maths. What bothers me is the statement:

"Note that this doesn't work in the other direction -- you can't have the positive-energy particle cross the horizon and leaves the negative- energy particle stranded outside, since a negative-energy particle can't continue to exist outside the horizon for a time longer than h/E. So the black hole can lose energy to vacuum fluctuations, but it can't gain energy."

It says (kind of) that something doesn't happen because it would be "embarrassing" to the those who believe negative energy particles should not exist for long. I am a bit uncomfortable with the idea that, because a negative energy particle cannot exist for long in normal space that its production in one circumstance (when it subsequently is captured by the BH) is OK but that in the other case (where its positive energy partner is captured) will not happen. Isn't the cause and effect direction getting reversed here?
 

Offline yor_on

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How do virtual particles evaporate black holes?
« Reply #12 on: 04/01/2011 02:35:54 »
Yeah, at first I was quite happy with the definitions though :)
==

But I agree, there might be some other way to express a Hawking radiation. You might see it as a Black Hole should be truly 'filled' with positive particles increasing the probability of that 'neg' meeting a 'pos' in 'time'? But then you have the ideas of how a Black Hole should 'expand' its Space inside the EV, possibly negating that concept.

And in the end, we don't really know, do we?
It would be good if someone had one of those alternative explanations he mentions there.
 

Offline lightarrow

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How do virtual particles evaporate black holes?
« Reply #13 on: 04/01/2011 12:49:46 »
Lightarrow, I think Hawking's idea can be interpreted that the particle falling into the hole has negative energy as observed from infinity (or at least a long way off).
I renounce to understand anything... :)
 

Offline Eric A. Taylor

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How do virtual particles evaporate black holes?
« Reply #14 on: 05/01/2011 07:22:55 »
I have heard of this being called a theory, yet a theory usually has some supporting evidence often obtained by experimentation. My gut feeling is that the science community is being nice to Mr Hawking due to his particular circumstances. I have no doubt that after his eventual demise this 'theory' will simply e lost.  How convenient to form a 'theory' that cannot be supported until after a googleplex of years has demised.

If I'm not hugely mistaken I think Hawking radiation has been seen at the LHC. As far as being "nice" to Hawking, you clearly don't understand how science works. I've seen very tough attacks on Hawking's theories.
 

Offline yor_on

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How do virtual particles evaporate black holes?
« Reply #15 on: 09/01/2011 05:13:41 »
You got that wrong Fortran. Science try to stay inside reason those days, not kiss ass. When it comes to Hawking I'm sure he thought a he* of a lot about his ideas before trying them out on the science community. That I argue about it is not because I doubt the radiation. I just want to understand it as good as I can. And considering that we have some pretty sharp guys here I have hopes :)
 

Offline Foolosophy

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How do virtual particles evaporate black holes?
« Reply #16 on: 09/01/2011 06:06:31 »
What happens is you get a bit of energy that turns into two particles, one negative and one positive. Normally the get back together very quickly becoming energy again.

I believe its the formation of a particle composed of matter and particle composed of anti-matter.

This is the reason they form pure energy when they recombine.

One of these particles escapes form the edge of the event horizon. The other is sucked in by the black hole

Hawking imposed the Quantum uncertainty principle at the event horizon region where this process is taking polace and stated that one particle escapes becuase it momentarily attains a speed greater than the speed of light.

(ie position is known at the event horizon, but its velocity is undeterminable - Heisenbeg Principle)

 

Offline Foolosophy

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How do virtual particles evaporate black holes?
« Reply #17 on: 09/01/2011 06:13:47 »
Lightarrow, I think Hawking's idea can be interpreted that the particle falling into the hole has negative energy as observed from infinity (or at least a long way off).
I renounce to understand anything... :)

The Ancient Greek Philosophers acknowledged that this realisation was the first step to enlightenment

We must be able recognise our glorious and infinte state of ignorance before we are able to even attempt to understand anything.
 

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Offline Geezer

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How do virtual particles evaporate black holes?
« Reply #18 on: 09/01/2011 06:41:02 »
Shrunk
We must be able recognise our glorious and infinte state of ignorance before we are able to even attempt to understand anything.

Are we using the royal we?
 

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Offline Geezer

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How do virtual particles evaporate black holes?
« Reply #19 on: 09/01/2011 06:51:46 »
Shrunk
We must be able recognise our glorious and infinte state of ignorance before we are able to even attempt to understand anything.

Are we using the royal we?

I was unaware that the Royals urinated???

Are you saying that the memebers of the Royal family are actually human?

Where do you get your stuff Geezer?

I'll take that as a "yes" then.
 

Offline lightarrow

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How do virtual particles evaporate black holes?
« Reply #20 on: 09/01/2011 13:16:04 »
Lightarrow, I think Hawking's idea can be interpreted that the particle falling into the hole has negative energy as observed from infinity (or at least a long way off).
I renounce to understand anything... :)

The Ancient Greek Philosophers acknowledged that this realisation was the first step to enlightenment

We must be able recognise our glorious and infinte state of ignorance before we are able to even attempt to understand anything.
Thanks.
Infact I've just realized that virtual particles don't exist in reality, so I've solved the problem...
 

Offline Foolosophy

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How do virtual particles evaporate black holes?
« Reply #21 on: 09/01/2011 14:31:56 »
Lightarrow, I think Hawking's idea can be interpreted that the particle falling into the hole has negative energy as observed from infinity (or at least a long way off).
I renounce to understand anything... :)

The Ancient Greek Philosophers acknowledged that this realisation was the first step to enlightenment

We must be able recognise our glorious and infinte state of ignorance before we are able to even attempt to understand anything.
Thanks.
Infact I've just realized that virtual particles don't exist in reality, so I've solved the problem...

well done

for a moment there I thought that you actually believed Quantum mechanics existed in reality

phew - that was a close one - wasnt it
 

Offline yor_on

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How do virtual particles evaporate black holes?
« Reply #22 on: 10/01/2011 01:38:24 »
Of course QM exist. Take a look in the hat box, see? It's waving at you, it's like the Ascot, either you are there, or you're a nobody as the colonel used to say.
 

Offline Foolosophy

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How do virtual particles evaporate black holes?
« Reply #23 on: 10/01/2011 10:47:16 »
Of course QM exist. Take a look in the hat box, see? It's waving at you, it's like the Ascot, either you are there, or you're a nobody as the colonel used to say.

That's Newtonian Mechanics -  You're anthropomorphising the atomic world

QM says that you are in the box and not in the box at the same time until the moment when the Wave Function collapses via some external input or trigger
 

Offline yor_on

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How do virtual particles evaporate black holes?
« Reply #24 on: 10/01/2011 17:03:48 »
True true, so true as someone said.
The collapsible hatbox.

But it's quite comfortable, one size fits all :)
 

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