LHC Black Holes

As I understand it (layman's explanation): each virtual particle/antiparticle pair which appears, draws the energy of its creation from the energy of the strongly-curved space-time in the vicinity of the black hole. The same is true for any virtual- particle-pair creation event... it "borrow" energy from the vacuum.

If the two virtual particles recombine, the energy is returned to spacetime. This is what happens in the case of the vast majority of such particle events, especially in flat or near-flat spacetime regions.

If, on the other hand, one of the two virtual particles escapes (and the other falls into the black hole), half of the "borrowed" energy escapes. The total mass-energy in the region drops by that amount.

Don't ask me to try to lay out the math for this... I don't pretend to understand the equations :-)

No, the hole loses mass turning the virtual particle into a real one.

Cheers

Phil Hobbs

I'm not asking for math, I'm looking for an understanding. If something can be extracted from the black hole by any mechanism, there would seem to be a fundamental conflict with the idea that the black hole is inexcapable.

I totally don't understand the idea of there being energy inherent in the curvature of space-time.

I've also never understood the details of spontaneous generation of particle pairs from the vacuum. Even if they recombine, they create a pair of photons. What happens to the photons?

So a "virtual" particle has negative mass? The black hole captures one virtual particle and the other becomes real. What exactly is the difference between a virtual particle and a real one?

This sounds a bit like tunneling. Matter leaves the black hole without ever crossing the event horizon.

It's a lot like tunnelling. For the rest, it's because quantum field theory.

Cheers

Phil Hobbs

At room

Since protons and neutrons are composite particles a MBH *might* snag a q uark out of a nucleon, but that would leave a color-charged diquark particl e as well as giving the MBH naked color, which Isn't Allowed.

Most likely result is that the color force would immediately pull anti-co lored quarks out of the vacuum; one to neutralize the diquark, and the othe r would fall into the MBH neutralizing its color.

But as you say, this would be rare indeed whether or not the MBH evaporat es (which it would, rapidly).

OTOH it could easily eat point particles like electrons but would also ra pidly build up charge and stop eating them due to Coulomb repulsion.

Photons? Sure, but MBHs are HOT and radiate very very brightly; we're tal king petawatts bright with a blackbody spectrum that peaks in the really sh ort gammas.

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That's really the bottom line. When it finishes evaporating things will b e locally somewhat exciting, but a mere blip on geological energy scales.

Mark L. Fergerson

Right, it's the kind of "so obviously true" thing, that thermodynamics is so good at. The mechanism doesn't matter: the temperature will be there.

The emissivity of that temperature reservoir might not be very good (like, consider the tiny and poorly coupled heat capacity of nuclear spins in most matter), or there might be secondary effects that don't invalidate the thermo but nonetheless do weird things (like if the death throes of a micro BH are quantized into extremely high energy emission states, to the extent that there's a stable ground state instead of complete evaporation).

As for the mechanism, you can also think of it as tunneling.

Consider: nothing inside the BH event horizon is actually "inside", to any significant meaning to an outside observer.

As matter falls in, it appears to slow down. Eventually, it appears to be just at the event horizon -- at the same point it has red-shifted to infinity.

So, realize: to an outside observer, /the entire black hole is at its surface/. It's a shell mass.

Gauss tells us that gravity doesn't care, so there's nothing at all strange about this idea. We have the same outside observations, regarding the region's mass, charge and spin.

But it's all at the surface, so it really shouldn't be surprising that:

- The entropy is proportional to area (that's where all the "stuff" is)

- The entropy is maximal (because a maximal amount of "stuff" is packed onto the surface)

- Tunneling can carry contents from the shell to the outside, with a probability determined by steepness of the potential at the surface, not by, say, distance from center.

NB: I forget if the actual mechanics of Hawking radiation have different statistics. I've heard of tunneling expressed as virtual pairs doing the same thing, and it's been long enough since school that I haven't worked these problems myself...

Tim

Sit down and wathc the video I posted. Smart guy talking about the "physics" of black holes. You have to do the math! To me it is a lot of fun. (I watched it again... some smart questions from the class too.) The sun is a good analog for a black hole, I missed that the first time.

He doesn't talk about the mechanism of exchange. (I've said this before, but you have this supieriority(sp) thing, which is kinda ugly.) George H.

Tim, Yeah I think all that is right. If you've got an hour to kill and the BW the Susskind video I posted says all of that. (with order of magnitude math/physics equations.) The sun is a good analog for a black hole. (I know I'm repeating myself. :^)

As far as the mechanism, (which only realy matters if you want to try and measure it.) I don't see tunneling as right... it's more like boiling water off a surface*. The BH has some energy (temperature) and can impart that to 1/2 of a virtual particle pair at the surface... which then has to "get out" of the gravity well... not all have enough energy.

George H.

A virtual particle is "borrowing" energy from the uncertainty principle, and then paying it back fast enough that nobody notices. In the language of quantum mechanics, energy and time are non-commuting observables, in the same way that position and momentum are.

A virtual particle becomes real when another thing gives the original system enough energy to pay back the loan, without relying on quantum subterfuge.

That is to say, over very short timescales the actual energy density of a region of spacetime is uncertain; uncertain enough such that random particles pop in and out of existence since they don't really "know" whether they should exist or not.

To my mind, a pretty interesting direction to head in would be to assume that our current understanding of QFT is a first-order approximation, which doesn't precisely apply on scales nearing the size of the observable Universe.

Hawking radiation is a very plausible hypothesis.

If the small back holes didn't get Hoovered up by larger black holes - and every galaxy seems to have at least one large black hole.

The fact that we haven't seen anything radiating anything that looks like H awking radiation isn't actually particularly convincing evidence that Hawki ng radiation doesn't happen, and everything else we know suggests that if b lack holes look anything like the way we think they do at the moment, they' d emit Hawking radiation.

The fact that LIGO has now picked up two black hole merger signals, from me dium-sized black holes (a few solar masses) does point up the fact that bla ck holes can merge, which might explain what might have happened to any sma ll black holes left over from the Big Bang.

Hawking's point was that Hawking radiation is a signal that comes from the event horizon. Black holes suddenly became a trifle less black, and there w as a way of assigning a temperature to the black hole.

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That's not what Hawking radiation is about. As Dirac pointed out, the Heise nberg uncertainty principle means that virtual pairs of particles and anti- particles are always popping up everywhere and - mostly - vanishing again a s they self-annihilate

If it happens at a back-hole event horizon, they can't self-annihilate.

A very pretty insight.

The only difference is that the virtual particles become real without one being captured by the black hole. They still don't explain why the matter/energy has to come from the black hole. Worse, no one has even attempted to explain the "how" in any meaningful way other than to say because of conservation of energy it *must* come from the black hole... not very satisfying at all. Why can't it come from my cat?

So how does the black hole provide that energy? Curvature of space/time is not energy that I am aware of.

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Because of the math blizzard that you don't understand at all, and I unders tand only a bit better, despite two quantum field theory courses in grad sc hool. "No one has ever attempted to explain" radar to a Hottentot either, I expect.

cheers

Phil Hobbs

I have considered similar ideas that our understanding of the universe which is limited in explaining the large scale observations will be expanded in the near future not unlike relativity expanded classical physics after the Michelson?Morley experiment showed there was no aether. There seems to be a lot of resistance to that idea. But consider how "fabricated" much of the explanation is involving dark matter and energy. I expect it will result in a very new theory of life, the universe and everything in the next 20 or 30 years.