View Full Version : What I don't quite get about Black Holes vaporziing thru hawking Radiation

2007-Oct-08, 09:34 AM
I run out of silly questions, so I haven't been here for a while. But I have one now that keeps bugging me.

The theory as I have understood it: a pair of virtual particles become real. Normally, because one is matter and the other is antimatter, they would instantly cancel each other out, but when the pair of particles comes into existence right at the event horizon of a black hole, one particle might fall into the black hole, while the other remains just outside of it.

This, at least that's how I interpreted what i read in various sources, is called Hawking radiation, and it cause the black hole to vaporize over time - the black hole sorta loses this one particle, which is distracted from it's mass...

I don't quite get this last thing... I would think the particle did not come from the black hole, so why should the black hole lose mass...

Or is it, because the particle falling in is an antimatter particle? Then, is this always the case? (the antimatter particle falling in, the normalmatter particle remaining outside? If there's a 50% chance, there shouldn't be a nett effect...)


Thinking of antimatter and black holes... Is a singularity itself still considered 'matter' (and thus, could a black hole also be made of antimatter?) Or is a singularity beyond the distinction between matter and antimatter?

If a black hole can indeed be made of either matter or antimatter, what would happen if they merge... A giant explosion? Or would the power of the explosion (or implosion?) be blown into a separate little universe (a bubble cut off from the rest of the universe)

Thanks for any clarifications!

2007-Oct-08, 10:50 AM
I have no idea what I am talking about but I'll take a stab at this:
I think it might be that the event horizon is a kind of information/energy boarder with the rest of the universe; there is the black hole and there is the Universe. The particle that escapes, into the rest of the Universe adds to the energy/matter/information of the Universe and so must be balanced by a negative, that is the particle that falls into the BH. So the net addition to the universe-bh combination is zero.
there- if that's too atm blame it on the groovy.

no i'm not drunk

2007-Oct-08, 11:06 AM
The 'evaporation' process is a complicated mathematical exercise that is not well understood, nor has it been directly confirmed by observation. Bear in mind the very existence of black holes is not entirely beyond dispute. That aside, the mathematical foundations are very good. The Unruh effect, an offshoot of the evaporation process [Hawking radiation], does have some decent observational evidence. The long and short of it is new physics appear necessary to uphold objections to black hole evaporation. The 'antimatter' black hole hypothesis is unrealistic. Since all interactions would occur inside the event horizon, the question is moot.

2007-Oct-08, 01:23 PM
I run out of silly questions, so I haven't been here for a while. But I have one now that keeps bugging me.

You're not the first. Here's a few, of more than a few:

Hawking Radiation and negative energy (http://www.bautforum.com/against-mainstream/5059-hawking-radiation-negative-energy.html)
About Hawking Radiation (http://www.bautforum.com/questions-answers/33281-about-hawking-radiation.html)
A few questions about hawking radiation (http://www.bautforum.com/astronomy/34787-few-questions-about-hawking-radiation.html)
Questions about Hawking Radiation... (http://www.bautforum.com/questions-answers/35116-questions-about-hawking-radiation.html)

Best advice is probably to see Usenet Physics FAQ: Hawking Radiation (http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/hawking.html).

Also the Wikipedia: Hawking radiation (http://en.wikipedia.org/wiki/Hawking_radiation) was said to have a digestable explanation, short form:

Physical insight on the process may be gained by imagining that particle-antiparticle radiation is emitted from just beyond the event horizon. This radiation does not come directly from the black hole itself, but rather is a result of virtual particles being "boosted" by the black hole's gravitation into becoming real particles.

A more precise, but still much simplified view of the process is that vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole whilst the other escapes. In order to preserve total energy, the particle which fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole). By this process the black hole loses mass, and to an outside observer it would appear that the black hole has just emitted a particle.

Kaptain K
2007-Oct-08, 03:04 PM
Both matter and antimatter have positive mass, so it doesn't matter which falls in and which escapes. the net result is that the BH loses one particle's worth of mass.
As for a collision between two black holes, one of mater and the other of antimatter, the resulting energy would be equivalent, since E=mc^2. Net result...a bigger black hole.
As Wheeler said, "black holes have no hair". All that is left to measure is mass and spin.

2007-Oct-08, 05:07 PM
Thanks people!!!

Before I'm gonna follow 01101001's links, just one remark

... the net result is that the BH loses one particle's worth of mass.

That is exactly what I don't get! It would seem to me that both the black hole and the rest of the universe outside of it, actually gain one particle. Two particles travelled from 'virtuality' into reality, so to speak.

Thinking of it: If you then (that is: after the gaining suggested above) divide the entire mass of the black hole by the entire mass of the rest of the galaxy, the mass of the black hole has even relatively gained more mass than the rest of the universe... (this is true as long as the black hole's mass is less then the mass of the rest of the universe)... but I think I'm polluting the forum now, so I'm gonna read where 01101001 directed me!

2007-Oct-08, 06:54 PM
This makes sense, and is very simple & short too:

The virtual particle creation creates two particles. A particle and it's anti-particle. This costs net energy, borrowed from the vacuum, and if the two annihilate, the energy is paid back.
But if this occurs near the event horizon of a Black hole, one can fall in, while the other can escape. This will cost nett energy then, which is subtracted from the energy of the Black hole.

posted by Heusdens on 19 May 2003, at 02:01 AM in this (http://www.bautforum.com/against-mainstream/5059-hawking-radiation-negative-energy.html#post85436) message.

2007-Oct-09, 09:15 PM
Didn't Hawkins change his mind?

2007-Oct-09, 10:15 PM
Didn't Hawkins change his mind?

Hawking said a lot of things about black holes. He changed his mind about some of them.

The most famous is: New Scientist: Hawking cracks black hole paradox (http://www.newscientist.com/article.ns?id=dn6151)

After nearly 30 years of arguing that a black hole destroys everything that falls into it, Stephen Hawking is saying he was wrong. It seems that black holes may after all allow information within them to escape.

Which is not to say he changed his mind about the possibility of Hawking Radiation (http://en.wikipedia.org/wiki/Hawking_radiation).

hawking.org :: Information (http://www.hawking.org.uk/text/info/info.html):

In 1974, Stephen Hawking discovered that when one fused the ideas of quantum mechanics with those of general relativity, it was no longer true that black holes were completely black. They emitted radiation, now known as Hawking radiation. This radiation carried energy away from the black hole which meant that the black hole would gradually shrink and then disappear in a final explosive outburst.

Spaceman Spiff
2007-Oct-10, 01:01 PM
In becoming real, the virtual particle pair borrowed the energy from the gravitational field of the black hole (or from the curvature in space-time). The tidal forces found near the black hole horizon can shear the two particles apart, allowing the possibility of one of them to escape. Since an equivalent of two electron rest masses was borrowed from the field to make them real, if one of the particles of the pair escapes, the black hole has lost 1 electron rest mass' worth of mass. Other virtual particles (even energetic photons) are created as well in the same process. The less massive the black hole, the more extreme are the local tidal forces (gradients in curvature of space-time), so the process accelerates.

I hope that helps.

John Mendenhall
2007-Oct-10, 01:16 PM
Interesting point, that whether matter or anti-matter, the BH loses one particle mass.