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Author Topic: Should Hawking radiation not cancel out?  (Read 3172 times)

Offline thedoc

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Should Hawking radiation not cancel out?
« on: 10/08/2012 18:30:01 »
Joash Hicks  asked the Naked Scientists:
   
My understanding of hawking radiation is that spontaneously a particle of matter and anti-matter burst into space. On one side of the event horizon the anti-matter annihilates some matter and on the other side matter escapes into space. Now it is said this happens all the time everywhere.

If that is so, wouldn't there be an equal proportion of anti-hawking radiation (the matter is on the inside of the event horizon and the anti-matter is on the outside) meaning the net effect of hawking radiation and anti-hawking radiation would be nothing.

What do you think?
« Last Edit: 10/08/2012 18:30:01 by _system »


 

Offline evan_au

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Re: Should Hawking radiation not cancel out?
« Reply #1 on: 10/08/2012 21:01:34 »
In theory, the dominant mass=energy loss from a black hole would be electromagnetic radiation. A micro black hole with the mass of the moon would emit radiation with an effective temperature of 2.7 Kelvin (and would absorb an equal amount of energy from the cosmic microwave background). But black holes smaller than this would slowly "evaporate", if no other matter fell into them.

It is only when the black hole is almost down to zero mass that the Hawking radiation becomes intense enough (in the form of Gamma rays) to produce large amounts of matter and anti-matter; gamma rays will produce equal amounts of matter & anti-matter.

So I don't think that Hawking Radiation can account for the matter/antimatter imbalance that we see in the universe around us.

Maybe the LHC will produce some pico-black holes, and then we will have some experimental evidence?
http://en.wikipedia.org/wiki/Hawking_radiation
 

Offline yor_on

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Re: Should Hawking radiation not cancel out?
« Reply #2 on: 12/08/2012 17:51:15 »
I don't know, the important thing here is that it always annihilate inside the EH. If it does there should be a imbalance in energy, with more energy inside than outside a Black Hole, well, as I think of it. The energy released in a annihilation shouldn't be able to disappear inside its Event Horizon even if 'matter' can transform. So even though a Black hole might shrink? What the he* happens to that energy.
 

Offline wolfekeeper

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Re: Should Hawking radiation not cancel out?
« Reply #3 on: 13/08/2012 01:31:09 »
There's a common misunderstanding about this.

Both matter and antimatter have mass, so the absorption of antimatter would actually increase the mass of a blackhole.

The reason that Hawking radiation reduces the mass of the blackhole is that the particles that are created around the blackhole are created in the deep potential energy well of the blackhole.

This is so extreme that it means that the particles that fall into the blackhole actually have negative energy, whereas the particles (both matter and antimatter, but mostly photons) that escape the blackhole have positive energy.

So the overall effect is to progressively reduce the energy of the blackhole due to the negative energy falling into it, until it eventually evaporates.
 

Offline yor_on

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Re: Should Hawking radiation not cancel out?
« Reply #4 on: 13/08/2012 20:48:14 »
Don't want to be impolite but could you be more precise?
Energy as an idea exist. Anti matter as an idea is also energy.
Unless you know about anti 'energy' there will always be a transformation
 

Offline Soul Surfer

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Re: Should Hawking radiation not cancel out?
« Reply #5 on: 13/08/2012 21:40:39 »
One thing that you have to remember.  For all but the very smallest black holes just about the only "particles" that they can produce is very low frequency photons.  Photons are their own antiparticles and are pure energy anyway.

Black holes only start to radiate visible light when they are down to about 60 nanometers across and weigh 10^16 metric tons.
 

Offline wolfekeeper

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Re: Should Hawking radiation not cancel out?
« Reply #6 on: 13/08/2012 22:43:01 »
Antimatter has the opposite charge, not negative energy.
Unless you know about anti 'energy' there will always be a transformation
Gravitational potential energy is negative. So if you create particle pairs close to a black hole they can have negative energy.

The particle that fell in, is produced close enough to have negative TOTAL energy, and the particle that escaped was formed slightly further away, and has positive total energy, and hence can escape to infinity.

That's all I know about it. You'd have to read Hawking's paper to find out more.
« Last Edit: 13/08/2012 22:46:33 by wolfekeeper »
 

Offline yor_on

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Re: Should Hawking radiation not cancel out?
« Reply #7 on: 14/08/2012 19:17:22 »
That one was new to me. That you can expect some annihilation's to take away energy? Then there is no conservation of energy either is it? If that is possible. And what about thermodynamics?
 

Offline wolfekeeper

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Re: Should Hawking radiation not cancel out?
« Reply #8 on: 14/08/2012 19:56:23 »
I have absolutely no idea what you're talking about, Hawking radiation is due to particles being created, not annihilated, and the total energy is conserved before, during and after that creation event.
 

Offline yor_on

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Re: Should Hawking radiation not cancel out?
« Reply #9 on: 14/08/2012 21:48:33 »
Maybe it's the way you define it?
What do you mean by 'gravitational potential negative energy'?

And are you thinking of it in mathematical terms or physical. To me all transformations involve 'energy, assuming this it then stands to reason that annihilation, as a anti particle meeting a particle, should leave a energy conserved, even inside a black hole?
=

And that is the imbalance I was referring too, somewhat like a Black Hole losing 'matter', but building up 'energy' as it annihilate by Hawking radiation inside the Event Horizon-
« Last Edit: 14/08/2012 21:52:42 by yor_on »
 

Offline wolfekeeper

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Re: Should Hawking radiation not cancel out?
« Reply #10 on: 14/08/2012 22:20:11 »
I suggest you google "gravitational potential energy" and read about it; gravitational potential is always negative.

The particles are created not in the black hole, but just outside the event horizon.

 

Offline yor_on

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Re: Should Hawking radiation not cancel out?
« Reply #11 on: 14/08/2012 22:42:44 »
I suggest you define what you mean :)

As for the creation then that is defined to the event horizon, but the annihilation of matter is inside it as I understands?
 

Offline wolfekeeper

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Re: Should Hawking radiation not cancel out?
« Reply #12 on: 14/08/2012 23:00:47 »
Forget it.
 

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Re: Should Hawking radiation not cancel out?
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