Hawking Radiation

[pgrmdave]

I don't know much about it, but Hawking radiation is emitted by black holes by virtual particles. Are they emitting energy that they've previously absorbed, or are they creating energy? I'm not sure I quite grasp the concept of the virtual particles, but it seems to me that energy is being created from nothing, is that right?

[Erasmus00]

I don't know much about it, but Hawking radiation is emitted by black holes by virtual particles. Are they emitting energy that they've previously absorbed, or are they creating energy? I'm not sure I quite grasp the concept of the virtual particles, but it seems to me that energy is being created from nothing, is that right?

 

Energy comes from the blackholes. The black holes evaporate due to the radiation.

-Will

[Bo]

the virtual particles are created by e.g. a photon, that is inside the black hole, so the black hole loses energy in that sense

 

bo

[UncleAl]

Heisenberg Uncertainty demands that the quantum vacuum not be empty - or we would exactly know its energy content (zero) over time. Each allowed electromagnetic mode has (1/2)h(nu) of uncertainty. Virtual photons are forever measurably popping into existence and going back into nothing, re the Casimir effect, vacuum Rabi oscillations, Lamb shift, electron anomalous g-factor... as long as conserved properities are overall conserved.

 

Given: a black hole's event horizon. A virtual photon appears out of the vacuum leaving a virutal hole of the same but opposite energy. One of them gets sucked in, the other is emitted, both becoming real and permanent. The energy to do this comes from the black hole. At a distance it looks like the mass of the black hole is evaporating by emitting photons (Hawking radiation). The smaller the black hole's mass, the sharper the curvature of its event horizon, the more energetic the process, the higher the apparent temperature of the black hole.

 

http://casa.colorado.edu/~ajsh/hawk.html

http://en.wikipedia.org/wiki/Hawking_radiation

[lindagarrette]

the virtual particles are created by e.g. a photon, that is inside the black hole, so the black hole loses energy in that sense

 

bo

Since a black hole loses energy over a period of time, it will eventually dissipate. Right? That's part of the increasing entropy in our system.

[Bo]

yes you would expect that, however balck hole entropy is something very strange.

It can be shown that the entropy of a black hole is constant during hawking radiation...

This is something tha is still hardly understood (you realy need quantum gravity to tackle these kind of problems).

 

Bo

[Erasmus00]

yes you would expect that, however balck hole entropy is something very strange.

It can be shown that the entropy of a black hole is constant during hawking radiation...

This is something tha is still hardly understood (you realy need quantum gravity to tackle these kind of problems).

 

Using Hawking radiation, you can show that the entropy of a black hole is, in fact, proportional to its surface area. As the blackhole shrinks, its entropy does go down.

-Will

[CraigD]

Since a black hole loses energy over a period of time, it will eventually dissipate. Right?

According to the conventional logic, not usually.

 

Because the surface area of a black hole’s event horizon (from its by Schwarzschild radius) increases as its Mass^2, while Hawking radiation decreases as its Mass^2, and a black hole absorbs any radiation that intersects its event horizon, a black hole over a certain size will always grow due to absorbing the ever-present Cosmic Microwave Background radiation.

 

If you had a black hole somewhere where there was no CMB or other significant radiation, it would eventually dissipate, so, in principle, it can happen. For instance, surrounding a black hole with a thick, super-cool shield would make it possible for it to lose mass.

[UncleAl]

Since a black hole loses energy over a period of time, it will eventually dissipate. Right? That's part of the increasing entropy in our system.

NO! Any black hole cooler than cosmic background radiation swallows more energy/time than it emits. Any naturally formed black hole will be cooler than its background and therefore will only grow and continue cooling. Think about it.

[coldcreation]

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). Like the CMB, Hawking radiation is a vestige from the Christ-antichrist asymmetry.

 

Hawking is unfortunately wrong, but that doesn’t make him an idiot. The idea that black holes emit radiation has a throb of raw genius; it will keep interest in them alive, with the expectation that they can someday be detected, offering a glimmer of hope. It will keep interest in him alive…forever.

 

Coldcreation

[lindagarrette]

Assuming the universe is expanding forever, someday there will be nothing around for a black hole to gobble up, right? Then what?

[Jay-qu]

Assuming the universe is expanding forever, someday there will be nothing around for a black hole to gobble up, right? Then what?

 

cosmic heat death - we get a very large homogenous universe

[CraigD]

Assuming the universe is expanding forever, someday there will be nothing around for a black hole to gobble up, right? Then what?

lindagarrette, you might find the article at this link interesting: http://en.wikipedia.org/wiki/Timeline_of_the_universe#The_Black_Hole_Age_-_from_1040_years_to_10100_years.

[lindagarrette]

lindagarrette, you might find the article at this link interesting: http://en.wikipedia.org/wiki/Timeline_of_the_universe#The_Black_Hole_Age_-_from_1040_years_to_10100_years.

 

Wow! The Big Rip theory, which has not been discarded, says that when everything starts to go, the end will be fast and furious. I hope by that time, humans have created some technology that allows intelligence to survive.