Hawking radiation

[RichIsnang]

From what I understand, hawking radiation is when two particles are created, either by a photon momentarily splitting into an anti particle-particle pair, or an antiparticle-particle pair being created out of nothing (within the limits of the Heisenberg uncertainty principle). One of these particles falls into the event horizon and the other doesn't, so one particle is created out of nothing and the black hole loses a small amount of mass (black hole evaporation).

 

This seems to me to be a little dodgy, it seems like quantum mechanics is being tricked. And as we have learnt from many many experiments, it cannot. For example, light from distant stars, coming in as a particle, people try and trick it by putting a double slit there and making an interference pattern. ( not a very good example I know as light is both simultaneously, but I hope you get the jist of what I'm talking about). Also I'm a little unclear on how the black hole loses a small amount of mass when a particle falls in, instead of gaining mass.

[MigL]

If you borrow $20 from the bank and then eat $10 of it, you still have the other $10, but you owe $20 to the bank so you have to use $10 of your own money to make up the difference. Banks and the universe are very strict about repayment of loans.

Edited August 12, 2012 by MigL

[ajb]

The original work of Hawking did not use quantum tunnelling of particles, rather they are more subtle than this. The first paper to try to understand Hawking radiation as a tunnelling process was [1]. This paper has the calculations closest to the heuristic picture of particle/antiparticles falling into the black hole.

 

Reference

 

[1] Maulik K. Parikh and Frank Wilczek. Hawking Radiation as Tunneling, Phys.Rev.Lett.85:5042-5045,2000. Also available as arXiv:hep-th/9907001v3

[RichIsnang]

I like the bank analogy, but you can fool the bank into giving you $20 and then eat half of it, but you can't fool the universe into giving you two particles on loan then eat one of them and not be able to give the other one back. The bank doesn't know what you will do with the money after it lends it to you, but quantum mechanics and the universe are timeless, they won't lend you the particles in the first place because they know what's going to happen.

[MigL]

You misunderstood the analogy. If the black hole eats one of the particles it still owes the energy of both particles back to the universe, in effect the black hole has to use its own mass-energy to make up the difference.

 

And the universe is not regulated like banks, it will lend to anybody, but HUP constrains the length of the mortgage.

 

If I remember correctly AJB, Hawking's original argument involved black hole entropy, which then implies a temperature and susequent black body radiation, or am I mistaken ?

[RichIsnang]

Yeah I got you, sorry I wasn't very clear in my post. What I meant is that the universe wouldn't lend you the particles in the first place because it would know that you won't be able to pay them back

[Delta1212]

Yeah I got you, sorry I wasn't very clear in my post. What I meant is that the universe wouldn't lend you the particles in the first place because it would know that you won't be able to pay them back

Except that the black hole does have enough money to pay back the loan, it just needs to be taken out of its savings instead of out of the loan. The universe doesn't really care how it gets paid back as long as it can balance the books at the end of the day.

[RichIsnang]

How does the black hole have enough money to pay back the loan? All it's savings are in a gravitational well so how can it just give some of that up?

[Alan McDougall]

You misunderstood the analogy. If the black hole eats one of the particles it still owes the energy of both particles back to the universe, in effect the black hole has to use its own mass-energy to make up the difference.

 

And the universe is not regulated like banks, it will lend to anybody, but HUP constrains the length of the mortgage.

 

If I remember correctly AJB, Hawking's original argument involved black hole entropy, which then implies a temperature and susequent black body radiation, or am I mistaken ?

 

Hawking postulated that information was being lost from the universe via Black Hole evaporation of some sort. This brought a Lot of the scientific community against him , because a fundamental of the universe is that energy cannot be lost it just goes elsewhere. Sorry a criminal simplification by me!

 

He changed this theory later to keep it within the laws of psychics and added to his theory that the information in reality was not being lost, just transferred out of our universe into another universe via again Black Holes. A bit silly in my opinion from a great physicist

[derek w]

Does the the energy for Hawkin's radiation come from the matter that is being pulled into the black hole by gravity?

Would the centre of a black hole be at absolute zero,because all the energy gets radiated out?

[MigL]

Conservation of information is a Quantum Mechanical concept.

Black holes are a General Relativistic phenomena.

 

Hawking radiation is a crude marriage of the two and may not account for all possible effects

A quantum Gravity theory is needed.

 

A black hole still has mass-energy which it can use to repay the 'loan', along with charge and angular momentum. And of course for Hawking Radiation to be possible, it also has to have temperature and entropy.

 

 

[Alan McDougall]

Conservation of information is a Quantum Mechanical concept.

Black holes are a General Relativistic phenomena.

 

Hawking radiation is a crude marriage of the two and may not account for all possible effects

A quantum Gravity theory is needed.

 

A black hole still has mass-energy which it can use to repay the 'loan', along with charge and angular momentum. And of course for Hawking Radiation to be possible, it also has to have temperature and entropy.

 

 

 

Nevertheless Hawking said at a recent conference that information is leaking from our universe into others via, his rabbit hole (Black Hole) He proposes this to keep his theories going

[ACG52]

We get very little in the way of detail from SH nowadays. And what we do hear from him sounds more and more speculative.

 

 

[ajb]

If I remember correctly AJB, Hawking's original argument involved black hole entropy, which then implies a temperature and susequent black body radiation, or am I mistaken ?

 

That is one way to get at the temperature. I am sure a derivation along these lines has been posted on this forum.

 

The issue here is that the microscopic degrees of freedom are not explored at all. In fact, this is quiet a difficult problem. String theory gives a candidate for these degrees of freedom and allows a statistical mechanics calculation.

[Alan McDougall]

That is one way to get at the temperature. I am sure a derivation along these lines has been posted on this forum.

 

The issue here is that the microscopic degrees of freedom are not explored at all. In fact, this is quiet a difficult problem. String theory gives a candidate for these degrees of freedom and allows a statistical mechanics calculation.

 

They tell us if we ever get to understand string theory and its proves factual, this will simplify astrophysics to a very great degree and maybe lead to the illusive "Theory of Everything"

 

Ed Witten is the main proponent of this theory , the very best scientific minds have difficulty understanding it. I am not one of them just an interested bystander

[MigL]

Don't remember if it was Hawking or his student Berkenstein ( sp? ) who first noticed the similarity between the increase of the event horizon and the increase in entropy, but the other then did a detailed calculation based on deg. of freedom to obtain entropy.

 

I was under the impression that Hawking had postulated that information is also conserved on the event horizon along with other quantities which have to abide by conservation laws.

[ajb]

Don't remember if it was Hawking or his student Berkenstein ( sp? ) who first noticed the similarity between the increase of the event horizon and the increase in entropy, but the other then did a detailed calculation based on deg. of freedom to obtain entropy.

 

Berkenstein's supervisor was John Wheeler. But yes, Berkenstein was the first to take the seeming analogy between event horizons and entropy seriously. He came up with a generalised form of the second law.

 

This was a thermodynamics based calculation and not a statistical physics one. The distinction is important as thermodynamics treats the macroscopic properties in bulk, as where statistical physics links the microscopic degrees of freedom with the macroscopic properties.

[RichIsnang]

Steven hawking proposes that information leaks into other universes? Shouldn't we be able to detect some leakage into our universe then?

Edited August 25, 2012 by RichIsnang

[Alan McDougall]

Steven hawking proposes that information leaks into other universes? Shouldn't we be able to detect some leakage into our universe then?

 

Very interesting question that leads to the possibilties of an infinite multiverse containing within it an infinity of universes, existing enternally, but always changing in great cycles of creation and destruction.