Virtual photon-antiphoton pairs?

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In summary: They would both be annihilated in the end.In summary, virtual particles are created when virtual photons and antiphotons collide. They can disappear again, or be absorbed by other particles. They don't have any real existence, and real photons don't experience time the way we do.
  • #1
johne1618
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I have heard of the phenomenon of virtual particle-antiparticle pairs popping out of the vacuum and then back into it within a time [itex]\Delta t \approx \hbar / \Delta E[/itex].

Do virtual photon-antiphoton pairs pop out of the vacuum in a similar way?

I understand that antiphotons are the "same" as photons - is that right?

In that case how would the two photons annihilate? Does one have positive energy and the other negative energy?

John
 
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  • #2
No, not at all. When we say that a photon and an anti-photon are the same, we really mean it. There is no such thing as an anti-photon, because if you apply the transformations on it that would in other particles yield their counterparts, you get exactly the same you started with.

What is to say, an anti-photon is just a regular photon like any other. They wouldn't annihilate, they would just interfere with each other and then go on their ways.

And if you do assume they annihilate... annihilation produces only more photons. So you would have two photons colliding, which would produce two more photons that would just go their merry way, without minding each other too much.
 
  • #3
There are no anti-photons. All photons have positive energy.

Two photons can not annihilate without creating a new particle/antiparticle pair, because of the conservation of energy.

If they have enough energy (more than 1.022 GeV in total), they can annihilate and create an electron-positron pair. If they have more energy they could also create other particles.

The electron is the lightest (=least energy) massive particle, so that is the first process that can happen.
 
  • #4
M Quack said:
If they have enough energy (more than 1.022 GeV in total), they can annihilate and create an electron-positron pair.

Wait, I didn't know that. So all annihilation processes can be time-reversed?
 
  • #5
Yes. It is one of the main mechanisms of how very hard gamma rays get absorbed - the second photon is usually a virtual photon of the electric field near a nucleus.

Look up "pair production" (Wiki entry is wrong because it give the impression that this can happen with a single photon)

http://www.icecube.wisc.edu/~tmontaruli/801/lect9.pdf
 
  • #6
Interesting. But I think it's misleading of you, or it may cause some confusion, to say that they 'annihilate' because, at least as far as I know, the concept is linked to the idea of a particle/anti-particle pair generating energy when in contact, and not the other way around :P
 
  • #7
Well, after the process you don't have any photons any more... Can you suggest a better word?

As far as "generating energy" goes, rest mass may be converted into energy (or the other way around). There is no energy generated in the strict sense. Total energy and momentum are conserved, along with charge, etc.
 
  • #8
True enough, I suppose.
 
  • #9
Coming back to the original question:

Yes, a pair of virtual photons can pop into existence for a short time and then disappear again. This can happen in vacuum and has even been measured in the Casimir effect.

http://en.wikipedia.org/wiki/Casimir_effect
 
  • #10
Here we go again.

There are at least three threads here where the argument that "Casmir proves virtual photons" is rebutted. One can calculate the Casimir effect without invoking virtual particles at all; therefore one cannot logically say it tells you anything about them.
 
  • #11
M Quack said:
If they have enough energy (more than 1.022 GeV in total), they can annihilate and create an electron-positron pair.
I wouldn't call that annihilation, though. They get absorbed by the created particles. In annihilation process, you are typically looking at a single world line that does a U-turn.

And yes, there has to be a virtual photon involved. Two light-cone photons aren't going to just interact in empty space to give you particle-anti-particle pairs.
 
  • #12
Vanadium 50 said:
Here we go again.

There are at least three threads here where the argument that "Casmir proves virtual photons" is rebutted. One can calculate the Casimir effect without invoking virtual particles at all; therefore one cannot logically say it tells you anything about them.

I'll leave that discussion to the experts then.

Can you give a better example/proof of virtual particles from vacuum fluctuations?

The Cotton-Mouton effect has not yet been observed in vacuum, I believe. And I am not sure if it would prove the eistence of virtual particles from vacuum. But then again I am not an expert, as you already know.
 
  • #13
If you want to discuss that, I suggest you continue on one of the Casimir threads.
 
  • #14
K^2 said:
I wouldn't call that annihilation, though. They get absorbed by the created particles. In annihilation process, you are typically looking at a single world line that does a U-turn.

And yes, there has to be a virtual photon involved. Two light-cone photons aren't going to just interact in empty space to give you particle-anti-particle pairs.

So there are no "real" antiphotons. Real photons travel on light-cones and don't "experience" time. Therefore there can't be any negative-energy photons traveling backwards in time to act like "real" antiphotons.

But if a photon is virtual then it can travel on a path off a light-cone.

If a negative-energy virtual photon travels on the time-reversed path would it then be a virtual antiphoton?

If virtual antiphotons can exist could virtual photon-antiphoton pairs be created from the vacuum?

I presume that at the edge of a black hole the gravitational field is strong enough to prevent the virtual photon-antiphoton pairs from annihilating so that one "real" photon can escape as Hawking radiation while the other "real" photon falls down the black hole.

Most elementary discussions of Hawking radiation describe particle-antiparticle pairs being pulled apart by the gravitational field. But the wavelength of Hawking radiation is of the same size as the black hole itself so it has to be of the form of photons and not massive particle/antiparticles like electron/positrons.
 
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  • #15
Vanadium 50 said:
Here we go again.

There are at least three threads here where the argument that "Casmir proves virtual photons" is rebutted. One can calculate the Casimir effect without invoking virtual particles at all; therefore one cannot logically say it tells you anything about them.

The Casimir effect can conveniently be calclulated using the concept of "virtual photons". I am not surprised that there are other formulations. I can also do quantum mechanics without using imaginary numbers. Nevertheless they are a useful concept, not more and not less.
 
  • #16
This particle-anti-particle concept has less to do with particles traveling backwards in time (a lousy trick of Feynman to draw funny pictures) but with the concept of charge. Photons don't carry charge, so they can can pop out in any reaction in any amount. You don't need to create them together with a particle carrying opposite charge.
 
  • #17
Do virtual particles and antiparticles annihilate because their wavefunctions are mirrors of each other in every respect and therefore exactly cancel?

If an electron/positron pair pops out of the vacuum I guess they have opposite spin as well as opposite charge.

If one of the spins was altered somehow would that stop them annihilating completely if they collided?
 

1. What are virtual photon-antiphoton pairs?

Virtual photon-antiphoton pairs are a type of quantum fluctuation that can occur in a vacuum. They are created from the energy of the vacuum and exist for a very short period of time before annihilating each other.

2. How are virtual photon-antiphoton pairs different from real photon-antiphoton pairs?

Virtual photon-antiphoton pairs are different from real photon-antiphoton pairs because they are not directly observable. They only exist as a mathematical concept and cannot be detected or measured with current technology.

3. What is the significance of virtual photon-antiphoton pairs in quantum field theory?

Virtual photon-antiphoton pairs are important in quantum field theory because they play a role in the calculation of certain physical quantities, such as the vacuum energy and the strength of the electromagnetic force. They also help explain the behavior of particles and their interactions at a quantum level.

4. Can virtual photon-antiphoton pairs be created in a laboratory?

No, virtual photon-antiphoton pairs cannot be created in a laboratory. They are a natural occurrence in a vacuum and require extremely high energy levels to be created. However, scientists have been able to indirectly observe their effects in experiments.

5. What are some potential practical applications of virtual photon-antiphoton pairs?

Currently, there are no known practical applications of virtual photon-antiphoton pairs. However, further research and understanding of their properties could potentially lead to advancements in technology, such as improved quantum computing or energy generation.

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