Is there such thing as an anti-photon?

Is there such a thing as an anti-photon? and if it did exist what would happen if it collided with a normal photon?
 

tom.stoer

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Photon and anti-photon are identical.
 

Drakkith

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A photon is it's own antiparticle.
 
there is no anti photon ..... some how if there is an anti photon and if they collide they end up in an explosion
 

DrChinese

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there is no anti photon ..... some how if there is an anti photon and if they collide they end up in an explosion
Welcome to PhysicsForums, space girl!

You may be thinking of the proton and the anti-proton, which release a lot of energy when they meet. Photons are different particles altogether, and do not act the same.

I might suggest reading up on what is called the "Standard Model of Physics" to gain a bit more understanding on the subject.
 
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When two photons cross each other (for example when shining two beams of light across each other) is there a noticeable difference between annihilation-creation and just passing through each other?

EDIT: Hm, on second thought this might be off-topic of me? I'm not sure? Please tell me if it is, didn't intend it
 
No I was not confusing photons with protons. Because I know that when a particle and an anti-particle collide (such as a proton and anti-proton) the immediately turn into energy such as photons and gamma radiation. And if photons are created during the collision then what would happen if they had a anti-particle collision.

Thank you for your responses. :)
 

cmb

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A photon is it's own antiparticle.
That would have been my stock answer.. but, hang on a minute...

At the quantum level, if we have two photons in anti-phase, each still has hv worth of energy. One cannot have '-hv' of energy!

So if the two are actually anti-particles, then where does the 2hv of energy go?
 

DrChinese

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No I was not confusing photons with protons. Because I know that when a particle and an anti-particle collide (such as a proton and anti-proton) the immediately turn into energy such as photons and gamma radiation. And if photons are created during the collision then what would happen if they had a anti-particle collision.
Photons do not annihilate in the same manner, as you say they are in fact a byproduct of other interactions. Photons (and "anti-photons") obey Bose-Einstein statistics, and can occupy the same region of space without issue.
 

tom.stoer

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At the quantum level, if we have two photons ... each still has hv worth of energy. One cannot have '-hv' of energy!
Antiparticles do not have negative energy.

This perception is perhaps based on some formal arguments introduced by Dirac regarding the "negative-energy-solutions" of his famous equation. Look at positrons (antiparticles of electrons) in bubble chambers: they have positive mass, energy and momentum.
 

cmb

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Antiparticles do not have negative energy.

This perception is perhaps based on some formal arguments introduced by Dirac regarding the "negative-energy-solutions" of his famous equation. Look at positrons (antiparticles of electrons) in bubble chambers: they have positive mass, energy and momentum.
Exactly, but what happens to the energy of two photons, if they act as each others anti-particles and 'annihilate'?
 

tom.stoer

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Two photons don't annihilate "to energy" b/c they carry energy which is conserved.

When two photons collide to lowest order NOTHING happens; they don't interact at all. In next-to-leading order they scatter elastically, i.e. two new photons are created. In addition there are processes (starting at a certain threshold) where other particles like electrons can be created.
 

PAllen

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Exactly, but what happens to the energy of two photons, if they act as each others anti-particles and 'annihilate'?
Two photons in, two photons out. It is called photon scattering, a rare process that needs to be mediated by virtual charged particles (e.g. charged vector boson or quark).
 

cmb

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So, what happens to the energy of the photons during destructive electromagnetic interference?
 
From my understanding is that nothing will happen.
 

jtbell

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So, what happens to the energy of the photons during destructive electromagnetic interference?
The photons are not destroyed. They're simply distributed differently than they would have been in the absence of interference.
 

tom.stoer

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Destructive interference does not mean that the photons will vanish completely, it does only mean that it's not allowed for the two photons to be detected at a certain location (they can of course be detected elsewhere).
 

cmb

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OK, so back to my question on 'does that mean negative energy'; if we go to a location where we measure destructive interference of the two photons in that location, then what energies do we measure there?
 

tom.stoer

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Zero energy.

A detector which "sees" destructive interference in a certain place sees nothing and cannot distinguish this "nothing due to destructive interference" from "no photon at all".
 

cmb

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So is there no energy there, or is it just this type of detector that cannot detect it.

And if not, then what sort of theoretical detector could detect the energy of the two anti-phase photons at the moment of their intersection? I mean, if we had an infinitesimal electromagnetic detector, then it'd be registering 'no energy' there, right?, but we're saying there is actually 2hv there, because they head off after their encounter?

So if an EM type detector could not detect the extant energy of two anti-phase photons at the moment of their intersection, then what sort of detector can?
 

ZapperZ

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This thread has gone completely off-topic.

Zz.
 

cmb

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This thread has gone completely off-topic.

Zz.
Please explain?

A particle and its anti-particle are a pair that annihilate. The question is therefore whether a photon and anti-phase photon can truly and instantaneously 'annihilate' and the energy then 'reappears' (as two 'more' photons, presumably?!!), or whether there is no process of annihilation and actually their presence, in proximity to each other, is simply undetectable.

So please explain why you think it is off topic? What do you understand by an 'anti-particle'?
 

PAllen

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Please explain?

A particle and its anti-particle are a pair that annihilate. The question is therefore whether a photon and anti-phase photon can truly and instantaneously 'annihilate' and the energy then 'reappears' (as two 'more' photons, presumably?!!), or whether there is no process of annihilation and actually their presence, in proximity to each other, is simply undetectable.

So please explain why you think it is off topic? What do you understand by an 'anti-particle'?
My understanding of the quantum basis of interference is simply a consequence of the probability of finding a photon (or other particle - interference in waves of cold atoms was a classic 20th century experiment) at a certain place. Where there is destructive interference, there is simply zero or near zero probability of finding a photon (or atom) at that location. Within the framework of quantum mechanics, it is no more mysterious than all those orbital shape diagrams showing where electrons are more vs. less likely to be found.

As I explained in another post, there is a phenomenon of photon-photon scattering that you could conceivably think of as photon annihilation. Normally it is treated simply as scattering, and it is very rare even for gamma rays because of the need for mediation by massive virtual charged particles. I am not even sure it has actually been observed yet.
 

ZapperZ

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Please explain?

A particle and its anti-particle are a pair that annihilate. The question is therefore whether a photon and anti-phase photon can truly and instantaneously 'annihilate' and the energy then 'reappears' (as two 'more' photons, presumably?!!), or whether there is no process of annihilation and actually their presence, in proximity to each other, is simply undetectable.

So please explain why you think it is off topic? What do you understand by an 'anti-particle'?
The thread has gone into the question of destructive interference. This has nothing to do with photon and its antiparticle.

Read the OP. The question has been answered within the first few posts. But somehow, it has now gone into the question of energy conservation in a destructive interference. A search of the forums will reveal that this issue has been dealt with several times.

Zz.
 

cmb

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The thread has gone into the question of destructive interference. This has nothing to do with photon and its antiparticle.
The issue I asked/raised was whether a photon and a photon out of phase to it are each other's anti-particle - or, implicitly, if not then what 'sort' of photon is an 'anti-photon'?

It seems to me that you are drifting the thread with an unneccesary criticism, seeing as PAllen has just now provided a useful and seemingly complete response that has 'squared the circle' in regards what can happen when photons meet. (Thanks, PA, that hits the spot for me.) I don't understand what you think your additional post has added.
 

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