# What happens when a photon meets a virtual photon of the same wavelength?

## Main Question or Discussion Point

As I understand it, photons are their own anti-particle, and at all points in space there are a lot of virtual particle-antiparticle pairs being created and annhilated (perhaps infinite?), so it would seem to me that on it's journey from point A to point B that there is at least some likeliehood that a photon might meet one of the virtual photons of the same wavelength, having been just created in a virtual phton-pair, and anhilate itself, freeing the virtual photon that was created in the 'pair' to become 'real' and no longer virtual, hellbent on it's own destruction. If I am wrong please correct me. But if this is the case, what is the probability of this occuring over a given distance in the travel of a photon, and will the virtual photon that is set free by this continue the original path and have the same polarization, etc., of the photon that interfered with the 'virtual pair'?

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Staff Emeritus
2019 Award
Virtual photons are not real, they don't have positions and they don't have wavelengths. Even real photons don't anihilate other photons when they meet.

Virtual photons are not real.
Thus, they should never be discussed. Ever.
After all, they're not real.

Bill_K
Even real photons don't anihilate other photons when they meet.
No I disagree, V50. When an electron and positron annihilate they produce two photons. In the time-reversal of this process, two photons annihilate to form an electron-positron pair. If one process can occur the other can also.

Staff Emeritus
2019 Award
Yes, but the interaction rate is highly suppressed. It's not what people think of when they think "matter-antimatter annihilation". The answer to the question "what happens when two photons meet" is, >99.99% of the time, "nothing".

I think the existence claim either way is for all intent and purposes a theory independent assertion. The theory just calculates, and does not care what is real or not. Claims of what elements of the theory that are not directly observed, only inferred, and you endow with ontological status one way or the other is pure interpretation, not theory.

Even the macroscopic objects we interact with require interpretation to endow with an ontological status. Even if we agree that they are ontologically real it still fails to dispel disagreements on the ontological status. For instance, are such ontologically real objects nouns or verbs?

Not a single interpretations, including the Copenhagen Interpretation, is required for QM to work just fine.

Doesn't interact 99.9% of the time or even 99.9999999% of the time, in a journey across the universe this leaves a huge number of possible interactions that 'something happens'. And recently the dynamic Casimir effect was demonstrated with a 'mirror' moving at about 5% the speed of light. But if there is an issue with this being a photon, then choose any other long lived particle that is flying through space at or near relativistic velocities.

Drakkith
Staff Emeritus
Doesn't interact 99.9% of the time or even 99.9999999% of the time, in a journey across the universe this leaves a huge number of possible interactions that 'something happens'. And recently the dynamic Casimir effect was demonstrated with a 'mirror' moving at about 5% the speed of light. But if there is an issue with this being a photon, then choose any other long lived particle that is flying through space at or near relativistic velocities.
Photons are not like massive particles. Such particles WILL interact in some way with nearby particles. I think V50 is saying that while photons of a certain energy can interact and produce particles, the vast majority of photons in the universe are far far below this threshold and will have effectively no interaction with each other.

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Ok, my friend, You can think whatever you want. Limitations are:
1. If you create a close system (box) around whatever you are saying means close system.
2. The energy of this close system never change, now you can predict any funny photon, electron, you wish.
3. If energy of this close box changed, you are doing it wrong (not science) otherwise, you are right.
4. If you changed energy of close box (system), you are God or it's not science or better you redo it.

Drakkith
Staff Emeritus
Energydady, I cannot see how your post is in any way contributing to this thread. Are you sure you are in the correct thread?

Your premise for points 2 thru 4 hinge on point #1. The Universe is a closed system. Has anyone ever proven irrefutably that the universe is a closed system? If so I would like to see it. If not points 2 thru 4 are irrelevant. Is there even an actual 'definition' as to 'what' the 'universe' really is?

But I think everyone is straying away from my original question. In accordance with contemporary theory, a particle may come into existence 'momentarily', borrowing energy from the vacuum. If we assume for argument sake that this indeed may occur, then my question remains unanswered.

And if the photon thing is an issue, please feel free to substitute another particle that you are more comfortable with. Proton? Electron? Neutrino?

Drakkith
Staff Emeritus
IF virtual particles exist, then there is still no interaction between the photon and virtual photon.

Yes, but the interaction rate is highly suppressed. It's not what people think of when they think "matter-antimatter annihilation". The answer to the question "what happens when two photons meet" is, >99.99% of the time, "nothing".
Well, it may happen a lot more than you think in our universe. It depends on the environment of the photons. $$\gamma \gamma \rightarrow M^{+}M^{-}$$ is a very valid solutions for photons which are concerned with high energy physics. Still while photons have no interactive forces, there is still the question of some kind of ''concentration'' or ''binding'' of photon energy to produce these new particles.

Drakkith
Staff Emeritus