I thought charge only existed when mass was present. Does this mean String Theory hypothesizes photons having charge?
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3Photons aren't charged? – BioPhysicist Nov 26 '18 at 14:51
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1Possible duplicate of Massless charged particles – AccidentalFourierTransform Nov 26 '18 at 14:55
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3Quanta of electric field $\neq$ quanta of charge. In other words, electrons $\neq$ photons. – probably_someone Nov 26 '18 at 14:57
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@AaronStevens I do not understand how something that is not charged can exist in electromagnetism. What are the photons responsible for? – Sam B Tz Nov 26 '18 at 14:57
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@probably_someone I thought photons were the quanta of electric fields, meaning electrons always emit them? – Sam B Tz Nov 26 '18 at 15:00
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1Photons aren't charged, and mass is not necessary for charge to exist. – Javier Nov 26 '18 at 15:05
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@Javier So how do two charges repel? How are the photons interacting? – Sam B Tz Nov 26 '18 at 15:07
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3On a microscopic level, two charges repel because one charge receives the momentum from photons that the other charge emits, and vice versa. The photons themselves do not interact with each other at all. – probably_someone Nov 26 '18 at 15:09
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I thought charge only existed when mass was present.
Forgive my presumption, but I would guess that you are thinking in classical terms, in that "something real" has to exist, in order for the electrical charge associated with it to accumulate upon it. But the elementary particles cannot, in any way, be considered as (very) shrunken versions of classical objects that we deal with in "ordinary/classical" electromagnetism.
If you look at the Photoelectric Effect experiments, you will see that electrons can be ejected from a metal surface simply by shining light (massless photons) upon it, so it is better to think of the transfer of momentum in this case, as well in the case in your question.
How we reconcile the idea of a massless particle as being capable of imparting momentum is pretty well explained in this article Photons & Momentum.
Does this mean String Theory hypothesizes photons having charge?
String theory has not met the predictive or experimental standards of other branches of physics, I'm amazed at how seriously it's taken. If you posted a question putting forward the same ideas as string theory as your own personal hypothesis, it would not be given 5 minutes on this site. Read Penrose, Veltmann, Woit, Smolin and many others on the issues surrounding it.
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Indeed there are no examples of massless charged particles. I am not aware of any underlying reason for this. Nevertheless it is not an argument that photon must have mass, since photons have no charge.
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