B Can I get clarification on the constant speed of light

[Orodruin]

Well, isn’t “light” the plural of “photon”?

No.

I have seen many discussions about double-slit experiments where it is claimed that “one photon at a time” still creates the fringe patterns, etc.

These discussions are usually very heuristic.

So it appears to be an empirical fact that one photon at a time can exist and be tested.

Truth with modification that needs qualifications and should not be taken too litterally.

It just seems to me that referring to a single photon’s behavior when explaining things would significantly reduce the confusion.

Certainly not. You cannot discuss photons properly without discussing QFT and quantification of gauge fields. Photons are among the most complicated objects in QFT and I suggest taking any heuristic discussion speaking about single photons with a huge grain of salt unless you understand the underlying theory properly.

 

[exmarine]

Quote: Oroduin, post #51

Would you care to explain your answers a bit more?

So light is not comprised of photons?

They have not done double-slit experiments “one photon at a time”? Or they have, but…. what?

As for studying QFT, I can do the math in Feynman’s All Paths version for a photon. Is that what you mean, or something else? Yes a photon is a complicated deal, but I don’t see why one can’t study, and measure – at least in theory, the speed of a single one. It covered some distance and took some component time, so…

Thanks.

 

[PeterDonis]

So light is not comprised of photons?

Not in the sense you are using the term "photon". Light is not comprised of little massless point particles moving at $c$.

They have not done double-slit experiments “one photon at a time”?

That's how it is often described in pop science articles, but it's not a good description of the actual physics involved.

As for studying QFT, I can do the math in Feynman’s All Paths version for a photon.

You may think that's what you're doing, but it isn't.

I don’t see why one can’t study, and measure – at least in theory, the speed of a single one.

Look up "Newton-Wigner localization" and how it does not work for massless quantum fields.

 

[PeterDonis]

Yes a photon is a complicated deal

If you want an entertaining introduction to the complications, try John Baez's "Photons, Schmotons" series:

http://math.ucr.edu/home/baez/photon/schmoton.htm