Why photons can't go any slower than the speed of light?

[Dale]

I don't see what acceleration of the field has to do with how fast its change will be felt at some distance away from it.

Then maybe you should study more and argue less.

The speed of propagation of the change is either always c or always instantaneous, regardless of the speed or acceleration of the field itself.

Yes, but that isn't what the paper you cited showed. The paper you cited was showing the aberration of forces, not the propagation of changes in the field (despite some confusion on the part of the authors - which is probably why the paper didn't pass peer review).

It is well known that the free propagation speed of changes in the EM fields is c. It is also well known that there is no aberration in the forces from a uniformly moving charge. Please study the lecture below and ask questions.

http://www.mathpages.com/home/kmath562/kmath562.htm

 

[Doc Al]

Here's another treatment of that standard result for a uniformly moving charge: http://farside.ph.utexas.edu/teaching/em/lectures/node125.html

"Note that E acts in line with the point which the charge occupies at the instant of measurement, despite the fact that, owing to the finite speed of propagation of all physical effects, the behaviour of the charge during a finite period before that instant can no longer affect the measurement."​

 

[KatamariDamacy]

The assumption that two charges can travel at c is wrong. If you allow that assumption then you get a contradiction, which is one way of proving that an assumption is false.

There is no any mass in those equations, charge is not implied, only fields. Just like you said Maxwell's equations permit fields without charges, so Coulomb and Lorentz force equations must too. In this thread here:
https://www.physicsforums.com/showthread.php?t=765250

...jtbell explained EM wave and he mentioned not only one negative charge, but also the second positive charge, and even referred to Lorentz force equation: F= qv x B. You said it makes sense, and I passionately agree.

Yes. Both the weird coincidence and the reason that it has no practical implication in reality are explained by relativity.

How is such peculiar coincidence explained by relativity, what explanation is that?

 

[KatamariDamacy]

Yes, but that isn't what the paper you cited showed.

I believe the paper showed experimental results match both equations that assume instantaneous change propagation and relativistic equations. They only attack Feyman's explanation of that paradox.

The paper you cited was showing the aberration of forces, not the propagation of changes in the field (despite some confusion on the part of the authors - which is probably why the paper didn't pass peer review).

Why do you think the paper didn't pass peer review, or that they themselves are not peer review institution? The paper is given in Wikipedia for reference to this article about Coulomb's law, if that means anything:

http://en.wikipedia.org/wiki/Coulomb's_law

 

[Dale]

Since you continue to argue and spout misinformation rather than learn, this thread is closed. If you choose to start a new thread, I hope it is with the intention of learning.

There is no any mass in those equations, charge is not implied

Since the equations are calculating the force on a charge, clearly charge is implied.

Maxwell's equations permit fields without charges, so Coulomb and Lorentz force equations must too

No. If you take Maxwell's equations and set q and j to zero then you get some non-trivial solutions. If you take Coulomb's law and the Lorentz force equation and set q to zero then you have only the trivial solution. You cannot blindly take statements made about one set of equations and apply them to other sets of equations. You must actually do the math and see what it says.

How is such peculiar coincidence explained by relativity, what explanation is that?

Read the links I provided earlier, particularly the "Purcell Simplified" link. If you have questions after studying those links then come back and ask your questions. We are glad to help people learn, but don't tolerate people arguing for things that are incorrect as though they were fact.