The nice thing about real electrons is that those bound in atoms and those flying through space in an x-ray tube all have the same mass, etc.
Also, real photons, which have zero rest mass, are condemned to fly always at the speed of light in vacuo.
Mass is difficult.
The free photon is the fundamental particle, & it annihilates aether, therefore it has mass (& momentum, & energy).
That
ELEKTRONS have the same charge as (free) electrons (& protons, but opposite) is a mystery.
I don’t think that we know for sure that canal ray electrons have the same mass as
ELEKTRONS (praps they do) – if they do then that is a mystery.
I reckon that neutrinos (each being a pair of photons) must have twice the mass of photons – but that would require that every photon has the same mass as every other photon (praps they do)(another mystery).
But i don’t know what to think about rest mass (in general), especially for a photon that is never at rest, a photon is always propagating at the speed of light.
And then we have radio waves (em radiation) – radio waves too must have mass (koz em radiation too annihilates aether)(& em radiation too propagates at the speed of light they say).
But, i already said that em radiation duznt kum in quanta – hence how can em radiation have mass? A continuum (like Einstein's continuums) can't have mass. Or can it. It’s a mystery.
Actually there is no such thing as em radiation. What we have is electric radiation, ie the charge field. And the movement or praps the acceleration of that field manifests as a magnetic field. The charge/electric field is primary.
So, i should have said that the charge field has mass – the magnetic field (a secondary field) is unlikely to contribute any extra mass.
But most of that is theory – until one day when we get empirical info.
Mass is difficult.
Just realized. Photons never propagate at the speed of light in vacuo, koz there is no such thing as vacuo.
Einstein said that light is slower when near mass, & everywhere in our infinite eternal universe is near mass.
Hence c km/s is an ideal that is never attained.
So, strictly speaking it is ok to talk of the speed of light, but it is not ok to invoke c anywhere at any time.
What we need to use is c', which is a little slower than c, when near mass (ie all the time, everywhere).
And, when light is inside say air or water or glass, that there c' bekums c", which is slower than c'.
c & c' & c" are all speeds of light, & c is the impossible speed.
In fact c' & c" are the same thing, the same effect, both are due to being near mass, except that c" is so close that it is actually inside mass (completely surrounded).
And, c & c' & c" are the speed in the aether, ie relative to the aether.
Hence if the observer feels an aetherwind of V then the observer can expect the speed of light to appear to be say c"+ V or c" – V.
And, the above considerations must apply to the speed of radio between antennas.