Re: In 1911, EInstein thought that photons had mass. Still in use 123 years after,

They deal with this aspect, after decades of thinking about mass
increasing with speed, in this way:
1. Relativist gave up, most of them in the last 25 years, the idea of
mass being a function of speed v. They now considered (most ones) that
MASS IS INVARIANT.
2. They transferred the gain in KE to a pure energy gained by the
accelerated particle. So, the energy gain is STORED into the air,
because mass is not affected. M = Mo, whichever v is.
The solution is to accept widely that the KE of a moving particle is KE
= (Y-1)Moc^2. where Mo is the mass at rest.
Of course, don't try to question this formula and ask WHERE the extra KE
is stored
There is no difference of this formula with the Newtonian KE = 1/2 Mv^2,
except that the extra KE is stored in the ELECTROMAGNETIC FIELD, given
by (Y-1)c^2 instead of 1/2v^2.
Mysteries of relativity (pseudoscience).
Don't forget that the above is calculated only for CHARGED PARTICLES,
but the influence of electromagnetism is WIDELY IGNORED. Prove that with
a grain of sand or a neutron.