Technically everything moves at c (the speed of light) through spacetime, all the time. Most objects that have mass spend the majority of their motion in the time part, and thus move relatively slowly in space. If an object moves fast in space (where fast is a significant fraction of c) then it moves noticeably slower in time because the total spacetime vector value is always c.
Photons, being massless, do not move through time at all, and move through space at c.
That’ll break a few brains. To elaborate with an example: From the perspective of a photon, it’s “life” is over as soon as it begins. Even though it takes about 8 mins for a photon to travel from the sun to the earth from our perspective, no time at all has passed for it.
I’m reasonably sure that Einstein’s breakthrough was more that he assumed light only travels at the speed of light and the all the equations worked.
Every experiment since has confirmed it.
Technically everything moves at c (the speed of light) through spacetime, all the time. Most objects that have mass spend the majority of their motion in the time part, and thus move relatively slowly in space. If an object moves fast in space (where fast is a significant fraction of c) then it moves noticeably slower in time because the total spacetime vector value is always c.
Photons, being massless, do not move through time at all, and move through space at c.
To add to this, this is always relative to an observer. If an object moves fast in space compared to you then it moves slower in time compared to you.
That’ll break a few brains. To elaborate with an example: From the perspective of a photon, it’s “life” is over as soon as it begins. Even though it takes about 8 mins for a photon to travel from the sun to the earth from our perspective, no time at all has passed for it.
(Correct me if I misspoke.)
Any speed that light travels is the speed of light
The real breakthrough
The other way around. Experiments said that light always moves at C and he deduced what follows from that for space time.