And because there is no special frame of reference, the view of the observer on the moving train is as valid as the view of the observer who isn’t moving. Either two events can be simultaneous, or one can come after the other, depending on how you are moving.

The light speed barrier is a kind of discontinuity in reality—we can’t assume that things will continue in a steady fashion after passing through it (if that were possible).

On the Electrodynamics of Moving Bodies

Since 1895, when Wells published his book, science has moved on with frightening speed. And that progress has included the theories that makes time travel possible in principle.

But Wells transformed it into science fiction (even though that term was yet to be invented), a fictional concept of practical, solid achievement, opening up speculation about how time travel might be achieved and what the implications of traveling back to the Crucifixion, or visiting the far distant future of humanity, might be.

However, we can’t dismiss that “glittering metal framework,” as the time machine is first described in the 1895 novel—it is hugely significant. Although traveling in time was not a new idea even then, fictional time travel before that book had relied on dreams or magic

Special relativity provides a double opportunity for time travel. If you travel at a sizable fraction of the speed of light, time for you slows with respect to the outside world. In effect, you move forward in time. And if you can travel faster than light, you will have a means to move backward in time.

All movement has to be relative to something, and when Einstein was floating along with the sunbeam, it was not moving with respect to him.

This different way of looking at light not only explained the photoelectric effect, but also provided the foundations of quantum theory.