Build Your Own Time Machine

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).

When the speed of light was fixed, measurements that had previously been constant—an object’s mass, its size, and even the passage of time it experienced—became variable.

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.

From this simple idea would come Einstein’s masterpiece, general relativity. This builds on the concept of special relativity to take in the real world where we aren’t restricted to steady motion, and acceleration and gravity play their part. But general relativity is much more than an enhanced version of the laws of motion. It describes the behavi

On the Electrodynamics of Moving Bodies

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.

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.

It all comes down to the relativity of simultaneity.

Two absolute essentials of real time travel are the linkage of space and time, and the influence of gravity on the space-time continuum.

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