Build Your Own Time Machine

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.

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.

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

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

Anything moving at near the speed of light, Einstein realized, would experience phenomena totally different from the everyday.

Einstein took literally the idea of the older German physicist Max Planck that light could be treated as if it came in little packets.

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).

However, most of the real mechanisms for time travel will involve moving spatially as well, reflecting the way that time and space are inextricably linked in the four-dimensional matrix of space-time.