Imagine that the ability to time travel to the past is eventually possible. Some future generation manages to travel back in time hundreds or thousands or tens of thousands of years. They don’t just travel back in time to observe events. They actually intervene in events.

This is known as Intervention Theory, and I just found out about it through a book called Intervention by Alan Butler. 

But there are rules with time travel. The classic example is illustrated with the grandfather paradox. Suppose you are able to go back in time and you kill your grandfather as a young boy. This means your father was never born, which means you were never born. But if that’s the case, how did you exist to go back in time in the first place?

Intervention Theory accounts for this and it is complicated. My best summary is that if you travel back in time, you cannot affect events in a way that did not happen. The history of events and the way they happened must remain preserved.

I suppose this theory is no crazier than the ancient aliens theorists who suggest that ancient civilizations were visited and helped by some beings not of this world.

What I do know is that we have the pyramids in Egypt and many megalithic structures around the world whose creation is shrouded in mystery. We don’t have the technology today to build some of these structures. So how did the ancient people do it?