It turns out that time travel into the past is actually relatively easy. All you have to do is make the universe spin.
The famous mathematician Kurt Gödel was a friend and neighbor of Albert Einstein in Princeton. He became incredibly curious about Einstein’s general theory of relativity, which was and continues to be our modern formulation of the gravitational force.
That theory links the presence of matter and energy to the bending and warping of space and time, and then links that bending and warping to the behavior of matter and energy.
Gödel was curious about whether relativity could allow time travel into the past. Einstein’s theory claimed to be an ultimate framework for space and time, and as far as we know, time travel into the past is forbidden. So Gödel figured that general relativity should automatically forbid it.
And Gödel discovered that in fact general relativity is perfectly fine with time travel into the past. The trick is to set the universe in motion.
Gödel constructed a relatively simple and artificial model universe to prove his point. This universe rotates and contains only one ingredient. That ingredient is a negative cosmological constant that resists the centrifugal force of rotation to keep the universe static.
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Gödel found that if you follow a certain path in this rotating universe, you can end up in your own past. You would have to travel incredibly far, billions of light years long, to do it, but it can be done.
As you travel, you would be caught up in the rotation of the universe. It is not only a rotation of the things in the cosmos, but of both space and time itself. Essentially, the rotation of the universe will change your potential paths so much that those paths will return to where you started.
You would set out on your journey never traveling faster than the speed of light and you would find yourself back where you started but in your own past.
The possibility of time travel backwards creates paradoxes and breaks with our understanding of causality. Fortunately, all observations suggest that the universe does not rotate, so we are protected from Gödel’s backward time travel problem.
But it remains a mystery to this day why general relativity is okay with this seemingly impossible phenomenon. Gödel used the example of the rotating universe to argue that general relativity is incomplete, and he may still be right.
This article was originally published by Universe Today. Read the original article.