Question: Can you slow down or reverse time?

Jose Eliel Camargo Molina answered on 15 Mar 2019:

Hi!

The only thing we can do, as far as our understanding of the universe and physics goes, is moving forward in time. You are already doing it, obviously, but it is also possible to change how fast time moves with respect to other people or in technical language, another observer. The quick answer to your question: It is possible for time to run slower for you compared to another observer, but it is not possible to reverse time.

One of the most fascinating things about the universe is that no matter where you are or how fast you are going, light always travels at the same speed. Even if you are moving in the same direction of the light, traveling super fast, and you measure how fast the light moves with respect to you, you will get the same number for its speed of light as someone that is standing still with respect to you.

That is really crazy. Because that is so (we only know it is so, not really why), it means that time has to be different for you and the person standing still.

So simply put, how you travel forward in time depends on how fast you are moving but also on the gravity you are exposed to.

GPS satellites are things that are doing both things, they are traveling really fast but also experience less gravity than you and me because they are farther away from earth. When you add up all the effects (which we can calculate precisely using general relativity), that means that the clocks in GPS satellites are running faster by 38 microseconds every day.

If we would not account for our time running slower in comparison, GPS satellites would be off by something like 11km per day at worst.

Now, traveling back in time? As far as we know this is not possible. But who knows? There might be new theories to prove and new ideas that might say time travel backward is possible.

But one thing is certain, based on all the evidence we have, and all the theories that we have shown work in describing everything we have seen, it is not possible to go back in time.