# How to accelerate time?

1. Oct 2, 2009

### Tominator

This question seems trivial, but I couldnt find an answer to it. I know that time slows down in strong gravitational field, but is there something even theoretically capable of accelerating time around it?

2. Oct 2, 2009

### A.T.

That would result in repulsive gravity. It was ever observed and I don't think GR allows it.

3. Oct 2, 2009

### pervect

Staff Emeritus
It *probably* doesn't actually exist in nature, but there are some articles by Bondi in the literature about negative mass in GR. See https://www.physicsforums.com/showpost.php?p=1129928&postcount=7 for the reference to the Bondi article, and some discussion.

This would provide the required "repulsive gravity" needed to accelerate time.

4. Oct 3, 2009

### Tominator

I asked this because I got an idea, when reading a book about general relativity. The Idea was to accelerate time around a moving ship and maintain the time flow inside, which would result in a movement faster than a light in an outside observers frame of reference (if I am not mistaken:) but actually the ship wouldnt travel faster than light, only the time around it would flow faster than time outside and inside.

Well, If there are gravitational waves, one amplitude should be stronger and the other weaker, than normal gravity in that area, am I right? Because from what I know, all waves have minimum and maximum, or positive/negative amplitude.

I have read somewhere, that dark matter is responsible for speeding up the expansion of our universe, isnt that an example of repulsive gravity in nature?

5. Oct 3, 2009

### A.T.

Well, that is actually what normal gravity does. You just need a massive ship. If you are inside a big mass, the time runs faster further away from the mass than your local time.
Movement of what relative to what? An outside observer would actually see you slowed down in the above scenario. Being close to a big mass you can observe far away things moving faster than light according to your clock. The light speed limit applies only locally.
That is an interesting question: could a G-wave make time run faster in a certain region than before the wave came? If yes, the effect of the minimum and maximum would cancel out, so it would be just a temporary state.

Last edited: Oct 3, 2009
6. Oct 4, 2009

### Tominator

Lets say, that you have a ship so massive that you experience only one second, while the outside observer one minute. Than if your ship travels at almost 300 000 km per (your) second the outside observer sees your ship moving 60 times slower that (his) speed of light. Well that would not be very helpful, if you wanted to get somewhere faster, because your maximal speed would be 60 times slower than the speed of ligt outside. On the contrary, if you were able to accelerate time around your ship and mantain the "normal" time flow inside the effect would be opposite and thanks to maintaining the time flow inside there would be no twin paradox. And if this repulsive gravity really exists it would not only help you to accelerate time, but it would repell any object with mass - so you would have a shield against micrometeorites as well.

Hm, yes, but I only wanted to point out, that if one amplitude of G-wave is attractive, the other would be repulsive.

7. Oct 4, 2009

### A.T.

This is not contrary but the same scenario: time inside the ship runs slower than around it. There is no absolute "normal time flow". Gravitational time dilation is a relative factor of clock rates between two points in space.

8. Oct 4, 2009

### Naty1

There is nothing "trivial" about time..we don't even know what it is. but we think we understand that it passes differenly for different observers...and is fairly unfirom throughout the universe because the universe seems pretty uniform....

"Time is nature's way of keeping everything from happening at once". This quote, attributed variously to Einstein, John Archibald Wheeler, and Woody Allen, says that time is what separates cause and effect..." (wiki) beyond that, it's pretty much a mystery....

Check the spacetime diagram here

http://en.wikipedia.org/wiki/Time#Spacetime

and note that as you move from little velocity to c, which is the edge of the lightcone "future" diagonal in the diagram slows...so you can "speed up time" in everyday life by minimizing your local speed.

9. Oct 4, 2009

### Tominator

Well you are right, the time inside massive ship runs slower than around it but that doesnt mean it is the same scenario. If you would observe those two ships from Earth - one super massive and the other with accelerated time (relatively to the observer) around it - the super massive ship would move like a slug, even though it is moving almost at it`s local speed of ligh. On the other hand, it would seem to observer, as if the second ship was moving much faster than light.
That is why the concept of massive ship would not be very practical to use for travel, not mentioning how much energy it would require to accelerate such a ship. But if the ship has negative mass there is no limit to its speed, because from what I know speed limit applies only on object with mass.

yes, but if you want to get from one point to another not moving wil not help you.