# Time Dilation & Gravity: Can You Go Back in Time?

• z0rn dawg
In summary, the conversation discusses the effects of time dilation on a person traveling at high speeds and being under strong gravity. It is stated that the faster a person travels, the slower time goes for them compared to someone who is not moving as fast. Additionally, the more gravity is acting on a person, the slower time goes for them compared to someone who is not under as much gravity. The conversation raises the question of whether these effects could be combined to potentially allow a person to go back in time. It is ultimately concluded that while these factors may result in slower aging, they would not cause a person to physically go back in time. The conversation also mentions the concept of gravitational potential as a factor in time dilation and discusses the attainability of
z0rn dawg
The faster you go, the slower time goes relative to someone who is not moving as fast. The more gravity is acting on you, the slower time goes relative to someone who is not under as much gravity.
If the two previous statements are correct, could you go back in time by going really fast and being under a lot of gravity? I don't know if the effects would combine or add to each other, but if they do, could you go back in time?

could you go back in time by going really fast and being under a lot of gravity?

Almost certainly not...there are lots of related threads on time travel here...Note that the individual "going faster" and/or "deeper in a gravity well" is locally unaware of any change in the passing of time.

You might also read about black holes,white holes and EPR bridges (wormholes) in Wikipedia. If and when relativity and quantum mechanics are "unified" we might have further insights...so far the most interesting locations, black holes and singularites, are rather obscured since we can can neither experimentally measure effects nor do we have unified mathematical (theoretical) descriptions...

You can also explore "future" and "past" realms inside black hole horizons.

Naty1 said:
Might also read about relativistic degenerated neutron stars only about three times as big as the stellar black holes of which we really don't know whether they exist. Rotating neutronstars; the remains of supernova explosions are really there and the discussion whether they exceed 1,44 Msolar is less interesting than the fact that they are really small, rotate fast and indeed are of the same candidacy as the socalled fancied black holes...

Maybe you don't have to travel faster than "c" to cross the universe.

As you accelerate towards the speed of light, sure time dilation does occur.
But also, most people forget that space also contracts by the same factor.

Speed is distance divided by the time taken to travel it.

So at near light speeds from the travellers perspective, your trip of millions of light years may for you, only be a few million kilometers and only take a couple of hours.

Unfortunately though, when you arrive, those loved ones left behind would have died many millions of years ago.

Keijo said:
As you accelerate towards the speed of light, sure time dilation does occur.
But also, most people forget that space also contracts by the same factor.

Speed is distance divided by the time taken to travel it.

Wrong.

For an observer on Earth, there is a time dilation on a spaceship (and vice versa). So the flight to Andromeda galaxy could take (by Earth clock) millions of years while for an austranaut it took only few years.

Inside a spaceship, distance to Andromeda is contracted and time flows as usual.

So you're right, austranaut benefits from time dilation OR space contraction, but from one at a time. I disagree with the world ALSO.

Dmitry.

Thanks, you are absolutely right.
I stand corrected by my wording.

I used the word "also" twice in my post.
By "also most people forget" I did not include physicists.
By "space also contracts by the same factor" is correct but for different observers.
I used the "also" only to link the effects.

I'm new to this forum and I'm only just learning how careful one has to be with one's choice of words here.

Thanks again and cheers.

So does anyone what would happen?
I understand that you wouldn't feel like you are moving any slower though time (or even backwards). In someone else's perspective, you would though...right?
If you go .95c and are somehow under extreme gravity, would you go back in time relative to someone else? I haven't gotten a definitive answer yet.

z0rn dawg said:
So does anyone what would happen?
I understand that you wouldn't feel like you are moving any slower though time (or even backwards). In someone else's perspective, you would though...right?
If you go .95c and are somehow under extreme gravity, would you go back in time relative to someone else? I haven't gotten a definitive answer yet.

The definitive answer is: No you would not. All combining time dilation due to velocity and gravitational time dilation will do is make you age more slowly than you would have by either alone.

Another point that should be made is that gravitational time dilation isn't due to strength of gravity but due to difference in gravitational potential. IOW, how much work it would take to move from one potential to the other. For example, a clock sitting at the center of the Earth would experience zero gravity, but would run slower than a clock on the surface which experiences 1g, since it would take work to lift the clock from the center of the Earth to the surface.

z0rn dawg said:
If you go .95c and are somehow under extreme gravity, would you go back in time relative to someone else? I haven't gotten a definitive answer yet.

I suspect the two time dilation factor for velocity and the time dilation factor for gravity would add the same way they add for two velocities,

*****u + v
w = ------------
****1 + uv/c^2

(The asterisks replace spaces)

where u is the dilation factor due to gravity (calculated by substituting the escape velocity for v in the Lorentz Transformation) and v is the velocity of the spaceship. w is the resultant velocity.

Janus said:
Another point that should be made is that gravitational time dilation isn't due to strength of gravity but due to difference in gravitational potential. IOW, how much work it would take to move from one potential to the other. For example, a clock sitting at the center of the Earth would experience zero gravity, but would run slower than a clock on the surface ...

Quantitatively, how great should the gravitational potential be to make the clock as slow as a thousandth and a millionth compared to a quite far way clock? And is this attainable on a surface of a very heavy star ?

skeptic2 said:
I suspect the two time dilation factor for velocity and the time dilation factor for gravity would add the same way they add for two velocities,

*****u + v
w = ------------
****1 + uv/c^2

(The asterisks replace spaces)

where u is the dilation factor due to gravity (calculated by substituting the escape velocity for v in the Lorentz Transformation) and v is the velocity of the spaceship. w is the resultant velocity.
Hi Skeptic2
Nice to see you have inspiration for finding new formulas... u needs to have the same dimension as v, and so distance divided by time. Or is u the escape-velocity itself?
greetings Jan

## 1. What is time dilation?

Time dilation is a phenomenon in which time passes at different rates for objects in different gravitational fields or moving at different velocities. This is based on Einstein's theory of relativity, which states that time can be affected by gravity and motion.

## 2. How does gravity affect time dilation?

The stronger the gravitational field, the slower time will pass. This means that time will pass slower for objects closer to a massive object, such as a planet or black hole, compared to objects further away.

## 3. Can time dilation allow us to travel back in time?

No, time dilation does not allow us to physically travel back in time. While time may pass at different rates for different objects, it still moves forward. However, time dilation can make it seem like time is moving slower for one object relative to another, which could create the illusion of time travel.

## 4. Is time dilation only caused by gravity?

No, time dilation can also be caused by high velocities. This is known as velocity time dilation and is also a key concept of Einstein's theory of relativity. The closer an object gets to the speed of light, the slower time will pass for that object compared to a stationary observer.

## 5. Can we observe time dilation in everyday life?

Yes, we can observe time dilation in our everyday lives. For example, GPS satellites have to account for time dilation due to their high velocities in space in order to accurately calculate the position of objects on Earth. Additionally, atomic clocks have been used to demonstrate time dilation in experiments on Earth.

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