# Forward time travel via strong gravitational forces

A scientist has recently invented a gravity machine. This machine pulls all mass within a certain radius (say 50 feet?) towards it at an adjustable rate.

The machine can...

• create as strong a gravitational field as wanted.
• not be effected by its environment.

The idea is that using gravitational time dilation this scientist can travel to the future!

My questions are...

• Does stronger gravity equal faster passage of time?
• How much stronger can gravity get before it kills humans?
• Would you even be able to travel in time fast enough to actually be effective (speeds like 10 days per perceived second)?

This is inspired by artificial gravity and inertia negation.

• Little things like oxygen, nitrogen and argon have mass. Your machine would pull toward itself all the surrounding air. Not to mention the surface the machine is located on. Both of those could create slight problems. Is the machine itself somehow (because science-based: how?) immune to its effects? Also, are there any limits on how much stronger gravity you are willing to deal with? Keep in mind that once the machine has collected a sufficient amount of mass in a sufficiently small volume, you get a black hole.
– user
Commented May 31, 2016 at 16:37
• Bottom line: I think we need to know a bit more about how this machine works and its effects, before we can provide reasonable answers.
– user
Commented May 31, 2016 at 16:38
• @Michael Lets say that this machine is not effected by any external forces (should I remove the science-based tag?) and the gravity can be set to as strong as you want without being dangerous to humans. Commented May 31, 2016 at 16:46
• "should I remove the science-based tag?" You may want to consider the reality-check tag instead, which imposes lower requirements on answers.
– user
Commented May 31, 2016 at 17:01
• "50 feet" doesn't work. The force falls off with the square of the distance. Commented May 31, 2016 at 21:25

1. Stronger gravitational force does in fact allow you to travel through time "faster" due to gravitational time dilation, as your link explains.

2. In order to have noticeable affects due to time dilation, it would basically kill you first. Mainly spaghettification and the maximum amount of force a human body can have for a duration of time and survive. Something on the order of 300 Newtons for a short time span if I can recall.

3. So... no. You probably won't even perceive the time dilation. I imagine you don't understand too much of the jargon from your gravitational link, but the basic point is that you'd have to be near a black hole to really get the effects. If you stood on top of the sun for a year (neglecting special relativity), you would probably miss only a few days at most. That's how much gravity you're dealing with.

Also note:

$$F_G\approx G\frac{M_1M_2}{r^2}$$

This formula describes approximately how much force there is. From this, it is obvious you cannot 'contain' the effects in 50 feet, gravitational force will simply stretch out and become weaker, but still noticeable.

SAFETY HAZARD: Do not try this experiment within the solar system for general safety.

• Sorry but your science is wrong. Very very wrong. Gravity does not cause time dilation, gravity does not cause spaghettification. What does cause time dilation is being at a lower gravitational potential (the integrand of gravity). What does cause spaghettification is tidal forces (which is the differential of gravity). In both cases you could (in theory) shape a gravitational field to serve your purpose. In practice, if you could shape space time that easily, you will have of course invented a device that could produce an Alcubierre metric (warp drive).
– Aron
Commented Jun 1, 2016 at 5:20
• @Aron I was just making this answer for the purpose of the OP. Commented Jun 1, 2016 at 11:32
• Don't take this the wrong way. It's good that you tried to answer. It's just not based on correct physics, not everyone understands GR after all.
– Aron
Commented Jun 1, 2016 at 11:46
• After thinking about it a bit more, applying the Shell Theorem, it is possible to do this with only semi-classical mechanics. A sufficiently massive symmetric shell would do exactly what the OP needs. en.wikipedia.org/wiki/Shell_theorem#Inside_a_shell
– Aron
Commented Jun 1, 2016 at 14:27
• @HDE226868 My point is that what most people consider to be "gravity" is the force field of gravity. Gravitational Potential and the Tidal Forces are the integrand and the Divergence respectively. Therefore it is possible to have an area which is locally without a gravity force field, but is at a potential that is different from the ground state. Also, it is possible to have a massive gravitation field, with only a small tidal force.
– Aron
Commented Jun 3, 2016 at 3:20

Actually, in your own link it says that: "The weaker the gravitational potential (the farther the clock is from the source of gravitation), the faster time passes." So the higher gravitational density would probably actually SLOW time down for him. To speed time up, it sounds like you would want a "negative" gravitational source, which is something we don't know for sure exists.

• Also, speeding time up for him inside the bubble would make the outside world seem to slow down by comparison. I don't know that actual time "travel" would happen either. perhaps the only way for him to actually seem to travel (from his perspective) is by being in stasis while the world changes around him. Commented Jun 2, 2016 at 23:30
• If time slows down for him, and the rest of the universe doesn't slow down, you would "travel forward in time" relative to the rest of the world. That's how time dilation works. Its like driving slow and having all the cars pass by you. Each car could represent 1 minute, 1 hour, 1 year, so this would be traveling forward through time. Commented Jun 3, 2016 at 0:24