# Sending someone into the future using the sun?

Ok so for starters, i am not nearly as smart as the least-smart person on here, but I have been reading a lot about all sorts of stuff.

We now know that the ability to "send" someone to the future is possible, by having that person travel to a black hole, orbit it for some time and return.

the biggest problem is that it is impossible in our current state for a human to travel the nearest black hole which is super far away, (unless the government or someone is holding out on some serious cryogenic technology on us).

Everywhere that I read has said this 'time travel' is possible with a black hole, however my thought is why hasn't anyone mentioned the next best thing that we could currently get to.... the sun?

We know that just by being in space, someone would already experience time slower than on earth, just the trip alone to the sun and back would allow for some significant time difference.

So, if someone were on a heavily leaded ship, with a vacuum layer or two, a highly efficient reflective side, and an awesome radiator on the dark side, wouldnt they be able to orbit close enough to the sun to experience time dilation in a relatively significant amount where upon a return of say 10 years wouldn't the Earth be significantly in the future?

obviously the closer the orbit possible the more time dilation correct?

also not considering a food source for that duration... would have to figure that out.

now I had read somewhere that if one were to orbit the nearest black hole for 15 years they would return to Earth and 50-75 years would have passed, (roughly calculated im assuming), so in theory wouldn't doing the same around the sun result in a time dilation but maybe not as intense... but even another 5-10-20 years would be something incredible.

so if this is dumb and everyone on here is like "wow youre a dummy" I apologize, but maybe let me know why that wouldn't work.

thanks,

• Sending someone into the future is easy - you just wait. Jun 29 '16 at 4:13
• The gravity of the sun won't make any appreciable difference. In order to get the desired effect, the gravitational potential well has to be so deep that it leads to strongly relativistic motion. In short... the movie "Interstellar" was totally nonsensical. Jun 29 '16 at 4:30
• If I calculated this correctly --- and I'm not sure I did --- after 100 years at the surface of the sun, you'd return to find your twin brother about 90 minutes older than you are. Jun 29 '16 at 5:02
• @WillO: "Such much?" :-) Jun 29 '16 at 5:12

For a spherically symmetric object the relative rate that time flows is given by:

$$\frac{d\tau}{dt} = \sqrt{1 - \frac{GM}{c^2r}}$$

where $G$ is Newton's constant, $M$ is the mass of the object (the Sun in this case), $r$ is the distance from the object and $c$ is the speed of light. The mass of the Sun is $1.989 \times 10^{30}$ kg and the radius of the Sun is about $6.957 \times 10^8$ m (this is approximate because the Sun isn't perfect spherical). If we put these figures into the equation above we get:

$$\frac{d\tau}{dt} = 0.99999894$$

So if you spent 100 years on the surface of the Sun you would age less than someone far from the Sun by about 56 minutes. Not a terrribly effective form of time travel.

• If I wanted to go 56 minutes into the future, I'd simply go eastward into the next time zone
– Jim
Jun 29 '16 at 13:08

As John Rennie points out, it's not worth it to use the Sun's gravity. But you may be able to use the Sun's energy. Consider a photon rocket that uses anti-matter fuel produced using solar energy. If you take some of the fuel and travel for some time and return, then in the rest frame of the factory a lot more time will have passed, so the next trip can be made at a much higher gamma factor. The trip after that can be made at a yet higher gamma factor, etc. etc..

• A photon rocket is very inefficient, though... and why travel, at all. The only problem to be solved here is to slow biological functions to a crawl, which nature can already do when required by evolution. A few genetic modifications on mammals and we are all good to go... at no more than the cost of a refrigerator energy bill. :-) Jun 29 '16 at 6:05