# Looking for future earth

1. Aug 6, 2012

### CuriositE

Given a particular earth latitude and longitude on a certain day (December 21, 2012), is it possible to know which direction to look into the starry sky to see future Earth (where it will be in exactly 1, 4, 9, whatever years)? If we know how earth revolves around the sun and how the sun moves around the black hole in the middle of the milky way, we should be able to predict its position relative to itself across many years of time right?

As a second question, is it possible to know where to look in the starry sky to look at where earth WAS in the past (whatever time interval, starting with a known latitude/longitude/time)?

2. Aug 6, 2012

### phinds

yes, all of that should be computable but why would you care? there's nothing THERE in either case so it seems pointless.

3. Aug 6, 2012

### CuriositE

Well, imagine if someone put something there...

If I were to shine a light into space (a SUPER intense electromagnetic wave, possibly with information encoded in it), would it not travel in that direction at 3E8 m/s? If we point it at where the earth will be at x years and point the light in that direction, the signal will arrive at some point along that ray x light-years (9.46E15 m/light year) away after x years.

Is there a solution for x? Or does the light ray always outrace the earth?

I assume the earth is too slow, but what if instead the signal were sent along a bouncy pathway? They are communicating with the mars rover via a satellite that orbits mars with like a 14 minute time delay. If we could set satellites into orbit around planets/the sun, could we not bounce the signal all over the place and increase the light signal's path-length such that there does exist a solution for x?

I'm thinking of an experiment where a known signal is sent flying at the speed of light through space-time for a huge length of time (years) and is compared with itself when it arrives at a receiver on earth far in the future. Would the signal be the same? or would some weird stuff happen to it? The signal could be anything, like a video recording or a string of numbers or whatever.

4. Aug 6, 2012

### CuriositE

Perhaps the total number of bounces could be just one: so the light signal forms a giant V in space, where one vertex is the earth at time 0 and the other vertex is the earth at time x, and at the angle is the satellite.

Aren't Voyager 1 and 2 still working on getting out of the solar system? If we send a signal to those and ask for it back how long does it take? Could we not send another ship just like that which travels out of the solar system a bit faster (maybe 0.9c or more) with advances in technology?

I've been curious about the nature of time. How many years can a signal travel through space without becoming completely distorted? Is 6000 years asking too much?

5. Aug 6, 2012

### Staff: Mentor

Without bouncing or bending around something the signal would quickly move away from us and never be seen again. We simply can't point it at where we would be in X years because light would reach that point far more quickly than Earth will.

They always outrace us.

We already send signals out into space and bounce them off of existing satellites. We even shoot radar beams out at asteroids and receive the signal minutes - hours later.

If we could send a signal out to about 50 light years, and bounce it off of something and receive it back here on Earth the round trip time would be 100 years. The only things I can think of that would happen to the signal would be loss of intensity from the cast distance and red/blueshift from the motion of Earth and the reflecting object.

6. Aug 6, 2012

### phinds

Man that's gonna require SOME kind of accuracy in the positioning of the reflecting object, and the synchronization that would require with Earth would probably be impossible.

7. Aug 6, 2012

### Staff: Mentor

It is impossible today, but the basic idea should be correct. I don't think you would need crazy accuracy because your signal is going to spread all over the place at that distance. Kind of like shining a laser at the Moon, it starts out a few millimeters wide, but by the time it gets to the moon the diameter is far wider. (Not sure if it was several meters wide or several kilometers)

8. Aug 6, 2012

### CuriositE

Thanks for the response Drakkith.

I figured something like his was possible, but like phinds says, the necessary accuracy would be ridiculous. Also, I assume the original signal would have to be extraordinarily powerful.

Here's my idea for how to line everything up: Send the signal-regenerating probe out of the solar system at ~0.9c and on a direct collision course with a known star (star A, 100 light years away). This way, given the known launch time/velocity/destination, and with positioning information sent back to earth, we could keep track of it for >100 years. Before it enters the new solar system and is affected by the new gravity, send a signal towards the star (might have to make a slight adjustment due to the movement of earth). The probe will be pre-programmed to re-angle the signal it receives using whatever math nasa already uses.

As for generating the signal, would it be possible to send or receive it from the surface of earth? I know the atmosphere causes problems, but what if you send it from a desert (like Egypt) so that relatively few water molecules are likely to distort the image? I'm imagining a sort of "cosmic time capsule," kind of like when you bury some personal stuff in a box underground and dig it up 50 years later. You can't depend on an earth satellite staying in orbit for 50-6000+ years, but if you had a receiver planted on earth, perhaps with the size and mass of the pyramids, such that no one is going to ever knock them down or move them, then once the signal is sent, all you'd have to do is calculate out the day/time for the signal to land right?

9. Aug 6, 2012

### Staff: Mentor

Absolutely.

A radio wavelength signal would be mostly unaffected by the atmosphere but you would run into bandwidth issues at that low of a frequency.

I don't know honestly. I am not familiar enough with this subject to say whether you would need detailed calculations of gravitational interactions or not. I also don't really see any point in doing this.