"Time Travel"

[Patashu]

Originally Posted by gausmaster

This is somthing I have been pondering for quite some time and I would like imput from a few high-level thinkers.
I know there are a couple impossibilities in this idea but please dont get hung up on them.
When you see a star at night, the light you are seeing is not what is happening right now but what was happening (perhaps) millions of years ago based on the speed of light and the extreme distance betwine the Earth and most stars.
So here is my theory.
Assume (by some freak act of phisics) that we found a way to rocket a shuttle many times faster then the speed of light. If we shot this shuttle very far away from earth and passed light for a long period of time would we be able to eventualy stop and (with a very powerful telescope) look back at the earth as it was thousands or perhaps millions of years ago? Just like we on Earth can see the birth of a star that has most likely already died out in real time, could we look back on Earth and see such things as living dinosaurs, or the Battle of Thermopylae? Or possably see yourself playing outside as a child? I'd like to hear your ideas.

yes that's right, and in fact if you can send signals at superluminal speeds back to earth just like you brought your rocket to such a speed you would be able to interact with earth's past - time travel
assuming special relativity holds FTL leads to time travel but it also means you've lost causality, as effect can now precede cause. that's generally not a good thing

[ryanisadouche]

Originally Posted by gausmaster

Also ponder this. If you were going faster than the speed of light and you looked out a rear window toward the earth that you are speeding away from would you be able to see anything at all while you were moving? Would it be complete darkness because no light is hitting you?

If you looked out the back of your rocket, since you're moving faster then light, the current light wouldn't have reached you yet and you would see what was there in the past. In other words, you'd see your own rocket travelling.

I could be horribly wrong but i think it makes sense given your original theory.

Originally Posted by devonin

If you focused your super powerful, incredibly accurate telescope back at Earth and looked at it, you'd get -A clear image of Earth right now exactly as you left it- (Or potentially a few seconds after you left it depending I suppose on how long it took you to travel that far away.

I think he meant using the same technology we use today. I wont pretend to know anything about astronomy, but logically it should be common sense. If we look at Star X from Earth, we'll see it as it was in the past n years ago, so if we could hypothetically relocate instantly to Star X, we would see Earth as it was n years ago too.

A telescope could never be made to see Earth as you left it, because in our hypothetic situation we have travelled faster then the light that is present time . A powerful telescope cannot make light speed up and reach its lenses faster, it can only magnify the light that is there at the moment. You would be seeing "old light", as you put it, which could potentially be magnified to see a clear image (given a path of space debris was somehow cleared). It wouldn't be time travel, but just viewing the past.

[Patashu]

Originally Posted by ryanisadouche

It wouldn't be time travel, but just viewing the past; you could never interact with anything you saw, since in present time nothing you see exists.

assuming special relativity holds true, if you can travel at superluminal speeds and send a superluminal signal or object you could interact with Earth's past

you need to understand the lorentz transformation for it and why it's a consequence of special relativity but: http://www.theculture.org/rich/sharp...es/000089.html

[gausmaster]

Originally Posted by Patashu

assuming special relativity holds true, if you can travel at superluminal speeds and send a superluminal signal or object you could interact with Earth's past

I am by no means an expert at any form of phisics or relativity, but I have a very serious problem with this theory.
I do not belive that any interaction with the past is possible, because I belive that time is stable and consistant. If you were to fire an object at earth at 40X the speed we were traveling it would hit the earth in "real time". If we could comunicate instantaniously with earth then that signal would be going infinity miles an hour, but still you would only be speaking with people on earth in "real time".

[MrRubix]

Assuming we could "get ahead of light" and somehow wind up on the other side of old light from years past, I don't think we'd be able to see anything meaningful. I think such light would have been dispersed and manipulated to the point where, even with a powerful telescope, we'd be unable to make out anything at the level of detail required.

We can see the light from things occurring years and years ago -- including things that could have already gone nova by now, but I can't think of an example where we have seen light from the past from an object comparable in size to the earth with the same level of detail. Normally when we look at "old light," they're for large-scale things where any small-scale high-level detail loss via light dispersion is made up for by the sheer AMOUNT of light coming in that makes up the larger image which, from our planet, makes up for a detailed picture. I would assume that for high-level detail, the light from something as tiny as our earth would simply become too dispersed/mangled to see. I'd think of it as trying to view crappy pixel art at high resolution. It's still going to be crappy pixel art.

[Patashu]

Originally Posted by gausmaster

I am by no means an expert at any form of phisics or relativity, but I have a very serious problem with this theory.

the fact is that if
-special relativity holds true
and
-we can travel at superluminal speeds
then
-we can send signals back in time (time travel)

it is a consequence of the theory deal w/ it

note that we don't have any physically plausible methods of achieving superluminal speed

[Cavernio]

About what you would see if you were moving faster than light, I agree with gausmaster in that you would simply not see the light you're moving away from. Even a beam of light that is 0.0000001mm away from your eye will never be able to reach your eye.
You wouldn't totally see nothing though, because what our eyes pick up is more than the 180 degrees in front of us. We actually see about 10 degrees behind us on either side, http://en.wikipedia.org/wiki/Visual_field , so in those 10 degrees, we'd see light. As a side note, the light we would see if we looked forward would be at least twice as 'bright' because we'd be seeing at least twice as much of it in the same amount of time.

I got into a discussion about this last night, and the other person said that we would be seeing light all distorted, and they gave an example which this morning I realized was incorrect. See, I've been thinking about this problem like light has individual particles. He was thinking about the light simply surrounding us, like, say, water in a stream. If we sit in a stream, we're surrounded by the water, just like if we sit in light, we're surrounded by light. Then he said, pretend we're moving in the stream, swimming downstream with it. At this point, if we're actively swimming in it, we're moving faster than the water is. Yet we're still surrounded by water, there's water touching us behind us. This stumped me for awhile, but there's one serious problem with this: the water changes speeds depending on where it can go. The moment we'd move in the water, the water comes flowing in behind us at a much much faster speed than it flows downstream. Light, however, doesn't do that, because we're saying we'd be travelling faster than its maximum speed.

[John McPain]

This is Gausmaster's new account.

Originally Posted by Cavernio

Even a beam of light that is 0.0000001mm away from your eye will never be able to reach your eye.
You wouldn't totally see nothing though, because what our eyes pick up is more than the 180 degrees in front of us. We actually see about 10 degrees behind us on either side, http://en.wikipedia.org/wiki/Visual_field , so in those 10 degrees, we'd see light. As a side note, the light we would see if we looked forward would be at least twice as 'bright' because we'd be seeing at least twice as much of it in the same amount of time.

I agree 100%, but what (in your opinion) happens to the light inside of the shuttle?

[Cavernio]

The light sources inside the shuttle would still be emitting light that would bounce of the walls and other objects inside it, so there'd still be light 'trapped' inside and moving with you. My very first thought on this is that it would look the same as if we weren't moving, at least once we reached our travelling speed. I don't think we'd get any doppler effect or anything, because relative to the light, our movement hasn't changed at all.
As for light that enters in the shuttle, and then would say, touch the wall...uhhh...I dunno! I don't know enough about the properties of light to answer that really. It light were matter, then it'd get 'stuck' to the wall. But light's not matter, so I dunno. I suppose if it were still to get 'stuck' to the wall, then there'd be a serious problem, wouldn't there be? The shuttle would melt from the heat from all the trapped energy or something.

This seems similar to another problem I was given in my grade 7 science class actually, one which I still don't think was answered properly at the time. (I'm not sure how it's similar, but it made me think of it.)
You have an airtight jar on a scale with a fly sitting on the bottom. Does the scale pick up the weight difference if the fly takes up and is now hovering in the air? Now, I *think* I was told at the time that yes, it did pick up the weight difference, but I have no idea who actually tested this or not. If the jar isn't airtight, than I think it would notice the difference for sure. Also, there's the extra pressure of the air being beat down by the fly onto the scale which you'd have to take into account, right?

[John McPain]

Mythbusters did this. They concluded that there is an aberation picked up by the scale but that was caused by momentum differences.
source = http://kwc.org/mythbusters/2007/04/e..._truck_bi.html

[Cavernio]

Bah, you posted too fast! I can't edit my other post anymore now. Not all matter would stick to the wall, if it were elastic matter, it might not. If we could call light matter at all, would it not be like 100% elastic matter and also bounce back at light speed + shuttle speed? If this is the case, then again, because we're also moving, to us, the light would just be moving at light speed.

[Shaydow]

http://www.youtube.com/view_play_lis...EFE6A7EA479666

I love this show, its one of the few things I personally set our dvr here at home to record ( that and House :P ).

A great walkthrough on Light and its speed, how the Universe can bend to accomedate the speed of light, how the Universe itself actually is expanding FASTER then the speed of light, and other neat stuff.

Enjoy.

[QED Stepfiles]

Originally Posted by gausmaster

This is somthing I have been pondering for quite some time and I would like imput from a few high-level thinkers.
I know there are a couple impossibilities in this idea but please dont get hung up on them.
When you see a star at night, the light you are seeing is not what is happening right now but what was happening (perhaps) millions of years ago based on the speed of light and the extreme distance betwine the Earth and most stars.
So here is my theory.
Assume (by some freak act of phisics) that we found a way to rocket a shuttle many times faster then the speed of light. If we shot this shuttle very far away from earth and passed light for a long period of time would we be able to eventualy stop and (with a very powerful telescope) look back at the earth as it was thousands or perhaps millions of years ago? Just like we on Earth can see the birth of a star that has most likely already died out in real time, could we look back on Earth and see such things as living dinosaurs, or the Battle of Thermopylae? Or possably see yourself playing outside as a child? I'd like to hear your ideas.

So, on the one hand, as you've put it, then yes, it's perfectly possible. Information cannot travel at past the speed of light, and so if we were somehow able to overtake the "information" of times past, then theoretically it would be possible to see the past. Of course, this is a bit of faulty reasoning, since if we were to go past the speed of light, then we in effect (as information) would be violating this rule...

In other words, it's not really meaningful to say "would this happen if we could travel past the speed of light," because if we could travel past the speed of light, then information can too, and really the entire discussion becomes a bit pointless.

EDIT: Whoops, for some reason I thought that I was responding to the most recent post in this thread, rather than the first post... sorry if I broke the flow...

[Cavernio]

Originally Posted by Shaydow

http://www.youtube.com/view_play_lis...EFE6A7EA479666

I love this show, its one of the few things I personally set our dvr here at home to record ( that and House :P ).

A great walkthrough on Light and its speed, how the Universe can bend to accomedate the speed of light, how the Universe itself actually is expanding FASTER then the speed of light, and other neat stuff.

Enjoy.

Yeah. Light clearly isn't matter, and your question's answered here gaus.

[Afrobean]

Originally Posted by Patashu

note that we don't have any physically plausible methods of achieving superluminal speed

Sure we do. We just don't have any practical applications of these physically plausible methods.



Incidentally, wormhole travel: does this fall under the category of superluminal? Your own speed would not be greater than the speed of light, but you'd still be able to arrive at a destination before light.

[Patashu]

Originally Posted by Afrobean

Sure we do. We just don't have any practical applications of these physically plausible methods.



Incidentally, wormhole travel: does this fall under the category of superluminal? Your own speed would not be greater than the speed of light, but you'd still be able to arrive at a destination before light.

I think I mentioned that one yeah

it's superluminal with respect to an outside observer but not for the wormhole traveller itself

[legato210]

well since this is all speculation, I found a video you might be interested in watching.

this man is a genius.

http://www.youtube.com/watch?v=w-prt5d6m6s

[devonin]

Whether you think he's a genius or not, a clip about futurists has nothing really to do with what we're discussing here.

[slipstrike0159]

Originally Posted by devonin

Nobody knows whether this is true or not because our understanding of physics says it is completely impossible to go faster than the speed of light.

I was going to post the video i saw on the discovery channel a while back called the universe, but i was beaten to the punch. This may now be approaching the realm of not true because according to the video, some scientists now believe that in the big bang theory (for matter of reference) the explosion threw particles out at speeds faster than the speed of light.

One thing i think is important to keep in mind with this whole theory (obvious impossibilities aside) is that you all refer to the analogy of seeing a star that may have already went through a super nova and its 'old light'. When you try to apply this logic towards trying to see 'old light' i think that its important to realize that, unlike a star, the earth does not give off light going at light speed. It is reflected light from our sun. As small of a difference as this may be, you would have to consider the fact that if you try to look at light coming off from the earth it might go less than the speed of light.
As a point of clarification, we can actually slow light through different mediums. So then would it not be possible that the light coming off of the earth would be going at speeds that are less than the speed of light in a vacuum? Of course thinking in terms of it as either going through the atmosphere or at least touching it enough to use the particles it hits letting it slow down.

Also, im a little shaky on the whole subject of 'looking back at the earth' after speeding away from it at faster than the speed of light. To be able to see that specific planet wouldnt you have to have a direct connection of light to it so you can actually 'see' it? To explain, of course you would have light still hitting you from different directions, but i was always under the impression that to see something through a telescope you have to have its specific light hitting you already. If you have breached the light that is reflected off of the earth (of course only considering you got outside the original light reflected off of the earth at its creation) then you wouldnt be able to see the earth at all.

One last thing, simply enough, if you were moving at extremely fast speeds AWAY from the earth, why would it matter if that somehow allowed you to see it in its previous states? I mean, you wouldnt be able to communicate with it (for radio waves and the like travel MUCH slower), and you wouldnt be able to even get back to it without the light catching back up and it making no difference anyway.
To think of it realistically, look at the theory of relativity. Time moves relative to the observer right? So time would seem to move at different rates for someone on the earth as opposed to someone living on, lets just say, jupiter. Outsides the bonds of our earth we would be trying to time everything according to the system we use ON the surface of the earth which simply would not be the universal system of all the bodies in the universe. Our measuring system in accordance with the rest of the universe would feel rather useless for no matter how fast you are traveling through space, time will always feel different. Thus, time travel in essence would be a virtually useless argument outside the bonds of our own time system, or rather outsides the bonds of time relative to wherever you are.

[Strider11o7]

Although I'm not saying that the OP's theory is possible, it would be much more efficient to just look at a clear, reflective surface from far away (like a man-made mirror and placed there or otherwise). It wouldn't require a rocket and you could look twice as far into the past, I think.