^^^ That's pretty close Startraveler except that the time slowing perception of the close to c travelling object is for an outside observer ie. time dilation/length contraction is only apparent from the outside stationary observer with respect to the observable. For the object itself, time ticks as normal. I may have to re-study SR/GR for the umpteenth time though. LOL, there's so much in my noggin that I continually have to let some things go to put new things in. But it's all good.

The above may confuse Zero of Deism though, my apologies.

for your question on whether or not we would see things change: no. since it happened in the past, after you caused it to happen, your memeories would change to fit that history and you would simply believe that the setting you are in has been that way forever

How would you even know that changes were made anyways , its still plausible

lol. Nice to see a mind of reason with a sense of humor. And a good idea too.

And to the comment about if you go light speed in outer space and come back everyone would have aged.
Like I was attempting to say (im not good at explaining things). It wasnt that some universal time went slower for you its just that the time of everything that was in and around you was less effected by everything else.
Now if time was nothing but the universe duplicating itself with slight alterations from its previous self. Like a Movie clip or one of those plastic cartoons like halloween stole christmas(or whatever it was called) then ya you could warp back to the previous clip of the universe.
But the universe isnt duplicating itself. It is constantly in change, in motion, in transformation. The atom of yesterday didnt stay in yesterday, he just moved to today.

Think about this: in back to the future II (just for sh**s and giggles), assuming that there is only one timeline, Marty travels into the future and is already there as an older man. Would that be possible? When he traveled to the future, in history, he just went missing in the past and no one ever found him so he couldn't be there as an old man until he goes back to the past and then history changes again and he never went missing. So the future he saw never even exsisted because he never went missing in the past.

Also (putting aside Back To The Future) if you were traveling around the world in circles at the speed of light for say a week, wouldn't you experience time exactly the same as everyone on earth does? The only difference would be that you are going really fast, but you would still experience the week that you were gone as a week. It would just be an annoying experience... and about traveling back in time... I don't think it is in any way possible...



I really like this idea and I think this would definately be possible (if we had a strong enough telescope and could travel faster than light of course). I think this is as close to time travel we could get.

By your own assumption that there's only one timeline (and that there's a future to go to) we know that there is no "until he goes back...". Since an older version of himself is present in the future we know that his younger self did return from his trip to the future. It has already happened and will happen in the future. It's all a matter of perspective.



Relative speed is the key to the difference in the way time appears to pass for you to somebody else. So any motion relative to somebody else results in some time difference. It just doesn't become noticeable until you're going pretty fast relative to the other guy. And you could never get up to exactly the speed of light, just close.

No, this is a common misconception. Imagine you have a space shuttle that travels
100 million light years in 1 minute. Say you wanna visit plantet JUSTFORKICKS in a cerain
WHATSITSNAME galaxy 100 million light years away. So at present JUSTFORKICKS is receiving images of earth's past. Set several watches(with detailed date and time settings) on earth to the accurate present time and date and take one of those watches with you in your space shuttle. Visit JUSTFORKICKS, take your powerful telescope and view images of earth's past(say, if your telescope is super powerful, maybe you can even look at dinosaurs), record some footage for say 1 hour and return back. The total time it would take you to accomplish this would be 1 hr 2 min( 1 min onward + 1 hr footage time + 1 min return.)

When you come back to earth you would notice that you have been away for just 1 hr 2 min and you would notice that your watch would be running exactly the same time as the other ones on earth. What makes you think the other watches would run faster and yours any slower? When you are following one standard time, it would make no difference at all: nobody would age faster or slower.

The further you want to record images of our past, the furhter (light years) you need to travel; the more detailed images you want to view, the more powerful telescope you would need. Maybe, you could even set up a instantaneous data transmitting device(that's another big suppose) that could transmit images to earth from JUSTFORKICKS in 1 sec. You would then be receiving a contineous feed of Earth's past. Certainly there are quite a few BIG ifs in what I said, but it certainly is theoritically possible.

Evidence of our past is there in light tapes far far away; we just need to figure out how to get them.

^That would perhaps be true in a universe in which special relativity didn't exist. But as it is there are limits to how fast one could travel (not quite one light-second in a second) and different velocities do get watches out of sync with each other. There is no such thing as 'one standard time.'

And in addition, your watch would be off regardless because clocks run faster in space than on the ground.



oh... heh... didn't catch that post. sorry.

I know there is no such thing as one standard time, I meant when we are referring to the same standard(Earth time), there wouldn't be any discrepancies.


Okay, maybe we could use our powerful telescope and constantly view time on a huge clock tower on earth from our space shuttle. Maybe we could make frequent short space trips in our super fast shuttle, measure the trip time from earth and derive a formula which could measure earth's time from the shutlle based on the distance and time measurements of the trip's data. I know there will be technical difficulties, achieving few things that I said. I never said all this is easy; all I said is, if we could achieve the things as I said above then we can look back into our past: achieving those things is again another story altogether.

Well not you leg would not just come off it wouldnt be affect because its on a different time line if you were there when you chopped of you own leg then it would be affected

Not according to the original Superman films (I forget which one). Superman travels so fast around the world that time goes backwards, and disaster don't occur.

If you could travel to the past, you would probably just wind up as a nonphysical astral observer since you cant undo what has already happened. The only use would be to view certain events that we have no idea how they actually occured (extinctions, murders, who said what). The future, which is as yet unwritten, could be visited but it would be a one way trip. Since theres no way to know the future unless you go, and no way to tell yourself about it once you get there, its kind of a risky crapshoot.
And what about the other 3 dimensions if you could time travel. It seems everyone is focusing on just moving through time. But what if, in moving through time, you wind up where something now rests but wasn't resting there when you left? Who knows if the building you left from hasn't been destroyed or reorganized, or if a new mountain range or ocean is there? Are you popped out to the nearest unoccupied space? Do you meld with the new item? And technically, what about the atoms that make up the air in the space that you are going to inhabit? (although i guess it would just make a little sonic boom and push aside for you. But i'd assume the air moving aside at speeds fast enough to accomodate a not there/there movement would burn you up).
If you did travel for a week at light speed, and then came back, wouldn't everything else be a light week older, while you were only 7 days older?
As you can probably tell, i dont really know much about physics, but i put my ideas on the table for the more informed to chew on and help me learn more myself.

"There's a shortage of perfect breasts in the world. T'would be a shame to ruin yours."-- Dread Pirate Wesley

Hello. I'd like to try making some definitions, because there are different concepts of time travelling and I'm kinda obsessed about ordering things. So here we go:

Definition 1: I define time travel as the manifestation of an information before it constitutes. The definition of before can be found in any document explaining general relativity.

I admit that I am not wholly satisfied with this definition, because in the so called "artist's paradox" there is no well defined event of constitution of the information.

I do intentionally refer to travelling backwards in time only, because travelling to the future is not really something special. My definition deals with information, because of the following. For any theoretical problems arising from time travel I've heard of so far, it makes no difference if I travel to the past in person or if I make a phone call to the past. On the other hand, if I could transfer matter to the past but its structural information would get lost thereby, that seems to me problemless but I would not call it time travel.

Now let's consider the original post. If you can leave the room with your two legged friend and chop off the leg of his past-self, you are not in your or his actual past. What I called time travel does not match this situation. The term before requires that time travel (as I defined it) can not change the past. This gives raise to the following definition.

Definition 2: With time sliding I mean transfering information to an alternative reality (i.e. parallel universe), which matches a time-shifted version of the originating reality until the transfer occurs.

The term time sliding is a reference to the TV show Sliders in which travelling between alternative realities is called sliding. Time sliding is sliding limited to a certain manifold of universes.

Now, if you time slide back and chop off your friends leg, his leg would not suddenly disappear. Neither in the reality you changed nor in the one you came from. When you return, you might be able to return to the future you came from, as seen in Time Trax. Your slide would show no effect. Or you might be unable to return to your original reality and instead travel to the future you created like Marty in Back to the Future or Homer Simpson in Time and Punishment(Treehouse of Horror V). There his leg would have been chopped off. But noone else than you would see it as a change. Nothing changes around us.

Also, each of the so called time travel paradoxa (which are actually in no way paradox but only defeat the concepts of causality and determinism) can not arise from a time slide.
While time sliding does not cause any fundamental problems, I don't know about any considerations which give raise to the assumption that sliding might be possible but limited to time sliding.

And finally I define a third kind of quasi time travel.

Definition 3: I define turning back time as reordering this physical universe or part of it to recreate a state which existed in the past.

If you turn back time one of two things can happen: Events might inevitably repeat until you turn back time again. This would leave the world trapped in a time loop.
Or, if there exists some kind of real coincidence, the time loop would repeat until something happens which stops you from turning back time. Even the most improbable event may happen to stop you, since things would repeat over and over until you don't push the button.

I hope these definitions will be helpful in discussing the topic. And I would feel honoured if you'd adopt them. You may want to alter or extend them. As I already mentioned, I am myself not satisfied with my definition of time travel.