What do we mean by time travel?

ah man my brain hurts!:(

how much time do you have? time as put onto a time line is only compared to by years which is what we understnad in order to have it make any sense at all. So if you want to travel through time first you pick a place in time? A place? What continent? What language is being spoken? And if you are lucky and you don't pick a date, If you know two of the four you can pretty much guess the year almost because of history and it's recorded events and locations when they occured but time travel into the future is 100% speculation

Well as long as time is moving history is being made. But once time stops, history stops being made. So I guess you can have time without history. But I don't think it is possible to travel back in time without travelling back through history. For history does indicate past events, not events happening in the future. So it is possible to move through time that hasn't happened yet without moving through history.

Time gives us a measure of change. No change means no time. At absolute zero ( 0 Kelvin ) nothing moves, so I recon that time, as we know it, ceases to mean anything at absolute zero. The universe is around 4 Kelvin at present - so a lot is changing and time marches on. If you want to look back in time just look at the stars. What you see is how they looked when the light left them - not as they are now.

yesterday is history tomorrow is the future and today is a gift thats why they call it a present. im a theoretical phycicist.

One explanation would be dimension travel where time would be in reference to the beginning of our solar system or if you believe in it the big bang. Its really a complicated question with many many answers tho

You gonna go crazy by 2014 if you carry on down this path.

Einstein published his Theory of General Relativity in 1915 but it was not until the late nineteen forties that, the Austrian mathematician, Kurt Gödel found a time travel possibility within a solution to some relativistic equations. He found, that if the universe is rotating then time travel in both directions should be possible. By both directions, I mean, into the past and back or into the future and back. Alas, recent observational work used to study the cosmic back-ground radiation has indicated that the universe has not rotated significantly since its creation. Hence, time travel into the past would appear to be impossible. However, Einstein's theory of Special Relativity allows 'time-dilated' travel into the future. If an astronaut sets off on a journey travelling at a high percentage of the speed of light, then his on board clock will run more slowly than an equivalent clock here on Earth. Thus, when the high speed traveller returns after a few years of his elapsed time; here on Earth many hundreds of years may have elapsed. The time dilation equation is given below: - t(Earth) = t(traveller) ..............._________ ...............√(1 - (v/c)²) Where 'c' is the speed of light and 'v' the traveller's velocity, which may be expressed as a percentage of the speed of light ((say) 0.99999c). Therefore, to summarise, the answer appears to be that you cannot travel through time into the past but you can travel into the future - at least theoretically! Thus, you could study the history, between when you left and when you returned, from the future but not necessarily take part in it!

The commonplace meaning of "time travel" is when a mass moves faster than normal through the natural forward time line or, somehow, travels in reverse of the forward time line. In the former case, the mass travels into its future while skipping rapidly over the intervening time interval. In the latter, the mass travels into its past...again skipping over the interval. Time in fact does need history to exist. But it's natural history, not mankind's history. Nature has its own history called entropy, which is a measure of disorder...of chaos. Time is linked to positive entropy that takes place contiinually throughout the universe. The laws of thermodynamics state that entropy can only increase; so time can only increase, which is why we say it has a forward time line. Entropy is a physical phenomenon that represents the decaying nature of the universe; so time is a physical phenomenon. And once something decays, it can not be restored; time cannot be backtracked. A prime example that time is indeed real is a phenomenon called time dilation. Under relativistc effects, time intervals can be and have been stretched out. For example, at 1/4 light speed, a one second interval on a mass traveling at that speed would take 1.03 seconds to tick off as measured by an observer sitting still outside the mass. Remarkably, if the mass could reach light speed, time on board the ship would stand still as far as that outside observer is concerned. But the bottom line here is that time can be altered; so it is real and not just a mental concept relying on the history of mankind. And, as you probably recognize, this is one way a person on board that mass (a spaceship) could travel into her future. But going into the future is still traveling forward, not backward, along the time line. Because of entropy, traveling backward remains impossible and only interesting fiction in scifi.