Why not? I am pretty sure we or something from us could go back to the past. I am not sure about the future though...

Consider a space ship traveling from Earth to the nearest star system outside of our solar system: a distance d = 4.45 light years away, at a speed v = 0.866c (i.e., 86.6 percent of the speed of light). The Earth-based mission control reasons about the journey this way (for convenience in this thought experiment the ship is assumed to immediately attain its full speed upon departure): the round trip will take t = 2d / v = 10.28 years in Earth time (i.e. everybody on earth will be 10.28 years older when the ship returns). The amount of time as measured on the ship's clocks and the aging of the travelers during their trip will be reduced by the factor \epsilon = \sqrt{1 - v^2/c^2}, the reciprocal of the Lorentz factor. In this case \epsilon = 0.500 \, and the travelers will have aged only 0.500×10.28 = 5.14 years when they return.

The ship's crew members also calculate the particulars of their trip from their perspective. They know that the distant star system and the Earth are moving relative to the ship at speed v during the trip. In their rest frame the distance between the Earth and the star system is εd = 0.5d = 2.23 light years (length contraction), for both the outward and return journeys. Each half of the journey takes 2.23 / v = 2.57 years, and the round trip takes 2×2.57 = 5.14 years. Their calculations show that they will arrive home having aged 5.14 years. The travelers' final calculation is in complete agreement with the calculations of those on Earth, though they experience the trip quite differently.

If a pair of twins are born on the day the ship leaves, and one goes on the journey while the other stays on Earth, they will meet again when the traveler is 5.14 years old and the stay-at-home twin is 10.28 years old. The calculation illustrates the usage of the phenomenon of length contraction and the experimentally verified phenomenon of time dilation to describe and calculate consequences and predictions of Einstein's special theory of relativity.

Source

Interesting topic.

1. If time travel is possible, why hasn't any future human come by and visit us? Given the infinite amount of time available in "future", surely humans would have invented a time travel machine if it is at all a possible feat.

2. The paradox of what would happen if you travel to your past and changed something to yourself. What would happen to your current self then? I do not agree the concept of journeying to a parallel universe counts as time traveling.

Your kidding right? I mean none of those explanations constitute hard evidence for the existence of time travelling.
And I usually believe in simpler explanations rather than thinking of the many fantastic possibilities.

Your arguments about time dilation merits some thoughts though.

time dilation has nothing to do with time travelling at all.

The twin paradox which is based on time dilation is just an effect observed from special relativity.

Those who studied special relativity should be able to understand twin paradox easily.

For those who don't, it's good for you to learn some.

Actually, anyone who travel on bike or car or plane would live a longer life compare to your friend standing on earth (the initial frame). However, the effect is too little (perhaps the range of less than few nano seconds) thus having no impact at all.

However, a number like 0.8c will have such effect by then.

Those who are interested you can study length contraction as well.

To TS, what you mention is wormhole, another theoretical proposal which still haven't been proven until today. However, i do believe wormhole exists as in GR but doesn't promote time travelling. GR is not really my field so my statement is not really correct. It is just a believe rather than a physics research.

I can't help recall a quote by someone,

'I notice that even people who claim everything is predestined, look before they cross the road'

Time travel would be an interesting issue if it was actually possible, (regardless of whether it is)

Just to play devil's advocate, I believe to us, from our 3-dimensional view of things, it must honestly seem impossible. If we had somehow be able to transcend and be a 4-dimensional being, time travel would actually be as simple as moving from point a to point b.

Anyone believe that if we could travel at the speed of light, we could accomplish time travelling? Imagine you travel at speed of light, ok lets not go that far, imagine we travel at the speed of an aeroplane, a speed of 245 m/s, slow if compared to the speed of light( i think...) we already burned and vanish to air, due to.... air friction?    and now u want to travel at the speed of light... 

I once imagined, blackhole and wormhole( i wonder if they are same ). If u are sucked into a blackhole, u probably be sucked to another dimension or possibly another time.. xD

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Added on June 15, 2009, 6:51 pmbtw, albert einstein promoted that quote where time travel is possible if u are able to travel at the speed of light.

Observing time traveler? Whee! We blew billions to create the universe's biggest history book

If the universe is predestined, you won't be traveling back in time, even as an observer. What you observe in the past may alter your present perception that will alter your future action. So if it's predestined, you shouldn't be changing your mind after reading what's in the past because that will alter the future.

In a predestined universe, Hitler will never get killed but WWII would still happen. It's contradicting because, if WWII were to still happen because it's being 'predestined'. Hitler would be predestined not to die as well
Actually no, space is full of space dust. At the speed of light, hitting a single sub atom is like the entire Jupiter slamming your body.

Outer space isn't actually void of nothing. If you travel beyond the border of universe, the empty 'space' is actually something. So it's sort of a perspective issue

Newton would have loved space. There is no air resistance. There is only gravity. Once a spacecraft is accelerated to a given speed, the engine is turned off and the craft coasts forever with its trajectory affected only by the force of gravity.

Source: http://helios.gsfc.nasa.gov/qa_sp_ms.html

Do you experience some sort of sense; for example;

Today, you dream about something.
About a week, you go some place that you never been and suddenly, you feel that you have visit that place, but can't recall when.

is it similar to time travel as well?