but how would we know?

I think the butterfly effect would keep them from interacting...

it's not time travel though, technically it's space travel. they're just traveling through a space that we've never been in...i think.lol

Logically, it sounds right. But when time traveling becomes real, logic goes out of the window. So we are back to square one.

The past cannot be changed. Everything that they came back to change, or went into the past to change, has already happened. Everything the time-travellers did was inevitable.

We are traveling in time now. When u move your hand while standing still, there's a slight displacement in time between your hand and body, it's just so slight it can't be percieved or measured. U might find this interesting. It was published in Nature Mag. several years ago. Some experimenters at Princeton, filled a tube with cesium atoms. They then shot a pulse of light (photons-much like electrons or matter) through the tube. The result was that the pulse exited the tube, before it had fully entered. Photons had traveled in time and ended up being in two places, at the same time. The light had exceeded it's own speed, and depending on your perspective(the light entering or the light exiting)one was witnessing it's future and the other it's past. So, yup, time travel is a reality. The question is whether biological units can survive or generate the speeds necessary. Personally, I strongly suspect there's another way. In the subatomic world, if you change the charge of a particle, it's counterpart changes it's charge simultaneously, regardless of distance. This effect could not be speed related(the distance is different and therefore the speed calcs. would have to vary accordingly, resulting in simultaneous change)I don't think these particles carry calculators. We may be looking at this from too linear a perspective; there may well be, another route. Hmmmmmm.....What's that they say about the shortest distance between two points? We may have to rethink that. =0]

Maybe we don't know what to look for - maybe they are amoung us now, maybe they got bored and left. Maybe we are they. Maybe I should go to bed.

Well there are a number of answers. One is that it requires such an amount of energy that it cannot be performed a lot, more than once, or even at all. Another is that they did and they were careful enough not to be caught (ufo's anyone?) Yet again, it may not be bidirectional, it may go to future only.

maybe nobody has come back to visit us yet because the future hasn't happened yet...or maybe this is the future..maybe it isn't the present at all...think about it

my secret is out, damn why cant i fix the flux capacitor. great scott

Time travel isn't possible. Unless it's also time/space travel. The Earth is always moving in space.

Good question. That could explain the UFO sightings around the world. UFOs have been seen for quite some time. Nevertheless, what they do is merely watch and leave. It could be people visiting us from the future.

they would be likely to travel back into parallel dimension. there are infinity of these so the chances of someone coming to our dimension is zero i.e. time travel is not possible.

Time is linear. You cannot travel back in time. If you were capable of creating a time travel device, it would take incredible amounts of energy, as silverxxx said. It would also most likely employ the use of a wormhole, which would be the actual time travel device. If you were able to maintain the opening of the wormhole, you would essentially have to drag one opening away at high speeds(light speeds). At these kind of speeds, time slows down, putting you further in the future than everyone that's moving at normal speed. The length of time you travel, and speed would have a bearing on how far into the future you go. You can now travel back to the time that the other opening of the wormhole exists in, by stepping through the wormhole, but never previous to the time that the wormhole is coexisting with everything else in the relative "present", and most definitely not before the existence of the time machine.