If time travelers arrived many years into our future to discover all mankind dead,  (see details)?
148905
This is called the Grandfather Paradox, if you go back in time and kill your grandfather, then you would not exist, so how could you go back in time and kill your grandfather? This is answered with a radical theory that I can't remember the name of, it states that their are multiple universes, and whenever you go back in time, you jump between universes, allowing you to kill your grandfather without consequence, but also killing off any possibility of ever finding your old universe.
727887
that sounds type apocalyptic, but i think that later on in the future around the year 2120 or so that humans would be far enough in technology to move to another planet thats habitable for life. i think that they would move because the world would be to hostile for them becasue of global warming, soon animals would dominate but scientists predict that the sun would inplode in about 3 billion years, so that would be the end of that....what a mouth full.
589080
I don't accept the premise that a time machine is possible, therefore I can't answer such a question, even hypothetically. I can give you a proof that time travel into the past is impossible. It goes like this. If time travel into the past were possible, then at some time in the future, the means to travel into the past will be developed. That being the case, then we could expect to have been visited by time travelers from the future, but we have not. Ergo, time travel into the past is impossible. However, time travel into the future is possible. From the time I started typing this answer, up to now, I have traveled into the future about two minutes. However, it is still now. It is always the present. Always and forever.
306527
yes it would. that's a very interesting question. I thoght about it a few times myself and i figured that it was because the time reversed it meant that all the life on earth would also.
30709
If time travel were possible some one fro the future would have already been here and become a Las Vegas Odds Maker.
1156662
No we cannot. The time travel stories are our over enthusiastic mind's work. It just cannot be possible. Unless we attain speed of light. Do u believe in relativity? think about it... maybe u will find answers there.
138234
Yes. Wormholes subconciously send a ray of time 100 Million years  later into our universe. Witch means we wouldn't notice that it use to be the dinosaurs time and a quasar or worhole zapped us here now! You can never enter a wormhole once you enter it its portal to time closes and anybody who goes in it is trapped in eternal nothingness.
1000407
Einstein was referring to Time Dilation.  Time dilation would make it possible for a fast moving clock to travel into the future, while aging very little. That is, the clock (and according to relativity, any human travelling with it) shows less elapsed time than stationary clocks. For sufficiently high speed the effect could be dramatic. For example one year of travel might correspond to ten years at home. Indeed, a constant 1g acceleration would permit humans to circumnavigate the known universe (with a radius of some 15 billion light years) in one human lifetime. The space-travellers could return to earth billions of years in the future (provided the Universe hadn't collapsed and our solar system was still around, of course). A scenario based on this idea was presented in the novel Planet of the Apes by Pierre Boulle.\n\nA more likely use of this effect would be to enable humans to travel to nearby stars without spending their entire lives aboard the ship. However, any such use of this effect would require an entirely new method of propulsion. A further problem with relativistic travel is that the interstellar medium would turn into a stream of cosmic rays that would destroy the ship unless stark radiation protection measures were taken.\n\nCurrent space flight technology has fundamental theoretical limits based on the practical problem that an increasing amount of energy is required for propulsion as a craft approaches the speed of light. The likelihood of collision with small space debris and other particulate material is another practical limitation. As a result, time dilation is not currently a major factor in space travel.\n\nIf you would like further explanation of this theory, just let me know.
734390
Theoretically, time travel is possible. But current technology does not permit it. An interesting article appeared in Popular Science a while ago on time travel physics (see link). You're right about the stars - in that we're not looking at them in real time. In a similar vein, light from the earth reaches outward into space. An alien civilisation looking at us from far away through a telescope could theoretically view our past history. But light also weakens the further it gets away from its source, so to really look way back into our past, we'd need a really powerful instrument to detect such light patterns.
1160950
The time machine wouldn't have been effected either way. It stays on it's own plane of existance, that's why, if you'd go back in time, no one but the person who created it would see it.
50535
OK, first fo all Mr cliffx has it backwards.  As you continue to acellerate tworads the speed of light time will slow down for you and stay normal for everyone else.  Thus at that speeds you could travel 10000 lightyear in only 1 year, your lifetime, but thousands of years could pass on earth.\n\nIt has been theorized that time travel is posible but you could not simply accelerate to that speed.  Even if we could travel that fast the economical need would be currently beyond what any country has, even if they put all there funding into that one project.  but I am getting off the subject.\nOne theory is to travel into a black hole.  The gravetational field in a black hole is so strong that it has been theoryzed that even time cannot escape.  Thus if we were able to travel into a black hole we could use the captuered time there, so to speak, and transverse the timeline.\n\nThen there are ideas of actually traveling on light waves, lasers, to allow us to travel to the speeds necisary.  Of course then we could only travel to the time of how long that peice of machinery is on.  Also we would have to convert ourselvesinto an electrical signale, data (essicially transport), which would then bring up the promblum of measuring matter without moving it and blah blah blah.\n\nSummery, Yes it is possible to travel through time.  We just do not havet he knowledge and/or technology to do it yet.
48065
Consider human technology we have today compared to the technology of 300 years ago.  To a person back then, who did not have electricity, think how advanced we would seem to him.  Our technology would seem unbelievably far advanced.  Now consider an alien species having similar intelligence as humans.  If they are 300 years or more advanced than us, their technology will seem unbelievably advanced to us.  Because species evolve over hundreds of thousands of years, an alien species will likely be far more than 300 years ahead of us, so their technology will be unimaginably more advanced.  (Of course, we would be more advanced than other alien species, but those species won't be able to come here to visit us.)\n\nHowever, any alien species would be very, very, very far away from us, so it is extremely unlikely any could visit here.  It would be an enormous expense of resources, so the motivation for them to come here and spy on us secretly is not enough to justify the resources.
1128700
My first answer is probably not, because we would see future people by now.\n\nHowever, what if UFO's are time machines from the future?
403108
I watched a Discovery Channel Feature bout time and space,\nand one guy said that the present laws of Physics do not\nprohibit time travel... so it is a possibility.\n\nThe concept is so real that I think people from the future are walking amongst us today. They are more stronger, tougher, faster, and smarter. From the future, they are sent to our time to rule everybody else. I know one. His name is Ben Wallace.
290582
If time was a loop (Stephen Hawking's worm hole theory) Yes in a gazillion years (you might live that long, Yeah right) we would be in the same spot in time. But the down side is that we would pass through a wormhole completely disintegrating everything.
104729
If by human-like you mean intelligent, then yeah, it's almost certain that there either has been, is, or will be other, or many other intelligent life in this universe. \n\nThe saddest part of living in this massive universe is that another intelligent civilisation could have existed, learned to travel at the speed of light, visited thousands of star systems, and then became extinct, all before the first dinosaur even existed. And there's a decent chance that after all that exploring they may never have found any evidence of another intelligent species.
599329
A resounding YES! The reason we haven't met them is quite obvious, really. The incidents of life as we know it are so far apart that it would take more time for them to reach us or for us to reach them than any given life form in the universe has. In other words, we will all die and all trace of our existance will be long gone by the time any other beings got here. Take it from an alien!