I don’t believe time travel will ever be possible. If it were, wouldn’t we know it already? Surely, someone would have came back by now 
The ocean of liquor, I drank to forget her, is gonna kill me, but I’ll drink till then.- George Jones Still Doin Time
Maybe time travel into the past is possible, but we destroy ourselves in the future before we invent the means to do it.
Those who do not learn from the past are condemned to relive it. Georges Santayana
accually time traveling into the past is physically impossible. you can only observe the past, not affect it.
but traveling in time to the future is possible. the only thing you need to do is to be put into stasis for some time. then when you wake up you will have traveled to the future from the time you were put into stasis.
bj0rn - just enjoying the ride!
All this science, I don’t understand. It’s just my job 5 days a week-- Rocketman
It’s a shame you missed the recent TBS movie “Time Shifters”. This is exactly what it was about. The simple answers is that the people from the future are very careful be remain undiscovered. They visit and leave before we find out about them.
Ha! They may think we’re not on to them, but I know better. These Merry Pranksters from the future are always popping in to my house, stealing socks from the dryer, hiding my car keys and moving the scissors when I know I put them down right there.
They also go around making footprints next to dinosaur tracks.
*aseymayo: They also go around making footprints next to dinosaur tracks. *
Just what I was going to say!
And by making those tracks, they made creationism last longer than it originally did, thus destroying the future continuum that they came from. Finding their existance gone, they went back again and crash-landed in North America during the last Ice Age. They ended up killing all of the wooly mammoths for food and clothing.
My favorite Quantum Leap was the one which showed what history was like the first time around, before Sam went back to Nov 22, 63.
SirJoe wrote:
Larry Niven once wrote that, if time travel into the past were possible, the odds would approach 100% certainty that someone, from some time in the future, would eventually travel back to the moment when time travel was invented and prevent it from happening.
So, if time travel is possible, we’ll never know. 
Tracer had the right idea. But Niven’s hypothesis is that if time travel is possible and will change the past, then someone will go back and make a change which prevents time travel from ever being discovered.
Heinlein explores at length in several short stories and novels the possibility of time travel in a deterministic plenum, where the acts of the time travelers do not thwart but rather result in the world as it is. His tour de force on this was one of his earliest stories, “By His Bootstraps.” Other books in which this is a plot gimmick include The Door Into Summer, Time Enough for Love, “…The Number of the Beast,” The Cat Who Walks Through Walls, and To Sail Beyond the Sunset.
It seems to me that time travel into the future would force us to answer some very big philosophical questions. If we travel into the future, does that mean the future is engraved in stone, and we simply travel along predetermined lines? Or, would moving into the future simply put us along the most likely future timeline?
And the problem with small furry animals
in corners is that, just occasionally,
one of them’s a mongoose.
Terry Pratchett, Witches Abroad
We travel into the future all the time. We’re doing it right now. And we are travelling at a rate of … hmmm … let’s take a reading here … exactly one hph (hour per hour).
Well, actually, that’s not accurate. Our planet and solar system is moving at some fraction of the speed of light, so an hour of real time seems to us like only 59 minutes and 59.9999999999999 seconds (or something like that). So I guess we’re really moving at more like 1.000000000000000001 hph. (By the way, this was experimentally proven on one of the Apollo (Gemini?) missions, where they lost almost a half-second in the course of a week or two.
Wanna travel into the future even faster? Take a nap. Works every time.
I believe that there is only one timeline and one future, but we simply don’t know what it is yet.
That “alternate timeline” stuff works only if the traveler can return to his/her starting point and make changes that affect the future. But then we’re left with that old paradox of killing your grandfather, aren’t we?
Try this: You go into the future and learn that your child becomes the equivalent of Hitler or Stalin, a dictator responsible for the deaths of millions. You’re doubly shocked because you don’t even have any children (that you know of). When you return to your origin, you immediately go to a doctor and get either a vasectomy or have your tubes tied, whichever’s appropriate.
You have just changed history, just altered the timeline and violated causality. Unless, of course it’s a child unknown to you who’s already been born, in which case, you’ve accomplished nothing.
Frankly, I think it’s a good thing that we don’t know the future. If we did know, it would ruin the surprise.
Those who do not learn from the past are condemned to relive it. Georges Santayana
Nice one, Keeves. Try this mind-bender. You’ve noted that we’re moving into the future at a given speed, and related that to the movement of Earth. Is it possible that the passage of time itself, as opposed to noting it as static (“frozen moment”), is connected to the fact that Earth does move?
Sorry, but I can’t help myself. I need to comment…
Relative to? Not relative to us, which is what is most important. The Earth is pretty still relative to most of us.
There ain’t no such animal as “real time”. In terms of measuring the passage of time, since we live on the Earth, it would be more meaningful to say that the Sun or the galactic center, or whatever, is travelling that 1.000000000001 hph
However, Undead Dude, we ARE in a constant one-g gravitational field, and that WILL slow our clocks down relative to someone far away from the Earth.
In fact, I believe it was this principal of General Relativity – not the special relativity of constant relative velocity – that altered the Apollo astronauts’ clocks. (Or should I say, failed to alter their clocks as much as ours on Earth were.)
Quite true.
Both would have an effect, but I am pretty sure that the special relativity effect is stronger for the experiments we can do.
I haven’t been able to find a specific reference to an experient done as a part of the Apollo program. Not sayin’ it didn’t happen. I just so far can’t find it.
The Hafele & Keating experiment in '71 showed directionally dependent time results using airplanes, which would suggest that at least in this experiment, SR effects dominated, as GR effects would not be direction dependent in this experiment. Of course going up in an airplane is not as nearly as much of a gravitational differential as going to the Moon.
The only experiment that I have found that specifically confirms the GR time dilation effect involved a comparison of atomic clocks at different (land-based) elevations.
Undead Dude asked me:
Technically, I think you’re right. But I never understood it, and this is why: It seems to me that the motion of our planet within our solar system is categorically different than the motion of our solar system within the galaxy or the galaxy within the universe. Those are prety much in a straight line or smooth curve, and it is easier for me to consider the solar system as stationary with the rest of the universe moving relative to it.
But it is very difficult for me to visualise the earth as stationary and the solar system moving relative to it, because the direction of movement is constantly changing. We are revolving on the axis, and orbiting around the sun, creating a helix-sort of path. It seems ridiculous to say that we are stationary and the sun is following this crazy path around us.
Therefore, even if we cannot point to anything in the universe as absolutely stationary, I do believe we can point to certain things as absolutely moving. We cannot say what their velocity is, relative to the theoretical absolute stationary object, but the velocity is definitely above zero. Therefore, we are experiencing a non-measurable amount of time dilation.
Well it is logical to think of the Earth as moving, but we still aren’t moving relative to ourselves, and that is what makes time dilation a reality. There is no point in saying that we are moving relative to “something”, because everything is moving relative to something. Not only that, but since the Earth is in free fall, it is furthermore not considered to be accelerating. The Earth is considered to be inertial, although it is inertial in a curved region of space.
So while describing the Earth as moving is simpler in terms of models and intuition, it is no more technically accurate to say that we are moving than it is to say that a random rock in deep space is moving. Keep in mind that even that rock in deep space it going to be following a curved path to some extent, because nothing is completely beyond the influence of gravitation.
It is perfectly reasonable for use to choose a different reference frame as our base (say, the galactic center), but unless we specify the frame, it is meaningless for us to refer to any sort of time dilation, except for the GR time dilation mentioned by tracer.