If I can travel faster than the speed of light, can I go back and forth in time?
140068
You will step on your own toes and feel it yesterday, remember?
459750
The concept of a time machine could exist, but it would take an almost infinite amount of energy.  The only way it could work is exactly the way you are asking,  You can only move forward in time, just at different rates.  So if you want to see the future then time would need to slow down for you and the world would have to speed up.  After a while you could return to earth and it would be the future.  \nFrom what is presently known about physics you can only move forward in time only at different rates from an observers point of view.  Believe me if we could travel back in time someone would have already screwed it up something big by now.\n\nThis is a one way trip, good luck
1002813
The key point to this whole question is if you could travel faster than light.  Since at our present knowledge of physics says no, and our current tech is not able to get anywhere remotely near the speed of light let alone faster than it, we will assume this hypothetical question implies these two things don't matter.\n\nIf so, then yes you could see into the past if you had an adequate viewing device which could discern the light you would receive at the end of your journey--light which you left behind by going faster than it.  But to see exaclty the number of years in the past as the light year distance you travelled, you woould have to move instantaneously.  If you had any non-relativistic travel time, you would have to consider time of your journey to determine how far in past you were seeing.  If you travelled 1.1 times the speed of light, you would only get to see .1*light year distance in years past.
68749
Rabid_Scientist is entirely correct.  Both you and your home see time in the other place as speeding up.  I do have something to add to that though.  If you maintain a constant velocity, it can only be measured relative to some other point of reference, so there is no way to determine which is faster, and consequenty it cannot be determined whose time is actually going faster.  However, if you are accelerating it's a whole different story.  As you speed up to that super fast speed where the time differental starts to be noticable, you will see time on your home planet speed up and they will see your time slow down. (Sorry, I'm not going to try to explain this, I'm not sure I entirely understand it myself).  If you were to go back to your home planet, far more time would have passed for them than for you.  This effect will be greater with greater acceleration and greater speed so in that regard time will pass on your home planet more quickly the faster you go.
1001554
According to Einstein and Stephen Hawking, travelling at the speed of light (for anything with mass, ie not photons) is impossible.  But travelling near the speed of light is theoretically possible.\n\nIf you were to travel close to the speed of light you would go into the future a lot quicker than those who don't travel close to the speed of light.  It would require huge amounts of energy.\n\nUnfortunately it would be a one way system.  To travel back it time it would be necessary to bend the whole universe.  Or you could find a way of travelling to parrallel universes (if they exist) and that would solve problems for both forward time travelling and back time travelling.
164691
According to Einstein, it's only possible to travel time to the future, although he never said that going back in time is impossible.\nTime slows down for you and your vechicle as you travel close to the speed of light (186,000 miles per second).  Anything outside is at normal time and speed obviously.\n\nTheoretically, if you travel 30 mins out into space at the speed of light and travel back to earth, you're only an hour old (by the way, at that speed, you've traveled an equivalent of six of our solor systems).  However, as you return to earth get ready to meet your great great grandson.\n***\nI don't know why.\nIf I did I'd own this freaking corporation.  *L*
689820
Neither you, nor the train, could ever travel at the speed of light since both of you have some non-zero rest mass.\nIn order to accelerate something with a non-Zero rest mass, an infinite amount of energy would be required....and in the whole universe, there is not an infinite amount of energy.\n\nBut lets say you were traveling just under the speed of light...at 99.99999999999999% of c and you began to run toward the front of the train, \nyou would still NOT be traveling at or above the speed of light (as seen from an outside, "stationary" observer) since at relativistic speeds such as this, velocities do not add in the normal Galilean way, you would still be traveling slower than the speed of light.
1139606
Im afraid I do not think time travel is possible.  Einstein’s theory says that as you move faster time slows down.  The problem lies in getting to a speed that is so fast that time actually moves backwards.  Anything with mass cannot reach the speed of light, because as its speed increases the amount for energy required to push it increases, so it would take an infinite amount of energy for something with mass to reach the speed of light.  Photons have a zero-mass and therefore light can travel at... well the speed of light :)\n\nSo if it was possible to break ourselves down into zero-mass pieces then it would be possible to travel the speed of light.  What is unknown is if you could travel so fast that you could actually "turn back time" which I do not believe is possible.  Or else we would see people from the future already coming back to the past.\n\nAnd then you would get those crazy little problems of ... if you went back in time and killed yourself at say 12 years old.   How would you have ever been old enough to actually travel back in time to kill yourself... because you would have been dead...\n\nIt could be possible to slow time down in relationship to yourself, so that the earth ages faster... If you consider that time travel.  Say for example you get into your space ship, and travel near the speed of light, then the earth would age faster relative to you.  If you consider that time travel then yes I believe that is possible.  But the thought of going forward, and back in time is not possible in my humble opinion.
303837
Time travel is possible when we travel forward not backward. IF you look to the history books there are no such thing of human come form the future. So that is the proof that has defined the theory that we can't go to the past. There are theory that we can move forward by using the method of speed. Once you increase the speed of travelling the time will change very fast, and you might be in the future. But to have that kind of machine to bring you forward needs a lot of discovery especially about the strenght of metal, fuel, speed, and a lots more. You can get the theory about speed from einstein. Whatever you want to know about it, you can get it there, BUT eventhough you learn about time travel, you won't get that technology while you still alive. Maybe you can use that information just for you knowledge. Not more than that.
27573
No. There is no practical possibility. Humans can't travel at a speed equal to or greater than that of light.
909079
Yes, it's possible but you would never be able to return from the future and you would have to travel close to the speed of light somehow.  According to Einstein's theories of relativity, if you travel close to the speed of light, time will slow down, so that hundreds of years could pass here on Earth while you travel at a fast speed.  So you would return to Earth in the year 3000 for instance at the same age as you are now, but you would never be able to travel back in time.  Time travel backwards is supposed to be impossible.
1003820
Depends. You want to go forward or back. \nI *cough* actually have an entire theory about time travel. \nAnd that is, that there can only be one of you in existence at a time. Thus- if you go forward your putting yourself in your future self's body. And if you go back your putting yourself in your younger self body.\nBut- if I'm wrong and quantum physics 'same thing in countless positions at the same time' is right. Then you can be in two places at once. Therefore time travel- where you keep the machine and keep yourself how it is now, is possible. Then... I have no idea how you would go about it.\n\nIf anyone tells you to plug in the toaster and stick a fork in where the toast is supposed to come out though. Don't do it. Them electrical burns hurt.
64267
Well, if you're traveling faster than light, then the light can never be in front of you.  There would be just a big nothing, probably drive you crazy if you looked at it.  I know, I come from andromeda.  We travel through space backwards so we can see where we're going.
532772
nothing but light can travel at light speed.  the faster you go, the more energy it requires to accelerate.  at speeds that are close to the speed of light, you would need what is basically an infinite amount of power to accelate.  with current technology, it is impossible.  the only reason light can travel that fast, is because when it is created it is already traveling that fast.  it doesnt have to accelerate.
4398
If you actually care, read "Time Travel In Einstein's Universe" by J. Richard Gott.  It actually proposes multiple ways this is possible.\n\nMy favorite which I learned in physics class is the fact that velocity warps time.  The closer you get to the speed of light, the slower time moves for you. I've read this, and it is definately true, we had to derive the formula in physics, and calculate the time, lenghth(which decreases with speed), and mass (which increases with speed) distortion as well. The new time which has passed is equal to the time passed of a stationary observer over one minus the square root of velocity squared over the speed of light squared.  The effects of this are very negligable unless you are moving at speeds very very close to the speed of light, at least over 90% of the speed of light, and we haven't gotten anywhere close yet.  But theoretically if you were traveling very close to the speed of light, you could rotate the earth for what seems like days to you and then have years pass on earth, thus in a way traveling into the future.  Also, it gets slower and slower so that it is thought that time would actually stop if you were moving at the speed of light, and so now what happens if you move even faster? Some think it might cause you to go back in time.  It is impossible to travel faster than the speed of light, however in his book, Gott discusses looping around strings(the strings from string theory) which warp space time, and discusses ways to "beat" light and actually show up someplace before you left.\n\nTime definately slows down with velocity, therefore time travel definately occurs, however, i actually have a problem with the time travel of humans.  Because along with time dialating, mass also dialates, and length contracts, if we were to approach speeds significant enough to distort time, our mass would increase and length would decrease.  Now since density is mass over volume, wouldn't that mean that our density would increase dramatically? wouldn't our blood then become so dense and viscous that it prevents blood flow and our cells become deprived of oxygen and we die? Because of this, I find it unlikely that we will ever be able to time travel, but if we can accelerate objects enough, we will probably eventually be able to send other things into the future.
467849
I think that there is the theory that you could travel back in time, but it is really all Star Treckie.  I don't think there is any possibility of travelling back in time, no matter how fast you can go.
169854
Of course.  We all travel forward in time, at a rate of 1 second per second.  ;)\n\nBTW, in the time dilation examples cited here, you don't actually travel back in time, it's just that one object travels forward in time at a slower rate as observed from the other reference frame.