That depends on who you ask. In Special Relativity, time involves the mathematical factor SQRT ( 1 - V^2 / C^2). If V is greater than C, the velocity factor becomes Imaginary. Imaginary numbers are a very important part of Physics, but they are misunderstood by many. An Imaginary number is any number that includes the square root of minus 1. Apparently many PopSci programs don't know this and claim that Faster Than Light (FTL) means backwards in time. PopSci programs also often claim that time travel is possible through Black Holes, Worm Holes, and things like this but PopSci programs are for amusement, not science. I am always amused when a PopSci program explains how the laws of Physics break down at the speed of light then they go right ahead and state what would happen at FTL.
You can't travel through something that does not exist. Time was created by man to organize his day. Sun dials and hour glasses were not good enough, a clock that divided the day into, more or less, equal segments, this finally got people to the dinner table on time. When man had a reliable clock he could measure the speed and distance of motion. Motion and space is the fabric of the universe. Earth is a mere speck in the cosmos. Why does it need time zones? Bodies in the universe are in constant motion and they never pass through the same space twice. If time did exist and someone wanted to move through it he would have to devise a way to arrange the universe into the precise configuration it was , or will be in, at the time he wishes to visit. Do you really think this is possible?
Frampy, that's not presentism. The wikipedia article explains it alright, but it doesn't justify what you claim. I wrote my thesis updating presentism and it's competitor, eternalism, to comply with modern physics. If I have time, I'll edit the wikipedia article to include some of that work, especially the quantum mechanical considerations. There are presentism and eternalism considerations of time travel, which I discussed in a recent answer: http://answers.yahoo.com/question/?qid=20080407075...
As for time travel, relativity allows time travel into the future by accellerating very quickly. It is a misconception that moving very fast will cause everyone elses time to speed up allowing you to travel through time. It's very much the opposite. When you move very quickly, everyone else sees your time move slower, but you see yourself as stationary and everyone else as moving very quickly, so you see their time move slower. However, when you turn around and go from moving very quickly in one direction to moving very quickly in the other, you are not in an inertial reference frame. You can feel your acceleration. During that time, you will see everyone else's time as moving very very quickly compared to yours. However, for such time travel to be practical, even if you ignore the incredible quantity of energy required, it would have to take you at most a few years to move forward in time at least a few minutes. (Really, you'd want it to take a few minutes to move forward a few years, but that's even more difficult). To do that your body would have to experience so much acceleration that the forces would flatten you. There'd be no way to survive it. You couldn't be protected from the forces because for the effect to work you'd have to actually experience them. Also, this method only allows travel into the future, not the past.
There is another option that may or may not be possible. If you create a path through spacetime and then separate the ends of the path through time, using relativity, you can then travel through one end of the path and come out the other end in another time. One way to do this is with wormholes. The physicis Ronald Mallett is working on a method that uses spinning lasers to create a relativistic time loop. This is the only way to travel back in time that hasn't been proven impossible yet, though if Mallett fails, he may end up proving that it was impossible all along. This method does not allow time travel to before the invention of the time machine, so there's no way we could have encountered any time travellers.
Yes. We progress forward in time one day every 24 hours. If you go close to the speed of light, you can make the rest of the universe go faster than that, but not yourself. It's still one day at a time every 24 hours for you.
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theoretically sure... but we wont be able to do it.
unfortunately.
That depends on who you ask. In Special Relativity, time involves the mathematical factor SQRT ( 1 - V^2 / C^2). If V is greater than C, the velocity factor becomes Imaginary. Imaginary numbers are a very important part of Physics, but they are misunderstood by many. An Imaginary number is any number that includes the square root of minus 1. Apparently many PopSci programs don't know this and claim that Faster Than Light (FTL) means backwards in time. PopSci programs also often claim that time travel is possible through Black Holes, Worm Holes, and things like this but PopSci programs are for amusement, not science. I am always amused when a PopSci program explains how the laws of Physics break down at the speed of light then they go right ahead and state what would happen at FTL.
You can't travel through something that does not exist. Time was created by man to organize his day. Sun dials and hour glasses were not good enough, a clock that divided the day into, more or less, equal segments, this finally got people to the dinner table on time. When man had a reliable clock he could measure the speed and distance of motion. Motion and space is the fabric of the universe. Earth is a mere speck in the cosmos. Why does it need time zones? Bodies in the universe are in constant motion and they never pass through the same space twice. If time did exist and someone wanted to move through it he would have to devise a way to arrange the universe into the precise configuration it was , or will be in, at the time he wishes to visit. Do you really think this is possible?
Frampy, that's not presentism. The wikipedia article explains it alright, but it doesn't justify what you claim. I wrote my thesis updating presentism and it's competitor, eternalism, to comply with modern physics. If I have time, I'll edit the wikipedia article to include some of that work, especially the quantum mechanical considerations. There are presentism and eternalism considerations of time travel, which I discussed in a recent answer: http://answers.yahoo.com/question/?qid=20080407075...
As for time travel, relativity allows time travel into the future by accellerating very quickly. It is a misconception that moving very fast will cause everyone elses time to speed up allowing you to travel through time. It's very much the opposite. When you move very quickly, everyone else sees your time move slower, but you see yourself as stationary and everyone else as moving very quickly, so you see their time move slower. However, when you turn around and go from moving very quickly in one direction to moving very quickly in the other, you are not in an inertial reference frame. You can feel your acceleration. During that time, you will see everyone else's time as moving very very quickly compared to yours. However, for such time travel to be practical, even if you ignore the incredible quantity of energy required, it would have to take you at most a few years to move forward in time at least a few minutes. (Really, you'd want it to take a few minutes to move forward a few years, but that's even more difficult). To do that your body would have to experience so much acceleration that the forces would flatten you. There'd be no way to survive it. You couldn't be protected from the forces because for the effect to work you'd have to actually experience them. Also, this method only allows travel into the future, not the past.
There is another option that may or may not be possible. If you create a path through spacetime and then separate the ends of the path through time, using relativity, you can then travel through one end of the path and come out the other end in another time. One way to do this is with wormholes. The physicis Ronald Mallett is working on a method that uses spinning lasers to create a relativistic time loop. This is the only way to travel back in time that hasn't been proven impossible yet, though if Mallett fails, he may end up proving that it was impossible all along. This method does not allow time travel to before the invention of the time machine, so there's no way we could have encountered any time travellers.
Yes. We progress forward in time one day every 24 hours. If you go close to the speed of light, you can make the rest of the universe go faster than that, but not yourself. It's still one day at a time every 24 hours for you.
Nope, following the theory of presentism.
Think of everything as atoms, right? The atoms that make me, were once, say, in the food i ate, right?
Well, if you went back in time, what would happen to the atoms that make the present me? do they vanish and go back to the food that they came from?
And, you can't go forward, because unless you believe in fate, it hasn't happened yet.
I explained it really badly, but you can check out on wikipedia
http://en.wikipedia.org/wiki/Presentism_%28philoso...
No it was a fiction
it is a fiction
and it will be a fiction
If so...would you not have already had a visitor?