Time travel

[Waterwolf]

What is the current scientific opinion on time travel?

[Sensei]

Some researchers did an experiment where a photon arrived at its destination point before it left its starting point. Theoretically, if you could travel faster than light, which, according to Einstein, no matter can do, you could 'see' back in time. Although, I often wonder if you were travelling faster than light and looking behind, would you see it anyway? There's lots of good stuff on the net about this subject. (Just stay away from the ones that are waiting for the mother ship to arrive!)

[buyrite]

What you probably mean by this question is time travel a la Dr Who. In other words you get into a machine push a few buttons and hey presto! you are in the 20th Century. This is physically impossible because every object in the universe has a time dimension. For example, if you went back to the latter part of the 20th Century particles in your body would be in two places at the same time. Time is as real a dimension as length. You would think it odd if you had a table which was 2ft long AND 4ft long, wouldn't you? It is only because time seems different that people are willing to believe in the Tardis but not in a table with two lengths. If you have a looser definition of time travel, then there are get out clauses which allow limited forms of 'time travel' - the most notable of these being the time dilation effect allowed for under Einstein's Theory of Relativity. The standard example is the case of two men with identical clocks. One stays on Earth, the other travels to Sirius and back at near the speed of light. When they compare clocks and calendars they might find that for the spaceman 10 years have elapsed but for the earthman 50 years have gone by (depending on the exact speed of the spaceship). It is as if the spaceman has time travelled into his own future. Of course, he hasn't really. As I pointed out earlier, the particles of which his body is composed have a time diemnsion and the particles are not duplicated elsewhere in the universe when he reunites with his colleague.

[comeleon]

Re-reading my posting I realise I need to correct one point. Sirius is so far away that you can't get there and back in 10 years. The spaceman's clock would have to show at least 17 years of elapsed time.

[Welshwizard]

I can see how looking back into old frames of light could display the effect of looking back in time but isn't the theory that travelling at near speed of light makes you go forward in time incorrect, if you were traveling near speed of light you could catch up or pass old frames of light containing images of time but as soon as you stop you would be back in the present, it's only images and we use lighter as a clock for time but it's not actually time it's self so speed and light together can not produce time travell. It like saying that if you are in a room with no windows and you turn the light out you can no longer see anything there fore time is stopped, and asyou know this is not so. If there was never anything alive to experiance time, would it exist? When it comes to the end of time and there is nothing left does that mean that time never really existed? There is only one what to go back in time and that is to take every single little thing in existance, choose the time you want to go back to and put every thing back to the way it was at that time, e.g imagine a cube, this cube is the universe, nothing else exists except for the cube and what is inside it, all that is inside is a small ball. For the firs second of the cubes life the ball is in the bottom left corner of the cube, for the 2nd second the ball is in the bottom right corner, to go back in time to the first second just put the ball back to the bottom left corner. Forget about numbers and light an our consepts of time for a minute is everything in this cubed unevers not as it was a second ago.....