Do you think that time is relative and different time periods are happening at the same time?

[jobsforall]

Is time an allusion.. and is that why scientists think time travel is possible? What happens to the past and why can't you get it back?

[baza]

Bit deep for an insomniac!

[jake-the-peg]

I think you mean an illusion - although on the other hand!

Time travel forward is not only possible it happens all the time, just very small amounts unless you get close to the speed of light. There are a number of effects that show it.

Muons are short lived particles created in the upper atmosphere we should see very few reaching the Earth before they decay but we see far too many - they travel so fast time slows for them.

Atomic clocks have been put on aircraft and flown around the world and they are out of step when they return.

Traveling back is more problematic. The laws of Physics are essentially symmetrical on the small scale with respect to time, meaning that in principle it could be possible. However on the large scale there are laws like the second law of thermodynamics which seem to oppose it.

There are also the paradoxes - I'm sure we all know the killing your own Grandfather one. This isn't impossible to avoid, when you travel back and kill your own Grandfather you would not be born in that time stream (or Universe) but you would have in another.

I think the general feeling in physics is that backwards time travel is probably not possible but I don't think holding the contrary opinion is quite as career damaging as say announcing faster than light travel.

Of course the practical difficulties of something as big as a human managing it and surviving are probably insurmountable - however it's interesting to consider the implications of send say a TV or Radio signal into the past - naturally you'd need a receiver so you'd be unlikely to get signals from before you'd created that

[heathfield]

Time flies when you're having fun, and stretches out when you're bored. So yes, time is relative. And if you're having fun, and someone else is bored, then different time periods are happening at the same time.

[Mosaic]

You will find a full explanation in 'The Thief of Time', Pratchett T, 2002