Time Travel

While there are so many fantasies in science fiction, what really gets my goat is travelling backwards into history. While what Einstein probably said is that  astronauts traveling at speeds comparable to light are likely to come back to earth younger than people staying on earth, it doesn't mean that they would get back into history. A moment passed is gone forever.

Film makers and some writers make the mistake of passing off their imagination as credibly scientific which is not correct in my opinion.

Any Comments?

I agree that sci-fi seems to be drifting away from hard science.  It frustrates me to see especially when related to more recent scientific discoveries, like genetics where they get it completly wrong.  Sorry I can't think of any examples off hand.  Personally I feel sci-fi is a lot harder hitting when it is solidly grounded in reality.

 But then again sci-fi is fiction and futuristic technology is a convenient Deus Ex Machina.

Were it possible to travel faster than the speed of light, one would not travel back in time. Instead, time, mass and length would all take on imaginary values, as the value inside the square roots of Einstein's special relativity equations would be negative. I am not so sure what would happen under general relativity, but I am sure that the result would be approximately the same. So, one would not so much travel back in time as perpendicular to it. Whatever that means.

Time travel is excellent in fiction, though. It was shown that a universe rotating at a sufficient rate would permit time travel, however our universe is not rotating.

At the speed of light, mass is infinite. It would thus take an infinite amount of energy to reach the speed of light. While the universe has a very very large amount of energy, it is a finite amount.

I think that qualifies as a megabump!

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The Earth is moving at an amazing speed as the universe expands. So, if you go back in history, let's say one hour, then you will pop out into open and empty space.

The earth moves relatively to the universe so it depends on what reference point you use to determine your location

So, you are suggesting that if I get in my time machine it has to have the power to move the universe back to the previous position? That seems a bit odd. Honestly I don't know enough about physics and astro to make a real argument