How can we exist if time travel were ever to be a realty?

Question

Do we just stop so another can go back and forth...

Answer 1

Time travel in the sense you are implying is strictly scifi stuff. In practice, there can be no time travel into the past, despite some theoretical stuff implying worm holes might be able to do this. Worm holes, if they do exist, are so weird, even on paper, that no one really knows if the laws of physics as we know them would even apply inside them.

Time travel into the future is problematic, but more doable from a practical point of view. If we travel at 50% the speed of light, time outside our space ship will seem to speed up by about 15%. Thus, for ten days passage on board the very fast space ship, more than eleven days will pass on Earth. So when you land and step off at the space port, you will find yourself one day into the future. If your trip lasted twenty days, you'd end up a bit more than two days in the future upon landing.

But, and this is a BIG BUT, it would take more power (energy per time) to accelerate to 50% of light speed than current technology can generate...especially for something the mass of a space ship. (But we can do near light-speed velocities on atomic and subatomic particles in a lab. This is how we've actually seen so-called time dialation, which is the reason we can theoretically go into the future.)

Further, assuming a crew can withstand only a one g acceleration for any length of time, it would take v/g = t time to get up to v = 150,000,000 m/sec velocity, which is 50% light speed. As g ~ 10 m/sec^2, we can see t = 150,000,000/10 = 15,000,000 sec to get to v = 1/2 c at a = g acceleration. That's a bit over 2.1 years. And then they'd need to slow down for the landing...probably a tougher thing to do as there would be negative g's involved.

Bottom line, your question has no valid answer because it makes the invalid assumption that time travel into the past can be done. Unfortunately, perhaps, scifi is way more fi than sci.

Answer 2

Surely primitive cultures feel the same way about the "magic" of our air travel.

For us to answer a question about the unknown possibilities of time travel would be akin to asking the primitive human about the ramifications of air travel. We have no clue.

One could think of time as being another physical dimension and going from physical "Point A" to physical "Point B" is similar to going from time/space "Point C" to time/space "Point D", but in the physical sense, the people in the vicinity of "Point B" can see and/or hear you coming. What will the perception of the people in time/space "Point D" be upon your arrival? (Maybe it'll make noise like the Tardis.)

I have long pondered time travel and such oddities as I have described here make me think time travel is a one way street that we are currently traversing at a set rate of speed. It may be possible to speed it up (isn't that part of Einstein's Theory of Relativity?), but there is No U-Turn.

Answer 3

Branching universe theory allows for time travel and alternate timelines without affecting the original time lines.

Pre-deterministic theory holds that even if time travel is possible, everything that has happened has happened and nothing that one does can change anything but efforts to change the past actually causes the past to happen.

Answer 4

I think you've been reading too much science fiction.

Try this experiment:

Take a piece of paper.

Fold it, and press down the crease.

Try to make the paper the way it was before you folded it.

Answer 5

Well you can't travel backwards in time, so there's no existential dillemma.