It's supposed to be puff, puff, pass, bro. Stop hogging the good shit. 

You mean to tell me Back to the Future 2 didn't actually happen?

You mean to tell me you didn't understand the 'fiction' part of r/sciencefiction you just posted to? Next you'll be telling us there is no such thing as a Hobbit from the Shire.

It’s why I like the stories where it’s really just the multiverse. You aren’t time traveling to 1902. You are going to another universe where it’s 1902 still.

That's why it's called science "fiction". Many people aren't as interested in the physics and mechanics of time travel itself. Instead, we're fascinated by what comes of time travel and the stories we can tell with people out of time and their impacts.

So most movies show that you made a vehicle that walks at speed of light and suddenly you go many years in past

No, they don't? What are you talking about? I'm not aware of a single movie that does time travel like that. Most time travel movies leave the details on how the time travel works unexplained.

The time travael is not a fiction.

It's real.

But only in one dorectionnanf we can't go back.

The reason time travel isn't possible from a physics standpoint has nothing to do with anything you said, as far as I know.

The problem is that you have to surpass the speed limit of the universe, causality, which takes energy (that of course just also happens to be the speed that photons -light- travels) According to the way we think the universe works, you would have to generate infinite energy to drive anything past that limit.

Cause always comes before effect. The arrow of time and such. You need infinite energy to break that.

It's even more impossible, if that's a thing, to drive an object with mass past the that limit, since every iota of mass subtracts an iota of energy, and any amount of energy less than infinity isn't enough.

So maybe by manipulating the framework the object is in, like in an Alcubierre field or something, you might be able to travel at or above light speed, there's no conceivable way (again, that I know of) to cheat causality for objects with mass.

And popular cheats, like jumping timelines or alternate universes, don't work because there's no known way to get actual mass there (or back) with real physics.

Even if one figured that out, you then need a craft capable of colocating itself to a place where anything is. The entire universe is constantly moving, and changing your place in time by default changes your place in space. If you want to be any particular place, like Earth for example, you need to be able to place yourself exactly where Earth was at that time, at exactly the right speed, rotation and momentum to be at rest on its surface or at a velocity you can recover from.

Whatever that place is, I guarantee it is not where you start from. Keep in mind that the place you are going to is moving through space at 67000 miles per hour, rotating at 1000 mph itself, in a solar system that is rotating at 514000 mph, and is orbiting the center of the galaxy at about the same speed.

That's not counting the amount the universe has expanded since the moment you turned on the time machine, which is about 150000 mph as well.

You need a lot of things humans don't know how to even begin to get to time travel, most of which nobody can tell how to ever get.

The reason they do this is an old misconception about time slowing down as you get closer to c. The Lorentz time dilation transform gives you negative numbers and that means the time dilation factor is imaginary. This doesn't have any physical meaning (that we know of anyway) but a lot of people just assume it would go negative.

This means that the curve would actually not be linear but kind of exponential just like it is on the positive side of the graph. If you look here:

https://www.fourmilab.ch/cship/timedial.html

You see that the graph goes way up after starting slow, so if the same thing applied as v>c you'd have a situation where as you got faster than light the time dilation would get slower (because the square roots would start getting bigger than 1).

But that's wrong, clearly, for both mathematical and physical reasons.

There was for a while the idea that tachyons might exist; these are particles that were first proposed in 1967, but there isn't any evidence for them. Anyhow the idea was that tachyons need energy to slow down -- they always go faster than light and can't got below that velocity. But again, there's no evidence for it.

What I do think is really funny in a way is that in Star Trek they have sometimes this thing of having to shoot someone into the future -- this was a theme on ST:Discovery, and the simplest way to do "time travel" forward is just travel nearly light speed (like 99.999%, which Trek ships clearly have the ability to do) and let time dilation do the rest. No wormholes or exotic stuff needed. at v/c = 0.999999999 1 day on your ship is 61 years. They'd be 900+ years in the future after only a week and a half or so.

At light speed doesn’t allow time travel in any setting as light speed keeps you in your own light cone.

You have to go faster than light. If you do that you can (hypothetically) make a closed-time-like -circle and return (or send a message back) to before you left.

The entire point is that you need to have a method of going faster than light, not at light speed, something that many things do right with in our own universe, including, you know, light.

Now, what happens if you do manage that hypothetical time travel is an open question which depends a lot on what version of quantum theory you buy into, or what other theories you think are reasonable.

EDIT: As there may be some confusion, it should be noted that this is not going into your actual past, it's outracing the effects of past actions and allowing for the opportunity to make changes before the effects of those actions occur, hence why this particular approach is called a 'time-like-loop', not actual time travel.