Debate Are we able to travel back in time?

Not necessarily. For all we know, the future is even more war-torn than us, or they time travel while cloaked or something. Timelines typically aren't something you want to disturb.

 

*dusts off the topic again*

Hooray Physics class! We just had a class to prove that travelling faster than light for matter is impossible. For those who have not been exposed to relativity or very little physics, avert your eyes. It will only hurt.

*Puts on physics-football-punting boot*

In Newtonian physics, v = U + v' (v is the velocity of object A with relation to object B, U is the velocity of object B, and v' is the velocity of object A). However, Einsteinian relativity disproved this, and, using the Lorentz contractions and time diolation equations, we now know that v = (U + v')/[1 + (Uv'/c^2)], where c is the speed of light. Using the same equations mentioned before, we can say that v/c = (a't/c)/([1 + (a't/c)^2]^(1/2), where a' is the acceleration of the object in a moving reference frame. If we substitute y = a't/c, we get v/c = y/(1 + y^2)^(1/2), which is always less than one. Because of this, the velocity of an object cannot exceed c.

\^_^/ IT'S GOOD!

 

While tachyons can theoretically move faster than light, they can also theoretically weigh less than nothing. I'd consider this branch of physics null and void for the purposes of this debate.

 

not entirely true. it all depends on whether or not light has a mass. it was always thought to be a wave and thus no mass, but we now know its a photon, (wave and particle) that suggests it may have a mass. if this is true, then it is possible to accellerate mass up to and past c.
but this doesn't mean people can. you've got to think about all the problem with using a human.

time dilation is accompanied by mass dilation too. so as you get a human to the speed of c, it would still have an almost infinite mass, and thus require an infinite force to accelerate it further.
there's also the problem with how long it takes to accelerate a human up to the speed of light without killing them. it would take a long time. and there's no idea what long term effects there are at living under 10g's for a rather large number of years.

 

Actually, time diolation is met with a momentum diolation, which only makes it seem as though there is a mass diolation. And it was proven that a photon (both mass and particle) has no mass. Even with acceleration at infinitely long periods of time, one cannot achieve light speed because that would be crossing that particular world-line's event horizon, which is impossible without completely rending the object destroyed. If I need to explain the terms, I'll be glad to, for anyone. Just to be nice.

 

well, lets get off topic for now, unless you dont want to, but IF you could go back in time, what would you do?

 

relative to another frame of reference yes, but wouldn't we be talking about an accelerating object? not one with a constant velocity?

 

Yes, and even in an accelerating reference frame, the amount of stuff in an object wouldn't change, just its momentum. At least, that's how I always understood it.

 

the amount of matter doesn't change, just the mass. (sounds stupid i know.) it's because its relative, like length. as the acceleration increased, mass increaes, length decreases. both are physical changes, not just illusions, even though they're not noticed in the frame of reference in whch the event is occuring. since they're physical changes, it would need more and more force to accelerate the object.
i can't remember for sure, but i think the enertia is constant, so as the velocity increases, the mass also has to increase to compensate?.

 

Honestly, at this stage, I'm not too sure. I'm just a freshman, after all. I've got another seven years ahead before I'm done with school, and then I'll be researching.

 

well i only did high school physics and a bit of other stuff i've read, so i'm getting in over my head

 

Well I really couldn't be bothered reading all the relpies to this topic.
Even though it is a topic that interests me a great deal.
No one knows if it's possible.
So essentially this is just a thread for peoples theories one it.
But at the end of the day modern physics cannot disprove time travel(jumping back or forward in time, by glancing over the posts it looks like time diolation has already been done to death by people who know more about physics than me).
So it may be possible.
I'd like to think that one day the human race will have reached a stage where we have mastered time and space.
It's a lot more hopeful and optimistic than moaning about how we're a stupid, doomed race and we're going to destroy ourselves.

But when you think about time travel there's just more questions and paradoxes that just do your head in.
I don't think the human race has reached a stage where it's ready for that kind of thing. I really doubt it will happen in our life time.

I think the rift between conventional physics and quantum physics is a good example of how little we really know about the laws of the universe.

So who knows, anything may be possible.