The impossibility of backwards time travel.

T

Tobias

Temporal Novice
The impossibility of backwards time travel.

Its being said and written by the experts that backwards travel would be impossible due to the problem of negative velocity. You can travel close to the speed of light, and move forward in time compared to everyone/everything else. Since you cannot move negatively, its not possible to travel backward in the same way you would forward.
Lets say that you are able to send one man away with the speed of light, and make him travel forward in time. By that claim you would also be able to send an object with him, like his timeship/spaceship. Now why not let his friend travel with him in that timeship. If all this is possible, there would be no actual rule to how many people, how many objects or even how much matter you could send forward in time.
Now imagine sending everyone and everything other than your own person forward in time. This would result in you being send back in time, compared to everyone other than yourself.

If forward time travel is possible, so is backward.
 
Its being said and written by the experts that backwards travel would be impossible due to the problem of negative velocity.
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Tobias,

What's the problem with negative velocity? Velocity is a vector quantity. If I have an object moving ----------> along the x axis the velocity is positive relative to some other object. Turn the object around and have it moving <--------- along the x axis and is has a negative velocity with respect to the same object.

Take two objects and have them accelerate directly toward each other. The two objects have precisely the same mass and when they collide both objects are traveling at precisely the same velocity. What is the total momentum of the objects?

Momentum is p = mv

Object A is traveling --------> it's momentum is mv

Object B is traveling <------- It's momentum is -mv

Total momentum is zero.

p(A) + p(B) = 0 (momentum of A plus momentum of B)

It's zero because one object is determined to have positive velocity and the other negative velocity with respect to each other. The mass is a scalar therefore it has no direction and its sign remains positive.

This equation is telling us that when the two objects collide they will either fuse and that new object will stop dead in place or the objects will rebound directly back along their original paths - each switching signs on their velocity.



The sign on the velocity is arbitrary. We can switch the positive and negative signs at will, just so long as we are consistent throughout the problem by reversing every sign.

Or maybe you're talking about some other "negative velocity"?
 
They're really nice equations, is my interpritation correct that what your saying is for example that two cars travelling really fast towards each other will on impact either fuse to make another car or rebound with negative velocity and travel back in time?
 
plasticdan,

They're really nice equations, is my interpritation correct that what your saying is for example that two cars travelling really fast towards each other will on impact either fuse to make another car or rebound with negative velocity and travel back in time?
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No - not at all. All I posted was some simple high school level Newtonian thermodynamics.

To set up an equation where, for instance, mass, energy and momentum are conserved you have to use the proper signs (positive or negative). No magic - just good algrbra.


Thus it is normal and expected to see negative velocities in such an equation.
 
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