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When approaching light speed why would this fail?

  1. Jun 3, 2015 #1
    Ok Little background knowledge im a huge scifi nerd I know some about modern physics mostly conceptual not mathematical The limit of my mathematics is the rocket equation. Anyway as most good ideas this one came to me in my sleep. I understand that the general convention is travel to the speed of light is impossible on the grounds that your essentially having to use proportionally more and more fuel for proportionally less and less acceleration and while I cant even remotely claim I understand the reasoning behind that I accept it as true.

    my dream involved a society that had mastered the concept of subatomic particle physics and could manipulate matter and energy at will through massive expenditure of energy. They had a starship in space that they managed to open a small wormhole in front of with a gravitational attraction of 10m/s . the end of the wormhole being set up within the outer edges of the openings gravitational sphere of influence. The achieved effect was a constant acceleration as the acceleration grew more intense they would slowly move the ends of the wormholes closer and closer together. This gave to there projectile (ship in this case) velocity derived without expenditure of fuel. Now in the real world why would this not work?

    Also upon waking I thought wouldn't it work better if they created a black hole infront of there craft at a fixed distance of say 100km out from the event horizon and they could create it such that it would have any ammount of acceleration at any vector they chose. and could dissapate it at will.
     
  2. jcsd
  3. Jun 3, 2015 #2

    russ_watters

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    There are a number of ways to get around the problem of carrying fuel, but none of them have anything to do with the issue you are facing.

    The issue is that velocities don't actually add together in a 1+1=2 fashion, so no matter what acceleration you give your spaceship over any time (or forever), it still won't ever reach the speed of light. See here for more:
    http://en.m.wikipedia.org/wiki/Velocity-addition_formula
     
  4. Jun 3, 2015 #3
    Wormholes probably can't exist. But if even if they can, they probably can't do what you say. The parts of the wormhole have mass (maybe negative?), and so they have momentum. Momentum is conserved, so accelerating your spaceship this way will require accelerating the wormhole somehow. Anyways, it's safe to say it's impossible.
     
  5. Jun 3, 2015 #4

    PeterDonis

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    Because you're assuming that wormholes can be created by "manipulating matter and energy". They can't. You would need exotic matter and energy, which nobody has ever observed, and which according to our best current theories can't exist.

    This is a little better, since in principle you could create a black hole by "manipulating matter and energy". But having once created it, you can't dissipate it at will, and the only effect of creating it is going to be that the ship will fall into it. So this won't work either.
     
  6. Jun 4, 2015 #5
    Even if you could dissipate a black hole, you still have conservation of momentum. The black hole has momentum. It has to go somewhere when you dissipate it.
     
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