I was recently reading about NASA Faster than Light proposed spaceship, it supposedly will bend spacetime behind the spacecraft, so technically instead of bringing the ship to the destination, "it will bring the destination to you." now, I have an understanding of calculus-based physics, and a basic understanding of relativity.

From my lackluster knowledge of relativity, by conventional means achieving the speed of light is nearly impossible if not impossible, according to Special Relativity. if I am not mistaken if we try using a spaceship, as we approach the speed of light because of relativity, wouldn't the mass of the spaceship go to infinity? and if we have infinite mass doesn't it mean we need an infinite amount of energy to push it?

Even so, if we travel to say alpha centauri, which is 4.4 light-years away it will probably take around a month to go there at the speed of light, which is not bad. It will take a month for the traveler to go there, what about those outside?

to put it simpler, if someone goes to Alpha Centauri at the speed of light and he comes back, how much time would have passed in Earth?

(I would have used, calculations to illustrate better, but I do not know how to use equations in Stack-Exchange yet.)

  • $\begingroup$ The equations on Physics.SE are from MathJax, a few details can be found here. $\endgroup$ – Kyle Kanos Jun 20 '14 at 1:41
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    $\begingroup$ Also, if something is 4.4 lightyears away, it will take 4.4 years to get there at the speed of light. $\endgroup$ – Kyle Kanos Jun 20 '14 at 1:42
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    $\begingroup$ That is their claim. Note, though, that they claim that it would be traveling faster than light, not at light speed. There is a lot on this site about the intended "warp drive" they think they can create. $\endgroup$ – Kyle Kanos Jun 20 '14 at 2:30
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    $\begingroup$ The fact is that you cannot travel faster than the speed of light in direct terms. There is a loophole in this theory. If you can bend space, using 'warp drive' (still a theoretical concept) you are travelling a shorter distance to reach your final destination. However, your displacement is much larger. As speed is the distance traveled divided by time taken, you never actually exceed the speed of light. You just find a shortcut. It's as if you're saying you can't travel faster than a car, but you can reach the destination faster if you find a shortcut. $\endgroup$ – Gummy bears Jun 20 '14 at 6:51
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    $\begingroup$ Are you asking how the Alcubierre drive works? Or are you just asking about travel times to stars using conventional drives. If the latter see How long would it take me to travel to a distant star?. If the former see Harold White's paper. $\endgroup$ – John Rennie Jun 20 '14 at 9:57

Well here's an easier way to see it: as the universe is a fabric of space and time, the fabric can be rolled up and spread according to our needs. The problem: large amounts of energy is necessary for this to happen. In the starting, the Big Bang provided the energy necessary to do it. The speed of light limit is on actual objects, not on expansion of space, as observed during the period just after Big Bang. Thus we can bend space behind us and expand it in front of us at speeds faster than light, appearing as if we are travelling faster than light.

  • $\begingroup$ I see, and that is why we can exploit the loophole that Dr. White mentioned in his paper, that exists on relativity. How would then though the time, appear for an observer? outside of the craft. would 4 weeks traveling at that speed means 4 weeks would have happened outside the craft? $\endgroup$ – Lucian09474 Jun 22 '14 at 17:45
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    $\begingroup$ Sorry for late reply. Well, I am afraid I am not exactly sure. However using a bit of logic, what I suppose: As you are not travelling faster than light, time dilation shouldn't be a problem. You are not even travelling close to the speed of light, rather just cheating light. Hence, time outside the space craft should be equal to the time passed inside the space ship. Time only becomes a problem when you speed up, as you are not speeding up here, you shouldn't have to worry about that. Difficult to say what the observer outside will see. Please keep in mind much of this is still theoretical! $\endgroup$ – Gummy bears Jun 23 '14 at 6:49

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