I have read that objects with non-zero rest mass cannot attain light speed $c$. But for the sake of this question let us assume that Mr. X can get as close to $c$ as he wants. So this means that an observer watching on from Earth see his time pass by normally whereas time slows down for X. No matter how many billions of years pass by in Earth only a few milliseconds pass by for X (obviously he doesn't realize anything).

Now consider that Mr. X never encounters any obstacles in his path to stop him. Will he reach the end of the universe - almost instantaneously in his own experience - both from the perspectives of time and space?

Note: I am imagining if the end of the universe was to occur it would somehow reduce X's speed significantly so that he will start to experience what is going on around him again.


EDIT : I am not altering the original question because some of the comments indicate that a few of our friends have understood what I actually meant.

To clarify, this article explains some of the possible theories for end of the universe https://en.m.wikipedia.org/wiki/Ultimate_fate_of_the_universe

Back to the questions,

  1. Will Mr. X witness any of these events?
  2. If the Universe has no end will he reach the edge of the universe (assuming it is finite)?

Please consider that Mr. X has a technology that will accelerate him close to $c$ and we need not bother about how he did it.


closed as unclear what you're asking by Ben Crowell, ZeroTheHero, Kyle Kanos, user191954, Yashas Nov 23 '18 at 15:55

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  • $\begingroup$ Interesting question :) Are you sure that the speed of light cancels out time for the object traveling with it? Remember, light itself requires time in order to get from point A to point B $\endgroup$ – Alex Doe Nov 22 '18 at 14:26
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    $\begingroup$ This is certainly mainstream physics. Suppose Mr. X accelerates at constant acceleration. The answer is yes he will reach the edge of the observable universe (14 billion light years away). According to this book: springer.com/gp/book/9783642372759 if he accelerates at g, he can reach the edge of the universe and back in 50 years. In the earth frame, this will take 28 billion years. In his frame, the universe length-contracts to the order of 10-100 light-years. (Of course in real life he would be fried by the CMB.) $\endgroup$ – Eric David Kramer Nov 22 '18 at 14:38
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    $\begingroup$ If someone wants to do fuel calculations, there are formulae on the classic Usenet relativistic rocket page. Note that merely going to Andromeda (2Gly) with constant 1g acceleration (without stopping) takes 4100 tonnes of energy per 1kg of payload, (i.e., 2050 tonnes of antimatter annihilating with 2050 tonnes of matter in a perfect engine). $\endgroup$ – PM 2Ring Nov 22 '18 at 15:05
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    $\begingroup$ What does "the end of the universe" mean? Current cosmological models don't have anything like a Big Crunch. $\endgroup$ – Ben Crowell Nov 22 '18 at 15:47
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    $\begingroup$ @deadpool The universe doesn't have an edge. Either it's infinite in spatial extent, or it has positive curvature & wraps back on itself, like the surface of a sphere. The Wikipedia article linked in my 2nd comment discusses various scenarios of the far future. $\endgroup$ – PM 2Ring Nov 24 '18 at 18:32