# What is the minimum time required to travel 1 light-year from Earth and turn back? [duplicate]

Suppose I have a very powerful and durable rocket that is able to reach speed of light minus $$10^{-1000^{1000^{1000}}}$$ in $$10^{-1000^{1000^{1000}}}$$ milliseconds. Very instant acceleration. I can also adjust the amount of acceleration. I want my rocket to travel to a location that is 1 light-year far from earth, and turn back. I want my rocket to come back as soon as possible according to my watch.

1. Is it approximately 2 years?

2. How much time would pass according to my rocket's watch?

3. Would the result be different if I want my rocket to come back as soon as possible according to its watch?

• Nothing with mass can travel at the speed of light, adding on to this question and V M's answer. Nov 9 '18 at 20:43

I see where you are going but I don't think you can trick the time. If we ignore the reality and assume that your speed is approaching the speed of light:

1. It would take you just a little bit over two years if the clock you are using to measure the time was not with you in the rocket.

2. On the rocket's watch, you would have a very little time passed, less than a minute or about it, as when you move with the speed that is approaching the speed of light, your time slows down exponentially. If you could reach the speed of light, your rocket's clock would stop.

• If the clock stops on the rocket when it reach the speed of light (if it could). That means, it would take infinite time for my watch. So there must be a point where the speed is maximized and time minimized. I'm asking if this is so. Nov 9 '18 at 19:04
• @Koray, Re, "There must be a point where the speed is maximized and time minimized." No. There is no such point, The more thrust your rocket produces, the closer the round trip time will come to 2 years (as seen by the outside observer), or to zero time (as experienced by a passenger aboard the rocket.) If there is no limit to the thrust, then there is no limit to how close the round trip time will come to zero time or 2 years time. Nov 9 '18 at 19:51
• @SolomonSlow so the answers of my questions: 1) yes - 2) Very close to zero - 3) No .... Are they? Nov 9 '18 at 20:19
• I don't understand. If the clock on the rocket stops, doesn't that mean that the clock on the Earth is ticking infinitely fast? Isn't infinity > 2 years? Nov 9 '18 at 20:25
• actually, the person in the rocket will see the clock at earth run slower than his, it is only during acceleration/decceleration that the guy in the rocket sees the clock to speed up to reach about two years
– user65081
Nov 9 '18 at 22:56