How fast would you have to travel (in terms of c) so the distance would be only 15 light-years?

Suppose you decide to travel to a star 90 light-years away. How fast would you have to travel (in terms of c) so the distance would be only 15 light-years?

How fast would you have to travel (in terms of c) so the distance would be only 15 light-years?
no matter how fast you traveled, the distance would be still 90 light years.





But I think you are looking for length contraction of 15/90 or 1/6





L' = L√(1-v²/c²)


1/6 = √(1-v²/c²)


0.0277 = 1-v²/c²


v²/c² = 1-0.0277 = 0.9772


v/c = 0.986 of the speed of light
Reply:Billruss' math is right, but his assertion is wrong.





If you go at that speed then in your frame the distance is indeed just 15 ly. He has failed to understand that there is NO abolsute space and NO absolute tiem. That is why it is called RELATIVITY.
Reply:You would need to travel at six times the speed of light (299,792,458 m/s) or 1,798,754,748 miles per second.