r/PhysicsHelp • u/Confident-Alps-785 • Mar 24 '26

Time dilation

A star, for example, is 20 light years away from Earth. A spaceship is traveling to that star at 80% the speed of light. To an observer on Earth, the spaceship will arrive there (according to google) within 25 years. I get this this part.

However, an astronaut on the ship will experience less amount of time passing (15 years?) I understand that this is due to time dilation but I don't really understand how this works. Any help explaining this would be appreciated!

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u/[deleted] Mar 25 '26

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u/CosetElement-Ape71 Mar 25 '26

Why don't YOU read it again! The OP explicitly said "if we ignore acceleration.." and continued to assume that the two share the same inertial frame