Q & A: Questions about relativity

Q:
Right, my head is fried trying to understand space time, relativity etc. I'm not that good when it comes to science although my curiosity does make me try to understand. I've been reading on the web for hours now to try and get my questions answered but the subject is so complex it results in most articles going off onto other tangents of the topic.So basically, Spacetime. Like in films such as Interstellar, I want to know, when someone returns to Earth after being away for, let's say 70 earth years, the people on Earth would have obviously aged by 70 years but in this scenario, the space traveller has barely aged at all due to the fast speed he was travelling etc. My question is, does the traveller FEEL like he has been gone 70 years? Or does it feel like a much smaller time similar to the ageing timeline of the traveller. Another question, if you were travelling at a constant speed close the the speed of light or whatever speed/G's a person can tolerate, would you be able to move freely on the vessel or would you feel the force as you do during acceleration? Last question. In our solar system, each of the planets have different amount of hours in their days and different amount of days in their years etc. I assume that's due to the speed of their spin, the distance in their solar orbit and the speed in which they travel that orbit. But would time itself change (slow down/speed up)?
- Daniel Moye (age 26)
Wales
A:

does the traveller FEEL like he has been gone 70 years? Or does it feel like a much smaller time similar to the ageing timeline of the traveller.

It's the second one. The traveler experiences whatever length of time passes on clocks in his reference frame, including "biological clocks" like an aging body. If he experiences one Earth day, he ages by one Earth day also, and one Earth day passes on his wristwatch.

if you were travelling at a constant speed close the the speed of light or whatever speed/G's a person can tolerate, would you be able to move freely on the vessel or would you feel the force as you do during acceleration?

If you were aboard your spaceship traveling in a straight line at constant speed, you wouldn't feel anything no matter how fast you were going. There's no limit to the speed a person can tolerate, although high acceleration can kill you. (Of course, if your propulsion system or whatever causes vibrations or something, you'd feel that. Or if you hit something. In our universe, you'd constantly collide with particles in space, and they'd look like high-energy radiation to you because of your high relative speed.)

You wouldn't feel anything traveling near the speed of light, but if your spaceship had windows, the view outside would . Another cool way to understand these relativistic effects is a free computer game developed by MIT called . It accurately portrays what you'd experience if the speed of light got progressively slower, eventually approaching walking speed.

In our solar system, each of the planets have different amount of hours in their days and different amount of days in their years etc. I assume that's due to the speed of their spin, the distance in their solar orbit and the speed in which they travel that orbit. But would time itself change (slow down/speed up)?

You're correct that the different lengths of days and years for planets in the solar system are caused by differences in rotation speeds and the time it takes to go around the sun. The outer planets have larger orbits, and they also orbit more slowly than planets closer to the sun. This difference in speed does cause relativistic time dilation between different planets, but it's extremely small—less than one part in a billion.

Hope that helps!

Rebecca H.

(published on 07/18/2015)