Space Twin Paradox

[HerbertSu]

Can somebody explain the Space Twin Paradox (the one where a twin goes into space and comes back younger than his/her other twin) in a simple, layman-like way? Thanks.

[Bill Angel]

My understanding is that there really isn't a paradox because one twin is subjected to non- inertial forces of acceleration and deceleration that the other twin is not subjected to.

[imatfaal]

Here is the Physics Faq section that deals with the twin paradox. It's a nicely written page with various explanations. Ask away if you have any questions.

[HerbertSu]

Thanks!

[nrobinson_12]

Okay, I just watched this documentary on this, and this is what I took away from it. The first thing to know is that standing still, we are already moving at the speed of light. Time spent traveling + distance traveled= lightspeed, therefore if you don't move, it doesn't take any time to get there, thus you are already moving at light speed. The second thing is frame of reference. If you were on a train that is moving very fast, and another person saw you on it from the window, and you would appear to be moving as fast as the train. Yet to you, you are sitting still on the train, and if you weren't able to look outside, it wouldn't seem like you were moving fast, only as fast as you were moving inside the train. If you both were on a train, lets say traveling 60 mph, and were to look out the window, it would appear that the other train is traveling at 120 mph, rather than 60. This is reference frame and can vary depending on the observer. So if one twin took off from earth in a rocket ship reaching speeds close to that of light speed (mind you, yourself are already traveling lightspeed just by sitting still), he would in essence be traveling almost double light speed, while the twin on earth was still traveling at just lightspeed, or barely faster. So, the faster the rocket ship goes, the closer to light speed it gets, means a larger distance will be traveled and time would slowdown to compensate for speed, because distance traveled + time spent traveling= Light speed. So if the twin left the earth at near light speeds, and was gone for 3 months, 80,000 years would have here on earth. If you think in a smaller scale, it's quite simple. It takes less time to get from point A to point B in a car, compared to if you were to travel the same distance on foot. So for the earth bound twin to travel the same amount of distance that the rocket ship did, it would take 80,000 years in he were walking, instead of 3 months......make sense?

[ACG52]

distance traveled + time spent traveling= Light speed.

 

I don't know what documentary you were watching, but if that's what they said, you might want to change the channel.

[IM Egdall]

I think the documentary was talking about speed through spacetime. This is a combination of speeds through space and through time. As I understand it, speed through spacetime is always c, the speed of light.