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Time dilation at the speed of light

Postby katana7t » Sun Aug 15, 2021 4:56 am

I am having a problem getting my head around this example......You are on earth and say goodbye to a friend who gets into a spaceship that can travel at the speed of light. They travel to alpha centauri 6 light years away, so on the spaceship it takes 6 years to get there and 6 years to get back, on the spaceship you have aged 12 years. On the earth you watched the ship take off and are waiting for the ship to return from its mission, would it not also take 12 years for the crew to return? If not how long would you be waiting for its return trip to alpha centauri and back?

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Re: Time dilation at the speed of light

Postby ctactawong » Sat Sep 04, 2021 6:26 am


The problem is called "Twin paradox". You can search it for various level of explanations. A few points for this problem:

1. It is impossible for any object to accelerate to the speed of light because it would need infinite amount of energy. It is more appropriate to reformulate the problem to, say, 50% of speed of light.

2. The friend on spaceship would observe length contraction. To him, the spaceship is at rest, and the earth and alpha centauri are moving at 50% of speed of light. He would see distance to alpha centauri shorter than what you would see on earth. So it would take him shorter time to go there and return. In other words, he aged less during the trip.

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