Everyone should be aware of the twin paradox experiment, which tells us that B returning from space travel will be younger than A on Earth. The reason given by SR is that there is an acceleration process when B leaves the earth, and a deceleration process when B returns to the earth, so this is the root cause of B's younger age.

So we redesigned the experiment:

A, B, C are triplet brothers, C stays on the earth, A and B drive the spacecraft away from the earth at the same time. When they arrive at the P1 position at the same time, A starts to decelerate and return to the earth, B maintains a constant speed v and continues to fly for 1 light year to the P2 position, and then B returns, and B continues to maintain the speed of v to return to the position where A and B separated (P1), and then B starts to decelerate and return to the earth.

In this process, A and B have exactly the same acceleration and deceleration process, the only difference is that B maintains a constant speed v and flies a distance of 2 light years (P1-->P2, P2--->P1).

So who will be younger, A or B?

James R was thrown into disarray.

Finally Janus58 gave an answer, he said that B will be younger. The reason given by Janus58 is: (P1-->P2, P2--->P1) , during this period, the earth is taken as the reference system, B has a speed v, and A is stationary, so B will be younger.

But Janus58, have you ever thought about it: if B is the reference frame, A has a speed of v, and B is stationary, A will be younger.

So when A and B meet again on the earth, who will be younger?

So we redesigned the experiment:

A, B, C are triplet brothers, C stays on the earth, A and B drive the spacecraft away from the earth at the same time. When they arrive at the P1 position at the same time, A starts to decelerate and return to the earth, B maintains a constant speed v and continues to fly for 1 light year to the P2 position, and then B returns, and B continues to maintain the speed of v to return to the position where A and B separated (P1), and then B starts to decelerate and return to the earth.

In this process, A and B have exactly the same acceleration and deceleration process, the only difference is that B maintains a constant speed v and flies a distance of 2 light years (P1-->P2, P2--->P1).

So who will be younger, A or B?

James R was thrown into disarray.

Finally Janus58 gave an answer, he said that B will be younger. The reason given by Janus58 is: (P1-->P2, P2--->P1) , during this period, the earth is taken as the reference system, B has a speed v, and A is stationary, so B will be younger.

But Janus58, have you ever thought about it: if B is the reference frame, A has a speed of v, and B is stationary, A will be younger.

So when A and B meet again on the earth, who will be younger?

__https://photos.app.goo.gl/CankWckRaMtsZ48b7__
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