Suppose two spaceships A and B have on them clocks A and B and are at positions A and B in space when both clocks say noon. And suppose their speeds differ by 161,000 miles per second, and they are set to collide with one another when clock A says 2 o'clock.

My question is what time will clock B say when the two spaceships collide? By symmetry, the answer should be 2 o'clock. However, according to special relativity, the answer is 1 o'clock. Which answer is right? They can't both be right.

This is a modification of a paradox found in Herbert Dingle's book Science at the Crossroads.

Suppose two spaceships A and B have on them clocks A and B move along the same straight line at uniform speeds differing by 161 miles per second. And suppose they are at positions A and B in space when both clocks say noon. And suppose that after noon, they are set to collide with one another when clock A says 2 o'clock.

My question is what time will clock B say when the two spaceships collide? By symmetry, the answer should be 2 o'clock. However, according to special relativity, the answer is 1 o'clock. Which answer is right? They can't both be right.

This is a modification of a paradox found in Herbert Dingle's book Science at the Crossroads.