# Which clock will dilate when one is moving towards the other [duplicate]

Suppose two children are standing 100m apart one of them starts running towards the other with relativistic speed...which clock would be slower?

Note- I thought this was similar to the twins paradox but according to the solution i found for the paradox some time is unaccounted because of change in velocity....this is obviously not the case here

• I got his answer but what if they stop and then compare? Commented Jun 2, 2019 at 5:18
• In that case, rotation of time axis would not be present right? Commented Jun 2, 2019 at 5:20
• You are right that if either twin accelerates, but they are basically at the same place as the other twin, the other twins clock does not move. There is another reason that the twin paradox starts with the twins comparing their clocks at rest: it is that they are then able to agree on what time the clocks are starting at. In some sense the only effect in relativity is this effect called the relativity of simultaneity: this time dilation effect is just a compounded version of lots of that effect stacked. They disagree about what simultaneous means at distant points in space Commented Jun 2, 2019 at 5:29
• So when the moving child stops and compares which clock will be slower? Commented Jun 2, 2019 at 5:34
• When they stop, they will both appear to be ticking at the same rate, but they might show a different number, Alice’s might show a time of 8, 9, 10 while Bob’s shows 10, 11, 12 at those same ticks. Now Bob explains this offset by saying that he set his to 0 when Alice’s was at 0 and her clock ticked slowly, 10s actually happened but her clock only ticked 8. Alice explains this offset by saying that Bob screwed up that first synchronization by starting early: When her clock read 0, Bob’s already read 5.6, then it slowly ticked 6.4 during the next 8s, coming to 12. Both explanations are correct. Commented Jun 2, 2019 at 6:25