>>533693236
>>533692983
>>533692781
>>533692651
>>533692564
Time Dilation. The equation I was looking for is t_1 = y t_2, where y = 1/Sqrt(1-(v^2 / c^2)). If I recall correctly, it also helps reconcile with the fact that the speed of light is the same in all frames of reference.
Final question. What are the current and old definitions of a single second? No need for exact numbers, just tell me what they used to measure the unit of time.