1, the theoretical basis of parallel universe is Einstein's theory of relativity;

2. In the theory of relativity, the speed of light propagation is 300,000 kilometers per second, because the speed of light is limited, which means that the propagation of light takes time;

3. In addition, it can be deduced from Einstein's theory of relativity that the time coordinate system of a moving object is different from that of a stationary object;

Now, suppose all the universes at this moment are regarded as one piece, just like cutting a loaf of bread. It is being cut at this time, so there will be no difference in time.