Cause of relativity, Lorentz transformation and non Euclidean geometry, it is said space and time can't be viewed as separate entities but must be merged into spacetime (because there is no universal time valid for all observers). So: This spacetime is immutable. It is a fixed structure, unchanging in time (there being no time outside of spacetime). There is no such thing as an expanding spacetime (of course an observer like us following his world line may see an expanding space). Am I right? Some have told me I am wrong, and the expansion of the universe proves it. But I think they don't understand what I mean.