Space and time or spacetime refer to concepts. They are conceptual tools.
I assure everyone here and the entire world that in reality, in the totality of existing objects and their relations, Space and/or Time or Spacetime does not
Why? Because space, time or spacetime lack Form. Notice how A through D are causal actions. Without an Object with Form an event of bending, containing, separating, expanding, contracting, or forming cannot possibly HAPPEN. Space has never formed an object, contained an object, separated an object, bent an object, let alone performed any sort of causal action on concepts such as light. Why? Because space is a concept. Concepts lack form and so are disqualified from the status of existence.
Humans worked out a concept and named that concept space. That is what we do. We name. We name objects and concepts. Concepts like space cannot expand or contract like a heart. Obviously Einstein made a blunder. If he truly thought in his heart of hearts and mind of minds that spacetime literally bends, then any normal person on this planet would laugh. The only reason this nonsense still gets preached is on blind belief and authority alone. Einstein's equations are valid, precise and have withstood the test of time therefore his thought about physical reality must be rational, valid, immaculate, perfect, unable to be challenged, etc. But mathematics and physics are two different animals. Heck, they are two different animal kingdoms. Math has nothing to do with reality.
Furthermore in the real world, Spacetime cannot possibly
A. be filled up with objects (or concepts).
B. be bent by objects (or concepts)
C. be flown across.
D. be traveled across.
Notice how the first two are change effects enacted by objects and the last two are relations with objects. In these scenarios spacetime is acted on by another object. Why can this not possibly happen? Because spacetime has no presence, no being, no form. Spacetime refers to a useful conceptual tool that has helped technology.
Again I assure everyone that this is a perfectly rational, completely sane, and thoroughly logical understanding of reality. If one supposes that in reality spacetime performs causal actions or undergoes change effects, related with other objects then that one has entered the realm of fantasy and science fiction.
At the end of one's life Einstein was no longer so sure of his thought. But of course today he is worshiped as a god. So it is very difficult pointing out his blunders to others. Again this takes nothing away from his bounty of good insights such as photoelectric effect (making the connection between light and electron), or his valid and beautiful math equations.
But physics is the study or reality. We must expose ideas and critically think. Spacetime has never performed a causal action or undergone a change effect in the entire history of the Universe. Spacetime cannot possibly relate with objects.
And besides in reality 4D is impossible. All my objects are mutually 3D. That is the only conceivable relation to make. Length, width, height. We use these ideas to measure objects. Time relates one's memory with two or more locations of an or objects. I think of where objects were previously located and their actions.