Faster-than-light communication is not allowed in this universe. Imagine a sister universe that looks much the same as ours but allows instant communication between any two points. In that universe, simultaneity can be established using instantaneous communication. How would that affect our* description of the universe through laws of physics? In such a universe, would speed of light still be constant? Would there be time dilation? Would objects elongate with velocity? ——— *Assuming human-like species would have evolved in such a universe.