According to the theory of relativity, there is no universal "now" that is simultaneous for all observers. The perception of simultaneity depends on the observer's frame of reference, particularly their relative motion and position in space-time.

For example, two events that appear simultaneous to one observer may occur in a different order to another observer moving relative to the first.

This phenomenon, known as the relativity of simultaneity, means that the concept of a single, absolute "present" moment does not hold across the entire universe.

While all observers experience their own subjective "now," these moments are not synchronized across different frames of reference.