What does "time" mean in the term space-time? I am trying to understand why anything that travels through space, from a proton to massive galaxies, is always referred to as traveling in space-time, not just space. Does this have to do with time being relative?
I understand that 3d space and time together constitute a space-time.
Can someone illustrate with a scenario to point out the need to describe things in terms of space-time.