There once was a really smart guy named Albert Einstein that had a lot of free time on his hands. He figured out that space and time were inseparably connected to one another. His earth-changing work which he eventually presented to us mortals turned physics upside down. In his theories he postulated that space and time individually were both compressible or capable of being warped while the combination of space and time (space-time) was not compressible. Therefore warping of space also warped time to result in zero net change. Space-time is the term used to represent this thing that can serve as a fixed reference for everything and represents all the known dimensions of space and time together. Before Einstein we really didn’t have a connection for space and time nor did we consider that either of them could be compressed or stretched. We thought they were fixed. Einstein showed and has been experimentally backed up that only the combined space-time is fixed.