Einstein’s thought experiments showed that our measurements of space and time are fundamentally linked. Our perception of time depends on how fast we are moving through space; our perception of space depends upon how fast we are moving over time. That linkage suggested to him a new entity—spacetime. Spacetime combines the time variable (t) with the three spatial variables (x, y, z) in a four-dimensional continuum (x, y, z, ct) where c represents the speed of light.
