Spacetime
Spacetime treats the three dimensions of space and the one of time as a single four-dimensional structure rather than as a stage and a clock kept separately. Hermann Minkowski introduced it in 1908 as a way of restating special relativity, and it works because different observers disagree about distances and durations while agreeing on a combined interval between events. In general relativity spacetime becomes flexible: mass and energy curve it, and what looks like the force of gravity is objects following the straightest available path through curved spacetime.
Why it matters
It is the geometry both relativity theories are written in, so the equations stay opaque until the picture is in place.
Also written: space-time
Where it comes up
Read about Spacetime on Wikipedia
Sources
- Spacetime English Wikipedia
- Space and Time: Inertial Frames Stanford Encyclopedia of Philosophy
- Relativity Britannica
