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How does special relativity combine space and time into space-time?

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Brian Greene sits in a living room, holding a pen, with handwritten equations m = E/c^2 and E = mc^2 on a whiteboard beside him, highlighting c^2 as the speed of light. — relativity Brian Greene kicking off his *Your Daily Equation* video series with Albert Einstein's famous equation E = mc².

In special relativity, space and time are combined into a single, four-dimensional continuum known as space-time because they are not absolute; rather, they depend on the observer's state of motion.123

Einstein’s theory demonstrates that because the speed of light is constant for all observers, measurements of distance and time intervals must change to remain consistent. This leads to phenomena such as time dilation and length contraction, which link spatial and temporal measurements.23

The German physicist Hermann Minkowski mathematically formalized this by showing that while individual distance and time measurements vary between observers, a specific quantity—the spatiotemporal interval—remains invariant. By incorporating the term $c T$ (where $c$ is the speed of light and $T$ is time), time is elevated to mathematical parity with the three dimensions of space. Consequently, the universe is described as a four-dimensional structure with coordinates for length, width, height, and time, representing an interwoven continuum rather than a flat, three-dimensional stage.134