Chapter 5.0 The four-dimensional universe

The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality. (Minkovski, 1908) Three years after Einstein published his paper on special relativity, his former teacher Hermann Minkovski forever transformed our view of the universe.

Einstein had predicted length contraction and time dilation, but Minkovski drew out their radical implications. As the famous quotation above suggests, Minkovski (pronounced Min-koff- ski) showed that space and time were mixed together in a sort of “union”. We do not live in a three-dimensional universe with time flowing through. Instead, we live in a four-dimensional spacetime.

Time is the fourth dimension.

These are strange claims. To assess them, the next two sections lay out some important philosophical issues in general terms. The following sections return to Minkovski and relativity theory.

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