Few ideas in modern science have reshaped our understanding of reality more profoundly than space-time: the interwoven fabric of space and time at the heart of Albert Einstein’s theory of relativity.

Space-time is frequently described as the fabric of reality. In some accounts, this fabric is referred to as a fixed, four-dimensional block universe, a complete map of all events, past, present and future.

In others, it’s a dynamic field that bends and curves in response to gravity. But what does it really mean to say that space-time exists? What kind of thing is it? Is space-time structure, substance or metaphor?