Space is a relation between things, not a thing itself
You may have heard that space is expanding, or that the fabric of space-time ripples quite literally like a wave. These are absolutely true – and awesome – statements, but what do they imply about the nature of space?
Concepts like expanding space or gravitational waves often lead people to think of space as having existence in and of itself. But space has no meaning without distinct objects; a truly empty universe is no universe at all. One might object that in a vacuum, virtual particles pop into and out of existence – but then such a universe isn't really empty, is it?
The expansion of the Universe, gravitational waves, and other phenomena are the function of physical objects acting according to physical laws; they do not necessitate that space itself physically exists. Until a future theory of quantum gravity weighs in on the issue, there is no reason to think of space as a thing.
Bottom line: Space is not a thing. Space is merely the only way to conceptualize the existence of distinct things in the Universe, just as time is the only way to conceptualize a Universe in which things change.
Other voices in the conversation:
Sean Carroll, theoretical physicist, California Institute of Technology: Space is overrated
Izabella Laba, mathematician, University of British Columbia: We can work with space without understanding its essence
David Albert, philosopher, Columbia University: Maybe there is no space