Humans have stared at the sky for millennia trying to figure out what is out there and what it tells us about our place in the universe. One of the most mysterious things is everywhere around us — in the gaps between planets and people and particles hums something that scientists and philosophers have spent a long time trying to understand: Space. For as fundamental to our existence and experience as space is, it's hard to describe and define it.

So, we asked four experts a deceptively simple question: what exactly is space?

• 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
• Bridget Falck, astrophysicist, University of Oslo: Space is a relation between things, not a thing itself
• David Albert, philosopher, Columbia University: Maybe there is no space