Gravity bends space. We can see this practically by light being bent when it goes close enough to a star yet it is not in an atmosphere. Space has a structure of some kind which probably dictates the cosmic speed limit of EMR and gravity. Some people have taken to calling it aether, after the old idea. However in an expanding universe, space itself is expanding continuously (unless more of it is being made which sounds unlikely). Over billions of years, the universe (as in space) is said to have gone from a point source to 158,000,000,000 light years across. But how can this happen without huge changes in the structure of space as it endlessly becomes "ever less dense" for want of a better term? Surely if space were really expanding, the speed of light would continually increase, atomic forces would decrease, etc and the universe would have ceased to exist long ago? A question I asked on another forum. Is space expanding through 3 or 4 physical dimensions? (forget time as 4D for now). 3D would be like a solid ball expanding and a definite centre to the universe. 4D would be a hypersphere, like the balloon model used to explain galaxies becoming ever further apart.