Nothing should be left as a guess. 'Energy' is a catchword used to describe ?? About anything you can think of, from 'space' to ?? To me it's a description of transformations and what happens 'in between', and as 'SpaceTime' is a whole description in relativity, not really dividable as I understands it, you also get your universal 'closed box' in where that which transforms from one thing to another do so by its 'energy'. So if 'space' would be a form of 'energy' and you take that away, what's left?

Gravity?

Nope, not as I think of it. 'Gravity' is according to Einstein the 'metric' of space, giving it its '3D shape'. To get it you either need accelerations or invariant mass. So with no mass, and no accelerations there can be no gravity. But 'space' then, pure 'space'?

It doesn't exist. Not if 'Gravity' is expected to be of a infinite reach, which it is. So a 'space' without gravity? No 3D, no 2D.. 1D? How do you measure a one dimensional 'space'? You can't as far as I can see.