damian 1727: You asked, "Is space/time a 'thing'? or do we just have ratios between things?" i kinda agree with lee smolin... ie that question needs an answer.

dcl: Special relativity introduced the concept of spacetime, written as a single unhyphenated word. Spacetime is seen as a four-dimensional entity and is visualized in terms of four mutually perpendicular directions, three of which are spatial and the fourth temporal, that is, forward and backward directions in time. Collectively, I suppose the four of them could be regarded as a thing, but it's not a material thing that you can touch or see. A common application of the concept is a two-dimensional diagram that can be drawn on a sheet of paper. It's called a "spacetime diagram". It can also be called a "space/time diagram" if one wishes. People will understand you whichever form you use. Both names appear in books and technical articles. The horizontal coordinate is a spatial direction with left and right. The vertical coordinate is time, with past downward and future upward. Light is depicted as a pair of lines at 45-degree angles to the vertical and horizontal lines. A special version of this diagram used to illustrate the meaning of the Lorentz transformation in special relativity is called a Minkowski diagram.

I don't understand your reference to Lee Smolin. The only context in which I've encountered Lee Smolin is string theory, and I don't think that's what you're referring to.