Is energy always conserved?

I might sound crazy, but for a very long time now (since I was about 13) I have thought that one day we'll discover a triple equivalence. I'm a first year physics student at university, and I hypothesize that we'll discover space-time will be equivalent to matter and energy. I truly believe that as energy and matter are different forms of the same thing, space-time is also. In this case the energy from the light could just be being converted into space-time through a process we do not yet understand, but know as Dark Energy.