Georgina,
1) From the maths` effectiveness, we know the universe is a logical system.
2) Such a logical system requires for its operation only one typeof stuff or process and only one type of cause. This is called a monism and there is only one existent out there (no apples and oranges)
3) It could be difficult to identify the substance and cause of the universe.
4) But it has already been done in 1993, unknowingly, by the physicist Bill Unruh. Below from (or arXiv:gr-qc/9312027v2 for this version)
A more accurate way of summarizing the lessons of General Relativity is
that gravity does not cause time to run differently in different places (e.g., faster far from the earth than near it). Gravity is the unequable flow of time from place to place. It is notthat there are two separate phenomena, namely gravity and time and that the one, gravity,affects the other. Rather the theory states that the phenomena we usually ascribe to gravity are actually caused by time's flowing unequably from place to place.
The time-process is the substance and a difference in its rate of evolution is the cause. After that, everything falls into place. Gravity, photons, particles etc. This is the metaphysics that underlies all of physics. Now, we may understand whta we know.
Marcel,