In an article about current scientific efforts to test Einstein's general theory of relativity on a cosmic scale--for the universe as a whole, the author writes:
"It is a striking fact that general relativity has remained unchanged since Einstein first proposed it in 1915. At its heart is our understanding of the force of gravity. Einstein put forward the idea that there is no force of gravity per se. Instead, what we perceive as gravity results from the geometry of space-time. If we place an object - a planet or a star, or indeed anything with mass - into space, it will deform it. Einstein's general theory of relativity gives us unique and exact rules for calculating the extent of this deformation." (Pedro Ferreira, "Unweaving the Cosmic Web," New Scientist, October 9, 2010.)
While it is true that general relativity says there is no force of gravity, several implications of this quotation are incorrect, I believe. It retains several vestiges of the theological conceptualization of the cosmos that Einstein tried to eliminate.
General relativity says that, without the presence of matter with mass, neither space nor time exist. Space and time are not, to make an analogy, like a container into which matter can be placed. Further, if there were, in the entire universe, only one object of matter, there would still be no space or time. Space and time arise, Einstein says, by the relative accelerated (curvilinear) motion of at least two objects. When two objects are, relative to one another, in accelerated motion, then the relationship of curved space-time comes into existence. In other words, space is not like a tightly stretched flat sheet that is deformed, when several bowling balls are placed on it, into a curved sheet with depressions under the balls. There is no sheet, no "space". What we measure as curved space-time is a relationship between two (or more) objects in accelerated motion relative to each other. A "relationship" has no existence independent of the objects in the relationship.
This concept is impossible to comprehend intuitively, because our everyday concepts of space and time are formed through our gross sensory experience (vision, touch, hearing, etc.) in situations of our physical activity--walking, running. Our ordinary concepts originated in evolution in simple, local, perception of bodies in slow motion in the visual theater of our environment created by our eyes with the function of getting us out of the way or in the way. But this experience does not correlate to the cosmos, where the speed of light, the motion of cosmic objects, and distances are beyond the apprehension of our sensory perception and are apprehended only by scientific instruments, such as telescopes.
If you are a cosmologist, I would appreciate your comments on my discussion.