I've had this on my mind for a while. I'm pretty confident that I have the right idea, but I can't find a formula that I could use to prove it to someone. So, here it is. Imagine a sphere of space-time with absolutely nothing inside of it. It is a large sphere, sun-size large. Now, take that sphere and insert something like the sun into it, so that the mass of the sun causes curvature on the surrounding space. Because the sun is in this sphere of space-time, the curvature of the sun will compress the entire sphere inward, and reduce the volume of the sphere. This reminds me of Einstein's universe without the cosmological constant. Is there any equation that shows this? If so, then what is it? My guess is that it would be one of Einstein's, but I can't find it anywhere.