“I don't think the curvature of space is necessarily a good way to understand this, as this curvature is really just another way to express the fact that gravity attracts.”
If you want to split hairs…
It doesn’t seem to me that Lurid’s explanation says much more than “gravity attracts” either. I mean, the answer to the question about why gravity doesn’t pull the planets into the sun is going to be based on how we are going to understand gravity. If the answer was simply “gravity attracts” then we haven’t really answered the question! That is, if talking about space curvature merely says “gravity attracts,” then this doesn’t work towards explaining why the gravity of the sun doesn’t attract the planets to fall into it.
To frame this all a little differently, it seems to me that Lurid is answering from a more “classic” perspective and I answer from a perspective of “Relativity”: we answer based on two different models of description. However, this doesn’t appear to make one model more useful than the other or make one explanation “better” than the other.
I mean, Lurid says, “The effect of gravity is to bend this straight path.” And this is very close to what I’ve said, except that on a relativistic model, gravity is the bends and dips of a straight path.
Look, Lurid’s explanation talks about velocity and strength of gravitational fields. In relativity, it seems to me, velocity gets cashed out as kinetic energy, which factors into the ‘E’ of “E = mc^2.” In turn, the energy is understood as contributing to mass of an object and it is the mass of an object that bends space around it.
Now Quantum has put forth the idea of the solar system being in a state of “dynamic equilibrium.” We can understand this in at least the two models that have been put forth. We can understand it on the “classic” model, more or less, as “each planet is zooming away from the sun, but being pulled toward it by gravity too, which balance each other out.” Or, we can understand it based on a relativistic model where each planet, due to its velocity and physical mass, bends space around it. The sun also does this—I imagine that many of us have been exposed to the “rubber sheet” picture where the mass of the sun is like a heavy object settled into “a valley” that it creates upon the rubber sheet. Now, the “dynamic equilibrium” here is that the planets carve out their own valleys within the larger “valley” that the mass of the sun creates. Each specific valley is dependent upon the way the other objects in the solar system also bend space; i.e., the dynamic equilibrium can be seen as a harmony of the various “valleys” that each object creates around itself. In other words, the specific valley that the earth carves out turns into an elliptical “trench” that carries it around the sun due the way that the earth curves space relative to the other bodies of mass that make up our solar system.
Again, it seems to me that either model gives us something to understand as to “why the planets don’t fall into the sun.” |
