glassynails wrote:Right, I've always wondered what causes gravity itself. We know that something falls towards earth, that's observable, but we don't know "why" it falls. What actually is pulling the object towards Earth? That's what I've always wanted to know.
So back to the question. It's gravity that keeping the planets from spinning outward in the spinning galaxy?
One theory (in fact that of Einstein, I believe!) is that the force of gravity is due to disturbances in space-time caused by mass.. there is a visualization where a massive object like the sun creates a sort of "well in spacetime" where un-perturbed spacetime would be a flat plane. So the objects sort of fall to the center of that well.
Interestingly, this theory predicts gravitational lensing should happen (light literally being bent by massive objects!) which has indeed been observed.
But of course it still doesn't exactly answer "why."
As for gravity and the galaxy, the stars in the galaxy could possibly be thought to be orbiting around the massive core similar to how the planets orbit around stars The force of gravity is what causes the orbit to work in the first place.
A very big problem with this: in many galaxies, the outer stars are found to revolve around the center at the same *angular* rate as those closer to the center, which cannot be accounted for by classical dynamics. Planets, on the other hand, have a much lower angular rate further from the star/sun, which is what we expect as the force of gravity falls off as 1/distance-squared and the circumference of the orbit is proportional to the distance.
That observation of stars orbiting is one of the reasons dark matter is theorized.. otherwise some sort of adjustment to classical dynamics would be needed to explain this phenomenon (in fact somebody did come up with something called Modified Newtonian Dynamics or MOND, which does mathematically fit the effect, but there may not be a real basis to believe it).
You ask a lot of deep questions, maybe you should go back to school and study physics and/or philosophy!