What are the theories concerning gravity?

Question

What are the current theories as to why its all over the place? Not "because the more mass you've got the more gravity" but why does mass have gravity in the first place.

Also is it theoretically possible to make energy from gravity? It sound plausible since gravity is like a force... but im guessing the reason this isn't considered much is because it goes against the laws of thermodynamics, i think, right? Or is it a possibility??

Answer 1

Hello Adrian - tough question.

Newton thought of gravity as a force, and he developed the equations to describe its "action at a distance." However, he knew at the time that he was only describing the phenomenon and not understanding why it works. His equations were certainly valid and his treatment of gravity as a force field is still an acceptable way of solving orbital mechanics problems.

When Einstein attacked the issue, he looked at it in a totally different way (like he looked at most things). The best way that I can describe his thought process is to discuss his thought experiment regarding the equivalence principal as applied to gravity. I will use a rocket instead of his elevator.

Picture yourself inside a rocket ship that has no windows. You stand on the floor of the ship as it sits on the surface of the earth. You feel the floor pressing against your feet with the force of 1G x your mass. Seems normal.

Now take the same ship far into interstellar space. You will float weightlessly inside the ship until you fire the engines. If you fire the engines and accelerate upward at 1G, you will feel the same force against your feet that you felt on the surface of the earth. With no windows, there is no way that you can tell the difference between these two events (neglecting the engine instruments).

What Einstein said was that the reason you cannot tell the difference between these two events is that THERE IS NO DIFFERENCE. Now think about that for a minute. That means that when you are falling off a cliff in free fall, you are accelerating RELATIVE TO THE EARTH, but there is no force being applied to you. You cannot feel a force pushing you; all you feel is weightless free fall. The force occurs when the ground STOPS you from going the way that gravity is trying to make you go.

So the force is really applied by the surface of the earth - and it prevents you from falling into the center of the earth by applying this force. How does gravity make you go in this direction without applying a force? Well, Einstein also pointed out that space and time are really two ways of looking at the same thing, and he said that gravity works by bending spacetime. If you are travelling straight past the earth, it bends spacetime just enough to pull your future path toward the earth instead of straight on by.

The old comparison with a ball distorting a rubber sheet is a decent analogy - the only problem is that it uses the effects of gravity on the ball and the sheet to explain gravity - kind of a circular argument.

The interesting part of the problem is to understand that spacetime is not as it appears. We are subject to the influence of distant stars by virtue of their effect on the spacetime that surrounds us. Space and time are connected, and gravity is the result of the curvature of that spacetime by a significant mass.

One more thing Einstein said (he was a really smart guy) - mass and energy are equivalent. So does energy warp spacetime and cause gravity? - well, probably not. But gravity does affect energy. As an example, look at the Hubble photos of gravitational lensing - this is the distortion of distant light by the gravity of galaxies that fall between the source and our eyes. Gravity is not the same as mass - it is the result of mass. So I think that gravity cannot create energy, but mass certainly can - and has - and is (in the sun for example).

There is more recent work being done on gravity that I do not understand well enough to discuss, but I'll leave that up to you in your future pursuits. Hope this helps.

Answer 2

newton's apple

Answer 3

look it up on google