MikeW saidCan some of you physicist types explain what gravity actually IS? I understand it is related to mass but how does it have an effect on other bodies at a distance? What is a 'gravitational field'?
What I'm really curious about is whether 'anti-grav' is even a physical possibility.
Newton described gravity as a force between 2 objects that was directly proportional to the product of their masses, and inversely proportional to the square of the distance between them.
Basically, the stronger an objects mass, the stronger the force of gravity on other objects. The farther you get away from the center of the object (where the mass is greatest), the weaker the gravity.
That's why on Earth, the higher in altitude you travel, the weaker the force of gravity because you're moving away from the Earth's center. If you drop an object off a tall building, it speeds up as it gets closer to the ground. The equator has a weaker gravitational force than the poles. And the moons gravity is much weaker than Earth because it has less mass.
Einstein, however, claimed gravity wasn't a force, but a result of the curvature of space time. Without an external force, 2 objects will always travel in a straight line. Einstein claimed the reason objects meet is because they aren't traveling on a straight line, they are traveling along a spherical path due to the curvature of space-time and that's what causes them to interact. This was the basis of General Relativity.
Of course, General Relativity has been modified by Quantum Mechanics, so we still don't really know the specifics of how gravity works.