I know gravity is equal to the mass of one object times the mass of a second object divided by distance squared. But what causes the attraction?
Well, it is the mass that causes the attraction, but this opens up lots of other questions.
What causes the mass to exist and to have gravity?
How is the gravity propagated or transmitted across space?
Newton didn’t know, he just called it action at a distance.
Eienstein didn’t know, but he said mass distorted space-time to create gravity ‘wells’ which caused massive objects to be experience a force towards each other.
Nowadays some people put the propagation of gravity down to particles called gravitons, although there are problems with this theory;
not all quantum gravity theories require gravitons, but put the effect down to variations in the vacuum foam itself.
SF worldbuilding at
http://www.orionsarm.com/main.html
Think of space as a flat rubber sheet and the planets as balls of metal sitting on that surface. The larger the ball the greater the indentation in the sheet. This can cause the smaller balls to fall into hollows caused by the larger object, creating a ‘virtual’ attraction towards that larger object.
I’m sure a real physicist will be along soon to expalin this much better than I can.
In General Relativity gravity warps spacetime, which means the topography of space around a massive object is altered so that other objects fall towards it.
Each object has gravitational potential energy which is at zero when it is outside of any gravitational field (which is impossible as gravitational fields only go to zero at infinite distances), this is a convention but it does have some correlation with reality as it is believed that GPE corresponds to the rest energy of an object. As an object moves towards another object it loses GPE as the GPE is converted to the kinetic energy of the attraction.
As mentioned above soem physicists have been searching for the elusive graviton, a particle which when exchanged communicates a gravitational effect.
In other words, if you figure out “what causes gravity,” you can go ahead and book your flight to Sweden.
[nitpick] The force of gravity, F = (G x m x m’) / r[sup]2[/sup]. G is the universal gravitational constant–bassically a conversion factor from mass to gravitational force, and is equal to 6.672 x 10[sup]-11[/sup]. you can find the acceleration due to gravity at the surface of a given body by substituting 1 for one of the mass values and entering the body’s radius for r. [/nitpick]
[slight hijack]
I thought I read an article on the Scientific American web site not too long ago that claimed that gravitational force did not act instantaneously and the lag could actually be measured when the objects were sufficiently far apart. The point was that this had significant implications in the “gravity is mass warping space/time” theory.
Anyone else remember this?
[/slight hijack]
That’s a central tenet of general relativity. The speed of gravity is, in fact, exactly equal to c.
Not a simple answer to this one (think string theory).
I find this site has pretty good info. attempts at lay explanations and w/ sources as well. As was said before, answer this question and you can write your own ticket.