Here is a great quote: http://math.ucr.edu/home/baez/gr/outline2.html QUOTE: Take any small ball of initially comoving test particles in free fall. As time passes, the rate at which the ball begins to shrink in volume is proportional to the energy density at the center of the ball plus the flow of x-momentum in the x direction there plus the flow of y-momentum in the y direction plus the flow of z-momentum in the z direction. Note: all of general relativity can in principle be recovered from the above paragraph! Also note that the minus sign in that paragraph is good, since it says if you have POSITIVE energy density, the ball of test particles SHRINKS. I.e., gravity is attractive. Math is interchangable with other types of language. A written language, for example, a novel? can be put into symbolic math form. Learning math is learning a new language! My 2 cents Please Register or Log in to view the hidden image!
