Re: How does a massive object deform space?

Hi!

    This is the way gravitational interactions are described in general
relativity - as a warping of space (and time), rather than as action at a
distance (like the Newtonial theory of gravity) or via the exchange of
particles (as in the quantum field theories of the weak, electromagnetic,
and strong forces). We can measure the amount that space is warped by the
presence of a mass by using light beams - we define a straight line to be
the path taken by a light beam, and then see how that path changes when a
mass is present (this has been done by looking at the light from stars as
they graze the limb of the sun during a total solar eclipse).

    The plots you see in books are an attempt to draw the result; they are
incomplete and can be misleading, as spacetime is four-dimensional already
(three space dimensions, one time), and warping is usually indicated by
distorting the drawing into another space dimension. That's why the
pictures just show two dimensions. You are correct, though, in that light
going directly towards (or away from) a mass will not be deflected (except
in the case of a black hole, which is infinitely deep, where it won't get
out at all). Light passing by will be deflected, however.

Here are some Web pages which give a basic introduction to general
relativity:

Eric's pages on general relativity:
http://ourworld.compuserve.com/homepages/eric_baird/gr_home.htm

General relativity, with references (this one is more historical):
http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/General_relativity.html

A brief introduction, with a description of the "rubber sheet" diagram:
http://webhome.idirect.com/~yanspace/einstein/grelativ.htm

The relativity FAQ:
http://math.ucr.edu/home/baez/physics/relativity.html