John Baez and Emory Bunn have written a freakishly simple introduction to general relativity, The Meaning of Einstein’s Equation. Baez also now hosts Chris Hillman’s link site, Relativity on the World Wide Web
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About relativity and Einstein,
You can find better explanation than “The Meaning of Einstein’s Equation” (John Baez).
http://settheory.net/cosmology
http://settheory.net/general-relativity
– It is directly applied to an important example (universal expansion)
– The expression is simpler (relating 1 component of the energy tensor
to 3 components of the Riemann tensor)
– The relation between energy and curvature is not only expressed but
also justified
– Both (diagonal) space and time components of the relation are
expressed and justified, resulting in showing their similarity “like a
coincidence”.