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How Critical Density Was Calculated.
Forum List  Follow Ups  Post Message  Back to Thread Topics  In Response To Posted by Alexander on July 2, 2001 23:53:39 UTC 
If you take a large cube containing many receeding galaxies (and other matter) with the total mass m, and calculate their: rest mass energy (mc^2) plus kinetic energy (from known Hubble constant) plus gravitational potential energy of interaction of galaxies, you will obtain some number which can be positive or negative depending on how much mass m you have per volume of this cube (i.e., on the average density of matter in the cube). It turns out, that at certain density (called critical  about 8x10^27 kg.m^3) total energy will be zero. This density corresponds to the border between closed (neg curvature) and open (pos. curvature) universe.


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