Posted by kid_A on August 7, 2002, at 13:40:44
In reply to Re: Cam « kid_A, posted by Dr. Bob on August 7, 2002, at 13:09:11
All the models discussed here start from the assumption that the usual rules of physics, including special relativity (SR) apply in any small region of the universe. This seems to be a pretty good approximation at least for our small region. Special relativity is important here because it tells us that we need to describe the universe in terms of 4-dimensional space-time. The geometric structure of the simplest space-times, those that are both homogeneous and isotropic, is described by the Robertson-Walker metric. The time evolutions of these space-times is given by a single scale parameter R which changes with time according to the Friedman equation.The models described here were first studied by Alexandr Friedman in 1922 and 1924, and independently by Georges Lemaître in 1927. It was not until 1935 that A. G. Walker and H. P. Robertson independently proved that what we now call the Robertson-Walker metric is the only metric consistent with a homogeneous isotropic universe. Universes of this type are therefore variously known as Friedman universes, Friedman-Lemaître universes, Friedman-Robertson-Walker (FRW) universes or Friedman-Lemaître-Robertson-Walker (FLRW) universes.
poster:kid_A
thread:28251
URL: http://www.dr-bob.org/babble/social/20020804/msgs/28253.html