Posted 11 March 2006 - 05:14 PM
There is a myth that space is static, while time is not. There is the hymn that "Time, like an ever-flowing stream" The metaphysical convictions which lie behind these words are common to most of humanity. Yet they have paradoxes. If time flows, then it must be flowing at a certain rate. Rates of flow are always with respect to time. So if time flows, it must be flowing with respect to itself. But nothing can flow with respect to itself. So the conclusion is that time doesn't flow. So it doesn't have a real direction. It is just as static as space. The movement of time is but an illusion. Time can be converted to space. This is the light speed. 1 second of time = roughly 300,000 square kilometer of space.
However, the theory that space is expanding in the Friedman model, which means that it must be more compressed in the past give the theory that there was a singularity when R=0.
This is neglecting the pressure of the universe. Normally if a substance is compressed, a pressure builds up to prevent further compression. It might be expected that in the cosmological case such a pressure would prevent the indefinite shrinkage of the universe as R = 0 is approached.
In general relativity, pressure is also a source of gravitation. Yet paradoxically, gravity also creates pressure, which means that the closer it gets, the more it should shrink to R=0.
However, a different model is proposed by Bondi and Gold. Which speculated that if the universe appeared the same from place to place, perhaps it also stayed the same from time to time. In that case the universe as a whole would not really change at all. Naturally, it must constinue to expand at the same rate. The expansion would reduce the density of galaxies in the universe, so to make the expansion consistent with the proposed lack of time evolution. New galaxies are constantly being formed to fill the gaps left by te recession of the existing ones.The material which goes to make up these galaxies is continually created, so there is no big bang. Matters enter universe all the time. The overall behaviour of this unchanging universe is therefore not static, but a steady state, with individual stars and galaxies evolving through their life cycles and decaying, and newly created matters always forming up to boost the population of young stars. Thus the universe has no beggining and no end.