There have been many oscillating, or cyclic, universe hypotheses since Albert Einstein investigated them briefly in 1930. In general, the idea is that the universe starts with a big bang, then, after a long period of time, collapses down to a big crunch due to the gravitational attraction of matter in the Universe. It then goes through the big bang/big crunch over and over again. These were shown to be fundamentally flawed, not least because of the build up of entropy, so several variations have been proposed over the years to overcome these difficulties. Most have been unsuccessful.
John Wheeler suggested that at the end of each cycle, the universe is "reprocessed probabilistically" to obtain the new particles, forces, constants and laws in the next cycle. Because nothing is passed on to successive cycles, there is no knowledge of previous cycles, what the physical laws were in those cycles or whether the Universe is finite or infinite in time. This avoids the issues of the accumulation of energy in the Universe over cycles, but it is still difficult to overcome the ever increasing entropy over cycles leading to each expansion having to result in an ever larger Universe.
I discuss the 2001, Neil Turok and Paul Steinhardt theory "The Steinhardt-Turok Brane Collision Model" and the 2007 hypothesis by Lauris Baum and Paul Frampton, "The Baum-Frampton Cyclic Model", in the next two parts of this section as they represent two interesting and feasible interpretations of cyclic universes.
Astronomy & Cosmology - Alternative Universes