: Fabien - your question about "indefinite cycles" in the universe is a little vague; anything with the word "cycle" or "cyclic" usually implies sense of definition, that is, it has a period and amplitude. There are many, many definite cycles in the universe. Every solar system, galaxy and planet with moon experiences orbital cycles, which are often very definite and well-defined. Our Earth is in one of these orbits around the sun, with a period of 365.26 days and an amplitude of approximately 93,000,000 miles. If you trace this out on a graph of amplitude versus time, you woudl see a very regular sinusoidal wave/cycle pattern. Other types of cycles are the cycles of starbirth, star-death and rebirth (in the form of new stars); although these cycles are more or less indefinite in terms of amplitude and period (that is, they will vary and be less than predictable for any given star), they nonetheless are a cycle of sorts - the stuff that makes a star is ejected back into the interstellar medium upon the star's death, and eventually finds its way to reignite in the nuclear furnace of a new star. It could be said that the universe itself is in a cyle of sorts (assuming a closed universe), in which the universe expands from a point, stops and reverses, and then deflates into a big crunch singularity. Whether this cycle actually occurs or theoretically repeats is a darn good question! There are many other cycles, mostly more subtle, that exist, but most are fairly definite in terms of period and amplitude. perhaps you could explain a little more specifically what an indefinite cycle would include...?

• Re: DO INDEFINITE CYCLE EXISTS IN THE UNIVERSE? - Nigel Ball - September 23, 1997 - 19:14 UTC