Is the idea that the universe oscillates (rather than, utterly begins) illogical?

Question

Is it possible at all?

Answer 1

It would it violate the monotonic growth of entropy, which appears to be the rule for our universe. But, what happens at the turn-around point is already recognized to be (as Don Rumsfeld might say) a "known unknown". In other words, such a possibility is contained within our presently vast "ignorance space".

Answer 2

Are you asking if a cycle of Bang/Crunch/Bang/Crunch is a valid universe model?  If so..."No."  There is not enough gravity to slow the expansion of the universe.  It will end in a cold decaying state.  It is not a matter of being illogical (I love Frost's poem "Fire and Ice").  It is a "romantic" and rather cool idea, but it is not supported by observation.

-Fred

Answer 3

I'm only a novice when it comes to Cosmology, but here's my two cents.  I'm guessing you want someone to speculate with you and not someone to give you a hard answer about what is known, so this is the sort of answer I'm giving.

We know that there are gravitational waves coming from certain sorts of phenomena, for instance neutron stars that orbit each other have been shown to have a very specific amount of orbital energy bleed off that is exactly in agreement with the amount predicted by general relativity (Einstein's theory of gravity) if they were emitting these waves.

So we are pretty sure that gravitational waves are real and not some figment of our highly developed imaginations.

These gravitational waves have very small amplitudes and even smaller effects on the things they encounter.

Now what if (and this is just pure speculation) there were gravitational waves that had both a huge amplitude (strength) and huge wavelength.  And when I say a huge wavelength, I mean a wavelength whose size is on the order of the observable universe.  And when I say huge amplitude I mean a size that could account for what we think is the expansion from the big bang.

That would be what I think you are describing.

Now whether this idea can fit the available observations of the Hubble expansion (the rate at which all the galaxies tend to move apart from each other) and the cosmic background microwave radiation is the key.  And whether that idea can fit within certain constraints of theory, such as what kind of spectra of gravitational waves would be internally consistent is also key.

But that is where I reach my limit on how much I know about Cosmology.  I don't know enough details about those two phenomena to know if they rule this idea out.  I also don't know enough about general relativity to know if these sort of huge amplitude, huge wavelength gravitational waves would be precluded by what the other amplitudes of other wavelengths might necessarily be.

Now, if we take this idea and run with it, we can do a rough calculation on how long one cycle of this expansion would be.

The visible universe is (roughly) a sphere with a diameter of 92 billion light years.  For waves, the period is equal to the wavelength divided by the wave speed.  If the wavelength is about twice the diameter of the visible universe (assuming that we are living near the center of an antinode), then the period of oscillation would be about 184 billion years.

Current estimates of the age of the universe are at 14 billion years.  So these are off by a factor of about 13.  I don't know if that is lethal to the idea or not, but at least it isn't less time, because I'm pretty sure that would be lethal to the idea.