Is there a beginning to chaotic inflation?

[Forestman]

Is chaotic inflation eternal into the past forever, as well as into the future forever. In the theory was there a beginning to it, or has it always been?

 

[Haelfix]

The question is fairly controversial actually. The initial models of chaotic inflation were found to be geodesically incomplete in the past, so they must have had a singularity at some point.

Later people realized that hinged on things like the assumption of the validity of various energy conditions. Energy conditions that now seem like they might possibly be violated in some quantum way. Further it also depends on specifics like whether you were in exact desitter or not, thermal conditions, extra dimensions and so forth.

 

[Forestman]

Thanks for the reply Haelfix. I sure hope that if chaotic inflation is true that there was no beginning to it. I find the idea of a beginning to be unappealing for aesthetic reasons. Even though I believe in the Big Bang because of the evidence, I wish that the steady state theory were true.

 

[Chalnoth]

Is chaotic inflation eternal into the past forever, as well as into the future forever. In the theory was there a beginning to it, or has it always been?

Yes, there basically has to be.

Think of it this way: inflation dilutes the universe. That is, if you start at some point in time with an inflaton plus a bunch of other junk in the universe, then very, very rapidly whatever junk is lying around gets diluted by inflation.

But what happens if you run the clock in reverse? Well, since the energy density of the inflaton is nearly constant, if you look backwards in time, any teeny tiny itsy bit of junk that you have sitting around in the late stages of inflation, going back in time, will overwhelm the inflaton and generate a singularity.

So unless you want to propose that the universe was truly empty except for the inflaton for all time, which destroys part of what inflation is supposed to explain in the first place, you have to propose that inflation had a beginning at some point in the finite past.

 

[Forestman]

You make a good point Chalnoth.