Inflated Expectations: a Cosmological Tale by Burton Howard;

Author:Burton, Howard;
Language: eng
Format: epub
Tags: Physics, Cosmology, Astrophysics, Philosophy
Publisher: Open Agenda Publishing
Published: 2020-10-02T00:00:00+00:00

Questions for Discussion:

What does it mean, exactly, for a field to be “fine-tuned” and what would a “solution” to the associated “fine-tuning problem” look like in principle?

To what extent might a “fine-tuning problem” be “solved” by invoking the anthropic principle?

What do you think Paul means, exactly, when he talks about “separating this degeneracy”?

IV. Two Major Issues

The initial value problem and eternal inflation

HB: And while this was going on, your thoughts on inflation as a principle—standard inflationary cosmology—are moving in what direction? What other concerns did you have?

PS: Well, shortly after inflation was developed, two big issues arose. Fine-tuning was not one of these first big two—I’m putting that as a third issue—so although that’s the one that most people spend their time on, that’s not one of the real problems, in my view.

The two big problems are:

First, we didn’t properly think through how inflation gets started. What we said is, “If you have some random distribution of matter and energy coming out of The Big Bang, inflation will smooth it out.” But we began with, “If you have inflation…”

Well, what does the inflation need? It turns out the inflation needs a universe which is rather smooth and flat to begin with, which was the very thing inflation was supposed to be doing for you.

And it needs it to be smooth and flat over a fairly large scale—larger than the size of the horizon, the largest distance that you could see at the time. So it has to occur over a scale in which normal, physical processes wouldn’t be able to interact. This is what we sometimes call the “initial conditions problem”: we don’t know how to initiate inflation.

That is, instead of it taking over easily, inflation can only take over if someone has already smoothed out the universe to a significant degree, which solves the problem that we wanted to solve to begin with.

Suppose we say that, coming out of the Big Bang, that’s very unlikely but it’s not impossible. It could be by chance that it came out that way. It seems like it requires a conspiracy over large scales, so it’s very, very unlikely. But it’s possible. That’s true. But, as unlikely as that is, it turns out that the condition you need to start inflation is exponentially more special, more unlikely.

So in order to explain your first unlikeliness, you’ve actually had to go to a situation which is exponentially more unlikely.

That was first pointed out by Roger Penrose using a very clever but subtle argument; and then, over the decades, other arguments have been developed.

HB: Wasn’t it 10 to the 10100 or something crazy like that?

PS: Yes, I like to describe it as the worst prediction ever. You’re trying to explain why we are the way we are by following this line of argument, and by using the statistical measure he proposed—which turns out to agree with other ways of doing the estimate—you end up saying, We’re only likely as one part in 10 to the 10100, as an upper bound.

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