3.2 The Unmitigated Disaster

summary

What inflation really predicts is that anything that can happen will happen.

In science, a theory that predicts anything can happen is not only a problem, it is an “unmitigated disaster.”
Inflation is a theory that is maximally unpredictive and untestable. There is no test you could construct to possibly disprove the theory, because anything you would observe by a test is physically possible. And anything that is physically possible can and will occur an infinite number of times in the multiverse.
To consider such a theory is a very radical thing in science.
Since humans first began practicing science, everything has been aimed at the idea that observations and experiments are key to testing our theories. Theories must stand against tests over and over again—that’s how we gain confidence in them. Yet this is a theory that is fundamentally untestable.

Can the idea of the 'measures' save inflation?

Theorists have been working for over 30 years to save the theory of inflation.
One idea they’ve come up with is called the measures.
The idea of the measures is this: develop a small rule that tells us how to weigh or count these bubbles, with the intent to argue that bubbles that look like ours are more probable. This would restore the theory to predictive power.
Among these measures is what’s sometimes called the anthropic principle. We include anthropic reasoning—or the fact that we exist becomes a selection principle—but this is just another kind of measure.

Inflation has merely transformed the problem it set out to solve.

Before we consider the idea of measures, think about the ramifications.
It’s a great leap backwards. Why did we invent inflation in the first place?
Coming out of the Big Bang, we couldn’t understand how we’d ever get the simple, smooth, and flat conditions we observe in the universe. So we invented inflation so that it would give us those conditions
But what we discovered is that it doesn’t give us those conditions (or at least not only those conditions). We have to admit that inflation has done nothing to solve the problems we began with, but only transformed the problems.

Any measures we can introduce fail miserably.

Suppose you could come up with a criterion as a measure to decide which bubbles are more likely. One such measure might be: “what kind of bubbles occupy most of the volume?” or “which kind of bubbles occur most frequently?” but calculating the likelihood of our kind of bubble existing in the multiverse results in something along the lines of one in a googolplex.
One reason that contributes to this huge unlikeliness is the following: These bubbles are being produced at different times in the history of this inflationary universe, and so we can think of bubbles having different ages. Our bubble would be about 13.8 billion years old.
But consider bubbles that have exactly the same properties as ours, created just one second later than ours. These bubbles are exponentially more likely to exist than ours. Why? Because during that one second, the universe underwent a huge amount of inflation; there was vastly more volume in which to make more bubbles, and therefore more bubbles of that age were made. The factor is something like 10^10³⁵.
Of course, it could be more than just one second younger, and this line of reasoning is how our likelihood becomes so small, just from looking at the subset of bubbles that are like ours in every respect but age.