1.2 The Myth of Inflation

summary

This Master Class will be focusing on a radical alternative to the theory of inflation.

- The key difference between these two ideas has to do with the overall history of the universe.
- In the big bang inflationary picture, there’s a well-defined beginning of time and space (the “bang”) and there’s an effective end to the universe, when dark energy takes over, and matter dissipates so much that there is essentially no observable matter in the universe.
- Stars, galaxies, and presumably sentient beings appear and reappear over and over again throughout the history of this universe, all occurring within the same region of space we occupy today.

The first question you might ask is: 'Why look for an alternative to inflation?'

- The theory appears to work beautifully, but the answer to this question is that
**the inflationary paradigm has failed.** - Not only has the theory failed, but we’ve known about the flaws in this picture for nearly 30 years—some of them even longer.
- If we’ve known about these flaws for so long, why are we still celebrating the inflationary picture?
- The theory works so beautifully that it compels us to believe any flaws can be fixed.

Inflation drives the early universe through a rapid expansion.

- The inflationary picture only requires a single ingredient—some source of inflationary energy that somehow occupies most of the energy in the universe in the first few instances after the bang, which drives the universe into this accelerated expansion.
- There are various candidates for what form this inflationary energy might take—the conventional example is a field called the
*inflaton*, the name for a hypothetical field yet to be explained. - The inflaton has strength everywhere in space. Depending on that value, it determines how much energy there is in a given volume of space that contains the field. We don’t actually know that the inflaton exists or how this energy varies with the strength of the field, so we hypothesize possibilities.
- If we look at a potential curve of the inflaton field, we see that there is a point where the energy reaches zero—that would describe the state of the universe today, according to the inflationary picture. But in order to drive inflation, we have to have a situation where, at the beginning of the universe, right after the bang, the field was lying in some state of higher energy, sitting there almost at rest. When these conditions are met, then inflation can start.
- The energy contained in that field quickly overtakes all other forms of energy, driving a rapid accelerated expansion. But the field can’t remain on that “hill,” and it rolls down the energy curve, eventually reaching the bottom. At the bottom, there is no more energy left in the field, and inflation ends. The energy that was contained in the field decays into matter and radiation that we observe today.

From the inflationary picture comes a number of marvelous results.

- Inflation transforms an arbitrary chaotic initial state into an ordered final state—one that is flat and smooth.
- Inflation explains a great deal about the universe we observe—uniformity, isotropy, and flatness.
- Inflation can predict a lot—many features of the cosmic microwave background, including cosmic gravitational waves.

The only problem is that none of these things about the myth are true.

- It’s not true that inflation transforms an arbitrary chaotic initial state into an ordered final state. In fact, what we learned about inflation is that it can only start is you already have very special conditions at the beginning.
- Not only do you need the inflaton field to exist, but you need a region of space in which the field was perched nearly at rest at the top of the plateau. It turns out that this condition is
*extremely*unlikely. - If we approximate the probability of the right initial conditions, one result shows it as less than a
*googolminex*. - A googolminex is 1 in a googolplex. Recall that a
*googol*is 10^{100}. A*googolplex*is 10 raised to the power of a googol, or $$10^{10^{100}}$$Thus, the probability of having the perfect initial conditions is $$P < \frac{1}{10^{10^{100}}}$$ - The inflationary theory has initial conditions that are unlikely to a level we have never seen in science.