The multiverse— particularly the Level II models that inflationary cosmology seems to require—continues to intrigue people. In order to evaluate multiverse models, one should possess a basic understanding of inflation. One recent inquirer posed the issue this way:
I have read your Who’s Afraid of the Multiverse? booklet and have been tracking your TNRTB articles. But one aspect still confuses me: the term “cosmic inflation.” It seems as though one really needs to have at least a basic understanding of the term in order to understand a lot about multiverse. I am only a lowly electrical engineer and not a physicist, and so I really don’t get it. Every time I try to read up on it, it seems like more attention is put on how inflation solves certain problems and not much attention is put on what it actually is.
I think I get the term “inflation” mixed up with the “expansion” of the universe. From what I have read, it sounds like inflation is some sort of super-expansion during the first 1E-38 (?) seconds or so.
I was hoping that maybe you might try to provide an explanation of what inflation is sometime in the future.
Good question. Scientists first proposed inflation to solve some issues plaguing big bang cosmology, but recent research confirms that some form of inflation is necessary to explain the universe in which we live.
Historically, because of a few shortcomings in cosmological models, scientists focused more attention on what inflation solves rather than what it is. For example, the cosmic microwave background radiation discovered by Arno Penzias and Robert Wilson confirmed that we live in a big bang universe, but the extreme uniformity of that radiation posed a problem. The temperature of the most distant locations viewable from Earth all measured at the same temperature (to better than one part in 10,000). However, if the universe’s expansion rate was similar in the beginning as it is today, then all of those distant locations would never have been in contact, thus preventing them from equilibrating to the same temperature. Cosmologists refer to this issue as the “horizon problem.” This and other issues, like the “oldness-flatness problem” and the “monopole problem,” demonstrated that standard big bang cosmology did not provide a complete explanation for our universe.
The classical big bang model holds that the universe started from a singular beginning roughly 14 billion years ago and then gradually expanded to the universe we see today. The continual gravitational attraction of all the mass/energy in the universe steadily slows down the expansion of the universe. (We also now know that a mysterious dark energy component also affects the expansion rate as the universe grows, but that is a more recent discovery.) Postulating a period of hyper-fast expansion in the earliest moments of the universe (before the universe was 10-34 seconds old) solves these three problems mentioned above quite elegantly. Scientists refer to this epoch of rapid expansion as inflation.
However, simply because inflation solves a number of problems does not mean it’s correct. Subsequent tests must confirm its validity—and many experiments indicate that something like inflation did occur. For example, inflation predicts a flat geometry for the universe and scientists’ measurements bear this prediction out (see pages 11, 39–40 of Who’s Afraid of the Multiverse?) Some form of inflation matches all the data available and scientists continue to formulate tests for future instruments. Thus far, all the evidence indicates that we live in an inflationary big bang universe.
The issues of whether inflation models also produce a multiverse and, if so, does that multiverse argue against a Christian worldview are separate issues. I argue that, multiverse or not, the case for the biblical God as Creator and Sustainer of the universe continues to grow as time progresses.
If you would like to see a question about the multiverse addressed in this forum, send it to firstname.lastname@example.org.