Daniel Díaz notes that most of the talk about the multiverse started to appear once it was realized that there was fine-tuning in nature:

Note:Prominent proponents of the multiverse have included well-known cosmologists such as Max Tegmark and Alexander Vilenkin, Brian Greene and Neil Turok, Alan Guth and Stephen Hawking. Opponents include theoretical physicist Sabine Hossenfelder ( “Why the multiverse is religion, not science”) and cosmologist George Ellis (“beyond the domain of science”) In the absence of evidence, the issue appears to be a philosophical one.News, “In an infinity of universes, countless ones are run by cats…” atMind Matters News

*Robert J. Marks:* I have to brag about one of my publications, one of my pieces of analysis about the multiverse. Some people say that in some parallel universe, this podcast would end right now. And in another universe, it would say that Daniel was in Miami as opposed to Columbia.

They use the multiverse to say that anything can happen. Now, there’s different versions of the multiverse. One is from quantum theory, which says every time there’s a quantum collapse, that the universe is split. There are other theories where these multiverses literally exist. And I visualize them as being side by side.

One of the most common one has about 10^{1000} universes in the multiverse. And that sounds like a lot. It does sound like there might be some place that this podcast ends right now. And there might be one where it doesn’t end right now. But if you look at the simple math behind it, it can’t happen.

Following on that, there’s a universe where I am bald. I still am not totally bald. It’s getting thin up there, but I’m not totally bald. How many universes would it require for me to be bald in one and not bald in the other? It would take two universes, right? Now, we talk about Ola. No offense, Ola, but in some universe you might be bald too.

*Ola Hössjer:* Yes, certainly.

*Robert J. Marks:* And so, what happens? How many universes do we need for that? We need four. Right?

*Ola Hössjer:* Yes.

*Robert J. Marks:* We need bald, bald. Bald, not bald. Not bald, bald. And then, the fourth one. We have four. Now, let’s put Daniel, who has a rich crop of beautiful hair. But in some universe, Daniel, you’re bald. How many universes would we need then?

*Daniel Díaz:* Eight.

*Robert J. Marks:* We would need eight. Every time we add a different contingency, we double the number of universes that are required.

*Daniel Díaz:* At least.

*Robert J. Marks:* At least. Yes. We’re only using binary counter distinctions here also. We could have one where you’re bald, not bald, and then maybe partially bald. We could do three or four or five. We would multiply it, instead of by two, we would multiply it by five. But let’s just stick with two. You take each added counter distinction, and it doubles the number of universes.

You can work backwards by taking… If you’re a nerd, you take the log base two of the number of universes to get the number of counterdistinctions. Anyway, if you go up to 10^{1000,} which is a common model … how many counter distinctions can you have? Well, if you take the log base two of that, you find out less than 4,000. There can only be 4,000 different things in these universes. Even though 10^{1000} sounds like a heck of a lot, there’s not a lot of things you can do with only 10^{1000,} parallel universes.

And then, there’s people that say, “Well, maybe we have an infinite number of universes?” That is pure speculative metaphysics. There’s nothing in our universe that is infinite. Everything is finite. Everything.

**News**, “In an infinity of universes, countless ones are run by cats…” at *Mind Matters News*

*Takehome:* Robert J. Marks points out that even 10 to the 1000th power of universes would only permit 3,322 different paths. Infinity is required but unprovable.

*Here are the previous instalments of Robert J. Marks, Ola Hössjer, and Daniel Díaz discussing the fine tuning of the universe for life:*

*The first episode:*

Ours is a finely tuned — and No Free Lunch — universe. Mathematician Ola Hössjer and biostatistician Daniel Díaz explain to Walter Bradley Center director Robert J. Marks why nature works so seamlessly. A “life-permitting interval” makes it all possible — but is that really an accident?

and

Fine-tuning? How Bayesian statistics could help break a deadlock Bayesian statistics are used, for example, in spam filter technology, identifying probable spam by examining vast masses of previous messages. The frequentist approach assesses the probability of future events but the Bayesian approach assesses the probability of events that have already occurred.

*The second episode:*

Life is so wonderfully finely tuned that it’s frighteningA mathematician who uses statistical methods to model the fine tuning of molecular machines and systems in cells reflects… Every single cell is like a city that cannot function without a complex network of services that must all work together to maintain life.

Can there be a general theory for fine-tuning? If you make a bowl of alphabet soup and the letters arrange themselves and say, good morning, that is specified. What are the probabilities? Ola Hössjer sees the beauty of mathematics in the fact that seemingly unrelated features in cosmology and biology can be modeled using similar concepts.

*The third episode*

Was the universe created for life forms to live in? How would we know? We can begin by looking at the fundamental constants that underlie the universe. The constants of the universe — gravitational constant, entropy, and cosmological constant — must be finely tuned for life to exist.

Why did Stephen Hawking give up on a Theory of Everything? Daniel Díaz and Ola Hössjer continue their discussion of the fine tuning of the universal constants of nature with Robert J. Marks. The probability, they calculate, that the fine tuning of our universe is simply random is down to 10 to the minus sixty — a very small number.

*The fourth episode*

Is life from outer space a viable science hypothesis? Currently, panspermia has been rated as “plausible but not convincing.” Marks, Hössjer, and Diaz discuss the issues. Famous atheist scientists have favored panspermia because there is no plausible purely natural explanation for life on Earth that would make it unnecessary.

Could advanced aliens have fine-tuned Earth for life? That’s a surprisingly popular thesis, considering how hard it is to account for life without assuming a creator. As Robert Marks, Ola Hössjer, and Daniel Díaz discuss, some prominent atheists/agnostics have chosen to substitute advanced extraterrestrials for God.

Our universe survived a firing squad and it’s just an accident? According to the Weak Anthropic Principle, if things weren’t the way they are, we wouldn’t be here and that’s all there is to it. Given the odds, a philosopher likens the Weak Anthropic Principle to surviving a firing squad and concluding, incuriously, well… that’s just the way things are.