Some science controversies arise in disputes over findings. The current flap over the James Webb Space Telescope data, for one. Others sound like clashes over philosophy — claims about the multiverse (countless universes out there) are a good example.

Theoretical physicist Sabine Hossenfelder takes on the multiverse in in her new book, Existential Physics: A Scientist’s Guide to Life’s Biggest Questions (2022). She also addresses the topic concisely — and wittily — in a short video and a blog post at Back(Re)Action. She looks at three popular multiverse models: Many Worlds, Eternal Inflation, and String Theory Landscape.

Here’s her take on Eternal Inflation:

We don’t know how our universe began and maybe we will never know. We just talked about this the other week. But according to a presently popular idea called “inflation”, our universe was created from a quantum fluctuation of a field called the “inflaton”. This field supposedly fills an infinitely large space and our universe was created from only a tiny patch of that, the patch where the fluctuation happened.

But the field keeps on fluctuating, so there are infinitely many other universes fluctuating into existence. This universe-creation goes on forever, which is why it’s called eternal inflation. Eternal inflation, by the way lasts forever into the future, but still requires a beginning in the past, so it doesn’t do away with the Big Bang issue.

In Eternal Inflation, the other universes may contain the same matter as ours, but in slightly different arrangements, so there may be copies of you in them. In some versions you became a professional ballet dancer. In some you won a Nobel Prize. In yet another one another you are a professional ballet dancer who won a Nobel prize and dated Elon Musk. And they’re all as real as this one.

Where did this inflaton field go that allegedly created our universe? Well, physicists say it has fallen apart into the particles that we observe now, so it’s gone and that’s why we can’t measure it. Yeah, that is a little sketchy.

Sabine Hossenfelder, “The Multiverse: Science, Religion, or Pseudoscience?” at BackRe(Action) (September 10, 2022)

Don’t miss her take on Many Worlds and the String Theory Landscape, especially if you wish to experience “elephants in the room which you coincidentally can’t see” — oh, and getting married to Musk (but maybe only in that universe). On a serious note, she later addresses specific claims from physicists who defend the idea.

The concept of a multiverse arises from an alternative interpretation of the movement of elementary particles in quantum mechanics — alternative, that is, to the more widely accepted Copenhagen interpretation. In the Copenhagen interpretation, if the particle goes left rather than right, the universe just updates. In the alternative Many-Worlds interpretation, a new universe is created in which the particle goes right. There are other versions but that’s the best known.

Hossenfelder, also the author of Lost in Math: How Beauty Leads Physics Astray, thinks that concepts like the multiverse are an example of mathematical reasoning trumping evidence from nature: “You may find the multiverse inspirational, or maybe comforting, or maybe just fun to talk about. And there’s nothing wrong with that – please enjoy your stories and articles and videos about the multiverse. But don’t mistake it for science.”

Here are some other articles you may enjoy about the multiverse concept:

In an infinity of universes, is another you reading this article?

In an infinity of universes, countless ones are run by cats

Multiverse cosmology is not a good argument against God

Here is a way we can be sure if we are living in a multiverse. (Eric Holloway)

We don’t live in a multiverse because the concept makes no sense. (Michael Egnor)

Is Big Bang Theory’s Sheldon right re the multiverse? (Robert J. Marks)