I recently interviewed Rabbis Elie Feder and Aaron Zimmer about the newly released second season of their podcast Physics to God. Rabbi Feder earned a PhD in mathematics, and Rabbi Zimmer studied physics, as well as philosophy, mathematics, and psychology. In the first season, they describe the evidence for design in the universe based on how the constants of nature appear carefully set (i.e., fine-tuned) for complex phenomena like atoms, molecules, stars, planets, and life. In the second season, they focus on the multiverse and “show why it fails as a viable solution for explaining fine-tuning, design, and order [in our universe] without an intelligent cause.” In the two-part interview (part 1, part 2), they outline the content of the second season. Here, I will summarize their explanations of the three premises behind a viable multiverse theory and the measure problem, which undermines the theory’s explanatory power. 

Multiverse Premises 

Two required premises of a multiverse theory that could potentially explain fine-tuning are the following:

• An infinite, or virtually infinite, number of universes exist. 
• The universes vary in terms of the structure of their physical laws, their physical constants (e.g., gravitational constant and mass of quark), and their initial conditions (e.g., initial expansion rate and initial order). 

An infinite number of varying universes is required, so that some universe could possess the correct properties to allow for the observed order in ours, allowing for life. 

Yet employing only these premises results in what Feder and Zimmer call the naïve multiverse, which predicts that anything and everything would occur. Some universes would look nearly identical to our own, but Taylor Swift is president of Uganda and Donald Trump is a pop singer. In contrast, some universes would have fire-breathing dragons or rivers that hover in the air. This framing of the multiverse has been explored by countless movies and TV shows ranging from The Avengers to South Park. 

As an even more extreme example, with an infinite number of universes, some universes would experience quantum fluctuations in the sky above a populated planet that result in a reverberating voice saying, “I am the LORD, you need to stop believing in a multiverse as an excuse to reject me as your creator.” The sound would not have resulted from an omnipotent deity, but it would have been one of countless bizarre yet random accidents. 

In terms of science, the central problem with the naïve multiverse is that it could explain any observation, so it really explains nothing. For the theory to have predictive power, it needs a third premise:

• We are typical observers in a typical universe. 

The typical universe premise also corresponds to multiverse theory’s one “prediction.” If a multiverse exists, we should not be extremely atypical observers, and our universe should also not be extremely atypical. The problem is that we do appear to be highly improbable observers in a highly improbable universe.  

Boltzmann Brains 

Standard multiverse models, such as those based on eternal inflation and string theory, predict that the odds are far smaller for a brain emerging from a gradual process in an ancient universe than for a brain emerging from atoms suddenly coalescing in a young universe. In other words, we are far less likely to possess a brain with memories of a real life history than possess what is termed a Boltzmann brain that emerged from quantum fluctuations in the recent past with fictitious memories.  

Since no one desires to believe in such freaky observers as Boltzmann brains, physicists have grappled with our being such seemingly improbable normal observers. In addition, our universe is highly atypical in its old age and its high level of order. Mathematical physicist Roger Penrose calculated that the odds of a universe appearing as orderly as ours to be 1 chance in 10 to the power of 10 to the power of 123 — a number that includes more zeros than the number of atoms in the visible universe. 

In response to these tensions, proponents of the multiverse have attempted to find other measures that affirm the third premise. In cosmology, a measure is a mathematical framework used to assign probabilities or weights to different outcomes in the multiverse, particularly to make meaningful predictions. To date, cosmologists have made no progress in finding the right measure to classify our universe as typical. The rest of the interview unpacked what cosmologists term the measure problem. 

The Measure Problem

Feder and Zimmer break the problem into three layers. First, the whole idea of introducing measures is ad hoc. Measures do not naturally emerge from the laws of physics, so they are arbitrary constructs without any objective basis. In addition, with an infinite number of universes, probabilities cannot be properly defined. Second, physicists have attempted for decades to find a measure that classifies our universe as typical, but every measure they examined results in Boltzmann brain’s being more likely than normal observers or comparable problems. 

Third, even if theorists found exactly the right measure, they have no way to justify favoring the one nonintuitive measure that just so happens to be tailored to classify our amazingly ordered universe as typical. That measure would have to be fine-tuned to affirm the third premise, so the problem of fine tuning is displaced from the constants and initial conditions to the measure. Thus, fine-tuning is not actually explained. 

The God Hypothesis

Feder and Zimmer concluded the interview by explaining the purpose behind their podcast, which is showcased in the name Physics to God. They identified the underlying reason scientists are willing to believe in an infinite number of unobservable universes and why they are desperately looking for measures to justify the typical universe premise, despite their efforts undermining the spirit and soul of science. Secular scientists are unwilling to consider the possibility of God’s existence. Our rabbi friends wish to illustrate that belief in the God of the Bible is both rational and consistent with the latest scientific discoveries.