Anthropic Argument for Three Generations

TL;DR

The paper argues that three generations of particles are naturally predicted by multiverse theory combined with anthropic reasoning, explaining why N_gen=3 is the most probable number in our universe.

Contribution

It introduces an anthropic argument linking the number of particle generations to multiverse probability distributions, providing a testable prediction for N_gen.

Findings

N_gen=3 is a natural prediction of multiverse and anthropic principles.

The probability of N_gen is expected to decrease steeply with increasing N_gen.

Supports the idea that our universe's particle generations are not coincidental but statistically favored.

Abstract

The standard model of particle physics contains N_gen=3 generations of quarks and leptons, i.e., two sets of three particles in each sector, with the two sets differing by 1 unit of charge in each. All 12 "predicted" particles are now experimentally accounted for, and there are strong (though not air-tight) arguments that there are no more than three generations. The question is: why exactly N_gen=3? I argue that three generations is a natural prediction of the multiverse theory, provided one adds the additional, quite reasonable assumption that N_gen in a randomly realized universe is a steeply falling function of number. In this case N_gen > 2 to permit CP violation (and so baryogenesis and thus physicists) and N_gen < 4 to avoid highly improbable outcomes. I thereby make a testable anthropic-principle prediction: that when a theory of randomly realized N_gen is developed, the probability will turn out to be steeply falling in N_gen.