the laws of physics must evolve
Delancey Place, 2023-04-26
The mechanism of natural selection I use is based on the methods of population biology that serve to explain how some parameters governing a system can be selected that make it more complex than it would otherwise be. Applying natural selection to a system to explain its complexity requires the following:
A space for parameters that vary among a population.
In biology, these parameters are the genes.
In physics, they are the constants of the Standard Model, including the masses of the various elementary particles and the strengths of the basic forces.
These parameters form a kind of configuration space for the laws of nature— a space called the landscape of theories (a term borrowed from population biology, where the space of genes is called the fitness landscape).
A mechanism of reproduction.
I adopt an old idea proposed to me by my postdoctoral mentor, Bryce DeWitt (1923-2004), which is that black holes lead to the births of new universes.
This is a consequence of the hypothesis that quantum gravity does away with the singularities where time begins and ends— a hypothesis for which there is good theoretical evidence.
Our universe has a lot of black holes, at least a billion billion of them, which suggests a very large population of progeny.
We can suppose that our universe is itself part of a line of descent stretching far into the past.
Variation.
Natural selection works in part because genes mutate or recombine at random during reproduction, so that the genomes of offspring differ from that of either parent.
Analogously, we can hypothesize that each time a new universe is created there is a small random change in the parameters of the laws.
Thus we can mark on the landscape the point corresponding to the values of the parameters for that universe.
The result is a vast and growing collection of points on the landscape, representing variations in the parameters of the laws across the multiverse.
Differences in fitness.
In population biology, the fitness of an individual is a measure of its reproductive success— that is, how many offspring it produces who thrive long enough to have children of their own.
The fitness of a universe is then a measure of how many black holes it spawns.
The number turns out to depend sensitively on the parameters.
It's not easy to make a black hole; therefore many parameters lead to universes that have no black holes at all.
A few parameters lead to universes that have lots of black holes.
These universes occupy a very small region of the parameter space.
We will assume that these highly fertile regions in the parameter space are islands surrounded by regions of much lower fertility.
Typicality.
We also assume that our own universe is a typical member of the population of universes, as that population is after many generations.
Thus we can predict that any properties shared by most universes are properties of our own.
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