3.2 Genetic Code of the Universe Review

summary

Are the laws of physics consistent throughout the multiverse?

At $t=0$, the universe began obeying the laws of physics—but there were no laws before then. So, which came first, the laws or the universe?
There may be one fundamental law of physics, like a single genetic code for the whole universe.
However, this law may have different realizations. For example, water can exist in liquid, solid, or gas form while still remaining fundamentally consistent. Somewhere in the “code” of water, this is allowable.

Quantum fluctuations during inflation can alter or mutate the genetic code in a small part of the universe.

Once a region “mutates,” inflation makes this region exponentially big. This is known as the cosmological mutation mechanism.
The scalar field may have different minima on the potential energy curve. When it occupies one minimum versus another, the same physical theory exists, but the scalar field takes a different value. When the scalar field has a different value, particles have different masses—an electron might be much heavier than it is in our region of the universe.
A “multicolored” universe means there are different laws of physics in different parts. Perhaps there is one unifying law of physics—string theory, for example—but it may have different realizations.
The landscape of eternal inflation: starting with just one “color,” quantum fluctuations can generate a huge, multicolored universe, with each of these regions being infinitely large and independent.
Even if you could somehow “jump” from one color to another colored universe, particles of your type could never exist in the other state, making this impossible.

Where is this genetic code written?

In string theory, the genetic code is written in properties of compactification of extra dimensions.
In one version of string theory, these strings have to live in 10-dimensional space-time (six more than our usual 3 spatial + time dimensions). These six extra dimensions are theoretically “curled up” or compactified into extremely small, complex shapes on the order of the Planck scale.
There are many different ways these dimensions can be compactified; in fact, there may even be up to 10⁵⁰⁰ different ways.
Some compactifications yield the universe that we observe, with the energy density of empty space almost—but not exactly—zero. This vacuum energy is theorized to be dark energy.
In other compactifications, the energy density could be huge. In that universe, galaxies would be torn apart by this expansion and unable to sustain life. Another possibility is for the energy density to be negative—but this universe would momentarily collapse.
There is only a small interval where the energy density is such that our universe can sustain itself, and this is something upon which the anthropic principle is built.
If we consider the multiverse, we can have many compactifications, with one part of the universe having one value for the vacuum energy, another part with a different value, and we can only live in those parts of the universe that allow us to do so.