Summary of Our Improbable Universe
Chapter 3: Strings and Quantum Things
This chapter deals with five stepping stones whose existence is relevant to the fertility of the universe for all time (not just to the beginning). Protons with a long life time is one example. If our matter were crumbling around us we could have never evolved. A similar issue concerns the instability of neutrons. It is very good that they are heavy enough so that they decay into protons. If this were not the case, very little hydrogen would have been left over from the Big Bang. Almost all of the matter would be fast burning stellar fuel. Stellar life times would be too short for intelligence to have evolved.
The three dimensional nature of reality is another stepping stone. If there were more than three dimensions stable planetary orbits would not be possible. Newton noted that the inverse square law of gravitational force was essential to orbital stability. It can be shown that this is due to the three dimensional nature of reality. It turns out that a force that falls inversely with distance also produces stable orbits but this would occur only in a two dimensional universe. Intelligence would be impossible there because complex neural networks with feed back could not be formed in only two dimensions.
Two more stepping stones have their roots in Quantum Mechanics. Without the wave nature of matter, that is assumed by Quantum Mechanics, all atoms and planetary systems would eventually become mini black holes. A unique quantum feature of electrons, protons, and neutrons called the exclusion principle helps in this respect. The Exclusion Principle also is at the foundations of complex chemistry. Without it every atom would promiscuously stick to every other atom. There would be no specificity about it.