“Looking for Life in the Multiverse” is the cover and feature article for the January 2010 Scientific American Magazine [pages 42-49 in print edition]. (The print version of the article contains a number of diagrams, illustrations, and sidebars not present in the above-linked online version.)
I truly enjoyed this article. Alejandro Jenkins and Gilad Perez brought this mind-boggling multiverse hypothesis down to our universe, if you will, and even within Scientific American (I’ve been a subscriber for three years and counting), this article possessed extraordinary insight and clarity. I shall attempt to summarize the article.
You may be familiar with the fine-tuned nature of the universe. If certain fundamental constants, e.g. the relative mass of the proton, were adjusted just slightly, stars would be unable to form and the universe as we know it would fall apart.
However, one revelation of the article is that if two constants are tweaked together, a universe may still be “congenial to life,” or be “compatible with the formation of complex structures and . . . forms of life.” This startled me. It looks like a simple idea once we already figured it out, but the concurrent tweaking of multiple constants is a novelty. It almost seems counterintuitive, as the scientific method normally calls for a control and the tweaking of one variable, or in this case, one constant, at a time. But, our universe becomes merely a soup of particles, so to speak, if only one constant is modified.
Okay, enough abstraction. The article then goes on to give an example—a drastic one—in which the possibility of life is retained. In the example, Perez and his team did not simply adjust a few few constants. They obliterated one of the four fundamental forces of nature: the weak nuclear force.
After tweaking several other constants, Perez’s team found a set of constants that would make the universe congenial to life, even with only three fundamental forces. Still, the “weakless” universe is different. In our universe, four protons can smash together into a nucleus, with two of the protons then decaying via the weak nuclear force into two neutrons, two electrons, and two antineutrinos. In other words, the four protons combine into a helium 4 nucleus. The formation of the helium 4 nucleus is fundamental to nuclear fusion.
In the weakless universe, this specific fusion process cannot occur. A proton cannot decay into a neutron because the weak force does not exist. Hence, stars burn dimmer, producing helium 3 instead, and although helium 4 is still possible to form, it is less common.
Basically, the point is that the weakless universe is capable of forming intelligent life. This revelation has, of course, profound philosophical implications. But I shall omit philosophy here.
A second revelation was found in the realm of quarks. In the “Tinkering with Matter” illustration, several manipulations of quark masses are given, and while some of them lead to congenial universes, others lead to no possibility of a stable carbon-like molecule, a requisite for life as we know.
I just thought this was interesting.