It is widely accepted that cosmologists, astronomers, physicists, chemists and geologists have detected fine-tuning and design in the universe. Most skeptical responses to this apparent design seek to explain the low probability of our life-friendly universe when compared to the vastly more numerous life-hostile universes. The “single possible universe” solution aims to rule out all but one of the seemingly infinite explanations. As Sherlock Holmes declared, “eliminate all other factors, and the one which remains must be the truth.” Others argue for a “life-force universe” where a yet undiscovered law directs the universe to support and develop life. Both of these models acknowledge the rarity of life, particularly advanced life.
In contrast, advanced life abounds in the multiverse. (A previous Multiverse Musings posting discussed some of the bizarre implications of life in the multiverse.) While the overall fraction of the multiverse containing advanced life might be small, the multiverse contains an infinite number of intelligent life-forms. The relevant question now becomes: Of all the possible life-forms capable of observing the universe, how likely is human life on a 4.5 billion-year-old rocky planet orbiting a third-generation star in an old, spiral galaxy in a 13.7 billion-year-old universe? At least one other option represents a far more likely possibility.
That possibility, known as a Boltzmann Brain (BB) argues against the order we discern in the universe around us. The idea behind a BB relates to the chance assembly of atoms into a sentient being due to thermal fluctuations permitted by the second law of thermodynamics. The popular rendition of the second law states that the total order of a system decreases over time. However, the order of some smaller part of a system may increase as long as the organization of the whole system still decreases. Thus, with some very small probability, atoms in a region of space will assemble into a being capable of observing the universe for some period of time. The probability dramatically decreases as the period of time grows longer and the orderliness of the region observed increases. Thus, a BB in a solitary solar system surrounded by a disorderly universe occurs far more frequently than a BB in a solar system contained within an orderly spiral galaxy.
Additionally, most of the natural ways to count the number of intelligent life-forms compared to BBs reveal that the BBs far outnumber ordinary observers. Thus, the typical observer in a multiverse should not see the well-ordered universe that we study. This multiverse proposed may not even adequately address the organized appearance of our detectable universe to support life and the fine-tuned sequence of events responsible for life arising. However, even if it does, it also raises equally serious issues which I’ll tackle next month.