A monkey randomly hitting keys on a keyboard will eventually produce the entire collection of Shakespeare's works–at least if the monkey types for an infinite amount of time.
The truth of the previous statement relies on (at least) two conditions. First, the monkey must actually use all the keys in a random fashion. Second, but more important, the keyboard must contain all the necessary letters and punctuation to produce Shakespeare's works.
An analogous situation arises when scientists try to connect the numerous solutions of string theory (see sidebar) to a proper description of our universe. It is an uncontroversial statement that our universe appears designed and fine-tuned to support life. The controversy begins when scientists put forth explanations for the design and fine-tuning. RTB's creation model asserts that a supernatural Designer created and fashioned this universe for the explicit purpose of supporting human life. By contrast, some naturalistic scientists argue for a model where an infinitude of universes (sometimes called multiverse) exist. In this model, the apparent design simply reflects a huge selection effect. In other words, of this infinite number of universes, most do not support life. However, our existence mandates that we reside in, and therefore observe, a life-friendly universe.
What might produce this multitude of universes? Two unsolved issues lend insight into this question. The first issue relates to scientists' attempts to unify gravity with the other fundamental forces (the electromagnetic, strong, and weak nuclear forces) using string theory. In part because string theory requires an extra six dimensions beyond the familiar three spatial and one time dimension, an incredibly large number of possible solutions exist in string theory. Some string models contain an infinite number of solutions. Each of these solutions describes potential universes that would operate with different laws of physics, different fundamental constants, and even different dimensionality. In order to match our universe, any workable solution must demonstrate how these extra dimensions remain small and undetectable.
The second issue involves the mechanism that caused the faster-than-light expansion–called inflation–in the earliest moments after the creation event. Scientists' current best theoretical understanding of inflation predicts that a multitude of other universes actually exist! However, in order to explain the physical properties of our universe such as the geometry, dark energy characteristics, initial density fluctuations, and gravitational waves, the mechanism causing inflation must abide by a set of restrictive rules.
Presently, the theories describing the early universe do not specify the inflation mechanism so scientists must insert some kind of mechanism into the models. However, many hope that a better understanding of string theory will specify the proper inflation mechanism. Thus, a significant amount of effort has been directed toward finding string theory solutions that match the physical properties of the universe.
Because of the enormous number of string theory solutions scientists typically restrict themselves to a particular subset of solutions where the proper calculations are possible. One group of cosmologists performed such a study to find string theory solutions that produced inflation.1 Even the restricted subset contained an infinite number of solutions. Detailed numerical investigations of these solutions demonstrated that, even though infinite in number, none of them produced an inflationary epoch like that observed in our universe!
This discovery highlights two important apologetic implications. Even if shown true, the multiverse may not provide an adequate explanation for the design and fine-tuning observed throughout our universe. Nothing guarantees that inflation/string theory mechanisms can produce our universe through strictly natural processes. It may be like a monkey using a keyboard with no vowels. No matter how long the monkey types, it will never produce Shakespeare's works.
More importantly, assuming that a multiverse scenario is correct and that the multiverse does sample all the possible universes, such a scheme brings major philosophical issues into the science arena. For example, scientists use the multiverse to explain the incredible improbability of the universe's ability to support life compared to far more abundant sterile possible universes. However, that same argument means that inhabitants of Matrix-like simulations also abound. (Recall that in the Matrix movie series sentient machines created a simulated reality.) In fact, inhabitants of these simulations far outnumber human beings on an earth-like planet.
Sir Martin Rees explains the consequences in this way:
All the multiverse ideas lead to a remarkable synthesis between cosmology and physics...But they also lead to the extraordinary consequence that we may not be the deepest reality, we may be a simulation. The possibility that we are creations of some supreme or super-being, blurs the boundary between physics and idealist philosophy, between the natural and the supernatural, and between the relation of mind and multiverse and the possibility that we're in the matrix rather than the physics itself.2
Given the unusual difficulties associated with multiverse solutions, perhaps the best explanation for the universe's fine-tuning is also the simplest one: the universe looks designed because a Designer fashioned it, just as the great classics of literature were written not by a tireless monkey but by a guy named Bill.
What Is String Theory?
Two remarkable theories warrant the description of "most extensively tested and verified." Quantum mechanics describes how energy and matter behave on subatomic scales. According to quantum mechanics, any measurable quantity (such as charge, mass, energy) comes in discreet amounts. On the other hand, general relativity describes how mass and energy interact with one another and with space-time. According to Einstein, gravitational attraction arises from energy and matter warping space-time, which consequently influences how other objects move through space-time. However, general relativity requires a continuous space-time.
While these two theories have passed every experimental test scientists have thrown at them, a fundamental problem exists. The enormous mass and energy density of the early universe necessitate using general relativity to describe the dynamics. The small sizes and immense temperatures of the early universe require a quantum mechanical description. However, the discreet nature of quantum mechanics fundamentally conflicts with the continuous nature of general relativity. Scientists strongly believe that a unified theory incorporating both quantum mechanics and general relativity (which properly describes the dynamics of the universe) exists.
These unified theories generically require the existence of additional spatial dimensions beyond the three large dimensions we commonly experience. String theory represents the most popular of these unified theories. The basic concept behind the theory is that two dimensional strings comprise all fundamental particles and interactions. This, in essence, imposes a fundamental smallest size to any physical thing, which, in turn, allows both general relativity and quantum mechanics to coexist.
According to scientists' best estimates, more than 10500 different solutions to the equations of string theory exist. The challenge is to find the solution(s) that describe this universe. However, this research demonstrates the difficulty of finding such a solution, which highlights the fine-tuned nature of our universe.