Multiverse Musings – Probability Arguments

Multiverse Musings – Probability Arguments

Last month I defined some terminology and provided a categorization of the different kinds of multiverses discussed by scientists. The least controversial multiverse, Level I, simply states that the universe does not end at the edge of the region observable by humans. The issue of the universe’s true size naturally arises.

Using the curvature of the universe measured by WMAP, scientists can put a lower bound, n, on the number of regions the size of our observable universe (referred to as Hubble volumes) that would fit in the universe. They estimate a minimum value of n=1000. However, if the current formulation of inflation proves correct, it predicts n=infinity for the Level I multiverse. That would seriously impact the strength of some apologetic arguments used for fine-tuning in the universe.

Consider the chances of drawing a royal flush from a standard deck of cards. Just four combinations of the 2,598,960 unique five-card possibilities make a royal flush. So the probability of drawing a royal flush on any single draw is 1 part in 649,740, but the odds grow with the number of draws available. If 10,000,000 draws occurred without a royal flush, one would wonder if the deck contained all the proper cards. An infinite number of draws assures a large number (actually an infinite number) of royal flushes.

Now consider the possible arrangements or states for the observable universe. Our Hubble volume (with a just-right Earth/Moon/Jupiter orbiting a just-right star at the just-right location in a just-right galaxy) corresponds to one state. Another state might look identical except Pluto does not exist. Many other states contain no planet remotely similar to Earth. One can envision a very large number of states in this manner, but the total number of possible states is finite. Consequently, the number of possible histories is also finite.

IF the universe is spatially infinite, Hubble volumes exhibiting all possible histories consistent with the laws of physics will exist somewhere—regardless of the improbability of any particular state! Humans exist only in the states meeting the requirements for their existence. The impact such a scenario has on many fine-tuning arguments is obvious. The question then becomes how does a Christian respond?

Here are a number of points to keep in mind:

  1. An infinite Level I universe does not impact the fine-tuning arguments regarding the gross features of the universe such as the strengths of the four fundamental forces.

  2. An infinite Level I universe does not argue against a Creator. It just removes one currently used apologetic argument.

  3. An infinite Level I multiverse still relies on the current formulations of inflation but those formulations remain far from experimental verification. A comment by the cosmologist George Ellis regarding the multiverse applies here as well.

    The multiverse situation seems to fit St Paul’s description: “Faith is the substance of things hoped for, the evidence of things not seen.” In this case, it is faith that enormous extrapolations from tested physics are correct; hope that correct hints as to the way things really are have been identified from all the possibilities, and that the present marginal evidence to the contrary will go away.

  4. Scientists often regard infinities arising in theories as a sign that the theory is breaking down. In this instance, many scientists embrace the spatial infinity predicted by inflation. Interestingly, the predicted actual spatial infinity derives from a reference-frame transformation involving a future potential time infinity.

The answer to whether the infinities of the Level I multiverse stand up under experimental scrutiny likely lies in the somewhat distant future. However, as Christians, we need to understand and feel the weight of these arguments in order to give an adequate response. As I will discuss next month, William Lane Craig argues that actual infinities do not exist because they lead to absurdities.