Sunday, April 30, 2017

Some Thoughts on a Multiverse

It may sound more like science fiction than serious science, but many scientists have recently embraced the idea that there may be many more universes than just our own.  Such an idea can produce a great science fiction story, such as that in the original Star Trek episode "Mirror Mirror" where a transporter accident causes Captain Kirk to move to an alternative universe that is more brutal and savage aboard its version of the Starship Enterprise.

There are a few different scenarios for producing many universes (or a "multiverse") within proposed scientific theories.  One mechanism is the probabilistic nature of quantum mechanics. The "many worlds" interpretation of quantum mechanics proposes that every time a quantum event occurs that has multiple possible outcomes, all outcomes are produced in some universe. This is similar to saying something like every time I flip a coin, if a "heads" shows up, then an additional universe branches off from ours in which everything is the same except the coin shows "tails." Not many scientists actually believe that quantum mechanics produces these universes, but some do.

A different scenario that produces many universes is called "eternal inflation" in which our universe is somewhat like one bubble in a boiling pot of water, but there are many other bubble universes that are also produced. This theory of eternal inflation1 is an extension of the inflationary big bang model in which our universe had a period of rapid expansion in the first 10-35 seconds. In the eternal inflation model, the rapid expansion may have stopped in our universe but continued in others producing many other universes.
Perhaps the most popular theory that includes a multiverse is string theory, that postulates the fundamental particles we know of, like quarks and leptons, are composed of "vibrating strings of energy."  String theory requires that the universe is actually composed of 10 dimensions, rather than just the three dimensions of space and one dimension of time that we are familiar with.  Different string theories can be derived from an even more exotic theory, called "M-theory" which requires an 11 dimensional universe.  I'm not an expert on string theory so I don't understand all of the calculations that produce the string theory landscape, but my understanding is that there are many different minimum energy states (vacua) within string theory and any universe could occupy one of those states.  Depending on certain assumptions the number of possible vacua is often estimated at something like 10500. This means that there are 10500 different kinds of possible universes, but since every one of these universes could be duplicated many times within string theory, there could even be many more universes than that unimaginably large number.

The actual existence of any one of these scenarios for a multiverse has been used as an explanation for the fine-tuning of this universe.  In other words, our universe may appear to be finely-tuned to allow life to exist and, therefore, extremely improbable, but that is only because we happen to be in one of the very few universes among the multiverse, that is capable of supporting higher life forms. It is a selection effect. Because this universe can support life, we are here, but the improbability is irrelevant because we wouldn't exist in any of the other universes inhospitable to life.

A discussion of the scientific, philosophical, and theological issues associated with a multiverse would take far more space than my usual blog entry.  In fact, just the above very brief explanation of a few multiverse scenarios nearly matches the length of many of my blog entries.  So in the remainder of this post, I'll briefly discuss a few of the ramifications of the multiverse proposal as I see them, then revisit this topic at a later time.

The first question to address is whether or not the multiverse is even a scientific idea at all.  As an experimental physicist I define our scientific knowledge, generally, as a set of theories that can be written mathematically and confirmed experimentally. Most multiverse theories have little or no hope of ever being confirmed experimentally because that would involve our ability to detect universes that are outside of our universe. Unless those alternative universes could somehow interact with ours or have left some evidence of previous interactions with our universe, it is hopeless to ever confirm the existence of a multiverse. Therefore, it is pretty challenging to incorporate the multiverse ideas within the framework of observational science.  In addition, many multiverse theories actually postulate some ludicrous conclusions including the suggestion that we are most probably only a computer simulation (like The Matrix), or that all possible universes actually exist (meaning in another universe a different Michael G. Strauss is writing this same blog but with maybe a few words changed here or there).

Still, it is possible that a multiverse could be true and the correct picture of reality. If we were ever to discover evidence of the multiverse, how would that affect arguments for God including the cosmological argument that this universe had a beginning, and the teleological argument that this universe appears designed? In response to the first question, most multiverse theories still require a beginning to this universe and the BGV theorem that strongly suggests this universe did have a beginning still holds. The effect of a multiverse on fine tuning arguments is much harder to gauge. First of all, it is impossible to make any definitive statement about the ramification of a multiverse without having an actual mathematical theory that has been verified and offers unambiguous predictions. Since we don't have such a theory, any conclusions are simply speculation without any observational verification or even theoretical predictions.

Nevertheless, there are definite implications of a multiverse that actually support the case for God. For instance, the extra dimensions of string theory would require that any creator exist in multiple dimensions, and then could easily perform miraculous acts in our four dimensions. A discovery of other universes or extra dimensions would, in some sense, increase the necessary magnitude of any creator. One could legitimately ask the question, "How many universes would an infinite God create?"

Other universes would mean that Carl Sagan's famous saying, "The Cosmos is all that is or was or ever will be" is most certainly incorrect since he was referring to our universe. If there are many universes then at least one form of a "supernatural" realm is verified, that our cosmos is not all there is and that there exists a "supernatural" realm beyond our known universe.

In a previous post I discussed the idea that even though we live in an immensely large universe, it is still the smallest one that could exist and yet have even one planet like the earth capable of supporting life. It is possible that if string theory is the underlying reality of our universe, then maybe, given the laws of physics necessary to uphold our universe, something like 10500 universes are necessary even if the end goal is to create one planet capable of supporting life. After all, when scientists first began to probe the vastness of our universe, I don't think anyone originally postulated that any smaller universe would not have been capable of creating a single earth-like planet. Is it possible that 10500 universes are required to create a single earth-like planet and that something like string theory is required as the underlying foundation to our universe? Maybe the landscape of sting theory will prove to be the ultimate expression of fine-tuning.

As an experimental scientist, I am excited to try to test some of these exotic ideas about the existence of a multiverse. As a scientist and a Christian I am passionate about discovering the truth about our universe and God. I am confident that future discoveries will continue to shed light on that truth and given the past track record, I am also confident that discoveries about the nature of our universe will continue to provide confirmation of the existence of a personal, transcendent deity.

For more a more detailed discussion of the multiverse and God, I suggest the small book, Who's Afraid of the Multiverse? by astrophysicist Jeffrey Zweerink.

1Guth, Alan, "Eternal Inflation and its Implications," J. Phys. A40: 6811-6826,2007
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1 comment:

  1. Interesting post on a topic that seems outside the normal scientific process and more an exercise in theoretical mathematics. My reference for the material before your post was Penrose' opus magnum "The Road to Reality". (I skip a lot of the advanced a biblical and Christian view it seems at odds with God's declared attributes that a trial and error approach would be required in His creative process to get to the "successful, as in "good", universe and our planet and lifeforms. From a secular view it seems logical to expect that among a countable infinite array of universes that one or more would over the eons have developed quite advance lifeforms that would seek to destroy all possibly aggressive life in other universes that they had found hackable, penetrable and destroyed them. Since we would have been such a candidate we would have been a prime candidate for destruction. Yet after 14 billion years here we still are with no evidence of any such attempt other than one giant asteroid and it quite premature. Such a scenario is by definition likely in an infinite array since by infinite every sort of happening, discovery, attitude..etc. would at some point occur. Keith E.