by Eric Steinhart
The following is a quick-and-dirty survey of the current literature on explanations of our universe:
It is widely thought that our universe is highly unusual. It has certain features that make it lovely. Note that the term “lovely” is merely a term of art. It has no connotations beyond designating that our universe has certain features. These include (a) the fact that the universe is lawfully ordered; (b) the fact that the laws of nature have certain mathematical forms; (c) the values of the fundamental physical constants; (d) the fact that the universe starts in a low-entropy state. These lovely features are significant because if they were slightly different, then our universe would not contain any things that have value. The values include complexity, life, intelligence, rationality.
It is also widely thought that these lovely features require some explanation. Finding that you live in a universe with lovely features is far stranger than finding a watch on the heath. These features raise the Leibnizian question: why is the universe the way that it is? It is sometimes said that if our universe weren’t lovely, we wouldn’t be here to wonder about its loveliness. That counterfactual is a verson of the anthropic principle. Obviously, it’s true. And, what should be equally obvious, that truth does not in any way explain the existence or nature of our universe. The anthropic principle is not a hypothesis about the existence or nature of our universe. It is consistent with every hypothesis listed below.
1. The Brute Fact Hypothesis. The universe just exists. Our universe does not require an explanation. The loveliness is neither special nor rare nor significant in any way. There is no reason to provide any explanation for our universe.
Objections to the Brute Fact Hypothesis. We have regularly sought explanations for complex phenomena; and we have regularly found them. The success of the search for explanations both in science and in mathematics provides overwhelming evidence that the Brute Fact Hypothesis is wrong. So it is reasonable to search for an explanation for the existence and nature of our universe. Worse, the Brute Fact Hypothesis is itself not based on any evidence at all. It is an unwarrented hypothesis. It can be given for anything. God exists. It’s just a fact. Don’t ask why. This hypothesis celebrates ignorance.
2. The Necessity Hypothesis. The Necessity Hypothesis says that there is only one way that a universe can be. The lovely features of the universe are like variables in a big equation. There is only one solution to this equation. Since the lovely features are the only possible features, it is not surprising that our universe has them.
Objection to the Necessity Hypothesis: It is not the case that there is only one possible universe (so that if any universe is actualized, it must be that universe). On the contrary, there are many possible universes. And many of them can be actualized. Hence the Necessity Hypothesis is false.
3. The Plenitude Hypothesis. The Plenitude Hypothesis says that all possible universes are actual. This is the hypothesis of David Lewis. The library of possible universe blueprints is complete. For every way a universe can be, there is some blueprint in the library. So there is a blueprint in the library that describes our universe. Every blueprint in the library is actualized. There is no selection. So for every way a universe can be, there is some universe that actually is that way. Since our universe is one of the ways a universe can be, our universe is actual.
Objections to the Plenitude Hypothesis: The Plenitude Hypothesis seems to be unable to account for the regularity of our universe. Our universe exhibits regular patterns up to the present time – it’s like a novel that makes sense up to the current page. But in the library of all possible novels, there are infinitely many other novels that are like our novel up to the present page, but then diverge into random nonsense. So, the Plenitude Hypothesis seems to undermine one of the things it is supposed to explain: the regularity of the universe. All universes may indeed be possible; but there must be a selection of the ones that are actual.
4. The Lottery Hypothesis. The Lottery Hypothesis says that the lovely features of our universe are explained by random selection. There is a super-cosmic bucket filled with blueprints for universes. A lottery was somehow held and the winner was the blueprint for our universe. The winner was actualized.
Objections to the Lottery Hypothesis: There are at least two problems with the Lottery Hypothesis. The first problem is that universes with lovely features are highly rare. It is highly unlikely that the blueprint for our universe would be picked in a lottery. The second and much more damaging problem is that the lottery itself needs an explanation. What is its mechanism? Is it necessary? Was it designed? Did it evolve? The Lottery Hypothesis just pushes the mystery deeper. The Lottery Hypothesis is rejected.
Objections to the God Hypothesis: Suppose our universe does have a designer-creator (a DC). There is no reason to believe that the DC is personal or that it satisfies any of the definitions associated with the God of Abraham. The problem of evil makes it hard to say that the DC is maximally perfect. Any features of the DC that enable it to explain our universe are features that demand their own explanation. Since the DC requires its own explanation, it is not an ultimate necessary being. But God is supposed to be an ultimate necessary being. Our universe may indeed have a designer-creator, but it certainly does not match the features of the theistic deity. It is not God.
6. The Fecund Universe Hypothesis. The physicist Lee Smolin developed the idea that universes give birth to baby universes through black holes. When a star collapses to form a black hole in some parent universe, a baby universe pops out in some other dimension. This baby universe can give birth to its own babies. So there is an evolutionary tree of universes. Universes whose features are finely tuned for making black holes have more babies. So, generation after generation, the percentage of universes finely tuned for making black holes increases. But universes that are good at making black holes are also good at making stars, complex elements, planets, and life. So the loveliness of our universe is explained by this cosmic baby-making. The Fecund Universe Hypothesis is an evolutionary explanation for the existence and loveliness of our universe.
Objection to the Fecund Universe Hypothesis. This is a great idea. But it is a highly speculative idea – nobody really knows what goes on in black holes. So the hypothesis may well be false. And even if it is true, it faces problems. The first one is that the so-called “universes” really aren’t maximal physical wholes – they’re just parts of some bigger physical whole. And the bigger physical whole is the universe. And the hypothesis it isn’t ultimate. It depends on deeper laws of universe formation. Why are universes such that they can produce offspring? Why are black holes involved? What is the explanation for the ultimate laws of physics?
7. The Evolutionary Algorithm Hypothesis. This is a generalization of the Fecund Universe Hypothesis (and thus includes that hypothesis as a special case). Our universe is generated by a process of super-cosmic evolution. Super-cosmic evolution starts with some initial universe. This universe exists necessarily and does not depend on anything else for its existence. The initial universe produces some more lovely versions of itself. Once started, this process of universe-evolution is self-sustaining and self-amplifying. Each universe in any generation produces some more lovely successor universes. These successor universes populate the next generation of universes. The result is a series of generations of universes. Here’s the rule: for every universe, for every way to make it more lovely, there exists a successor universe that is more complex and congenial in that way. From generation to generation, the successor relation defines a growing tree of universes. As the tree grows, the universes in the tree become ever more lovely. Eventually, our universe appears.
Objections to the Evolutionary Algorithm Hypothesis. This is a highly speculative idea. As stated, it is also vague. It needs to be refined. And, since it is so abstract, it isn’t really even a hypothesis – it’s a type of hypothesis. More work must be done.
All the hypotheses in this list are speculative. They are all metaphysical, in the sense that none of them can be empirically tested. The hypotheses up to the God Hypothesis all suffer from very strong objections. The God Hypothesis and the Evolutionary Hypotheses (including the Fecund Universe Hypothesis) are based on analogies. This gives them some extra strength – they gain some weak empirical support from processes that we already know can produce things with lovely features (e.g. intelligent human design and biological evolution). However, the God Hypothesis faces inconsistencies. The Evolutionary Hypothesis is thus arguably the strongest hypothesis. Of course, it is really only a type of hypothesis – it needs to be worked out in detail and carefully studied.