Objections to the Idea of Anthropic Coincidences
The subject of anthropic coincidences is extremely controversial in the scientific community and provokes a wide spectrum of responses. Many scientists react with hostility or even anger to the mention of these ideas. There are a number of reasons for this.
In the first place, almost all scientists are instinctively and professionally suspicious of anything that smells like “teleology.” As the reader will remember from chapter 3, teleological explanations are explanations of things or events in terms of their supposed purposes, goals, or ends. For almost two millennia this kind of thinking prevailed in the physical sciences, and it is generally agreed that it led nowhere. Teleology was found to be a sterile approach to understanding the physical world. Many accounts of the history of science emphasize that the Scientific Revolution occurred only when scientists abandoned teleology in favor of investigating the physical mechanisms that underlie phenomena. That is why any talk about how certain features of the physical world are necessary in order for human life to exist seems to many scientists like a giant step backward, an attempt to smuggle discredited teleological notions back into science. They sincerely worry that people will be led astray from the high road of scientific thinking into the barren wastelands of fruitless metaphysical speculation.
These fears are well illustrated by the following comments that were made by the editor of a major physics journal reacting to a paper on anthropic coincidences that he had received for publication:
Anthropic arguments of this type are in fact anti-scientific in a very fundamental sense: The essence of the scientific enterprise is the attempt to understand the regularities that we observe in nature; the anthropic argument says that we should not bother.… Anthropic arguments can be constructed to “explain” many phenomena, from the daily appearance of the Sun in the eastern sky, to the equality in magnitude of the electron and proton charges, which most of us now believe to have more conventional scientific explanations.1
The basic point that this scientist was making is quite reasonable. One could indeed attempt to explain the fact that the Sun rises every day by saying that if it didn’t, we’d never know it—we wouldn’t be here. And if people had been content with that as an explanation they would never have attempted to understand how the Sun and planets move, or how the Sun formed and how it generates light and heat. Teleological thinking can indeed be a showstopper as far as doing real scientific research is concerned. For many centuries it was.
Such concerns do not explain all the negative reactions to discussions of anthropic coincidences, however. It is not just the specter of teleology that some scientists fear, but religion. It does not require much imagination to see where thinking about anthropic coincidences can lead.
On the other hand, there are many scientists who disagree that there is anything “unscientific” about investigating anthropic coincidences. In fact, many of the most eminent physicists of our era have taken quite a lively interest in them. The list of those who have written papers on the subject includes such redoubtable names in physics and cosmology as Brandon Carter2, Andrei Sakharov3, Bernard J. Carr and Martin Rees4, Yacov B. Zel’dovich5, John Barrow6, Steven Weinberg7, Lev Okun8, Andrei Linde9, Alexander Vilenkin10, and Stephen Hawking.11 One of the scientists who has done the most to make anthropic arguments respectable in the scientific community is Steven Weinberg, a Nobel Prize winner, a main architect of the Standard Model of particle physics, and arguably the leading theoretical particle physicist in the world. In recent years he has written a series of papers which point out that the value of the cosmological constant may have an anthropic explanation.
The scientific community, then, is quite divided on the subject of anthropic coincidences. This is illustrated by the case I just referred to, where the editor of a major physics journal criticized a paper on anthropic coincidences as “anti-scientific.” One of the authors of that paper was, as it happens, himself a former editor of that journal.
I should emphasize that most of the scientists who take an interest in anthropic coincidences do not attribute any religious significance to them. Certainly, for example, Weinberg, who is an atheist, does not. I have already quoted his famous statement that the universe seems “pointless.” Most of the authors I have listed take the view that the anthropic coincidences—if they can be explained at all, and are not really just coincidences—have a natural scientific explanation in terms of what is sometimes called the Weak Anthropic Principle, an idea that I will explain later. Therefore it is very important to draw the distinction between the “coincidences” themselves and how they are explained or interpreted. There are both religious and non-religious interpretations of them, as we shall see in chapter 17.
In this chapter I am going to deal with some objections that are commonly raised against the very idea that there even are anthropic coincidences at all, or at least that such coincidences have been shown to exist.
There are basically three objections to the idea of anthropic coincidences:
1. The Requirements for Life Are Unknown
All anthropic coincidences say that if the universe or the laws of nature had been different in some way, then life would not have been able to evolve. A very basic objection to this is that we cannot really know what is required for life to evolve. The living things we are familiar with have very particular characteristics, which include the following: (a) their life processes are based on chemistry; (b) their chemistry is critically based on carbon, oxygen, hydrogen, and certain other elements, and on certain critical compounds made from those elements, such as water; and (c) the energy that powers life derives ultimately from nuclear reactions taking place inside stars. But how do we know that life of a very different sort could not exist?
For example, it is an old suggestion that life could be based on silicon rather than carbon, or on ammonia rather than water. Some have even suggested that chemistry which uses only the single element hydrogen could be rich enough to lead to living organisms.12 Life can even be imagined that makes no use of chemistry at all: perhaps the structure of an organism and its life processes could be entirely nuclear rather than chemical. It has even been proposed that life could be based on processes which go on in the hot plasmas in the interior of stars. Alien life might, for all we know, exist inside the Sun. On the other hand, one can imagine life arising even if there were no stars. There are other processes in nature that release energy besides stars, such as gravitational collapse or radioactivity.
To sum up, the supposed anthropic coincidences may all be based on a simple failure of imagination. Who is to say that had the laws of nature been different life could not have arisen in some way that we are unable to conceive?
2. Conventional Scientific Explanations May Exist
A second objection to anthropic coincidences is that the facts which are argued to be necessary for, or at least conducive to, the evolution of life may have conventional scientific explanations. In fact, physicists are already in a position to make good guesses about what some of those explanations are. For example, consider the fourth anthropic coincidence that I discussed in chapter 15, namely the strength of the electromagnetic force, i.e., the value of the fine structure constant. It is tempting to explain the value of this constant of nature by saying that it allows the existence of a variety of chemical elements, and therefore life. However, there is a conventional scientific explanation of the value of the fine structure constant that is based on the idea of the “grand unification” of forces.
Particle physicists have strong reasons for believing that the three non-gravitational forces of nature—the electromagnetic force, the weak nuclear force, and the strong nuclear force—are all parts of a single underlying “unified” force. In fact, there exist very promising theories, called “grand unified theories,” in which this is true, and there are even more ambitious theories, called “superstring theories,” in which all forces including gravity are unified. A characteristic of such unified theories, not surprisingly, is that the strengths of the different forces are tied to each other. One thing that grand unified theories tend to predict is that the strong nuclear force is much stronger than the weak nuclear force, and that the weak nuclear force is somewhat stronger than the electromagnetic force. In fact, in the simplest grand unified theory,13 knowing the strength of the weak and strong forces it is possible to calculate what the value of the fine structure constant is. This calculation gives an answer that is correct to within about half a percent. This is one fact that gives some theoretical physicists confidence that grand unified theories are on the right track.
To take another case, the seventh example of an anthropic coincidence that I gave in chapter 15 was the extreme “spatial flatness” of the universe. Here again, scientists think they may have at least a partial explanation of this fact based on the idea of “cosmological inflation.” (I have already discussed this idea at some length in chapter 7.)
It is true that most of the facts that I have given as examples of anthropic coincidences are not yet fully explained scientifically. However, the fact that plausible explanations already exist for some of them gives some grounds for hope that most or all of them will eventually be found to have quite conventional scientific explanations.
3. There May Have Been No Room for Choice
The third objection to anthropic coincidences is that one is really not entitled to ask what the universe would be like were some particular feature of the laws of nature different. The reason is that we are not sure which features of the laws could have been different. In fact, there is a sense in which we are not sure that any of them could have been different.
For example, consider the fine structure constant again. In our present theory of particle physics, the Standard Model, the fine structure constant is a “free parameter.” In other words, the basic principles of that theory do not require the fine structure constant to have a particular numerical value. In the context of the Standard Model, therefore, it makes perfect sense to ask what would have happened had the fine structure constant had a different value, with everything else in the laws of nature being just as it is. The trouble, however, is that very few physicists think that the Standard Model is the ultimate theory of physics. It is almost certainly only an approximation to some deeper theory, such as a grand unified theory or superstring theory. In such a deeper theory it may not make sense to consider a hypothetical situation in which only the fine structure constant were different. As we just saw, in a grand unified theory the electromagnetic force is tied together with the other forces. Therefore—assuming grand unification is true—had the fine structure constant been different, certain facts about the other forces would have been different also.
In other words, in a deeper theory facts that previously seemed unrelated to each other are often seen to be tied together. Before the principles of electromagnetism were discovered, it would have seemed reasonable to contemplate hypothetical universes where magnetic forces were stronger than in our universe while electric forces were the same. But now that these two forces are understood to be aspects of the same force, it is clear that one of them cannot be different without the other being different also.
The question, then, is whether the kind of reasoning that goes into demonstrating an anthropic coincidence really makes any sense at all. When we know the ultimate mathematical theory of all physical phenomena, it may turn out that everything is so tied to everything else that nothing can be changed without destroying the whole structure of the theory. In the ultimate theory, in other words, it may turn out that everything has to be just as it is. This is what Einstein meant when he famously said, “What I’m really interested in is whether God could have made the world in a different way.” Many theoretical physicists believe that in the ultimate theory there will be no freedom: what kinds of particles exist, what kinds of forces there are, how strong those forces are, the number of dimensions of space and time, and all the rest, will be uniquely determined by some powerful and simple set of fundamental principles. If that proves to be the case, then it would be those principles, rather than the requirement that life be able to evolve, that would account for why things are the way they are.
In recent decades many physicists have speculated that it will turn out that the laws of nature are, in some sense, unique: the laws could not have been different than they are. This is a bold idea indeed. What lies behind it?
One thing that lies behind it is the trend in physics toward ever more unified theories: Newton found that the same laws governed earthly and heavenly bodies. In the nineteenth century, electrical, magnetic, and optical phenomena were discovered to be aspects of a single thing called electromagnetism. Quantum theory showed that particles and forces were really two manifestations of the same “quantum fields.” Einstein showed that space and time were inseparable parts of a four-dimensional “space-time.” In the late 1960s and early 1970s, electromagnetism and the weak interactions were discovered to be parts of a unified “electroweak” force. And there is a great deal of circumstantial evidence that the electroweak force and the strong force are parts of one grand unified force, and even that all forces including gravity are unified.
Another thing that lies behind the idea of a unique form for the laws of physics is that the structure of some parts of our present theory, the Standard Model, is found to be completely dictated by certain powerful principles—often, symmetry principles. A very good example is the part of the theory that describes how particles called “gluons” interact with each other by means of the strong force. The structure of these interactions is completely dictated by the symmetry called SU(3)×CP obeyed by the strong force. There is no choice left to be made once it is laid down that the strong force must respect this symmetry: the gluons must interact with each other in a unique way. The same thing is believed to be true about superstring theory, which many physicists think may be the ultimate unified theory of all physical phenomena. All the parts of superstring theory fit together so harmoniously that nothing can be changed without the theory ceasing to be mathematically self-consistent. No one yet knows what the profound underlying principles of superstring theory are. But whatever they are, they appear to completely dictate the mathematical structure of the theory.
As yet there is no direct experimental evidence that superstring theory is really the right theory of nature. One reason that many physicists nevertheless suspect that it is the right theory is that it is the only way that is presently known of reconciling the principles of Einstein’s theory of gravity (i.e., the General Theory of Relativity) with the principles of quantum theory. If one attempts to apply quantum principles to Einstein’s theory, the theory ceases to make mathematical sense: calculations that ought to give finite answers give infinite answers instead. In the technical jargon, Einstein’s theory of gravity is “non-renormalizable.” For decades, theorists tried to find a satisfactory quantum theory of gravity, but without success. It seemed an insuperable problem—until superstring theory came along. It may be that superstring theory is the only mathematically consistent way to combine quantum theory and Einsteinian gravity.
1. The Requirements for Life
The first objection to the idea of anthropic coincidences was that we do not really know with certainty what the requirements for life are. And, indeed, this is quite true. We do have limited imaginations, and life conceivably could take forms utterly different from the life we know about. It could be based on different physics and arise in different ways.
What this means is that anthropic arguments will always have a question mark attached to them. They cannot achieve the rigor and certainty of mathematical demonstrations. However, this should not overly concern us. As I stated at the outset, and have had occasion to remind the reader since, this book is not about rigorous proofs. It is not a question of whose view, the theist’s or the materialist’s, can be rigorously proven from the scientific facts, but rather whose view is rendered more credible by the scientific facts. Materialists have long claimed, with great assurance, that the facts discovered by science render incredible the idea that the universe was designed with us in mind. If nothing else, the anthropic coincidences show this claim to be unjustified.
Moreover, while absolute certainty is not possible with regard to anthropic coincidences, a great deal of confidence is possible in some instances. For example, we cannot know exactly how long the universe had to last for life to have time to evolve, but we do know with virtual certainty that it had to last much longer than a “Planck time” (i.e., 10-43 second), since the very idea of time as we know it breaks down for anything shorter than that. Because the processes of organic life, and, even more, the gradual evolution of organic life, require enormously complex sequences of events, they must require a very large number of Planck times to unfold. This already implies that certain numbers such as the cosmological constant and the spatial flatness of the universe must be extremely small.
Other anthropic assumptions are not as certain as this, but are nonetheless very solid. For example, in chapter 15 we saw that if certain aspects of the laws of nature had been different only the element hydrogen would have existed, and it would have been unable to combine through nuclear fusion to make the nuclei of heavier elements (see examples 1 and 5). In that case, there would have been no chemistry to speak of, since the only chemical compound that hydrogen can form by itself is the hydrogen molecule, H2, consisting of a pair of hydrogen atoms. Even though it has been suggested, I think few scientists would find it plausible that life could be made using only the chemistry of hydrogen. Furthermore, if hydrogen had been the only stable nucleus around, it is reasonably certain that nuclear processes could not have substituted for chemical ones as the basis of life. If all this is not bad enough for the prospects for life, without nuclear processes there would not have been stars. Now, it is true that even on Earth there are organisms that do not derive their energy from the Sun. For instance, there are bacteria, which live in volcanic vents deep under the ocean, that thrive off of geothermal energy. However, even geothermal energy comes ultimately from nuclear processes. It is radioactivity that keeps the earth’s interior hot, and radioactivity comes from the decay of large nuclei. If only hydrogen nuclei had existed, this source of energy would have been just as impossible as energy from the Sun. So, while it is not totally inconceivable that life of some sort could evolve in an all-hydrogen universe, it seems extremely far-fetched.
To sum up, while we cannot know with absolute certainty what physical conditions would preclude the evolution of life, it is possible to make intelligent arguments about it and to reach some conclusions in which we can be reasonably confident. Since we are interested in the question of what is plausible or credible, rather than what is rigorously provable, such arguments are quite sufficient.
2. Conventional Scientific Explanations
The second objection was that many if not all of the facts that are cited as anthropic coincidences are likely to have conventional scientific explanations. I believe this to be true; however, I do not believe that it constitutes a real objection to the idea of anthropic coincidences. The essential point was well expressed by the astrophysicists B. J. Carr and M. J. Rees:
One day, we may have a more physical explanation for some of the relationships … that now seem genuine coincidences. For example, the coincidence αG ≈ (me/mw)8, which is essential for [nucleosynthesis], may eventually be subsumed as a consequence of some presently unformulated unified physical theory. However, even if all apparently anthropic coincidences could be explained in this way, it would still be remarkable that the relationships dictated by physical theory happened also to be those propitious for life.14
In other words, even if all the physical relationships needed for life to evolve were explained as arising from some fundamental physical theory, there would still be a coincidence. There would be the coincidence between what that physical theory required and what the evolution of life required. If life requires dozens of delicate relationships to be satisfied, and a certain physical theory also requires dozens of delicate relationships to be satisfied, and they turn out to be the very same relationships, that would be a fantastic coincidence. Or, rather, a series of fantastic coincidences.
If the objection we are considering is an attempt to argue that there is nothing coincidental in the anthropic coincidences, then it very obviously fails. However, there is another possible point to the objection. That point is that while there may really be anthropic coincidences, they do not imply that God or anyone else deliberately “arranged” things to allow life to evolve. The reason is that all of the things that might have been “arranged” were already inflexibly fixed by fundamental physical principles. Understanding it this way, the second objection really boils down to the same thing as the third objection.
3. Did God Have a Choice?
The third objection was, in essence, that God had no choice, and, therefore, that there was really nothing for God to do. He did not “decide” that the fine structure constant was to be small; rather the principles of grand unified theories required it to be small. He did not “decide” that space was to be flat; rather, the dynamics of cosmic inflation forced it to be flat. He did not “decide” that an energy level of carbon 12 was to have the right value to enhance the production of carbon in stars; rather, the locations of the energy levels of carbon are fixed by the structure of the fundamental theory of physics. This brings us to a critical question: How much choice was there in how the universe was put together?
To answer this, let us turn to the example that I have already used many times: the fine structure constant. In the Standard Model this is a free parameter; it could have been anything. But in a grand unified theory it is tied to various other parameters. Typically one finds that in simple grand unified theories the fine structure constant comes out to be quite small. If we find that the world is described by a grand unified theory, therefore, we will have at least a partial explanation of why the fine structure constant is a small number. However, that is not to say that “there was no choice” about what the fine structure constant could be.
In the first place, even though the value of the fine structure constant is tied to other parameters in a grand unified theory, many of those other parameters are free. For example, in grand unified theories there is a parameter called the “unification scale.” This parameter has to do with how the unified force is broken apart into the separate electromagnetic, weak, and strong forces. If our universe is described by a grand unified theory, then there was a choice to be made about the numerical value of the unification scale. A different value of the unification scale would have meant a different value of the fine structure constant.
In the second place, there are an infinite number of different grand unified theories; so there was also a choice to be made among them. Many of them do not even have such a thing as an electromagnetic force. Others have no strong nuclear force. In fact, the kind and number of such “gauge forces” could have been practically anything, and so could their relative strengths, depending on which grand unified theory had been chosen.
Finally, there was the choice whether the structure of the universe would be that of a grand unified theory at all. There is no law of logic that says that it had to be. Mathematically speaking, as far as we know, a grand unified theory is no better than a non-unified theory such as the Standard Model.
Let us take another example: the spatial flatness of the universe. It is true that in a physical theory in which cosmological inflation takes place, the spatial flatness of the universe can be explained. However, the same points can be made as in our previous example. First, in a theory that gives cosmological inflation, the amount of inflation, and therefore the degree of spatial flatness that results, depends on the values of various parameters of the theory. Second, there are an infinite number of possible mathematical theories of cosmological inflation. And, third, there are also an infinite number of theories in which cosmological inflation does not occur. Thus, here also, there were many choices to be made by God.
But what are we to reply to those who suggest that the ultimate “theory of everything” will turn out to be so constrained by its fundamental principles that no room for choice exists within its framework? The reply is very simple: there was a choice of framework. It may be that the underlying principles of superstring theory, say, leave no further room for choice, but there was the choice of whether the universe would be based on the principles of superstring theory in the first place. It may be that the only framework that incorporates both the principles of quantum theory and the principles of Einstein’s theory of gravity is superstring theory. If so, then a universe based on quantum principles and including Einsteinian gravity would have to be a superstring universe. But there was the choice of whether the universe would have Einsteinian gravity or not. And there was the choice whether the universe would be based on quantum principles or not.
When people say that the ultimate laws of physics will turn out to be “unique,” what they really mean is that they will turn out to be the unique laws that satisfy certain conditions. But what conditions did the universe have to satisfy? And who decided that those conditions and not some other conditions had to be satisfied?
If we remove all arbitrary preconditions, and simply ask how many different mathematical structures there are that could serve as the laws of some hypothetical universe, the answer, quite simply, is infinite. The only thing we must clearly require of any hypothetical universe is that it be mathematically and logically self-consistent, and there is no limit to the number of different universes that would satisfy those minimal requirements. To make matters simple, let us stick to hypothetical universes that are based on classical rather than quantum principles. In the first place, such a universe could have any number of space dimensions. That already gives an infinite choice. Second, if the universe contains matter, that matter could be in the form of particles, or fields, or an infinite variety of other kinds of things (like strings or membranes). If the matter consists of particles, say, the universe could contain any number of particles—which gives another infinite choice. There could be one type of particle, or several types—even an infinite number of types—differing from each other in mass or in other properties. The forces experienced by particles could depend on their types, positions, or other properties in an infinite number of possible ways.
I have not even gotten into such questions as the geometry of space or space-time, and in particular whether it is Newtonian or Einsteinian. And I have limited myself to classical rather than quantum physics. If any theoretical physicist were paid a dollar for every possible universe he could think up, he could get rich very quickly. Would these universes be mathematically beautiful? For the most part maybe not. Would they be such that if they existed life would be able to evolve in them? Probably not, in the overwhelming majority of cases. But who says that those things should matter? The simple and absolutely undeniable fact is that the universe did not have to have the particular laws it does have by any sort of logical or mathematical necessity. In other words, God had a choice—in fact, an infinite number of choices.