April 14, 2013

Fine Tuning and Physical Necessity

Hello Dr. Craig,

I'm looking for some clarity regarding your argument about the explanation for the fine-tuning of the cosmos for intelligent life, in which you identify either physical necessity, chance, or design as explanatory options.

You rule out necessity by saying that the laws of nature (and/or their values) are contingent and could have been different. This seems intuitively correct to me, and I have heard secular scientists like Brian Green state similar views on his PBS documentary (only in the context of the multi-verse). However, I'm wondering what kind of evidence we have for such a claim (i.e., that the weak/strong nuclear forces or gravity could have taken on different values, or be reversed, or have completely different characteristics all together)?

Evidence aside, you imply (but haven't explicitly stated) that such necessity would be disconfirming of theism. This is inferred by the way you dichotomize necessity from design. However, I don't see why the necessity of physical reality could not be merged with design. Wouldn't a grand unified theory (if it could show that the natural laws and their values COULD NOT have been any different) just bring up an even more important question...that is, 'why does a life permitting universe HAVE to exist?' Would this question be incoherent in the light of proven physical necessity? Otherwise, it seems to me that a proof for the necessity of the physical laws would be strongly confirming of theism (i.e., necessity by design), especially in the absence of a multi-verse.


United States

Yes, Aaron, it seems to be pretty widely acknowledged that the constants and quantities in question are not physically necessary. This is because they cannot be predicted on the basis of current physical theory or any envisionable extension of current physical theory. Several years ago Stephen Hawking addressed your question at a cosmology conference at the University of California, Davis. Notice the alternative answers which he identifies to the fundamental question he poses:

Does string theory, or M theory, predict the distinctive features of our universe, like a spatially flat four dimensional expanding universe with small fluctuations, and the standard model of particle physics? Most physicists would rather believe string theory uniquely predicts the universe, than the alternatives. These are that the initial state of the universe, is prescribed by an outside agency, code named God. Or that there are many universes, and our universe is picked out by the anthropic principle.1

Notice that the options mentioned by Hawking are precisely the three alternatives which I address. Hawking argues that the first option, physical necessity, though the option most physicists would prefer to be true, is a vain hope: “M theory cannot predict the parameters of the standard model. Obviously, the values of the parameters we measure must be compatible with the development of life. . . . But within the anthropically allowed range, the parameters can have any values. So much for string theory predicting the fine structure constant.” He wrapped up by saying,

even when we understand the ultimate theory, it won’t tell us much about how the universe began. It cannot predict the dimensions of spacetime, the gauge group, or other parameters of the low energy effective theory. . . . It won’t determine how this energy is divided between conventional matter, and a cosmological constant, or quintessence. . . . So to come back to the question. . . Does string theory predict the state of the universe? The answer is that it does not. It allows a vast landscape of possible universes, in which we occupy an anthropically permitted location.

In fact, this idea of a “cosmic landscape” predicted by string theory has become something of a phenom in its own right.2 It turns out that string theory allows around 10500 different universes governed by the present laws of nature, so that the theory does not at all render the observed values of the constants physically necessary. Moreover, even though there may be a huge number of possible universes lying within the life-permitting region of the cosmic landscape, nevertheless that life-permitting region will be unfathomably tiny compared to the entire landscape, so that a randomly thrown dart would have no meaningful chance of striking a life-permitting universe.

All of this is said just with respect to the constants. The arbitrary quantities which are put in as initial conditions, like the universe’s initial low entropy condition, are in no way predicted by current physical theory.

As to the second part of your question, I think you’ve misunderstood me if you believe that I have implied that physical necessity is disconfirmatory of design. Given a disjunction like “P or Q or R” (P∨Q∨R), it would be logically fallacious to infer that because P is true, therefore R is false. What may be validly inferred is that if P and Q are false, then R is true, which is the form of my argument. But I take it that God could have designed a universe in which the laws of nature do determine the values of the constants and quantities, as you suggest. In that case a different sort of argument for theism would be in order, such as the one you put forward.


1 S. W. Hawking, “Cosmology from the Top Down,” paper presented at the Davis Cosmic Inflation Meeting, U. C. Davis, May 29, 2003.

2 See Leonard Susskind, The Cosmic Landscape: String Theory and the Illusion of Intelligent Design (New York: Little, Brown, & Co., 2006).