To the editors:
Lawrence Krauss has clearly framed the issue: Does fine-tuning convey an illusion of design or design itself? Some very notable physicists have thought that the illusion of design was no illusion at all. “A common-sense interpretation of the facts,” Fred Hoyle remarked,
suggests that a super-intellect has monkeyed with physics, as well as with chemistry and biology, and that there are no blind forces worth speaking about in nature. The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question.1
Krauss remains underwhelmed. Life, he argues, evolved to match the physical parameters of the universe. No one believes that our legs “are remarkably fine-tuned to touch the ground.” Why think otherwise with respect, say, to the fine-structure constant? Life might have existed in many other forms, each governed by different physical parameters. “When one imagines such possibilities,” Krauss writes, “the connection between small values of the cosmological constant and the inference to design flickers briefly and then disappears.”
If the connection does not vanish on its own, its importance may otherwise be diminished. Some key fine-tuning parameters, Krauss observes, have been explained by reference to more fundamental laws of physics, and if some, why not all?
Should these arguments prove unavailing, there remains the multiverse. “The anthropic argument [based on multiverses],” Krauss writes, at least “makes quantitative sense. Design does not.”
If Krauss remains underwhelmed by arguments in favor of design, I remain underwhelmed by arguments in favor of Krauss. We are both underwhelmed. The fine-tuning of many physical parameters is not only necessary for the existence and emergence of life on earth, but for the existence of stable galaxies and rocky planets. Absent a finely tuned cosmological constant, the universe would have either collapsed or blown apart. However bizarre another life-form might be, stable galaxies and rocky planets would seem ineliminably necessary for the origin and evolution of any form of life, Krauss’s extremophiles included. They could not have existed in a universe dominated by black holes or filled with a diffuse soup of hydrogen.
Could a different set of physical parameters have enabled the evolution of radically different forms of life? Krauss believes so. Although biologists have found it difficult to agree on a comprehensive definition, they do agree on some things. All forms of life must maintain a boundary; and they must perform integrated sets of complex chemical reactions within that boundary. This is beyond the power of simple hydrogen or helium atoms. Producing atoms more complex than helium requires significant fine-tuning of the cosmological constant, the masses of quarks, and the ratio between the strong nuclear and electromagnetic force. It also requires a universe in which the Pauli exclusion principle constrains the allowable quantum states of fermions. Fine-tuning precedes any biologically relevant process of evolution.
If fine-tuning cannot be dismissed, can it otherwise be explained? A few fine-tuning parameters, Krauss observes, depend on more fundamental parameters. He anticipates the discovery of a universal law without any free or contingent parameters. He has an example in his favor. When an underlying fundamental physical theory of the strong force governing the formation of protons, neutrons, and nuclei was developed, it was recognized that the configuration of nuclear states was in fact determined by basic fundamental physics, deeply removed from the specifics of carbon nuclei.
Krauss is appealing to the well-known story of Hoyle’s prediction, and Willie Fowler’s confirmation, of a specific carbon resonance level above its standard ground state. Hoyle predicted this level because he thought it must exist in order for carbon-12 to form from beryllium-8 and helium-4.2
To explain how carbon-12 could form, Hoyle devised a theory about how collapsing stars could synthesize carbon from lighter elements under specific conditions.3 His theory implied that getting beryllium-8 and helium-4 to combine to make carbon-12 would, in turn, depend upon a multitude of contingent factors and forces, many of which had to be precisely fine-tuned and balanced. The strengths of the strong nuclear and electromagnetic forces, the ratio between the gravitational and electromagnetic forces,4 and the masses of light quarks all had to be tuned and coordinated within very narrow tolerances to allow the synthesis of large amounts of carbon inside stars. The excitation energy required for the production of carbon-12 is possible only if beryllium-8 and helium-4 have precise associated kinetic energies, and that in turn requires the precise fine-tuning of the strength of the gravitational force constant. Rather than a reduction in which several contingent features of the universe are derived from a single more general law of physics, carbon resonance shows that the derivation is itself contingent on a host of other contingent features.
Nor is there reason to expect that the discovery of some other more general law will eliminate, or explain, all free parameters. Consider the law that describes a simple harmonic oscillator. Hooke’s law and the equations derived from it describe its harmonic motion.5 The wire, when plucked, will oscillate in the form of a sine wave at some regular frequency. To know the resulting wave’s precise amplitude, physicists must know the initial condition of the wire. Hooke’s law and its derived equations do not tell physicists how strongly the wire was plucked. That information must be provided by measurement. Just as Hooke’s law does not determine how hard a piano string is plucked, the fundamental laws of physics do not determine the finely tuned initial configurations of mass and energy (or initial entropy) at the beginning of the universe. That represents a contingent factor not determined by the fundamental laws themselves.
Nor do the laws of physics determine or explain the finely tuned values of their own constants of proportionality. These must be determined by measurement, as well. The values of the physical constants represent information about the net effect of all factors that affect the magnitude of the forces. These constants provide information about the universe itself; and that information is extrinsic. It comes from beyond the laws.
Appealing to some as yet undiscovered law to explain the fine-tuning of the physical constants is implausible for another reason. How could any more fundamental general law explain why the fundamental constants have the values they do when the values they have are utterly idiosyncratic? Why is it that, for example, the permittivity constant in Coulomb’s law should have the value 8.85 × 10–12 coulombs per newton-meter, and the electron mass should have exactly the value of 9.11 × 10–31 kilograms, and the electron charge to mass ratio should be exactly 1.76 × 1011 coulombs per kilogram, and the Higgs field vacuum expectation should have the value of 246 GeV?6 These constants specify a highly irregular array of values that describe either ratios between completely different types of quantities or completely different quantities.
Finally, Krauss suggests that the multiverse serves better as an explanation than any appeal to design. The idea of a multiverse requires both many universes and various mechanisms for producing them. The first is necessary to improve the odds of generating a life-friendly universe; and the second is necessary to produce them. Different universe-generating mechanisms are at work in different cosmological models. Inflationary cosmology assumes that an inflaton field caused the expansion of the universe.7 As the inflaton field expands, the field’s energy sporadically decays, giving rise to lower-energy bubble universes. These, in turn, decay to lower energy states as the original inflaton field continues to expand. Since new bubble universes expand more slowly than the bubbles that contain them, collisions rarely, if ever, happen. A multiverse of causally isolated nested bubble universes is the result.8
In string theoretic models, the roughly 10500 to 101,000 solutions to the string theoretic equations correspond to specific vacua, each corresponding, in turn, to a separate universe with different laws and constants of physics.9
Do either of these cosmological frameworks provide a better explanation of the fine-tuning than intelligent design?
Richard Swinburne has argued one obvious point: “Given that … a theory is simpler the fewer entities it postulates, it is far simpler to postulate one God than an infinite number of universes, each differing from each other.”10 The multiverse requires two universe-generating mechanisms to explain two types of fine-tuning. If inflationary cosmology explains the initial conditions of the universe, it does not explain the fine-tuning of its laws and constants; and if string theory explains the fine-tuning of its laws and constants, it does not explain its initial conditions.
The ensuing clumsiness has led Raphael Bousso, Joseph Polchinski, and Leonard Susskind to embrace an inflationary string landscape model, the best, or worst, of both worlds.11 In theory, at least, the inflationary string landscape model can explain the whole range of fine-tuning phenomena, but only at the cost of a profligate and bloated ontology.
Both inflationary cosmology and string theory require universe-generating mechanisms that themselves require fine-tuning. It would seem that fine-tuning, like certain dental drills, goes all the way down. Consider inflationary cosmology. Inflation explains the homogeneity and flatness of the universe. This is its great triumph. Yet for inflationary cosmology to explain the homogeneity of the cosmic background radiation and the flatness of the universe, the inflaton field would require a certain minimum initial energy to drive its exponential expansion. Having blown up, the inflaton field would also need to decay in just the right way to produce a habitable bubble universe.
These conditions imply that the shutoff energy of the inflaton field requires precise fine-tuning—something on the order of between 1 part in 1053 and 1 in 10123, depending on the inflationary model. The shutoff interval of the inflaton field must also be precisely finely tuned. In some models, inflation begins at around 10–37 seconds after the Big Bang and ends at about 10–35 seconds afterward, during which the radius of space itself expands by a factor of at least 1026.
Sean Carroll and Heywood Tam have shown that the overwhelming majority of universes positing a hypothetical inflaton field will not inflate and develop in a life-conducive way.12 They note that the inflaton field is, in theory, subject to random quantum fluctuations, the majority of which would generate universes incompatible with life. In particular, they have shown that the fraction of realistic cosmologies—cosmologies generating life-friendly universes—resulting from inflation is exceedingly small, roughly 1 in 1066,000,000. This vanishingly small ratio, and corresponding degree of improbability, implies the need for additional sources of extreme fine-tuning.
This is sobering enough; worse now follows. Inflationary cosmology makes the fine-tuning associated with the initial low-entropy state of our universe exponentially worse. The massive energy of expansion during inflation increases the entropy of the universe more than the expansion envisioned by standard Big Bang cosmology. Since inflationary cosmology posits an exponentially larger surge of energy than standard Big Bang cosmology, it generates exponentially more entropy. A lower set of entropic initial conditions is thus required at the beginning of the universe.
Very similar issues arise in string theory. Theorists imagine a particular compactification of space decaying and then exploring the landscape of possible universes. As this process continues, new universes with new laws and physical constants arise. In order to ensure that a given universe cascades to a multitude of hospitable universes, the initial universe must start in an extremely high energy level. Very high energy universes are as rare as 1 part in 10500 or even 101000.13 Fine-tuning is necessary.
Specific string-theoretic models invariably manifest other forms of fine-tuning. Cyclic ekpyrotic models peg the creation of new universes to the collision of two branes; and they must be precisely positioned. The two branes, Renata Kallosh, Lev Kofman, and Andrei Linde have shown, must maintain parallel position in order to prevent large inhomogeneities in the resulting universes.14 The two universes must remain parallel in the multidimensional space that contains the branes to better than 1 part in 1060 across a distance 1030 times greater than the distance between them in order to produce a life-conducive universe. Kallosh, Kofman, and Linde have also shown that the energy potential associated with the multidimensional colliding branes has to be fine-tuned to 1 part in 1050.15
Why does fine-tuning justify an inference to intelligent design? It does so because in our uniform and repeated experience, systems with multiple improbably fixed parameters that also exemplify functional specifications invariably arise from the action of a purposive or intelligent agent.
Richard Dawkins has famously argued that “the universe we observe has precisely the properties we should expect if there is, at bottom, no design, no purpose … nothing but blind, pitiless indifference.”16 Yet this hypothesis does not lead naturally to the expectation of a finely tuned universe.
Cosmological fine-tuning exemplifies just the kind of evidence we would expect to find if a purposeful and intelligent agent had acted in the past to design the universe as a fit habitat for life. It does not seem to be the kind of evidence that one would expect if the universe had arisen from “blind, pitiless indifference.” Nor do Professor Krauss’s arguments alter this probability calculus.
Stephen Meyer
Lawrence Krauss replies:
Stephen Meyer’s arguments in favor of intelligent design are not new. His specific examples may be updated, but the message is almost always the same: Puzzling results, beyond our current understanding, are evidence for a divine intelligence.
Alas, however, lack of understanding is not evidence for God. It is rather evidence of a lack of understanding.
Meyer’s broad scholarship is laudable, but he nevertheless manages to distort the fundamental science behind a number of concepts that he presents in his letter. It is true, when expressed in MKS units the constants of nature appear to have widely different, and otherwise inexplicable values. But what does that prove? Without a fundamental underlying theory, it is likely that any set of values will seem arbitrary. And as I pointed out in my essay, the history of physics suggests that such arbitrariness tends to go by the wayside as we understand the fabric of reality on ever-deeper levels. This is not a guarantee that at some point we will be stymied, throw up our hands, and concede evidence for direction and design. But we are far from that point now.
As for the key detail about the cosmological constant that he seemed to miss when reading my essay here, I will repeat it explicitly. Had the cosmological constant been exactly zero, no one would have argued that it was finely tuned. And such a universe would be more hospitable to life than our own. If there was a designer, she did a poor job designing, just as she seemed to do a poor job in designing a breathing pathway that coincides with an eating pathway in humans, or in combining a reproductive pathway with an excretory one. As for arguing against a multiverse from inflation (of which there are many proposals that differ from the chaotic inflation proposal of Andrei Linde) the claim is that a multitude of universes is less simple than one God. But of course the multitude results from a simple theory, which might in the end have zero free parameters. In this case zero is simpler than one. Not to mention that arguing for a single, complex, omnipotent God’s presupposes a multitude of questions about how that complexity might have arisen.
Finally, arguing that cosmology provides evidence that the universe is a fit habitat for life like ours really gives short shrift to the nature of most of our own universe.
If, as Meyer seems to require, life must be like the life we experience on earth, presumably designed in the image of God, then the Universe is a horribly poor environment. In almost every other location we see in the Universe, life like our own cannot arise. Indeed, even here, our survival involves a constant battle against a harsh and seemingly indifferent universe that is trying to kill us, as it eventually will. But why must life be like our own? Meyer argues, without any underlying evidence, that life has to exist on rocky planets like our own. But some, like my late colleague Freeman Dyson, argued cogently that in the long run, other sorts of intelligent life could arise even in the very “diffuse clouds of hydrogen” that Meyer finds so inhospitable—the black clouds of Fred Hoyle. The rules for such life-forms would undoubtedly be very different than for us.
Once again the argument for purpose and design seems to come down to a lack of imagination, and a lack of faith, not in God, but in the possibilities of existence and the ability of science to eventually unravel most, if not all of them.
