Intelligent Design

Debunking the debunker: How Sean Carroll gets the fine-tuning argument wrong

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In a new 9-minute video, physicist Sean Carroll eviscerates the fine-tuning argument for the existence of God. Or does he? Apart from its science-of-the-gaps optimism, the video’s main flaws are that it fails to state the fine-tuning hypothesis correctly, and employs poor Bayesian reasoning. But first, let’s have a look at the video, which was posted on Youtube by a user named bdwilson1000:

The text of Dr. Sean Carroll’s video can be found in the opening speech of his debate with Professor William Lane Craig on the topic, “God and Cosmology: The Existence of God in Light of Contemporary Cosmology” in March 2014.

Professor Jerry Coyne has provided a handy summary of Dr. Carroll’s five main points in a post over at Why Evolution Is True (December 31, 2015).

1. We don’t really know that the universe is tuned specifically for life, since we don’t know the conditions under which life is possible.
2. Fine-tuning for life would only potentially be relevant if we already accepted naturalism; God could create life under arbitrary physical conditions.
3. Apparent fine-tunings may be explained by dynamical mechanisms or improved notions of probability.
4. The multiverse is a perfectly viable naturalistic explanation.
5. If God had finely-tuned the universe for life, it would look very different indeed. [Carroll considers this his most important point. Here he goes into not only the cosmos, but the nature of human culture which, Carroll avers, comports much better with naturalism than with theism.]

I have to say that the new 9-minute video is quite a slick production: it’s just the right length and it sounds like a very convincing debunking to anyone who isn’t familiar with the fine-tuning argument. I have previously critiqued a 53-minute video by Dr. Sean Carroll attacking the fine-tuning argument, but in my opinion, his new one is much better, for a public audience. Viewers of Dr. Carroll’s latest video were highly impressed. Wrote one: “Damn this guy is well-spoken. And brilliant arguments as well.”

So, what’s wrong with Sean Carroll’s argument? Quite a lot, actually. Dr. Carroll makes five points in his video, so I’ll confine myself to just five points in my reply.

1. Mis-statement of the fine-tuning hypothesis

In his fifth point, Dr. Carroll remarks: “[I]f you played the game honestly, what you would say is, ‘Here is the universe that I expect to exist under theism. I will compare it to the data and see if it fits.'” Evidently Carroll thinks we should take two hypotheses – theism and naturalism – and compare their scientific predictions about the universe we observe. If theism makes superior predictions, it warrants acceptance; otherwise, it fails.

But the fine-tuning hypothesis doesn’t merely state that God exists: it states that the universe He made was fine-tuned for life, and especially intelligent life. Now, why would that be? After all, as Dr. Carroll points out in his video, God could have easily produced intelligent life in a universe that wasn’t fine-tuned. If fine-tuning is not required in order to generate the desired product (intelligent life), and if it is no easier for the producer (God) to make the product in that way, then the only possible reason for fine-tuning must have to do with God wanting to be known by us. In other words, God fine-tuned the universe because He wants us to discover His existence through the fine-tuning of the cosmos.

So the fine-tuning hypothesis should be stated as follows:

(FH) There exists a Being Who made the cosmos in order to produce intelligent beings who would discover scientific evidence of His existence, in the cosmos. By contrast, the null hypothesis denies the existence of a God Who wants to make Himself known scientifically.

NOTE: As philosophy professor John T. Roberts of the University of North Carolina, Chapel Hill, points out in an article (which I blogged about here) titled, Fine-Tuning and the Infrared Bull’s-Eye (Philosophical Studies 160(2):287-303, 2012), the fact that our universe is life-sustaining is part of our background knowledge B. The fact that the universe is fine-tuned for life is the evidence E for the fine-tuning hypothesis. The reason why I mention these points is that in many “standard” formulations of the fine-tuning argument, fine-tuning is treated as part of our background knowledge – which makes no sense at all, because the discovery of fine-tuning a few decades ago came as a surprise to scientists – while the existence of life is treated as part of the evidence for theism, despite the fact that it is old evidence, which we knew about all along. I find Roberts’ new presentation of the argument highly persuasive.

The reader will also note that my formulation of the fine-tuning hypothesis (FH) above does not make any explicit reference to fine-tuning – otherwise, it would commit the fallacy of assuming the very evidence it is supposed to explain. However, the occurrence of fine-tuning would certainly be a very natural corollary of the fine-tuning hypothesis: if there is a Creator Who wants to make His existence known to us scientifically, then the fine-tuning of the cosmos would be about as clear a signal as you could possibly get, from a scientific standpoint. (I’ll say more about miracles and signs in the heavens below: as we’ll see, they’re more ambiguous than fine-tuning.)

Stated in this way, the fine-tuning hypothesis is opposed not only to atheism (which denies the existence of a cosmic Creator), but also various versions of theism in which the Creator either does not wish His existence to be discovered by us (i.e. a Deity Who wishes to remain hidden), or does not wish His existence to be discovered by us through fine-tuning, but in some other way (i.e. a Deity Who refuses to provide scientific evidence for His existence, preferring us to rely on philosophical arguments or evidence from miraculous signs, instead). If confirmed, the fine-tuning hypothesis does not confirm theism as such, but a particular version of theism.

This way of stating the fine-tuning hypothesis reveals the fallacy in Dr. Carroll’s second point, where he states:

… God doesn’t need to fine-tune anything. We talk about the parameters of physics and cosmology: the mass of the election, the strength of gravity. And we say if they weren’t the numbers that they were then life itself could not exist. That really underestimates God by a lot, which is surprising from theists, I think. In theism, life is not purely physical. It’s not purely a collection of atoms doing things like it is in naturalism. I would think that no matter what the atoms were doing God could still create life. God doesn’t care what the mass of the electron is. He can do what he wants. The only framework in which you can honestly say that the physical parameters of the universe must take on certain values in order for life to exist is naturalism.

Now, if God’s aim were solely to create intelligent life, then Dr. Carroll would have a legitimate point. But if God’s aim is to create intelligent beings who are capable of inferring His existence on scientific grounds, as the fine-tuning hypothesis listed above states, then it could be argued that He does need to create a fine-tuned cosmos – or some other cosmos with a “fingerprint of the Deity” which is equally impressive.

“But why does God need to create intelligent beings with bodies?” the reader might ask. “Why couldn’t He create disembodied intelligences?” Well, the short answer is that He may very well have done so (after all, that’s what angels are, in Christian theology), but that in any case, there is an objectively good reason for God to create embodied moral agents. As cosmologist Luke Barnes puts it:

Richard Swinburne and Robin Collins have argued that we expect that God would want to create a universe with moral value. Embodied moral agents are good things. In particular, embodied agents can influence their environment and each other for good or evil, granting them significant moral responsibilities. And so the theist (it is argued) has a ready explanation as to why we observe a universe that evolves and sustains embodied moral agents.

I might add that Dr. Carroll is gratuitously assuming the possibility of finite, disembodied intelligences in his argument. We don’t know that such intelligences are possible, even on the hypothesis that God exists. Theism does not imply the truth of dualism. It may be that while the notion of an Infinite Spirit makes sense, the notion of a finite spirit turns out to contain metaphysical and/or scientific contradictions. As a Christian who defends dualism, I certainly wouldn’t argue that way myself, but Dr. Carroll has no right to assume that a Deity should be capable of creating finite, disembodied intelligences. We don’t know that.

Finally, I should point out that the fine-tuning hypothesis does not require that the Creator of the cosmos be identical with the God of classical theism: a God Who is being Itself, and Who is omnipotent, omniscient and omnibenevolent. The God of the fine-tuning argument is an extra-cosmic Intelligence Who, having created its laws, is not bound by any of them. As such, this Deity is transcendent – but that’s about all we can say about Him/Her/It. (If I use the pronoun “He” in this post, it is purely for the sake of convenience.)

2. Poor Bayesian reasoning

In his fifth argument, Dr. Carroll contends that if the fine-tuning hypothesis were true, you would expect the following:

(a) just the right amount of fine-tuning but not too much (falsified by massive over-tuning of the cosmological constant);
(b) the particles and parameters of particle physics should be just sufficient to allow life to exist, and they should have some structure that points to their having been designed (falsified by the existence of a “particle zoo” and the apparent arbitrariness of many physical parameters);
(c) life should play a special role in the universe (falsified by the relative insignificance of our Earth in the solar system, of our Sun in the Milky Way galaxy, and of our galaxy in the cosmos);
(d) the existence of a Creator should be perfectly obvious (falsified by the fact that many rational people doubt or deny God’s existence);
(e) religious beliefs should be universal (falsified by the plethora of conflicting religious beliefs in the world today);
(f) religious doctrines should remain stable over a long period of time (falsified by the observation that doctrines frequently adapt, to meet the social needs of a community);
(g) moral teachings of religion should be transcendent and progressive (falsified by the existence of many religious moral teachings which are backward in their thinking – e.g. teachings on sexism and slavery);
(h) sacred texts should give us interesting as well as useful, life-saving information, e.g. “Diseases are spread through germs” (falsified by the absence of such information in religious texts);
(i) biological forms should be designed (falsified by the discovery that these forms are the product of historically contingent events in the evolution of life on Earth – e.g. the asteroid impact that occurred 66 million years ago, making the rise of the mammals – and our own existence – possible);
(j) minds should be independent of bodies (falsified by the fact that brain injury can cause not only forgetfulness, but also complete personality change);
(k) evil, where it exists, should be explicable (falsified by the occurrence of random suffering);
(l) life should be essentially just, and the universe should be perfect (falsified by the fact that we live in a very messy, unfair universe).

Clinching his argument, Dr. Carroll delivers his knockout blow:

Now, I know what you’re thinking. You’re thinking, “But I can explain all of that.” I know you can explain all of that—so can I. It’s not hard to come up with ex post facto justifications for why God would have done it that way. Why is it not hard? Because theism is not well defined. That’s what computer scientists call a bug, not a feature.

Now let’s concede for the sake of argument that Dr. Carroll is right here. My question is: “Where are the numbers, in this argument?”

To see why the numbers matter, consider the following scenario. Let’s suppose that the evidence for fine-tuning favors the hypothesis of a Creator Who designed the universe in order to make His existence known to us, and let’s suppose that the evidence from fine-tuning favors this particular theistic hypothesis over the rival hypotheses of naturalism, a hidden Deity and a science-spurning Deity, by a factor of 10^40 to 1. In particular, calculations by Brandon Carter show that the ratio of the electromagnetic force to gravity must be finely balanced to a degree of one part in 10^40, because if its value were to be increased even slightly, stars would burn out too quickly to support complex life, while if it were decreased significantly, stars would be incapable of producing heavy elements. (NOTE: In going with the figure of 10^40, I’ve chosen a very conservative estimate; other estimates in the fine-tuning literature go far higher, with figures of 10^60, 10^120 and even 10^(10^123) being commonly cited.)

Now let’s generously suppose that the twelve pieces of contrary evidence cited by Carroll are all mutually independent of one another (which is clearly false, but let that that pass), and that they all favor the null hypothesis (of either no Deity or an indifferent Deity) over the fine-tuning hypothesis of a science-friendly Deity (which is highly debatable, but we’ll let that pass, too), and that each piece of contrary evidence favors the null hypothesis over the fine-tuning hypothesis by a factor of 10^3 to 1.

Let me spell that last one out. What I’m granting (for argument’s sake) is that the following twelve facts – over-tuning of the cosmological constant, the particle zoo, the insignificance of Earth in the cosmos, the existence of religious skeptics, the existence of multiple competing religions, changes in religious doctrines, barbaric religious moral teachings, sacred texts devoid of useful information, biological forms whose designs are the product of historical accident, minds which can be radically altered by physical occurrences, the occurrence of inexplicable evils, and the essential injustice of life – are each 1,000 times more likely under the null hypothesis than under the hypothesis of a God Who wants His existence to be scientifically knowable.

Now, it should be apparent to the reader that the figure of 1,000 is likely to be a massive over-estimate. After all, the fine-tuning hypothesis says nothing about whether the Creator is interested in revealing religious or moral truths to anyone. It only states that He wishes to reveal the fact of His existence – and nothing more. (For instance, the American freethinker Tom Paine believed in such a Deity. And I might add that one drawback of miracles, signs in the heavens, and revelations from “on high” is that they don’t necessarily imply the existence of a transcendent Creator Who is outside the cosmos: even witnessing these spectacles, you might wonder whether you had been duped by technologically advanced aliens.) The fine-tuning hypothesis also says nothing about whether the Creator is just, unjust, or sublimely indifferent to earthly affairs. (Perhaps the Creator simply wants to make His existence known, and leave the rest to us.) Additionally, the fine-tuning hypothesis says nothing about which particular mechanism the Creator would favor, in order to generate intelligent beings: special creation, intelligent designed evolution, or evolution without any scientifically detectable evidence for design. (The last option doesn’t square well with the hypothesis of a Creator Who wishes to make His existence known scientifically; however, the Creator of the universe might reason that the existence of cosmic fine-tuning constitutes sufficient evidence for intelligent beings to infer His existence, without the need for additional, biological evidence.) Nor does the fine-tuning hypothesis say anything about whether these intelligent beings would have spiritual souls (as dualists hold), or whether they would be purely physical entities (as the Christian apologist and discoverer of oxygen, Joseph Priestley, maintained). Nor does the fine-tuning hypothesis require life-friendly planets to be abundant throughout the cosmos. (The Creator might reason that one such planet is enough, and that the discovery of other intelligent life-forms might confuse us.) Nor does the fine-tuning hypothesis require the fundamental particles and/or parameters of physics to form a nice, orderly family: indeed, that might work against the Creator’s aims, as it might mislead His intelligent creatures into thinking that some sort of underlying mathematical symmetry explained the life-friendly features of the cosmos, without the need for a Creator. Finally, while the over-tuning of the cosmological constant is a puzzling feature of the cosmos, “it’s not hard” (to cite Sean Carroll’s own words) to think of a reason why a Creator might want to do that: perhaps He wanted to throw that in as an artistic flourish, just to show us what a skillful Fine-Tuner He really is. That’s an ad hoc hypothesis – but it’s quite plausible, and I’d be inclined to rank its likelihood as somewhat higher than 1 in 1,000.

In short: the only two pieces of evidence cited by Dr. Carroll which create genuine difficulties for the fine-tuning hypothesis are: (i) the over-tuning of the cosmological constant and (ii) the observation that some biological forms are the product of what appear to be “historical accidents” in the evolution of life on Earth.

Now I’m going to administer my own “knockout blow,” against Carroll’s argument. Multiply Carroll’s twelve likelihoods together, and you get a collective set of evidence which favors the null hypothesis (of naturalism, or an indifferent and/or science-spurning Deity) over the fine-tuning hypothesis by a factor of 10^36 to 1 (since ((10^3)^12)=10^36). But by a very conservative estimate, the fine-tuning evidence favors the fine-tuning hypothesis over the null hypothesis by a factor of 10^40 to 1. It therefore follows that even after we take all of the evidence together, in its totality, the fine-tuning hypothesis of a Creator Who wants His existence to be scientifically discoverable is still favored over the null hypothesis by 10^4 to 1, or 10,000 to 1. ((10^40)/(10^36)=10^4.)

In plain English: even on a conservative estimate of the strength of the evidence for fine-tuning, and a ridiculously generous estimate of the strength of the evidence against fine-tuning, the fine-tuning hypothesis is still 10,000 times more reasonable than the null hypothesis which denies the existence of a God Who wants to make Himself known scientifically.

3. Science of the gaps

Dr. Carroll confidently assumes that as more scientific discoveries are made, the evidence for the fine-tuning hypothesis of a science-friendly Deity will gradually recede. He even cites his own favorite example, in his third point:

There’s a famous example theists like to give, or even cosmologists who haven’t thought about it enough, that the expansion rate of the early universe is tuned to within 1 part in 10^60. That’s the naïve estimate, back of the envelope, pencil and paper you would do. But in this case you can do better. You can go into the equations of general relativity and there is a correct rigorous derivation of the probability. If you ask the same question using the correct equations you find that the probability is 1. All set of measure zero of early universe cosmologies have the right expansion rate to live for a long time and allow life to exist. I can’t say that all parameters fit into that paradigm but until we know the answer we can’t claim that they’re definitely finely-tuned.

I should point out that Dr. Carroll is very much in a minority when he suggests that the fine-tuning of the universe may only be apparent, rather than real. In his rebuttal to Dr. Sean Carroll’s opening speech, Professor William Lane Craig put up a slide listing some prominent scientists who have defended the reality of fine tuning:

Barrow, Carr, Carter, Davies, Hawkins,
Deutsch, Ellis, Greene, Guth, Harrison,
Hawking, Linde, Page, Penrose,
Polkinghorne, Rees, Sandage, Smolin,
Susskind, Tegmark, Tipler, Vilenkin,
Weinberg, Wheeler, Wilczek

The list was supplied to Professor Craig by cosmologist Luke Barnes, who comments:

The references are all in the paper. These scientists all agree that there is enough evidence for fine-tuning that we should do something about it. The list is a roughly equal mix of theist, non-theist and unknown. The non-theists often reach for the multiverse. The theists are divided between those who think that the multiverse is a good scientific solution (especially Page) and those who think that God is required.

Note: putting Dawkins on that list is a bit cheeky on my part. He’s not a cosmologist or a physicist. In an endnote to The God Delusion, he mentions that there are objections to fine-tuning by Stenger. I think he’s taking the advice of Martin Rees on these matters and so takes fine-tuning seriously.

I should add that if Dr. Carroll wishes to deny the reality of fine-tuning, he really should rebut the (very detailed) scientific arguments contained in cosmologist Luke Barnes’ Arxiv paper, The Fine Tuning of the Universe for Intelligent Life (December 21, 2011). Dr. Barnes makes a very powerful case.

In his fourth point in his 9-minute video, Dr. Carroll describes the multiverse as “an obvious and easy naturalistic explanation” of the phenomenon of fine-tuning. The multiverse, according to Carroll, is “a prediction of physical theories that are themselves quite elegant, small, and self-contained that create universes after universes.”

What Dr. Carroll overlooks is that there are no less than five killer arguments against the multiverse. Dr. Carroll thinks he can answer one of these arguments – the “Boltzmann brains” argument – but that still leaves four arguments which he hasn’t answered. However, the most telling argument, put forward by physicist Paul Davies in a recent interview with Robert Lawrence Kuhn, is that if the multiverse is real, then we probably live in a fake universe with fake physics. Davies warns that using multiple universes to explain all existence is “a dangerous, slippery slope, leading to apparently absurd conclusions.” Davies is not alone. Physicist Paul Steinhardt, who helped to create the theory of cosmic inflation but now rejects it, writes: “The multiverse idea is baroque, unnatural, untestable and, in the end, dangerous to science and society.” Even MIT Professor Alan Guth, a strong supporter of the theory of inflation (which he helped originate) and the multiverse, finds the notion of the multiverse troubling. He points out that in an infinitely branching multiverse, “there are an infinite number of one-headed cows and an infinite number of two-headed cows” – which seems to imply, bizarrely, that one-headed cows and two-headed cows are equally common!

What about Dr. Carroll’s claim that the apparent fine-tuning (to 1 part in 10^60) of the expansion rate of the early universe can be explained away as a natural consequence of general relativity?

Now, I’ve been in touch with a couple of physicists, and I happen to know that Dr. Carroll’s claim is bogus. One of them told me that while he hadn’t followed the issue very closely in the literature, he recalled reading that the measure defining the probabilities for the “just-right” expansion rate is highly contentious. That fact alone should make us wary of Carroll’s outlandish statement.

The other physicist who contacted me stated that the figure of 10^60 was cited by no less an authority than (atheist) Stephen Hawking, and that it is quoted by another general relativity theorist, whose credentials are superior to Carroll’s. He adds that he would love to see a citation in the scientific literature for Dr. Carroll’s claim that the probability of a just-right expansion rate under general relativity equals 1, since such a claim would be “rather famous” if it were true. Finally, he suspects that Dr. Carroll’s claim follows from inflation theory (a refinement of the Big Bang model) rather than general relativity. This suspicion appears to be confirmed by a 2002 EDGE interview given by inflationary theorist Alan Guth, in which Guth declares that inflationary theory explains two puzzling features about the expansion rate of the early universe.

However, Guth’s interview was given 11 years before the publication of a 2013 paper by Anna Ijjas, Paul J. Steinhardt and Abraham Loeb, titled, Inflationary paradigm in trouble after Planck2013, which I blogged about here. The authors of the paper question the cosmological theory of inflation, which postulates that the universe underwent a period of extremely rapid expansion shortly after the Big Bang, and that it has been expanding at a slower rate ever since. Briefly, they contend that inflation can smooth out the universe only if it’s already very smooth to begin with. In other words, the initial conditions of the universe are not random: they have to be tweaked for inflation to work.

A second oddity uncovered by the 2013 Planck satellite data is that the version of inflation they support is one that involves so-called plateau-like models, which themselves require a lot of fine-tuning in order to make them work. This is odd, because other things being equal, another version of inflation, called power-law inflation, is exponentially more likely than plateau-like inflation. What’s more, power-law inflation doesn’t require any fine-tuning to make it work.

Finally, the whole logic of inflation theory is that it implies the existence of a multiverse, a vast (and perhaps infinite) ensemble of universes, including our own universe. But in a multiverse, where the parameters can vary in any possible way, you would never expect to find a universe whose parameters all had typical values. That would be just too much of a coincidence – like the discovery of a human face which is free from all traces of displeasing asymmetry, making it surprisingly beautiful, like the face of Grace Kelly (pictured above). But the odd thing about the new satellite data is that all of the parameters measured for our universe agree with the values that one would naively expect them to have. None of them are odd, or unusual. In the authors’ own words:

In a multiverse, each measured cosmological parameter represents an independent test of the multiverse in the sense one could expect large deviations from any one of the naive predictions. The more observables one tests, the greater the chance of many-sigma deviations from the naive predictions. Hence, it is surprising that the Planck2013 data agrees so precisely with the naive predictions derived by totally ignoring the multiverse and assuming purely uniform slow-roll down the potential.

But if our universe was intelligently designed, instead of being just one of countless universes in an infinite multiverse, this agreement with “naive predictions” is precisely what we might expect to find. What it tells us is that the universe was designed to be beautiful.

Nevertheless, the authors reject any attempt to explain the Planck2013 satellite data appeal to the anthropic principle (which states that the laws, parameters and values of the physical constants of the universe must all be compatible with the existence of intelligent observers, or else we would not be here). Their reason is that “Planck2013 disfavors the simplest inflationary potentials while there is nothing anthropically disadvantageous about those models or their predictions.” In other words, the existence of intelligent life is perfectly compatible with the simplest versions of inflationary theory – which are inherently much more likely than the more complicated (and exponentially less likely) plateau models of inflation. However, it is only the latter models which are compatible with the Planck2013 satellite data.

However, as I pointed out in a previous post, the fine-tuning hypothesis goes far beyond the anthropic principle in its predictions. The fine-tuning hypothesis doesn’t merely predict that the physical properties of the universe are compatible with intelligent life; what it says (at least, in the version which I am defending) is that these physical properties were designed in order to enable intelligent beings to infer the existence of a Creator of the cosmos. In other words, life-friendly parameters are not good enough for fine-tuning: what it demands are parameters which are life-compatible, but also very fragile, so that even a tiny variation in these parameters would be fatal to life. That is why the fine-tuning hypothesis would predict a plateau model of inflation to hold, rather than the much simpler power-law version of inflation – assuming, of course, that the inflationary theory is true, which some cosmologists deny.

In short: Dr. Carroll’s appeals to inflation theory, in an attempt to explain away the “just-right” expansion rate of the early universe (which appears to be fine-tuned to 1 part in 10^60), backfire on him, as the only versions of inflation theory that are compatible with the Planck2013 satellite data are themselves highly fine-tuned.

4. Carroll overlooks the “fly-on-the-wall” argument

In his first point, Dr. Carroll speculates that for all we know, life of some sort could exist under a variety of conditions: “Sadly, we just don’t know whether life could exist if the conditions of our universe were very different because we only see the universe that we see.”

On this point, Carroll may very well be right. But even if he is correct, it is neither here nor there, as far as the fine-tuning argument is concerned. The argument does not focus on the (unimaginably large) totality of all possible universes; instead, it is concerned only with those in our immediate neighborhood, which differ only slightly from our own: perhaps one or two parameters are altered, while the other parameters continue to be held at the values which obtain in this universe. The point is that if we confine ourselves to the possible universes within our neighborhood, it turns out that the number of changes in physical parameters which are fatal to life vastly outnumbers the changes that can be made which are compatible with life.

Or as the philosopher John Leslie put it, using his now-famous “fly-on-the-wall” analogy:

“If a tiny group of flies is surrounded by a largish fly-free wall area then whether a bullet hits a fly in the group will be very sensitive to the direction in which the firer’s rifle points, even if other very different areas of the wall are thick with flies. So it is sufficient to consider a local area of possible universes, e.g. those produced by slight changes in gravity’s strength, or in the early cosmic expansion speed which reflects that strength. It certainly needn’t be claimed that Life and Intelligence could exist only if certain force strengths, particle masses, etc. fell within certain narrow ranges… All that need be claimed is that a lifeless universe would have resulted from fairly minor changes in the forces etc. with which we are familiar.”
(Universes, Routledge, London and New York, 1989; paperback edition, 1996; Taylor and Francis e-Library edition, 2002, pp. 138-139, section 6.20.)

Dr. Carroll makes no attempt to engage the “fly-on-the-wall” argument. For that reason, his attempt to undercut the fine-tuning argument by appealing to the possibility of life existing in universes radically different from our own, simply misses the point.

5. Over-elastic definitions of “life”

In a blog post reviewing the first of Dr. Sean Carroll’s five replies to the fine-tuning argument, cosmologist Luke Barnes accuses Dr. Sean Carroll of playying fast-and-loose with the definition of life when he states: “We just don’t know whether life could exist if the conditions of our universe were very different because we only see the universe that we see.”

Dr. Barnes comments:

I don’t know how a theoretical cosmologist can make a statement like that. Compare:

“We just don’t know what the cosmic microwave background (CMB) would look like if the conditions of our universe were very different because we only see the universe that we see.”

“We just don’t know what Mercury would do if it obeyed Newton’s law of gravity because we only see the universe that we see.”

If Carroll’s problem here is an in principle problem, then his objection amounts to a denial that we can do theoretical physics. The job of the theoretical physicist is to take a given law of nature (and its constants), and predict its consequences. This usually involves solving the equation. Asking whether a given set of laws and constants would produce life is the same type of question as whether they would produce atoms, rainbows, galaxies or a CMB.

Granted, life is a more difficult task. But, as noted above, we can be conservative. Rather than identify every island that life may or may not inhabit in parameter space, we can just note the huge lifeless oceans.

In his first point, Dr. Carroll suggests we can define life in very broad terms, as “just information processing, thinking or something like that.” I would put it to him that if we’re talking about life existing in some universe, then at the very least, it would have to be material, composed of atoms, complex and highly structured. It therefore follows that universes in which atoms are incapable of forming, or in which atoms decay very rapidly, cannot possibly support life.

Well, that’s five points, so I’ve said all that I promised I would say in this post. I’d now like to throw the discussion open to readers. What do you think of Dr. Carroll’s debunking of the fine-tuning argument?

22 Replies to “Debunking the debunker: How Sean Carroll gets the fine-tuning argument wrong

  1. 1
    kairosfocus says:

    VJT, yet another interesting piece, a happy new year to you. I find it hard to escape the impression that it seems to me there is a subtext of desperation leading to selective hyperskepticism at work in the sort of dismissive arguments we so commonly see. KF

  2. 2
    chris haynes says:

    Dr Carroll’s statement about the cosmological constant misses the obvious point:

    He says we should see just the right amount of fine-tuning but not too much (falsified by massive over-tuning of the cosmological constant)

    Now it’s been known for over 80 years that, when taken together, the cosmological constant, the mass of the universe and the gravitational constant are very very fine tuned.

    But Dr Carroll is referring to something different. He is referring instead to the fact that the cosmological constant is said to differ by a factor of 10^120 from the value predicted by quantum field theories. But such a difference is not an example of the cosmological constant’s being fine tuned. It is proof that quantum field theory is wrong.

  3. 3
    gpuccio says:


    With all respect and admiration for your detailed arguments, I will offer my short ones:

    1. We don’t really know that the universe is tuned specifically for life, since we don’t know the conditions under which life is possible.

    Life as we know it has a lot of obvious constraints. And not only life, but practically every form on the universe: galaxies, planets, matter itself. That is the essence of the fine tuning argument. There are infinite sets of the basic parameters of the universe which would make any interesting form impossible. Including life as we know it. Carroll’s first argument is only bad philosophy, which denies all that we do know about the universe and physical reality.

    2. Fine-tuning for life would only potentially be relevant if we already accepted naturalism; God could create life under arbitrary physical conditions.

    We only have to accept the existence of an ordered reality based on laws. That is not naturalism. Naturalism means to believe that an ordered reality based on laws is all that exists, and that the laws are more or less those that we understand. IOWs, naturalism is simply an arrogant and unjustified assumption.

    OTOH, if we accept that the reality we know is ordered and based on laws (even if we may not understand all of them), then it is no more true that “God could create life under arbitrary physical conditions”. If God has created reality and its laws, there is no reason why He should contradict those laws in the rest of his working.

    This second point is not only bad philosophy, but especially awful religion.

    3. Apparent fine-tuings may be explained by dynamical mechanisms or improved notions of probability.

    Not sure what he means.Is that more wishful thinking?

    4. The multiverse is a perfectly viable naturalistic explanation.

    The multiverse, if it exists, is no explanation of anything. First, let’s show that infinite universes exist. Then, let’s see is they are fine tuned or not. We cannot reason about fundamental things just assuming that something exists, or assuming what it is, without any possible empirical confirmation.

    And of course, it is always possible that “improved notions of probability” make the multiverse a strong argument for fine tuning! 🙂

    5. If God had finely-tuned the universe for life, it would look very different indeed.

    I really don’t understand all these people who have such a clear idea of what God would do or not do. Are they specially inspired? Are they just recycling the old problem of evil, discovering for the first time that we live in an apparently imperfect world? Do they really believe that all those who have believed is some god were thinking that the universe is devoid of any limitation or imperfection? Do they think that all those people were simply morons?

    This is not only bad science, bad philosophy and bad religion, it is simply bad human behavior, and the obvious conflation of a personal (and very gross) philosophical view about a fundamental problem in human thought and a simple scientific argument which has nothing to do with it. His a-l “arguments” are so philosophically trivial and scientifically irrelevant that they really don’t deserve any answering.

    VJ, you say:

    “Now, if God’s aim were solely to create intelligent life, then Dr. Carroll would have a legitimate point.”

    I think that I disagree with you on that point. While I appreciate your idea that God wants us to be able to understand, even scientifically, that He exists (it is absolutely true, IMO), I am also absolutely convinced that even if God’s purpose had simply been to create intelligent life, the fine tuning argument would retain all its validity just the same.

  4. 4
    vjtorley says:

    Hi kairosfocus,

    A Happy New Year to you, too. I’m glad you enjoyed reading my post. Sad to say, Dr. Sean Carroll’s video is a perfect example of hyperskepticism within the scientific community.

    Hi gpuccio,

    Thank you very much for your reflections on Dr. Carroll’s arguments. They’re a lot more concise than mine.

    Re your last point: the reason for my concern is that under the mere hypothesis that God exists, it can’t be shown that fine-tuning is significantly likely: there may be infinitely many alternatives to a fine-tuned universe, so the likelihood of fine-tuning given that God exists could be infinitesimal. That’s not good mews, if you’re trying to demonstrate the superiority of the theistic hypothesis to naturalism, as an explanation of fine-tuning. That was why I felt I had to add a “minimal motive” on the Creator’s part: the desire to be known by the intelligent beings He creates.

  5. 5
    jerry says:

    Even MIT Professor Alan Guth, a strong supporter of the theory of inflation (which he helped originate) and the multiverse, finds the notion of the multiverse troubling. He points out that in an infinitely branching multiverse, “there are an infinite number of one-headed cows and an infinite number of two-headed cows” – which seems to imply, bizarrely, that one-headed cows and two-headed cows are equally common!

    It is much more bizarre than that and in a direction that Sean Carroll would not like. I will make my argument against the multi-verse that I have presented before. It is sort of an argument from ab surdium

    The only multi-verse argument that has any traction is that the multi-verse is infinite. If it is not infinite then the actual finite number will always come up short in the fine tuning argument.

    If the multi-verse is infinite then all possibilities are possible including the one we live in.

    But specifically, there must be an infinite number of universes where the Judeo-Christian God arises. Here is the argument I have frequently made on this. If an infinite number of universes are postulated, then this leads to an entity of infinite intelligence.


    If there is an infinite number of universes, there will be a subset also infinite in number that develops intelligent entities. Then one could rank the infinite number of universes with intelligent entities by the level of intelligence present in each universe. This would lead to a ranking with no limit on the scope of the intelligence as one goes higher up the rankings. One could never find a universe where the intelligent beings in it were higher than in any other universe.

    Then jokingly I made the comment that an infinite subset of these intelligent entities would say “Let there be light.” And to make even more fun out of this absurdity, I said an infinite subset of this group would say it in English.

    An infinite number of universes is self contradicting, an infinite number of two headed cows and an infinite number Judeo/Christian Gods. Also what is to prevent an infinite number of three headed cows.

    So we have to be left with some finite number but for every finite number we postulate the fine tuning numbers would never have enough resources to get a stable universe. And why wouldn’t there be just one more. What is to prevent it? Why would there a cap on the number of universes?

    One absurdity after another.

    The techniques of calculus are finally becoming handy. The argument of the multi-verse is infinitely absurd because everything is infinitely possible.

  6. 6
    JDH says:

    Carroll is obviously very smart and has studied a lot of stuff. But for the life of me I don’t understand how he can be so foolish.

    He makes the statement –

    But more importantly, if you take the multiverse as your starting point you can make predictions.

    Now that is a really interesting statement because he implicitly asserts in it…
    1. He is an individual that has the ability to choose to start with an abstract never observed model and initiate a discussion about it.
    2. He assumes that those who choose to read his argument are individuals with the same ability to start with an abstract model and draw never observed conclusions.
    3. He assumes the ability to do this abstract thinking evolved from random activity of unintelligent particles obeying unchanging physical laws.

    In my mind, this is the show stopper. I don’t think they can make a case that this is possible.

    They can generate all kind of noise and appeal to the science of the gaps, but I believe they will never be able to create a consistent and believable model of how an intelligence capable of initiating abstract discussion about a never before seen occurrence evolves from dumb particles making random motions under the influence of unchanging physical laws. I believe the reason they will never come up with a consistent model of this is because it never has happened and never will.

  7. 7
    kairosfocus says:

    VJT, I note that way back, on decision theory, we were always advised that when an agent was involved, attempting to use a probability distribution rather than an evaluation of intent and values of reasonably expected outcomes was not best praxis. When we play a game against nature, the reasonable odds play a role. As we know from say attempts to analyse chess or go games and managerial or strategic decisions, someone with expertise uses insight and intent to choose a credible best path given a balance of factors. So it is appropriate to highlight the local isolation of the operating point of the physics of our cosmos joined to how our physics and circumstances invite exploration in many ways and where reasonable results of such consistently point. It may be speculated that the Leslie wall has areas with veritable carpets of flies, the fact remains the local patch is empty, save of the remains of just one fly neatly drilled by a single bullet that seems to have come from a tack-driver of a rifle . . . itself something that requires extraordinary fine tuning. KF

  8. 8
    kairosfocus says:

    JDH, well put.

    Jerry, food for thought.

    GP, points to ponder as usual.


  9. 9
    jerry says:


    A couple things about Sean Carroll.

    First, he has given the game away. What is the purpose of the multiverse argument? Certainly not legitimate science. No it is an admission that the fine tuning argument is devastating. There is no answer to it but absurdity which I facetiously pointed out in my comment. The multiverse must be infinite to have any traction as a reason for our universe or else it to had a beginning without a cause and only limited possibilities for what is possible. And once it is infinite, then there is no universe that is off the table of possibilities including an infinite number that are very similar to ours. So there are two headed cows and an infinite number of Judeo/Christian Gods or whatever else one can think of.

    Read one of Isaac Asimov most enjoyable short stories which begins with a discussion of reversing entropy, a frequently hot topic here:

    Second, Sean Carroll is not a nice person. We tend to get persuaded by appearances. We should pay more attention to behavior. I posted a comment about Carroll almost 3 years ago which shocked Sal Cordova who was defending him as a reasonable person. Here is my comment from then:

    Sean Carroll is intellectually dishonest, a bully and a coward. A few years ago there was a discussion by John McWhorter with Michael Behe on Blogging heads. Carroll went ballistic and essentially told Blogging Heads he would organize a boycott of the site if they ever did anything like it again. McWhorter was forced to apologize for talking with Behe.

    Carroll is one of those guys who hides behind a nice smile and polite personality but will use his minions to silence anything he is opposed to. Remind you of anyone else in this world.

    I am very familiar with Carroll, having purchased his course from the Teaching Company on Dark Matter and Dark Energy and bought his book on the nature of time. He is a pleasant lecturer but his other behavior indicates what he is really like.

  10. 10
    kairosfocus says:


    Yes, the game is up when in the name of science we see a quasi-infinite unobserved and arguably unobservable multiverse being put up as the best vision of reality from a naturalistic perspective.

    It also quietly implies the force of the fine tuning discussion.

    It is saddening to see the underlying pattern you point to there.


  11. 11
    Ken_M says:

    The one thing that I have never been able to grasp is the argument that the universe is finely tuned for life. If this is so, why have we never found life, or any indications of life, anywhere other than on earth. The vast bulk of the universe is very hostile to life.

  12. 12
    kairosfocus says:

    K-M: Start here, noting onward linked discussions. As a beginning, note that the physics of the cosmos is such that for small changes in many key terms, the resulting cosmos would be radically incapable of sustaining C-chemistry, aqueous medium, terrestrial planet cell based life. KF

    PS: Admins the captcha is doing odd things.

  13. 13
  14. 14
    Phinehas says:


    Because the fine-tuning of the universe is necessary, but not sufficient for life? Because the earth includes additional fine-tuned variables that are also necessary, though not sufficient for life?

    Really, just the whole necessary, but not sufficient thing.

  15. 15
    Mung says:

    PS: Admins the captcha is doing odd things.

    There’s a way now to refresh the captcha that I had not noticed before.

  16. 16
    RexTugwell says:

    With regard to the notion that the vast bulk of the universe is very hostile to life or as was repeated in the movie Contact, “If it’s just us, it seems like an awful waste of space”, I have to ask what does one expect from a universe that has been expanding for the past 13.7 billion years? If there were no expansion (and consequently lots of “wasted space”) the Big Crunch would have happened long ago.

    Given the very unlikely conditions necessary for life to exist, IMO it’s not surprising that there would only be life on this pale blue dot in a universe that is tens of billions of light-years wide.

    …unless of course the designer also chose to create life elsewhere without our permission. 😉

  17. 17
    HeKS says:

    @Phinehas #14

    Because the fine-tuning of the universe is necessary, but not sufficient for life? Because the earth includes additional fine-tuned variables that are also necessary, though not sufficient for life?

    Really, just the whole necessary, but not sufficient thing.

    You’re exactly right in your reply to Ken_M, and this is something I think is not addressed enough. This is a fundamental flaw/error in anti-fine-tuning arguments from people like Carrol and Neil Tyson. They may be intelligent scientists, but they come across as philosophical simpletons, as the distinction between necessary and sufficient conditions is a very basic logical/philosophical concept.

    They make this argument that the universe isn’t fine-tuned for life because most of the universe doesn’t seem to have any life in it at all, at least that we’ve been able to find. At this point, their audiences often tend to break out in a little laugh (“hah, hah, those silly faithheads!”). Somehow both the speaker and the audience have failed to grasp the basic fact that the universe must be fine-tuned as it is in order for it to be capable of sustaining life anywhere within its confines. That is – as you’ve said – the fine-tuning of the universe is a necessary condition for the existence of intelligent life. It is not, in itself, a sufficient condition for the existence of intelligent life. Many other aspects of a local environment must be further fine-tuned in order to be capable of sustaining life (i.e. they are also necessary). And yet, those instances of local fine-tuning required to sustain life are not enough to produce life, and furthermore, they themselves would be pointless and generally impossible were it not for the fine-tuning of the universe itself (i.e. the local conditions, while necessary, are also not sufficient).

    I think the recognition of this simple distinction has further implications regarding common arguments used by these people with regard to the origin and evolution of life, showing them to be bankrupt, but I don’t have the time to write any more at the moment. I hope to check in later.

    Take care,

  18. 18
    HeKS says:

    @RexTugwell #16

    I think your point could be added to by factoring in the motive of the designer wanting its existence to be known.

    In addition to the fine-tuning, one of the strongest arguments for the existence of such a designer (whom I believe to be God) is the origin of the universe itself. In order for us to know it had an origin we need evidence. The evidence is the expansion of the universe, which is what led us to the Big Bang Theory.

    As such, the very evidence that points us to the origin and creation of a well-ordered and law-governed universe such as ours requires that the universe eventually be very large even if the entire purpose of the physical universe existing was to have a single planet populated by embodied, intelligent, moral beings. It would also almost certainly require certain features of the universe to be over-tuned with respect to life itself in order to ensure the scientific discoverability of the evidence pointing to its origin and fine-tuning, including things like the ability to get a good look at the CMB to confirm the Big Bang.

    Take care,

  19. 19
    Jack Jones says:

    Happy new year to the UD article contributors and UD posters, Hope you had a good Christmas.

    A nice rebuttal Mr Torley.

    Don’t the naturalists always make the claim that things that aren’t reproducible are not scientific, they make the claim that nature is testable and so science is based on assuming natural causes and yet they appeal to things that are not testable when it suits them, just like the multiverse.

    “In science, explanations must be based on naturally occurring phenomena. Natural causes are, in principle, reproducible and therefore can be checked independently by others.”
    “Science, Evolution, and Creationism,” 2008, National Academy of Sciences (NAS), The National Academies Press, third edition, page 10.

    Yet now Carroll is claiming the multiverse as a natural explanation and yet that contradicts how the term is used other times by naturalists. Sometimes it suits the naturalist but then they throw out their own rule when it does not suit them.

    Doesn’t that bring up the impossibility of an infinite regression of universes having to be passed to get to this moment in time?

    If everything is natural then doesn’t the word natural lose any meaning?

    If there are an infinite amount of universes then that would make it likely that there is a Deity connected to at least one of the universes which would defeat his argument.

    It seems that Sean Carroll believes in the tautological oxymoron of “infinite finiteness” with his belief in an infinite amount of past finite natural events.

    He has thrown out logic but he will appeal to those materialists that do not critically examine what he is saying or are not capable of doing so.

  20. 20
    gpuccio says:


    As others have pointed out, the initial fine tuning of the universe is necessary for life to exist, but absolutely not sufficient.

    Indeed, the whole point of ID theory is that no fine tuning, in itself, is sufficient to explain life: life, being based on huge quantities of complex functional information, requires specific conscious engineering, not only fine tuning of some environment. That’s the difference between ID and TE.

    That’s why there are two different basic ID arguments:

    a) The cosmological argument, in its detailed version based on fine tuning, which states that the whole universe could not exist as it is if it were not designed.

    b) The biological argument, which states that life could never exist in this universe, if it were not specifically designed in time and space in the universe itself.

  21. 21
    Phinehas says:

    One wonders whether now this is an aspect of the argument that Ken-M can grasp, should he be interested in doing so.

  22. 22
    sekharpal says:

    It is not actually necessary that fine-tuning of certain parameters will have to be there for proving the existence of God, because existence of God can also be proved even if there is no fine-tuning. For this one can see the following link:

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