Debunking the debunker: How Sean Carroll gets the fine-tuning argument wrong
|January 4, 2016||Posted by vjtorley under Intelligent Design|
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?