Last time, I started a review of the Carroll vs. Craig debate with a (mostly historical) overview of the back-and-forth about the beginning of the universe for the last 90 years of modern cosmology. Here, I’ll have a look at fine-tuning. I should start by saying how much I enjoyed the debate. They should do it again some time.
In his speeches, Sean Carroll raised five points (transcript) against the fine-tuning of the universe for intelligent life as an argument for the existence of God. I want to have a look at those five. Carroll (here) and Craig (here, here and here) had a few points to make post-debate, too.
Here is fine-tuning reply number one:
First, I am by no means convinced that there is a fine-tuning problem and, again, Dr. Craig offered no evidence for it. It is certainly true that if you change the parameters of nature our local conditions that we observe around us would change by a lot. I grant that quickly. I do not grant therefore life could not exist. I will start granting that once someone tells me the conditions under which life can exist. What is the definition of life, for example? If it’s just information processing, thinking or something like that, there’s a huge panoply of possibilities. They sound very “science fiction-y” but then again you’re the one who is changing the parameters of the universe. The results are going to sound like they come from a science fiction novel. 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.
Is the debate over the definition of life a problem for fine-tuning? Sean and I had a brief discussion on this point during my talk at the UCSC Summer School on Philosophy of Cosmology. My response was (roughly) as follows.
Consider chess. In particular, I’m wondering whether minor changes to the laws of chess would result in a similarly interesting game. Wait a minute, you say, you haven’t defined “interesting”. In fact, different people are going to come up with different definitions of interesting. So how can we know whether a game is interesting or not?
It’s a good point, but instead of considering this question in abstract, consider this particular example. Change one word in the rules of chess: instead of “Knights may jump over other pieces”, we propose that “Bishops may jump over other pieces”. If we were to rewrite the 530 page “Silman’s Complete Endgame Course“, we would need just one page, one paragraph, two sentences: “White bishop moves from f1 to b5. Checkmate.”
My claim is that this particular case is so clear that by any definition of interesting, this is not an interesting game. The game is no more interesting than tossing a coin to see who goes first. It is too simple, too easy.
There are changes we can make to the laws of nature that result in a universe so simple, so barren, that by any definition of life, this isn’t it. The cosmological constant is a good example: we have a 120 orders of magnitude to play with, but after even 10 or 20, the universe contains nothing but an expanding hydrogen soup. Such a universe is very easy to predict – the universe never leaves the “linear regime”. We can solve the equations of cosmological structure formation. Compared to calculating the behaviour of our universe, this one is a doddle.
Carroll says: “The results are going to sound like they come from a science fiction novel.” I think that that statement is false. Consider a universe with too large a cosmological constant. Shortly after the beginning of the novel, the only thing that happens in the universe is two hydrogen atoms colliding every trillion years or so. The results will make for the most boring science fiction novel conceivable.
Certainly, these universes will be unusual. But – and here’s the crux of the matter – these other universes are usually extremely simple.
Carroll’s response to my chess argument is interesting. He says in the video:
“My intuition here is the opposite. It is blindingly obvious to me that there is a very strong cognitive bias to think that life is kind of like us, so that when things are very different, we think there would be no life. I think that we should strongly try to do better than that before we make statements about how life [forms?]”
(I’m not sure what that last word is. It’s at 22:30-35 in the video.)
Note that this is an off-the-cuff comment from the audience, so he couldn’t say everything. However, it does raise a few questions:
1. What is the evidence for this cognitive bias? Historically, fine-tuning was a surprise. For example, Hoyle spoke of the “remarkable relation” of the energy levels in carbon and oxygen allowing their production in stars. Linde speaks of the anthropic limits on the parameters of our universe as being “amazingly strong”. It is surely not insignificant that scientists’ belief in the fine-tuning of the universe for life only came after some scientific calculations. The discovery of fine-tuning seemed to go against the biases of its discoverers.
Moreover, that’s a very specific bias to be hardwired into the human psyche. Why think that the unenlightened human mind has any opinion whatsoever on the fate of other life-forms in other universes?
2. Why fight it? Why think that this particular bias should be opposed? Human’s are biased to see causal patterns in nature, and we believe that scientists have confirmed such a belief. Why not just take the hint, and conclude that these other universes really are as lifeless as we think?
In fact, I think there is a definition of life that is relevant to this case. The wrangling over the biological definition of life need not detain us. The key is noting what particular state of affairs that theists argue is likely if God exists. 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.
If that is the hypothesis under consideration, then that is the relevant definition of life. This doesn’t mean that we can easily calculate which universes satisfy our definition. But there is at least a starting point. (Or, perhaps, the atheist could argue that the inability of the God hypothesis to produce any precise prediction “smears” the definition of “life” over wide open spaces of parameters space. More of that soon.)
“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.”
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.
Conclusion: what we don’t know
I don’t think that this line of argument nullifies the fine-tuning argument on its own. The best-understood cases of fine-tuning are too dramatic to think that nit-picking over the definition of life would make any difference. Carroll point is essentially appealing to an as-yet-unknown fact about life that will hopefully reveal why, against all appearances, it could form and survive in a wide range of universes. In the absence of any specific idea about what this unknown fact might be, it is just as likely that what we don’t know about life will make it rarer in possibility space, i.e. more fine-tuned than we think.
Barrow, Carr, Carter, Davies, Dawkins, Deutsch, Ellis, Greene, Guth, Harrison, Hawking, Linde, Page, Penrose, Polkinghorne, Rees, Sandage, Smolin, Susskind, Tegmark, Tipler, Vilenkin, Weinberg, Wheeler, Wilczek.
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.