A YouTube video has been brought to my attention, which seems to show physicist Roger Penrose refuting the idea that the entropy of the universe is fine-tuned for life. The crucial section starts at 16:05. The video is jarringly edited: we aren’t shown what the interviewer actually asked before this section. The longer, complete interview is linked to, but I haven’t watched it.
Penrose: “It’s a gross course tuning. The entropy in the gravitational field is ridiculously small compared with the entropy in matter. There’s nothing fine-tuned about it – it’s just huge.”
[Abrupt cut]
Interviewer: People had argued that there are these constants that are fine-tuned for life, and he said “look at the entropy. That could be much much higher and life would still be here, so that’s not fine-tuned for life.
Penrose: I absolutely agree with that. The entropy in the gravitational field could have been far larger without disturbing life, as far as I can see.
Penrose’s comments are completely correct. My problem is not with Penrose, but with the editors of the video. They rely on an ambiguity regarding the term “fine-tuned for life.”
Here’s one way to approach fine-tuning. When we look at the deepest laws of nature that we know, is there is anything noteworthy or rare or interesting or unexpected? Or are these just any old laws? Is there anything about our current deepest laws of nature that might point the way to something deeper still, whether physical or metaphysical? For example, if we discovered that the laws of fundamental particles wrote “made by Brian” on every atom, then we would be suspicious of the claim that these are just any old laws.
To that end, we might want to know: what would just any old universe look like? A systematic and practical way of attacking this question is to vary the fundamental constants and initial conditions of our universe. If I just picked just any old universe from this set, what would it be like? And the answer is: almost certainly dead.
For example, when we look at all the ways the initial conditions of our universe could have been, the fraction that permit the existence of any conceivable life form is extremely small. Penrose himself established this.
To summarise,
fine-tuning compares
the set of universes that permit the existence of life
with
the set of possible universes.
By contrast,
fine-tuning does not compare
the set of universes that permit the existence of life
with
the properties of our universe.
Only the first approach actually addresses our inquiry into the fundamental laws. The second is interesting but not necessarily relevant.
In my review paper on fine-tuning, I warned about the “cheap binoculars fallacy”:
If a dart lands 3 mm from the centre of a dartboard, is it obviously fallacious to say that because the dart could have landed twice as far away and still scored a bullseye, therefore the throw is only fine-tuned to a factor of two and there is “plenty of room” inside the bullseye. The correct comparison is between the area (or more precisely, solid angle) of the bullseye to the area in which the dart could land. Similarly, comparing the life-permitting range to the value of the parameter in our universe necessarily produces a bias toward underestimating fine-tuning, since we know that our universe is in the life-permitting range.
For the case of the bullseye, the following statements are both true.
- The distance between where the dart actually landed and the centre of the board could have been much larger and still scored a bullseye.
- Only a very small subset of places where the dart could land score a bullseye.
Now, let’s look carefully at what Penrose said. His first paragraph compares the “entropy in the gravitational field” with the “entropy in matter”, noting that the former is much smaller. He says there’s “nothing fine-tuned about it.” This is correct – the mere fact that one quantity is smaller than another is not sufficient to establish fine-tuning.
But then an abrupt cut has Penrose commenting that, “the entropy in the gravitational field could have been far larger without disturbing life, as far as I can see.” He is again correct, but he is not addressing the fine-tuning of the universe for life. When he says “could have been far larger”, he is obviously making a comparison to our universe. That’s the claim that he “absolutely agrees” with. But it doesn’t at all touch fine-tuning. The following two statements are both true.
- The initial entropy of our universe could have been much larger and still permitted the existence of life.
- Only a vanishingly small subset of initial conditions of the universe would have permitted the existence of life.
Penrose affirms the first, but in so doing does not deny the second. And the second is the one that fine-tuning is interested in.
Some people – including myself in the past, if I wasn’t being careful – have presented fine-tuning as the claim that changing our universe’s constants by a tiny fraction would render it inhospitable to life. However, this is ambiguous – a tiny fraction of the possible range of values, or a tiny fraction of the value in our universe? It’s the former, not the latter. (Just to complicate things, the latter is usually sufficient but not necessary to establish the former.)
Finally, to any would-be fine-tuning refuters out there: please learn the definition of the term “fine-tuning for life” before you start. Perhaps a book on the topic would help.
In recent academic paper, Man Ho Chan answers almost all traditional objections to it, systematically compare different hypothesis with mathematical analysis, and shows that theistic explanation is best.
And if you think, this is just some other paper, it is very comprehensive paper with more than 120 references, which is reviewed and approved by reputable University. It is somewhat long, but worth it.
Here’s direct link to paper:
https://repository.hkbu.edu.hk/cgi/viewcontent.cgi?article=1447&=&context=etd_oa&=&sei-redir=1
Hello sir,
As I have gives link, I am not sure whether you’re read or not, so I just wanted to make sure you read previous link of academic paper I just commented. I would like to hear your thoughts on this.
Thank you🙏🙏