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. (more…)
Letters to Nature 