May 7, 2018


Did the dying Stephen Hawking really mean to strengthen the case for God? (Philip Goff, 7 May 2018, The Guardian)

Scientists have discovered a surprising fact about our universe in the past 40 years: against incredible odds, the numbers in basic physics are exactly as they need to be to accommodate the possibility of life. If gravity had been slightly weaker, stars would not have exploded into supernovae, a crucial source of many of the heavier elements involved in life. Conversely, if gravity had been slightly stronger, stars would have lived for thousands rather than billions of years, not leaving enough time for biological evolution to take place. This is just one example - there are many others - of the "fine-tuning" of the laws of physics for life.

Some philosophers think the fine-tuning is powerful evidence for the existence of God. However, in his 2010 book The Grand Design (co-authored with Leonard Mlodinow), Stephen Hawking defended a naturalistic explanation of fine-tuning in terms of the multiverse hypothesis. According to the multiverse hypothesis, the universe we live in is just one of an enormous, perhaps infinite, number of universes. If there are enough universes then it becomes not so improbable that at least one will chance upon the right laws for life.

In Hawking's older version of the multiverse hypothesis, there is great variety among the laws in different universes. In some gravity is stronger, in some weaker, and so on. However, physicists have come to see problems with such a heterogenous multiverse, especially if the number of universes is infinite. We work out the predictions of a given multiverse hypothesis by asking how probable our universe is according to that hypothesis. But if there is an infinite number of universes, that question becomes meaningless. And hence in his final paper, A Smooth Exit from Eternal Inflation?, Hawking and his co-writer, Thomas Hertog, formulate strict limits to the kind of universes that populate the multiverse.

The problem is that the less variety there is among the universes, the less capable the multiverse hypothesis is of explaining fine-tuning. If there is a huge amount of variation in the laws across the multiverse, it is not so surprising that one of the universes would happen to have fine-tuned laws. But if all of the universes have exactly the same laws - as in Hawking and Hertog's proposal - the problem returns, as we now need an explanation of why the single set of laws that govern the entire multiverse is fine-tuned.

Physics is the case for God.

Posted by at May 7, 2018 4:30 AM