The facts are not scientifically in doubt. There are a dozen or so physical constants (the strength of gravity, the size and charges of fundamental particles, etc) which control how our universe has developed since the big bang, and if some of them had been even a little different, the universe would have collapsed back in on itself long before now, or flown apart, or have remained a thin soup without stars or planets.

It makes some people think that the probability of all this occurring by chance is so small that it must have been designed. But others argue that the logic is all wrong and probability doesn't make sense in this case. How does the argument go?

In his 1996 book Arguing for Atheism, philosopher Robin le Poidevin of Leeds University argues that there are two concepts of probability that may be applied, but neither is valid:

- Frequency theory relies on doing an action many times (say tossing a coin) and then calculating the probability - i.e. how things tend to work out in the long run. But le Poidevin argues this cannot be applied to the universe because it has only happened once.
- Propensity theory is based on understanding the processes by which an event occurs, and assessing the probabilities of these processes occurring under different conditions. In this case we ask how likely is it that our well-designed universe could have occurred if God exists, and how likely if there is no God? But, he argues, this approach is also invalid because we just don't know the conditions under which God would create or chance would cause our "fine-tuned" universe.

In their 2005 paper Problems with the Argument from Fine Tuning, Colyvan, Garfield and Priest also conclude the argument fails because of "fallacious probabilistic reasoning". Their arguments are not so easy to summarise, but the main difficulty they raise is that, if we assume all these cosmic numbers could have had any value in an infinite range of numbers, the probability of the universe occurring by chance is zero, which they say is nonsensical.

How should these objections be answered?

- We don't have to be able to calculate a probability to conclude that one event is less likely than another. For example, how likely is it that another Shakespeare will be born this year? We don't know, but surely we can say that it is less likely than that someone of lesser ability will be born?
- Roger Penrose is an eminent mathematical physicist who worked with Stephen Hawking on the theory of black holes. As a former professor of mathematics at Oxford University, he would also know a bit about probability. In his book, The Emperor's New Mind, Penrose actually calculates the probability that a universe like ours could have occurred by chance, and it comes out at the impossibly low probability of 1 in 10^10^123.

I find this quite compelling. The philosophers say it can't be done, but the scientist/mathematician has done it.

Read more about the scientific facts in it looks like it was designed, a discussion of the facts in was the universe designed for us?, and a presentation of the argument from design at In Defense of the Fine Tuning Design Argument.

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