Saturday, July 14, 2007

The improbable universe?

Thought this worth including as main post (previously in the comments on my review of Why There Is Something Rather Than Nothing below).

Some argue like this:

Surely we can know that something exists, yet also know that its existence is highly improbable, improbable enough to demand some sort of explanation?

Isn't precisely this true of the existence of the universe?

The playing cards

Here's a Swinburne-type illustration of the general point. Suppose I am asked to guess each one of 52 cards, one by one. If I ever get one wrong, my brains will be blown out.

I start guessing, and amazingly, I get all 52 cards correct. Now you may say, "What's so improbably about that? After all, the probability of you getting them all right is 1, as you wouldn't be here otherwise would you?"


But of course, there's a sense in which something deeply improbable has happened. So improbable, in fact, that it would be reasonable for me to suspect this result wasn't just a matter of chance.

Some of those who favour fine-tuning arguments for the existence of God argue that, similarly, the fact the fact the we do exist does not show that there isn't something extraordinarily improbable about the universe, by chance, being just right for life. So improbable, in fact, that we can reasonably suppose that its "fine-tuned" character is not an accident, but the result of deliberate design.

The firing squad

Here's another classic example of the general point. As a condemned spy, you are put before a firing squad of twenty expert marksmen, who load aim, and fire at your heart from close range.



Amazingly, they all miss. You feign death, and survive.



Pure luck that they all missed? Possibly. But highly unlikely.

Far more likely that the miss was deliberately arranged.

 It won't do to now say, "But their all missing is not amazing at all. It's wholly unremarkable. After all, had they not all missed, I would not be here to ponder my luck!"


In the same way, its argued, we can ponder the improbability of the universe (of its being "fine-tuned" for life, etc.), despite its epistemic probability now being 1. We can't dismiss this alleged improbability by saying "But it's not improbable at all - after all, if the universe had not been just right for life, we would not be here!"

One of the commentators on Why There is Something Rather Than Nothing below, does make this move. It's not uncommon. But I don't buy it.

7 comments:

Joe Otten said...

I tend to agree that the anthropic argument is unconvincing. But at the same time there seems something wrong in the original shocked reaction to an improbability.

Yes, this outcome is unlikely. But so are all other outcomes. Whoever wins the lottery, it was very unlikely that they did.

What badly-tuned universe would be any more likely than our fine-tuned universe?

I have a distrust of the cavalier use of probability with hindsight. I think very few people know what they mean when they talk about the probability of anything, with the possible exception of the "classical" probability of repeatable experiements: coin tosses etc.


Anyway, of course if the fine-tuning argument were good, it would apply just as well to any designer. How unlikely that the designer should be like this, compared to the infinity of possible designers?

The retort will be that only one kind of designer is possible. The same might be true of the universe. And in the latter case it may even be possible to find supporting evidence.

The Barefoot Bum said...

The weak anthropic principle is best understood as counter-argument on the basis of sampling bias. I go into more detail in Probability and the anthropic principle.

By itself, an improbable occurrence isn't astonishing: Shuffle a deck of cards; the probability of the resulting arrangement is 52! = ~1:10^67; do it again and the probability of the two successive arrangements is 1:10^166.

We are really surprised about not just improbable occurrences but improbable coincidences. And, of course, one must carefully quantify the probability to evaluate the effect of sampling bias.

Tony said...

I think it depends on the context - that we exist in the one and only universe which is tuned perfectly to accept life is, as you say, improbable. That there is an infinite multitude of universes, almost all of which do not accept life and we are in one of the few that do, is hardly surprising. Whether there is only one or a multitude is still entirely unknown.

Or the explanation might be wholly different, of course.

Paul Power said...

It seems to me this argument, for and against, can only apply to what happens to the universe after it has come into to existence.
I say this because we can meaningfully think about how our universe could have turned out differently if some of its fundamental laws (such as those relating to gravity) were other than as they are.

However we do not know what laws, if any, were in play to produce the universe. We cannot meaningfully think about the question of the probability of our universe existing. Indeed I would go further: the process by which the universe came into being is beyond scientific investigation. The reason I make this claim is that how the universe came into being was an event that is not just unique but also of a kind that is unique. We have nothing to compare it with. By contrast, if we find or make a single individual of a new animal species, although it is unique we can still compare it scientifically with other animals. We cannot do this with the universe.

I hope you can get past my clumsy expression of this idea to see what I am getting at.
A

snafu said...

I *strongly* recommend Sober's paper on the design argument, available here:

http://philosophy.wisc.edu/sober/design%20argument%2011%202004.pdf

It requires a basic knowledge of probability theory (i.e. the difference between epistemic and classical) and Bayesian inference, but explains very clearly why these fine-tuning arguments are suspect. As a bonus, the firing-squad analogy is criticised as well. (In short, there is a deep disanalogy compared with the universe: knowledge of firing squads' behaviour is much better grounded in classical probability).

Bill Jefferys (a physicist specialising in Bayesian inference with astronomical data) has a characteristically scientific view. Not un-criticisable, but well worth a read.

http://quasar.as.utexas.edu/anthropic.html

Also, worth noting that claiming 'physical constant X has to be within 10^-N of it's current value for life to exist' is assuming the validity of the Principle of Indifference. In my opinion, the PoI is itself suspect, due to (1) Russell's paradox, and (2) evidence that the history of knowledge is not littered with successes due to its application.

Finally, one more firing squad comment (from Sober). Let's say 10 survivors of a certain firing squad were locked in a room together. They have no knowledge of how many executions (successful or otherwise) have been attempted. It could be anything from 10 to 10 billion billion. Can they validly infer that the squad is rigged? I think most people would say 'no', for obvious reasons. Now, take 9 people and do the same...you see where this is going: in that case how can the one original prisoner infer design...?

The above paragraph starts to suggest analogies with multiverse hypotheses. Whilst it's still early days, these are just starting to get a foothold in inflationary cosmology. Exciting times...

The Barefoot Bum said...

Another good article on probability theory with respect to the weak anthropic principle is The Anthropic Principle Does Not Support Supernaturalism by Michael Ikeda and Bill Jefferys.

Anonymous said...

Another possibility is that the existence of the universe is so improbable as to be impossible, ergo, it does not in fact exist at all. Instead, it is an illusion entertained by our collective consciousness.