From: Iain Strachan <igd.strachan@gmail.com>

Date: Fri Aug 17 2007 - 03:57:30 EDT

Date: Fri Aug 17 2007 - 03:57:30 EDT

On 8/16/07, David Heddle <heddle@gmail.com> wrote:

*>
*

*> Moorad,
*

*>
*

*> That is *exactly* right and yet a point often missed. The stength of the
*

*> fine tuning argument is so-often incorrectly linked to the probability of
*

*> the constants. That, in turn, leads to obfusacting and irrelevant
*

*> discussions about how we possibly could, a priori, estimate those
*

*> probabilities. Well, we can't.
*

*>
*

I'm not sure I agree here. The sensitivity of the constants to suitability

for life is the correct form of fine-tuning. However, when you say we can't

a priori estimate the probabilities, I think you're overlooking the fact

that from a Bayesian perspective, one always has a prior estimate of the

probability distribution, and if one can't estimate it at all, then one

chooses an "uninformative" (ie containing no information) prior

distribution, which would usually be a uniform distribution. So if a

parameter lies between (1-eps)*x and (1+eps)*x, and the physically possible

values of x are between 0 and 2 with a uniform distribution, then one can

argue fine-tuning if eps << 1 because of the probability. However, if (by

some science) we can find (for reasons other than the suitability for life)

that it can lie only in the region (1-eps)*x ... (1+eps)*x, then clearly you

can't claim fine tuning because any of the physically allowable values would

be suitable for life.

So I would say it has to be linked to a probabilitic argument, otherwise to

talk about "sensitivity" has little meaning.

I think probabilistic arguments are perhaps one of the motivations behind

"multiverse" theories - by invoking astronomical numbers of universes, all

with different parameter sets, one greatly increases the probability of at

least one having just the right values. Buy one lottery ticket and you are

extremely unlikely to win the jackpot - but every week millions are bought,

and someone usually wins.

[Incidentally this kind of multiverse is very different from the "many

worlds" type with which I started this thread. In the MWI, all the

universes obey the same physical laws and have the same constants].

Iain

-----------

To unsubscribe, send a message to majordomo@calvin.edu with

"unsubscribe asa" (no quotes) as the body of the message.

Received on Fri Aug 17 03:57:53 2007

*
This archive was generated by hypermail 2.1.8
: Fri Aug 17 2007 - 03:57:53 EDT
*