ABSTRACT
The Anthropic Principle and the argument from density

"Why are things the way they are?" is a question which everyone addresses at some time.  Science does an excellent job of explaining complex things in terms of simpler ones but eventually there is no more simplification that can be done: the Fine Structure Constant, for instance, cannot be explained further, it just is.  For those who do not believe that the world as a whole arose from the intentional act of an omnipotent Creator, this is awkward.

Anthropic arguments recognise that our very existence imposes constraints on the laws of nature, since if they were significantly different from what they are then life, and thinking beings, could not exist.  A 1% change in a particular nuclear energy level would mean no carbon, and hence no carbon-based life.

Unfortunately anthropic arguments cannot sustain the weight that is put on them, as the following thought experiment will show.  Imagine a small change in a fundamental constant of nature: if this change precludes the existence of intelligent life, halve the size of the change and try again.  Eventually (by continuity) the change will small enough that intelligent life can exist, and you will have constructed a universe different from ours but still containing intelligent beings.

The alternative defence against having to invoke a Creator may be called an inclusivist one: "whatever can exist, does exist somewhere".  "Somewhere" is variously taken to be remote from us in time (bouncing big bangs), in space (beyond the light horizon) or in some other sense (many-universe theories).  The implication is that if anything that can exist does exist, then there is no need for a creator who can choose which things are to be given existence and which left uncreated.

I propose an "argument from density" to show that such an inclusivist ontology has catastrophic implications for common-sense notions of personal identity and responsibility: that if inclusivism is right I cannot meaningfully talk of me at all.  Since personal identity is one of the things that people still largely believe in, a reductio ad absurdum shows that "why are things like this?" cannot be arbitrarily dismissed but remains a genuine question that needs an answer.

Keywords: anthropic principle, possible worlds, many-universe theories, ontology, existence, argument from density, creation, metaphysics.