HWT@bnr.ca (H.W.) (10/19/90)
My understanding of the notion of anthropic principle is that there are two of them: The laws of nature and universal constants are currently found to permit life as we know it only at values within 5-10% of those currently observed. For example, if the energy released on fusing hydrogen as about 10% higher, there would be no long-lived stars. If it were 10% lower, there would be no warm planets. Variations in gravity on the same order would prevent galaxies and planetary systems. 1) the 'weak anthropic principle' (generally accepted) The universe appears to be hospitable to life. However, this is only because there is life to observe it. 2) the 'strong anthropic principle' (not generally accepted) The universe appears to have been designed to be hospitable to life. The weak anthropic principle asserts implicitly that the existence of life is irrelevant to the properties of fusing hydrogen - just coincidence. Essentially the strong anthropic principle is the 'argument from design' for the existence of God. And that's fairly old and familiar, I hope. Reference: try 'A Brief History of Time' by Stephen Hawking. There are no equations, so do not fear the book. [I find these arguments interesting. But it's hard to know what to make of them. E.g. suppose that the universe is cyclical, and each time we get a random collection of constants. This might be the only one out of 10**10 times that life developed. Of suppose that other values permit other sorts of interesting things than "life as we know it". If those values occured, the entities that existed then would also think how amazing it was that the right parameters existed. --clh]
ncramer@bbn.com (Nichael Cramer) (10/22/90)
HWT@bnr.ca (H.W.) writes: >The weak anthropic principle asserts implicitly that the existence of life is >irrelevant to the properties of fusing hydrogen - just coincidence. But to reiterate the critical point, while it is true that it is just coincidence, the WAP says that we _can_ say something _about_ the properties of fusing hydrogen _becuase_ there is life. (Note that this is _very_ different from saying that those properties had to be what they are in order for there to be life.) >[I find these arguments interesting. But it's hard to know what to >make of them. E.g. suppose that the universe is cyclical, and each >time we get a random collection of constants. This might be the only >one out of 10**10 times that life developed.... In which case of course, no one would be sitting around discussing the WAP. >... Of suppose that other >values permit other sorts of interesting things than "life as we know >it". If those values occured, the entities that existed then would >also think how amazing it was that the right parameters existed. >--clh] One needs to be careful here, if I read your use of "amazing" correctly. The argument of the WAP is _not_ in any way that those "right" parameters _must_ have existed. Rather it argues that we can infer certain bounds on these parameters precisely _because_ there is life. The existence of life tells us something about these parameters. There is nothing for your beings to be amazed about, any more than there is anything for us to be amazed about wrt our set of parameters; they weren't pre-set, they just are. (Their parameters might be quite different than ours but that would be reflected in the set of assumptions that they make.) In short, it's a sufficiency argument, not a necessity argument. To make a cheap analogy, if one knows where I work, one can place reasonable bounds on where I live. For example, one can say "If you work in Cambridge, then you live in eastern Massachusetts". However, one cannot read this statement to mean that when Mr X founded this company 10yrs before I was born he picked the "right" location so that I would work here and so be "amazed" that I happen to living where I am. >Reference: try 'A Brief History of Time' by Stephen Hawking. There are no >equations, so do not fear the book. This is a good reference (for the AP and much else). Given the amount of metaphysical gibberish and miscomprehension that has grown up around the AP, it's nice to see what can be done with it in hands of a master like Hawking. Also, for those who _really_ want to get their feet wet, you might try _The Anthropic Cosmological Principle_ by Barrow and Tipler (Oxford). N