X-Message-Number: 5540 Date: Thu, 4 Jan 1996 21:18:17 -0800 From: (Eric Watt Forste) Subject: Re: nightmares In message #5537, Doug Skrecky wrote: > Frank Tipler has advanced the view that we are alone because we are > the first technologically advanced civilization to arise in our galaxy. > ETI's never killed themselves off because thery never existed. The > December issue of Equinox magasine contains an article entitled "Earth: > There's No Life Like It" written by Terrence Dickinson, which outlines a > number of reasons why the survival of life on earth can be regarded as an > extremely low probability fluke. Another reason why we might be first, which I've often wondered about, but have never seen mentioned in the literature, is the amount of time required for a sufficient density of heavy elements (what astronomers call "metals", but including carbon, oxygen, and nitrogen) to build up. I'm very curious about this, but I haven't got the necessary math and astrophysics background necessary to make even rough calculations on my own yet. When the universe first started, it was almost entirely hydrogen and helium, mostly hydrogen. After the first stars formed, they started cooking heavy elements in their cores, and as they exploded (the ones that did explode), they released those heavy elements to the interstellar medium. Now I know that on the cosmic timescale, type O and B stars are going off like flashbulbs all the time; their total lifetime is in the millions, not billions, of years. However, they are very rare compared to other sorts of stars. (The vast majority of stars are red dwarfs, which, as far as I understand, do little or nothing to enrich the interstellar medium with heavy elements.) Now most of the "Where are they?" discussions I've seen *seem* to assume that life could have sprung up just about anytime since the beginning of the universe. But clearly, life could only have sprung up easily after the interstellar medium reached a certain level of richness in such elements as carbon, oxygen, and nitrogen. And the stars that make these elements and release them to the interstellar medium are comparatively rare. I'd be very interested in seeing any competent astrophysicist's estimates of how metallicity of the interstellar medium (remember, astronomers call oxygen a "metal") has changed during the life of the universe. It may be that there were simply not *enough* heavy elements concentrated in the universe for life to have gotten going much sooner than it got going on Earth. This was about five billion years ago, about halfway to three-quarters through the life of the universe, depending on whose numbers you like. If anyone has any more information that might support or disconfirm this idea, I'd be very interested in hearing about it. My hunch is that we just happen to be the first on the block. I'd like to know how the answer to this question I've raised jibes with my hunch. Eric Watt Forste <> http://www.c2.org/~arkuat/ Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=5540