X-Message-Number: 587 Date: 22 Dec 91 05:22:07 EST From: "Steven B. Harris" <> Subject: Limits to Growth Kevin Brown writes: >>David, if you look REALLY long-term, population control still appears necessary, even if we scatter throughout space in all directions at almost the speed of light. This is because, unless we change our habits, population will grow exponentially with time (R^T for some R > 1) whereas the space available for that population can grow only polynomially with time ((cT)^3). Eventually, the exponential function will overwhelm the polynomial function (although I am not sure that that will happen within the lifetime of this universe).<< Comment: Well within the life of the universe! It's a straightforward problem best worked just as you present it: If you start with 5e9 immortal humans and assume a population doubling time of 40 years (about our present rate), and you give each immortalist a jail cell sized living volume allotment of (say) 15 cubic meters, then you find that we absolutely run out of any more room in our light cone to put new people, between 163 and 164 doublings. In other words, in a bit less than 6500 years. Of course, if you look at the number of people implied in this calculation (6.5e58 or so), it's at least tens of millions of times more mass than the *universe* is thought to contain, so obviously the limit to exponential reproduction is availability of MATTER before volume. (The basic reason for this, if you want to look at it that way, is that matter in our universe is distributed a lot more thinly than the density of people in apartment complexes, and a good thing too or it would all have collapsed long ago). Actually, I suspect the real limit to exponential growth is likely to be the availability of free energy.* Just for the fun of it, how much are we limited by avail- ability of mass alone, exclusive of free energy? I estimate that if we had unlimited ergs we can turn the solar system entirely into people, at our present growth rate, in only 2500 years (yum- - soylent chips, anyone?). Of course, by that time the advancing front of humanity will have enveloped and eaten another billion stars, but all that matter will keep us going only another 1200 years, and not too far and not long after that we'll have more appetite for stars than we can get to at speed ~c. If we eliminate Death and Electric Bills, then, my math implies that by 4,000 years from now, even Roman Catholics will have to accept condoms. Helpfully, Steve * Actually, now that I REALLY think about it, the limit is likely to be stupidity. But that's another story. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=587