cjh@csin.UUCP (07/20/83)
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REM@MIT-MC@sri-unix.UUCP (07/22/83)
From: Robert Elton Maas <REM @ MIT-MC> Here's my view on this. We certainly can't prove life elsewhere impossible until we've examined every little nook and cranney in the Universe, which makes the question moot since at that point we've filled every nook and cranney with our own stuff and probably dumped contamination around which has evolved in strange ways. What we can do is set an upper bound on the extent of life elsewhere, the same way we set upper bounds on other quantities such as deviation from inverse-square law (last I heard F=m1*m2/r^k where k=2.0000000000000 plus or minus some small number in that last place, or somesuch). So far we have shown ETI hasn't conquered Earth in any gross way or jammed our communications. With our next series of experiments we hope to either **FIND** intelligent life elsewhere or set a new upper-bound that on hundreds of nearby stars no major broadcasting such as TV or radar is occurring presently. As years go by we will continue to crank down the limit on life elsewhere or actually discover some out there. It's literally we can't refute the hypothesis "there is life elsewhere", thus that literal hypothesis isn't scientific. But we can refute "The Galaxy is teeming with civilizations as advanced as hours" within the next 50 years, and "The Galaxy is teeming with microscopic life on every little planet that happens to be at the right temperature" within the next few hundred years, or sooner if we get those Alpha Centuri and Epsilon Eridani probes launched in time. Therefore statements about specific amounts of "teeming with life" are indeed scientifically valid. In particular, Sagan's major question, whether there are billions of advanced civilizations in this galaxy or just a handful, can be decided within the next 50 years.
dietz%usc-cse@USC-ECL@sri-unix.UUCP (07/24/83)
I seem to recall reading in SPACEFLIGHT (a British Interplanetary Society publication) that all-sky radio searches have already set an upper limit of about 20,000 on the number of very advanced civilizations in the galaxy (where very advanced means with beacons we could detect). A recent issue also pointed out that even with a manufacturing efficiency of .1% antimatter would make sense as a rocket fuel, and antimatter reaction engines would not be difficult to build (p + anti-p reaction produces mostly charged pions, which can be directed aft with strong magnetic fields). To get some idea of the energy involved, one gigawatt for one year is about 10 kg; at .1% efficiency 10 tons of antimatter would need about 10 million gigawatts for one year. This is the amount of sunlight passing through a square several thousand kilometers on a side in earth orbit, in one year.
dgd@ukc.UUCP (D.G.Dixon) (08/01/83)
perhaps planetary civilisations only emit radio communications for a brief developing stage in their history. we seem to be moving more toward tight-beam communications, cables, optical fibres etc. even radar may be replaced by laser systems so in a few generations earth may become radio-quiet once again. douglas adams writes a good story but are dolphins really as intelligent as he/l.niven et.al. would like to think? dgd ...!vax135!ukc!dgd
ucbesvax.turner@ucbcad.UUCP (08/07/83)
#R:ukc:-388700:ucbesvax:8700006:000:3290 ucbesvax!turner Aug 3 23:56:00 1983 Re: Radio emissions as a decades-long blip in E.T. civilizations If we can assume that most technological civilizations go through the same phases in communications (radio to optics), then this might be a clue in itself. By watching the skies for radio activity that lasts only a few decades, we have a fair indication of a civilization that is moving toward the ability to receive and send transmissions. Some major objections to this argument: 1 Would it be detectable against the background radio noise present in the stellar locality? 2 Don't some (non-sentient) objects out these have periodic behavior of this sort (more noise, of a more deceptive kind)? The argument that radio will become passe has some weight, but only for those civilizations that have no interest in or little awareness of space. (Laser technology will have to improve fantastically in order to match radio achievements like the Deep Space Network.) That's not to rule it out. A very large cloud-covered planet with no moon might take a long time discovering that their planet went around the sun rather than vice versa. This might not be a real impediment to technological advancement--although I see strong arguments to the contrary, given the pivotal role of astronomy in the sciences of antiquity. We might be thinking about how important it is to have a moon; or a planet small enough that its size can be measured by the techniques of the early Greek geometers; or having a neighboring planet far enough away, and with moons far enough from *it* (i.e., a "jupiter"), that the finiteness of light-speed can be measured by Galilean (?) techniques; or an orbit large enough to make stellar parallax a reliable technique for determining at least the orders of magnitude involved in stellar distances. Astronomy provided alarming evidence that counter-intuitive perceptions of the universe, based on barely visible phenomena, might have some weight. The persistence and insight of a pitifully small number of people had a staggering impact on history. Astronomy was, perhaps, the first real science; and optics had to be at least empirically understood to get beyond a certain point. It would be a very lucky race to live in a planetary system where all these effects were visible with their native optical equipment (i.e., "eyes".) Good clocks were also important, but this is a little easier. Having materials for the fabrication of lenses seems to be the crucial thing. Without knowing much more than we do about the "average" planet out there, it's going to be hard to come to an assessment of current SETI strategies. The only major breakthrough I've seen is in paleobiology: some researchers have begun to think that spontaneous protein synthesis was a lot less chancy than they originally thought--it just seems to fall right out of the early chemistry of our planet. Perhaps this has bearing on the chances for life elsewhere, and hence, the chances for intelligent life. Another breakthrough is cryogenic circuits, which operate best at temperatures near the background temperature of the universe. Here at Berkeley, they are making Josephson junction receivers which are *very* sensitive. Perhaps good "ears" can be made from these. Michael Turner ucbvax!ucbesvax.turner