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Sunday, January 28, 2007


The Fermi Paradox is "why, if we are soon going to be able to go out into the galaxy & the number of stars similar to our own is so great have aliens not already come here".

They certainly have not come in any noticeable way. Whatever Von Daniken says any visitor's effects left in hard vacuum, such as orbit or the Moon, would last billions of years & clearly noting sizeable exists.

I you take the popular analogy of the history of the planet being a month long & Jesus being born at 2 seconds to midnight & assume that we can populate the galaxy in between about 20,000 & 200,000 years you will see that the aliens have between 2o seconds & 2 minutes to find us. If they haven't managed it in a "month" it seems unlikely & therefore unlikely they will.

This is part of a discussion on in which I participated
New Scientist article which says if we keep exploring at a couple of stars every 50 years we & putative aliens, would never find each other
- Roland Dobbins

It's all in the numbers. But suppose we set out to settle the galaxy with generation ships traveling at 1% of the speed of light. Build two generation ships. It takes 1,000 years to go from star to star. When you get there, it takes 1,000 years to build a civilization capable of building two more star ships. That's 2,000 years doubling time, with each generation ship building two more. I leave the resolution of this exponential to the readers, but you can see why Freeman Dyson says there is only one intelligent race per galaxy.

FRIDAY I think you're an optimist. Although recent astronomical discoveries say that many stars are likely to have planets, the likelihood of a suitable Sol-like star having a suitable Terra-like planet and lying within ten LY is pretty small. You might have to extend your sphere to 100 LY and your travel time to 10,000 years to reach a really good planet. Even then, and even assuming that the generation ship survives such a journey, many apparently suitable Sol-like stars would turn out for one reason or another to be unsuitable, although in many cases that could not be determined until the generation ship had already arrived. Scratch one generation ship.

Furthermore, some proportion of the generation ships, presumably a relatively large proportion, would encounter disasters during the trip or soon after arrival that would kill most or all of their passengers. Even if everything went as planned, the number of people that would fit on a generation ship are a pretty fragile start for a new civilization. If they run into stobor, they might be wiped out or have their skill sets reduced to the point that it would take them far, far longer than 1,000 years to develop to the point that they'd be ready to produce generation ships of their own.

I guess I just think the galaxy is a much larger and deadlier place than you and Dr. Dyson do.

-- Robert Bruce Thompson

Fiddle with the numbers as you will, exponentials are exponentials: in a billion years the galaxy will be populated under the most pessimistic assumptions. It isn't, so there were no intelligent species a billion years ago. Probably none 100 million years ago. Unlikely even a million years ago...


Subject: Populating the galaxy

Dr Pournelle

Robert Bruce Thompson finds fault in the argument on the technical side: likelihood of each ship finding a Terra-like planet smaller than expected; radius of required flight greater than expected; time required for each colony to achieve industrial capacity to replicate the adventure greater than expected. As you point out, this merely protracts the outcome: the curve will still go asymptotic.

The fault, dear Brutus, lies not in our stars but in ourselves. What race has the will to maintain a policy of populating the galaxy for millions of generations? Ain't gonna happen.

Time is the great leveller. When we go to the stars -- I believe -- we are unlikely to find another race to share the galaxy with. But -- I believe -- we are very likely to find the artifacts of races long, long dead.

BTW 1% C is fast! At 1% C a ship would fly from the Earth to the Moon in under 13 seconds.

Sincerely h lynn keith ....

SATURDAY Casual reflections on the Fermi Paradox:

Why is nobody here?

1. We're alone. Also means we're unique. I have violent objections (call them religious; Mr. Heinlein did) to this possibility. I could be wrong; I'm not uncertain.

2. The Einstein limit is absolute and cannot be circumvented economically (or even as a desperate last-gasp effort). Every intelligence civilization that arises eats itself to death unable to cross the stars to salvation. This assumption is unfortunately far too plausible. Maybe our information will travel between the stars, but we never will.

2.1. Note that every "practical" system for interstellar travel presumes some sort of widget (warp drive, whatever) that has the net effect of assuming a threshold power level (typically on the order of 100 kilotons/second per vehicle, or about 4E14 Wts) at which the Einstein limit breaks down and interstellar travel becomes effortless. Note that 4E14 J is the kinetic energy of 1 kg of mass traveling at 9,145 km/s or 3% of c, and note again that I said the power assumed is per vehicle and not per kg mass of vehicle.The two derived scenarios are:

2.1.1. The "trick" is so difficult to identify few or no species ever develop the capability. 2.1.2. The "trick" is so easy that everyone gets it in time, which reduces to the same solution set as 3.

3. We're quarantined (either totally, or a few select people are in the "know.") Need not assume the possibility of FTL travel, though that does make things easier. Not implausible, but there are several corollaries:

3.1. The "classic" UFO/aliens scenario. The aliens who have us quarantined are not much in advance of us; enough to get here, but not enough to offer a serious military threat at the end of an interstellar logistics chain even with advanced technology. So they try to get whatever they want by subterfuge and manipulation. Note that this covers all of the possibilities from benign intervention to "they want us to worship their gods" to clandestine conquest.

3.2. The "galactic punctuated equilibrium" scenario. Probably most dramatically exemplified by Stephen Baxter in Manifold Space: Every "X" years (Baxter seems to equate X to the mean time between mass extinctions), intelligent species pop up everywhere simultaneously (with perhaps a technological development dispersion equivalent to a few hundred years -- a lot, if you're considering Moore's Law). Everything goes to pot for a few hundred years, after which the colliding expansion waves have decimated our corner of the galaxy, and everything stays quiet for a another sixty million years until the next wave simultaneously evolves.

3.3. The "Pax Organia/Prime Directive" scenario. One race gets far enough out on the power (literally) curve to dominate all the others in their corner of the galaxy, and are benign and confident enough in their own self-preservation to impose a "peace of the greater guns" on all the less nobly inclined species in their neighborhoods, and leave developing civilizations alone

3.4 The "Planetary Defense" scenario. They're eventually coming to eat us -- if not literally (though that can't be ruled out), then at least metaphorically by taking our materials and means of production for their own racial preservation. Nobody will protect us (3.3 fails) so when they finally arrive we're on our own.


I guess you'd call Janissaries -- what? A classical UFO/aliens scenario?
Or that the race between physical expansion & any intelligent race's ability to destroy itself also inherently involves faster geometric growth for destruction (60 years ago we could destroy 2 cities, now we could probably manage every city in the world, possibly by chemical & bacteriological means too.. In which case probably all we can do is build Dr Asimov's law abiding robots & send them as far away from us as possible.

On that basis I find emergence of the Rare Earths hypothesis, since it suggests that the bottlenecks in survival have mostly been passed, a happy development.

Your assessment of expansion is clearly right in general terms since it works by compound growth whereas the New Scientist article assumes human society will grow at an arthmetic rate taking as long to reach our 50,001st after the 50,000th star as to get from here to Centauri. Living systems don't do arithmetic growth for long.

Neil Craig

Which has sent my hitmeter soring.

The Rare Earths hypothesis is that various sorts of accidents must be so statistically common that it is a very very lucky planet indeed (ours) that doesn't get knocked back to the microbial level far faster than intelligent life can develop - being hit by comets, solar variablity or lack of variability (our sun is about 40% warmer than it used to be & we have managed to escape both freezing & a greenhouse effect under both by being lucky in the make up of the atmosphere both times) etc. The arithmetic that life is rarer than previously thought is compelling. Beyond that the effect of our Moon (a moon this comparative size must be rare because the experts can't explain it) may have produced a tidal effect that got life onto land.

A really off the wall suggestion I would like to make is to make use of the Everett multiple universe theory, that every possible outcome on the atomic level actually takes place & that a new universe is created each time, though they tend to fold back into themselves if the turn out to be exactly the same as another infinitude of universes. As a concept this is mind boggling which doesn't in any way prevent it being true.

If you add to this that the theoretical chance of a molecule with enough links to self replicate seems to be orders of magnitude more than the number of number of molecules formed in the history of the universe & we get the possibility that life is so unusual that its creation branched off into a whole new universe. If this were so then no life not related to us would exist. Alternately the branch point might be the development of self aware or even intelligent life. This is one reason why I would like to find if there is microbial life on Mars where conditions about as severe as the Antarctic seem to exist. If there was no life it would suggest our uniqueness, if there were some clearly unrelated to ours it would suggest life is common. If we found life which might have travelled from (or to Earth) by meteor or light pressure it would prove ...?

The counter to this, which is probably really more likely is that there are some reasons that make the formation of self replicating which we just don't understand yet. Some molecular affinity or some simpler self replication that was viable in an empty Earth but has died out since. One thing in favour of this is that we know that life appeared almost as soon as the earth had cooled but if it was a once only rare event there is no particular likelihood of this. Complex life & life broadly self aware made MUCH later appearances which is why it would also be possible that they are the improbable occurences.

Or God, or the Time Experiment Committee of 50,000AD in which case all bets are off.

One this case everybody is in a position of trying to deduce the location of a black cat in the Carlsbad caverns while wearing blindfolds, never having seen a cat, & not sure if such a creature exists.

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