it comes in pints?

Who's Afraid of a Martian Probe?

Apologies in advance. I didn't realize how long this had gotten until I finished, and since I have stuff going on tonight and tomorrow, I'm not going to try to edit it down to a reasonable length. You have been warned, but I, in my infinite mercy, have hidden it below the fold for those of you not interested.

Continuing the discussion from last night, and trying to refrain droning on, I looked up Nick Bostrom. He's the one who thinks we're living in a computer simulation. Well, that's not quite accurate but it might explain a lot. Dr. Bostrom is a philosopher at Oxford. Somehow, I suspect if he were an evolutionary biologist or a physicist, he wouldn't be nearly so pessimistic.

Dr. Bostrom's thesis may be summarized as follows:

1) There are no other civilizations out there, because if there were they would have colonized us already.

2) Therefore, there must be a "Great Filter" (giggle) that prevents the formation of spacefaring civilizations. This GF is a probability barrier which makes it vastly unlikely, even impossible, for civilizations to reach the stars and colonize the galaxy.

3) This GF must lie either in our past or our future, i.e., it must either prevent the emergence of advanced societies, or these societies must destroy themselves before they can reach the stars.

4) If we were to find evidence of life on Mars, it means the GF is less likely to lie in our past.

5) If the GF does not lie in our past, then it must lie in our future, and we are doomed to destroy ourselves before we reach the stars.

Jeez. That's depressing. No wonder the poor fellow is terrified of finding life on Mars. Fortunately for us, he's wrong on all counts. Let's tackle them in turn.

1) There are no other civilizations out there, because if there were they would have colonized us already.

Dr. Bostrom's argument is that technologically advanced societies that do not destroy themselves must reach the stars and colonize the galaxy, even the entire Universe. In a nutshell, it would take barely 20 million years, at 1% of the speed of light, for a civilization to colonize the galaxy once it achieved space flight. Well, he's right there; even if it took longer, it's a mere blink in the history of the galaxy, so time is not the barrier.

But where he falls down is in the dismissal of other reasons a civilization may not do so.

Various schemes have been proposed for how intelligent species might colonize space. They might send out "manned" spaceships, which would establish colonies and "terraform" new planets, beginning with worlds in their own solar systems before moving on to more distant destinations.

IF they moved on. I'm down with terraforming the local planets, that's a no-brainer. But sending manned craft beyond a solar system is a huge technological leap. I have my doubts about its feasibility even in the far distant future.

It has been pointed out, of course, that at one time people couldn't travel around the world. "But technology triumphed!" and now we can jet around the globe. And:

Considering that space travel was science fiction a mere half-century ago, we should, I think, be extremely reluctant to proclaim something forever technologically infeasible unless it conflicts with some hard physical constraint. Our early space probes are already out there: Voyager 1, for example, is now at the edge of our solar system.

Fine, but when it comes to interstellar travel we are butting up against a hard physical constraint, not technical trivia. Unless there is a new revolution to shake up physics, we won't be thwarting the speed of light.

And just as we should "be extremely reluctant to proclaim something forever technologically infeasible", we should be extremely reluctant to proclaim that we will overcome any technical barrier. Yes, the computer revolution and rocket ships are amazing things, but I'm still waiting for my flying car. Actually, a more accurate analogy might be thermonuclear reactors. They've been just around the corner for 50 years but they still aren't here. The point is, we will have many new technologies, but there may well be technological barriers that are insurmountable or too expensive. Star travel may well be one, and could easily explain lack of contact.

Of course, there are other methods besides manned craft:

But much more likely, in my view, would be colonization by means of so-called von Neumann probes, named after the Hungarianborn prodigy John von Neumann, among whose many mathematical and scientific achievements was the concept of a "universal constructor," or a self-replicating machine. A von Neumann probe would be an unmanned self-replicating spacecraft, controlled by artificial intelligence and capable of interstellar travel. A probe would land on a planet (or a moon or asteroid), where it would mine raw materials to create multiple replicas of itself, perhaps using advanced forms of nanotechnology. In a scenario proposed by Frank Tipler in 1981, replicas would then be launched in various directions, setting in motion a multiplying colonization wave.

Okay, that sounds technologically feasible. But what would be the point? There are two main reasons for space travel: to send people (perhaps to save the species from the inevitable death of the local star) or to gain something of value, especially knowledge. Unless all those generations of self-replicated probes are capable of sending back information (at no more than the speed of light, remember) why would anyone choose to do so?

Even if an advanced technological civilization could spread throughout the galaxy in a relatively short period of time (and thereafter spread to neighboring galaxies), one might still wonder whether it would choose to do so.

Is there an echo in here?

Sorry. Continue.

Perhaps it would prefer to stay at home and live in harmony with nature. However, a number of considerations make this explanation of the great silence less than plausible. First, we observe that life has here on Earth manifested a very strong tendency to spread wherever it can. It has populated every nook and cranny that can sustain it: east, west, north, and south; land, water, and air; desert, tropic, and arctic ice; underground rocks, hydrothermal vents, and radioactive-waste dumps; there are even living beings inside the bodies of other living beings. This empirical finding is of course entirely consonant with what one would expect on the basis of elementary evolutionary theory.

But it misses a big point: that spread was mostly passive (certainly in the case of bacteria), into places immediately reachable (unlike other stars), and it was mostly at the margins (meaning that as populations increased, some individuals were pushed out to find new food sources - Malthus wasn't completely wrong).

Second, if we consider our own species in particular, we find that it has spread to every part of the planet, and we have even established a presence in space, at vast expense, with the International Space Station.

Okay, but remember that, with the exception of space, Antarctica, and a few islands, all of that was reached on foot before the coming of advanced technology. And it was because people were searching for food sources. Back when life was "nasty, brutish, and short" people didn't travel away from food sources.

Third, if an advanced civilization has the technology to go into space relatively cheaply ...

Ay, there's the rub. We get back to the technological barriers. Even if it's relatively cheap (and it probably is) to expand within a solar system, interstellar travel is a whole different ballgame.

... it has an obvious reason to do so: namely, that's where most of the resources are. Land, minerals, energy: all are abundant out there yet limited on any one home planet. These resources could be used to support a growing population and to construct giant temples or supercomputers or whatever structures a civilization values.

Problem is, this directly contradicts the von Neumann probe idea. Either you bring back those resources to the home planet or you send part of the population to exploit them onsite. A von Neumann probe would be useless. And neither idea lends itself well to interstellar travel.

Fourth, even if most advanced civilizations chose to remain nonexpansionist forever, it wouldn't make any difference as long as there was one other civilization that opted to launch the colonization process: that expansionary civilization would be the one whose probes, colonies, or descendants would fill the galaxy.

Yes, but again it comes back to whether interstellar travel is feasible and inexpensive enough. It also ignores other possibilities. Perhaps civilizations always have, as we do, chattering classes that want to spend money at home instead of space. Perhaps the end stage of civilizations is Luddism.

Or maybe, maybe even likely, it would be difficult to find people willing to leave the home solar system. Think about our own history of colonial expansion. The first explorers were sent by their respective kings to stake claims, find riches, and one-up the competition. After this, there were some missionaries and padres out so save souls of natives, a few settlements commissioned by the kings, and some religious nuts. But when it came time to populate the Americas and enslave the native populations, by and large the immigrants were poor folk with few options and societal outcasts of varying sorts. The rich didn't leave their riches. The middle classes didn't leave their comfortable homes (except for new business ventures). So not only are we a nation of immigrants, we are largely a nation of outcasts.

What does this mean for space travel? I suspect that a society sufficiently advanced to acquire the capability of space travel is also a very wealthy society. Wealthy people will go on jaunts into space. The less wealthy among them may well be interested in jobs exploiting the resources of their solar system. But it may be difficult to find people willing to spend the rest of their lives in a ship heading on a multi-year, maybe even multi-generational, voyage to distant stars. I think this explanation is at least as plausible as any other to explain why we haven't been colonized already.

In any case, I don't think it at all implausible that advanced civilizations could flourish without conquering the galaxy, which would make the Fermi Paradox no paradox at all.

Well, I think I may have spent too much time on this part, so let's move on. Fortunately, most of the argument above takes care of them as well, so they will be quick.

2) Therefore, there must be a "Great Filter" that prevents the formation of spacefaring civilizations. This GF is a probability barrier which makes it vastly unlikely, even impossible, for civilizations to reach the stars and colonize the galaxy.

3) This GF must lie either in our past or our future, i.e., it must either prevent the emergence of advanced societies, or these societies must destroy themselves before they can reach the stars.

The idea of a probability barrier to spacefaring civilizations is not too far off base, but I think Dr. Bostrom has an incorrect view of it.

If the filter is in our past, there must be some extremely improbable step in the sequence of events whereby an Earth-like planet gives rise to an intelligent species comparable in its technological sophistication to our contemporary human civilization.

It really should be thought of as a series of filters, with a cumulative probability. Thus, the argument that it lies either in our past or our future is way off base. It can, and almost certainly does, lie partly in both, and the actual probability is the product of the probabilities of all steps. Any or all of these may be extremely improbable, or all may be fairly probable yet have a cumulative probably that is very small (so that we may be the only one) or large enough that there may be many such civilizations.

What would these steps itoward ntelligent, technologically advanced civilizations be? Dr. Bostrom identifies some:

1) The origin of self-replicating cells

2) The origin of eukaryotic cells from prokaryotes

3) The rise of multicellular organisms

4) Sexual reproduction

I really don't know why he would consider sexual reproduction a requirement for advanced civilization. I suspect it (or some other form of gene shuffling/exchange within species) is a probable result of evolution rather than a requirement, but that's a different discussion.

Oddly, one he didn't mention was the rise of intelligence itself. It is true that

Some people seem to take the evolution of intelligent life on Earth for granted: a lengthy process, yes; complicated, sure; yet ultimately inevitable, or nearly so.

but others aren't so sure. Stephen Jay Gould, for one, was very pessimistic about the odds that human-like intelligence could evolve twice, even given eukaryotes, vertebrates, even mammals as a starting point. I'm not nearly so pessimistic, but I certainly don't consider it inevitable. In fact, I might rank it second least probable on the list, eukaryotes being number 1.

Unlike Dr. Bostrom (who only discusses the first step above), I don't actually consider the rise of self-replicating cells to be all that unlikely.

For example, perhaps it is very improbable that even simple self-replicators should emerge on any Earth-like planet. Attempts to create life in the laboratory by mixing water with gases believed to have been present in the Earth's early atmosphere have failed to get much beyond the synthesis of a few simple amino acids. No instance of abiogenesis (the spontaneous emergence of life from nonlife) has ever been observed.

Um, well, yeah. A few weeks is obviously not enough time, and we are at only the most tentative first stages of being able to probe the possibilities.

The oldest confirmed microfossils date from approximately 3.5 billion years ago, and there is tentative evidence that life might have existed a few hundred million years before that; but there is no evidence of life before 3.8 billion years ago... Nevertheless, several hundred million years elapsed between the formation of Earth and the appearance of the first known life-forms. The evidence is thus consistent with the hypothesis that the emergence of life required an extremely improbable set of coincidences, and that it took hundreds of millions of years of trial and error...

I suppose it is consistent with that. But it's also likely to be an inherently slow process. The first self-replicating molecules and proto-cells could not have been very efficient. I would go with a lot of others who suggest that a few hundred million years is probably a very short time to advance from an "organic soup" to living organisms, so life formed early, perhaps surprisingly early. And if that's the case, it suggests the formation of the most primitive cells may well be very probable, perhaps even inevitable in the right conditions.

Of course, there are still a lot of other stages required, of varying probabilities. And this has gotten far too out of hand so I will not even bother with my cropper argument and just say that I think some form of life is highly probable under the right conditions (maybe under a wide range of conditions); multicellular, differentiated organisms much less so, intelligent life fairly (but not prohibitively) improbable. But given the vast number of potentially habitable planets out there, I think it highly likely that other advanced civilizations exist. Perhaps not very many and probably well-scattered, but I think it highly unlikely we are the only one.

Jeez, before I get any further off track, let's finish this up.

4) If we were to find evidence of life on Mars, it means the GF is less likely to lie in our past.

5) If the GF does not lie in our past, then it must lie in our future, and we are doomed to destroy ourselves before we reach the stars.

But again, that would only be if it is assumed inevitable that advanced civilizations will achieve interstellar travel if they don't kill themselves.

Well, not much more to say about it besides what I spouted already. I think Dr. Bostrom is flat wrong to think that advanced civilizations must self-destruct. True, he has company; CW worries that advanced civilizations (and we in particular) pollute themselves out of existence before reaching the stars. Our buddy John is less worried than CW and less wordy than I.

But I think Dr. Bostrom is probably right on this point:

If the Great Filter is ahead of us, we must relinquish all hope of ever colonizing the galaxy

More accurately, I think it is unlikely we will ever colonize the entire galaxy, but I would not relinquish the hope because I don't believe the Great Filter (one last giggle) necessarily lies ahead of us. I suspect the technological hurdles will be too great for some Galactic Federation to be formed, and that if people leave the Solar System it will be few and just a way to ensure survival of the species beyond our Red Giant future. But I'd like to be wrong about it.

Meantime, assuming we don't exterminate ourselves prematurely, which I do NOT consider in any way inevitable, even if we don't quite make it to the stars we can still have a great ride for the next few billion years plundering the Solar System and mocking "The View".

Posted by Ken S at May 2, 2008 06:33 PM | TrackBack (0) |