It seems to me that, if evolutionary theory is correct, then the simplest von Neumann probe would be something that seeds microorganisms into solar systems about the galaxy. A percentage of the seeded systems would subsequently evolve advanced civilizations that would eventually hit upon a similar scheme of von Neumann probes. The generation time between probes would be billions of years (assuming Earth is average). This makes for very slow expansion; however, a single probe could seed a great many solar systems.
I'm joking, of course, but discussions of this seem to make me, as a non-practicing atheist, think of the classic contemplations of the likelihood of there being a god (or gods.) So, some random, nearly-theological thoughts: Regarding a "universal constructor," or a self-replicating machine- a von Neumann probe. Why would one assume the self-replicating "thing" was a machine.? Why not an organic system that was designed to check conditions and create organisms that could replicate and evolve? Or just lots of various organisms. Dump it on planet, give it a few billion years and you might get - ta da - US! As far as I'm concerned, that's as plausible as Genesis. You might even be able to do it without building or powering probes. Just land on interstellar visitors passing through your system and seed them. Lots of them would be cheaper than a few man-made probes. Secondly, I suspect that intelligent civilizations are not likely to survive long. We've been around for only a fraction of a percent of the history of our planet, yet in a century, we've managed to mess it up almightily! Burned most of our hydrocarbons, fouled the air with pollution once and cleaned it up, only to find another mess we've created. Allowed chemists free rein and they may have created the biggest factor in future evolution, mimicking hormones and feeding hundreds to everybody, messing up our development and reproduction. How do you expect any civilization to last long enough to create a blip in the universe? Anybody know a Utopian experiment that worked? And where would they get the energy? We certainly do not have adequate power to do something like this and unless we discover something that offers basically unlimited power without using more natural resources or creating more climate or pollution problems, our development will be limited. Has everybody forgotten Malthus? We already have more population that the planet can support with a US lifestyle and people don't care - they simply will not "live within their means" either environmentally or financially. Malthus blamed population growth on a desire for reproduction but I see the problem we face as greed. What happened to that optimistic youth I once was?
The complexity of our civilization is predicated on cheap energy. To date, photosynthetically reduced carbon stores. It is debatable whether we will develop sufficient means within the next 50 years to 'power' the 9b person civilization. Most 'alternative' technologies aren't up to the task <10%). Carbon transformation (coal into oil) is temporary at best. Easy energy (oil, coal, fission) will soon deplete out (~250 years). Photosynthetic oil (e.g., algae into oil) might just do it, but our human scale is limited to the scope and efficiency we can work from that process.
Not withstanding, for the timelines relative to this article, if we (or any civilization) wish to expand beyond the easy access depleation economy or the sun coupled energy 'economy,' we need to crack the fusion nut.
We might speculate that any economy will not recognize the fusion question until it self-generates a complexity only achievable with significant size and energy consumption. At the same time and for the same reasons, it may likely be at the precipice of energy exhaustion. If it solves the fusion riddle, it can carry on with higher levels of complexity (space travel for instance), making use of all the Hydrogen typically found in a solar system, and about the universe.
If a civilization can't solve the fusion challenge, it will deplete out its "easy" energy stocks and eventually revert back to what it can sustain photosynthetically. That might be significant, or it might be minor. If it is not significant, we revert back to a pre-industrial agrarian economy within 1000 years, and centers of higher learning like MIT and mechanisms like the Internet cease to exist. With the easy energy gone, a sophisticated civilization will never re-arise until a re-banking of reduced carbon is created (5-15m years).
If we're able to make the photosynthetic energy-drive function, we may still be limited in our carrying capacity (2-5b), but could be extremely sophisticated (e.g., biotech advancing) until we reach the fusion breakout, assuming we can manage the population drawdown without disabling our civilization in the process.
We have some big make or break challenges ahead. On behalf of all life on this planet, we need to get focused. Time is short, and when the provervial s__t hits the fan, everything's going to be that much tougher to accomplish. The tipping point is coming.
although i agree on most of your points i have to say im not so pesimistic on the fact that we can and will find a way to derive our power from fusion reactors within the next 20 or 30 years. that will be a great day when that happens.
I would make a case for several "great filters" along the evolutionary path from primitive microbe to spacefaring civilisation. Evolving intelligence is one, but so would be evolving hands (or equivalents) to manipulate the world around - dolphins may be as intelligent as us - but they don't build anything.
How many other species on earth evolved intelligence? Did the dinosaurs make weapons and write? Well - if you wiped us out with an asteroid and came back 65 million years later, would there be any evidence that humans were intelligent? Almost nothing we construct would survive that long.
Personally I'd love to find evidence of life on mars (although if it's still there we might have trouble terraforming it). I think life is everywhere, but intelligent spacefaring life might indeed be rare.
Or it might be common, but faster than light travel might be impossible - no star wars or star trek. Would a spacefaring civilisation be bent on colonising planets? If they can build starships that will run for the thousands of years required to travel between stars, then they have artificial worlds and don't need planets to live on. All the resources they need can be obtained from rocky worlds nearby.
Unless they notice our radio waves (perhaps only a hundred years old) there might be no need to send anything our way. They don't need us unless we are in space an therefor a potential threat. And the nearest spacefaring civilisation might be thousands of light years away.
And in fact spacefaring civilisations might be rare - several per galaxy at any one time
"From these two facts it follows that the evolutionary path to life-forms capable of space colonization leads through a "Great Filter," which can be thought of as a probability barrier."
But those two facts are an overwhelmingly flimsy basis for the conclusion that a "great filter" exists.
Frank Drake's famous SETI Institute has so far extensively listened to something on the order of one thousand (1,000) stars....
Yes, 1,000 out of 200 billion+ (200,000,000,000) in our galaxy (The Milky Way Galaxy is estimated to have between 200-600 billion stars, and stars like brown dwarfs, which were previously not considered to be possible hosts of alien life, are now considered good potential candidates).
Using that fact to draw ANY conclusions about the prevalence of ET beyond the 50 or so + light years in our immediate neighborhood (in a galaxy with a diameter of 100,000 light years) is patently absurd.
....and The SETI Institute and other programs like SETI@Home so far have only done any kind of listening approaching significance with regards to one and only one form of communication: radio. Considering that SETI efforts have been based on the assumption that ET will be using a technology that the human race has possessed for roughly only ~100 years (there are people alive today who are older than the first successful wireless radio signal), and that there may be interstellar communication technologies we have yet to even imagine, it seems supremely naive to assume that the fact of SETI's hitherto lack of success could somehow conclusively confirm a null hypothesis.
As far as other astronomical evidence of ET in the vast observable universe, the author is making the baseless assumption that we possess the capability to easily detect such evidence.
Signs of astro-engineering, even on the kinds of scales that scientists can currently imagine, would be exceedingly difficult to detect and would be anything but obvious.
http://physicsworld.com/cws/article/print/33579
"If the Great Filter is indeed behind us, meaning that the rise of intelligent life on any one planet is extremely improbable, then it follows that we are most likely the only technologically advanced civilization in our galaxy, or even in the entire observable universe. (The observable universe contains approximately 1022 stars.)"
He's got an incredibly remarkable definition for "extremely improbable".
"Extremely improbable" could be 1 in 1 million, it could be 1 in 10 million, 1 in a 100 million, 1 in a billion, even 1 in a 100 billion...
Even if intelligent life were so improbable that the odds were 1 in 200 billion (1 in 200,000,000,000), it would mean that we are the only civilization in a galaxy of 200 billion stars, but it would also mean that there must be billions of alien civilizations in the observable universe even if only 1 in 200,000,000,00 star systems will ever give rise to intelligent life, since there are billions of galaxies in the observable universe each with billions of stars.
To suppose that we might be the ONLY civilization in the observable universe, indeed, that it's "most likely", is an utterly incredible conclusion.
Jill Tarter recently made a great analogy regarding SETI's efforts and the possible existence of ET, (not verbatim): What if you walked along a beach and could see the ocean stretch out along the horizon, seemingly into infinity, and hypothesized that large fish might exist in that ocean.... So if you took a drinking glass, dipped it into the water near your feet, raised it up, and see only water and grains of sand, could you conclude that fish must not exist?
Basically, it's absolutely impossible to even draw the faintest hints at anything conclusive since we do not possess the capability to detect evidence of ET civilizations with engineering technology that we can imagine, and we have only extensively listened to radio signals from ~1,000 stars within our immediate neighborhood.
The author's article is blatantly defying Occam's Razor: The simplest explanation as to why we haven't detected extraterrestrial intelligence yet is because we haven't looked hard enough and we don't have good enough tools.
We cannot make judgments about the hundreds of trillions of stars in our observable universe based on the results of listening for directed radio signals from ~1,000 stars within our immediate neighborhood or the inability to detect astroengineering with our extremely primitive detection capabilities.
To call the notion of a "filter" premature would be an understatement...
First, listening for radio spectrum signals will not mean anything when all long distance communications will be quantum entanglement based. As we can see with current technology developments, the use of the radio spectrum is becoming increasingly restricted. This being the case, it is not clear that we could even hear 'spillover' signals from nearby systems with our current tools.
Second. He ignores the case of progressive filters. The premise that we can hypothesize THE Great Filter is an interesting thought exercise, and invites such analysis and discussion. But we see in nature that the 'filter' is actually a progression of events. Cumulative probabilities may well be sufficient to assist in making the same case, but the "either/or" dilemma is obviously flawed.
Third is the point that Mars itself will prove nothing one way or another. It's proximity to Earth clearly brings it into close probability relationship with Earth regardless of what is found. This point was also made above.
Fourth, as a famous man, now retired, once said, "we know the knowns, and we know the known unknowns, but we do not and cannot know the unknown unknowns." Here is where the whole argument fails before it has even progressed to the flaws outlined above.
There is simply no rational conclusion available except to say, "who knows?".
"This being the case, it is not clear that we could even hear 'spillover' signals from nearby systems with our current tools."
You're right.
In point of fact, we do not currently possess the technical capability nor is there currently any active project to detect "spillover" radio from alien civilizations that would be comparable in strength and directionality to signals such as television radio broadcasts from Earth.
This is a common urban myth and widely-held misconception among the public at large, and I suspect the author of the article as well.
SETI's scientists act to detect an intentionally directed signal; they act on the assumption that it is likely that an alien civilization older than us will already be aware of the existence of life on Earth, potentially through spectral analysis of our atmosphere (there is no known natural mechanism to account for the amount of oxygen in our atmosphere without the existence of life), and send a directed signal at our planet.
SETI has to operate on the assumption that ET will send an intentional directed signal to our planet; if that assumption is wrong, then SETI is doomed to failure.
Even if there were hundreds of millions of Earth-like civilizations in our galaxy, each sending out unintentional spillover radio waves from global multimedia broadcasts, it's overwhelmingly remote that we would currently happen to live in a time period that would coincide exactly with the moments when such broadcasts wash over the Earth since such technology apparently seems extremely short-lived (we've only used it for ~100 years and we're already replacing radio broadcasting with fiber-optics and satellites).
...and even if such Alien spillover were washing over the Earth right now, if it were at all comparable to the type of spillover we've sent out into space throughout the last 50+ years, we would not currently have the ability to detect it.
So in point of fact, SETI isn't really looking for "extraterrestrial intelligence" per se; SETI is ONLY searching for extraterrestrial intelligence that is intentionally sending a radio signal to the Earth.
Even if SETI were to thoroughly listen to every single star in the Milky Way Galaxy and come up with no success, all that we could reasonably conclude is that there is no intentionally directed radio signal being sent to Earth by an extraterrestrial civilization in our galaxy.
There is some potentially good news though;
Scienists at the SETI Institute predict that if the new Allen Telescope Array is fully completed as envisioned, and if Moore's Law regarding computing power remains true, then they will be able to complete an extensive survey of the entire observable Milky Way galaxy "within decades".
If the basic assumption behind SETI's work is correct, that an alien civilization in our galaxy is intentionally sending a radio signal to Earth, then SETI will succeed within the next few decades.
This is why SETI's Seth Shostak recently made the bold prediction that SETI will detect an alien signal within the next 20 years; because if SETI's basic assumption is correct, then its success is inevitable.
The problem is, SETI's assumption may not be correct. Since our civilization is a relative infant in terms of the timescales of the universe, we may not yet possess the capability to comprehend the motives or behaviors of more advanced civilizations; we may be completely wrong in assuming that they would use radio to signal an emerging civilization or even that they would want to.
It all starts with the question: "If aliens exist, why haven't we met them already?" This fails to put "already" into its proper context of how short human history is compared to the other timescales being considered.
Perhaps ET last looked in on us 5,000 years ago, and is due back soon to check up on whether we've invented the wheel yet.
This post points out a simple truth. The distances and times are so great, and we have been dealing with this for such a small time and with such limited powers that the 'answer' or 'answers' are likely not given to our most learned speculation. I do however appreciate Nick Bostrom's effort, which I for one, have learned much from.
dmm
137
von Neumann probe