The science fiction museum in Seattle has a marvelous "wheel of fortune" style display on this topic, with each segment of the wheel containing a different answer to the Fermi Paradox.
One answer I never see mentioned is "The Killing Star" hypothesis proposed in the book of the same title, written by Pellegrino and Zebrowski.
The concept is: IF faster-than-light travel is impossible, and IF civilizations inevitably develop the ability to accelerate "large" masses to a substantial fraction of the speed of light (e.g. relativistic interstellar travel), then any sufficiently advanced civilization would be compelled to pre-emptively destroy any other civilization it detects.
The reason is that any relativistic vehicle is also a very good bomb, and if "large" masses can be accelerated to relativistic speeds, then you have the capability to easily destroy entire ecosystems and civilizations. And in the absence of FTL travel, you would be unable to detect and thus defend against any carefully planned relativistic attack until it was too late.
In such a world, the moment you detect a neighbor, let's say 50 light years away, you MUST start making plans to destroy them. Because by the time you pick up the radio waves from their fledgling civilization, they may have already developed relativistic travel, and they might have already launched their own undetectable, unstoppable, relativistic planet-buster in your direction. Even if your neighbor is just sending a friendly exploration or colony ship, a little incompetent piloting by the captain might end your civilization.
A grim concept, but an interesting one, and I applaud Pellegrino and Zebrowski for coming up with it.
I find Nick's thoughts to be very insightful and logical. Here are some additional ideas:
The Great Filter is The Great Filter. At some point, every technologically advanced civilization of intelligent beings would ponder The Great Filter just as Nick has done. As evidence mounts that the Great Filter is ahead of them and most likely derived from some technological advancement, that civilization loses its push for technological advancement. They realize and accept their limitations because they don't want to become extinct. They realize that their species has a greater chance of survival if they live in harmony with nature. Ponderance of The Great Filter could lead many advanced civilizations to confine themselves to home. Perhaps this is a wise course of action or non-action.
However, I believe we are facing The Great Filter right now. Global Warming, climate change, energy crisis...whatever you want to call it. The Great Filter is finding an efficient means of producing vast amounts of energy with no negative impact on the home environment.
But, but but... Life on Mars? Of course there is! Edgar Rice Burroughs, through the notes of Civil War veteran John Carter, thoroughly covered the diverse life forms of Barsoom (including humanoids in the colors of Red, White, Black, Yellow and Green) starting nearly 100 years ago and continuing over about 40 years in an 11 book series. Start with "A Princess of Mars". http://www.amazon.com/gp/product/0345331389/ref=dp_proddesc_1?ie=UTF8&n=283155
More seriously, your article content is a bit scary to me as it nearly mirrors exactly the content of net posts that I have written myself over the years. I am also of the opinion that "intelligent" life in our galaxy is rare and/or non-existent, that Earth just happened to get the lucky break. But as you also note, it is difficult to intellectually rule out life across our whole universe. After all, the Milky Way galaxy is only about 100,000 thousand light years in diameter. There are billions, if not trillions of other galaxies in our universe (and there may even be multiple universes in a bigger metaverse). IF we are the only intelligent life, then we need not worry about some future "filter". Eventually, we will find a way to travel among the stars, expanding outward from Mother Earth, a subject that many SF books and movies have explored in detail.
Personally, I think we are wasting real money and resources hunting for signs of other intelligent life forms. The window of opportunity to pick up any such signals is very small. What if we did pick up a signal that was clearly from intelligent life, but was from a star system 10,000 light years away? It would be old news. What would we do with this [out-of-date] information? Even if we were able to send a reply, it would take another 10,000 years to get back.
No, the money spent hunting for intelligent life could be better spent developing working fusion technology, harnessing the power of the sun, working on anti-gravity, etc. And perhaps eventually, working on something like worm hole technology that would seem to be the only feasible way to travel among the stars in a reasonable time frame.
Recently we are beginning to discover that the universe seems to consist of 95% 'dark matter'. We don't yet know what it is made of, still we expect the intelligent life forms to choose to exist in 'our' physical environment, where the speed of light seems to be a limitation and energy is a scarce resource. Also, theories suggest that there are more dimensions than the ones that we move in. What if it is more pleasant to exist in a less hash set of dimensions? Every truly intelligent life form may have discovered that, and are having a nice pic-nic there right now. Our dimensions may seem as hostile as the Sahara desert to others.
The author mentions the anthropic principle, but has he considered that this principle may be protecting us from any future Great Filters?
My reasoning is like this:
1) Assume that there are an infinite number of 'parallel universes' with slightly different outcomes of quantum events, or maybe even different rules of physics (see Max Tegmark's "Mathematical Universe" hypothesis). Intuitively, this fits nicely with the anthropic principle because we'll inevitably find ourselves in a universe with intelligent life.
2) When a Great Filter wipes us out in one universe, there will be a nearly identical universe where it didn't wipe us out. The anthropic principle dictates we'll always find ourselves in the universe where we are alive.
3) From our point of view, alien civilizations have no such protection against Great Filters. The anthropic principle doesn't prevent us from observing that alien civilizations perish. This neatly explains the Fermi paradox if we assume that there are indeed alot of these "Great Filters" threatening intelligent life.
Conclusion: we may be doomed to be alone among the stars, but we will not perish.
wcoenen (wcoenen@gmail.com) (logged in with bugmenot)
The Drake Equation proposes not a GREAT filter but numerous lessor filters that combine to a GREAT filter. Using the existing most popular theory, the GREAT filter is mostly located between us and primative life if found on mars/eurpoa/exoplanets etc.
I would suggest, that you are only adding something interesting, if you idea can stand-up to the current most popular theory, which it cannot.
Also, numerous idea's in the post over extrapilate the existing data. 1. I don't see anything therfore nothing exists. (False) 2. Events must be Universially rare/common because they are localy rare/common. (False)
Finding life on mars would be a tremedous find, it would mean, WE are capible of finding life.
Although all explorations of this subject have huge limitations, this is a clearly argued exploration of one possible scenario--much better than many other efforts in the field.
There is one point that many of those who have responded seem to miss. Humans discovered the laws of physics, chemistry, and much of biology within the past few centuries. We should not project forward into the future the continued discovery of new laws of nature. In fact, it seems quite likely that the overwhelming majority of the technologically relevant principles of physics have already been discovered, and that chemistry and biology are simply complex instances of these laws at work. It is conceivable that a theory of quantum gravity might have technological implications, but I think it is much more likely that the relevant energy scales will remain beyond human manipulation for time scales much longer than would be needed for us to develop interstellar travel. We are just beginning to explore the technological possibilities of the known laws of physics, but we shouldn't be expecting new laws to rewrite the rules of the game. The agreement of current measurements with the standard model are just too good to allow much technologically relevant new physics.
farcast
1
The Killing Star hypothesis
One answer I never see mentioned is "The Killing Star" hypothesis proposed in the book of the same title, written by Pellegrino and Zebrowski.
The concept is: IF faster-than-light travel is impossible, and IF civilizations inevitably develop the ability to accelerate "large" masses to a substantial fraction of the speed of light (e.g. relativistic interstellar travel), then any sufficiently advanced civilization would be compelled to pre-emptively destroy any other civilization it detects.
The reason is that any relativistic vehicle is also a very good bomb, and if "large" masses can be accelerated to relativistic speeds, then you have the capability to easily destroy entire ecosystems and civilizations. And in the absence of FTL travel, you would be unable to detect and thus defend against any carefully planned relativistic attack until it was too late.
In such a world, the moment you detect a neighbor, let's say 50 light years away, you MUST start making plans to destroy them. Because by the time you pick up the radio waves from their fledgling civilization, they may have already developed relativistic travel, and they might have already launched their own undetectable, unstoppable, relativistic planet-buster in your direction. Even if your neighbor is just sending a friendly exploration or colony ship, a little incompetent piloting by the captain might end your civilization.
A grim concept, but an interesting one, and I applaud Pellegrino and Zebrowski for coming up with it.