Why doesn't the poll have any options for not believing that aliens have visited Earth? I believe that the universe doubtlessly contains a myriad of life-bearing worlds right this moment. But there is no evidence to suggest any industrial and spacefaring extraterrestrial animals have voluntarily visited our planet, and much evidence to suggest they have not. I believe pretty strongly that we have not been visited, and even more strongly that reports of evidence and sightings are at best merely conjectural and at worst directly fraudulent.
The Fermi Paradox fails to recognize the youth of the universe and the immense amount of time it might take to build a civilization spanning many stars. It posits that because we do not see other civilizations, that either intelligent life is rare, or civilizations inevitably die. It ignores other possibilities:
1.) Old stars do not have enough metallicity to have a good chance of producing stable life-bearing planets. The best planets may be too young.
2.) No FTL travel will ever be possible and any race intelligent enough to travel the stars will be wise enough to see the futility in spanning the galaxy for the sake of spanning it. Perhaps these civilizations spread much more slowly--like millions of years or slower.
3.) Humans may be particularly unique in being both a tool user and a resource conqueror. Maybe most advanced civilizations are are more ecologically-focused, or the more ecologically-focused ones are less likely to kill themselves.
4.) Maybe large civilizations have much fewer EM emissions than we like to think, because their trans-stellar communications use lasers. They could be silently conquering the majority of the Milky Way outside of our view, and we could be in a backwater sector they don't really visit.
5.) Earth life may have evolved particularly quickly. Peering back through our life's history, we see that the Earth has had an almost regular cycle of major extinction events, delivering just what we needed when we needed it. Stronger extinction events could have sterilized the planet while weaker ones may have failed to spark the special adaptations we now take for granted. Life on Earth has been hard at work making huge leaps since the beginning, and it took the majority of them to get to multicellular eukaryotes. The bacteria in your body is more similar to you than it is to the first living cells on Earth, by a long shot.
- And I want to continue on this possibility a bit further. When we look at Earth-like life-supporting planets, there is a distinct set of ranges it has to fit in. The star has to be at least an orange dwarf or else it'll be a flare star and kill its life. But if it's larger than a yellow dwarf it won't last more than a few billion years to incubate its life. What if we're the fluke, and most spacefaring people's planets need to evolve for 6-8 billion years, or more? Maybe the stars are too large and too small at the same time. Add to that the role that stellar metallicity plays. The metal-rich stars are already mostly young. If life needs 8 billion years to become space-faring, look at the stars we have. Even today there's not a lot of good candidates out there, surely 8 billion years ago there were much fewer good candidates. Maybe in 4-8 billion years the galaxy will be teeming with civilizations. Maybe we're one of the first.
6.) Maybe us being space-faring is an incredibly rare conglomeration of traits. Perhaps most planets with intelligent life never develop spacecraft or other things we like to think of as advanced technology. Maybe normal intelligent life is more like our dolphins, our octopuses, our crows, and not like our apes. Maybe even the other Earth apes would never make spacecraft.
The Drake Equation attempts to find a ballpark figure of how many civilizations we can expect to find when there's too many factors we cannot calculate very well. Several of the listed factors on the equation can be reasonably estimated by us today. The problem with this is that the most important variables cannot be reasonably estimated by us, and even worse, several of the most important variables (as I have spoken about in depth above) are not even listed in the equation.
This is a portion of the criteria listed:
* Fraction of stars that form planets
* Average number of habitable planets per star
* Fraction of habitable planets where life emerges
* Fraction of these where intelligent life evolves
* Fraction of these capable of interstellar communication
Some people make some very bold numbers here without even acknowledging that the very criteria themselves are flawed to the point of not being answerable.
What fraction of stars form planets? Depends what you're willing to call a planet. Probably 99.99% of them have some kind of planets. But it also depends in what part of the universe they formed. In a very low metallicity star cluster maybe almost none of them have a single sizable terrestrial planet, while in a high metallicity star cluster they may almost all be littered with terrestrial planets in all the orbitals that aren't swept clean by giant planets or stellar companions. We definitely don't need a planet like Earth to form life, even if we don't know all of the ways it could form or what capabilities it could have there. Some life on Earth can survive on Mars, Venus, or Titan today and they aren't considered life-supporting by our standards. Maybe planets isn't exactly what we should be looking for, maybe life can form on moons, comets, asteroids, gas belts, planemos, rogue planets, or even inside the cooler stars. There is life at the bottom of Earth's oceans which is totally dependent on geothermal energy sources. Maybe life can form deep in oceans, mantles, or gas/ice giant liquid or superfluid atmospheres.
How can we know how many habitable planets there are per star when we don't have a way to define how many planets there are per star, and we have a very rudimentary grasp of what constitutes habitable? Not only could there be many ways for life to start which are alien to us, but there could be limiting factors we don't even realize we rely upon. The water and land distribution of this planet had a lot to do with why it took life roughly 2 billion years to first evolve to produce oxygen and then fully oxidize the surface of the planet. The plate tectonics also played a role. There are so many factors at play it is not unreasonable to perceive a planet in which the surface oxidizes in only 500 million years, or one in which it does not for 4 billion years. The former may kill its weak, rudimentary, unevolved life and become sterile. The latter may cost its life an extra 2 billion years before it can explore the galaxy. This is just a hypothesis I brainstomed just now for this very article. There are many more possibilities you, I, and the scientists haven't even thought about.
There's no way for us to know in which fraction of habitable planets life emerges when we don't yet fully grasp what habitable means. Maybe habitable means only the planets in which life truly can form, therefore basically a hundred percent of them form life--only those which experience a cataclysm immediately after becoming habitable actually fail. Maybe it means all the planets in which any life can possibly survive, but that could be virtually all of the planets out there, even barren rocks can theoretically support some advanced life form which evolved somewhere more hospitable first. And so once again we have this huge chasm of possibility and no clear place to draw the line even so much as to define the question. There's no way to answer it.
Fraction of life-bearing worlds in which intelligent life evolves: we still are only beginning to grasp what intelligence really means. We like to think of it as a trait that gives animals large brains and makes them talk or bash things with rocks, but that's an awfully ethnocentric view of intelligence. Even here on our planet, we see many kinds of advanced complex brains that perform many intricate functions in order to link data together to form solutions and ultimately increase their chances of reproduction. If we define intelligence as the ability to crunch data flexibly without resorting to pre-programmed instincts, we could outline what intelligence is. But to do this would require we first abandon nearly all notions we already have of intelligence. It is not our intelligence which tells us the coconut can be opened with blunt force trauma. It is our instinct to deliver blunt force trauma to random objects which leads us to deliver blunt force trauma to the coconut. It is only after we accidentally rupture its shell that we discover, under a much more rudimentary intelligence, that it was the trauma which gave us coconut to eat. And it is not our intelligence that passes this information to our others, but rather it is our instinct for teaching and learning from each other. The crow is exactly as intelligent as the human, but the crow does not have the instinct nor the limbs to bash random things with sticks and rocks, nor does it have the language or teaching instinct to be told what lies inside a coconut. Surely the crow can learn if you were to provide it with a ruptured coconut, yet it would not know a way to open an unruptured coconut because it is ill-equipped to do the job; you also do not know how, were you a crow, to open a coconut. So first we must learn to understand what intelligence is, only then can we come to the realization that the question makes no sense because intelligence comes in many forms and, just as with all other criteria so far in this list, there is nowhere to draw the line. In fact this is a case in which intelligence may not even be necessary. It remains unproven that an animal species cannot create interstellar communications entirely through instinct.
What fraction of intelligent-life-bearing worlds can produce interstellar communication? Shouldn't we ask what percentage actually do so? But then we are trying to guess their motives. We humans are fully capable of broadcasting signals to other stars which we with our current technology could receive and translate those signals upon arrival. But we are not doing so. Our radio broadcasts are exceptionally weak and would not easily be picked up among the background radio noise in the interstellar medium in our sector. We could put far more effort and energy into sending intense signals, but we've only sent very few and don't seem interested in sending more. The reason for this is simple: it's expensive and we're not convinced anybody is listening. How do we know they aren't out there silently assuming we're not listening?
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