The Fermi paradox or Fermi's paradox, named after physicist Enrico Fermi, is the apparent contradiction between the lack of evidence and high probability estimates for the existence of extraterrestrial civilizations. The basic points of the argument, made by physicists Enrico Fermi (1901–1954) and Michael H. Hart (born 1932), are: There are billions of stars in the galaxy that are similar to the Sun, many of which are billions of years older than Earth. With high probability, some of these stars will have Earth-like planets, and if the Earth is typical, some might develop intelligent life. Some of these civilizations might develop interstellar travel, a step the Earth is investigating now. Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.According to this line of reasoning, the Earth should have already been visited by extraterrestrial aliens. In an informal conversation, Fermi noted no convincing evidence of this, leading him to ask, "Where is everybody?" There have been many attempts to explain the Fermi paradox, primarily either suggesting that intelligent extraterrestrial life is extremely rare or proposing reasons that such civilizations have not contacted or visited Earth.
I would give this a read: https://waitbutwhy.com/2014/05/fermi-paradox.htmlFunny, broad discussion of various solutions.
My own current opinion is that there are multiple filters, great or not, that collectively reduce the number of outward-expansion-oriented ETI civilizations existing at any one time to a very low number, possibly zero.The first great filter would be the "Rare Earth" hypothesis, that the combination of circumstances needed to provide a suitable home for advanced life on the surface of a planet is very rare. From what we know and are learning, while microbial life might be very common in the Galaxy, more advanced life seems to require numerous highly improbable circumstances.The second great filter could be the eukaryotic grade of single-celled life -- while multicellular eukaryotic life originated numerous times, eukaryotic life itself apparently originated only once in Earth's history. This, or something equivalent, appears to be necessary to allow higher organisms to develop.The third great filter would be a sustainable technological civilization, that develops into something that can last without destruction by any of numerous causes. Once a certain technological level is reached, it becomes possible for individuals or small groups to devise ways to destroy that civilization -- for example through genetically engineered "superbugs". All it would take is ONE individual with the desire and ability, to possibly destroy that civilization. I suspect that eventually, the civilization would develop means to avoid this sort of disaster, but until then it would be vulnerable to self-inflicted destruction.The fourth great filter (of a sort) might be an inward turn of highly advanced civilizations. The individuals comprising that civilization might quite possibly shift to a virtual reality where the individual entities could live as long as they wish, with a vastly larger range of experiences than is possible in the physical world. In which case their civilization might stop expanding outward and stay as a fixed number of "core worlds", each with a sphere of automated outposts to guard against potential physical threats.If these great filters are real, you would indeed observe a Universe that appears empty.
Quote from: Mongo62 on 10/23/2017 12:52 pmThe fourth great filter (of a sort) might be an inward turn of highly advanced civilizations. The individuals comprising that civilization might quite possibly shift to a virtual reality where the individual entities could live as long as they wish, with a vastly larger range of experiences than is possible in the physical world. In which case their civilization might stop expanding outward and stay as a fixed number of "core worlds", each with a sphere of automated outposts to guard against potential physical threats.That last one was always my guess.
The fourth great filter (of a sort) might be an inward turn of highly advanced civilizations. The individuals comprising that civilization might quite possibly shift to a virtual reality where the individual entities could live as long as they wish, with a vastly larger range of experiences than is possible in the physical world. In which case their civilization might stop expanding outward and stay as a fixed number of "core worlds", each with a sphere of automated outposts to guard against potential physical threats.
Our ancestors were just as intelligent as us going back for 50,000 or even 200,000 years, but radio technology was invented a little over a hundred years ago. The Galaxy maybe filled with alien civilizations, but we could be the only technological civilization.
8. With the technology in their possession, they could easily monitor the entire rest of the galaxy for other emerging civilizations, via automated non-reproducing but durable probes in every planetary system in the galaxy, that each send periodic updates. This could probably be paid for by the equivalent of a minor Kickstarter campaign, given the size of their economy.
So anyone have any solutions to this? I'm leaning towards either inter-stellar civilisations aren't feasible, or we're incredibly lucky and potentially one of the first that have evolved in the galaxy. Either way, it seems that we may have to be the ones that spread intelligence throughout the galaxy, rather than waiting for it to come to us.