Contemplating big questions is fun and humbling. One of those questions is: how is it that among all the life supporting planets out there in the universe(multiverse?), planet earth is the only planet on which complex life had evolved. Where are the aliens?
-K1 civilizations, as developed as ours. Capable of harnessing only the hosting planet's energy.
-K2 civilizations, more advanced. Exploits sun's energy.
-K3 civilizations, can harness the entire galaxy's energy.
Paradoxes come in all shapes and forms: logical paradoxes, visual paradoxes( Penrose triangles), and scientific paradoxes( Ceasar and the tortoise).
Fermi was a physicist who contributed to nuclear energy efforts, left Italy for the US and worked as an academic. He used to ask "Fermi questions" that start with an explicit guess to train the mind to come to a close enough estimate. e.g: "how many piano tuners are there in Chicago?" Fermi, at a lunch in 1950s, once posed the question: "where is everybody" amid talk of flying saucers and trash cans disappearing. It was a Fermi question. He came up with an equation to estimate the number of Extra terrestrial creatures ETCs(N), later came to be known as the drake equation. It involved coefficients like, star formation in a year, stars with planets, stars with planets that support life, planets that developed life. Planets that develop intelligence n culture and time. Several renown figures weighed in with answers such as time it takes to reach us, they don't want to communicate, we're not ready, they're already here, we're the first civilization in the galaxy.
The solutions to the paradox:
They are here and they're Hungarians. The theory that Martians landed in Hungary and blended in with Europeans and they had unique traits like different language and superior intellect. Von Newman was born in Budapest along with other 2 mathematicians that did great things. Could they have been aliens?
They are meddling in our affairs. Most of the reported sightings of UFOs can, upon further investigation, be turned to IFOs. Could be light reflections of some kind manifesting in shapes or form or other natural phenomenal that are not worth the time of scientists. But also, that doesn't prove that we're not being communicated with. The stories of crop circles, abductions, and stuff usually are not supported with strong evidences but are hoaxes made up for profits.
They've visited us long ago. The tunguska event was caused by a meteorite, no traces of radioactivity. Bridges on the moon are an illusion( we used to wonder about the 41% of the moon we can't see). Probes could be parked in places like the 5 lagrangian points( L4, L5) where one mass can orbit at a fixed distance from 2 bigger orbiting masses, provided the intermediary is at least 25 times bigger( earth-moon?). What is the deal with the mysterious delayed radio signals?. Mars Cydonia's faces( dated imaging techs) satellites(asteroid expected to hit mars surface in 40 m years), and canals are illusions.
Instead of leaving engineered things, could they have left information? Like messages as DNA artifacts. Not likely.
Panspermia( directed by probes or traveling haphazardly on asteroids): the idea that life originated in space and earth was seeded with life giving spores( microbes) to whose existence we own ours. Do we originate from aliens?
The zoo scenario: ETCs locked us away in a zoo( earth), and they don't want us to reach them.
The interdict scenario: ETCs have formed a galactic club and elected to not make contact with primitive solar systems( life bearing planets orbiting stars). Relativity makes it hard to believe this could be the case.
Planetarium hypothesis. Are we in a simulation? The limit is 100AU at which point we will we be able to find inconsistencies in the simulation; is the universe real. The Boltzmein limit of information encoding capacity gives plenty of room to the planetarium programmers.
Stars are far away: Interstellar travel is not impossible( Laws of physics decline to comment). Our space travel techs are so slow and requires thousands of years to reach even the closest star. There are suggestions like generation ship( space arks) but we need ships that travel at light speeds and where time dilation effects can be significant so that the humans on board will be able to reach destined planets in their lifetimes otherwise we will need to freeze fertilized eggs or actual humans.
Self contained rocket proposals: anti matter rocket( annihilation of particles and anti particles producing energy) Ramjet rocket( scoop up hydrogen in space and pump it into a thurmo nuclear reactors). Honourable mentions: Ion rockets; warp drives( ship sailing on a spacewave), wormholes, zero energy zones( energies in vaccum), tachyons( imaginary masses) laser sails( photon energy exertions pushing sails in space)..
Temporal expansion paradox: They haven't had time enough to reach us. Age of universe is 13 billion years and different models show that ETCs need between 1-500 million years to colonize galaxy. Short times on the univeral calendar
Percolation theory: the idea that ETCs drives to colonize may vary and it follows certain patterns in filling out systems: spanning clusters, clusters, sparse colonies. We might be in the void among these colonies but mother colonies should somehow communicate with daughter colonies and we can't seem to
Bracewell-Von Newman probes: inspired by Von new man probes( with a constructor and a program equipped with instructions to that constructer). ETCs can send probes that can, upon arrival, fire up their constructor and reproduce themselves by scavenging the host planet's material, then doing so an another planet, ad infinitum, until they have colonized the whole galaxy. That might take 4 million years. Very short period in the universal scheme of things. Probes would act as species as opposed to replicas.
Solar chauvinists: ETCs might not prefer to live on planets orbiting stars_that harness just 1 billionth of the sun's energy_ but they would rather( provided they're k2 civilization) be travellers who move from one place to another so they might choose any star and construct a Dyson sphere around it so that they can harness its full energy, that is until it goes supernova; they'd then move to maybe black holes or other stars and do the same.
They stay at home: But is it wise to put all your human eggs in one planetary basket?
They live in virtual realities of their own and no longer interested about the real world( Metaverses?).
We don't know how to listen: ETCs might use one of these three communication mediums:
- Electromagnetic waves EM: k2 civilizations could leave inadvertent beacons in the form of infrared waves( Dyson spheres), radioactive waste( displayed through alteration of the stars' chemical components)
- Gravitational waves: far weaker than EM waves and requires astronomical masses of matter.
- Communication via cosmic rays: Particles can travel at intergalactic speeds, but the nature of space curvature( stars are constantly changing position) makes it hard to infer their directions. Also experimented with as means of communication were Neutrino telescopes to detect supernova events, and Tachyons( if they exist at all). Could be that ETCs have what to us is unimaginable means of communication. Like, show a radio engineer from 1939 how we communicate now; they would never be able to conceive of fibre optics .
We don't know what signal to listen to: the visible part of the EM spectrum represents a tiny part of the spectrum. We have gamma rays, x-rays, and microwaves, but the range where signals will be clear is between frequencies of 1-30 GHZ( outside of this range, signals will be interefed with by a ton of background of noise). Forty years of looking and we were able to narrow down the search significantly to what is now known as the waterhole range. But we still haven't found nothing of significance save for that wow moment that might or might have not been of an alien origin( proxy emanated from man-made satellite). This incoclusiveness might indicate the absence of k2 n k3 civilizations.
Faulty search strategy : Wide area search would be more effective than in-depth, focused search.
The signal is in the data: Could we have already recorded an alien data but failed to recognize it amid the noise? Occam's razor would tell us to interpret data in terms of simplest explanations. Redshift? might be attributed to a universe expanding instead of fuel traces left from an alien spaceraft leaving mankind behind. In our search. Our hope is that aliens emit distinguishable signals. Hopefully we have sufficiently sensitive instruments to detect those signals just in case they are submitted.
We haven't waited long enough.
Everyone is listening no one is transmitting signals(?)
Berserker scenario: ETCs build devices akin to doomsday weapons that, you guessed, it go berserk( pose a threat even to its own creators) and prevent any civilization from arising and wipe out any existing ones.
Etcs don't want to communicate: because of some galactic agreement to not include earth in the club on the grounds that either we're not yet ready to contribute something valuable, or advanced civilizations don't interact with inferior creatures, or maybe etcs are just not curious or find the prospect of traveling long distances just not worth it. It's not likely that all the possible ETCs have opted to stay uninterested in any forms of life out there.