Realizing how vast our Universe is, we can easily assume that somewhere in neighboring galaxies there is life too. Not necessarily reasonable, and certainly unlikely in everything to be identical with ours, earthly.
Who said that they are certainly gray and short humanoids with huge eyes, which are often shown to us in various science fiction films and series (as well as in popular science and pseudo-documentary films)?
Some scientists are 99% sure that by 2040 at most we will definitely discover this extraterrestrial life (well, or it will “discover” us - the main thing is that this does not happen exactly as it has been repeatedly shown to us in films about the mega-apocalypse caused by the attack of cruel aliens on our mother Earth).
As for the appearance of this life, so to speak, today there are at least 10 reasons to suppose that it does not at all resemble us:
10. Planets have different gravity
One of the most important variables that affect the evolution and appearance of living organisms on a hypothetical planet is gravity. It is thanks to her that all living things adapt to various environmental changes.
But far to go, let’s take the Earth as an example. Remember the theory of evolution: when the creatures that lived in the waters of the ancient world ocean first came to land, they had to grow limbs and develop a strong skeleton, because there was no more water around their bodies that compensated for the effects of Earth's gravity.
And if Earth's gravity were, for example, twice as large as the current one, then we would most likely be low, stocky and had thick bones. And vice versa: if it turned out to be half as much, then all the animals on our planet, including humans, would be taller, thinner and more elegant. Therefore, the appearance of inhabitants of unknown planets, we are unlikely to predict.
9. Planets have a different atmosphere
Another major factor for the emergence and development of any life form is the presence of the atmosphere and its composition.
So, for example, again, recalling the most ancient history of the Earth, we delve 300 million years ago. Then, in the Paleozoic (or rather, in its Carboniferous period), the oxygen concentration in the air on the planet was not 21%, as it is now, but as much as 35%. And at that time there lived creatures that were much larger than many of the current ones: meganeuvers (giant ancient dragonflies, whose wings reached 75 cm in size), brontoscorpio - huge 70-cm scorpions, arthropleura - 2.5-meter centipedes and other monster-like arthropods .
By the way, on Earth, scientists have discovered several dozen species of multicellular organisms, which in principle do not require oxygen for their existence. Then why can't life begin on planets that have a qualitatively different atmosphere or do not have it at all?
8. The basis of alien life may be other chemical elements.
Those who remember even the basics of organic chemistry are aware that carbon is always present in the composition of any organic compounds (and, therefore, in the organisms of all living things on Earth).
And biology experts will tell you that you still need water for life (which, as you know, consists of hydrogen and oxygen). Earthly living organisms also have DNA that stores genetic information and passes it on to future generations (the composition of which most of us also know).
But some very famous scientists (including Stephen Hawking and Karl Sagan) seriously argued that life, for example, silicon, could become the most likely and most representable alternative to earthly - "carbon" - life. And, of course, outwardly it will be very different from what we are used to (well, at least for the reason that silicon needs much higher temperatures than average Earth temperatures to achieve a reaction state).
7. Perhaps alien life does not need water
By the way, why not imagine that theoretically possible extraterrestrial beings do not need water for existence?
Yes, on Earth it is both a universal and very effective solvent, and a "transport mechanism", and a catalyst for chemical reactions, etc.
But suddenly, somewhere in the Universe, some other liquid is successfully replacing water?
So, scientists offer such versions of alien "water substitutes" as ammonia and liquid methane. For example, in several scientific articles prepared on the basis of the data accumulated by the Cassini US-European unmanned vehicle, it was stated that methane-based life could one day be discovered even on Titan, the largest of Saturn’s satellites. Moreover, both ammonia and methane can remain in a liquid state of aggregation when the water would have frozen for a long time.
Naturally, if life without water is still possible, then it will be completely different.
6. DNA Alternative
Until recently, it was believed that only DNA can store and transmit genetic data.
But about 10 years ago, an international group of scientists (from the USA, Great Britain, Belgium and Denmark) synthesized molecules that could become an alternative to DNA and RNA.
And in 2012, 6 so-called xenonucleic acids (XNA) were created, which quite successfully performed this task. Yes, and, in fact, all earthly life consists of various combinations of only 22 amino acids, while there are actually hundreds of them in nature (and these are only those that are formed naturally, apart from artificially created by scientists in scientific laboratories).
So why alien life could not be based on other amino acids and proteins, and other DNA variants?
5. What if an alien life lives in a different environment?
On our Earth, which has a very complex relief, 5 large biomes (ecosystems) with their variations and sub-variations are conventionally distinguished: tundra, steppe, forest-steppe, desert and the oceans.
And in each of them different creatures live, adapted to live in this particular environment and, most often, generally not able to survive in another (on the same planet!).
For example, living organisms that live in the depths of the ocean feel great in the cold and generally without light (besides under enormous pressure of water).
But in another ecosystem (on the surface), they will die immediately. And vice versa: bears do not survive underwater. Naturally, on a planet having a different relief, different lighting, surface temperature, etc., etc. life will definitely be fundamentally different from earthly life.
4. They may be significantly “older” than us
The age of our universe, according to scientists, is approximately 13.8 billion years. And if somewhere in distant (or even in neighboring) systems there are reasonable forms of life, this does not mean at all that they appeared at the same time when a person appeared on Earth.
It is likely that they were technologically highly developed even when terrestrial Australopithecus first guessed to grab the sticks and kill them with running past game.
Perhaps they explored space a couple of billion years ago, when eukaryotes (cells with a nucleus) just appeared on Earth. This means that during this time they (that is, intelligent aliens) could not only significantly evolve naturally, but also “adjust” and “correct” this process artificially: for example, adapt their own organisms for long space travels, increase life expectancy, get rid of “ uncomfortable restrictions ”(the need to eat, breathe, remove“ waste ”from the body, etc.) or to modernize them even more radically - with artificial parts, etc.
Why not? After all, we have also practically learned how to genetically change (in the direction we need) both plant seeds and animal embryos. Bioengineering is the future.
3. Life on wandering planets
Say what you like, but our planet is still very comfortable (in the sense - favorable for the existence of a diverse life on it). And most importantly, thanks to this, we need to say to our Sun: it is thanks to him that all life on Earth does not freeze, and plants also have the ability to photosynthesize (and thereby supply food to many animals).
If the Sun suddenly leaves us, then most of the terrestrial organisms will die out in a matter of days. But in fact, in the Universe there is a huge number of so-called "wandering" planets (there are about 200 billion of them in our galaxy alone). They do not have “their” stars, but simply fly through space.
And some scientists argue that life is possible on them, in theory (if only for it there is a suitable source of energy). For example, if the core of the planet turns out to be hot enough, then it can “heat” its surface.
A planetologist David Stevens suggested that if a wandering planet forms a very dense atmosphere, then it can not only store heat, but also maintain the seas in a liquid form. And there life may also be born.
2. Non-biological forms of existence
Re-read point 4. And if the inhabitants of distant planets may well be much “older” and more technologically advanced than us, then why should they not create any artificial, that is, non-biological, organisms by this moment?
For example, they could construct intelligent robots for a long time (or replace their biological bodies with mechanical ones for reasons of efficiency and convenience).
Yes, we ourselves are quickly approaching the creation of artificial life, thanks to the shocking progress of robotics, cybernetics and nanotechnology.
By the way, such famous people in the scientific world as Stephen Hawking and Elon Musk have long expressed serious concerns about artificial intelligence. Like, as if everything on our planet did not happen according to the script of the cult "Terminator", where the Skynet revolted, got out of control and destroyed humanity almost without exception.
Well, who will say for sure that extraterrestrial life cannot exist even without a “material carrier”, so to speak? And if the aliens are just some “energy entities” communicating through telepathy or some other unknown (and incomprehensible) to us methods and moving in space without special complex devices? Evolution is unpredictable ...
1. The factor of chance
And now back to where we actually started: why did we decide that intelligent life must necessarily be humanoid?
Once again: evolution is unpredictable. And if dinosaurs didn’t suddenly die out once, but develop (over millions of years) a humanoid intelligence? Or was it not humanoid apes that gained intelligence, but, for example, representatives of the cat family?
Well, well, we will limit the selection of “potentially intelligent” terrestrial creatures and imagine that dolphins or crows have “grown” to intelligence comparable to ours. In any case, the result would be a completely different civilization.
As for the huge (almost infinite) Universe, then life in it can evolve in the same infinitely many ways.
So there are chances that there are beings, somewhere at the other end of the Milky Way (or on the Alpha Centauri, in the Andromeda nebula, somewhere else in the expanses of space ...), creatures that are even very distantly similar to us - people, so small that hope for early contact with humanoids is almost pointless.