Given the size of the universe, there are good reasons to assume the existence of life outside of the earth. And some scientists strongly believe it will be discovered by 2040. But what do intelligent extraterrestrial life forms really look like (if they really exist)?
For decades, science fiction has described aliens to us as short, gray humanoids with large heads and generally not much different from the human species. However, there are at least ten good reasons to believe that intelligent extraterrestrial life is not at all like us.
The planets have different gravity
Gravity is a key factor in the development of all organisms. In addition to limiting the size of land animals, gravity is also the reason organisms can adapt to various environmental changes. You don't have to go far for examples.
All the evidence is in front of us on Earth. According to evolutionary history, organisms that once decided to emerge from water onto land had to develop limbs and complex skeletons as their bodies were no longer supported by the fluidity of water that compensated for the effects of gravity.
And although there is a certain range of how strong gravity can be in order to simultaneously support the planet's atmosphere and at the same time not crush everything else on its surface, this range can vary, and, therefore, the appearance of organisms that have adapted to her (gravity).
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Suppose the Earth's gravity is twice as strong as it is today. This, of course, does not mean that all complex living organisms will look like dwarf tortoise-like creatures, but the likelihood of bipedal bipedal people will be sharply reduced.
Even if we can maintain the mechanics of our movement, we will become much shorter and at the same time will have denser and thicker bones of the skeleton, which will allow us to compensate for the increased force of gravity.
If the force of gravity is two times lower than the current level, then, most likely, the opposite effect will occur. Terrestrial animals no longer need powerful muscles and a strong skeleton. In general, everyone will get taller and bigger.
We can endlessly theorize about the general characteristics and consequences of the presence of high and low gravity, but we are not yet able to predict the finer details of the organism's adaptation to certain conditions.
However, this fitness will definitely be traced in extraterrestrial life (if, of course, we find it).
The planets have different atmospheres
Like gravity, the atmosphere also plays a key role in the development of life and its characteristics.
For example, arthropods that lived during the Carboniferous period of the Paleozoic era (about 300 million years ago) were much larger than modern representatives. And all this is due to the higher concentration of oxygen in the air, which was up to 35 percent, compared to 21 percent, which is now.
Some of the species of living organisms of that time, for example, are mega-neuras (ancestors of dragonflies), whose wingspan reached 75 centimeters, or the extinct species of giant scorpions, brontoscorpio, whose length reached 70 centimeters, not to mention arthropleura, giant relatives of modern millipedes. whose body length reached 2.6 meters.
If a 14 percent difference in the composition of the atmosphere has such a high impact on the size of arthropods, then imagine what unique creatures can be obtained if these differences in the volume of oxygen are much more significant.
But we have not even touched upon the question of the possibility of the existence of life, which does not require oxygen at all. All this gives us limitless possibilities of guessing what this life might look like.
Interestingly, scientists have already discovered on Earth some types of multicellular organisms that do not require oxygen to exist, so the possibility of extraterrestrial life on planets without oxygen does not seem as crazy as it seemed before. Life on such planets will definitely be different from us.
Other chemical elements may serve as the basis for extraterrestrial life
All life on Earth has three identical biochemical characteristics: one of its main sources is carbon, it needs water, and it has DNA that allows it to transmit genetic information to future offspring.
However, it would be a misconception to assume that all other possible life in the universe will follow the same rules. On the contrary, it can exist according to completely different principles.
The importance of carbon for all living organisms on Earth can be explained. First, carbon easily forms bonds with other atoms, it is relatively stable, available in large volumes, and complex biological molecules, which are required for the development of complex organisms, can appear on its basis.
However, the most likely alternative to the basic element of life is silicon. Scientists, including the famous Stephen Hawking and Carl Sagan, have discussed this possibility. Sagan even coined the term "carbon chauvinism" to describe our preconceptions that carbon is an integral part of life anywhere in the universe.
If silicon-based life really exists somewhere, then it will look completely different from what life on Earth looks like. If only because silicon requires much higher temperatures to reach the reaction state.
Extraterrestrial life doesn't need water
As stated above, water is another essential requirement for life on Earth.
Water is necessary because it can be in a liquid state even at a large temperature difference, it is an effective solvent, serves as a transport mechanism and is a trigger for various chemical reactions.
But this does not mean that other liquids cannot replace it anywhere in the Universe. The most likely substitute for water as a source of life is liquid ammonia, as it shares many qualities with it.
Another possible alternative to water is liquid methane. Several scientific articles, based on information gathered by NASA's Cassini spacecraft, suggest that methane-based life may exist even within our solar system. Namely, on one of Saturn's moons - Titan.
In addition to the fact that ammonia and methane are completely different substances that can nevertheless be present in water, scientists have proven that the two substances can be in a liquid state even at lower temperatures than water. Given this, it can be assumed that life not based on water would look completely different.
Alternative to DNA
The third key puzzle of life on Earth is how genetic information is stored. For a very long time, scientists believed that only DNA was capable of this. However, it turned out that there are alternative storage methods.
Moreover, it is a proven fact. Scientists have recently created an artificial alternative to DNA, XNA (xenonucleic acid). Like DNA, XNA is capable of storing and transmitting genetic information during evolution.
In addition to having an alternative to DNA, extraterrestrial life is likely to produce other types of proteins (proteins) as well. All life on Earth uses a combination of only 22 amino acids to make proteins, but there are hundreds of other naturally occurring amino acids in nature, in addition to those we can create in laboratories.
Therefore, extraterrestrial life not only can have "its own version of DNA", but also other amino acids for the production of other proteins.
Extraterrestrial life evolved in a different habitat
While the planet's environment can be constant and versatile, it can and vary greatly depending on the characteristics of the planet's surface.
This, in turn, can lead to the formation of completely different habitats with specific unique characteristics.
Such variations can cause the emergence of different paths for the development of life on the planet. Based on this, five main biomes (ecosystems, if you will) can be distinguished on Earth. These are: tundra (and its variation), steppes (and their variation), deserts (and their variations), water and forest-steppe (and their variation).
Each of these ecosystems is home to living organisms that had to adapt to certain environmental conditions in order to survive. Moreover, these organisms are very different from living organisms in other biomes.
The creatures of the deep oceans, for example, have several adaptive features that allow them to survive in cold water, without any source of light and still under high pressure. These organisms are not only not at all just unlike humans, they are unable to survive in our terrestrial habitats.
Based on all this, it is logical to assume that extraterrestrial life will not only radically differ from terrestrial life according to the general characteristics of the planet's environment, but it will also differ according to each biome on the planet.
Even on Earth, some of the smartest living organisms - dolphins and octopuses - do not live in the same habitat as humans.
They may be older than us
If we believe the opinion according to which intelligent extraterrestrial life forms can be more technologically advanced than the human race, then we could safely assume that these intelligent extraterrestrial life forms appeared before us.
This assumption becomes even more probable if we consider that life as such in the entire Universe did not appear and develop at the same time. Even a difference of 100,000 years is nothing compared to billions of years.
In other words, all of this means that extraterrestrial civilizations not only had more time to develop, but also more time for controlled evolution - a process that allows you to technologically change their own bodies depending on needs, instead of waiting for the natural course of evolution.
For example, such forms of extraterrestrial intelligent life could adapt their bodies for long space travel, by increasing their lifespan and eliminating other biological restrictions and needs, such as breathing and the need for food.
This kind of bioengineering could definitely lead to a very peculiar state of the body's body, and perhaps even led extraterrestrial life to replace their natural body parts with artificial ones.
If you think that all this sounds a little crazy, then know - humanity is moving towards the same thing. One striking example of this is that we are on the verge of creating “ideal people”. Through bioengineering, we will be able to genetically alter embryos to acquire certain skills and characteristics of the future human, such as, for example, intelligence and growth.
Life on wandering planets
The sun is a very important factor in the existence of life on Earth. Without it, plants will not have the ability to photosynthesize, which will ultimately lead to the complete destruction of the food chain.
Most life forms will die out within a few weeks. But we are not yet talking about one simple fact - without solar heat, the Earth will be covered with ice.
Fortunately, the Sun is not going to leave us in the near future. Nevertheless, in our own Milky Way galaxy alone, there are about 200 billion "rogue planets". These planets do not revolve around the stars, but only senselessly float through the impenetrable darkness of space.
Could life exist on such planets? Scientists put forward theories that under certain conditions, this is possible. The most important thing in this matter is what will be the source of energy for these planets?
The most obvious and logical answer to this question may be the heat of your internal "engine", that is, the core. On Earth, internal heat is responsible for the movement of tectonic plates and volcanic activity. While this is likely to be far from sufficient for the development of complex life forms, there are other factors to consider as well.
One theory was proposed by planetary scientist David Stevenson, according to which rogue planets with a very dense and thick atmosphere could trap heat, which would allow the planet to keep the oceans in a liquid state.
On such a planet, life could evolve to a fairly advanced level, similar to our ocean life, and perhaps even begin the transition from water to land.
Non-biological life forms
Another possibility that should also be considered is that extraterrestrial life may be non-biological forms. These can be both robots, which were created to replace biological bodies with artificial ones, and species created artificially by other species.
Seth Shostak, head of the program for the search for extraterrestrial civilizations (SETI), even believes that such an artificial life is more than likely, and humanity itself, thanks to the development of robotics, cybernetics and nanotechnology, will sooner or later come to this.
Moreover, we got as close as possible to the creation of artificial intelligence and advanced robotics. Who can say with certainty that humanity will not be replaced by robust robotic bodies at some point in its history?
This transition is likely to be very painful. And such famous figures as Stephen Hawking and Elon Musk already realize this and believe that in the end, the AI created can simply rise up and take our place.
In this case, robots can only be the tip of the iceberg. What if extraterrestrial life exists in the form of energetic entities? After all, this assumption also has some ground under it.
Such life forms will not be constrained by any restrictions of physical bodies and ultimately, theoretically, will also be able to come to the aforementioned physical robotic shells. Energy entities, of course, without a doubt, will not at all look like people, since they will lack a physical form and, as a result, a completely different form of communication.
The random factor
Even after discussing all the possible factors described above, one should not rule out randomness in evolution. As far as we (humanity) know, there are no prerequisites to believe that any intelligent life must necessarily develop in the form of humanoid forms.
What would have happened if dinosaurs hadn't become extinct? Would a humanoid intellect develop in them in the process of further evolution? What would happen if a completely different species evolved into the most intelligent form of life on Earth instead of us?
For the sake of fairness, it might be worth limiting the sample of potential candidates for the possibility of development among all animal species to birds and mammals. Even so, however, there remain a myriad of possible species that could evolve to a level of intelligence comparable to that of a human.
Representatives of their species, such as dolphins and crows, are indeed very intelligent creatures, and if evolution at some point turned to face them, then it is quite possible that they were the rulers of the Earth instead of us.
The most important aspect is that life can develop in a variety of (almost endless) ways, so the chances that there is intelligent life in other parts of the Universe, very similar to us humans, are astronomically very low.