Alien Life

Can life be out there? What should we do if we find it?

Definition of life[]

A living organism is a piece of matter that has life. In order to be considered it has life, it must respect the following 5 laws. In the 19th century, people were arguing that also crystals are alive or even rocks are alive in a way we don't understand. So, by comparing an object with these 5 laws, we can say if it really is alive or not.

As one can see, some future artificial creatures might be able to be considered alive.

Law 1 - limited growth[]

Any living creature, if it has conditions, grows up to a specified limit. Beyond that, growth is very slow. Humans tend to grow up to 1.80 meters, bacteria grows to a specified limit, when it divides, animals (from worms to vertebrates) also grow to an adult size, then limit their growing.

The same rule works for plants. They grow up to a specified size. You will never see grain crops reaching 10 meters high or trees climbing to 1 km. The limit depends on conditions, in a denser forest plants will grow higher to reach light.

Law 2 - self reproduction[]

This is maybe the most interesting feature of life, to create new individuals that will look similar to their parents and will follow the same life cycle. Even in cases of worms (for example, some parasites have multiple hosts and many stages and a complex life cycle), each new individual is repeating parts of the same life cycle.

Mutations might appear, but those individuals will still have many common features with their parents. Differences between generations are so small that on a short time scale they can be ignored.

The self note is important. Parasites are able to self-reproduce, even if they are inside a host. This works even for parasites like malaria, that stay inside a cell. However, viruses are NOT able to multiply on their own. They will enter in another cell's nucleus and will simply be copied and assembled into copies by the cell itself. Also, prions are kept out of living organisms because of this.

This law is not respected by all individuals in a population, but the population, as an all, must be able to self-reproduce. For example, in an ant colony, only the queen and a few males are able to reproduce.

A population of castrated organisms is still alive, because they could reproduce if they were left alone. This is also true for a population of sub-age or overage organisms. Also, infertile individuals are alive.

Self reproduction can be achieved by cloning, perhaps an advanced Civilization would mate like this, only cloning perfect specimens, creating a race that only has features they want it to have. They would not be that resistant to a virus as a large amount of them would be the same, obviously having the same Genetic code. But still, they respect law 2, because they will have the power to self-reproduce, even with the help of technology.

In case of cyborgs or robots, as long as they can create new individuals with their own power and not by control of an external force (an advanced race), they respect law 2.

Law 3 - separation from the environment[]

Every living organism is separated from the surrounding environment. In case of a bacteria, the barrier is cellular membrane. In case of animals, that is the skin. This offers protection and keeps internal matter separated from surrounding matter.

Law 4 - biochemistry[]

A living organism must have biochemistry. This is marked by the presence of 3 small laws:

Chemical reactions. As long as the organism is alive (except for hibernation periods), molecules inside are transforming. Some sort of energy is used to keep chemical reactions going on.
Complex composition. Any living organism has complex molecules, with a more complex structure then the surrounding environment.
Exchange with surrounding environment. Any living organism is exchanging matter with surrounding environment. One note: Matter that enters has a different chemical structure then matter that exits the organism. This is what powers the carbon cycle on Earth, after all.

Law 5 - trying to stay alive[]

Any living organism, when facing a threat, is trying to find a solution, to survive. Unicellular organisms, when facing a poison in their environment, try to find a way to survive (this is why bacteria gets used to antibiotics). Animals try to migrate. If plants don't have enough light, they will try to grow higher. Without water, they will have longer roots.

This law is found at all living organisms. Just try to push a worm with a heated needle, it will instantly move away.

Sub-life[]

What if on a remote world we find something that does not respect all 5 laws? That could be considered sub-life. Even on Earth, we have something like that: viruses. It can be accepted as sub-life can miss one or two laws. An object that respects only one or two laws will not be accepted as sub-life. This is what keeps things like crystals or rocks away from sub-life but still allows some sub-organisms to be included.

Exception from law 1 (limited growth)[]

A sub-organism excepted from law 1 will grow unlimited. We can imagine a thing like a gray goo, growing forever, as long as it has conditions. When it no longer has what it needs, it will simply die. If it has a DNA, it must not be inside a central nucleus, but in many copies throughout the entire organism.

Exception from law 2 (self reproduction)[]

There are 3 types in theory: things that reproduce with help of others, sub-organisms that will not create similar descendants and sub-organisms unable to reproduce.

The self note is important. Parasites are able to self-reproduce, even if they are inside a host. This works even for parasites like malaria, that stay inside a cell. However, viruses are NOT able to multiply on their own. They will enter in another cell's nucleus and will simply be copied and assembled into copies by the cell itself. Also, prions are kept out of living organisms because of this.

If descendants will not look like their parents, things are getting interesting. They are degrading (and the sub-life species will soon parish) or they are evolving extremely fast. It might be dangerous for settlers to land on such a world. It might look like in sci-fi movies, where an alien bacteria becomes able to live inside a human body.

In the third scenario, where sub-organisms are unable to reproduce, they will simply die at some point. Please don't get confused. A population of castrated animals are alive, not sub-alive, because if they were left alone, they could be able to reproduce.

What kind of microorganisms have sub-life? Think about an organic soup, like what is supposed was the primitive Earth. At some point, with the help of a lighting, some sub-life creatures might be created, but are unable to make perfect copies of themselves. The first generations will be dramatically affected and at some point they will no longer be able to reproduce. In such an environment, sub-life is continuously (or from time to time) created, but is unable to sustain itself.

Exception from law 3 (separation)[]

For larger organisms, this might not look possible. However, we can imagine microorganisms doing that. We can think about a bacteria with no membrane. It will have a central DNA molecule. All other compounds should be hanging on that molecule. The sub-organism will be exposed to environment changes, so that it will require an extremely high stability from surrounding environment.

Exception from law 4 (biochemistry)[]

It is hard to imagine an organism that does not have biochemistry. The organism must keep continuous chemical reactions, it must have a complex internal composition and must sustain exchanges with surrounding environment. There is only one exception, hibernating organisms are excused.

In sci-fi movies, a replicant is an artificial creature, able to create endless copies of itself, a self-replicating robot. It will respect all laws, except that of biochemistry. Or will it? A replicant might keep going some chemical reactions, in order to transform materials into what they need to grow. They might be using a chemical engine (even it seems unlikely, more efficient would be a pocket-size fusion engine). A chemical battery might be useful, for limited energy crisis. A replicant will definitely have a complex internal composition, even if it will not be organic. It will also have some exchanges with surrounding environment, since it will need to eat to get energy and raw materials to grow. Unneeded materials can be excreted. So, could be a replicant alive? Depending on how much it respects from law 4, it can be alive or sub-alive.

Exception from law 5 (stay alive)[]

An advanced human civilization can create robots to be served of them. However, robots will remain the same as long as they will only execute their masters' will. They will be alive only when they will try to stay alive.

An organic sub-life that does not respect law 5, can also be imagined. Sub-organisms will not try to avoid dangers or to defend. For vertebrates, that is simply not imaginable. Just think at a dog allowing you to cut its head with a knife. It might be possible for some microbes.

Definition of intelligence life[]

Intelligence life can be defined by respecting a few laws. Please note that the borders of each law are not well defined.

Law 1 - central control[]

The intelligent organism must be able to control the vast majority of its movements, except for function of its inner organs.

A horse's movement is controlled 20% of its neural cortex and 80% of other neural structures.
A dog's movement is controlled 50% by the brain cortex and 50% by other neural structures.
A human's movement is controlled 80% by its neural cortex and only 20% of other neural structures.

What we humans don't control by our brain is limited: heart beating, respiration (partially), digestive functions and some reactions (for example, to move your body away from an intense heat).

Law 2 - complex thinking[]

A dog can be teached to count. You can make a dog bark four times when you hold four apples in your hand. However, it is impossible to teach a dog the multiplication board.

Law 3 - control above instincts[]

Animals are drawn by their instincts. There are 3 major instincts: nutrition, relation and reproduction. These are found also at humans, but a human has control above the instinct, while an animal does not. For example, a human can decide to go on a diet to improve health and lose weight, an animal will never do that on its own. A human can decide to change friendship relations anytime. And about reproduction, humans are able to protect themselves from getting pregnant, while animals need to be artificially castrated.

Law 4 - creativity[]

Humans are able to create things that are non-logical as seen from instincts. For example, a human can host paintings in its house only for decorative reasons. Animals build their homes because they need them. Animals do try to look better, to attract breeding partners. Humans get dressed and use make-up sometimes just for pleasure.

Law 5 - communication[]

Humans use a complex way to communicate. We are not speaking here about our language, but also about the many signs we use (like road signs, writing and body language). Animals do have some of these, but by far not as many as humans.

Frequency of alien life[]

Have we ever found alien life? The answer is no. So, we know nothing about alien life. It can be near us, in our solar system, or it can be found nowhere in our galaxy. Life on Earth has proven existence of maybe billions of species of life, but only two-three species of intelligent life. We could conclude that life might be found at some point, but intelligent life is something extremely rare.

What would alien life look like?[]

Majority of scientists think that life can exist, but intelligent life, if it exists, must be very rare.

Chemistry[]

We tend to think about something similar to Earth life. But is that the case? Life needs complicated molecular structures and there are not many elements able to support that. From all elements, only the 4th group (carbon, silicon, germanium) create complex molecules, since each one can be combined with other four atoms. The other elements in 4th group are metals: tin and lead, while the last one, flerovium, is a short-lived radioactive element. So, life will have a higher chance to be centered on these 3 elements: carbon, silicon or germanium. From all 3, carbon is the lightest. Its compounds are found as solids, liquids or gasses. Silicon oxide, for example, is sand. Carbon has a stronger chemical activity and is also lighter. So, life based on carbon is the most likely to be found. Silicon is also common in the universe, but germanium is more rare. It could be more rare (but not impossible) to see life based on other elements. Another possibility is to find life based on metals, some sort of robots. Could a metallic microbe exist? Interesting question.

Life would need an information storage device, something to organize its behavior. On Earth, this is solved by DNA molecules. Some people argued that alien life could use other things, like a crystal. However, the system will be massive and with low efficiency. Life without DNA could also be possible, but far less able to react to conditions of the surrounding environment.

Environment[]

We humans live in a specific environment. Conditions needed by alien life can be very strange. We look for a Habitable Zone with liquid water, but aliens might have other liquid materials. For example, in a cold environment, life can use liquid methane or even liquid oxygen. Unconventional metallic microbes might exist even in the hot environment of a very hot planet, with lava oceans. Life might be found in places with extremely high pressures, like a gas giant, but also on very low pressure bodies. When the first men walked on the moon, when returned, they stayed in quarantine, because scientists worried about possible contamination with possible lunar germs (later, it was proven that Luna is a dead body).

NASA sent probes into outer space and sometimes also germs with them. Surprising, when some probes returned, microbes also were found to be alive. Some people speculated that life on Earth was first brought from Mars, while others argue that it is possible for Earth microbes to have traveled to Mars via a meteorite before us. There is no way to prove this, but it looks interesting.

Life can be in different environments: on ground, in an underground ocean or deep inside caves. Life could exist in the atmosphere of a gas giant. Also, life can be brought to a place where it did not exist. Many Earth-like life forms can live on Mars.

How would they look like[]

There is no way to know. The most common form should be microbes. We can find them in the water (or whatever liquids exist there), in the ground or the air. We really have no way to know until we get there. Organisms might be like a carpet covering the ground. They could be like a mass of gelatin or hard like a rock. Their size can vary from a tiny microbe to a whole mountain. Some might be moving, some not. Some might have feet (we don't know how many), some will use other ways to travel.