The first thing coming to mind on Alien Life are Intelligent Aliens but...

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Extraterrestrial Life

Extraterrestrial Life refers to life that is not present on Earth.

The first thing coming to mind would be aliens intelligent like humanity, but there are three broad categories of life.

Microbial life are microbes and unicellular organisms. Alien animals are an ideal kind of species but may not be as intelligent as humans. The rarest is Intelligent life which we refer to by the term 'Alien'.

Our galaxy The Milky way is 120,000 light-years wide. It feels strange that this unimaginably huge expanse of space has only one intelligent species in a pretty insignificatnt system of a star and planets located in a remote corner.

Research was conducted for finding any aliens, simulations rolled and probabilities calculated. One of the most popular works is the Drake's equation given by Frank Drake in 1961.

Drake's Equation

The parts of the equation are as follows -:

1. N - The number of active alien civilizations in our galaxy.
2. R* - The number of new stars created in our galaxy every year.
3. Fp - The fraction of such stars that have a system of planets.
4. Ne - The fraction of such planets that have the right conditions for life or have an ESI (Earth Similarity Index) of 8 and above.
5. Fl - The fraction of such planets where life develops.
6. Fin - The fraction of such kind of life that evolves into an intelligent species.
7. Fc - The fraction of such kind of intelligent species that develop radio technology. 
8. L - The lifespan of each civilization judged by the duration of radio transmission.

The answer? We have estimated that there are about 36 civilizations in our galaxy alone. This means we live with 35 other species in 120,000 light-years expanse.

But how do we talk to them? Radio Transmission.

This has two advantages. First, we can send our messages over long distances for aliens to receive and send another message to us. Secondly, radio transmission would make the conversation intact. 

Electromagnetic Spectrum (By Google)

If we were to send a message in light radiation, due to Doppler Effect (stretching of waves due to the present expansion of the universe) they would stretch and distort our message. Because radio waves are the longest Electromagnetic Waves, they cannot be stretched theoretically. So the message would remain intact.

Throughout our history, rulers projected their strengths and technology. Is there any scale where we can compare the theoretical technologies of aliens? Quantitive usage of energy can be a unit of measure. Hence, in 1964 Nikolai Kardashev created the Kardashev scale. 

The Kardashev scale shows the hierarchial Type of civilizations in terms of energy use. Kardashev originally thought of 3 types of civilizations.

1. Type 1 Civilization - This civilization, better known as a planetary civilization, is capable of harnessing energy in the form of natural sources all over the home planet. Technically, these types of civilizations have already found the solution for global warming.
2. Type 2 Civilization - Better known as stellar civilization, they can control and harness the energy of their parent star and other planets. This means they can alter the orbits of asteroids and comets, and shift the orbits of planets as much as they please. A fully functional Type 2 civilization would have already completed the biggest megastructure around their star: A Dyson sphere or a Dyson swarm.
3. Type 3 Civilization - This type of civilization is known as Galactic civilization. These species can control and harness the entire energy of their host galaxy. What makes them so strong is that not only they can go easily between stars and steal their mass for their uses, they can control the energy of supermassive black holes. This means they can understand dark matter, time travel and other cosmic phenomena. Basically, to any civilization of the galaxy, they are the ultimate gods.

Geoengineering - The kind of engineering that makes daily life machines and stuff in such a way and with such materials that the environment is not polluted. This idea is still hypothetical and is at the same stage as terraforming.

Terraforming - This is a hypothetical process that can change the composition of the atmosphere and surface of a bare planet.

Dyson Sphere and Dyson swarm - The Dyson Sphere is a sphere of a shell of materials orbiting the sun closer than the planets. But the material need to be fire and blast-resistant. Also, comets can nudge the sphere closer to the sun, making it vulnerable to burning. Instead, we can use a Dyson swarm. It is a series of energy-capturing satellites in orbit around the sun. The engineering would be cheap.

Coming back, Nikolai Kardashev did not add more types because the science and machines required for intergalactic travel are way beyond the current human capabilities and even our imagination. But to represent our civilization, which did not fit the scale and other civilizations, astronomers modified the scale.

• Type 0 Civilization - This species generates energy only through fossil fuels. Since humans have already constructed dams and windmills to get electricity, humanity today ranks as a Type 0.72 civilization.
• Type 4 Civilization - The civilization that can control its entire supercluster of galaxies is a Type 4 civilization.
• Type 5 Civilization - This civilization can control the entire universe. Hence, we can say they are our gods and the creators of our 93 billion light-years wide expanse.

Hope you readers have enjoyed the post and learned something new. 

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Aditya VN Kadiyala