A theory proposed by Enrico Fermi, an Italian-American physicist, suggests the apparent lack of evidence for extraterrestrial civilizations elsewhere in the Milky Way galaxy despite the high probability of these existing is paradoxical.

Basic Hypotheses

These hypotheses demonstrate how weird it is that we haven’t been visited by other life forms yet.

• Multitude of Stars – There are billions of stars in the galaxy that are similar to the Sun and many of these are way older than the sun
• High numbers – Because there are so many, there is a higher chance some of these stars have Earth-like planets
• Wiser Civilizations – Because these planets are much older than Earth, the civilizations may have developed interstellar travel

Based on these logic-based hypotheses, Earth should have already been visited by some form of extraterrestrial civilization by now.

The Kardashev Scale

The Kardashev scale is a method of measuring a civilization’s technological advancement. This is done by categorizing civilizations into 3 categories, based on the amount of energy they are able to use.

• Type I civilization – this type of civilization can use and store all of its planet’s energy. We are not quite there yet, but we are slowly getting closer (we’re roughly at 0.7)
• Type II civilization – this type of civilization would be able to store and use all of their host star’s energy
• Type III civilization – this incredibly advanced civilization would be able to access such power comparable to that of the entire Milky Way galaxy

Although these civilizations’ energy resources sound hard to believe, you must keep in mind they got roughly 3.4 billion years more than what we got. In 3.4 billion years, we might achieve such levels of greatness… If we don’t extinguish ourselves.

The Fermi Paradox

So, if there were Type III civilizations in the universe, or civilization advanced enough to have figured out interstellar travel… Where is everybody?

All we can do for now is suggest a series of possible hypotheses, and explanations, based on the information we have. However, in this article, we are going to explain the main ones, as well as the most interesting ones.

There are no signs of higher civilizations because there are no higher civilizations

Mathematically, this hypothesis makes no sense, as there are supposed to be so many higher civilizations that even if 99.9% of all of these did not come into contact with us, we would still have met the other 0.1% by now. This must have been caused by something else. This something else is known as The Great Filter.

This sets an imaginary filter that causes civilizations to die out whenever they try to acquire a major evolutionary leap. The situations are the following:

• We are rare – we have already passed this great filter and it is, therefore, behind us
• We are unique – we are the first civilization to have ever passed this filter. This would explain the absence of other life forms visiting us
• We are not there yet – the great filter is ahead of us and it’s going to exterminate us

The Type II and Type III civilizations are out there but there are logical reasons why we have not heard from them

• We were not here when they visited – humans have been around for roughly 50,000 years, which is very little, compared to Earth’s total lifespan
• Our galaxy has already been colonized but we are in some rural area of the galaxy – we might be so distant from the galaxy’s urban zone that there is no alien influence here
• Aliens stopped thinking about colonizing and are just enjoying themselves – why bother searching the emptiness of the universe if you are living a utopia? Makes sense
• We might be too primitive to perceive them – our intelligence may be proportional to ants compared to theirs. Even if they tried to communicate we wouldn’t understand
• We are in a simulation  – read more here

Conclusion

This article is very intense, but it gives you an idea of what the Fermi Paradox is, as well as all of its related theories. It gives some simple rational motivations for why we haven’t met aliens yet. 

Sources: www.waitbutwhy.com, islandone.org, wikipedi.com, seti.org

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There are an estimated 100 billion in our galaxy alone; considering the fact that there are about 10 trillion galaxies in the universe, that adds up to a total of 1,000,000,000,000,000,000,000,000 stars. We know they did not just appear out nowhere, so how did they form?

Initial Ingredients

Just like many things in the universe, stars start as really small. In this primordial state, they are just particles floating around in vast clouds of dust and gas. 

These nebulae remain cold for an uncertain amount of time and then stir up. This is due to the disturbance generated from a streaking comet or the shockwave from a distant supernova. These forces move the cloud particles, making them move faster and collide more often. These particles then form groups which then grow more mass, therefore increasing the gravitational pull.

Growth

As the primordial star gains more mass, for about one million years, its center becomes denser and hotter. This group of particles then grows into a small but dense body called a protostar. This keeps on gaining mass, as its gravitational pull increases. 

When the protostar becomes hot enough, it starts an atomic reaction, called nuclear fusion. Its hydrogen atoms start fusing, producing helium as a consequence, as well as an outflow of energy. 

However, to be able to contrast the now increasing inward gravitational pull, the star still needs more outward energy. 

Stabilization

Finally, after millions of years, the star stabilizes. This happens when enough mass collapses into the protostar and bipolar flow occurs. Bipolar flow is when two massive gas jets erupt from the protostar, blasting the remaining gas and dust away from its surface. Once the star stabilizes, it reaches a point where its output exceeds its intake, meaning the outward pressure from the nuclear hydrogen fusion fully overcomes gravity’s inward pull.

Death

The star will stay roughly the same until it will run out of fuel. The lifespan of a star depends on its mass. A sun sized star would take about 10 billion years to die out.

Conclusion

Stars are definitely something particularly astonishing. Their lifespans’ steps look simple, yet they take billions of years to take place. 

Sources: wikipedia.com, www.universetoday.com, science.howstuffworks.com, nasa.com

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