The whole universe is about 90 billion light-years in diameter. There are at least 100 billion galaxies, all with upwards up 100 billion stars each. For every grain of sand on Earth, there are 10,000 stars out there. If 5% of those stars are “sun-like”, meaning they are similar in size, temperature, etc. to that of the sun Earth orbits around, there would be 500 quintillion “sun-like” stars out there. If only 20% of those stars contain an “Earth-like” planet, then there would be 100 quintillion “Earth-like” planets or 100 planets capable of containing other intelligent life for every grain of sand in the world. In The Milky Way galaxy alone there are 100 billion stars, meaning there are 5 billion sun-like stars, 1 billion “Earth-like’ planets, and if only 0.1% of those have developed to contain life as advanced as Earth’s, there would be 1,000,000 intelligent civilizations in The Milky Way (Urban).What is a more fascinating idea? That there are millions or possibly billions of other intelligent life civilizations in the Milky Way right now or that Earth is all there is? What is the chance that there is other intelligent life in the universe? One man who tackled this unfathomable question was Frank Drake. He listed all the variables and their respective numbers that would need to be considered to determine this percentage. From this, he realized that if all the variables were multiplied together, the product would be the desired chance. The Drake Equation was born. The Drake Equation is N = R* x fp x ne x fl x fi x fc x L. N is the number of extraterrestrial civilizations in our galaxy. R* is the average rate of stars forming in The Milky Way. fp is the number of those stars that have planets orbiting them. ne  is the number of those planets that are Earth-like and could potentially support life. fl  is the number of those planets that actually can go on to support life. fi  is the number of planets in which that life would develop into an intelligent civilization. fc  is the number of those intelligent civilizations that can develop technology capable of sending messages into space. L is the length of time such signals take to reach Earth.    Even if there are other alien civilizations in other galaxies, there is very little chance humans will ever know about or encounter them due to dark energy, a mysterious force that causes the speeding up and expansion of the universe, anything outside of Earth’s “Local Group” is out of our reach forever. A planet’s Local Group includes its own galaxy and other nearby galaxies. Even with incredibly fast spaceships, the unfathomable speed of the expansion of the universe would cause these journeys to other galaxies to take billions of years.     Human’s best chance of encountering life would have to take place within The Milky Way galaxy. The Milky Way is roughly 13 billion years old and the first habitable planets were born 11 billion years ago. However, Earth is only 4 billion years old so there have been billions of chances for life to develop on other planets. More than likely, one of those planets would be far more developed than Earth, maybe even harnessing intergalactic travel. If only one of those civilization had developed such capabilities, humans would have noticed by now. What would such a civilization look like? Would they be similar to humans?    There are three categories of civilizations, which are grouped using “The Kardashev scale”, a method of measuring a civilization’s level of technological advancement. The scale was proposed by the Soviet Astronomer Nikolai Kardashev in 1964. A “Type I” civilization would be able to access all the energy available on its planet. The human civilization is currently rated at a 0.7 on the scale and it is estimated that it will reach Type I within the next 200 years. A “Type II” civilization is one capable of harnessing all the energy of its host star. This would be possible with a concept like the Dyson Sphere, a system of energy collection constructed around the host star. Some scientists theorize that alien civilizations are doing something similar to that of the sphere due to the massive amount of radiation in the universe with nowhere to trace it to, that radiation is known as dark matter. A “Type III” civilization is one that can control is whole galaxy’s energy. The feeble mind of even the brightest scientists in the world cannot begin to explain how such a thing would be possible.     Given the amount of sun-like stars, habitable planets orbiting those stars, and the considerably more time other civilizations have had to develop, that arises the question – Where is everybody?     Welcome to the Fermi Paradox where there is no answer, just possible explanations. One possible explanation is called “The Great Filter.” It theorizes that at some point in a civilization’s development there is a barrier which is almost impossible to overcome. They come in different degrees of terrifying. The three main theories within The Great Filter are about when exactly it occurs. Theory one is that it is behind us. This would explain why there are no other civilizations that we know of. It means that we would be one of the few exceptions that have made it to this point. But, what point have humans passed that was the one everyone else cannot get through? One possibility is that leap from semi-intelligent life (chimpanzees) to intelligent life (humans). Evolution is not inevitable, species are not forced to do it, it just happens. Steven Pinker best sums it up by saying:”Since evolution does not strive for a goal but just happens, it uses the adaptation most useful for a given ecological niche, and the fact that, on Earth, this led to technological intelligence only once so far may suggest that this outcome of natural selection is rare and hence by no means a certain development of the evolution of a tree of life.” Possibility Two is that the Great Filter is right are the beginning – it may be very hard for life to start at all. After Earth came into existence, there was a gap of billions of years before life happened. The process in which life begins has not yet been figured out and the conditions needed may be incredibly rare. If this is The Great Filter, it would mean that humans are unique and there is a high chance that there is no other intelligent life in the universe. The second theory is that humans are approaching The Great Filter. This is the most terrifying of the three theories. Life like ours may exist all around us in the universe but when it reaches a certain point of technological development, their civilization is destroyed. Three main examples of this would be nuclear war, climate change, and other future, unknown technology. Another thought is that there is a Type III civilization watching over us, like a god, and they destroy civilizations around them whenever they are too advanced. The third theory is simply that there is no other life in the entire universe. Its main argument is that the universe has been highly hostile since its beginning and only recently has it been calm enough for intelligent life to develop. Maybe humans are in a perfect time in which they can be the first intelligent species.     “The Great Filter” is wonderful at explaining why all other alien civilizations may have died off. What if there are other civilizations out there? What is stopping them from making contact on Earth?     Possibility 1 is that extraterrestrials have already visited Earth. The Earth is only 4.54 billion years old and recorded history only goes back as far as 5,000 years. Aliens could have visited the dinosaurs or ancient nomads and humans would have no way of knowing.  Many disputers of this possibility claim that it is based on pure assumption and there are no recent cases. However, recently many NASA astronauts have openly said UFOs have been seen and the evidence is kept a secret by the US government. However, the only real evidence that the public has seen is crop circles and sketchy UFO sightings. (COLLECTive evoluytin) Possibility 2 is that there is plenty of  “noise” out there, humans just aren’t advanced enough to understand it. Given how many other civilizations should be out there, chances are there are some just as developed or even more developed than humans so they should have the technology to send a message across the galaxy. However, it is not certain that their language or way of communicating is similar to that of humans. Michio Kaku best describes this by saying: “Let’s say we have an anthill in the middle of the forest. And right next to the anthill, they’re building a ten-lane super-highway. And the question is “Would the ants be able to understand what a ten-lane super-highway is? Would the ants be able to understand the technology and the intentions of the beings building the highway next to them?” Maybe humans are just ants compared to aliens.Possibility 3 is the “Zoo Hypothesis”. The Zoo Hypothesis is the belief that there is a super advanced civilization watching over us like a god. These alien civilizations would be so much superior to us that they are capable over overseeing Earth without the knowledge of humans. They could be waiting for humans to reach a certain itelligence point and then they will decide what to do with the planet.Possibility 4 is there are predator civilizations scaring other intelligent life from sending signals. Just like here on Earth, there are weaker civilizations and stronger ones. Why do civilizations take over one another? The answer to gain resources to increase their power. Extraterrestrial civilizations would work the same way. Other civilizations could be aware of these predator civilizations and could be avoiding sending out signals because they are scared of giving away their position.Possibility 5 is we are constantly being visited by extraterrestrials. This goes back earlier to what was mentioned about the constant sketchy sightings of  “UFOs”. What if these claims are not just make believe? As a population humans have not fully accessed anything higher than the third dimension. Type III civilizations could have accessed the 4th dimension or even higher and apply it to their daily lives. If they were operating in these higher dimensions, when they visit Earth, humans would not even be able to see them.

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