The Fermi Paradox refers to the dichotomy between the high probability that extraterrestrial intelligence exists and the fact that we have no evidence for such aliens. This paradox was described by the late British science-fiction author, Sir Arthur C. Clarke, who said: "Two possibilities exist: Either we are alone in the universe or we are not. Both are equally terrifying."
Many experts since have grappled with the same question. Why, considering the multitude of planets and stars in the Milky Way, have we not heard from anyone?We call this problem the Fermi Paradox, and there are a number of possible solutions — some more unnerving than others.
The Fermi Paradox is a problem that asks, where are all the aliens(opens in new tab) in the universe? If life is so abundant, why haven't we been visited by, or heard from, anyone else? According to NASA(opens in new tab), in just the last two decades we have found more than 4,000 planets beyond our solar system, with trillions of stars thought to exist in our galaxy — most of which host their own planets.
Considering life sprang up on Earth, would we not have expected it to start in at least one other location in the last 14 billion years of the universe?
The Drake equation is an idea, proposed by the American astronomer Frank Drake in 1961, that the number of potential civilizations in the universe can be calculated if we know a few key variables. The formula for the Drake equation is: N = R* x ƒp x ne x ƒ1 x ƒi x ƒc x L R* = average rate of star formation in Milky Way ƒp = fraction of stars supporting planets ne = average number of planets that could potentially support life for each star that hosts planets ƒ1 = fraction of those planets that "could" support life that actually develop life ƒi = fraction of planets that develop intelligent life, and thus intelligent civilizations ƒc = fraction of those civilizations that develop a technology to communicate their existence L = length of time over which these civilizations send those detectable signals into space.
By including all of these factors in the equation, the idea is you might be able to work out how many other intelligent civilizations exist in the universe. This "simple" formula, Drake once said, would be akin to estimating the number of students at a university by multiplying the number of new students entering each year by the average number of years a student will spend at a university, according to SETI.
As of yet, however, a number of key variables in the equation remain unknown, meaning we can't yet come up with a possible number for other species of intelligent life.
Simply stated, the Great Filter says that intelligent interstellar lifeforms must first take many critical steps, and at least one of these steps must be highly improbable. Indeed, the premise of the Great Filter is that there's at least one hurdle that is so high virtually no species can clear it and move on to the next.
In 1964, Kardashev came up with the idea that the status of a culture, as a whole, depends on two primary things: Energy and technology. He theorized that a civilization's technical advancement runs parallel to the amount of energy that the civilization is able to harness and manipulate. Essentially, the more energy that a society can produce, the more technologically advanced they are (this was originally just tied to energy available for communications, but has since been expanded).
In other words, according to this theory, a culture's development (in the very widest sense) is a product of energy and of technology: Through technology, energy is harnessed, and as social systems are expressions of this technology, the status of a culture rests upon (and is determined by) the amount of energy that is harnessed. The scale has a number of different categories (levels of classification).
In recent years, scientists have expanded this scale to measure hypothetical civilizations—civilizations that are galactic, intergalactic, and even multiverse in nature.