There is a dichotomy between the high probability of extraterrestrial intelligence and the fact that there is no evidence for it.
The British science-fiction author, Sir Arthur C. Clark, said that there were two possibilities, either we are alone in the universe or we are not. Both are frightening.
Many experts have wrestled with the same question. The problem of the Fermi Paradox is that we haven't heard from anyone, even though there are many planets and stars in the Milky Way.
What is the truth behind the Roswell incident?
The question of where all the aliens are in the universe is called the Fermi Paradox. If life is so abundant, why haven't we been contacted by anyone else?
In the last two decades, NASA has found more than 4,000 planets beyond our solar system, with trillions of stars thought to exist in our galaxy.
Considering life sprang up on Earth, would we not have expected it to start somewhere else in the last 14 billion years of the universe?
Who came up with the idea of the Fermi Paradox?
The scientist in his lab is Enrico Fermi. The image is courtesy of Corbis.
According to the Planetary Society, the Italian-American physicist Enrico Fermi created the Fermi Paradox. He is said to have come up with the idea when he asked where everyone was at lunch in 1950.
He wondered if we would have expected someone to visit us by now, since our planet was relatively young compared to the universe.
After Fermi died four years later, there was not much time to ponder the question. His idea has led to the search for extraterrestrial intelligence.
What are the solutions to the problem?
Are we alone in the universe? Scientists are hoping to find the answer. An illustration of an alien planet. The image was taken by MEHAU KULYK.
There are many solutions to the problem. It's obvious that we haven't looked hard enough to find other life, and that it's difficult to travel between stars.
The first planets outside our solar system were discovered in the 1990s. We have barely begun to study other worlds.
Upcoming telescopes are expected to be able to detect planets that look like Earth, but are actually planets that are outside the solar system.
The distances between star systems are large, making it difficult to travel between them. Alpha Centauri is four light-years away. The journey from Earth to Neptune would take decades with current technology.
It is possible that intelligent aliens did not visit us or did not leave any trace.
It is possible that life is so rare that the chances of two intelligent species being positioned relatively near each other is very slim.
There is a suggestion that we are alone in the universe. Our world was the only one where life was so rare that it happened.
Most scientists don't think this is possible. There is a chance that a Great Filter might prevent civilizations from progressing far enough to make contact elsewhere.
What is the Great Filter?
The idea of the Great Filter is that catastrophic events, either natural or man-made, will cause intelligent life to be extinguished on worlds that are not in the solar system.
There are many things that these events could be. They could be solar flares, climate change, asteroid impacts, or something of the planet's own doing like a nuclear apocalypse.
It's not clear if we have already passed this filter or not.
What is the Drake equation?
Frank Drake proposed the Drake equation in 1961, which is an idea 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 used.
R* x fp x ne x f1 x fi
Average rate of star formation in the universe.
The fraction of stars supporting planets is called fp.
The number of planets that could potentially support life for each star is calculated.
The fraction of planets that could support life.
A fraction of planets have intelligent life.
The fraction of civilizations that have developed a technology to communicate their existence.
L is the length of time that these civilizations send signals into space.
The idea is that by including all of these factors in the equation, you might be able to figure out how many other intelligent civilizations exist in the universe.
Drake once said that this formula would be similar to estimating the number of students at a university by dividing the number of new students entering each year by the average number of years a student will spend there.
A number of key variables in the equation remain unknown, meaning we can't yet come up with a number for other species of intelligent life.
Can we find a solution to the Fermi Paradox?
An artist's conception of a telescope. The image is from NASA GSFC/CIL.
Many scientists hope that we can solve the problem. NASA's James Webb Space Telescope will be launched in December 2021, and will be able to study the atmospheres of exoplanets like never before.
By finding more planets in the right places around their stars, where temperatures are right for liquid water to exist, scientists could narrow down the possibility of other Earth-like worlds in the universe.
Scientists need more data in order to understand the Fermi Paradox. It might suggest that intelligent life is rare if it turns out that there are many habitable planets.
Are we alone in the universe?
Scientists hope to answer the question of if we are alone in the universe in the coming years.
NASA's Perseverance rover on Mars could give us vital clues. Perseverance is collecting samples that will be returned to Earth in the 20th century and could contain signs of past or present life on Mars.
If we can discover simple life on Mars or another planet like Jupiter or Enceladus, that would be proof that life existed in at least two places.
It would suggest life is not limited to our planet. It would raise the possibility of intelligent life in our universe.
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