Why haven't we found aliens yet?
A paper on Fermi's paradox makes you have to believe that we may never find aliens.
Image credit: Dior Lee/Vox.com
I remember when I was a kid, on a summer night, my mother and I recognized the twinkling stars, meteors, and planets in the night sky.
Suddenly, I saw a glowing object whose light fluctuated from light to dark, not flashing red like an airplane navigational lamp, and moving too slowly to resemble a meteor.
Obviously, it was an alien spaceship.
My excitement didn't last long, as my mom explained that it was sunlight reflected by a satellite as it orbited. I went to bed disappointed: "The X-Files" was running on TV, two episodes a week, directed by Chris Carter and others and starring David Duchonny, Gillian Anderson, and others. I'd love to find something that proves the story in The X-Files is true.
To this day, people are still willing to believe in the existence of extraterrestrial creatures. Hollywood movies and people's imaginations are all about it, and even scientists are hopeful about it. Around the beginning of the 20th century, shortly after the advent of radio technology, scientists began searching for extraterrestrial signals. Since the 1980s, teams of astronomers around the globe have been formally searching for extraterrestrial civilizations (SETI).
Yet the ongoing search seems to only prove the lack of life in the universe.
Now, a team of researchers at the University of Oxford has come up with a new perspective on the puzzle. In early June, Anders Sandberg, Eric Drexler, and Toby Odder of the Future of Humanity Institute (FHI) published a paper that might once and for all solve the Fermi paradox — the contradiction between our overestimate of the existence of foreign civilizations and the lack of relevant evidence.
Taking a completely new statistical approach, the paper re-asks the question, "Are we the only ones in the universe?" and concludes groundbreakingly: Not only may we Earthlings be the only intelligent beings in the Milky Way, but there's a roughly 50 percent chance that we're also the only ones in the entire observable universe.
This finding helps to think about the possibilities of extraterrestrial life, and they may be even more important for us to re-understand the risk of extinction that life on Earth may face in the near future.
Where are they?
One day in 1950, Enrico Fermi, a physicist working at Los Alamos National Laboratory, asked his classic question over lunch with colleagues: "Where are they [those aliens]?" ”
He has been pondering the question of why there is surprisingly little evidence of other life beyond Earth. In a universe that has been around for about 14 billion years and has bred more than 10 trillion stars, Fermi deduced that there must be other intelligent civilizations. So where are they?
We still don't have an answer to this question, and the Fermi paradox will only gain more support over time. Since the 1950s, humans have landed on the moon, launched probes into the outer solar system, and even put an electric sports car in orbit around the sun for fun. If we can go from rudimentary wooden tools to such superb engineering in less than 1 million years, then in this universe that has existed for 13.8 billion years, there should be a great chance that other civilizations will develop to a similar level, or even far beyond this level?
As their civilization expanded, there must have been some residual radio signals or visual cues that we observed.
How does this paper solve the Fermi Paradox in a different way?
The universe is so vast that it is not easy to accurately estimate the possibility of the existence of the Little Green Man (alien).
In 1961, astronomer Frank Drake proposed a formula that multiplied 7 "parameters" to estimate N, the number of civilizations that could be found in our galaxy at a given moment:
Image source: Xu Ming
The Drake equation is just a crude tool for scientifically calculating the possibility of extraterrestrial life. However, in the absence of other better methods, it is still the only way for astronomers to calculate the possibilities of extraterrestrial intelligent life. This formula is difficult to come up with with a definitive result, because while some of these parameters, such as R*—the number of new stars forming each year—are relatively clear, there is still huge uncertainty in the selection of other parameters.
Take L as an example, which represents the average lifetime of a detectable civilization. Looking back at the average length of Earth civilizations in the past, it is not too much to conclude a very low hypothesis. And if you refer to the history of the Romans, Incas, or Egyptians, the value of this parameter seems to be hundreds of years at most. But on the other hand, if a civilization could develop to the point where it could travel interstellarly, you would think that its lifespan would last at least billions of years.
Such great uncertainty makes the outcome of the Drake equation ultimately depend on whether the people who use it are optimistic or pessimistic. This is also why the N values obtained in the papers of predecessors range from 10 to billions.
As astronomer Gil Tate, one of SETI's founders, relentlessly pointed out in a 2000 interview with National Geographic: "The magic of Drake's equations is computing on things we can't know for sure."
To overcome this uncertainty, people try to pick different estimates for each parameter, some conservative, some optimistic, and some some in between, and then take their averages.
However, FHI researchers questioned this approach in their paper titled "Solving the Fermi Paradox." In the paper, they demonstrated how assigning a parameter value in this way could yield an N value that was too high, and thus mistakenly thought that the paradox was correct.
This is because simply and crudely selecting some estimation points and cramming them into the Drake equation does not weigh our different views on each parameter very well. For example, suppose three scientists have different views on the valuation of L:
Illustration: A scientist believes: "L is between 1 and 10"
Scientist B believes that "L is between 10 and 100"
Scientist C believes that "L is between 100 and 1000"
If you take a basic linear average of all possible integer values from 1 to 1000, it means that the opinion of scientist C will have 90 times the effect of scientist A, because in his range of values, the number of possible integer values is 90 times that of scientist A. If you use a logarithmic scale, a nonlinear measurement scale, based on orders of magnitude, the quotient between each scale is a certain value, when there is a large range of differences in quantity. Let each scientist's range of opinions correspond to an order of magnitude, then these three views will be treated more equally.
So the researchers converted all the estimates to a logarithmic scale and performed millions of simulations to obtain a statistically more reliable N value. They then analyzed these results using bayesian methods, which mathematically included in the calculations information that we had not yet discovered extraterrestrial intelligent beings (because the evidence that no aliens existed was itself evidence!).
After these two stages of computational analysis they came up with amazing results: based on the knowledge of astrobiology that we have so far, 53% to 99.6% of us may be the only civilization in the Milky Way, and 39% to 85% may be the only civilization in the observable universe.
This means that life is so incredibly rare. Even if there are other intelligent beings, they may be far beyond our cosmic horizon, so we will never see them.
But life shouldn't be so rare, should it?
To be clear, the authors of the paper do not seem to explicitly assert the existence of aliens; However, with the information we currently have about these seven parameters, we are likely to be the only ones in the universe. As we have more information, this new information will correspondingly change the likelihood of alien existence. For example, if we observe a comet or other planet having another process of generating primary life from non-living matter, the uncertainty of the fl parameter will be greatly reduced.
Despite the lack of a definitive conclusion, their findings caused a stir without suspense, especially as SpaceX CEO Elon Musk tweeted about it:
That's why we have to become space civilizations and extend our lives to other planets in order to preserve the seeds of human intelligence.
— Elon Musk (@elonmusk), June 25, 2018
Many people think that this paper is the result of "anthropocentrism" and "narrow thinking", and in their view, anyone who thinks that we earthlings are somehow special is nothing more than human arrogance.
This is understandable to some extent, because the idea that intelligent life is extremely rare in the universe is completely counterintuitive. Since we humans are real, and some other intelligent life such as dolphins and octopuses are also real, in the same way, life that can exist on earth must also exist outside the earth.
But this alone does not prove that intelligent civilizations are everywhere. Whether it's a one-in-two true probability or a tiny one in 1036, just being able to be soberly aware of the problem and ask ourselves back means that life has successfully originated.
This phenomenon is known as the observer selection effect – because the observer's observation of the likelihood of an event itself affects his judgment of the event, resulting in an observational bias. Since we have only one data point (ourselves), we don't have a reliable way to predict the true likelihood of intelligent life. The only conclusion we can confidently draw is that it (extraterrestrial intelligence) could exist.
If we really are the only one in the universe, is this good news or bad news?
We may exist alone in the universe, and whether you agree with it or not, you will have to face serious scientific and philosophical problems that arise from it. Should we feel extremely fortunate about this? Or should I be disappointed? If humans are the only conscious and thinking entities in the universe, what does this mean for us?
This last question is extremely important. Not only because we are consuming natural resources at a high rate that disrupts the ecological balance, but also because for the first time in human history, our technology has reached such a height, and whether the whole of humanity can have a future depends entirely on ourselves. The nuclear weapons we have built in a few years are enough to kill everyone on the planet many times, and we have placed them under the willful control of our leaders, threatening to erupt. In each decade we have developed new technologies that have brought great benefits as well as great disruption.
As the New Year's bell rings, the Bulletin of Atomic Scientists sets the Doomsday Clock to the closest to midnight. At the same time, estimates by numerous survival risk experts suggest that by the end of the century, the probability of complete extinction is between 5% and 19% – because the stakes are for the survival of human beings, which is too great to accept.
This dark gamble affects not only the 7 billion people who are alive today, but also the chances of survival for tens of billions of people in the future. It is clear that, if we are responsible for the future, there is an urgent need for joint action.
As Carl Sagan famously said in his 1990 speech on Pale Blue Dot: "In this vast expanse of space, no savior will come down from the sky to save us from the predicament we have set ourselves." Earth is the only known world to nurture life. ...... The earth is where we stand. ”
He was right, especially given the paper's conclusions. If humanity is really the only civilization that can exist in the universe, then we are truly shouldering the responsibility of the cosmic scale.
BY: Liv Boeree
FY: Renee
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