Scientists have some ideas about why we haven’t found aliens yet. They think there are two possibilities: either there’s a lot of life in the Universe, or almost none at all. A study published in the International Journal of Astrobiology gives some reasons for this mystery. Scientists searching for aliens believe that there should be many advanced civilizations out there besides ours. They used math and logic, based on the work of John Haldane, to explain why we haven’t found any extraterrestrial civilizations yet. Imagine a group of planets like Earth. You’d expect life to appear on all of them or none of them. There’s no clear reason why only half of these planets would have life. This idea can be shown on a U-shaped graph: on one side, there’s a high chance that no planets have life, and on the other, a high chance that many do. In the middle, there’s a low chance that only some planets have life. The two lines of the U-shaped curve correspond to either no life on any planet, or life on a small number of planets, and life on a large number of planets. Between the lines is the so-called valley, which corresponds to low probability and represents half of the planets with life. (Image credit: David Kipping/Geraint Lewis) The Drake Equation: What Is It? Scientists used Haldane’s logic to change the famous Drake equation. Astronomer Frank Drake made this equation to guess how many alien civilizations might be in the Milky Way. The Drake equation looks like this: N = R* x fp x ne x fl x fi x fc x L N is the number of civilizations. R* is the rate of star formation. fp is the number of stars with planets. ne is the number of planets that could support life. fl is the number of planets where life actually develops. fi is the number of planets where intelligent life develops. fc is the number of planets where intelligent life exists and tries to communicate. L is how long these civilizations last. Astronomers know a lot about star formation and how many stars have planets, but they’re less sure about the number of planets that could support life. The rest of the equation is still a mystery, so scientists have to guess. The study’s authors say the first six parts of the Drake equation talk about how alien civilizations might be born. The last part, L, talks about when these civilizations might disappear. A New Formula for Counting Alien Civilizations By splitting up the parts of the Drake equation, scientists found a simpler way to look at it: the average number of alien civilizations in the galaxy equals the rate at which they are born multiplied by the rate at which they die. This means scientists don’t need to worry too much about the unknown parts of the Drake equation. They also added a new idea called the population fraction, F. A high F, close to 1, would mean almost every planet has life. A low F, close to 0, would mean very few or no planets have life. The problem is that, based on what scientists have seen, F is probably not close to 1. If it were, we would’ve already found aliens building things or sending radio signals into space. This means that if we’re not alone in the Universe, F might be closer to 0.5, which puts us in the unlikely part of the U-shaped graph. This suggests that intelligent life is rare in the Universe. Scientists believe that if alien civilizations ever existed in the Milky Way, they could have spread across the galaxy in 10-100 million years. Even if they disappeared, we should still find evidence of their existence. Since we haven’t found anything, it seems like alien civilizations are rare and don’t last long. If Aliens Do Exist, Why Haven’t We Found Them? The authors also suggest that if we ignore the lack of evidence, the Drake equation shows that the Universe might be full of life or almost empty. If the Universe is full of life, F would be close to 1, and this could still be possible under certain conditions. Maybe alien civilizations stay in their own part of space, and our solar system isn’t a place they visit. Maybe traveling between stars is too hard, or they just don’t need to do it. It’s also possible that while there’s a lot of complex life in the Universe, there are very few technologically advanced civilizations, or it takes a long time for them to develop. There’s even a chance that the birth and death rates of alien civilizations haven’t balanced out yet, so we might still have time to find them. But, considering how old the Universe is, this seems unlikely. The post Where are all the intelligent aliens: scientists have found the answer appeared first on Anomalien.com.