The Internet has become preoccupied with an old question lately: where the heck are the aliens?

The Internet has become preoccupied with an old question lately: where the heck are the aliens?
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Ever since this video came out in May, a puzzle that has bugged scientists since we started sending out radio signals has regained popularity online: when you think about how big the universe is, it's really weird that we haven't detected any aliens.

Aliens. On the one hand, anyone who says they've seen or met them is probably a liar or an idiot. On the other hand, mathematically speaking, the universe should be crawling with them. The universe is both big and old, meaning that life should have had plenty of time and chances to develop, advance, and spread across each galaxy. The fact that it hasn't, as far as we can see, either means we're alone (unlikely), most life goes extinct before then (depressingly likely), or there's a horrifying race of super-robots out there that will wipe us out once we're advanced enough (unlikely, but would make a pretty good video game series). This problem, also known as the Fermi Paradox, is the subject of the video above by animator and explainer Kurz Gesagt, and since debuting on May 6, it's sparked a small renaissance on the topic.

Here's Gesagt's follow-up video with possible solutions to the paradox:

If you'd like to read a super in-depth explainer of the paradox and all the possible solutions to it, check out Wait But Why's opus on the topic.

Basically, it comes down to the Great Filter: whether it's nuclear weapons or some other extinction-causing factor, something seems to be preventing life from advancing to the level of technology necessary to spread across a galaxy. Either that, or advanced civilizations all prefer to download their brains and live eternally in a digital world (where, because processing speeds would be so fast, you could theoretically experience eons of time while only seconds pass in the real world). It's some pretty esoteric stuff, but science is really working on it. We've recently been trying to measure stars and galaxies for excess heat, which could be signals that massive civilizations are harnessing their home stars for energy:

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Wondering about this dates back to before the 20th Century—War of the Worlds was written in 1897, and H.G. Wells probably got the idea when Italian astronomer Giovanni Schiaparelli thought that he saw canals dug across the surface of Mars in 1877, which he presumed to be irrigation works by a highly advanced civilization. But with the advent of radio signals, flight, and rockets, the question became one of serious scientific merit—which is when Enrico Fermi, after discussing the topic with his fellow physicists at Los Alamos National Laboratory, formulated the paradox in 1950. This most recent burst of interest in the topic is just the latest round of humanity's hand-wringing over why we're alone, but if you were wondering why everyone is talking about it all of a sudden, at least now you're not alone.

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