字幕列表 影片播放 列印英文字幕 I'm Fraser Cain, the Publisher of Universe Today The Universe is enormous. In the observable Universe, there are more than one-hundred-and-seventy billion galaxies. In our galaxy alone, there are as many as four-hundred billion stars, and most probably have planets. A few of those planets must contain useful minerals for life, and fall within their star's habitable zone, where liquid water is present. Based on this, many believe the conditions for life exist throughout the Universe. So, where are all the aliens? The Universe has been around for thirteen-point-eight *billion* years. Humanity got its start a mere two-hundred-thousand years ago, only zero-point-zero-one-percent of the age of the Universe. There has been plenty of time for an intelligent species to arise on any one of countless worlds, and broadcast their existence to the entire galaxy. Or perhaps, if a species developed interstellar travel, they could completely colonize our galaxy within a few tens of millions of years; that's only a heartbeat in the age of the Universe. We've got the potential for life everywhere, and an incredible span of time for it to migrate itself all around the Universe. Yet, as far as we know, Earth is the only place in the Universe where life has arisen, let alone developed an intelligent civilization. So *where* are all the aliens? This baffling contradiction is known as the Fermi Paradox, first described in nineteen-fifty by the physicist Enrico Fermi. Scientists have been trying to resolve this mystery for decades, listening for radio signals from other worlds. They've sampled only a fraction of the radio spectrum, and to date, haven't detected anything that could be a signal from an intelligent species. So, what are our options? It could be we are the only planet in the entire Universe to develop life. Perhaps, we're the first civilization to reach this level of advancement in the entire Universe. If we're assuming there's life, with so many worlds out there, both seem unlikely. *OR* Civilizations destroy themselves when they reach a certain point. Nuclear weapons, global warming, killer epidemics, and overpopulation could all end humanity. Asteroids could strike the planet and wipe us out. But would this happen to every single civilization? one-hundred-percent of them? Even if ninety-nine-percent of civilizations destroy themselves, we could still have a couple that make it through to fully colonize the galaxy. And if there are actual aliens, why we haven't met them: Perhaps, they're just too far away, and our signals can't reach each other. But why wouldn't they just build self-replicating probes that could traverse those distances and leave a local artifact in every single star system? Maybe we haven't the ability to receive their signals or recognize their artifacts. Sure, but if aliens constructed a series of artifacts on Earth, I think we'd notice them. I'd like to assume if they've mastered space travel, that they'd have experience creating obvious structures. They could be just *too* alien and we can't understand them. Or we're too insignificant, and they don't think we're worth talking to. But we don't need to talk to them to know they exist. If they flew through our Solar System, ignoring us, we'd still know they're around. Perhaps, they're not talking to us on purpose, and we're really in some kind of galactic zoo. Or "aliens" have a Prime Directive, and they're not allowed to talk to us. Maybe some aliens have these rules. But all of them? Not a single sympathetic alien has broken the rules and snuck us some evidence? There are many other potential solutions to the Fermi Paradox, but I find them all lacking. The Universe is big, and old, and if extraterrestrial life is anything like us, it wants to multiply and spread out. The most unsettling idea is that something happens to one-hundred-percent of intelligent civilizations, and that prevents them from exploring and settling the galaxy. Maybe it's something good... Like the discovery of a transportation system to another Universe. Or maybe it's something bad, like a destructive technology, or discovery that has destroyed every single civilization before us. How do you feel about the Fermi Paradox, and how do you propose we resolve the contradictions? Whatever the solution is, it sure is fun to think about. Thanks for watching.