10 Possible Reasons We Haven't Found Aliens

This simple, yet powerful argument became known as the Fermi Paradox, and it still boggles many sage minds today. Aliens should be common, yet there is no convincing evidence that they exist.

1. There aren't any aliens to find. As unlikely as it seems in a galaxy with hundreds of billions of stars and as many as 40 billion Earth-size planets in habitable zones, we could be alone.

1. Intelligent species lack advanced technology. Currently, astronomers utilize radio telescopes to listen intently to the night sky. So if alien species aren't broadcasting any signals, we'd never know they existed.

3.Intelligent life self-destructs. Whether via weapons of mass destruction, planetary pollution, or manufactured virulent disease, it may be the nature of intelligent species to commit suicide, existing for only a short time before winking out of existence.

1. Space is big. The Milky Way alone is 100,000 light years across, so it's conceivable that the focused signals of intelligent aliens, which are limited to the speed of light, simply haven't reached us yet.

1. The universe is a deadly place. On cosmic timescales – think billions of years – life may be fleeting. All it takes is a single asteroid, supernova, gamma ray burst, or solar flare to render a life-harboring planet lifeless.

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1. Space is big. The Milky Way alone is 100,000 light years across, so it's conceivable that the focused signals of intelligent aliens, which are limited to the speed of light, simply haven't reached us yet.

2. We haven't been looking long enough. Eighty years. That's the amount of time that radio telescopes, which allow us to detect alien signals, have been around. And we've been actively searching for aliens for maybe sixty years. That's not very long at all.

3. We're not looking in the correct place. As previously mentioned, space is big, so there are tons of regions to listen for alien signals. If we're not listening precisely in the direction from which a signal is originating, we'd never hear it. As Andrew Fain explained at Universe Today, it's like trying to speak with your friend on a 250,000,000,000-channel CB radio, without any knowledge of the frequency on which they are transmitting. You'll probably be channel flipping for a long time.

4. Alien technology may be too advanced. Radio technology may be commonplace here on Earth, but on far-flung worlds, alien societies may have graduated to more advanced communication technologies, like neutrino signals. We can't decipher those just yet.

5. Nobody is transmitting. Instead, everybody may be listening. That's basically how it is here on Earth. Apart from a few paltry efforts to broadcast strong signals over a narrow frequency band towards the stars above, we've barely made our presence known in the universe. In fact, if aliens have radio telescopes similar to what we have on Earth, our television and radio broadcasts would only be detectable up to 0.3 light-years away. That distance doesn't even transcend the farthest reaches of our solar system.