The Fermi Paradox

The Fermi Paradox is a blog post written by Tim Urban on Wait But Why in 2014. It tackles the Fermi Paradox, the question of why, despite there being so many stars and Earth-like planets, there is no life other than humans.

It starts with a count of stars and planets in the universe. Even with the most conservative estimates on the number of sun-like stars, not total stars, just the ones like the sun (which are not the most common type) just in the observable universe, is 500 billion billion. After going with the conservative estimate on the number of Earth like planets in the observable universe orbiting sunlike stars is 100 billion billion.

This means there are 100 Earth like planets, each around a sunlike star for every grain of sand in the world.

And even if only 1% of those planets developed life, and only 1% of those planets developed intelligent life there would still be 10 quadrillion intelligent civilizations in the observable universe.

Using the same math and proportions for just the Milky Way (which has 100-400 billion stars of all types in total), there would still be 1 billion Earth-like planets and 100,000 civilizations as intelligent as humanity in our galaxy alone.

It further states how intelligent life on Earth is relatively new. Other planets could have evolved human level life much sooner than Earth, and would have gone on to be much, much more advanced than humans. Considering a difference of only a thousand years, exponential growth would mean such a civilization would be even more shocking to humans than present day humanity is to a medieval person. A head start of 1 million years is like humans to chimpanzees. And planetary lifespans mean aliens could be billions of years ahead of humanity.

It then introduces the Kardashev Scale. Type 1 civilizations can harness the full energy of their planet (humans are 0.78), type 2 civilizations can harness the energy of our star (like Dyson Spheres), and type 3 civilizations can harness the full energy of their galaxy.

The post also notes how in a concerted effort, an alien species can colonize the whole galaxy in 3.75 million years, barely a small length of time on galactic scales.

It then details the two main camps and their solutions regarding the Fermi Paradox, each with noted thinkers on both sides.

The first camp believes that humans are the only intelligent species to exist because of something called the Great Filter, a barrier that prevents life from progressing beyond a certain point.

There are three scenarios for the Great Filter:

The first possibility is that the Great Filter is behind us, and life on the level of humans is a very rare occurrence for unknown reasons. This could be because the jump from simple prokaryote cells to vcm[lex eukaryotic cells is rare, that life itself is rare, or that intelligent life does not develop on many planets with life because evolution does not lead to such species and that humans are an exception. Another possibility are the very particular situations in our solar system, like an unusually large moon for a planet of that size.

A second possibility is that the conditions in the universe have only just settled down for intelligent life to be able to develop, and it's a coincidence that humans are the only species. Humans are merely the first.

The worst case scenario is that the Great Filter is ahead of humanity, making it very likely humans will also end soon. Some scientists who believe in the Great Filter believe that the less evidence of life, the better, as it makes it more likely that the Great Filter is behind us.

The second camp believes that humans aren't special and that there are other reasons that intelligent life hasn't been sighted. Many possibilities are listed in the article.

It ends with Tim noting how despite all our advances, this paradox fills him with a sense of awe, seeing the planet's greatest minds debate and have no real answer. He thinks future generations will look at this debate with the same contempt and pity the way the present looks at those who believe the Earth was flat.

**Editor's note:**

The following addition to this article comes from the AI blog post, but since it concerns the Fermi Paradox, it's best to include it here:

Destructive AI isn't a Great Filter candidate because the AI will still exist, and the Fermi Paradox is about why no life is seen in the universe. Because of that, those who believe superintelligent AI can be developed soon by a civilization on our level are mostly in camp 1. In any case, due to the danger and benefits of superintelligence, if humans contact alien life, it's more likely to be artificial than biological.

## Full post:

https://waitbutwhy.com/2014/05/fermi-paradox.html