Recently during conversation, a friend brought up this concept of the Fermi Paradox. It goes something like this:

Premise	Low estimate
There are a huge amount of sun-like stars in our Milky way.	100 billion
Some of these sun-like stars should be surrounded by Earth-like planets.	20%, or 20 billion
Some of these Earth-like planets should develop life.	0.01%, or 2 million

So, there should be roughly two million life forms in our solar system alone. That’s a lot of life forms, right?

Well… why haven’t we seen any indications of life? With two million life forms around us, shouldn’t we should at least see some indication of life. Where the heck is everybody?

Welcome to the Fermi Paradox.

There are three main hypotheses for The Fermi Paradox, which introduces us to this notion of The Great Filter.

The Great Filter

The Great Filter theory suggests that at some point during life, there’s a wall that life, or attempts at life, have to hit. This wall makes the evolutionary process extremely unlikely or impossible for life to get beyond. That stage is The Great Filter.

If this is true, the question is, where in our timeline does this great filter occur?

Theory 1: We’re rare (The Great Filter is behind us)

One hope we have is that The Great Filter is behind us—we managed to surpass it, which would mean it’s extremely rare for life to make it to our level of intelligence. One theory as to this filter we’ve managed to overcome includes the transition from a prokaryote cell to an eukaryote cell.

Theory 2: We’re the first

This suggests that for the first time in history, conditions in the universe are reaching a place that would allow intelligent life to develop. In that case, we may be well on our way to super-intelligence, and it’s simply happening for the first time ever. Existence, let alone our existence, is unprecedented.

Theory 3: We’re really screwed (The Great Filter is in front of us)

If we’re neither rare nor early, many would conclude that The Great Filter must be in front of us. This would suggest that life regularly evolves to where we are, but that something prevents life from going much further and reaching high intelligence in almost all cases—and we’re unlikely to be an exception.

This can be unsettling to think about, since it means that if we discover life forms other than us, it suggests that there are few Great Filters behind us. Worse, if we were to find complex life in our Milky way, it very much suggests that the Great Filter is most probably in front of us, thereby dooming our species. As Oxford professor Nick Bostrom puts it, “the silence of the night sky is golden.”

Whatever the case, it’s comforting to know that in a way, life is really special. Whether we’re alone or not, it’s clear that for our immediate surroundings, there aren’t any signs of life that we can see. And regardless if this is due to extreme luck, necessity or the presence of a God, this is a wonderful mystery, and one that makes life quite precious.

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For more on this topic, check out this post by Wait but Why.