The Fermi Paradox and the Great Filter Or, Why Isn't Anybody There? By Kenny Bolster

The Great Filter This term is taken from the paper “The Great Filter – Are We Almost Past It?” (1998) by Robin Hanson A paper expressing a similar idea with somewhat better readability is Nick Bostrom's “Where Are They? - Why I Hope the Search for Extraterrestrial Life Finds Nothing” (2008)

What is the Great Filter? We don't see evidence of aliens According to our calculations, we should have seen evidence of aliens already The Great Filter is whatever unknown factor(s) is/are preventing civilizations from colonizing the galaxy

Advantages of Colonization You may notice the picture in the bottom right as our own dearly beloved “Bold Traveler”. The green specks in the picture of the center are Pseudomonas syringae, a bacteria that lives in clouds.

How to Take Over the Galaxy This is an artist's rendering of a von Neumann probe. Chief resource needed by an interstellar civilization is energy/negentropy Best source of that is stars Solar panels, Dyson spheres, Star Lifting All the light shining off of the stars in our galaxy is being “wasted” Why can we still see those stars?

Colonization Speed Average distance between stars: 5.4112 light- years Acceleration possible using solar sails for interstellar travel: 1 mm/s^2 Total diameter of the galaxy: 120,000 ly Typical estimates for the rate of acceleration possible using solar sails can be used to calculate the rate at which it would be possible to colonize the galaxy Average distance between stars: 5.4112 light-years Acceleration possible using solar sails for interstellar travel: 1 mm/s^2 Total diameter of the galaxy: 120,000 ly

Colonization Time 10,077,066.666... years

In 13,000,000,000 Years...

The Drake Equation

Hanson's Argument The right star system (including organics) Reproductive something (e.g. RNA) Simple (prokaryotic) single-cell life Complex (archaeatic & eukaryotic) single-cell life Sexual reproduction Multi-cell life Tool-using animals with big brains Where we are now Colonization explosion

How to Find a Filter Left is Nick Bostrom Right is Hanson Bostrom proposed two ideas: development should have taken a long time, and only happened once Hanson pointed out a flaw in one of them: Assuming that there is a limited window in which a development can occur, observing how long it took doesn't give you much evidence, as long as you know it happened. This assumes the window, which is questionable, but the “only happened once” thing works fine

How Right is the Right Star?

That First Magical Molecule Russel's white smoker theory Primoridial soup, which could have formed under a layer of ice, which would protect it from UV rays RNA World, but it's difficult to see how it could start Persperia, which makes Great Filter even worse

Little Bugs We're not sure exactly how first cells formed Important thing to note is that if the white smoker hypothesis is correct, formation of single celled organisms happened multiple times, in different ways It also seems pretty easy to have some sort of gene in an RNA which would cover that RNA and give it some sort of protection

The Incompetent Predator Key things: seems objectively improbable, and it only happened once Or maybe not. Chloroplasts?

Why Do We Get Naked, Again? If you go to the wiki page on “Evolution of Sexual Reproduction”, you find lots of discussion of how sex is advantageous from a natural selection perspective, but there are very few plausible ideas about how sex could have actually gotten started Best theory says that a bacteria engulfed an archaea, that had been infected by a virus at a certain stage of its life cycle, etc Cambrian Explosion happened basically right afterwards

Something Like Actual Aliens Multicellular animals appeared more than once It looks like it happened all over the place once we had eukaryotic cells and sex

Cave-Aliens with Clubs Has happened a lot Basically anytime you have social pack hunters, you get intelligence A lot of the time, they use tools

Is It Safe to Come Out Now?

We need something on the order of: So What's the Total? We need something on the order of: If the evolution of life on earth involved 1 in a million events, two would be more than enough Assuming that the earth pathway is the only pathway, so our filter is probably smaller than we would think Also assuming we don't find out that sex and eukaryotes were really easy developments Also don't forget origin of life

What Else Could Go Wrong?

Final Thoughts