The Universe Within 12.5 Light Years

When the Fermi Paradox was first posited, scientists and engineers seemed to believe that interstellar travel was soon to be technologically achievable, a few decades, maybe centuries for the less optimistic. Progress around space propulsion has kind of stalled since then and we should maybe question the possibility of interstellar travel as this would give an easy but unpleasant answer to the famous paradox.

Right- “where are all the aliens?” is answered by either “they don’t exist” or “they do but physics of the universe prevent them from moving between solar systems.”

Or: we're the first (or among the first). The history that led to space travel (modern human technology) has passed through an insane amount of unlikely scenarios.

A few of these:

* Astronomical: the sun is unusually calm for a star. Jupiter blocks comets. Saturn blocked Jupiter from destroying the Earth.

* Earth is 4.5 billion years old. In the next 0.5-1 billion years Earth will become unhabitable because the sun's luminosity is increasing. We're in the twilight years of the (life-supporting) planet.

* Above point + think about all the species that came before us. Life appeared 3.5-3.8 billion years ago. It took that long to get to humans.

* Dinosaurs got wiped out. Would humans have even evolved if a cosmic event hadn't cleared the board?

* We think that human ancestors dropped down to about 1000-100,000 individuals about 900k years ago.

There's also the question of how many sun-like stars in terms of metallicity there are that preceded the sun. Our sun inherited a lot of heavier elements from a previous generation of star(s).

Add all of these together and we might be early to the party.

I can’t vouch for its scientific plausibility, but one of my favorite bullets to add to this list comes from Frank Robinson’s novel-length scifi exploration of the plausibility of extraterrestrial life:

“The next step is crucial. The simple organic molecules have to be shielded from the ultraviolet radiation of the primary. That requires a large body of water—an ocean—to protect them. No protection and the molecules break up as soon as they're formed. And oceans of water are … extremely rare.”

…

“But something else is rarer still. The next step in the creation of life is when the amino acids form into long chains.

Left in the ocean, they drift apart as easily as they join together. There has to be a means of concentrating them. Once a certain level of concentration is reached, they'll form long chains, more complex molecules, automatically. Heating isolated bodies of water would help, say tidal pools warmed by hot lava and occasionally replenished by the sea.”

…

“Do you understand, Sparrow? Tidal pools implies tides and that means a moon large enough to raise them—though not too frequently, because you might dilute the pool too much. A combination of the primary and the moon would raise larger tides less often, and that would be a happy medium. What's required, then, is a planet that has land surfaces, oceans, and a large enough satellite to raise suitable tides. The action would concentrate the simple amino acids and they could combine into the longer chains.”

The novel is The Dark Beyond the Stars, and I recommend it highly.