Let's assume that aliens had a 1% head start on us. They were 1% faster at evolving. That's not a crazy idea - Earth spent 2 billion years going from photosynthesis to multi-cellular life. The cretaceous extinction could've been a 50 million year setback, how close were Dinosaurs to getting sentience?
We're at 13 billion years on the global clock right now, so 1% of that is 130 million years. An alien with a 130 million year head start on us. Imagine that.
Now let's assume there are 40 billion habitable planets in the galaxy. That seems like a lot. And let's assume it takes a really long time for a planet to go from "just colonized" to "ready to produce more interstellar colonies". Say 100,000 years - longer than recorded human civilization. We'll make a vague approximation - every inhabited planet can colonize another planet once per 100,000 years. That seems conservative.
It takes about 35 generations for a doubling population to reach 40,000,000,000.
35 generations. So with a generation taking 100,000 years, that means 3.5 million years.
In 3.5 million years we see a species go from "sentient" to "every habitable planet in the galaxy".
You can play with the numbers, but the result speaks volumes: geometric growth is fast, and the universe is old.
It is highly unlikely that we're the first. And if we're not the first, and interstellar colonization is possible, then every planet in the galaxy should already be colonized, because it would take a blink of an eye in galactic timescales.
There's also the argument that galactic conditions haven't been "right" for advanced civilizations until somewhat recently.
Specifically that the metallicity of stars would need to exceed a minimum in order for civilizations to have the necessary building blocks for technology.
It's hard to build a fusion reactor without the right elements. And it would be impractical to synthesize them in any practical amount. Especially since that would balloon your energy needs drastically.
Let's assume that aliens had a 1% head start on us. They were 1% faster at evolving. That's not a crazy idea - Earth spent 2 billion years going from photosynthesis to multi-cellular life. The cretaceous extinction could've been a 50 million year setback, how close were Dinosaurs to getting sentience?
We're at 13 billion years on the global clock right now, so 1% of that is 130 million years. An alien with a 130 million year head start on us. Imagine that.
Now let's assume there are 40 billion habitable planets in the galaxy. That seems like a lot. And let's assume it takes a really long time for a planet to go from "just colonized" to "ready to produce more interstellar colonies". Say 100,000 years - longer than recorded human civilization. We'll make a vague approximation - every inhabited planet can colonize another planet once per 100,000 years. That seems conservative.
It takes about 35 generations for a doubling population to reach 40,000,000,000.
35 generations. So with a generation taking 100,000 years, that means 3.5 million years.
In 3.5 million years we see a species go from "sentient" to "every habitable planet in the galaxy".
You can play with the numbers, but the result speaks volumes: geometric growth is fast, and the universe is old.
It is highly unlikely that we're the first. And if we're not the first, and interstellar colonization is possible, then every planet in the galaxy should already be colonized, because it would take a blink of an eye in galactic timescales.