Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asking the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and add free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

This episode is brought to you by Skillshare.

As we celebrate one more trip around our star, we can look forward to traveling to many

new stars.

As we wrap up the year 2020, we are also wrapping up our becoming an interplanetary species series

with this epilogue on becoming an interstellar species.

This is tricky for more reasons than just difficulty of traveling to distant stars and making

homes under alien suns, because to become an interstellar species would also imply you were

just one species, and that's part of the problem. Interstellar distances are so immense that even

objects which could cross our whole world in a second take years to get to the nearest star,

and our fastest man-made object would still need longer than all of recorded history to reach

that star. Indeed, our galaxy alone is so immense that even signals, let alone spaceships, need

as long to cross the galaxy as modern humanity has been around.

Even ignoring things like genetic engineering, which might play a big role in humanity settling

new worlds, simple exposure to radically more diverse environments than we see on Earth, would

presumably cause species

diversity faster than ships could settle our galaxy, even if traveling at a good fraction

of light speed, while the speeds of our fastest modern spacecraft, an effort to colonize

the galaxy would take more like a billion years, and a billion years is considerably more time

...