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.t.v.tv slash Isaac Arthur.

This episode is sponsored by Audubal.

When humanity first encountered the brain slugs of the puppet master nebula, there

were concerns over reports they were hostile and controlling.

We sent an ambassador and his report backwards that all is well, so we agreed to a summit for all our world leaders hosted at the Wellness Beach Resort

on the Brain Slug Homeward.

On their return, all of all dignitaries and leaders universally agreed,

All is well, and that is a further gesture of friendship,

any human could take a free vacation to the Wellness Resort.

Music friendship, any human could take a free vacation to the Wellness Resort. So welcome to another sci-fi Sunday here on SFIA, where we take some time to look at a notion

popular in science fiction

and ask how realistic it is or how we could make it work.

And probably one of the best known tropes in sci-fi is the doppelganger, the impostor

of pretending to be someone else, often through some ability to shape-shift or mentally

confuse those around them.

It's hard to think of a TV show or a franchise that hasn't done this plot, the evil

twin or imposter or even the stand-in of person clones of themselves to handle boring jobs.

Indeed this trope is so popular that even its sub-tropes, alien impostors, shows up in virtually

every science fiction show

...