Updated: June 07, 2017
MONSTERS PHOTO GALLERY #19
We currently search for signs of alien intelligence by scanning the sky with SETI and similar efforts. It's a noble effort, but one that makes a needle in a haystack look like a five minute job. The universe is very, very big while our current communications capability is very, very small. Which is lucky, because it limits the volume of universe contaminated by reality TV. Some propose the idea of using one of our greatest fears - self-replicating robots - to realise one of our greatests dreams: extra-terrestrial contact.
A Bracewell probe is a spacecraft containing all the information we might want to send an alien civilization. Since communications can only proceed at lightspeed, any attempt at long-distance chatter would take years to travel each way (so if E.T. had ever managed to phone home, it would have taken an awful long time, never mind the wicked long-distance charges). Instead of saying "Hello, how are you? Over" and waiting a few decades for a response, we can bundle anything we think is cool into the ultimate intercivilization care package and hope that somebody returns the favor.
Shooting these probes off at random is still trying to hit a bulls-eye by throwing darts out of a plane - and if we knew where to send it, we'd sort of be done already. This is where the Von Neumann machines comes in - a device built with the ability to construct a perfect copy of itself. The idea is that stars take to long to get to, so instead of sending one ship on an extreme long haul we send a self-replicating army. The robots build exact copies of themselves as they progress, and while it takes them just as long (or longer) to arrive, they reach millions of destinations simultaneously so it's much more efficient.
If an exponentially multiplying army of space robots seems like a bad idea to you, then well done, you've seen any sci-fi movie ever. Plus, building a vast army of brainless drones which occasionally discover something interesting, but mainly just repeat their own message along networks designed for communication? That's just a space internet. But (justified) fear of reproducing machines aside it does seem like the most sensible option. Expanding into the universe based solely on the resources of a single orbital rock is obviously limited - to say nothing of the problems caused by digging up our finite material supplies and throwing them into space. Using what we find up there will be essential strategy - and making the machines wait until we arrive to do it for them would be too slow.
We just have to hope they don't find someone they like better while they're up there.