After centuries of wondering, mankind has at last realized an ancient dream. We have discovered proof of civilizations other than our own.
In the decade we have been exploring the Outer Belt in earnest, humanity has uncovered artifacts from more than forty different cultures… all represented by robot starships… all apparently long dead.
What happened here?
And why were all those long-ago visitors robots?
Back in the late twentieth century, some scholars had begun to doubt that biological beings could ever adapt well enough to space travel to colonize more than a little corner of the Milky Way. But even if that were so, it would not prevent exploration of the galaxy. Advanced intelligences could send out mechanical representatives, robots better suited to the tedium and dangers of interstellar spaceflight than living beings.
After all, a mature, long-lived culture could afford to wait thousands of years for data to return from distant star systems.
Even so, the galaxy is a big place. To send a probe to every site of interest could impoverish a civilization.
The most efficient way would be to dispatch only a few deluxe robot ships, instead of a giant fleet of cheaper models. Those first probes would investigate nearby stars and planets. Then, after their explorations were done, they would use local resources to make copies of themselves.
The legendary John Von Neumann first described the concept. Sophisticated machines, programmed to replicate themselves from raw materials, could launch their “daughters” toward still further stellar systems. There, each probe would make still more duplicates, and so on.
Exploration could proceed far faster than if carried out by living beings. And after the first wave there would be no further cost to the home system. From then on information would pour back, year after year, century after century.