A Jonbar Point is any point of divergence between two very different outcomes. What if the Confederate States of America had won the American Civil War? What if the Roman Empire had realized the potential of Hero’s steam engine? What if you’d ordered the Guinness last night instead of the Rickard’s Red?

The term comes from The Legion of Time a swashbuckling SF novel written by Jack Williamson in 1938. Denny Lanning, the novel’s protagonist, first encounters women from the future while studying at Harvard College in 1927. It turns out his actions will play a part in determining earth’s distant future. In particular, his actions will affect the life of one John Barr. In one possible future, Barr will become an influential scientist whose discovery will change world history; in another, he dies, penniless, and a variation of his discovery is made nine years later by less ethical individuals. The utopian city of Jonbar dominates the world of one possible future. In another, the dystopic Gyronchi scars our world. Representatives of both futures want to manipulate Lanning to ensure their version of the future will be the one to exist. Of course, having two alternate futures tamper with the past is paradoxical, to say the least. This may be one of those situations when time travel in science fiction just doesn't make any sense.

Williamson wasn’t the last SF writer to be taken by the concept which he named. An entire sub-genre of science fiction addresses alternate history. These include Kim Stanley Robinson's The Years of Rice and Salt (what if the Bubonic Plague had wiped out nearly all of Europe?) William Gibson and Bruce Sterling’s The Difference Engine (what if Charles Babbage's nineteenth century computer had been built?), Robert Sawyer's Neanderthal Parallax novels (what if homo neanderthalensis had become the human race?), and hundreds of novels and stories wherein the Axis powers win World War II.

Jonbar points also provide the opportunity for personal reflection. What if you’d kept dating that unforgotten ex? What if you hadn’t gone camping that fateful summer night? What if you hadn’t ordered that last pitcher of Long Island Iced Tea? What if you were doing something more interesting than reading this node? Granted, some might argue that each of these alternatives do take place in some alternate universe, but since we can only experience the outcomes in this one, that hardly matters to us.

Note: According to the Oxford English Dictionary, Williamson also coined the terms “genetic engineering” (Dragon’s Island) and “terraforming” (Seetee Ship).