I’m rereading Robert Heinlein’s most elegant juvenile novel, Time for the Stars. This 1956 book was inspired by Paul Langevin’s 1911 “twin paradox” in Einstein’s theory of special relativity in which one twin zooms off in a spaceship that accelerates to close to the speed of light. After a roundtrip of many light years, he returns to Earth. Which one is now older? But if everything is relative, how can you say one twin was traveling faster than the other?
Don’t ask me.
But the heart of Heinlein’s book is a trippy set of brainstorms about what it’s like to be an identical twin inspired by Einsteinian wordplay: consecutive chapters are entitled “Relativity,” “Relations,” and “Relatives.”
Heinlein’s insight is that everything is relative to identical twins. The differences between them that seem minute to the outside world loom very large to them.
The narrator, while away from his identical twin brother on the star trip, comes to realize that he’s been pushed around all his life by his more dominant twin, that big jerk. But eventually his shipmates make clear to the narrator that, yeah, his twin is a big jerk, but that without his brother around, he’s 99.9% as big of a jerk.
I suspect this book has had a sizable impact on my intellectual development over the last 45+ years. Heinlein’s insight that the objective size of differences and similarities between people (or, more generally, between sentient creatures) doesn’t have to be closely related to the subjective scale of differences and similarities.
By the way, earlier this year, astronaut Scott Kelly was reunited after a year in space with his Earthbound twin brother, retired astronaut Mark Kelly (the husband of former Congresswoman Gabrielle Giffords, who so remarkably survived being shot in the head by a lunatic in 2011). The time dilation effects of going into Earth orbit are almost infinitesimally small, but they do exist.