“Station Eleven” by Emily St. John Mandel was published in 2014. That book imagined the world after a pandemic had wiped out, well, almost everyone. It’s a gorgeous novel with a particular emotional power: it helps you grieve a life you still have. But then came a real pandemic, not as lethal as the one Mandel imagined, but a shock nonetheless. And “Station Eleven” — already a beloved international best seller — found a second life. Mandel became known as a pandemic prophet. “Station Eleven” became an acclaimed HBO Max series. “Sea of Tranquility” by Mandel is written from within the hothouse of that strange kind of celebrity. The author put a version of herself in there, struggling with fame and parenthood and quarantine and too much travel. But there are also moon colonies, and time travel, and hints that we live in a computer simulation. If “Station Eleven” explores how calamity could change the world, “Sea of Tranquility” wonders what happens if it doesn’t. This conversation begins in the weirdness of the simulation hypothesis, but winds its way to much more fundamental questions of being human right now. There is so much we could lose, so much we already have lost; why is it so hard to live with the gratitude our lives should inspire, or the seriousness the moment demands?