This is a story about choices and consequences, so let’s start with DC’s decision in 1961 to publish a landmark issue of The Flash called “Flash of Two Worlds!” In the story, created by Gardner Fox and Carmen Infantino, the Flash of the Sixties (Barry Allen) meets the Flash of the Forties (Jay Garrick) by crossing from Earth-One to Earth-Two.
“As you know — two objects can occupy the same space and time — if they vibrate at different speeds!” Allen explains with a superhero’s typical fondness for exclamation marks. “My theory is, both Earths were created at the same time in two quite similar universes! They vibrate differently — which keeps them apart!” As the fastest man on (his) Earth, Allen vibrated so fast that he “tore a gap in the vibratory shields separating our worlds!”
Allen’s account of the physics may have been somewhat unreliable but readers didn’t flinch. Two worlds, two Flashes? Got it. That was how DC entered what the science-fiction writer Michael Moorcock would soon christen the “multiverse”.
Right now, the multiverse is box-office gold, as Doctor Strange and the Multiverse of Madness collides with the extraordinary word-of-mouth hit Everything Everywhere All At Once. The Marvel Cinematic Universe (MCU) has already been universe-hopping in Spider-Man: No Way Home and Loki; DC will follow suit with next year’s The Flash. While writing Everything Everywhere All At Once, directors Dan Kwan and Daniel Scheinert (known collectively as Daniels) saw multiverse storylines in Spider-Man: Into the Spider-Verse and Rick and Morty and worried that the concept would be old hat by the time their movie was out. Not a bit of it.
The multiverse began as an alternative answer to a confounding question. In the Twenties, experiments in the revolutionary new field of quantum mechanics demonstrated that sub-atomic particles such as electrons behaved as if they were in many places at once, like a waveform. Yet as soon as they were observed, these myriad coexisting possibilities concertinaed into a single, measurable state, which we call reality. How? In the traditional Copenhagen interpretation, the act of observation itself causes a phenomenon known as waveform collapse. This made sense to quantum physicists but not to anybody else.
One sceptic was Erwin Schrödinger. In 1935, he illustrated this paradox with a “ridiculous” thought experiment. A cat is placed in a box with a vial of lethal poison which will only break open if a radioactive atom decays. The odds are 50/50. If it were equally possible for the atom to have both decayed and not decayed until it is observed, Schrödinger argued, then it would be equally possible for the cat to be both alive and dead until the instant that the box is opened. Yet we instinctively feel that the unseen cat must be either alive or dead at any given moment, not alive and dead.
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