DAVID HAMBLINGlooks at current thinking about the multiverse and its dizzying implications
SCIENCEDAMNED DATA, NEW DISCOVERIES AND RADICAL RESEARCH
Parallel universes, once an obscure concept for science fiction geeks, have entered public awareness. This is not from science education but is thanks to the Marvel Cinematic Universe’s “Multiverse” and popular movies like Everything Everywhere All At Once. These fictional representations often include a handwaving mention of quantum physics as evidence that other universes are real. What do we really know about parallel universes and could they help explain strange phenomena?
The idea of alternate realities is surely as old as humanity. Whenever you are faced with a choice, you end up wondering about the possibilities you missed. What if you had moved to another country, applied for a different job, dated someone different? It is easy to imagine different versions of you living in different worlds.
Such daydreaming gained a potential scientific basis in the early 20th century when researchers found that objects on a subatomic scale did not behave as expected, but acted more like waves than particles. For example, in the double slit experiment, light passes through two narrow openings, and is diffracted. It makes perfectly good sense for light to be a wave, but the weird thing is that even if a single photon – one particle of light – is fired at a double slit, the same thing happens and diffraction occurs. Common sense says one tiny photon must go through one slit or the other, but the experiment shows that it appears to go through both at once. The particle seems to be a wave.
If you observe a single photon, the act of observation causes ‘collapse of wave function’ and it acts like a particle. But until you observe it, the photon is in a strange probabilistic state of being in more than one place. This phenomenon is famously expressed in the thought-experiment of Schrodinger’s Cat, a cat in a box which is both alive and dead until the box is opened. As soon as an observer looks inside, the wave function collapses and the cat is fixed in one state or the other.
The most usual explanation is the so-called Copenhagen Interpretation, which says that observation forces a quantum wave into a single state. But in 1957 American physicist Hugh Everett III proposed an alternative, the Many Worlds Interpretation, or MWI. In Everett’s version, whenever an observation is made, the universe splits into two: one universe where the cat is alive and another where it is dead
