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Are multiverses real? If so, what do they look like? How do you get there without disturbing time? – Emily, age 9, Pune, Maharashtra, India
The idea of a multiverse – a hypothetical collection of all possible universes – is one that
science fiction fans love to explore. But does the multiverse actually exist?
To answer the question of whether the multiverse is real, we first need to agree on what it means for something to be real. As an astrophysicist who studies cosmology – the large-scale history and structure of the universe – and the philosophy of physics, I’ve thought about this question more than a few times over my career.
The most immediate definition of “real” might be that you can see and touch it. My lunch is real in this sense, because I can taste it and you can hear me chewing it (hopefully not too loudly). So “real” might be defined as something you can perceive with at least one of your five senses.
But that would leave out a lot of things that are also real. The microwaves that heat up your food are real, but you can’t directly perceive them – only their effect, heated food. So some real things you can “see” only indirectly by the evidence they leave behind. The existence of dinosaurs is another example – you can see only their fossils.
So, you can ask two versions of the question of whether the multiverse is real. One: Can you see, hear, touch, smell or taste it? Two: Even if you can’t, is there any evidence of its effects?
Quantum mechanics of the multiverse
The answer most researchers would offer to whether you can perceive the multiverse with your five senses is probably not. But there are lots of real things that aren’t real in this sense, such as microwaves. So can we see any indirect evidence of the multiverse, such as the effects it might have on the observable world?
The short answer is yes, sort of.
The multiverse is one way to understand the behavior of very, very small things, such as atoms and subatomic particles. Scientists call the rules governing how these very small objects behave quantum mechanics. In quantum mechanics, it’s never certain what the outcome of an experiment will be. You can only write down the chance – that is, the probability – of something happening.
Schrödinger’s cat illustrates how multiple possibilities can exist at the same time.
It’s like rolling dice: You can’t be sure what number you’ll get, but you can say you have an equal chance of getting one, two, three, four, five or six on top of the dice. However, if you knew enough information about the dice – such as its exact shape and mass, the air patterns around it and the exact way you threw it – you…
