How Big Can Schrödinger’s Kittens Get?
Scientists are slowly scaling up quantum effects from atomic to human size.
BY PHILIP BALL
Its time we thought again about quantum theory. Theres nothing actually wrong with the theory itselfit works fantastically well for understanding how atoms and subatomic particles behave.
The problem is how we talk about quantum theory. We keep insisting that its weird: waves becoming particles, things being in two places (or two states) at once, spooky action at a distance, that sort of thing. Isnt it perverse to clothe in mystery a theory that scientists use routinely to understand the world?
Part of the issue is that everyday objects are discrete, localized, and unambiguous, and so, very different to quantum objects. But why is that the case? Why is our everyday world always this or that and never this and that? Why, as things get bigger, does quantum physics turn into classical physics, governed by laws like those that Isaac Newton wrote down over three centuries ago?
This switch is called the quantum-classical transition, and it has puzzled scientists for many decades. We still dont completely understand it. But over the past two or so decades, new experimental techniques have pushed the transition to ever-larger sizes. Most scientists agree that technical difficulties will prevent us from ever putting a basketball, or even a human, in two places at once. But an emerging understanding of the quantum-classical transition also suggests that there is nothing in principle that prohibits itno cosmic censorship separates our normal world from the weird world that lurks beneath it. In other words, the quantum world may not be so weird after all.
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