Schrödinger’s cat is famous in the physics world. It’s a curious thought experiment dreamt up by Erwin Schrödinger in which a cat is enclosed in a box with a vial of poison. Until someone opens the box, the cat is both dead and alive—we have no way of knowing which until we observe it. The analogy illustrates the principle of quantum superposition: any subatomic particle inhabits all of its possible quantum states (the set of numbers determining the particle’s characteristics) at once—until we measure it.
Superposition is a feature of the microscopic world—not the macroscopic. But how big is too big before Schrödinger’s cat ceases to be relevant? For example, can we quantum superimpose a real-life cat? Here’s Edwin Cartlidge, writing for Physics World:
In recent years physicists have been placing ever-larger objects into states of quantum superposition – the curious state that Schrödinger’s cat finds itself in. Now, researchers in Germany have devised a way of quantifying just how macroscopic those objects are and how much ground still needs to be made up before cats and other familiar items can be held in two or more quantum states at the same time.
There are some obstacles to macroscopic superposition. But even if scientists could overcome them, Schrödinger’s cat, if it were real, might just be too fat. Researcher Stefan Nimmrichter noted:
“One should never say never, but we will probably never be able to put a cat in a quantum superposition.”
Experiments like these could help them find out whether or not a boundary exists—and if it does, where—between the quantum and classical worlds.