Tony Leggett has two questions that he likes to ask audiences of physicists.The first concerns the double-slit experiment with single electrons: does each electron pass through just one of the slits to make the interference pattern? The second is about Schrödinger's famous thought experiment with a cat in a box: will the cat definitely be either alive or dead before the box is opened?
Tony Leggett has two questions that he likes to ask audiences of physicists.The first concerns the double-slit experiment with single electrons: does each electron pass through just one of the slits to make the interference pattern? The second is about Schrödinger's famous thought experiment with a cat in a box: will the cat definitely be either alive or dead before the box is opened?
The physicist Erwin Schrödinger described, back in 1935, one aspect of this strange phenomenon. He placed his cat in a sealed box with a piece of radioactive material which might or might not send out a sub-atomic particle. If it did, the Geiger counter was designed to trigger a release of poisonous gas in the box, and thereby kill his cat. The counter was set up to be triggered just enough to give a 50-50 chance of a particle being detected, and therefore the cat an even chance of being poisoned or not. (In those days, this sort of experiment was acceptable, particularly as it was only a thought experiment.) Radioactive behaviour is unpredictable (except in a general, statistical probability kind of way). There is no rule for working out whether or not the Geiger counter will be triggered. If the sub-atomic event does not occur, the cat lives. Otherwise, it dies. Just as a photon (in that famous experiment from ‘real-life’ physics) will quite happily go through both of two parallel slits in a screen – until someone tries to measure or detect it, at which point what the physicists call ‘the collapse of the wave function’ takes place – the particle can both trigger the poison gas and not trigger the poison gas. That is, until someone looks, Schrödinger’s idea is that his cat, for a while, is both alive and dead!
This preprint introduces a novel thought experiment—two sealed double-slit apparatuses, one with which-path detectors and one without—to resolve Schrödinger's cat paradox using only classical logic and standard quantum formalism. The interference pattern (or lack thereof) on each screen is determined by the experimental operational setup, not by later observation. Macroscopic objects like the cat reside in a quantum mixed state, not a quantum superposition state—which must be a pure state—even in a closed box. These concepts form the foundation of the Logical Interpretation of Quantum Mechanics, a minimalist approach that preserves Aristotle's laws of thought, requires no supplementary postulates, and resolves paradoxes (measurement problem, EPR, cat) as linguistic artifacts. The interpretation aligns fully with quantum predictions and recognizes indistinguishability as the primary source of quantum behavior.
The physicist Erwin Schrödinger described, back in 1935, one aspect of this strange phenomenon. He placed his cat in a sealed box with a piece of radioactive material which might or might not send out a sub-atomic particle. If it did, the Geiger counter was designed to trigger a release of poisonous gas in the box, and thereby kill his cat. The Geiger counter was set up to be triggered just enough to give a 50-50 chance of a particle being detected, and therefore the cat an even chance of being poisoned or not. (In those days, this sort of experiment was acceptable, particularly as it was only a thought experiment.) Radioactive behaviour is unpredictable (except in a general, statistical probability way). There is no way of working out whether or not the Geiger counter will be triggered off. If the sub-atomic event does not occur-the cat lives. Otherwise, it dies. Just as the photon (in Problem 93) will quite happily go through both slits until someone tries to measure or detect it, at which point what the physicists call ‘the collapse of the wave function’ takes place, the particle can both trigger the poison gas and not trigger the poison gas. Until someone looks, Schrödinger’s idea is that his cat, for a while, is both alive and dead!
In 1935 Erwin Schrödinger proposed a thought experiment to show the absurd consequences of applying quantum mechanics to everyday objects. Schrödinger imagined placing a cat in a box, along with a vial of deadly poison that is connected to a radioactive atom. If the atom decays, it releases the poison and kills the cat. When the box is closed we do not know if the atom has decayed or not, which means that it can be in a "superposition" of two states (decayed and non-decayed) at the same time. Therefore, protested Schrödinger, the cat can be both dead and alive at the same time – which is clearly absurd. There was obviously, he thought, some boundary between the microscopic world of atoms and quantum mechanics, and the macroscopic world of cats and classical mechanics.
Schrödinger's cat has always been an elusive beast, but physicists may have finally trapped one in the laboratory. In the great Austrian physicist's thought experiment, the fate of a cat was linked to the quantum indeterminacy of a radioactive atom—half decayed, half undecayed. The cat, as a result, was both alive and dead. Now physicists at the National Institute of Standards and Technology in Boulder, Colorado, report in this issue ( p. 1131 ) that they have created what one observer calls a “Schrödinger's kitten,” in which they excite an atom into a superposition of quantum states, then ease those two states apart so that the atom appears to be in two distinct physical locations simultaneously.