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BY REMOVING INFORMATION about things that have happened, a quantum eraser seemingly influences past events. In a fanciful example, a cat may have scampered around both sides of a tree at once if information about which way it went is later erased.
SLIDESHOW: Quantum Erasing in the Home, and other web extras for this article Image: MATT COLLINS
Notoriously, the theory of quantum mechanics reveals a fundamental weirdness in the way the world works. Commonsense notions at the very heart of our everyday perceptions of reality turn out to be violated: contradictory alternatives can coexist, such as an object following two different paths at the same time; objects do not simultaneously have precise positions and velocities; and the properties of objects and events we observe can be subject to an ineradicable randomness that has nothing to do with the imperfection of our tools or our eyesight.
Gone is the reliable world in which atoms and other particles travel around like well-behaved billiard balls on the green baize of reality. Instead they behave (sometimes) like waves, becoming dispersed over a region and capable of crisscrossing to form interference patterns.
This article was originally published with the title A Do-It-Yourself Quantum Eraser.