Some of the greatest scientific minds have grappled with this experiment. Thomas Young devised it in the early 1800s to show that light behaves like a wave, and in doing so opposed Isaac Newton's view that light is made of particles. But then quantum mechanics was born and Albert Einstein showed that light comes in quanta, or particles. Einstein and Niels Bohr-two of the formidable founders of quantum mechanics-then debated over the nature of reality as revealed by the double-slit experiment. When done with single particles of light or particles of matter such as electrons or even molecules, the double-slit experiment becomes a conundrum to behold. How can a single particle behave both like a particle and a wave? Does a particle, or indeed reality, exist before we look at it, or does looking create reality, as claimed by some adherents of the orthodox Copenhagen interpretation of quantum mechanics? Richard Feynman said the double-slit experiment embodies the central mystery of the quantum world. But even he underestimated the experiment's power. Decade after decade, hypothesis after hypothesis, scientists have returned to it to help them answer more and more profound questions about quantum reality. With his extraordinarily gifted eloquence, Ananthaswamy takes the reader on an exploration of the past, present, and future implications of the double-slit experiment. Thomas Young's simple contraption-which began as a pinhole punched into a window shutter to let through a sunbeam-has surpassed its humble (yet paradigm-shifting) origins. The redoubtable experiment, reimagined and redesigned, yet untainted in its conceptual simplicity, has been used to explore all aspects of the quantum world that make it so mysterious, such as wave-particle duality, quantum superposition and entanglement (which Einstein called "spooky action at a distance"). The experiment is asking profound questions about our descriptions of reality. Do our theories represent what's actually out there, or do they represent our best knowledge of the quantum world? Is there a quantum-classical divide, where the quantum world ends and the familiar classical world of our daily lives begins, and if so, can we find it? The double-slit experiment is even being used by physicists to question the Copenhagen interpretation. Is there a real world of particles and waves out there, as David Bohm said? Or are new worlds being created each time something goes through a double-slit, a quantum fork in the road, if you will? And what's gravity got to do with all this? Through Two Doors at Once simultaneously celebrates the elegant simplicity of an iconic experiment and its profound reach. Anil Ananthaswamy travels around the world and through history, introducing readers to revolutionaries like Einstein and Bohr and Heisenberg and Schr dinger, as well as visionary contemporary physicists such as Roger Penrose, Alain Aspect, and Anton Zeilinger, who have all grappled with this experiment, whether in the lab or in thought. It's an unforgettable journey.

Author Biography

Anil Ananthaswamy is a consultant for the London-based New Scientist magazine, a guest editor in science journalism at UC Santa Cruz's renowned science writing program, and teaches in the science journalism workshop at the National Centre for Biological Sciences in Bangalore, India. He has worked at New Scientist in various capacities since 2000, including as a staff writer and a deputy news editor. He is a freelance feature editor for the Proceedings of the National Academy of Science's Front Matter. He has also written for National Geographic, Discover, The Times, and The Independent and is a columnist for PBS NOVA's The Nature of Reality blog. His first book The Edge of Physics was voted book of the year in 2010 by Physics World, and his latest title, The Man Who Wasn't There, won a Nautilus Book Award in 2015.