Schrödinger's Pendulum Experiment Will Search for the Quantum Limit

There's a rift in reality - an invisible border that separates two utterly different realms. On one side lies our everyday world, where things obey commonsense rules: objects never occupy more than one place at a time, and they exist even when we're not looking at them. The other side is the dreamscape of quantum mechanics, where nothing is fixed, uncertainty reigns and a single atom or molecule can be in multiple places simultaneously, at least while no one is watching.
Does that mean reality has one set of laws for the macrocosm and another for the micro? Most physicists instinctively dislike the idea of a bifurcated universe. Sougato Bose, a theorist at University College London (UCL), certainly does.
"My view is that quantum mechanics hasn't been seen [at large scales] because we have not yet been able to isolate things well enough," he says, meaning that researchers haven't found a way to shield big objects from their environment, so their quantum properties are apparent. Like most physicists, Bose believes that quantum mechanics applies to all things great and small. He and three colleagues - two in the U.K.
and one in India - hope to put that view to a stringent test within the next year or two with an intriguing experiment that ultimately aims to determine whether or not large objects obey the strange rules of quantum theory.
The experiment, described in a recent issue of Physical Review Letters, harks back to a conundrum vividly framed nearly a century ago by Erwin Schrödinger, one of the founders of quantum mechanics. What would happen, Schrödinger asked, to a cat trapped in a closed box with a vial of poison that has a 50-50 chance of shattering and killing the cat? According to quantum mechanics the cat is at once alive and dead, existing in both states until someone opens the box and looks inside.
That's because it's only when an observer makes a measurement of the system - opens the box and checks - that the two possibilities have to collapse into one, according to quantum theory. The story is meant to illustrate how applying these quantum rules to big things - basically, anything visible to the naked eye - leads to absurdities.
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So if quantum mechanics is true - and it has been a phenomenally successful theory for predicting the behavior of particles - why do we never see cats that are both dead and alive? Do the laws of quantum mechanics break down at a certain level? Some physicists see that as a possibility.
But most would argue that the apparent absence of quantum effects in our own experience of the world arises because the countless interactions of atoms with the surrounding environment blur the true nature of things. As a result we perceive a kind of dumbed-down, nonquantum version of reality.
If that's the case, then a carefully designed experiment that isolates an object from nearly everything in its environment should allow physicists to glimpse the actual quantum behavior of that object, even if it's relatively large. That's the goal of the experiment proposed by Bose, Debarshi Das, also of UCL, Hendrik Ulbricht of the University of Southampton in England and Dipankar Home of the Bose Institute in India. "There are two possible outcomes," Home says.
"One is that quantum mechanics is valid [at all scales. The other is that] there is a region where quantum mechanics does not hold."
Most of the hardware needed for the experiment is already in place and fits on a tabletop in Ulbricht's lab. (He's the lone experimentalist of the group; Home, Das and Bose are theorists.) The experiment will use lasers to suspend a single nanocrystal of silica - a microscopic glass bead - as it oscillates around the focal point of a small parabolic mirr...