De-Spooking Quantum Mechanics
Einstein wouldn’t have found entanglement so strange, if he’d thrown out a key pre-twentieth-century misconception.
July 13, 2011
University of Western Ontario
There’s a picture of Wayne Myrvold
in Greenwich Village, New York, holding a concertina surrounded by hundreds of other ancient looking musical instruments. If you didn’t know him, you’d be forgiven for thinking the associate professor from the University of Western Ontario in London, Ontario, Canada, is a trained musician.
In fact, Myrvold is a philosopher of science and he has no idea how to play the concertina. But rather than take conventional music lessons, he enjoys the challenge of trying to figure out the instrument in his own way. Myrvold takes a similar approach to understanding quantum mechanics: He knows the standard answers from physicists, but he hopes that his own philosophical take will illuminate some of the theory’s famous peculiarities and will show that its spooky reputation is unwarranted.
"If someone tells me that quantum mechanics is weird, counterintuitive and strange, but you should just accept that we live in a strange counterintuitive quantum world, I’ll say okay but tell me what kind of world that is," Myrvold says.
In the weird quantum realm, subatomic particles can be in two places at once, or exist in multiple energy states, before anyone looks at them. The standard explanation is that before you observe it, a quantum object is described mathematically by a smeared out wavefunction
, which tells you the probability of finding it in any one location, or energy state. When you make a measurement, that wavefunction "collapses" into one set location and energy level. Prior to that observation, however, you could not predict what the outcome of the measurement would be.
That’s the textbook answer. But, says Myrvold, even if you can wrap your head around wavefunction collapse, another quantum phenomenon—entanglement—makes everything problematic. Entangled particles are intertwined in such a way that measuring the properties of one seems to instantaneously affect the properties of its partners. Einstein famously denounced entanglement as "spooky action at a distance" because this communication appears to happen faster than the speed of light—violating the universe’s speed limit, set by his theory of relativity. This feature of quantum mechanics is called non-locality.
"To comply with relativity, you don’t want the possibility for faster than light signaling," explains FQXi-member Daniel Bedingham, a physicist who has also wrestled with wavefunction collapse, independently from Myrvold, at Imperial College London, UK.
Myrvold, however, believes that any seeming violation of relativity is an illusion. He argues that if we throw out one of our pre-20th
century misconceptions, we’ll understand that there’s nothing spooky going on at all. The troublesome notion that should be consigned to the garbage is called "separability." It is the idea that if we know everything about one particle in one location and everything about another particle in a second location then we know everything about their combined system.
Could a new philosophy shed light on photon experiments?
Credit: IQOQI, University of Vienna
Separability is something we take for granted in every day life, and that may be why it is so embedded in our minds. But in quantum mechanics, the whole is much more than the sum of its parts, explains Myrvold. "If you take quantum mechanics seriously, it’s separability that you have to give up," he says. "When particle A and particle B are in an entangled state then telling you everything there is to say about particle A and telling you everything there is to say about particle B doesn’t tell you everything there is to say about the combined state about the particle A plus particle B system."
If you can free yourself from assuming separability, Myrvold argues, then when you observe one part of an entangled system, you will not be fooled into thinking of it as a separate object and become sidetracked worrying about how it can influence other separate objects. Myrvold believes that this misunderstanding leads us to falsely associate a single reference point in time with that part of the system, skewing our perception of what can happen to the rest of the system and when.
With an FQXi grant of over $56,000
, Myrvold will be working out just how to weave non-separability into quantum mechanics explicitly, so that its not longer perceived as a strange and mysterious byproduct of the theory, but as a central—normal—feature. In addition to preparing a series of papers, he plans to work with other experts, both in philosophy and physics, at various workshops.
If you take quantum mechanics
seriously, it’s separability that
you have to give up.
- Wayne Myrvold
Tim Maudlin, a philosopher at New York University, says that Myrvold is one of the few people who appreciate the subtle implications of entanglement with its correlations between objects separated by long distances. However, he does not think that focusing on non-separability will be enough to create a local theory—one that does not seem to violate the speed of light—that also fits with quantum observations.
"If you believe that those correlations are correctly predicted by quantum mechanics then you are stuck with non-locality," says Maudlin. "The deal is not about how do I get around it, but how do I deal with it and work it into my physics in a clearer way."
Bedingham, who last year won FQXi’s Most Courageous Postdoc prize
, has his own strategy for bringing quantum mechanics into line with relativity. In this model, the two entangled particles are on two unique, but interacting, hyperspaces. When one particle is observed, its wavefunction collapses sending out a ripple in that hyperspace. The second particle’s properties change when that ripple effect is felt on the adjacent hyperspace. (Read our Q&A with Daniel Bedingham
for more details.)
At present, it is difficult to think of a test that could discriminate between theories of wavefunction collapse. Myrvold notes that arguments about these issues date back to the birth of quantum mechanics, with little resolution. "It might look like people are just going around in circles and getting nowhere," he admits. "But even if we haven’t reached consensus, we have a much better appreciation for what the viable options are and how to think about them."
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ERIC STANLEY REITER wrote on August 5, 2012
read all article comments
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