Dec. 8, 2014
Mr. Rothstein is a professor of physics at Carnegie Mellon University.
It is good to see movies such as Interstellar and The Theory of Everything achieving critical and box-office success—the latest evidence that the ideas involved in relativity and quantum mechanics can capture the imagination.
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Physicists, such as myself, who work on these abstract subjects are funded predominantly by dwindling government grants and have an obligation to communicate these ideas to the public. But relating abstract mathematical ideas to those with less training is difficult, and it requires some pedagogical shortcuts that by necessity are oversimplifications. Quite often one must rely on metaphorical tools that, while vaguely capturing the idea, can often lead to false conclusions.
The classic example of this comes from Albert Einstein. When trying to explain the concept of time dilation predicted in the theory of relativity, he said, “When you are courting a nice girl, an hour seems like a second. When you sit on a red-hot cinder, a second seems like an hour. That’s relativity.”
The maestro’s explanation is romantic, but it is also misleading: What Einstein was referring to is a psychological phenomenon, while time dilation is physical, as wonderfully depicted in Interstellar when the protagonist, Cooper, is forced to spend time in the proximity of a black-hole horizon, where his clock slows down relative to the Earth’s clock. Upon returning to Earth, he finds that his daughter, who was a teenager when he left, is now elderly, while he is still a young man.
Understanding the fundamental nature of space and time gives us an appreciation of our place in the universe. But we should be careful not to extrapolate these ideas improperly. The possible implications of quantum entanglement in particular have resonated in modern culture—whether in the physics-infused movies of the moment or in the poet and essayist Christian Wiman’s My Bright Abyss: Meditation of a Modern Believer (2013). He wrote: “If quantum entanglement is true, if related particles react in similar or opposite ways even when separated by tremendous distances, then it is obvious that the whole world is alive and communicating in ways we do not fully understand. And we are part of that life, part of that communication.”
While this is lovely prose, the conclusion is misleading. Quantum entanglement is a phenomenon in which two particles—say, electrons—are produced in such a way that they are correlated. So, if we know that one of them is spinning in one direction, then we know the other is spinning in the opposite way. What is remarkable about quantum mechanics is that we don’t know which way either particle is spinning until we measure it.
Moreover, the spin of each particle is “fuzzy”—in some sense, in multiple spin states at the same time—until this measurement is made. But once we measure one particle’s spin, the other particle’s spin is fixed instantaneously, even if they were on opposite sides of our galaxy. (This seems to violate the idea that nothing can travel faster then the speed of light, but that’s another story.)
Yet this quantum entanglement is extremely fragile and is destroyed by interactions with the surrounding environment. Trying to keep particles entangled at macroscopic-distance scales is a significant challenge for experimentalists. The truth is that humans are not interconnected by entanglement, at least not in the sense related by Mr. Wiman. I find it remarkable and inspiring that some of the discipline’s esoteric ideas have percolated into public consciousness, but we should be wary of applying them to matters that are better left to philosophers and theologians.
With millions of moviegoers seeing Interstellar and The Theory of Everything, the temptation is stronger than ever to misapply modern ideas of physics in viewing the world. But we don’t need science to illuminate how we are interconnected—it is our humanity and our shared experiences, our joys and sorrows, not quantum mechanics and relativity, that bind us.
Maybe that’s why the concept of time fascinates us so. After all, time is the fabric into which our lives are woven and in some sense defines the human condition. If we could only understand time better, maybe by finding the one “final equation”—as sought in “The Theory of Everything” by Stephen Hawking ( Eddie Redmayne ) and in “Interstellar” by Jessica Chastain ’s astrophysicist character—we would find some underlying secret that would shed light on the nature of our existence.
Personally, I can say that my research on black holes hasn’t helped me get any closer to the most effective answer to my children’s most profound question about time and space: “Are we there yet?”
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