a flaw in the theory of relativity -- 12/16/15
Today's selection -- from Spooky Action At A Distance by George Musser. Even as Albert Einstein championed his theory of relativity, and even though that theory has revolutionized modern life in countless ways, Einstein knew of a phenomenon that directly contradicted that theory. Specifically, action upon one of two photons that are entangled with each other, (in other words photons who interact in ways such that the quantum state of each particle cannot be described independently), immediately impacts the other, even when separated by hundreds of miles. This implies causality at a speed faster than the speed of light, which, according to the theory of relativity, is impossible. Einstein described it as "spooky action at a distance." This highly controversial phenomenon, sometimes referred to as nonlocality, may revolutionize physics and our understanding of the world:
"If anyone has taken it on himself to show the world what quantum entanglements look like, it's [Colgate University's Enrique] Galvez. Entanglement is the best known of several types of nonlocality that modern physicists have observed, and the one that spooked Einstein. ... On the day I visit Galvez's lab, one of his optical benches is given over to the entanglement experiment, and ... Galvez is ready to take some data. To verify that everything is working properly, he first simulates flipping ordinary coins by setting the waveplate to produce unentangled photons. The meter reads about twenty-five coincidences per second. For comparison, you'd get one hundred coincidences per second if every single photon in every single pair made it through the filters. So, the coincidence rate is about a quarter of its maximum possible value. This is just what you'd expect from the laws of chance. If you take two coins and flip them, each will come up heads about half the time, so both will be heads about a quarter of the time. Now Galvez adjusts the waveplate to generate entangled photons.
"The coincidence rate jumps to about fifty per second. A change from twenty-five to fifty on a digital readout in a basement lab might not seem like much. But that's physics for you. It takes effort to peer beneath the surface of the world around us, and the clues are subtle, but they are no less dramatic for that. All those years of waiting and preparing for this moment have paid off, because when I see that fifty, I realize what I am seeing, and I shiver. The photons are behaving like a pair of magic coins. Galvez flips thousands of such pairs, and both always land on the same side: either both heads or both tails. That kind of thing doesn't happen by pure dumb luck.
Normal Coins | Quantum Entangled Coins | ||
Left Coin | Right Coin | Left Coin | Right Coin |
heads | tails | heads | heads |
tails | tails | tails | tails |
heads | heads | heads | heads |
tails | tails | tails | tails |
tails | heads | tails | tails |
tails | heads | tails | tails |
heads | tails | heads | heads |
heads | heads | heads | heads |
"If a friend of mine did this trick at a party -- flip pairs of coins so that both came up heads twice as often as they rightfully should -- I'd assume it was a practical joke. My friend might have gone to a magic shop and bought double-sided coins, which look the same on both sides, making the outcome of a flip preordained. ...
"I go over and look at the optical bench again. Those filters are separated by the width of my hand. Experiments by Zeilinger and others have stretched the distance to one hundred miles, and researchers at the Centre for Quantum Technologies are working on a space-based version that will go even farther. For a tiny particle, that might as well be the other side of the universe. The photons manage to coordinate their behavior across that gap. They are not in contact, and no known force links them, yet they act as one. ... What happens on the left affects the photon on the right, even when there's no time for any kind of influence to cross the gap. Indeed, such an influence would need to travel from left to right instantly -- that is, infinitely fast, which is plainly faster than light, in apparent defiance of the theory of relativity. This is one of the many mysteries posed by nonlocality. Physicists have commented that it is as close to real magic as they've ever seen.
" 'Students love it,' Galvez says. 'The good students say, "I want to figure this out." '
"Is nonlocality just a carnival freak show -- fun to ooh and aah over, but having no broader implications -- or does it belong on the center stage of physics? For most of the twentieth century, physicists treated it as a freak show, and as a student I adopted this attitude, too. ...
"Einstein ... fretted that nonlocality defied the theory of relativity. Physicists can't give up quantum theory; it passes all experimental tests. For relativity to be wrong is equally unthinkable. In a lecture in 1984, Bell concluded, 'We have an apparent incompatibility, at the deepest level, between the two fundamental pillars of contemporary theory.' ...
"[But there has been] a surge of interest in entanglement. Experimentalists, realizing that the phenomenon wasn't as useless as they'd thought, were beginning to exploit it for cryptography and computers. For instance, Artur Ekert, a physicist at the University of Oxford and currently the director of the Centre for Quantum Technologies, proved in 1991 that entangled particles can create a communications channel so secure that not even the sneakiest government surveillance program could listen in. Once physicists were clued in to the importance of entanglement, they began to see it almost everywhere they looked. It occurs even in living organisms. In photosynthesis, entanglement accounts for the unexpectedly high efficiency with which molecules transfer light energy into chemical energy, thereby helping to enable life on our planet.
"By the turn of the millennium, Einstein's paper [on nonlocality] that got it all started had become one of the most widely cited articles in the history of physics."
author: |
George Musser |
title: |
Spooky Action at a Distance |
publisher: |
Scientific American / Farrar, Straus and Giroux |
date: |
Copyright 2015 by George Musser |
pages: |
18-23 |
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