- Important: All passwords were reset on 06/15/11. Old passwords will no longer work. Click here to retrieve your password.
- Subscribe to Our Free Dewsletter
We are non-commercial, all volunteer and supported by our readers. Please help sustain the Dew by making a donation.
Science’s Sacred Cows: Realism
In the previous post, we discussed a fiendishly clever gedanken experiment posed in 1935 by Einstein and co-workers and designed to expose presumed flaws in quantum mechanics (QM). When the so-called “EPR paradox” was finally tested experimentally in 1977 at Lawrence Berkeley Laboratory, the results were a resounding victory for QM, while ringing the death knell for Einstein’s cherished principle of local causes. The “EPR paradox” — and Bell’s Theorem, which ultimately led to its resolution — firmly established the notion of quantum entanglement. Further experiments over the past three decades have moved entanglement from the status of novelty into the mainstream of physics. Today we discuss further experiments involving entanglement that call into question another of science’s tacit assumptions: realism.
Realism is the philosophical stance of most sane human beings, scientists included. Realism asserts: “All measurement outcomes depend on pre-existing properties of objects that are independent of the measurement.” In layman’s terms, there’s a real world out there independent of us (although we may see it differently because of variations in our measurement devices, i.e., our eyes and lenses). After all, if I ski down a slope and collide with a tree in my path, it makes little difference whether or not I believe the tree is real. Most persons — a few Zen philosophers excepted (“What sound does a falling tree make if no one hears?”) would assert that the tree has a reality all its own, independent of me. But in the microscopic world of the quantum, things are so very different than our macroscopic experiences would lead us to believe.
Recall from the previous post that the paper by Einstein, Podolsky, and Rosen (hence the moniker “EPR”) involved two-particle (say two photon) systems in which twin particles are spatially separated by a vast distance. Certain implications of QM, fretted Einstein, suggested that measuring the polarization of one photon would instantaneously set the polarization of its twin, violating the principle of local causes.
Let’s carefully parse Einstein’s words when he sprang the EPR trap to conclude that QM is incomplete.
“One can escape from this conclusion [that quantum theory is incomplete] only by either assuming the measurement of [photon 1 telepathically] changes the real situation at [photon 2] or by denying independent real situations as such to things which are spatially separated from each other. Both alternatives appear to me entirely unacceptable.”
By referring to “the real situation” and “independent real situations,” Einstein explicitly assumed physical realism. Furthermore, by assuming that spatially separated particles could not instantly “communicate,” he invoked the principle of local causes. Thus Einstein made two fundamental and independent assumptions: locality and realism.
Because of the profound implications of entanglement, researchers around the world continue to propose and conduct experiments to further clarify the remarkable phenomenon. To summarize their collective results prior to 2007: experiments based upon Bell’s Theorem prove “that all hidden-variable theories based on the joint assumption of locality and realism [emphases added] are at variance with the predictions of quantum mechanics.” The logical conclusion from these results is that theories based on local realism fail to be consistent with the predictions of QM because at least one assumption fails. But which?
In 2007, a group of researchers at premier institutions in Austria and Poland collaborated to perform yet another stunning EPR-like investigation. The experiment, by Simon Gröblacher and a host of coworkers, tested a new theorem by A. Leggett (2003) that further refines Bell’s theorem. Leggett’s theorem yields a mathematical inequality that, when combined with Bell’s inequality, permits the independent testing of Einstein’s two assumptions: locality and realism. The results of Gröblacher’s team, published in Nature (April 19, 2007), once again validated quantum mechanical predictions. That was to be expected. The unexpected occurred in identifying which assumption of local realism failed. Locality or realism? Surprisingly, both. The authors concluded:
“Our result suggests that giving up the concept of locality is not sufficient to be consistent with quantum experiments, unless certain intuitive features of realism are [also] abandoned.”
An independent reality, it now appears, has become the latest casualty of QM. The universe is nonlocal, nondeterministic, and apparently “unreal” as well. Haldane was right: the universe, at least at the quantum level, is “queerer” than we can imagine.
- Image: Licensed by LikeTheDew.com at 123RF.com
Worthy of Comment
Also on the Dew
That’s what the spouse said when I wrote him how surprised and disappointed I was to discover that Michelle Nunn has gratuitously endorsed the XL pipeline from Canada, because buying oil from “neighbors” is better than from overseas, as well as to read a report that Nunn wants changes to Obamacare to allow cheaper policies for the young. Like they don’t have car accidents and sports injuries, etc? (Read the other day that there’s a chance auto and workmen’s comp insurance rates are going to decrease now that people have health insurance. Ripple effect). He went on to observe that “Kenny and Tracy hav Read on →
Ever hear of "due diligence?" That's a term often seen in business stories, particularly when public accountants are working at checking the financial background of companies who might want to buy or sell to one another. Some people at the University of Georgia apparently don't understand or use the term "due diligence," especially when it comes to recruiting football players. One group defines "due diligence" in two ways: 1. An investigation or audit of a potential investment. Due diligence serves to confirm all material facts in regards to a sale. 2. Generally, due diligence refers to the care a reasonable person should take before Read on →
"Where your treasure is, there will your heart be also." -- Matthew 6:21. On April 4, 1967, exactly one year before he was assassinated, Martin Luther King, Jr. made public his opposition to the Vietnam War, articulated in his iconic "Beyond Vietnam" speech. Presented at Riverside Church in New York City, "Beyond Vietnam" was the most controversial speech King ever delivered. In it, he confronted head-on America's "triple evils" -- racism, economic injustice, and militarism -- and called for "a radical revolution of values" to restore our nation's integrity. Afterwards, many supporters, black and white, abandoned him for daring to mix the Read on →
How many of you are aware that Albert Einstein taught a physics class at Lincoln University (an HBCU in Pennsylvania) in 1946? In doing so, the Nobel Prize-winning scientist once said, "The separation of the races is not a disease of colored people. It is a disease of white people. I do not intend to be quiet about it.” Another noted figure, Martin Luther King, once said, “Our lives begin to end the day we become silent about the things that matter.” But we have become silent, for I don’t see the human outcry about where we are today. We have be Read on →