The Universe Is Not Locally Real, and the Physics Nobel Prize Winners Proved It

The Universe Is Not Locally Real, and the Physics Nobel Prize Winners Proved It

One of the most disturbing discoveries in the past 50 years is that the universe does not exist locally. “Real” refers to objects having definite properties that are independent of observation. An apple can be red even if no one is looking. “Local” means objects cannot be influenced by their environment and any influence cannot travel faster that light. These two things cannot be true, according to quantum physics research. Instead, evidence has shown that objects are not affected solely by their surrounding and may also lack definite property prior to measurement. Albert Einstein famously said to his friend, “Does the moon really exist when you don’t look at it ?”

?”

This is, of course a stark contrast to our daily experiences. Douglas Adams said that the loss of local realism has caused a lot of people to be very upset and was widely regarded as a bad decision.

The blame for this achievement has been laid squarely upon three physicists: John Clauser and Alain Aspect . They equally split the 2022 Nobel Prize in Physics “for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science.” (“Bell inequalities” refers to the pioneering work of the Northern Irish physicist John Stewart Bell, who laid the foundations for this year’s Physics Nobel in the early 1960s.) Colleagues agreed that the trio had it coming, deserving this reckoning for overthrowing reality as we know it. It is amazing news. It was long overdue,” Sandu Popescu, a quantum scientist at the University of Bristol, said. “Without any doubt, the prize is well-deserved.”

” The experiments that began with the earliest Clauser one and continued on, show that this stuff doesn’t just have philosophical value, but is real–and, like other real things–potentially useful,” said Charles Bennett, an IBM quantum researcher.

“Every year I thought, “oh, maybe that is the year,”” David Kaiser, a historian and physicist at the Massachusetts Institute of Technology, said. It was a great year. It was very emotional–and very thrilling.”

Quantum foundations had a long journey from fringe to favour. From about 1940 until as late as 1990, the topic was often treated as philosophy at best and crackpottery at worst. Many scientific journals refused papers on quantum foundations. Academic positions that were willing to indulge in such investigations were almost impossible to find. In 1985, Popescu’s advisor warned him against a Ph.D. in the subject. Popescu states that his advisor warned him against pursuing a Ph.D. in the subject. “He said, “Look, if I do that, you will have five years of fun, and then you’ll be jobless.”

Today quantum inform science remains one of the most exciting and influential subfields of physics. It connects Einstein’s general theory about relativity with quantum mechanics through the still-mysterious behavior black holes. It explains the function and design of quantum sensors, which are increasingly used to study everything, from earthquakes to dark matter. And it clarifies the often-confusing nature of quantum entanglement, a phenomenon that is pivotal to modern materials science and that lies at the heart of quantum computing.

” What makes a quantum computer “quantum”?” Nicole Yunger Halpern is a National Institute of Standards and Technology (NIST) physicist. “Entanglement is one of the most popular answers. The main reason we understand entanglement and the grand work performed by Bell and these Nobel Prize-winners is why it is so important. Without that understanding of entanglement, we probably wouldn’t be able to realize quantum computers.”

For Whom The Bell Tolls

The trouble with quantum mechanics was never that it made the wrong predictions–in fact, the theory described the microscopic world splendidly well right from the start when physicists devised it in the opening decades of the 20th century.

What Einstein, Boris Podolsky and Nathan Rosen took issue with, laid out in their iconic 1935 paper, was the theory’s uncomfortable implications for reality. Their analysis, which was known as EPR, was based on a thought experiment that showed how quantum mechanics can be broken or produce nonsensical results. This contradicted everything we know about reality. EPR can be simplified and modernized to look like this: Two pairs of particles are sent in different directions from one source. They are targeted for Alice and Bob, who are each at opposite ends of our solar system. Quantum mechanics states that it is impossible to measure the spin of individual particles. Alice measures one of her particles and finds that its spin is either up down .. Although her results are random, she quickly recognizes that Bob’s corresponding particle must have down .. This may seem odd at first glance. Perhaps the particles are similar to a pair of socks: if Alice has the right sock Bob must have the left.

But quantum mechanics states that particles are not , and only after being measured can they settle on a spin up down .. This is the key problem in EPR: If Alice’s particles don’t have a spin until measurement, how can they determine what Bob’s particles will do when they fly out of this solar system in the opposite direction? Alice measures and quizzes her particle about what Bob will get if it flips a coin. up , down ?. The odds of correctly predicting this even 200 times in a row are 1 in 1060–a number greater than all the atoms in the solar system. Despite the distances between the particle pairs, quantum mechanics claims that Alice’s particles can still correctly predict, even though they are separated by billions of kilometers.

Although the idea of quantum mechanics’ imperfections is intended, the results of real-world EPR thought experiments reinforce the theory’s most astounding tenets. Quantum mechanics states that nature is not local real. The particles lack properties such spin or spin before measurement. They seem to talk to each other regardless of distance.

Physicists who were skeptical of quantum mechanics suggested that there were “hidden variable” factors. These variables existed in an imperceptible realm below the subatomic realm and contained information about a particle’s future state. They believed that hidden-variable theories would allow nature to regain the local realism it was denied by quantum mechanics.

” One would have thought that the arguments from Einstein, Podolsky, and Rosen would create a revolution at that time, and that everyone would have started to work on hidden variables,” Popescu states.

Einstein’s “attack” on quantum mechanics, however, did not catch on among physicists, who by and large accepted quantum mechanics as is. This was often less a thoughtful embrace of nonlocal reality, and more a desire to not think too hard while doing physics–a head-in-the-sand sentiment later summarized by the physicist David Mermin as a demand to “shut up and calculate.”

The lack of interest was driven in part because John von Neumann, a highly regarded scientist, had in 1932 published a mathematical proof ruling out hidden-variable theories. (Von Neumann’s proof, it must be said, was refuted just three years later by a young female mathematician, Grete Hermann, but at the time no one seemed to notice. )

Quantum mechanics’ nonlocal realism problem would continue to be a problem for three decades before being finally solved by Bell. Bell was averse to quantum orthodoxy from the beginning of his career. Inspiration struck him in 1952, when he learned of a viable nonlocal hidden-variable interpretation of quantum mechanics devised by fellow physicist David Bohm–something von Neumann had claimed was impossible. Bell worked as a particle physicist at CERN for many years and mulled over the ideas for years.

In 1964, Bell rediscovered the same flaws in von Neumann’s argument that Hermann had. And then, in a triumph of rigorous thinking, Bell concocted a theorem that dragged the question of hidden variables from its metaphysical quagmire onto the concrete ground of experiment.

Normally, hidden-variable theories as well as quantum mechanics predict identical experimental outcomes. Bell discovered that there can be an empirical discrepancy in the results of both theories, provided they are applied under specific circumstances. The Bell test, an evolution of the EPR thought experiment, gives Alice and Bob identical paired particles. However, they now have two different detector settings: A and B, B, and b. These detector settings enable Alice and Bob to ask different questions to the particles, which is an additional trick to discredit their apparent telepathy. Local hidden-variable theories are preordained, so particles cannot outsmart this extra step. This is why they can’t always achieve perfect correlation. For example, Alice measures spin while Bob measures spin up . Quantum mechanics shows that particles are connected and more correlated in quantum mechanics than they were in local hidden-variable theory. They are, in other words, entangled.

Measuring correlation multiple times for many particles pairs could prove which theory is correct. If the correlation is below a limit determined by Bell’s theorem this would indicate that hidden variables are real. If it exceeds Bell’s limit then quantum mechanics’ mind-boggling tenets would prevail. Even though it has the potential to determine the nature of reality, Bell’s theorem was not noticed for many years.

The Bell Tolls for You

In 1967, John Clauser, then a graduate student at Columbia University, accidentally stumbled across a library copy of Bell’s paper and became enthralled by the possibility of proving hidden-variable theories correct. Two years later, Clauser wrote to Bell asking if anyone had ever performed the test. Bell received the first feedback from Clauser in his letter.

With Bell’s encouragement, five years later Clauser and his graduate student Stuart Freedman performed the first Bell test. Clauser had obtained permission from his supervisors but not much in the way of funding so, five years later, Clauser and Stuart Freedman performed the first Bell test. Clauser’s setup was a kayak-sized apparatus that required careful tuning by hand. Two pairs of photons were sent in opposite directions to detectors that could measure their state or polarization.

Unfortunately, Clauser’s obsession with hidden variables led to him and Freedman concluding that strong evidence was against them. The result was not conclusive because of several “loopholes” that could have allowed hidden variables to slip unnoticed. The most worrying was the “locality loophole”: If either the detectors or the photon source could have somehow shared information (a plausible feat within a kayak-sized object), then the resulting measured correlations could still be derived from hidden variables. Kaiser put it succinctly: If Alice tweets Bob which detector setting she is in, that interference makes it impossible to rule out hidden variables.

Closing the locality loophole can be difficult. It is important to change the detector setting quickly while photons are moving at lightning speed. This means that it should be done in just a few nanoseconds. In 1976, a young French expert in optics, Alain Aspect, proposed a way for doing this ultra-speedy switch. His group’s experimental results, published in 1982, only bolstered Clauser’s results: local hidden variables looked extremely unlikely. “Perhaps Nature is not so queer as quantum mechanics,” Bell wrote in response to Aspect’s initial results. “But the experimental situation is not very encouraging.

Other loopholes, however, still remained–and, alas, Bell died in 1990 without witnessing their closure. Even Aspect’s experiment could not completely rule out local effects as it was conducted over too short a distance. Clauser and others realized that if Alice or Bob didn’t have a representative sample of particles to analyze, they could draw incorrect conclusions.

Anton Zeilinger, an ambitious and gregarious Austrian scientist, was the one who jumped in to close these loopholes. In 1998, he and his team improved on Aspect’s earlier work by conducting a Bell test over a then-unprecedented distance of nearly half a kilometer. The era of divining nonlocality’s reality from kayak-sized experiments was over. Finally, in 2013, Zeilinger’s group took the next logical step, tackling multiple loopholes at the same time.

“I was actually interested in engineering before quantum mechanics. Marissa Giustina, a quantum researcher at Google and Zeilinger’s collaborator, says that she enjoys building things with her hands. “In retrospect, a loophole-free Bell experiment is a giant systems-engineering project.” One requirement for creating an experiment closing multiple loopholes was finding a perfectly straight, unoccupied 60-meter tunnel with access to fiber optic cables. The dungeon at Vienna’s Hofburg palace proved to be a perfect setting, aside from the fact that it was covered in dust for over a century. Their results, published in 2015, coincided with similar tests from two other groups that also found quantum mechanics as flawless as ever.

Bell’s Test Reaches the Stars

One last loophole remains to be closed or at least narrowed. Any previous physical connection between components can affect the validity of a Bell Test’s results, regardless of how far back they may have been. They share a past if Alice shakes Bob’s hands before they depart on a spaceship. Although it seems unlikely that a local hidden-variable theory would exploit such loopholes, it is possible.

In 2017, a team including Kaiser and Zeilinger performed a cosmic Bell test. The team used telescopes in the Canary Islands to source its random decisions for detector settings. They used stars sufficiently far apart in space that light from one star would not reach the other for hundreds upon centuries, creating a gap of centuries in their shared cosmic history. But quantum mechanics still won the day.

The main problem in explaining the importance and significance of Bell tests to the general public, as well as skeptical physicists, is the perception that quantum mechanics was an established fact. After all, researchers have measured many key aspects of quantum mechanics to a precision of greater than 10 parts in a billion. “I didn’t want it to be a part of my work. I thought, “Come on, this is old physics.” Giustina said that we all know what’s coming. However, quantum mechanics accuracy cannot rule out local hidden variables. Only Bell tests could.

“What attracted each of these Nobel winners to the topic and what attracted John Bell to the topic was actually [the question], “Can the world work this way?” Kaiser said. “And how can we really know with confidence?” Bell tests allow physicists remove the biases of anthropocentric aesthetic judgements from the equation. They purge from their work those parts of human cognition which recoil at the possibility eerily unexplicable entanglement or that dismiss hidden-variable theories. This award is given to Zeilinger, Aspect, and Clauser. However, it is a testament to all those researchers who were not satisfied with superficial explanations of quantum mechanics and who asked questions even though they were not popular.

“Bell tests,” Giustina concludes, “are a very useful way of looking at reality.”

ABOUT THE AUTHOR(S)

    Daniel Garisto is a freelance science journalist covering advances

    Read More