Posted on August 20, 2018
"If a conspiracy takes place to simulate quantum mechanics through a mechanism that is actually classical, that mechanism would have had to begin its operations ̵
Last year, physicists at MIT from Vienna and elsewhere strongly supported quantum entanglement, the seemingly distant idea that two particles, no matter how far away they may be in space and time, can be inextricably linked to each other Contradict rules of classical physics.
Take, for example, two particles sitting on opposite edges of the universe. If truly entangled, their physical properties should be correlated, according to quantum mechanics theory, so that each measurement of a particle could immediately provide information about future measurement results of the other particle correlations that Einstein viewed skeptically as a "scary, distant effect."
In the 1960s, the physicist John Bell calculated a theoretical limit beyond which such correlations must have a quantum theory rather than a classical explanation.
But what if such correlations are? Result not from quantum entanglement, but from another hidden, classical explanation? Such "what-ifs" are known to physicists as loopholes for tests of Bell's inequality, the most stubborn of which is "freedom of choice": the possibility that a hidden, classical variable may influence the measurement an experimenter chooses to act on an entangled particle so that the result looks quantum correlated although it is not.
Last February, the MIT team and its colleagues curtailed freedom of choice by using the 600-year-old starlight to determine which properties of two entangled photons should be measured. Their experiment proved that if a classical mechanism had caused the observed correlations, it would have had to be set in motion more than 600 years before the light of the stars was first emitted and well before the actual experiment was conceived]
In an article published today in Physical Review Letters, the same team has significantly broadened the argument for quantum entanglement and further limited the scope for freedom of choice. The researchers used distant quasars, one of which emitted 7.8 billion years ago and the other 12.2 billion years ago its light to determine the measurements on pairs of entangled photons. They found correlations of more than 30,000 photon pairs to an extent that far exceeded the limit that Bell originally calculated for a classically based mechanism.
"Earth is about 4.5 billion years old, so any alternative mechanism – unlike quantum mechanics, who could have produced our results by exploiting this gap, would have needed to be Earth long before the very existence of a planet silent about an MIT, "adds David Kaiser, the Germeshausen professor of science history and professor of physics physics at MIT. "So we brought alternative explanatory patterns back into cosmic history at a very early stage."
The co-authors of Guth and Kaiser include Anton Zeilinger and members of his group at the Austrian Academy of Sciences and the University of Vienna, as well as physicists at Harvey Mudd College and the University of California at San Diego.
Two members of the current team, Jason Gallicchio and Andrew Friedman, proposed an experiment to generate entangled photons on Earth – a fair process standard in quantum mechanics studies. They planned to direct each limb of the entangled pair in opposite directions toward light detectors, which would also make a measurement of each photon using a polarizer. The researchers would measure the polarization or orientation of the electric field of each incoming photon by adjusting the polarizer at different angles and observing whether the photons pass – a result for each photon that researchers could compare to determine if the particles were the same have predicted characteristic correlations
The team added a unique step to the proposed experiment, using light from ancient remote astronomical sources, such as stars and quasars, to determine the angle at which each polarizer was tuned. As each entangled photon was in flight and approaching its detector at the speed of light, the researchers used a telescope located at each detector location to measure the wavelength of the incident light from a quasar. If this light were redder than a reference wavelength, the polarizer would be tilted at a certain angle to make a specific measurement of the incoming entangled photon – a measurement choice determined by the quasar. If the light of the quasar were bluer than the reference wavelength, the polarizer would flip at a different angle and perform another measurement of the entangled photon.
In their previous experiment, the team used small backyard telescopes to measure the light from stars near 600 light-years away. In their new study, researchers used much larger and more powerful telescopes to capture the incoming light from even older, distant astrophysical sources: quasars whose light has traveled to Earth for at least 7.8 billion years – objects that are incredibly far away and yet they are so luminous that their light can be observed from the earth.
On January 11, 2018, "the clock had just clocked in after midnight local time," Kaiser recalls, when about a dozen members of the team gathered a mountain peak in the Canary Islands and began data from two large, 4 -meter-wide telescopes The William Herschel Telescope and the Telescopio Nazionale Galileo, both located on the same mountain and about one kilometer apart.
One telescope focuses on one particular quasar, while the other telescope looks at another quasar in another part of the night sky. Meanwhile, researchers at one station formed pairs of entangled photons between the two telescopes, radiating particles from each pair in opposite directions to each telescope.
In the fraction of a second before each entangled photon reached its detector, the instrumentation determined whether a single photon arriving from the quasar was more red or blue, a measure that then automatically matched the angle of a polarizer who finally received and recognized the incoming entangled photon.
"The timing is very difficult," says Kaiser. "Everything has to happen within very narrow windows and update every microsecond."
The researchers performed their experiment twice for about 15 minutes each and with two different pairs of quasars. They measured 17,663 and 12,420 pairs of entangled photons for each run. Within a few hours of closing the telescoping domes and looking at preliminary data, the team found that there were strong correlations between the photon pairs, beyond the limit calculated by Bell, suggesting that the photons were quantum mechanically correlated.
Guth conducted a more detailed analysis to calculate the – albeit small – chance that a classical mechanism might have produced the correlations observed by the team.
He calculated for the best of the two runs the likelihood of a mechanism based on classical physics. The observed correlation would have been about 10 to minus 20 – that is, about a part of one hundred billion billions, "outrageously small," says Guth For comparison, the researchers estimated the likelihood that the discovery of the Higgs boson was only a random trap of about one in a billion.
"We have made it incredibly unlikely that a realistic theory of physics could underlie the universe," says Guth.
And yet, there is still a small opening to the electoral gap. To further delineate, the team offers ideas to look further back in time and to use sources such as cosmic microwave background photons, which were emitted as leftover radiation immediately after the Big Bang.
"It's fun to think about new kinds of experiments that we can design in the future, but for the moment we are very glad that we could tackle this particular gap so dramatically." Our experiment with quasars sets extremely narrow limits for different ones Alternatives to quantum mechanics As strange as quantum mechanics may seem, it still fits in with any experimental test we can develop, "says Kaiser.
The Daily Galaxy via MIT
Credit: Thanks to Robin Dienel / Carnegie Institute of Science