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Thread: Crowdfunded physics project sheds new light on the nature of... light

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    Master OptiBoarder rinselberg's Avatar
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    Crowdfunded physics project sheds new light on the nature of... light

    The nature of light, more or less. The project involves experiments using photons, which are the quantum scale foot soldiers that cause light. And who better than an audience of opticians (Eye Wear professionals) and ODs and MDs (Eye Care Professionals) to appreciate a discovery related to light, which is nothing if not the lifeblood--the raison d'ętre--behind the creation of this online discussion forum. But I digress. Let me regress:

    In a setback for Quantum Reverse Causality or "Time Reversal" boffins, a crowdfunded physics project at the University of Washington seems to have arrived at a dead end, running up against an inherent or underlying "No Quantum Weirdness Allowed" property of nature that was suspected, but not considered a certainty by what passes for consensus among the quantum physics community.

    This crowdfunded project depends on quantum entanglement, which is a testable and repeatable real world phenomenon, as demonstrated by a number of recent and somewhat recent experiments conducted in physics research labs around the world. I've been fumbling at my keyboard, trying to come up with my next sentence. Instead, I will just plug into Monday's report on the NBC Science News webpage:
    One of the longest-running and weirdest examples of a crowdfunded scientific experiment is finally reaching the end of the road, and the results will come as a disappointment to anyone who wishes the "Back to the Future" movies could really happen: Quantum interference foils what once looked like a plausible strategy for influencing events in the past.

    "The trick doesn't work in its present form," John Cramer, a physics professor emeritus at the University of Washington in Seattle, told NBC News.

    Cramer suspected that would be the case, but back in 2006, he was interested in figuring out exactly why it wouldn't work. The trick involved trying to flip a switch that would have an effect not only on photons going through a complicated set-up of lasers and mirrors, but also on entangled photons that had gone through the set-up about 50 microseconds earlier.

    "We were looking at whether there might be a loophole that would allow you to do this," Cramer said.
    To cut to the chase:
    Cramer thought he could use a wedge-shaped mirror to split a photon beam into two signals that were partly entangled and partly coherent. Theoretically, he should have been able to analyze the interference patterns to see how fiddling with one signal affected the other one microseconds earlier.

    It turned out not to be that easy.

    "We analyzed it up, down and sideways, and concluded that what happens is, yes, you have a switchable interference pattern," Cramer said. "But because you have no coincidence measurement, you can't look at just one interference pattern. You have to add up two patterns. And they always add up to no signal."
    In other words:
    When you analyze the quantum signal from earlier in time, you have to include an "anti-signal" in your calculations. Thus, the future leaves no fingerprints on the past. "Nature appears to be well-protected from the possibility of nonlocal signaling," according to Cramer and his co-author, Nick Herbert.
    NBC Science News: "Reverse Causality Research Ends in a Quantum Muddle"

    If you want to see how Cramer and Herbert reported their results for the quantum physics community--perhaps you're a "scientist", or failing that, stayed overnight at a Holiday Inn--it's accessible online:

    "An Inquiry into the Possibility of Nonlocal Quantum Communication"

    That's an abstract, with links on the righthand sidebar to access the complete writeup.

    Looking back to what one of the most foundational physicists of the 20th century thought about the possibility of Nonlocal Quantum Communication, Einstein has been famously quoted as having dissed the likelihood of quantum entanglement as "spooky action at a distance". He didn't expect that this conjecture from the pioneers of quantum physics would stand up to the test of laboratory experiments, which depend on technologies like lasers and super-fast electronics that were only developed to a high enough level after his lifetime. The history of quantum entanglement experiments only goes back as far as about 15 or 20 years (for the most part), with the most provocative experiments only in the last 10 or 12 years.

    There is a discussion from 2011 (in the archive of another online forum) about a conjecture that the Large Hadron Collider or LHC (world's most powerful "atom smasher") could detect a Higgs boson traveling backwards in time: i.e., a Higgs boson caused by an experiment at the LHC facility that was on the LHC scientists' "drawing board" or "To Do List", but an experiment that they had not yet started to run using the actual machinery of the LHC.

    "High Energy Physics: Looking for particles traveling backwards in time"
    Last edited by rinselberg; 04-08-2015 at 12:37 PM.

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