Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Friday, October 14, 2022

Nonlocal and unreal

This year, the Nobel Prize in Physics went to three scientists who have proven beyond a shadow of a doubt that our common-sense perception of how the universe works is very, very far off from the reality.

What that reality actually is remains to be seen.

John Clauser, Alain Aspect, and Anton Zeilinger were the recipients of the award this year "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science."  Their experiments established a mind-boggling fact: the universe is not locally real.

What that means, in non-technical language, is harder to pin down.  In physics, the concept of locality has to do with the fact that information transfer has a speed limit -- the speed of light.  If an event occurs at one point in space, then that event can only affect another point in space if it's nearby enough that light has enough time to travel between one and the other.  Reality means that an object's properties are independent of observation; it's a hard-science version of the time-honored question, "if a tree falls in the forest, and no one is there, does it make a sound?"

While the "locality" piece isn't perhaps something that impacts us on a daily basis -- light travels so fast that on the scales we usually deal with, it may as well be instantaneous -- "reality" certainly does.  Even the physicists balked for decades against the hints they were getting that locality and reality were on shaky ground.  No less a luminary than Albert Einstein said, "Do you really believe that the Moon is not there when you are not looking at it?"  But ever since Northern Irish physicist John Stewart Bell first proposed that there was something at the heart of quantum mechanics that called local reality into question, way back in 1962, the loopholes for avoiding that bizarre conclusion have been closing one by one.

The heart of the problem lies with entanglement.  The idea here is that you can create a pair of particles such that you know if one has a particular property (such as a spin axis pointing up) the other will have the opposite property (spin axis pointing down).  So far, nothing too weird about that.  It's no odder than putting each of a pair of gloves into a sealed box, and handing a box to your friend; if when your friend opens his box, he finds a left-handed glove, you automatically know your box must contain the right-handed one.  The system was set up that way.

But what Bell implied was that this wasn't the case.  The gloves were neither right nor left until you opened one of the boxes; if your friend did that, and observed a left-handed glove, the glove in your box "sensed that" (whatever the hell that means!) and instantaneously became right-handed, regardless of how far apart they were at the time.  The measurement process somehow created the state of the system, even if the parts of it were separated by a distance too great for light to cross.

For a long time, the prevailing approach amongst physicists was just to pretend it wasn't happening, an approach David Mermin summed up as "shut up and calculate."  Perhaps there were "hidden variables" that made some sort of locally real explanation account for the strange phenomenon of entanglement; using our analogy, that the gloves were what they were even though they hadn't been observed yet, no superluminal communication necessary.  And for a while, they kind of got away with it.  But with a series of ingenious experiments, Clauser, Aspect, and Zeilinger conclusively showed that there are no hidden variables; the universe, it seems, is not locally real.

What exactly is happening is another matter.  The three recipients of this year's Nobel Prize in Physics have shown that what John Stewart Bell proposed sixty years ago is spot-on correct, as crazy as it sounds.  There is something about the process of observation that does lock the observed object into a particular state faster than should be possible; Schrödinger's long-suffering cat seems to be not a wild metaphor but how the universe actually works.

I find this whole thing fascinating but a little overwhelming.  It's hard to imagine how our physical surroundings can behave in a manner so completely opposite to our common-sense notions.  But Clauser, Aspect, and Zeilinger have demonstrated conclusively that they do -- and it lies with the rest of the physics community to tell us laypeople exactly what that means.


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