Quantum pigeons

I have a fascination for quantum physics.  Not that I can say I understand it that well; but no less than Nobel laureate and generally brilliant guy Richard Feynman said (in his lecture "The Character of Physical Law"), "If you think you understand quantum mechanics, you don't understand quantum mechanics," so I figure I have a pretty good excuse for my lack of deep comprehension.  I have a decent, if superficial, grasp of such loopy ideas as quantum indeterminacy, superposition, entanglement, and so on, but that's about the best I can do.  At least I understand enough to find the following joke absolutely hilarious:

Heisenberg and Schrödinger were out for a drive one day, and they got pulled over by a cop.  The cop says to Heisenberg, who was driving, "Hey, buddy, do you know how fast you were going?"

 
Heisenberg says, "No, but I know exactly where I am."

 
The cop says, "You were doing 85 miles per hour!"

 
Heisenberg throws his hands in the air and responds, "Great!  Now I'm lost."

 
The cop scowls at him.  "All right, pal, if you're going to be a smartass, I'm going to search your car."  So he opens the trunk, and there's a dead cat inside it.  He says, "Did you know there's a dead cat in your trunk?"

 
Schrödinger says, "Well, there is now."

Thanks, you're a great audience. I'll be here all week.

In any case, the topic comes up because of a paper in Proceedings of the National Academy of Sciences called, "Experimental Demonstration of the Quantum Pigeonhole Paradox," by a team of physicists at China's University of Science and Technology, which was enough to make my brain explode.  Here's the gist of it, although be forewarned that if you ask me for further explanation, you're very likely to be out of luck.

There's something called the pigeonhole principle in number theory, that seems kind of self-evident to me but apparently is highly profound to number theorists and other people who delve into things like sets, one-to-one correspondences, and mapping. It goes like this: if you try to put three pigeons into two pigeonholes, one of the pigeonholes must be shared by two pigeons.

See, I told you it was self-evident.  Maybe you have to be a number theorist before you find these kind of things remarkable.

[Image licensed under the Creative Commons Razvan Socol, Rock Pigeon (Columba livia) in Iași, CC BY-SA 3.0]

In any case, what the research showed is that on the quantum level, the pigeonhole principle doesn't hold true.  In the experiment, photons take the place of pigeons, and polarization states (either horizontal or vertical) take the place of the pigeonholes.  And when you do this, you find...

... that when you compare the polarization states of the three photons, no two of them are alike.

Hey, don't yell at me.  I didn't discover this stuff, I'm just telling you about it.

"The quantum pigeonhole effect challenges our basic understanding….   So a clear experimental verification is highly needed," study co-authors Chao-Yang Lu and Jian-Wei Pan wrote in an e-mail.  "The quantum pigeonhole may have potential applications to find more complex and fundamental quantum effects."

It's not that I distrust them or am questioning their results (I'm hardly qualified to do so), but I feel like what they're claiming makes about as much sense as saying that 2 + 2 = 5 for large values of 2.  Every time I'm within hailing distance of getting it, my brain goes, "Nope.  If the first two photons are, respectively, horizontally polarized and vertically polarized, the third has to be either horizontal or vertical."

But apparently that's not true. Emily Conover, writing for Science News,writes:

The mind-bending behavior is the result of a combination of already strange quantum effects.  The photons begin the experiment in an odd kind of limbo called a superposition, meaning they are polarized both horizontally and vertically at the same time.  When two photons’ polarizations are compared, the measurement induces ethereal links between the particles, known as quantum entanglement.  These counterintuitive properties allow the particles to do unthinkable things.

Which helps.  I guess.  Me, I'm still kind of baffled, which is okay.  I love it that science is capable of showing us wonders, things that stretch our minds, cause us to question our understanding of the universe.  How boring it would be if every new scientific discovery led us to say, "Meh.  Confirms what I already thought."

****************************************

Timey-wimey light

I don't always need to understand things to appreciate them.

In fact, there's a part of me that likes having my mind blown.  I find it reassuring that the universe is way bigger and more complex than I am, and the fact that I actually can parse a bit of it with my little tiny mind is astonishing and cool.  How could it possibly be surprising that there's so much more out there than the fragment of it I can comprehend?

This explains my love for twisty, complicated fiction, in which you're not handed all the answers and everything doesn't get wrapped up with a neat bow at the end.  It's why I thoroughly enjoyed the last season of Doctor Who, the six-part story arc called "Flux."  Apparently it pissed a lot of fans off because it had a quirky, complicated plot that left a bunch of loose ends, but I loved that.  (I'm also kind of in love with Jodie Whittaker's Thirteenth Doctor, but that's another matter.)

I don't feel like I need all the answers.  I'm not only fine with having to piece together what exactly happened to whom, but I'm okay that sometimes I don't know.  You just have to accept that even with all the information right there in front of you, it's still not enough to figure everything out.

Because, after all, that's how the universe itself is.

[Nota bene: Please don't @ me about how much you hated Flux, or how I'm crediting Doctor Who showrunner Chris Chibnall with way too much cleverness by comparing his work to the very nature of the universe.  For one thing, you're not going to change my mind.  For another, I can't be arsed to argue about a matter of taste.  Thanks.]

In any case, back to actual science.  That sense of reality being so weird and complicated that it's beyond my grasp is why I keep coming back to the topic of quantum physics.  It is so bizarrely counterintuitive that a lot of laypeople hear about it, scoff, and say, "Okay, that can't be real."  The problem with the scoffers is that although sometimes we're not even sure what the predictions of quantum mechanics mean, they are superbly accurate.  It's one of the most thoroughly tested scientific models in existence, and it has passed every test.  There are measurements made using the quantum model that have been demonstrated to align with the predictions to the tenth decimal place.

That's a level of accuracy you find almost nowhere else in science.

The reason all this wild stuff comes up is because of a pair of papers (both still in peer review) that claim to have demonstrated something damn near incomprehensible -- the researchers say they have successfully split a photon and then triggered half of it to move backwards in time.

One of the biggest mysteries in physics is the question of the "arrow of time," a conundrum about which I wrote in some detail earlier this year.  The gist of the problem -- and I refer you to the post I linked if you want more information -- is that the vast majority of the equations of physics are time-reversible.  They work equally well backwards and forwards.  A simple example is that if you drop a ball with zero initial velocity, it will reach a speed of 9.8 meters per second after one second; if you toss a ball upward with an initial velocity of 9.8 meters per second, after one second it will have decelerated to a velocity of zero.  If you had a film clip of the two trajectories, the first one would look exactly like the second one running backwards, and vice versa; the physics works the same forwards as in reverse.

The question, then, is why is this so different from our experience?  We remember the past and don't know the future.  The physicists tell us that time is reversible, but it sure as hell seems irreversible to us.  If you see a ball falling, you don't think, "Hey, you know, that could be a ball thrown upward with time running backwards."  (Well, I do sometimes, but most people don't.)  The whole thing bothered Einstein no end.  "The distinction between past, present, and future," he said, "is only an illusion, albeit a stubbornly persistent one."

This skew between our day-to-day experience and what the equations of physics describe is why the recent papers are so fascinating.  What the researchers did was to take a photon, split it, and allow the two halves to travel through a crystal.  During its travels, one half had its polarity reversed.  When the two pieces were recombined, it produced an interference pattern -- a pattern of light and dark stripes -- only possible, the physicists say, if the reversed-polarity photon had actually been traveling backwards in time as it traveled forwards in space.

The scientists write:

In the macroscopic world, time is intrinsically asymmetric, flowing in a specific direction, from past to future.  However, the same is not necessarily true for quantum systems, as some quantum processes produce valid quantum evolutions under time reversal.  Supposing that such processes can be probed in both time directions, we can also consider quantum processes probed in a coherent superposition of forwards and backwards time directions.  This yields a broader class of quantum processes than the ones considered so far in the literature, including those with indefinite causal order.  In this work, we demonstrate for the first time an operation belonging to this new class: the quantum time flip.

This takes wibbly-wobbly-timey-wimey to a whole new level.

Do I really understand what happened here on a technical level?  Hell no.  But whatever it is, it's cool.  It shows us that our intuition about how things work is wildly and fundamentally incomplete.  And I, for one, love that.  It's amazing that not only are there things out there in the universe that are bafflingly weird, we're actually making some inroads into figuring them out.

To quote the eminent physicist Richard Feynman, "I can live with doubt and uncertainty and not knowing.  I think it's much more interesting to live not knowing than to have answers which might be wrong.  I have approximate answers and possible beliefs and different degrees of certainty about different things, but I'm not absolutely sure about anything."

To which I can only say: precisely.  (Thanks to the wonderful Facebook pages Thinking is Power and Mensa Saskatchewan for throwing this quote my way -- if you're on Facebook, you should immediately follow them.  They post amazing stuff like this every day.)

I'm afraid I am, and will always be, a dilettante.  There are only a handful of subjects about which I feel any degree of confidence in my depth of comprehension.  But that's okay.  I make up for my lack of specialization by being eternally inquisitive, and honestly, I think that's more fun anyhow.

 Three hundreds years ago, we didn't know atoms existed.  It was only in the early twentieth century that we figured out their structure, and that they aren't the little solid unbreakable spheres we thought they were.  (That concept is still locked into the word "atom" -- it comes from a Greek word meaning "can't be cut.")  Since then, we've delved deeper and deeper into the weird world of the very small, and what we're finding boggles the mind.  My intuition is that if you think it's gotten as strange as it can get, you haven't seen nothin' yet.

I, for one, can't wait.

****************************************

A smile without a cat

Every time I hear some new discovery in quantum physics, I think, "Okay, it can't get any weirder than this."

Each time, I turn out to be wrong.

A few of the concepts I thought had blown my mind as much as possible:

• Quantum superposition -- a particle being in two states at once until you observe it, at which point it apparently decides on one of them (the "collapse of the wave function")
• The double-slit experiment -- if you pass light through a closely-spaced pair of slits, it creates a distinct interference pattern -- an alternating series of parallel bright and dark bands.  The same interference pattern occurs if you shoot the photons through one of the slits, one photon at a time.  If you close the other slit, the pattern disappears.  It's as if the photons passing through the left-hand slit "know" if the right-hand slit is open or closed.
• Quantum entanglement -- two particles that somehow are "in communication," in the sense that altering one of them instantaneously alters the other, even if it would require superluminal information transfer to do so (what Einstein called "spooky action-at-a-distance")
• The pigeonhole paradox -- you'd think that if you passed three photons through polarizing filters that align their vibration plane either horizontally or vertically, there'd be two of them polarized the same way, right?  It's a fundamental idea from set theory; if you have three gloves, it has to be the case that either two are right-handed or two are left-handed.  Not so with photons.  Experiments showed that you can polarize three photons in such a way that no two of them match.

Bizarre, counterintuitive stuff, right there.  But wait till you hear the latest:  three physicists, Yakim Aharonov of Tel Aviv University, Sandu Popescu of the University of Bristol, and Eliahu Cohen of Bar Ilan University, have demonstrated something they're calling a quantum Cheshire Cat.  Apparently under the right conditions, a particle's properties can somehow come unhooked from the particle itself and move independently of it -- a bit like Lewis Carroll's cat disappearing but leaving behind its disembodied grin.

The Cheshire Cat from John Tenniel's illustrations for Alice in Wonderland (1865) [Image is in the Public Domain]

I'll try to explain how it works, but be aware that I'm dancing right along the edge of what I'm able to understand, so if you ask for clarification I'll probably say, "Damned if I know."  But here goes.

Imagine a box containing a particle with a spin of 1/2.  (Put more simply, this means that if you measure the particle's spin along any of the three axes (x, y, and z), you'll find it in an either-or situation -- right or left, up or down, forward or backward.)  The box has a partition down the middle that is fashioned to have a small, but non-zero, probability of the particle passing through.  At the other end of the box is a second partition -- if the particle is spin-up, it passes through; if not, it doesn't and is reflected back into the box.

With me so far?  'Cuz this is where it gets weird.

In quantum terms, the fact that there's a small but non-zero chance of the particle leaking through means that part of it does leak through; this is a feature of quantum superposition, which boils down to particles being in two places at once (or, more accurately, their positions being fields of probabilities rather than one specific location).  If the part that leaks through is spin-up, it passes through the right-hand partition and out of the box; otherwise it reflects back and interacts with the original particle, causing its spin to flip.

The researchers found that this flip occurs even if measurements show that the particle never left the left-hand side of the box.

So it's like the spin of the particle becomes unhooked from the particle itself, and is free to wander about -- then can come back and alter the original particle.  See why they call it a quantum Cheshire Cat?  Like Carroll's cat's smile, the properties of the particle can somehow come loose.

Whatever a "loose property" actually means.

The researchers have suggested that this bizarre phenomenon might allow counterfactual communication -- communication between two observers without any particle or energy being transferred between them.  In the setup I described, the observer left of the box would know if the observer on the right had turned the spin-dependent barrier on or off by watching to see if the particle in the left half of the box had altered its spin.  More spooky action-at-a-distance, that.

What I have to keep reminding myself is that none of this is some kind of abstract idea or speculation of what could be; these findings have been experimentally verified over and over.  Partly because it's so odd and counterintuitive, the theories of quantum physics have been put through rigorous tests, and each time they've passed with flying colors.  As crazy as it sounds, this is what reality is, despite how hard it is to wrap our minds around it.

"What is the most important for us is not a potential application – though that is definitely something to look for – but what it teaches us about nature," said study co-author Sandu Popescu.  "Quantum mechanics is very strange, and almost a hundred years after its discovery it continues to puzzle us.  We believe that unveiling even more puzzling phenomena and looking deeper into them is the way to finally understand it."

Indeed.  I keep coming back to the fact that everything you look at -- all the ordinary stuff we interact with on a daily basis -- is made of particles and energy that defy our common sense at every turn.  As the eminent biologist J. B. S. Haldane famously put it, "The universe is not only queerer than we imagine -- it is queerer than we can imagine."

**********************************

Some of the most enduring mysteries of linguistics (and archaeology) are written languages for which we have no dictionary -- no knowledge of the symbol-to-phoneme (or symbol-to-syllable, or symbol-to-concept) correspondences.

One of the most famous cases where that seemingly intractable problem was solved was the near-miraculous decipherment of the Linear B script of Crete by Alice Kober and Michael Ventris, but it bears keeping in mind that this wasn't the first time this kind of thing was accomplished.  In the early years of the nineteenth century, this was the situation with the Egyptian hieroglyphics -- until the code was cracked using the famous Rosetta Stone, by the dual efforts of Thomas Young of England and Jean-François Champollion of France.

This herculean, but ultimately successful, task is the subject of the fascinating book The Writing of the Gods: The Race to Decode the Rosetta Stone, by Edward Dolnick.  Dolnick doesn't just focus on the linguistic details, but tells the engrossing story of the rivalry between Young and Champollion, ending with Champollion beating Young to the solution -- and then dying of a stroke at the age of 41.  It's a story not only of a puzzle, but of two powerful and passionate personalities.  If you're an aficionado of languages, history, or Egypt, you definitely need to put this one on your to-read list.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

The library of possibilities

In the brilliant Doctor Who episode "Turn Left," the Doctor's companion Donna Noble finds out that a single decision she made on a single day -- whether to turn right or left at an intersection -- creates two possible futures, one of them absolutely horrific.

It's a common trope in science fiction (although in my opinion, it's seldom been done as well, nor as poignantly, as in "Turn Left"), to look at how our futures could have been significantly different than they are.  I even riffed on this in one of my own novels -- Lock & Key -- in which there are not only multiple possible outcomes for each decision, there's a library (and a remarkably grumpy Head Librarian) that keeps track of not only what has happened, but what could have happened.  For every human being who ever existed, or who ever might have existed.

If you want to know how I handled the idea, you'll just have to read the book.

In reality, of course, the number of possible outcomes for even a simple series of choices increases exponentially with each successive decision, so in any realistic situation the possibilities are about as close to infinite as you can get.  Which makes a paper that came out in Nature last week even more extraordinary.

In order to see how amazing it is, a brief lesson in quantum mechanics for the non-physics-types in the studio audience.

One of the basic concepts in quantum physics is superposition: any measurable property of a wave (or subatomic particle) exists in multiple states at the same time.  The distribution of these states -- more specifically, the probability that the particle is in a specific state -- can be described by its wave function.  And the completely counterintuitive outcome of this model is that prior to observation, the particle is in all possible states at once, and only drops into a particular one (in a process called "collapsing the wave function") when it's observed.  (Regular readers of Skeptophilia may recall that I did a post on a particular part of this theory, Wigner's paradox, a few weeks ago.)

So that's amazing enough.  Particles and waves exist as a multitude of present possibilities, all at the same time.  But now, a collaboration between physicists at Griffith University (Queensland, Australia) and Nanyang Technological University (Singapore) have gone a step further:

They have developed a prototype device that generates a quantum state embodying all of the particle's future states simultaneously.

 My first thought was, "That can't possibly mean what it sounds like."  But yes, that turns out to be exactly what it means.  "When we think about the future, we are confronted by a vast array of possibilities," said Mile Gu of Nanyang Technological University, who led the study.  "These possibilities grow exponentially as we go deeper into the future. For instance, even if we have only two possibilities to choose from each minute, in less than half an hour there are 14 million possible futures.  In less than a day, the number exceeds the number of atoms in the universe."

So having even a simple system that generates all possible futures at the same time is somewhere beyond amazing, and into the realm of the nearly incomprehensible.

"Our approach is to synthesize a quantum superposition of all possible futures for each bias," said Farzad Ghafari, of Griffith University.  "By interfering these superpositions with each other, we can completely avoid looking at each possible future individually.  In fact, many current artificial intelligence (AI) algorithms learn by seeing how small changes in their behavior can lead to different future outcomes, so our techniques may enable quantum enhanced AIs to learn the effect of their actions much more efficiently."

"The functioning of this device is inspired by the Nobel Laureate Richard Feynman," added Dr Jayne Thompson, a member of the Singapore team.  "When Feynman started studying quantum physics, he realized that when a particle travels from point A to point B, it does not necessarily follow a single path.  Instead, it simultaneously transverses all possible paths connecting the points.  Our work extends this phenomenon and harnesses it for modeling statistical futures."

So I'm sitting here, trying to wrap my brain around the implication of this research.  Quantum indeterminacy indicates that we don't live in a completely deterministic universe; there's always some uncertainty, built into the actual fabric of the universe.  But the idea that we could, even in principle, create a system from which we could analyze all of the possible futures is stunning.

As Maggie Carmichael, the Assistant Librarian in Lock & Key, puts it:

All of our actions, even the smallest ones, make a difference.  Most of us never find out what that difference is.  All choices have consequences, however insignificant they seem at the time.  However, the truth of that statement is only evident here in the Library, where we can see what would have happened if we had acted otherwise.  Without that information, what happens simply… happens.

***********************************

This week's Skeptophilia book recommendation is a fun one; Atlas Obscura by Joshua Foer, Dylan Thuras, and Ella Morton.  The book is based upon a website of the same name that looks at curious, beautiful, bizarre, frightening, or fascinating places in the world -- the sorts of off-the-beaten-path destinations that you might pass by without ever knowing they exist.  (Recent entries are an astronomical observatory in Zweibrücken, Germany that has been painted to look like R2-D2; the town of Story, Indiana that is for sale for a cool $3.8 million; and the Michelin-rated kitchen run by Lewis Georgiades -- at the British Antarctic Survey’s Rothera Research Station, which only gets a food delivery once a year.)

This book collects the best of the Atlas Obscura sites, organizes them by continent, and tells you about their history.  It's a must-read for anyone who likes to travel -- preferably before you plan your next vacation.

(If you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!)

Quantum pigeons

After yesterday's screed about the anti-education stance of this administration, today in the interest of reducing my likelihood of spontaneously combusting out of rage I'm going to retreat to my happy place, which is: weird and cool scientific discoveries.

I have a fascination for quantum physics.  Not that I can say I understand it that well; but no less than Nobel laureate and generally brilliant guy Richard Feynman said (in his lecture "The Character of Physical Law"), "If you think you understand quantum mechanics, you don't understand quantum mechanics."  I have a decent, if superficial, grasp of such loopy ideas as quantum indeterminacy, superposition, entanglement, and so on.  Which is why I find the following joke absolutely hilarious:

Heisenberg and Schrödinger were out for a drive one day, and they got pulled over by a cop.  The cop says to Heisenberg, who was driving, "Hey, buddy, do you know how fast you were going?" 

Heisenberg says, "No, but I know exactly where I am." 

The cop says, "You were doing 85 miles per hour!" 

Heisenberg responds, "Great!  Now I'm lost." 

The cop scowls at him.  "All right, pal, if you're going to be a smartass, I'm going to search your car."  So he opens the trunk, and there's a dead cat inside it.  He says, "Did you know there's a dead cat in your trunk?" 

Schrödinger says, "Well, there is now."

Thanks, you're a great audience.  I'll be here all week.

In any case, a paper came out last month in Proceedings of the National Academy of Sciences called, "Experimental Demonstration of the Quantum Pigeonhole Paradox," by a team of physicists at China's University of Science and Technology, which was enough to make my brain explode.  Here's the gist of it, although be forewarned that if you ask me for further explanation, you're very likely to be out of luck.

There's something called the pigeonhole principle in number theory, that seems kind of self-evident to me but apparently is highly profound to number theorists and other people who delve into things like sets, one-to-one correspondences, and mapping.  It goes like this: if you try to put three pigeons into two pigeonholes, one of the pigeonholes must be shared by two pigeons.

See, I told you it was self-evident.  Maybe you have to be a number theorist before you find these kind of things remarkable.

[Image licensed under the Creative Commons Razvan Socol, Rock Pigeon (Columba livia) in Iași, CC BY-SA 3.0]

In any case, what January's paper showed is that on the quantum level, the pigeonhole principle doesn't hold true.  In the experiment, photons take the place of pigeons, and polarization states (either horizontal or vertical) take the place of the pigeonholes.  And when you do this, you find...

... that when you compare the polarization states of the three photons, no two of them are alike.

Hey, don't yell at me.  I didn't discover this stuff, I'm just telling you about it.

"The quantum pigeonhole effect challenges our basic understanding….  So a clear experimental verification is highly needed," study coauthors Chao-Yang Lu and Jian-Wei Pan wrote in an e-mail.  "The quantum pigeonhole may have potential applications to find more complex and fundamental quantum effects."

It's not that I distrust them or am questioning their results (I'm hardly qualified to do so), but I feel like what they're saying makes about as much sense as saying that 2+2=5 for large values of 2.  Every time I'm within hailing distance of getting it, my brain goes, "Nope.  If the first two photons are, respectively, horizontally polarized and vertically polarized, the third has to be either horizontal or vertical."

But apparently that's not true.  Emily Conover, writing for Science News,writes:

The mind-bending behavior is the result of a combination of already strange quantum effects.  The photons begin the experiment in an odd kind of limbo called a superposition, meaning they are polarized both horizontally and vertically at the same time.  When two photons’ polarizations are compared, the measurement induces ethereal links between the particles, known as quantum entanglement.  These counterintuitive properties allow the particles to do unthinkable things.

Which helps.  I guess.  Me, I'm still kind of baffled, which is okay.  I love it that science is capable of showing us wonders, things that stretch our minds, cause us to question our understanding of the universe.  How boring it would be if every new scientific discovery led us to say, "Meh.  Confirms what I already thought."

*******************************

A particularly disturbing field in biology is parasitology, because parasites are (let's face it) icky.  But it's not just the critters that get into you and try to eat you for dinner that are awful; because some parasites have evolved even more sinister tricks.

There's the jewel wasp, that turns parasitized cockroaches into zombies while their larvae eat the roach from the inside out.  There's the fungus that makes caterpillars go to the highest branch of a tree and then explode, showering their friends and relatives with spores.   Mice whose brains are parasitized by Toxoplasma gondii become completely unafraid, and actually attracted to the scent of cat pee -- making them more likely to be eaten and pass the microbe on to a feline host.

Not dinnertime reading, but fascinating nonetheless, is Matt Simon's investigation of such phenomena in his book Plight of the Living Dead.  It may make you reluctant to leave your house, but trust me, you will not be able to put it down.