Sciency Words: Quantum Entanglement

Hello, friends, and welcome to a special Halloween edition of Sciency Words!  Today, we’re talking about the spookiest of scientific terms.  And that super spooky term is:

QUANTUM ENTANGLEMENT

Quantum mechanics is the study of the tiniest of tiny things in our universe: things like atoms and quarks and electrons.  And these super tiny things do some pretty weird stuff, if our current mathematical models are to be believed.  Stuff that seems to defy our human notions of common sense.

In the 1930’s, when quantum theory was still brand new, Albert Einstein did not approve of all that common-sense-defying stuff that quantum mechanical models were predicting.  So in 1935, Einstein and two of his colleagues, Boris Podolsky and Nathan Rosen, published a paper that was supposed to prove quantum theory was incorrect, or at least that it was woefully incomplete.

The Einstein-Podolsky-Rosen paper (or E.P.R. paper, as it’s now commonly known) didn’t quite get the job done.  Quantum theory survived the attack.  In response to the E.P.R. paper, Erwin Schrödinger (of Schrödinger’s cat fame) wrote a letter to Einstein.  It was in this letter, from Schrödinger to Einstein, that the word “entanglement” was first used in reference to quantum theory.  Well, actually, Schrödinger used the word Verschränkung, a German word which translates into English as “entanglement.”  (The relevant section of Schrödinger’s letter is quoted in this article from The Stanford Encyclopedia of Philosophy.)

Entanglement refers to the way a pair of quantum particles can interact with each other and then remain “entangled” with each other after their interaction is over.  If you measure the quantum state of one entangled particle, the other will instantaneously change to match.  This implies that entangled particles can somehow exchange information at faster-than-light speeds.  As Schrödinger wrote in his letter, this is not just a weird quirk of quantum theory; it’s the “characteristic trait” that makes quantum mechanics so radically different from classical physics.

Einstein was still not happy.  Neither was Schrödinger; however, as I’ve come to understand the story, Schrödinger was able to set his personal feelings about quantum theory aside and continue his research.  Einstein, meanwhile, kept trying to prove quantum theory was wrong until the day he died.

You might even say the idea of quantum entanglement haunted Einstein for the rest of his life.  In 1947, in a letter to another physicist named Max Born, Einstein referred to entanglement as spukhafte Fernwirkung, a phrase which is commonly translated into English as “spooky action at a distance.”  (The relevant section of Einstein’s letter is quoted in this book.)

Thus, quantum entanglement is the spookiest scientific term.

The Nine Lives Hypothesis, or Why Schrödinger’s Cat Can Never Die

Today’s story was inspired by my recent Sciency Words post on Schrödinger’s cat.  I cannot emphasize enough that this story is not meant to be taken seriously.

It is often said that anyone who claims to understand quantum mechanics is either lying or delusional.  In 1935, world-renounced physicist Erin Schrödinger proposed an experiment to demonstrate the true absurdity of all things quantum.  The experiment came to be known as Schrödinger’s cat. Now today, despite the vehement protests of animal rights groups, researchers at Omni-Science Laboratories have conducted the first ever real world test of the Schrödinger’s cat experiment.

A cat is placed inside a test chamber, along with a sample of cesium-131, a radioactive isotope.  A contraption within the test chamber will either kill the cat or spare the cat’s life, depending on what that cesium isotope does.  If the cesium undergoes radioactive decay, the cat will die.  In not, the cat will live.  The conditions of the experiment are so devised that the cat should have an even 50/50 chance at survival.

But according to the bizarre laws of the quantum world—the world of atoms, including radioactive cesium atoms—nothing is real unless it is being observed.  In the absence of an observer, anything and everything that can happen does happen, all at once, all jumbled together in a coexistent meta-state.

And so once the test chamber is sealed and its contents can no longer be observed, the laws of quantum mechanics should take over. The cesium isotope simultaneously does and does not decay.  The killing apparatus simultaneously has and has not been triggered. The cat simultaneously is and is not dead.  And so the situation should remain, until the scientists reopen the test chamber and observe its contents.

Researchers at Omni-Science originally intended to run the experiment only a dozen times, but the test results were so surprising and so confusing that additional tests were warranted.  In total, 63 cats were put through the experiment.  And to the astonishment of everyone involved, all 63 cats survived.

“We’re at a loss to explain it,” says Dr. D.C. Bakshali, principal investigator on the Schrödinger’s cat project.  “Statistically speaking, roughly half the cats should have died, and half should have survived.  But the survival rate was 100%.  We didn’t lose one cat.  Not one!”

Several hypotheses have been proposed to explain these surprising results.  One possibility is being referred to as the nine lives hypothesis.  Since cats are said to have nine lives, perhaps whenever a cat dies in the test chamber it immediately resurrects itself.  Although this notion was initially suggested as a joke, one Omni-Science researcher latched onto the idea and even proposed a mechanism that may explain how unobserved cats are able to continuously revive themselves.

“Even in the 1930’s,” says Dr. Haru Hoshiko, “it was pointed out that a cat is perfectly capable of observing itself.  But has it not occurred to anyone that only living cats are able to make such observations?”

Hoshiko goes on to explain: “So long as Schrödinger’s cat remains alive, it observes itself as living.  The moment it dies, however, there is no longer an observer present.  The laws of quantum mechanics reign once more, the cesium has once again simultaneously decayed and not decayed, and thus the cat is once again simultaneously dead and alive. But the living version of the cat is capable of observing itself to be alive, causing the superposition to collapse.  Thus, Schrödinger’s cat can never die!”

According to Hoshiko, the nine lives hypothesis should more accurately be called the infinite lives hypothesis, as there is no theoretical limit to how many times a cat—or any other animal, for that matter—would be able to revive itself in this manner.  Hoshiko’s paper on the subject has been accepted for publication in Nature.

Needless to say, the results of the Schrödinger’s cat experiment have profound implications for our understanding of quantum mechanics and, indeed, the nature of reality itself.

Sciency Words: Schrödinger’s Cat

Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:

SCHRÖDINGER’S CAT

Quantum physics has a mascot: a cat.  Specifically, it’s a cat that is somehow, almost magically, both dead and alive at the same time.  Does that sound weird?  Confusing?  It should.  This simultaneously living and dead cat has come to represent everything that makes quantum physics such a weird and confusing subject.

I’m not going to go into the details of how quantum mechanics works because A) I don’t have the math skills to do that properly and B) even if I did, it’s way too big a topic to cover in one blog post.  For the purposes of a Sciency Words post, it’s enough for you to know this: based on a strict interpretation of quantum mechanics, you would be forced to conclude that nothing is real unless it is being observed.

If you find that hard to accept, you’re not alone.  Many of the scientists who came up with quantum mechanics couldn’t accept it.  In 1935, German physicist Erwin Schrödinger—a man who’d received a Nobel Prize for his contributions to quantum theory—had had enough, and he published this article titled “The Present Situation in Quantum Mechanics.”

Don’t let that stolid title fool you.  Schrödinger was mad.  I’d characterize his article as an angry rant about everything wrong with quantum mechanics, or at least everything that was wrong with the strict interpretation of quantum mechanics.  That strict interpretation was becoming increasingly popular among Schrödinger’s colleagues, and it remains very popular among physicists today.

It was in the middle of this angry rant that Schrödinger first presented his now famous cat-in-a-box paradox.  Schrödinger first describes a killing contraption worthy of a James Bond villain.  A radioactive isotope is placed in a box.  A Geiger counter is rigged to trigger a hammer, which will smash a flask of hydrocyanic acid if the Geiger counter detects radioactive decay.  Lastly, a cat is placed in the box.  The box is sealed up so that no one can observe what’s happening inside, and it’s left undisturbed for one hour.

There’s a fifty-fifty chance that that radioactive isotope will decay before the hour is up.  Therefore, there’s a fifty-fifty chance that the cat will die.  So until we open the box and make an observation, a strict interpretation of quantum mechanics would have us believe the isotope simultaneously has and has not decayed.  The Geiger counter simultaneously has and has not gone off, and the cat simultaneously is and is not dead.

Schrödinger’s cat was meant to demonstrate that a strict interpretation of quantum mechanics leads to nonsensical conclusions. “The rejection of realism has logical consequences,” Schrödinger warns us.

No one has ever tried this experiment with an actual cat (I hope), but according to this article from Quanta Magazine, the Schrödinger’s cat phenomenon can and does happen in real life.  Quantum mechanics is weird.  It’s confusing.  It defies common sense.  But as author John Gribbin writes in his cleverly titled book In Search of Schrödinger’s Cat:

Common sense has already been tested as a guide to quantum reality and been found wanting.  The one sure thing we know about the quantum world is not to trust our common sense and only believe things we can see directly or detect unambiguously with our instruments.