S03E03:The Gothowitz Deviation

In tonight’s episode of The Big Bang Theory, the writers dared to go where most physicists will not,  to the philosophical underpinnings of quantum mechanics.  When Penny asks Sheldon to dance with her, he replies:

quote

To tackle a description of the Many Worlds Theory of quantum mechanics (more often called an “Interpretation” rather than “Theory”), we first need to delve into quantum mechanics itself.

Before physicists realized that quantum mechanics was necessary, their view of the world held that the outcome of any event could be completely determined–as long as you had precise enough measurements beforehand.    If you dropped a rose petal into a hurricane, all you needed was the positions and velocities of every molecule of air at just one moment and then you could calculate the final location of the rose petal with certainty.   (OK, you would also need to know all about all the birds and pieces of vinyl siding flying around too.)  As a practical matter, you could never really do this, but at least in principle it would have been possible.

This view changed forever with the discovery of quantum mechanics in the 1920’s and its experimental tests over the following decades.  The outcome of  many situations can never be predicted with certainty.  Take for example carbon-11, a radioactive atom used in life-saving medical imagers called PET scanners.   That carbon atom’s “half-life” is 2 minutes, meaning that half the carbon-11 atoms you possess at any one time will decay and disappear in 2 minutes.  But what if you had only one atom of carbon-11?  No physicist can ever say when it will decay with certainty.  The best we can do is say  that it has a 50% chance of still being around 2 minutes from now; a 25% chance 4 minutes from now; and 1 in a billion chance of being around an hour from now.   To know the exact fate of any one atom  is not a matter of not being able to see well enough inside the atom.  There is no way of ever knowing.

This fundamentally probabilistic description of nature bothered some physicists.   Even Albert Einstein objected famously:  “I am convinced that He [God] does not play dice”.   Convinced as he may have been, and as brilliant as he may have been, experiment trumps genius.    Clever experiments have shown that there is no room for what Einstein was sure of:  hidden deterministic variables that underlie the probabilistic laws of quantum mechanics.

Philosophical questions arise when you put the atom in a box for say 2 minutes and let no one check on it.  Meanwhile the condition of the atom during that time can still affect other measurements, so descriptions of the atom during this time turn out to be both important and open to interpretation.   The founders of quantum mechanics, working largely in Copenhagen, believed that the best way to view the situation was that the atom was simultaneously in a decayed and un-decayed state.   They said that only after some observer comes along and looks in the box would the atom be forced into one state or another.   In the Copenhagen Interpretation, the act of observation changes the universe.  Such is the typical training that physicists such as myself received as undergraduates.

The Copenhagen Interpretation raises difficult, perhaps unanswerable questions:  How large does something have to be to constitute an observer?  If the atom bounces into  another atom that detects its presence, is that other atom an observer?  Is a large, complicated detector a valid observer?  Must the observer possess consciousness?  Must it be human consciousness or can it be a cat’s?  Does another observer that does not know the outcome possess a different “reality”?  The most likely answer to such question is “Shut up and calculate!”.

Thus things stood for decades.  An alternative, the so-called “Many Worlds Interpretation”, emerged from the 1957 Ph.D. thesis of Hugh Everett at Princeton.  Everett never labeled his interpretation “Many Worlds” but rather originally titled his paper   “Wave Mechanics without Probability” ( “wave mechanics” meant “quantum mechanics”)  He later changed the title to something more abstruse to placate his Ph.D. committee.

In Everett’s interpretation, the probabilities were only a consequence, not an elemental part of the theory.   Not only is the state of the atom described by the equations of quantum mechanics, so are all the detectors and observers in the world.   When an object and observer meet, the two affect each other according to the usual rules of quantum mechanics.  No new process happens at the moment of observation.    Of course when an experimentalist observes the atom he or she perceives it as decayed or not; but the experimenter is now part of the system including the atom, experiencing only an “inside” view.  Meanwhile someone else, with an “outside” view, still entertains all outcomes.  The interpretation does not rest on dice.

The persistence of both outcomes in Everett’s interpretation is often described as two different worlds that propagate forward and independently in time:   one where the atom decayed and one where it did not.   Had the life of a cat  hinged on outcome of the decay,  it is often said that our world branches into two worlds, one with a live cat and one with a dead cat.  (Here we are adopting  Schrodinger’s cat, described in the season-one finale, S01E16.  These are hypothetical experiments only—no cats were harmed.)  The critical question of why we experience the world as 100% live or dead cats, never as a mixture,  was left by Everett as an exercise for the reader.

Soon after completing his Ph.D. thesis, Everett ventured to Copenhagen to explain his ideas to Niels  Bohr.  He failed miserably.  Everett left academia, never to return. The world took little notice of his work.

But times have changed.  At a recent meeting of quantum physicists, the Many Worlds Interpretation received more votes than the old Copenhagen interpretation as the picture closest to the participants’ own views.  Still, physics is not a popularity contest.   These were personal opinions, much like Einstein’s unsubstantiated claim about dice.   For the debate to be meaningful there needs to exist some prediction for which the two differ.   Hope exists in some quarters to find such tests, but I can find no specific experiment put forward.   It remains that no matter how opposed the views of two physicists on the topic, they will all calculate exactly the same outcomes of experiments.  Without an experimental prediction that differs, the fight is just a war of words not physics.  A distinction without a difference.

Except for one.  Science fiction writers and physicists alike have entertained one intrepid experiment.   The means of distinction rely on an experimenter having no fear of  approaching quantum suicide–by playing a game of quantum  Russian Roulette.  The observer  shoots a gun at his or her own head with a 50% chance of having a bullet vs. a blank.  After many trials the physicist will know if Many-Worlds is favored, since there is no experiencing a world where you are dead.  Many Worlds predicts that the observer will eventually live in a world having survived the game 100 times or more.  Unfortunately, we can never can never know what result our brave physicist friend found.  There is no way for the survivor(s), if any, to tell us.

I’ve done some stupid things for physics…

firewalk

but I won’t be volunteering for the quantum suicide experiment.  It violates my university’s ethics protocols for experiments involving human subjects.

In the Many Worlds Interpretation, some measurements can encompass an infinite number of final states, or as Sheldon characterizes it:  an infinite number Sheldons in an infinite number of universes.   Luckily for us, the number of Sheldons is not just an ordinary infinity, but an even larger one called  uncountably infinite number of Sheldons.



14 Responses to “S03E03:The Gothowitz Deviation”

  1. shellorz Says:

    I tried on a fan site to explain this evocation too.
    There once was a brilliant documentary on PBS (Nova I think) about Everett and the MWI by having his son (rock band Eels’ frontman) rediscover who his dad was (well you learn that in THIS universe we’re sharing right now and in an infinite number of them, he also was an alcoholic).
    I disagreed, mathematically on what Sheldon said about the fact that in “a few of them, he’s a clown made of candy”. In theory, it’s in an infinite number of universes.😉
    But since there’s a priori no possible communication between these universes, the result is the same as if there was one universe with a dice settling the thing for every decoherence.🙂

  2. Mr. Jody Bowie Says:

    Just wanted to say thanks for creating this blog. I am a high school physics teacher with many students who are fans of the Big Bang Theory. I use clips whenever possible in lecture. That said, I appreciate the level at which you write. Some of my classes will surely benefit from your writing as it will become required reading, certainly for my AP class. Keep up the good work. I look forward to many good seasons of the show and some great explanations of complex concepts here, too.

  3. Tony Says:

    I really enjoy your approach to blogging the physics behind the episodes — informative but also accessible and fun.

    This blog entry reminded me about J.S. Bell’s famous papers about quantum philosophy (collected in the book “Speakable and Unspeakable in Quantum Mechanics”).

    Thanks to Google Books, I’m able to dig up a favorite quote:
    “So it is another feature of contemporary progress which reminds me of the title of Koestler’s book [The Sleepwalkers]. This progress is made in spite of the fundamental obscurity in quantum mechanics. Our theorists stride through that obscurity unimpeded… sleepwalking?
    The progress so made is immensely impressive. If it is made by sleepwalkers, is it wise to shout ‘wake up’? I am not sure that it is. So I speak now in a very low voice.”
    Too awesome…!

  4. Chris Radcliff Says:

    Another entertaining and enlightening post, Dr. Saltzberg. Thanks for sharing these with us, and please do continue! Like with the show, the science is as entertaining as the humor.

    I’ve noted a few typos in the posts and logged them on a site called Emend:

    http://emend.appspot.com/sites/thebigblogtheory.wordpress.com

    Feel free to correct them or not as you see fit. I won’t mention them in comments from now on. I’ll stick to praise and science commentary.🙂

  5. Ashish Says:

    Thanks for the informative posts. Would it be possible for you to explain the old seasons’ episodes’ too.

  6. Claudia Says:

    The Cat Theory (dead cat and non-dead cat) is a theme in Flashforward. I wish you could bring some light in this series as well. Please?🙂

    • David Saltzberg Says:

      That was also a major theme for the episode at the end of season 1. If I ever go back to the old episodes, that would surely get explained. For now, I can just barely keep up with the new episodes.

  7. Traducción: “S03E03:The Gothowitz Deviation” « The Big Blog Theory en Español Says:

    […] Artículo original por David Saltzberg […]

  8. José Says:

    I actually blogged about this topic, but instead of playing quantum Russian roulette, I preferred the much less risky “quantum whiskey drinking contest” in which there will always be a world in which the whiskey will have no effect and I will remain sober.

    The principle is the same (I hope since my college education is on computer science not physics) and for bohemians it’s much easier to sink in🙂

    Loved the post, and love the Blog.

    Congratulations for your efforts in bringing science to the public!

  9. Tradução: “S03E03: The Gothowitz Deviation (A Deviação Gothowitz)” « The Big Blog Theory (em Português!) Says:

    […] comentários a respeito de incorreções fatuais.) Tradução feita a partir de texto extraído de The Big Blog Theory, de autoria de David Saltzberg, originalmente publicado em 5 de Outubro de […]

  10. Massimo Says:

    The Whiskey/Russian roulette would just prove a statistically improbable event has occurred.

    rather, if multiuniverses exist, all such “dice throwing” events are equally probably, so why don’t we routinely see some extremely improbable happening?

    (it stands to reason to argue we probably live in a universe that is not at the extreme of the probability distribution, as in those extreme universes, what happens is that you never get big deviations from the expected average)

    since we don’t routinely see the extremely improbable happening, multiuniverses don’t exist (beside I suspect they’d impinge on free will).

  11. Philipp B Says:

    I agree that everett’s quantum multiverse theory is pretty speculative or either interpretative…But I don’t see why this is the only reasonable Interpretation of him saying “multiverse” he could also mean p.e. a String Multiverse, with another Calibu-Yau Constellation or simply a place far beneath our cosmic horizon (which also concludes to multiverses if you belive that the space is infinite), or also Another (from inside infinite) bubble in the bubble multiverse of the inflation-Field

    • David Saltzberg Says:

      But he says “Many Worlds theory” in the first part of that quote, so I think we can assume that is what he is talking about.

      On Sun, Feb 17, 2013 at 11:14 PM, The Big Blog Theory

      • Philipp Says:

        Ah…I just realized that the many worlds theory in english is more specific than its german translation (Im from Germany)

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