So long, Copenhagen - I'm a Many Worlds believer now

This is adapted from a status update I posted on Facebook

I am pleased to announce that, in large part due to the wonderful explanations by physicist Sean Carroll, I now subscribe to the Many-Worlds Interpretation (MWI) of quantum mechanics.

MWI is not at all new to me. It's been kicking around since 1957 when it was first proposed by Hugh Everett while he was a graduate student at Princeton. I was certainly aware of it when I started my physics studies back in the early 1970s.

I had never taken the interpretation seriously, mostly because I was put off by the notion that the act of measuring a physical system generated new worlds somehow, one world for each of the possible values of the result of that measurement. This elevator-pitch description of MWI struck me as both magical and untestable and, so, not really worth my time.

Recently, though, I have decided to revisit the topic.

The so-called Copenhagen Interpretation of quantum mechanics on which I and most physics graduate students of my generation were weaned has not really weathered well. In some respects, it was considered provisional even back then, a placeholder waiting for something better to come along. I had counted on the fact that its own magical elements - the putative role of consciousness in measurement and the non-local collapse of the wave function - would have been put on a stronger intellectual footing in the last forty years. But that hasn't really happened.

Thanks to Sean, whose thoughts on some of the central philosophical questions of modern physics have become a go-to resource for me, I decided to take another look at MWI and now frankly could kick myself for not investigating it sooner.

Now, I understand that MWI is a straightforward outcome if you take the equations of quantum mechanics at face value and don't add the unnecessary - and problematic - assumption that observers somehow exist outside the physical systems that they observe. Indeed, Hugh Everett's dissertation had the title, The Theory of the Universal Wave Function (PDF) which proposes an approach which breaches the classical wall that separates observer and observed. His key insight is, “[h]owever, from the standpoint of our theory, it is not so much the system which is affected by an observation as the observer, who becomes correlated to the system.”

[In his dissertation Everett also addresses a colorful criticism leveled at conventional interpretations of quantum mechanics by Einstein that “he could not believe that a mouse could bring about drastic changes in the universe simply by looking at it.” Everett turns this on its head: “The mouse does not affect the universe - only the mouse is affected.” So much for spooky action at a distance.]

I do think that there are problems hewing to the popular interpretation that of many worlds branching off as observations occur. This is one reason why Sean and others prefer to call MWI “Everettian Quantum Mechanics.” And I would have to admit that I’m not quite sure what meaning to attribute to the ever increasing number of quantum states with which we find ourselves involved as required by the theory. Perhaps they are worlds in some sense, but certainly not the dynamically created universes of the multiverse theories that have captured the attention of string theorists over the last several decades.

In any event, there’s a lot for me to learn here, but I feel like I've finally gotten my arms around a very profound physics question that's been bothering me for a long time.

Does Anyone Understand Quantum Mechanics?

This is the second in a series of informal posts to be used as background for the Atlanta Science Tavern discussion Quantum Physics and Human Consciousness.

Richard Feynman, Los
Alamos ID badge

Richard Feynman, one of the great physicists of the 20th century, offered this somewhat discouraging claim in his book, The Character of Physical Law, "I think I can safely say that no one understands quantum mechanics."  Given that Feynman was not only a technical but also an intuitive master of the subject - the likes of which will seldom be seen again, I might add - it would be pointless for me to try to contradict him.  But I think it is reasonable to suggest that this oft-quoted statement might benefit from some clarification.

Certainly, as a practical endeavor, many, many thousands of scientists and engineers around the world today understand quantum mechanics.  They use it routinely in their work, whether designing computer circuits or predicting the outcome of the collisions of the protons that hurtle toward each other at near light speed at the intersections of the beam lines of the Large Hadron Collider outside of Geneva, Switzerland.  Indeed, the related theory of Quantum Electrodynamics, of which Feynman was a pioneer, is, hands down, the most successful physical theory ever devised as far as the precision of its predictions is concerned.  It would be hard to beat.

Compact Muon Solenoid at
the LHC at CERN

Yet it comes as a surprise to lay people, who find themselves beguiled by the mystery of quantum physics, to learn only a fraction of physicists are troubled, at least professionally, with the philosophical questions that it raises.  The dictum. "shut up and calculate!" holds sway in laboratories and universities, with the meaning of the theory being no more and no less than its thoroughly demonstrated correctness and utility.

And this is where, to a certain extent, they part company with Feynman, whose discouraging words might more accurately - and perhaps more hopefully - be expressed as, "no one understands yet what quantum mechanics means."  The fact of the matter is that, after almost nine decades of earnest striving, there is no agreed upon interpretation of what quantum physics says about the very nature of the world it so successfully models.  Some have more currency than others, but none has proven so superior that it has vanquished its competitors.

In my opinion it is our failure to formulate a convincing interpretation that fuels the controversy that surrounds the question of quantum physics and consciousness which has motivated the discussion at hand.  The absence of a conclusive answer to the stubborn question of meaning has been an invitation for all contending interpretations of quantum mechanics, of whatever stripe, to enter the fray.

That said, I do think that the central concepts of quantum physics are in fact understandable by "ordinary" people, that is if they are willing to let go of preconceptions and to imagine themselves, instead, as inquisitive travelers to an unexplored country.  This will be the topic of the next post in this series.


Does Anyone Understand Quantum Mechanics? by Marc Merlin is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.
Based on a work at thoughtsarise.blogspot.com.