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instrumentalism vs realism: part 3

I wrote two posts in January of this year ("instrumentalism vs realism" and "instrumentalism vs realism part 2") and wrote "to be continued..." at the end of part 2. The main point of both of them was really to voice my thoughts on the Copenhagen Interpretation of quantum mechanics, to see if I could make any sense of it, and to compare it to the Many Worlds Interpretation, which has always seemed easier for me to understand.

Several new things have happened since then. I started thinking along these lines to try to come up with some material for the microtalk I gave at FreezingWoman in March 2015. I ended up deciding to avoid the dicey subject of realism vs instrumentalism, and even for the most part avoided the entire topic of quantum mechanics. Instead focusing on the question of "what is the universe made of?" and keeping to things I feel that I understand well such as relativity and some aspects of quantum field theory. By the time I finished putting it together, I realized that I had a pretty good case that something more like neutral monism is the right way to look at metaphysics rather than materialism. The idea that metaphysics is even meaningful sort of presumes realism over instrumentalism. And yet because I defined "neutral monism" in my talk as "none of the above" (metaphysical theories) I felt like I left it a little bit open that perhaps instrumentalism is true after all and we just need to give up metaphysics entirely.

After returning from Freezing Woman, I spent a month and a half expanding my 5 minute microtalk into a 15-minute video presentation, which I released on Vimeo and linked to on Facebook and Google+. A handful of my friends viewed it and gave me positive feedback, some of them resharing it, but overall it didn't get a lot of attention. Then later, I found out that someone on Youtube had downloaded the Vimeo video and uploaded it to their Youtube channel, where it did get a lot of attention. (13,467 views, 164 upvotes, and only 5 downvotes... with lots of positive comments from people, many asking if there will be a sequel!):

Materialism and Beyond: What is Our Universe Made Of?

This weekend I uploaded it to my own Youtube channel, which I had been meaning to do (apparently, hardly anyone is on Vimeo; I original chose it primarily because I don't like the idea of ads being inserted in the middle of my video). So far not much action there either, but we'll see I guess.

I can't remember when it was, but at some point this year (maybe around May?) I ran across a *really* interesting post that my adviser in graduate school, Tom Banks, made defending the Copenhagen Interpretation of quantum mechanics:

http://www.preposterousuniverse.com/blog/2011/11/16/guest-post-tom-banks-on-probability-and-quantum-mechanics/

(There's another version of it hosted by Discover magazine but the mathematical equations don't show up right there.) I was shocked that this has been online since 2011 and I somehow managed to not find it until 2015. Not only because it is written by someone I knew personally and hold in great regard, but because it basically explains almost everything I've ever wanted to understand about quantum mechanics in one shot. I often wanted to ask him about this subject, but I was always too shy to do it. I guess I felt like to him, it might be considered a waste of time. But if he could have summed it up this well in one sitting, I would have surely asked and gotten a lot of benefit out of it. Sadly, I finally find it now long after I've quit physics.

So, it took me a while to understand everything he says there. He does make a lot of simple mistakes in his explanation, which confuses things. (For example, he uses the term "independent" several times to mean "mutually exclusive", something anyone--including him--who knows anything about probability knows are two very different things.) Nevertheless, there is a core of what he's saying that turns out to be very important. At first when I read it I sensed that, but it hand't fully sunk in. Since then, I have read a lot more things, gotten into some discussions and debates with people coming from different perspectives on this (one being a mailing list I got invited to as a consequence of people liking my video), and mulled it over in my head. And gradually, it sunk in and I feel like I have now absorbed the message. And it's a really important message that I had sort of suspected before but hadn't really understood.

This week I was thinking through this stuff again and went back to read the Koopman-von Neumann (KvN) formulation of classical mechanics Wikipedia page again (for like the third time since reading my advisor's post about KvN, which I had never heard of until then). (And in connection with the mailing list I'm on, just before that reading some more about Quantum Darwinism and Zurek's existential interpretation of QM). And suddenly halfway through the week, I felt like everything clicked. After all of these years, I finally understand Copenhagen. And it's a lot more coherent than I had imagined.

This doesn't mean I have converted now to a Copenhagenist. I'm still not sure whether I prefer Copenhagen, Many Worlds, or something in between. (And almost certainly, the right answer is somewhere in between, at least compared to what Bohr's original ideas were and what Everett's original ideas were.) And while I call my advisor a Copenhagenist, I'm not even sure he uses that term. I think his view is a modern version of Copenhagen, but does include all of the insights that have been gleaned since the time of Heisenberg and Bohr.
(Although I think he denies that those new insights have significantly changed anything about the interpretation.) I've also read a bit more about consistent histories lately and decided that there are slight differences between it and Copenhagen, it's not just a clarification of Copenhagen because in some ways, it does away with the idea of quantum measurement (or makes it less central/important to the theory). I still think QBism is a form of Copenhagen, although some of its advocates seem to think it has features which distinguish it from Copenhagen.

At any rate, using the broad definition of Copenhagen which I have always used (to include modern versions of it rather than a more narrow one focusing strictly on Bohr and Heisenberg's writings), I'd like to try to sum up the new insights I've absorbed. This was my intention in writing this post, but since I've only introduced that intention and not gotten there yet, I'll start my summary in part 4.

To be continued...

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