Thursday, October 14, 2010

Perhaps I'm finally reaching that existential crisis...

I've been reading an excellent series on quantum physics the last couple of days. It's really helping me intuitively grasp some of the ideas there, at least as much as it's possible to intuitively grasp the quantum (i.e. real) world.

I've noted before that some people -- like myself -- feel liberated by an atheistic/scientific worldview, that it is simultaneously a relief (because the theistic worldview is so terrifying) and a sense of wonderment; whereas others -- like my wife -- while willing to accept the truth, feel a great existential disappointment about the whole thing.

One of the things Elezier's series pushes is that he is a proponent of the Many-Worlds hypothesis. All fine and good; in many ways I already found that the most reasonable of the many quantum interpretations (I wanted it to be the Hidden Variables hypothesis, but Bell's Theorem handily disposes of that). Still, it didn't particularly trouble me, because even if there would be an uncountable number of separate "me"s a picosecond from now, at this exact moment in time it still seemed there was one definite "me" -- perhaps with a gazillion twins in other alternate worlds, but there still seemed a certain subjective reality to the "now-me", even if there was no objective preference for this particular possible reality.

But Elezier's writings, in particular this post, has me now sort of discounting even the subjective reality of the instantaneous "now-me". It is difficult to put this into words... but somehow I was more or less okay with the thought of there being a single thread of "me-ness" hurtling through a vast space of possible histories, as opposed to the picture Elezier is painting in my head: That this idea of "possible histories" is itself an illusion, a hallucination brought about by the decoherence of various volumes of configuration space.

My mental image before was of a vast infinitesimally branching tree, an uncountable number of timelines springing out of each other, with parallel "me"s riding along each possible branch. Now I just see a static volume within an uncountable-dimensioned configuration space -- for which I might arbitrarily choose a cross-section and call that a subjective reality, but which doesn't exist independently of the rest of the configuration space in any sense whatsoever.

I guess, ironically perhaps, the most disturbing change in thinking is from a quantized tree of possible realities into a great smeared smudge of a single reality -- a reality that is sans even an instantaneously identifiable subjectivity. You could not take every "possible reality" and give it a serial number, and then choose a particular serial number and look up all of the serial numbers of the parent realities that led to it.

And that's the loss, I guess. I used to think that if I could pause reality and somehow "step outside of it" (this is a thought experiment, remember), that I could pick out one unbroken line of the infinite possible histories and say, "This is 'me', right at this moment, and this here is 'my past.'" It doesn't work that way. It's just one great big smudge. If I wanted to pause reality and "step outside of it", I couldn't just choose a point in configuration space and extract a "me" from it, I'd have to choose a compact volume of arbitrary size that hadn't yet decohered -- and even then that particular smeared-out "me" (which is already a much less satisfying "me" than an enumerated point would be) could not trace a line through configuration space -- or even a multi-dimensional tube throw configuration space, for that matter -- and say, "This was 'my past.'" "I" have no past. Just a big smear of quantum amplitudes.

Finally, that existential angst hits me. I'm going to go have some coffee; I may be nothing more than a smear of particles with no past and no future, but coffee still seems to taste good.

Addendum: Wow, the very next post in Elsevier's series deals with this problem of there being no "objective population count," as he puts it. GMTA or something. He's mostly dealing with it in showing that it is not a valid objection to the idea of decoherence, though. Still leaves me with the existential crisis. Jerk...


  1. If you don't get at least one existential crisis from studying quantum mechanics, you haven't studied enough quantum mechanics.


    Abandoning the "Copenhagen" view of collapsing wave functions and bringing decoherence into your picture doesn't necessarily entail the MWI. Plenty of folks more knowledgeable (and, I suspect in some cases, smarter) than I am have abandoned the Copenhagen view and not become Many-Worlders. Mathematical physics guru John Baez is one; he advocates a much more epistemic (as opposed to ontological) view of this whole wavefunction business, and plenty would agree. You also have Mermin's correlationalism, Rovelli's relational interpretation and probably more I haven't heard of.

    Somewhere along the way, I picked up (I think from Moshe Rozali) a low regard for most "interpretations of quantum physics" talk, as it very often seems to fail to take relativity really seriously. The very fact that "interpretations" are almost always phrased in terms of single- or few-particle QM instead of quantum field theory — the more fundamental theory — speaks to this. Epistemic treatments of wavefunctions (Baez/Fuchs) have been less bad about this, in my experience.

  2. In other words, I'm a Christmas-and-Easter member of what Matt Leifer calls The Church of the Smaller Hilbert Space, whose sixth commandment is, "Do not commit murder, since there is no 'other branch of the wavefunction' in which your victim will survive."

  3. Great comments!

    I am aware there are other interpretations that do not involve collapse, but as of yet I don't "get" them. Then again, my primary exposure has been skimming the Wikipedia pages describing these interpretations :) I will check the links you recommend and try again.

    Part of why I think I bought into this so much is a) I really like Elsevier's polemical style (even if the reason for it appears to be related to some of his IMO dubious transhumanist beliefs -- maybe more about that in another post), and b) because I had already been leaning towards either MWI, "shut up and calculate", or Hidden Variables (but I'm more or less convinced that Bell's Theorem is 100% sound and rules out Hidden Variables, so that's that). On the other hand, that may again be just because MWI is the only interpretation I grok that doesn't involve this ridiculous notion of wavefunction collapse.

    I feel like MWI can be phrased in terms of QFT -- though I don't pretend to understand QFT well enough to make a competent attempt myself. In fact, it seems to me this little shift in my understanding of MWI was basically to extend it from the single-particle to the quantum field -- instead of a digitally branching tree of individual reactions, it's just a big smear.

    That said, even if I do accept that interpretation, my existential crisis has diminished slightly. Since all of the physical processes related to my own (illusion of?) subjective reality are prone to undergo decoherence in a matter of picoseconds, I still can -- more or less, I think -- visualize "my" history as being one path through a vast branching network of tubes through configuration space. The tubes don't have discontinuous boundaries, of course, but their boundary is pretty sharp and identifiable -- but I already came to terms with that many years ago in terms of body boundary (when I shake hands with you, there are innumerable atoms and even molecules for which it is impossible to say whose body they belong to) so adding another layer of fuzzy boundary to my existential perception is not all that big of a deal.

    (Funny story how I came to have a visceral feel for the body boundary problem all in an instant... but that's for another time)

  4. Glad I could pass some links along! (If you're in the mood for a sardonic look at transhumanism, check out Greg Egan's new novel Zendegi.)

    Now, to clear a few other items off my brain-queue. Some days, the Internet is definitely a net drag on my productivity.