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turchin comments on The Philosophical Implications of Quantum Information Theory - Less Wrong Discussion
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I like your article, but have some naive questions: Where starts the original research part? That is how differs your article from existing interpretations of QM?
Will your interpretation of QM present any new testable predictions? Will it allow any new useful things?
What is the nature of observer in it?
None of this is original research on my part. My only contribution is pedagogical. QIT doesn't make any predictions that QM doesn't make because it's an interpretation, just another way of looking at the math. But the reason it's a better way of looking at the math is that it solves the measurement problem. It explains measurement in terms of entanglement. It reduces two mysteries to one. IMHO that's progress.
How far does it go in solving the measurement problem? Can you derive the Born rule? Can you settle the single/many world dichotomy?
Yes.
That depends on what you mean by "settle". The only thing that you can definitively say is that the transition between the quantum and the classical is gradual, not abrupt. Because of this, any statement about a classical world is necessarily an approximation of some sort, and all approximations break down if you lean on them in the right way. Copenhagen breaks down most easily because it only applies under some very particular circumstances. Those circumstances happen to be very common, which is why Copenhagen is not completely useless, but nowadays it is common to do experiments under which the Copenhagen approximation conditions do not apply. Multiple-worlds is mathematically tenable, but it has some very serious problems as an explanatory theory and it makes predictions that even its adherents seem unwilling to accept.
Personally, I find the rhetoric of QIT/relational-QM/Ithaca to be far less taxing on my intuition than multiple-worlds. These interpretations acknowledge that classical reality is a slice of the wave function, that there are many different ways to slice up the wave function to obtain a classical reality, and therefore there are many potential classical realities. But there is one classical reality that is privileged to me because it happens to be the one that I'm living in, which is to say, it's the reality that is mutually entangled (and therefore classically correlated) with the massively-mutually-entangled system that is me. In an absolute sense I am no more or less real than all the other potential mes that you get by slicing up the wave function in different ways, but I don't care about that except in the abstract. Day-to-day, what matters to me -- this me, the one that is writing these words -- is what is correlated with (this) me.
The cool thing about this is that if you are reading these words -- the ones written by this me -- then you are entangled with me and therefore classically correlated with me and therefore we are both emerging from the same slice of the wave function, and so the exact same argument applies to you: both of us can proceed on the assumption that our classical reality is the One True Classical Reality even though we can both understand in the abstract that this isn't really true, and that by doing the right kinds of quantum experiments we can actually demonstrate to ourselves that it isn't really true. For me personally, that makes QIT the best approximation to use because it's the one that applies in the greatest variety of circumstances and has the fewest conceptual problems. But it's ultimately a matter of personal preference.
Doesn't the QIT you describe make the exact same predictions, also the Russian roulette you mentioned?
But there's no single privileged future you, right?
Nope.
There is no single privileged future me now, but when my future becomes my present there will be. (Also, see note below.)
You can actually do this experiment: listen to a geiger counter, or tune an old-school TV to an inactive channel and watch the snow on the screen. The math says that during this process there are an inconceivably vast number of you's being split off every time the geiger counter clicks (or fails to click) or every time you perceive a light or dark pixel on the screen. But you will only ever experience being one of those you's. Yes, all those other you's do exist, but the you that you perceive yourself to be can never interact with any of them, so they may as well not exist for the one you that you perceive yourself to be. And so the one you that you perceive yourself to be may as well live your life as if all those other you's didn't exist even though they really do.
(NOTE: there is really no such thing as "now", and you don't even have to go quantum to see that. Simultaneity gets tossed out the window with special relativity. There is my "now" and there is your "now" and they will not, in general, be the same.)
Hi lisper,
I found your paper easy to follow and maybe insightful (I'll have to read it more carefully the second time) but like qmotus, I don't understand your reasoning in this thread. I'm assuming MWI is just an interpretation of unitary QM, so makes all the same mathematical predictions as other non-collapse theories. And the roulette story is just one way of looking at it, from the perspective of what I consider my (classical) self and what I call the future.
Since you are not claiming that QIT makes different mathematical predictions than MWI, how can you claim they make different predictions at all?
QIT and MWI don't make any different predictions that are testable in a single classical universe (obviously, because QIT and MWI are just different interpretation of QM, so they both make the same predictions for all observables, namely, the predictions made by QM).
QIT and MWI are simply differences in perspective -- the God's eye view (MWI) versus the mortal's-eye-view (QIT). Neither view is "correct", but since I (the thing engaged in this conversation) am a mortal, I choose the mortal's-eye-view as more relevant for day-to-day decision making. But as I keep saying, it's ultimately a matter of personal preference.
The problem with quantum roulette is that it takes a prediction made from a God's-eye-view and tries to apply it in a mortal's-eye-view context. Yes, God will be able to see that there is a you that survived the process and went on to live the life of Riley. But whether or not you will be able to see that is a very open question. (God will also be able to see a lot of branches of the multiverse containing your friends and loved ones mourning your untimely death.)
Note that playing quantum roulette successfully depends crucially on the speed with which you can kill yourself. Trying to play by slitting your wrists, for example, doesn't work because once you see that your wrists are slit you can't roll that back. So the success of the enterprise depends entirely on killing yourself fast enough that you don't become aware of your imminent and (in the relevant branches of the multiverse) unavoidable death. How fast is fast enough? Well, that is (literally!) the sixty-four-million-dollar question. Unless you have an answer that you are very confident is the correct one, it seems to me like an imprudent risk to take.
(This comment is a reply to another branch of this discussion as well.)
I disagree. To keep things simple, let's suppose that the bullet, if it hits, really will kill the participant with practically 100% certainty and will do so practically immediately (I'll come to this a bit later). In that case the only outcome the participant can expect to experience, and that they will experience with certainty, is that the gun didn't fire. This is exactly what happens if you take the mortal's-eye-view; God, as you mentioned, will notice that elsewhere in the multiverse, the participant did get hit. Now, whether the participant cares about their loved ones or the copies that die in the attempt is a matter of preferences, but if we're simply talking about which outcome to experience, this is how it goes, I think.
With this I agree, which is why I think the quantum Russian roulette or quantum suicide scenarios are mostly interesting as a thought experiment, as they're intended to be. But there are practical situations that are somewhat analogous: think, for example, about a terminally ill patient who faces an almost certain death within several days. Should they expect to survive or continue to experience things, and if so, in what way? My understanding is that according to quantum mechanics, there are all kinds of weird scenarios with non-zero probability that make "survival" possible, such as simply surviving one more day indefinitely despite all odds, being miraculously cured, or maybe being resurrected by a hyper-advanced future civilization in a simulation. Note that, in principle, this probably applies to any possible life-and-death situation.
I used the word "experience" a number of times there, which brings me to a point you made in another comment:
I don't think this can of worms is that bad. We have a pretty good grasp of what it means to be conscious, even if we can't define it exactly; and also we're (at least I am) pretty confident that it's a purely physical phenomenon with nothing supernatural and thus subject to the laws of QM. I think that's enough. Where it does get a bit problematic is when we're talking about scenarios like the one with the terminally ill patient; presumably there's also a possibility that the patient's consciousness degrades until it no longer makes sense to call them conscious, since there's probably no clear line anywhere separating conscious and non-conscious in this way. (This might also imply that if we should expect to die, we should expect to do so by very slow decay, like patients with Alzheimer's, which doesn't sound too good to me.)
I agree with most of what you say. Consciousness is not supernatural. But it is still problematic because:
"Only outcome you can experience" is not quite the same thing as "Will experience with certainty." Let's go back to the case where you survive in both branches. The outcome you do experience is the only outcome that you can experience. The trick is that this is really two statements disguised as one. After the event there are two you's, you1 and you2. The outcome that you1 do experience is the only outcome you1 can experience, and the outcome you2 do experience is the only outcome you2 can experience. This remains true (I believe) even if one of those experiences is the null experience of having your consciousness enter the cosmic void.
Reasonable people could disagree, I suppose. We can never know what the null experience "feels like" because by definition it doesn't feel like anything. Personally, I find even the possibility that this argument could be correct to be sufficient reason for me to avoid playing quantum roulette. But everyone needs to choose their own risk posture.
Yes, that's the point. Every future version of you will of course call themselves "you".
Although I don't want to advocate performing the roulette experiment, I do disagree. If it's a quantum certainty that all future branches of you die off, perhaps due to a conservation law, then only those versions of you which didn't go down that branch will be conscious.
Even if it isn't certain, because it seems like we are more likely to experience the branches that match our classical explanations in the following scenario after a few minutes I would expect to be version 3. Version 1 is of course impossible and only with a very short-sighted definition of self do I need to consider version 2.
Well, I'd rather say that I will perceive being every one of them; it's just that no future me will perceive being more than one of the future mes. The terminology gets quite confusing here, but I think the Quantum Russian Roulette you mentioned (and quantum suicide and immortality, by extension, for example) is one situation where this aspect of quantum theory becomes somewhat apparent, which is why I think it would be interesting if you elaborated a bit more on how you think the predictions QTI and MWI make differ from each other.
It depends on what you mean by "I". This is the crux of the matter. MWI takes a God's-eye perspective and looks at the whole wave function. On that view, there are many you's (i.e. many slices of the wave function that contain macroscopic systems of mutually entangled particles that perceive themselves to be you).
QIT takes the perspective of the-you-that-you-currently-perceive-yourself-to-be. You will only ever perceive one of that kind of you.
For the purposes of making decisions it makes more sense to take the latter perspective because it's the-latter-kind-of-you that is making the decisions and has to live with the consequences.
I would say that a major difference between MWI and various collapse interpretations is that there are situations where according to collapse interpretations there most likely will be no future you; but according to MWI there surely will, although their amplitude is low (the aforementioned Russian roulette is one such situation, for instance). I find it somewhat difficult to think about those from the perspective you advocate.
No. Not "will". IS. If you're going to take the God's eye view then you have to let go of your intuitions about time along with your intuitions about classical reality. The wave function is a static four-dimensional thing. Time emerges from the wave function in exactly the same way that classical reality does. You have to be careful not to apply terminology from the mortal's-eye-view to the God's-eye-view. That's how you get yourself into trouble.
UPDATE: Here is a popular article about how time emerges from entanglement.