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Critique My Explanation of QM re: the Observer,

  1. Nov 11, 2004 #1
    Hi, I recenlty had a friend whose interested in QM email me an article: http://www.space.com/searchforlife/quantum_astronomy_041111.html , asking for more explanation. This is the explanation I sent in a sleep-deprived state of mind (in fact, I'm still in said mind state as I post this now :) ). Anyway, I was hoping that someone me would critique and tell me how well I did in terms of complying with accepted knowledge. Thx, it'd be much appreciated. The email follows:

    Haha, I don't know why people continue to overlook a much more intuitive explanation regarding this experiment. I had an idea several months ago where I came up with an intuitive, no no-nonsense explantation of what's happening, and I now believe I have a clear and simple view of what is going on. Bear in mind, clear and simple are relative terms and this is a revolutionary science that requires revolutionary thinking.

    Like I was saying before in the previous email, the photon doesn't travel through both slits, the photon that we observe is actually bumped off course by photons that exist outside of the collapsed wave function that we perceive through a process called quantum interference. I will explain the jargon terms later. This is not my idea and not what I had the epiphany about. And it IS actually hard to explain beyond the jargon, but I've been told that I'm good at dejargonizing and I relish any opportunity I have to do it for the enlightment of others. Of course, I haven't slept in a long time so I'll prob suck at it now.

    Another way to say it is that the photon we observe is bumped off course by photons in other universes. This is Deutsch's explanation, but it is still misleading. I've actually explained this to two people before (Alhaji and my sister :) and both understood, but it's much easier to do in person - even though this sounds really funny, the hand gestures I use really help :) ).
    This is where my epiphany comes in and I think it's a good concept to help further understanding of this - and it's simple once you can wrap your head around it. The problems we face as human observers or the limitations we are sewn into lie in the way our brains operate, i.e. consciousness exists within a stream of collapsed wave functions, i.e. a sequence of discreet collapsed wave functions that are we percieve as being tied together in time. This however gives us only the SLIGHTEST (almost an infinitesimally small) view of the true nature of the universe. The universe, in reality, is a big fuzzy mass of probability. Again, the double slit experiment amid other compelling evidence (including the very physical structure of the universe) proves this. A "collapsed wave function" is just a term scientists use to explain why the universe seems the way it does to us. E.g. physicists say that when you're not looking an electron exists in a fuzzy probability cloud and when you are looking an electron exists as a discrete particle. What the **** does this mean??? Well, this is because the observer "collapses" the wave function (they collapse that cloud of probability into one discrete location in which the electron exists) because we (humans or more precisely our brains) operate within collapsed wave functions, whatever they may be. Even when we're not looking, our brains are "collapsing wave functions" :)

    OK, hold up your finger and look at it. You see your finger in one location, sitting there stably (unless you've had a little coffee like me and you're getting a little jittery). In "reality" your finger is a wave, it's in several places nearby all at once. In fact, you are too. This is the God's Eye view of you (so to speak). At the same time, within that wave exist discrete locations of where your finger can be (depending on what physical laws permit happening). This is evidenced by the fact that it dovetails with our experience. In "reality" though your finger exists in this probability cloud where it can be a half a millimeter up, half down, someone can walk into your office right now and cause you to put your hand down all together, or they may not. It's a game of dice, right? But, we can intuitively discern that our brains don't operate at this meta-discrete quantum level - unless you're having an acid flashback, your finger should not look like a wave right now. No, our brains are not moved by a probability cloud of neurons firing or maybe firing or not or whatever. We experience a distinct "choice" in what happens. A probability cloud of electrons doesn't strike your retina causing you to see a blurry blob of where something might be sitting in a wave-like state - no, a distinct path is taken, the wave function is collapsed, either you experience the electron hitting your retina here, or maybe there, or maybe missing it all together. This is what is meant by "collapsing the wave function". And, so even though you experience your finger being where you see it now, in another collapsed wave function, "another you" may exist and that space twin version of you ends up observing your finger as being in a different location. Quantum mechanics says that Einstein was wrong - God does in fact play dice and I hear he has a serious gambling habit. And so, admittedly no one really knows what a "Collapsed wave function" is or what consciousness means in these terms or how it works. Does that make sense? I'm doing really badly but bear with me. So, we only get to see a small piece of the action. A small snippet of the universe at any one time. Only one set of discrete states per discrete unit of time. Oh yes, time is quanitized too. It flows like a computer processor, stop and go between discrete states.

    Then, and this is the even more interesting part, and the message that "What the BLeep Do We know?" tried (and failed on behalf of those without some prior knowledge of this subject, judging by all of the reviews I read) to convey. Who makes the decision regarding how the wave function collapses as experienced by us. God? Is it random? Or... do we have some say in the matter? Of course, the movie hints that the latter's probably true. And they may be right to some extent. Can we really shape how events unfold? Is this what we experience as free will?
     
    Last edited: Nov 11, 2004
  2. jcsd
  3. Nov 11, 2004 #2
    Brilliant

    I think you have a wonderful grip on a very difficult subject. In fact I have not spoken with many people as astute as you are about Quantum Mechanics. I joined the group here just to tell you that, since previously I have only occasionally skimmed the posts but never replied. I'll be looking for more work from you, you can count on it. Your friend is lucky to have you to explain it, and if I come across anything you need to be corrected on, I will bring it to your attention, but for now, your record is impeccable.
    Keep up the good work.

    In pursuit of knowledge o:)
     
  4. Nov 12, 2004 #3
    This is correct in places, but I think you are gratuitous in your use of the term "collapsed wave function" without even saying what it is, or even what a wave function is. Furthermore, when you say "electron cloud" and it interacting with the retina, what you really mean is photon cloud, because when you look at something, it is not the electrons of the object that interact with your retina via virtual photons, it is transverse photons which interact with the object which then carry some information over to your retina.
     
  5. Nov 12, 2004 #4
    Right, I meant 'photons'. Do you see it as being incorrect in any places? How would you define "collapsed wavefunction" as far as what it truly is, you know in like a "metaphysical" type of sense - beyond equations or anything like that. The books I've read that aim to target the layman on this subject, I've always found, left it with this aura of ineffable mystery and never really lead anywhere in explaining it. Do you think this would be a more comprehensive way of explaining for non-scientists?
     
  6. Nov 12, 2004 #5

    Kane O'Donnell

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    It doesn't seem to be any less confusing than any other colloquial account of Quantum Mechanics. At the end of the day, you cannot reduce what is precisely a mathematical framework for describing nature to simple explanations in English. Trying to invent lovely flowing flowerly explanations that make people feel like they 'understand' the universe is misleading.

    If real physicists don't 'understand' QM (I use understand in a *very* loose sense, because I suspect the definition of 'understand' itself is a problem in this context), then laypeople won't. Besides, it would be much better for laypeople to understand what the *results* of QM are - ie, interference HAPPENS, probabilities HAPPEN. Forget the why. There isn't an answer to 'why' that will make everyone suddenly have an epiphany. QM works, and we know how to use it. What else do you need to know, if you aren't a physicist? What it's useful for? There are heaps of reasons, it takes 30 seconds and a google search to find a gazillion reasons - the fact that it explains and predicts all of chemistry is where I would start. Is it complete? NO. Is it as simple to understand as Newtonian mechanics - NO, because it incorporates a more involved mathematical structure than just calculus.

    Regards,

    Kane O'Donnell
     
  7. Nov 12, 2004 #6

    ZapperZ

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    I think I cringed a few times when I was reading your explanation. :)

    First of all, let's get this out of the way. That movie is a complete, utter, and unqualified GARBAGE. Having been "coerced" to see it, and having read several reviews of it, it is clear that NONE of the so-called "experts" in the movie are physicists. This movie sets back the general public's knowledge of physics by decades and does more harm than good.

    Now, back to your response. The problem I have is that you mixed and matched the "standard" explanation with those that are still highly controversal and unaccepted (many-world). You could have just said "look, this is what most physicist use. It is what we teach in schools, so it is the most widely accepted, but just keep in mind that it is not the only one", and start from there.

    Secondly, this "collapsing" thing needs to be mentioned more carefully. I can make an observation, and yet, I can still not "collapse" the superposition of a wavefuction. How? By making a measurement of an observable that does NOT commute with another observable. I can make an accurate determination of an energy state of a system, and yet, I still have not collapse the position of, let's say, an electron in the system - I still have no clue where it is and in fact, it still spread out over the system probabily (refer to the H2 molecule scenario that I've explained umpteenth times). Thus, we should always be specific that we are making a position measurement, a momentum measurement, an energy meansurement, an angular momentum measurement, etc. etc... because that is the observable (and all the commuting ones) that is being singled out.

    Thirdly, I am guessing that you were describing the double slit experiment at the very beginning. Take note that within the standard interpretation of this experiment, one single photon DOES passes through BOTH slits. One can see this clearly if one look at the superposition of PATHS that a photon can take. This again is an example of the manifestation of a more general principle in QM, which is the principle of superposition. This is one of THE weirdest, classically, of any QM principles, which resulted in the infamous Schrodinger Cat thought experiment. Thus, the doublt-slit experiment is idential to the H2 molecule, is idential to the Delft-Stony Brook's SQUIDs experiment, etc... which are all demonstrating the validity of such superposition phenomenon. I don't think we need to make this any more complicated by invoking virtual interactions nor many-world theory.

    Zz.
     
  8. Nov 12, 2004 #7
    Fred Alan Wolfe was in the film :smile: . Look, I thought most of it was crap too. Ramtha was funny, though, you must admit :smile: But I take the many worlds interpretation seriously. You're right, I should've mentioned that my view relies on the many worlds interpretation. I find this to be a more elegant and meaningful description of what is going on. I'm not interested in instrumentalist view of QM (well actually I am interested in the nuts and bolts too). But I'm more curious right now about the "whys". I think that the greatest power of any theory can ultimately be in answering "why?" and not just "it works so what does it matter why it works".

    I'm actually an autodidactic student of QM so I'm more than happy to have faults in my thinking pointed out. But, isn't the many worlds interpretation becoming more and more acceptable? It makes more sense to me that this is what's actually happening. The wavefunction collapses arbitrarily? I think it's more sensible to see it as collapsing into evey different possible position, however we only experience one of these possibilites, and we should consider as a caveat that somone else is experience the collapse as resulting in a different position in "another world or history", what have you. E.g. : < ...This is one of THE weirdest, classically, of any QM principles, which resulted in the infamous Schrodinger Cat thought experiment. > I find it less weird when looked at with a many worlds perspective. If this is true, then the point about the brain possibly holding some sway over what results as the observed collapse has to be at least given some attention and this was like the singular point I took from the film :smile:

    And excellent, your second point was very helpful. I appreciate you taking the time to share your insight with me - and I extend the same thanks to everyone else who's replied to my thread.

    Much Thanks,
    Chris
     
  9. Nov 12, 2004 #8

    ZapperZ

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    But I can also point out some "conceptual difficulties" with many-worlds scenario. If I were to make a measurement, I have gone into one of the many "parallel" universes that are available in which this particular measurement had existed definitely. But here's the kicker. I've also dragged EVERYONE ELSE, and everything in the entire universe, into that universe that I've measured. The entire universe have now been deprived of ever going into all of the other parallel universe that had existed before my measurement. Those other universes are no longer accessible by anyone or anything. This occurs every time there's a quantum measurement of an observable! Many people find that very hard "conceptually" to accept.

    And I am not sure that many-worlds are becoming "more acceptable", considering that there are still problems with it.

    http://xxx.lanl.gov/abs/gr-qc/9703089

    Again, I have my own take on the "philosophical issues" of QM. However, whenever I have to explain to other people on various concepts, I take the "party line" and try not to confuse them on what is generally accepted to what I would prefer or interpret. Those two can be different things, and I would imagine, can only add to the confusion of they later on hear or read from a different source.

    Zz.
     
  10. Nov 12, 2004 #9
    This conversation is getting very interesting!

    I see your point and I see how people could have problems stomaching that conceptually, philosophically, etc.

    At the same time, though, if you take this view,the person making the measurement would move into every possible "parallel universe" too, each "parallel" observer experiencing a different measurement - a "parallel" observer for every possible outcome of observation, as the observer, pre-observation, exists in a state of superposition as well.

    If I were to make a measurement, I have gone into one of the many "parallel" universes that are available in which this particular measurement had existed definitely.

    So, in actuality, you (or parallel versions of you) haven't just gone into one of the possible "parallel" universes by making a measurement, you + "parallel" versions of you have gone into all possible "parallel" universes. So each "parallel" observer doesn't drag the entire universe with them. Every possible outcome of observation, every possible measurement, is still observed in each "parallel" universe by "parallel" versions of the observer and isn't limited by the single discrete observation of just one "parallel" observer.

    :) Admittedly, this is the kind of stuff that leads to spontaneous head explosions :)

    I found the following on wikipedia. This is what made me think this interpretation was growing in popularity:

    It should be noted that, despite the name, which conjures up less the image of science than of science fiction, many worlds is a very widely accepted interpretation. According to a poll of 72 leading physicists conducted by the American researcher David Raub in 1995 and published in the French periodical Sciences et Avenir in January 1998, MWI is widely accepted:

    Yes, I think MWI is true 58%
    No, I don't accept MWI 18%
    Maybe it's true but I'm not yet convinced 13%
    I have no opinion one way or the other 11%

    Among the supporters of MWI are Stephen Hawking and Murray Gell-Mann. Among the skeptics are Roger Penrose. Richard Feynman is also said to have accepted MWI (although not in this poll, since he died in 1988).


    -Chris
     
  11. Nov 12, 2004 #10
    At the same time, though, if you take this view,the person making the measurement would move into every possible "parallel universe" too, each "parallel" observer experiencing a different measurement - a "parallel" observer for every possible outcome of observation, as the observer, pre-observation, exists in a state of superposition as well.

    I should add to this: assuming that every possible measurement/state actually exists in a "seperate universe", which is what this interpretation asserts.
     
  12. Nov 12, 2004 #11
    Too much a long text to be about physics.
    Sorry.
     
  13. Nov 12, 2004 #12
    Gell-Mann and Feynman agreed on a "many-histories" version of quantum mechanics in which every history of the universe is possible but there's no reason to believe that any other than one single history becomes real. People can believe in these other universes as real if they want but it's a personal belief and not a scientific one, as is also the belief that only one becomes real. :smile:

    It's probably not something all that new as some philosopher probably suggested long before quantum mechanics that someone's free will to choose to go for a walk or stay at home splits the universe into two universes, one in which they did go for a walk and one in which they did stay at home and that we experience only one of those universes.
     
    Last edited: Nov 12, 2004
  14. Nov 12, 2004 #13

    ZapperZ

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    However, I think that isn't the same thing (and philosphers get this wrong all the time especially if they didn't study any QM).

    Whether you go for a walk, or stay home, are two separate conditions that never somehow overlaps with each other to produce an unusual effect. This is not the case in quantum phenomena. Before a measurement, an electron in an H2 molecules IS occupying both H locations SIMULTANEOUSLY. This is even when we find that, upon a position measurement, it is in either one, or the other. So how do we know it is occuping BOTH locations before a position measurement? The existence of the energy gap between the bonding and antibonding states! The presence of an overlap between the two H atoms produces this purely non-classical effect. An energy measurement (which does not commute with the position measurement) allows us to infer the simultaneous mixing of the positions without having to disrupt such superposition.

    So if you apply this to the many-worlds scenario, the difficulty doesn't just comes in when you actually make a measurement that pushes you (and the rest of the universe) into one universe or another, it also comes in BEFORE a measurement, because it means that these separate, orthorgonal universes are "interfering" with each other, producing all of these non-classical effects. The universe where the photon passes through the left slit interferes with the universe where the photon passes through the right slit to produce the interference pattern. It is only when you unambiguouisly determine which slit the photon passes through is when you have chosen which universe you are in and the other one disappears (for that particular photon).

    Like I said, if we go by just on "conceptual problems", every single QM formulation isn't lacking in any of these.

    Zz.
     
  15. Nov 12, 2004 #14
    So if you apply this to the many-worlds scenario, the difficulty doesn't just comes in when you actually make a measurement that pushes you (and the rest of the universe) into one universe or another, it also comes in BEFORE a measurement, because it means that these separate, orthorgonal universes are "interfering" with each other, producing all of these non-classical effects.

    True, that's my understanding. The many worlds interpretation of the dual slit experiment explains the inferference pattern as being the result of interference amonst photons and their "counterparts", which exist in "other universes". I don't see how this creates a greater conceptual problem than saying that one photon's superpositioned path is causing the interference.
     
  16. Nov 12, 2004 #15

    ZapperZ

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    But that's my point. You can't say you are more "comfortable" with one and NOT the other. I did not advocate one over the other. I however disagree with your original contention that it is easier to accept many-worlds concepts than the "standard concept". At best, they are equally "weird".

    It means that choosing one over the other isn't "physics", but rather a matter of tastes.

    Zz.
     
    Last edited: Nov 12, 2004
  17. Nov 12, 2004 #16
    ah, you took the words out of my mouth, however: i think the many worlds interpretation actually tries to get at an explanation of why this phenomena occurs, while the standard doesn't bother with explanations... and this is my beef

    both views "work"

    Have you ever read anything by Deutsch though? Now I'm gonna have to hunt up his book :smile:
     
  18. Nov 12, 2004 #17

    ZapperZ

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    However (now don't you just hate that word?), there is a problem with the "why" of many-worlds - you cannot VERIFY it. There appears to be nothing that we know of to indicate that this is what is actually going on "under the covers". If that's the case, what's to prevent the acceptance of other scenarios that also cannot be verified? Let's play with a pilot wave, shall we?

    I'd rather just stop at the "how" of the standard formulation and leave the rest as "speculation" till there are some ways of distinguishing one from the other. At the very least, we're keeping philosphers of science employed or something to speculate on.

    Zz.
     
  19. Nov 12, 2004 #18
    i know what you're saying. that's why i asked you about Deutsch though... it's been a while since I read him so i don't remember all the details but he proposed a plan to prove many world interpretation... all i remember is that it would take some powerful quantum computers... let me see if i can find book

    maybe we'll find out in our life times :smile:
     
  20. Nov 12, 2004 #19
    BTW, I'm only acquiescing and giving up the fight to get you on board the many worlds bus because I'm insanely exhausted :smile: - i've been up for many moons, my friend :smile:
     
  21. Nov 12, 2004 #20
    Final thought:

    Excerpted from "Fabric of Reality" by David Deutsch [on dual slit experiment]:

    ... The key fact is that a real, tangible photon behaves differently according to what paths are open, elsewhere in the apparatus, for something to travel along and eventually intercept the tangible photon. Something does travel along those paths, and to refuse to call it 'real' is merely to play with words. 'The possible' cannot interact with the real: non-existent entities cannot deflect real ones from their paths...
     
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