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Thread: What is it like to be a quantum object ?

  1. #1 What is it like to be a quantum object ? 
    Moderator Moderator Markus Hanke's Avatar
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    This is something that has been captivating me for some time : what it is like to be a quantum object ? What does the rest of the universe look like if you were to take a ride on, say, an electron ? Much has been said and written about what quantum objects look like to us, and how we can describe them, but what about the other way around ? There is of course a deeper reason why I am pondering this question ( and it is not philosophical ), however, that aside I would like to hear other member's opinions on this topic...basically I am looking for a fresh perspective, some new ideas.

    So, what is it like to ride an electron ? Is this question even meaningful ? What would the rest of the world look like as seen through the "eyes" of an object that is both particle and wave, and obeys all the laws of quantum mechanics ? Let's leave aside relativistic effects for the moment and consider only objects with v << c.

    Comments ?


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    Quote Originally Posted by Markus Hanke View Post
    So, what is it like to ride an electron ? Is this question even meaningful ? What would the rest of the world look like as seen through the "eyes" of an object that is both particle and wave, and obeys all the laws of quantum mechanics ?
    I'm not sure if I understand the subject well enough to participate, but just how "wide" is or can the wave aspect of the duality be?


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    Can you tell us that deeper reason? I have no idea how to approach this question in general If you want to say couple inertial frame to free moving electron than in principle you could. But still the electron would be described probabilisticaly (some wave packet) and your inertial frame would have group velocity of that packet. Now if you would like to measure electron in that inertial frame you would run into same problems (Heisenberg relations) that you run into in some lab frame. I don`t think there are some reference frame issues in QM.

    You may want to couple your inertial frame origin to position of electron therefore you measure position and get wavefunction as delta function in space. But then you are xxxxxx because you have arbitrary momentum (speed) and you cannot define frame velocity. If you want to couple your frame to hae exact speed as that electron you would measure momentum, get wavefunction as plane wave but then you are xxxxxx as your electron is everywhere and you cannot place origin of reference frame to exact position of electron.

    You would run into much worse problems with photons. Say you have some photon wavepacket containing single photon. You run this through beamsplitter. Then your wavepacket probability will split, one half of probability would pass, other half would reflect and until you do measurement (something like which path experiment) you IN PRINCIPLE cannot say which way photon went. Important here is IN PRINCIPLE, this doesn`t mean that you don`t know, this means that it is probabilisticaly in both paths. (see Bomb testing paradox - it`s really very unintuitive and also fundamental aspect of QM Elitzur)
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    Particularly intriguing for me is the question of what it means for photons to be travelling at C.

    I am thinking in terms of the muon test of relativity as highlighted here: Muon Experiment in Relativity

    It means that time dilation delays the decay. From the perspective of an object travelling at C, there would be zero time between absorption and emission. But what does that say about the photon and how we perceive it from our perspective? Does it allow whatever the configuration of a photon is to include aspects denied to massive particles?
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

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    Moderator Moderator Markus Hanke's Avatar
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    You would run into much worse problems with photons.
    Particularly intriguing for me is the question of what it means for photons to be travelling at C.
    Ok, I would like to leave photons aside for the moment, along with all other relativistic effects, as this will only complicate an already very difficult matter. Let's just focus on an isolated, slowly moving quantum object, such as an electron, with v << c.

    You may want to couple your inertial frame origin to position of electron therefore you measure position and get wavefunction as delta function in space. But then you are xxxxxx because you have arbitrary momentum (speed) and you cannot define frame velocity. If you want to couple your frame to hae exact speed as that electron you would measure momentum, get wavefunction as plane wave but then you are xxxxxx as your electron is everywhere and you cannot place origin of reference frame to exact position of electron.
    Yes, this is one of the issues. So let's say you were going for a ride on a highly localised, slow electron - by the laws of QM your momentum is widely spread out ( since it is the Fourier transform of your position function ), so of course there can't be any way for you to tell your own velocity in relation to anything else in the universe with any degree of certainty, or else the HUP would be violated. So then, how would the rest of the universe look like to you ? From the electron's point of view, what prevents it from telling its own momentum in relation to, say, a distant star ? How does that distant star appear to the electron ? Surely it must appear in a way that stops you from using it as a point of reference to determine your own momentum. So my question would be just how it would "look" like - and by "look" I mean not necessarily in a visual kind of sense ( since not very many photons will hit you if you are the size of an electron ), but how it would be detected in general, in terms of all possible interactions. See below also.

    Can you tell us that deeper reason?
    Hm, ok, I don't really want to go into too many details ( for various reasons ), but the basic question I am pondering is whether all the various quantum effects ( such as the HUP for example, or deBroglie waves ) could, at least in principle, be artefacts of a non-trivial geometry and topology of space-time itself, rather than inherent properties of these objects. In other words - I am pondering whether the wave functions we use to describe quantum objects really are inherent properties of those objects, or whether they rather describe relations between observers in some non-trivial space-time. This is in some way analogous to relativity - for example, speed is not actually an inherent property of an object, but rather something which defines the geometric relation between observers in space-time. The "speed" of a single, isolated object is in itself a physically meaningless concept unless there is some outside point of reference, just as a generic wave function that represents the superposition of all possible states is a physically meaningless concept unless it is collapsed through the act of observation by another observer, yielding actual observables.
    Anyways, I am examining the possibility that quantum effects are observer-dependent artefacts rather than inherent properties of a particle or system ( the "true" nature of which shall remain unspecified for now - I simply don't know ! ). The question arose when I took the dog out for his nightly walk, and started thinking about quantum field theories in highly curved space-times ( as you would if you are a nerd like me ).

    I put the issue in yet another way - just as relativity tells us how locally inertial frames are globally connected, and how to go from one frame to another, is there a way to geometrically view the relation between macroscopic and microscopic frames of reference, in such a way that the quantum effects are just artefacts of the transformations between those frames, just as in relativity the various relativistic effects are artefacts of the relations between observers in space-time ? Can we eliminate quantum effects as being inherent in an object, and attribute it to observer relations instead ? What this would mean is that space-time on a microscopic scale would need to look much different than it does on a macroscopic scale - which, interestingly enough, is exactly what modern hypotheses such as Causal Dynamical Triangulations tell us ( in a general sense anyway ). Is there a specific reason or requirement why we assume space-time to be the same on microscopic scales, even on scales of the order of, say, a nucleus, apart from mathematical convenience ? I don't think there is, to be honest - it is a tacit assumption we are making, but I would like to explore the implications of what would happen if we abandon or at least relax this assumption. For example, what if space-time on microscopic scales were to have only two effective dimensions, and a fractal topology, as CDT tells us ? Would it be possible to retrieve all the usual quantum effects from the relation of such a space-time to our "normal" macroscopic world by way of a simple transformation from one reference frame to another ?

    Not sure if I am making myself clear - what I am really contemplating is surprisingly hard to describe in words, and at the moment I couldn't even begin to put any maths around this either.
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    [QUOTE=Markus Hanke;475777]

    Ok, I would like to leave photons aside for the moment, along with all other relativistic effects, as this will only complicate an already very difficult matter. Let's just focus on an isolated, slowly moving quantum object, such as an electron, with v << c.
    Hi Markus. A very interesting question. I would very much like to see more from you experts on these questions. Unfortunately I am only an avid reader so cannot help with the details but I thought I would add my 2c worth to hopefully get momentum rolling and get more forum participation in this thread.

    One of the problems I have with the statement above is that from a QM perspective does there really exist a completely isolated wave function such as an electron? From my understanding of entangled systems the entire universe comprises only one wave-function. I have always assumed a problem with the conventional interpretation of the wave-function in that what is being described represents, for experimental convenience, an arbitrary boundary created around a limited group of particles that are sufficiently isolated from the remaining universal wavefunction that it's impact is ignored. Adopting this 'fragmentary and reductionist' approach in my opinion could lead to potential misinterpretations of QM phenomena.

    Leading on from this viewpoint you perhaps could see how I might conclude that some of the problems of unification between QM and GR may in fact be attributed to a possible obfuscation attributed to a notion that fundamental particles can be treated in isolation. For example, a whimsical interpretation I have been playing with is in the context of the properties that are attributed to an arbitary selected wavefunction would be defined by the universal wavefunction it is embedded in. Using this analogy I at least appear to get more headway in understanding how it is only through an observation/ interaction that a hypothetical particle is attributed properties by virtue of its relationships with the rest of the universe. Prior to observation the hypothetical particle is completely undefined and can take any of its allowable property values (multivariate). Anyway, this viewpoint is philosophical musings at its best.

    In other words - I am pondering whether the wave functions we use to describe quantum objects really are inherent properties of those objects, or whether they rather describe relations between observers in some non-trivial space-time.
    You can see from my response above that this would also be my take, but for different reasons.


    Addendum: With regards to the uncertainty relation, I have wondered whether all physical values attributed to spacetime is a conjugate variable and whether this represents some sort of connection by symmetry between QM and relativity assuming spacetime is quantized and is therefore expressed by the uncertainty relation and is manifest by the resulting non-commutative nature of physical properties.

    I will leave it to the experts from hereon :-))
    Last edited by Implicate Order; October 23rd, 2013 at 07:27 PM.
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    Well I think that on fm scales and maybe a bit deeper the spacetime should look like standard 4D Minkowski. Thats because cannonical field theories are based on flat Minkowski metric and on such scales it works extremely well. But even our GSW standard model and chromodynamics are still understood as effective field theories, phenomenological constructs that seek to describe physics based on measured couplings, principles of minimal lagrangians and simplest possible models. The physics of superimbaextramega high energies is most certaily quite different. However some approaches to QFT are based on topography, quantization methods that I am completely unfamiliar with.
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    Thank you for posting this Markus! Really got me thinking...
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  10. #9  
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    Quote Originally Posted by Markus Hanke View Post
    This is something that has been captivating me for some time : what it is like to be a quantum object ?
    I love this question, so thanks for asking it. I've tried to think of that very thing ever since I came across Gamow's Mr. Tompkins stories. It has been many years since I've read those, so I will use your question as an excuse to revisit Gamow.
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  11. #10  
    Moderator Moderator Markus Hanke's Avatar
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    Quote Originally Posted by Gere View Post
    Thats because cannonical field theories are based on flat Minkowski metric and on such scales it works extremely well.
    Yes, I agree, they do work well, as can be seen in the empirical evidence available. However, that doesn't stop me from pondering the question of whether or not we can model the quantum behaviour in completely different terms, as topological or geometric properties of space-time itself. If that were so, we could completely do away with field theories, and look at everything geometrically or topologically, as, for example, the amplituhedron does by reducing scattering amplitudes to volume operators, thereby greatly simplifying an otherwise extremely difficult and lengthy calculation.

    Please do not get me wrong - I am not making a claim here. I might be completely wrong, and completely off-track, in fact I would consider this very likely. All I am trying to do is ponder possibilities, always knowing full well that such possibilities might not lead us anywhere. My only point in this thread is to perhaps get some fresh perspectives and ideas on the subject matter from other people.
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