Quantum Mechanics : !?

Discussion in 'Physics & Math' started by The God, Jun 1, 2017.

  1. The God Valued Senior Member

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    What is QM, for that one may refer to various sources available. In this thread I wish to discuss some interesting stuff which appear non intuitive and may provide interesting insight on the subject. To start with..

    1. Consider two objects separately, an electron and the Earth. What are the eigen states of these two quantum particles or systems?

    2. What are the wave functions for these two?

    3. What all information this wave function will have?

    4. What is the difference between observation and measurement? Beyond the obvious, the idea is will they impact the quantum system differently?

    5. What is the wave function collapse and will it happen both during observation and measurement?

    6. When actually the wave function collapse happens? Say a guy is measuring some parameter of a quantum system and for that he sends a probe signal....so the collapse takes place when the signal is emitted from test device or when it hits the quantum system or when the signal is recorded back by test device after its interaction with the object?

    7. How do we claim to know the prior state of system, just before measurement?

    8. And if we consider our solar system as quantum system and some aliens in the far universe decide to measure our solar system, so wave function of our solar system will collapse, and assuming that this collapse has some physical impact, then what?

    9. On a lighter vein, if I stare (measure) a person, the fellow starts feeling uncomfortable or may confront me or may give some weird reaction.....is it kind of his/her wave function collapse??
     
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  3. Seattle Valued Senior Member

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    What an unintelligible mess. This is what happens when you take a dictionary of quantum terms, give it to a non-native English speaker and ask him to start a thread.
     
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  5. The God Valued Senior Member

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    This is a big problem with people like you. Instead of indirectly boasting about you being a native English speaker, which does not guarantee good knowledge of English, (Any Indian or Chinese can put majority of native English speaker to shame on the knowledge of language), respond on the subject, if you know anything at all.
     
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  7. Seattle Valued Senior Member

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    How can I respond on the subject when the post is gibberish?

    Our Solar System isn't a quantum system.

    You want to know the Eigenstate of a particle and our Earth?
     
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  8. The God Valued Senior Member

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    I am sure you understand the scaling, the size of our solar system when we talk of cosmological scales.

    And what makes you think that QM is not applicable on earth or on our solar system? Shd we talk about De Broglie wavelength for our earth first?
     
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  9. Seattle Valued Senior Member

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    Coherence is lacking.

    Maybe others find this interesting. Have at it.
     
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  10. The God Valued Senior Member

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    So you are back to language.

    Your silly posts after posts give me an impression that you are not conversant with the subject beyond a few briefings.
     
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  11. Seattle Valued Senior Member

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    You are correct.
     
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  12. exchemist Valued Senior Member

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    You know (or can easily work out) the momentum of the Earth, so why don't you tell us - and then tell us why you think it is of interest. Then you might get some people interested in a discussion.

    Without that, it just looks like an exercise in trying to give scientists silly things to do.
     
    Last edited: Jun 1, 2017
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  13. river

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    Depends on the number of observers
     
  14. The God Valued Senior Member

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    Try OP and let's see, I think associating collapse with any physical change may turn out to be silly.
     
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  15. exchemist Valued Senior Member

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    Go on then, look up the momentum of the earth, plug it in de Broglie's formula and post the wavelength for us all to see. OK?

    Then we can talk about it.
     
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  16. The God Valued Senior Member

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    You are misdirecting, my one of the key point in OP is about physical relevance of wave function collapse.

    And for your kind information we can have De Broglie wavelength for entire universe, so pl do not pursue the troll line as taken by Seattle.
     
  17. exchemist Valued Senior Member

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    I am not misdirecting. It was you that asked (I quote you) " And what makes you think that QM is not applicable on earth or on our solar system? Shd we talk about De Broglie wavelength for our earth first?"

    So do you want to talk about that, or was that just a bit of misdirection on your part?

    I am serious about this, because I suspect that when you find out what the wavelength is, it will answer some questions about why we do not generally find it useful to employ QM for systems at the macroscopic scale.
     
    Last edited: Jun 1, 2017
  18. Dinosaur Rational Skeptic Valued Senior Member

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    I think wave function collapse is a misleading term. The semantics seem strange to me.

    The wave function provides information about the probabilities of various future events occurring. When one of the events occurs, it is said that the wave function collapsed.

    First: the wave function is analogous to a table of dice toss probabilities. Saying that it collapsed is semantics implying that it is some physical object like a building or abridge.

    Second: when a dice throw results in 9, we do not say "the list of dice probabilities collapsed to a 9." We say "A 9 was thrown" or "The shooter rolled a 9."
    I have often wondered about the origin of waht seems like strange semantics.

    I have an excellent education in mathematics (most of which I remember) & a much better than mediocre education in physics, but could be misunderstanding the semantics of wave function collapse.
     
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  19. Confused2 Registered Senior Member

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    Imagine you are looking at the screen of a single photon Double Slit Experiment (eg http://www.teachspin.com/two-slit-interference--one-photon-at-a-time.html ). It is fairly easy to map the probability of detecting a photon (High School wave interference) - the thing is - when a photon is actually detected - what happened to the probability of it being detected at any other point? Somehow (I have no idea how) nature arranges to 'instantly' remove the possibility of detecting the photon anywhere else where 'anywhere else' could be a considerable volume of space. The map (of probability) collapses to a point when/where the photon is detected.
     
  20. Dinosaur Rational Skeptic Valued Senior Member

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    from Confused2 Post #16
    Imagine your above statement reworded to refer to a table of dice probabilities after the shooter rolls a 9.

    Before the dice throw as well as before detecting the photon, there is more than one possibility for the outcome. After the dice throw does anyone wonder what happened to the probability of the other possible throws occurring? To me, it seems silly to ask what happened to them. It similarly seems silly to me to ask what happened to the other possible locations for the photon after it is detected at some particular location..
     
  21. Seattle Valued Senior Member

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    It seems to me the issues being talked about here (some of them) are interpretations of QM. Those are not necessarily anything more than opinions. If they were currently testable (falsifiable) they wouldn't be "interpretations".

    One distinction between the dice example and most examples in QM is that a dice isn't something on the quantum scale. It can have a wavefunction but it's too small to be relevant due to the size and energies involved. In that case talking about the possibilities before rolling the dice has to be informational only.

    One interpretation of QM has the waves there being informational only. Other's say it is literal but until that aspect can be tested it's just an interpretation. The math works and that is what QM really is until one of the interpretations can be tested as well.

    To me QM and the larger world is similar to GR and the larger world. They both apply technically but the effects are too small to be significant in most cases. Time may slow down when you are running compared to when you are sitting but it's not significant.

    The Earth may have a wavefunction or an individual but it's insignificant so why discuss it?

    I'm not an expert on either of these subject yet I'm also not a crank. I'm always open for correction or being educated further.

    My original impression still stands and that is that the OP is crank related at least until further refined.
     
  22. QuarkHead Remedial Math Student Valued Senior Member

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    Actually it is the absolute square of the wavefunction that gives the probability of a quantum event

    Actually it is when a measurement is made that the term term "collapse" is used.

    Using your "excellent education in mathematics" and your "much better than mediocre education in physics" you should know that

    1. In QM, the principle of superposition applies. This means that (except in special cases) every quantum state is the superposition of at least 2 other quantum states, each of which can be scaled by a complex number. So it seems reasonable to describe QM state space as a vector space of wave functions - at least in the Schroedinger formulation of QM

    2. Any possible measurement (or observable) property of the QM system is given by an operator acting on this vector space

    3. The actual measurements made on the system are called the eigenvalues associated to this operator

    4. Every eigenvalue (measurement) is associated to an eigenstate (a vector).

    5. In QM, experiment shows that successive determinations of eigenvalues (measurements) are not identical, but may be averaged. This average is called the "expectation value" for the system

    No it is not

    Precisely. None of the above refers to the non-quantum regime
     
  23. exchemist Valued Senior Member

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    I think The God wants to prove QM absurd for some reason, but it may just be teenage rebellion or something and it is not bad in itself to mount such challenges as a way of discovering more.

    I rather think he would do well to look up the "particle on a ring" QM problem. I was having a look at that this evening: the energy levels are quantised according to how many waves you can fit round the circumference of the ring (orbit, in the case of the Earth). However in the expression for the energy, the moment of inertia of the particle, with respect to the centre of the orbit, appears in the denominator, while Planck's constant appears in the numerator. So you are going to get energy level spacings which are absolutely minuscule. This will mean it won't be possible to assign the Earth to a single energy level (uncertainty principle) and consequently it will be represented, in QM terms, by a wavepacket of billions of different states, which will only interfere constructively at one point in the orbit and will progress around the orbit at the classical speed. Which will look......exactly like the classical description of an orbiting planet.

    At least, that is the sort of thing that my admittedly very rusty QM suggests will happen. Or he could try the full hydrogen atom solution, but I'm fairly sure he'll find something similar, with energy level spacings so close together that a wavepacket with classical behaviour will be the outcome.

    The solutions to his other questions will eventually come out a bit like this one, I suspect, though I can't be arsed to jump through all the hoops he has set out for us. The logical absurdity he hopes for will elude him.
     
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