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Thread: Wave-particle properties at the macro level2051 days old

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    Default Wave-particle properties at the macro level

    http://www.youtube.com/watch?v=nmC0ygr08tE

    The silicon droplet guided by its wave exhibits some properties of the quantum world .

    The model attempts to explain quantum mechanic as a deterministic theory.
    http://en.wikipedia.org/wiki/Pilot_wave
    IMO,one of the inconsistencies of this model is the wave that seems to be traveling ahead of its particle which doesn't seem to be the case in the quantum world,it also fails to explain the weirdness of subatomic particles (the sudden collapse of the wave-like property whenever an observer is involved) as demonstrated by the double slit experiment .
    http://www.youtube.com/watch?v=Xmq_FJd1oUQ


    Do you think that simplicity ultimately lies on the far side of the complexity of the quantum world?

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    Quote Originally Posted by moleson View Post
    http://www.youtube.com/watch?v=nmC0ygr08tE

    The silicon droplet guided by its wave exhibits some properties of the quantum world .

    The model attempts to explain quantum mechanic as a deterministic theory.
    http://en.wikipedia.org/wiki/Pilot_wave
    IMO,one of the inconsistencies of this model is the wave that seems to be traveling ahead of its particle which doesn't seem to be the case in the quantum world,it also fails to explain the weirdness of subatomic particles (the sudden collapse of the wave-like property whenever an observer is involved) as demonstrated by the double slit experiment .
    http://www.youtube.com/watch?v=Xmq_FJd1oUQ


    Do you think that simplicity ultimately lies on the far side of the complexity of the quantum world?
    I don't understand the full reach of these experiments, since I am not a theoretical physicist, but the fact that single "walkers" can reconstruct a diffraction pattern when traversing a pair of slits makes me think that the non-deterministic nature of Quantum Mechanics is all bullshit, like Einstein used to affirm. I mean, the traditional explanation for the double-slit experiment is that an electron is delocalized (i.e., it doesn't have a precise spatial location) and therefore it can interfere with itself to produce a diffraction pattern. The "walkers", being drops, are evidently localized and therefore, as far as I understand, they prove that there is no need to appeal to a probabilistic theory in order to explain the formation of the diffraction pattern. If this is true the current understanding of the subatomic realm, which is based entirely on probabilities, would have to be replaced by a deterministic paradigm.

    - - - Updated - - -

    I've read the article itself, which can be found here:

    http://users.isy.liu.se/en/jalar/kur...Couder2006.pdf

    The droplets, unlike the electrons, go through only one of the slits, but the waves caused by the droplets go through both slits. The interactions between waves traversing through different slits cause the interference pattern. The limitation here is that, as far as we known, subatomic particles don't move in a carrier medium similar to this surface. In other words, here we can separate the droplet (particle) from its wave (the undulations on the surface) because we have a medium, whereas in the subatomic world we can't separate them. So, this experiment is interesting from a statistical point of view, but it doesn't change our understanding of the subatomic world.
    Last edited by Crypto; 2013-12-05 at 22:48.

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    Quote Originally Posted by Crypto View Post
    I don't understand the full reach of these experiments, since I am not a theoretical physicist, but the fact that single "walkers" can reconstruct a diffraction pattern when traversing a pair of slits makes me think that the non-deterministic nature of Quantum Mechanics is all bullshit, like Einstein used to affirm. I mean, the traditional explanation for the double-slit experiment is that an electron is delocalized (i.e., it doesn't have a precise spatial location) and therefore it can interfere with itself to produce a diffraction pattern. The "walkers", being drops, are evidently localized and therefore, as far as I understand, they prove that there is no need to appeal to a probabilistic theory in order to explain the formation of the diffraction pattern. If this is true the current understanding of the subatomic realm, which is based entirely on probabilities, would have to be replaced by a deterministic paradigm.
    I am not a physicist too.
    You are right, walkers can reconstruct an interference pattern but this model fails to explain the sudden collapse of the wave function when a particle is measured/observed.
    Once a particle is measured it loses its wave function and doesn't create an interference pattern which shouldn't be the case if this theory was right.
    You're also right about the physical dimensions of a fundamental/elementary particle,a photon's size is measured by its wavelength.

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    Quote Originally Posted by Crypto View Post
    I don't understand the full reach of these experiments, since I am not a theoretical physicist, but the fact that single "walkers" can reconstruct a diffraction pattern when traversing a pair of slits makes me think that the non-deterministic nature of Quantum Mechanics is all bullshit, like Einstein used to affirm. I mean, the traditional explanation for the double-slit experiment is that an electron is delocalized (i.e., it doesn't have a precise spatial location) and therefore it can interfere with itself to produce a diffraction pattern. The "walkers", being drops, are evidently localized and therefore, as far as I understand, they prove that there is no need to appeal to a probabilistic theory in order to explain the formation of the diffraction pattern. If this is true the current understanding of the subatomic realm, which is based entirely on probabilities, would have to be replaced by a deterministic paradigm.

    - - - Updated - - -

    I've read the article itself, which can be found here:

    http://users.isy.liu.se/en/jalar/kur...Couder2006.pdf

    The droplets, unlike the electrons, go through only one of the slits, but the waves caused by the droplets go through both slits. The interactions between waves traversing through different slits cause the interference pattern. The limitation here is that, as far as we known, subatomic particles don't move in a carrier medium similar to this surface. In other words, here we can separate the droplet (particle) from its wave (the undulations on the surface) because we have a medium, whereas in the subatomic world we can't separate them. So, this experiment is interesting from a statistical point of view, but it doesn't change our understanding of the subatomic world.
    Think of it differently. If we set up the same experiment in a laboratory, and keep all conditions constant, we will see that the measurements are different eigenvalues of the wavefunction. Our original wavefunction was simply a superposition of different eigenstates and no matter how many times we measure the wavefunction we will not be able to repeatedly predict the location of the particle. The wavefunction, being the complete physical description of a wave-particle, does not allow us to measure a definite value of the wavefunction but rather an eigenstate. For example, the position or momentum we measure (when the wavefunction collapses) is nothing more than one component of a superposition of eigenstates which make up the total quantity. We can see this by recognizing that our expectation value <x> is simply the result of applying the position operator to our wavefunction <Psi|x|Psi>. Therein lies the strength of using the wavefunction as a probabilistic tool. As I've probably already stated, you and I can both conduct exact experiments for measuring position of such an electron, and we're both likely to acquire different eigenvalues. But upon taking a great quantity of measurements, we'd acquire the same information that the wavefunction already provides us with; we'd notice that the particle is more likely to be found in certain regions than others. The probabilistic interpretation of the double slit experiment means that just like we cannot always know the position of the particle (even under exact laboratory conditions), we cannot know where one lonesome electron will hit the screen. But we know that given repeated measurements (electrons hitting the screen), the pattern on the screen will follow a pattern that we can fairly accurately predict and recognize. Perhaps the "straightforwardness" of the double-slit experiment is one of the reasons it's the first thing you learn in quantum mechanics. It's much harder to accept the probabilistic interpretation when applied to something such as an infinite square well or quantum tunneling, but not so much a double slit experiment. When we bounce a ball on a wall, we see that the ball bounces back. Our wall is our potential barrier, and unless our ball has enough energy to overcome that barrier, it will simply bounce back. Similarly a marble in a "ditch" will stay within the "ditch" unless it possesses the energy to overcome it. However, a quantum particle, through its wave-particle duality and the probabilistic interpretation of quantum mechanics, allows us to predict that the wave has SOME probability of tunneling through the barrier, as long as the barrier is not infinite. Of course, the larger the barrier, the less the probability will be, but it remains that there is some probability in quantum mechanics that is not present in classical mechanics. Therein too, lies the strength of a probabilistic representation of quantum mechanics; that the experimentally expected effects described by the probabilistic theory, are in fact present.

    As for determinism, we can take the simple case of a 1/2 spin system. Our pauli matrices will have eigenvalues of either +1 or -1. For one of our pauli matrices (depending on our orientation) we will always have eigenvalue one. However, for another one of our pauli matrices our eigenvalue will be +1 or -1, each with a 50% probability. Therefore we cannot have determinate values for both pauli matrices describing the same system.

    Similarly we cannot measure the postion and momentum to great accuracy simultaneously as it is constrained by the schrodinger uncertainty relation....or the Lz and Ly components of angular momentum, as measuring one modifies the probability of finding a given result for the other two.

    So even though the wavefunction is deterministic (as I have earlier stated that it is a complete physical description of a particle) our measurements cannot be (they are probabilistic), and to my knowledge such has been proven experimentally.

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