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Reason for wave-particle duality?

  1. Aug 18, 2013 #1
    Recently been thinking about the double slit experiment, and Schrodinger's cat thought experiment. And realized that quantum mechanics only applies to the atomic, and subatomic level of the universe as far as we know. And whats more that I realized that gravity does not play any significant role in the subatomic level.

    What I questioned out of curiosity, was could it not just be the fact that since subatomic particle's do not have much mass/energy that they do not affect spacetime its self, being the reason that they can behave as a wave, and spontaneously be in different places until actually measured at a certain time?

    I'm no physicist yet btw, so if I missed something big that could make that question seem childish, I apologize only in high school.

    Thanks for reading,and contributing ideas and knowledge to this thread.
  2. jcsd
  3. Aug 18, 2013 #2
    Hi Fast77,

    You are basically on the right track. Because the mass of subatomic particles is so small, their gravitational effects are negligible compared to nuclear forces (strong and weak) and the electromagnetic force. So physicists can make accurate predictions while ignoring gravity. Also, as de Broglie initially showed, a particle's wavelength is inversely proportional to it's mass. So for everyday objects, the wavelength is so small that it has no measureable effect.

    You also mentioned how something can behave as if it were in different places at once (or simultaneous paths, as Feynman would describe it). How the wave function collapses upon a measurement is still an eerie mystery.

  4. Aug 19, 2013 #3
    It is inversely proportional to its canonical moment, no his mass, where canonical moment is the magnitude that is conserved because QM postulates, and its value from a composite system is the sum from the moments for the
  5. Aug 19, 2013 #4


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    This actually is not correct. For example, in the neutron drop experiment, the MASS of the neutron is definitely a factor where the gravitational potential energy comes into play.


    So while the mass of elementary particle often is not a factor in the quantum properties, this experiment by itself negates the idea what you proposed.

  6. Aug 19, 2013 #5
    Hi ZapperZ,

    Interesting point. I also recently read an article about a proposal to do the double slit experiment with the slits horizontal. The idea is to use particles heavy enough, and moving slowly enough, so that the gravitational potential (different for the two paths) causes each path to see a different time interval. The experiment will be a test of quantum and gravitational effects simultaneously. The experiment is a ways off, though, due to the technical challenges.

    But, I think Fast77 asks interesting questions and he/she recognizes that the turnover between quantum and classical behavior is a continuum.

  7. Aug 19, 2013 #6

    I was trying to avoid the use of "canonical momentum" since Fast77 mentioned he/she is in high school and has not had much physics yet. But I agree with you - a more accurate description would have been to state that the wavelength is inversely proportional to momentum. And for the purposes of this question, no need to refer to or define "canonical".
  8. Aug 19, 2013 #7


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    No, we don't know that. We have seen "large" conglomerate that exhibits quantum effects, including a super current consisting of 10^11 particles. The transition between quantum and classical is still being studied and still not known. So I don't know where you got the idea that it is a continuum.

  9. Aug 19, 2013 #8


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    First of all one should emphasize that according to "modern quantum theory" (discovered in 1925/26) there is no such thing as wave-particle duality but only the probablistic description of the behavior of matter in quantum theory. So, it's best not to worry about "old quantum theory" and to try to understand an inconsistent picture about quantum phenomena like "wave-particle duality" of "old quantum theory".

    Further one should say that, according to our present knowledge, quantum theory applies to everything, not only subatomic particles. The challenge is more to understand, why classical physics works so well in everyday life for macroscopic objects. The answer is that it is very difficult to isolate macroscopic objects from their interaction with the environment and that we are not able to describe their behavior in all tiny little details of the motion of each of their microscopic constituents. Instead, we use a few macroscopic observables like the center of mass of a solid body to define it's location and velocity when moving. Such macroscopic observables are averages over very many microscopic degrees of freedom which are interacting all the time with the environment and among themselves. Averaging out all the microscopic details leads, using the concepts of quantum-statistical mechanics, leads to the classical behavior of macroscopic objects.

    Nowadays pretty large objects could in fact be isolated well enough from the environment to establish also quantum-mechanical behavior for them. The double-slit experiment could be performed successfully with Buckyball molecules (a molecule shaped like a soccer ball consisting of 60 carbon atoms). To that end you had to make sure that the Buckyballs are cooled down to very low temperatures so that their intrinsic vibrations were reduced to a minimum. One could also show that the Buckyballs behaved classical, i.e., they were showing no "wave-like interference effects" anymore when heated up slightly, so that the emitted a few soft photons throught ("heat radiation") when flying throuth the slits. This is precisely the "decoherence effect" leading from quantum-mechanical behavior to classical behavior through "coupling to the environment", in this case exciting the electromagnetic field through the intrinsic motion of the atoms in the molecule (excitation and deexcitation of higher-energy states due to the finite temperature of the molecules).

    The quantum behavior is even not restricted to single molecules. Even macroscopic objects like diamonds can be brought to show quantum behavior, even so very unusual behavior as described by quantum-theoretical entanglement (leading to non-local correlations, unknown to classical stochastic systems):

  10. Aug 19, 2013 #9
    I was merely saying that physicists don't take account gravity when working with quantum mechanics. Correct me if I'm wrong there.
  11. Aug 19, 2013 #10
    Yes I've also heard of this disturbance theory if you will, where it's suggested that since everyday objects are consistently being measured(gravity, light etc.) that it's the reason they do not behave so strangely as they should according to QM. Which is why we use classical physics for macroscopic. That's great and it even goes with what I'm suggesting.

    I think many of you misunderstood what I'm trying to say. I'm just suggesting that perhaps the reason for wave-particle duality is gravity its self. I'm suggesting that since subatomic particles don't have as much energy/mass as a neutron or proton that they are not affected by SPACETIME, so they can behave as a wave, and this wave function collapses because we measure it at a CERTAIN TIME. We are presenting time in the measurement of the particle. In the end its about measurement.
  12. Aug 19, 2013 #11
    Is there actually any research being done on what I'm suggesting?

    Thanks for the replies
  13. Aug 19, 2013 #12


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    I did correct you! I cited an experiment that took into account the quantized drop due to gravity!

  14. Aug 19, 2013 #13
    It's not feasible yet but some have suggested that it may be testable one day. Note the 4-year period has passed and I haven't read/heard anything:
    If an Electron Can Be in Two Places at Once, Why Can't You?

    Another approach:
    Testing Gravity-Driven Collapse of the Wavefunction via Cosmogenic Neutrinos

    Does gravity induce wavefunction collapse? An examination of Penrose's conjecture
    Last edited: Aug 19, 2013
  15. Aug 19, 2013 #14
    Never apologize for asking questions. You CAN be embarrassed for NOT asking questions if you like! Great insights, by the way, for someone in high school.

    Instead of direct answers, I'll first provide you some general insights for perspective. I have found those are tough to find..so when I do, I make notes:

    mostly from prior discussions in these forums:
    [My explanatory comments thus {}.

    {Interference is a result of superposition. Have you had any trigonometry??....if so you will probably recognize things like
    Sin2X =2SinXCosX..... So a wave function describing a system has all sorts of underlying wave functions....and they can come together [superimpose] in constructive ways [where you find a particle] and destcructive ways [where the wave functions cancel] ..} Note that in this view 'discretness' of quantum theory is not so prominent.

    Using these ideas, here is what a prominent physicist has to say:
    Unfinished revolution

    A broader, more comprehensive description:
    I'd say ok as a start, but note that quantum theory also apply to large....as Vanhees71 posted. Here is an example: The Horizons of black holes. Have you heard of black holes??
    If you have or are interested, there are LOTS of discussions about them in these forums.

    The idea that there is an absolute limit to information on the other side of such a horizon is known as Bekenstein’s bound. The information of the volume [everything inside the horizon] resides on the enclosed horizon surface!; as if that were not crazy enough, the information is quantized....in discrete morsels...planck sized pixels....that's why it is FINITE...if it were continuous as prescribed by General Relativity the information content would be infinite!!

    So we discovered black holes via a continuous theory [general relativity] but discovered it has quantum mechanical characteristics!! Reconciling such views is what quantum gravity is all about.....melding the discrete with the continuous.....and the deterministic [exact] with the probabilistic [somewhat random].
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