Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is superposition dependant on the measurement of sound as well as sight?

  1. Jan 1, 2012 #1
    I understand that an object can exist in many possible locations, and that when you're not looking, it is a wave. It's only when you look that it manifests itself into a particle. But Is that also dependent on the measurement of sound? Does an object materialize when you hear it, or feel a force from it? (like if someone taps you on the shoulder)Do objects only exist in the perception of the observer? And to what extent?
  2. jcsd
  3. Jan 2, 2012 #2
    Quantum mechanics is the mechanics at atomic scales, sound is a macroscopic pressure wave that propagates through solid objects and fluids. Atoms don't "sound" like anything in the same way they don't "look" like anything, the way something "looks" in our macroscopic world is ultimately due to which wavelengths (colors) of light are absorbed by the atoms outer electrons (they only absorb specific quanta) and re-emitted, so the way something "looks" is really due to the electron orbitals of the atoms that make it up as well as programming in our brain (which can easily be fooled) the extrapolates things like distance and position in three-dimensional space, thus it makes no sense to ask what the nucleus (inside the electron orbitals) "looks" like.

    Perhaps it's better to think of smell. Their are certain shapes of molecules that our nose has evolved to basically have a specially shaped slot for, it's kinda like a lock and certain molecules are the key. If one of these locks gets a key put in it it sends a message to our brain and we detect a specific smell. This is why most things are odorless, it wasn't evolutionarily worthwhile to specifically evolve receptors for them so we don't have them. Gasoline is a good example, it's odorless. You might think it's not but that "gasoline" smell is actually due to another chemical they specifically add TO give gasoline a smell, that way we don't accidently blow ourselves up. But the point is that before the industrial age gasoline wasn't a part of our early-man lives so we have absolutely no receptors for it. So with this in mind what then does an atom "smell" like? It's a meaningless question. Smell isn't actually an intrinsic property of matter.

    The point being that hearing, seeing, smelling, touching and tasting are NOT fundamental things they're specific "experimental apparatus" our species has evolved to detect certain things in the macroscopic world. You can't take that intuition into the quantum world. However, a person is quite large, any large system is going to be entirely classical. There is no aspect of "quantum weirdness" in tapping your friend on the shoulder.

    P.S. in quantum mechanics vibrations in a solid (i.e. sound) itself is quantized into what are called phonons.
  4. Jan 2, 2012 #3
    I guess I'm just confusing myself. I think I'm asking a question that's much more abstract. I'm a little ahead of myself, since I'm very young, and new to the ideas of superposition and Schrodinger's cat. Lately I've been asking myself about the existence of things, what's truly real, and what's just a product of my perception. Sorry for my ignorance =)

    I'm also new to forums, so I don't even think I'm replying correctly.
  5. Jan 4, 2012 #4
    What is real? Physics has no answer for that. "I think therefore I am" is the only unalienable truth (at least in my books). Regardless of the philosophical nature of reality the math and laws of physics seem to be an excellent model of what we find around us.
  6. Jan 4, 2012 #5


    User Avatar
    Gold Member

    In addition to Maverick's excellent responses, I would add for your benefit that there is a confusion caused by the concept of "observer" that you would do well to look into. It is NOT just people observing things that can cause wave function collapse, and this gets to be a bit of a deep subject with differing points of view.
  7. Jan 4, 2012 #6
    I have a question to piggyback with the OP's

    How about the gravitational forces of the particle? How are other particles attracted to another particle that is currenlty in a superposition of states? Does the gravity vector correlate to the wavefunction? Is and outside particle being pulled in several different directions with a magnitude correllated with the probability distribution? This can't happen because the gravity is an observation, no? How does that not collapse the wavefunction?
    Last edited: Jan 4, 2012
  8. Jan 4, 2012 #7
    Firstly, gravity is an absolutely tiny force relative to those at the quantum level and is almost always neglected. Secondly, the machinery of general relativity is incompatible with quantum mechanics (or quantum field theory rather) and unifying the two is one of the biggest open questions in fundamental physics. That being said NEWTONIAN gravity can easily be added to quantum mechanics and its effects have been experimentally confirmed. In such a case gravity is simply another component of the energy of the system, like an electric field. Its effects are minor except in a few very clever experiments and it does not collapse the wavefunction.
  9. Jan 4, 2012 #8
    Well that fact we don't have a GUT doesn't mean that the wave function can ignore gravity, also the fact that its a tiny force doesn't mean that it doesn't send information does it? If i was sensitive enough I would know an electron is pulling me towards it.

    But much like a eletric field, the force of gravity, is a vector, and thus us where the origin of the force is i.e. location of the mass? Im still not grasping why it wouldn't collapse like it would using any other souce of observation...
  10. Jan 4, 2012 #9
    When you produce a solution to the Schrodinger equation, including the forces/interactions in the evolution operator, do you include all the forces acting on the system - for example, if two forces are acting on the system, but one force is stronger (so in some respect cancels a bit of the other force out), do you include the other force's part that isnt cancelled out, or including the cancelled out part?
  11. Jan 4, 2012 #10
    Well you can include them both and since they're vectors whatever components cancel will cancel by themselves. You don't have to do it explicitly.
  12. Jan 4, 2012 #11
    When one SOLVES for the wavefunction one solves the schrodinger equation whose (time-independent) form can simple be said to be

    [tex] \hat{H} \psi = E \psi [/tex]

    where [tex]\psi[/tex] is the wavefunction and E is the energy. H is called the Hamiltonian and encodes all the contributions to the energy of the system. Thus, if a system has gravity (or an electric field) in it then the Hamiltonian has an extra term in it and [tex]\psi[/tex] will be a different wavefunction. In other words, one doesn't figure out what the wavefunction is AND THEN adds the effects gravity, the effects of gravity come in at the very beginning when one defines the energy of the system and thus the result will be a different wavefunction. To find the wavefunction one first considers all the source of energy, that becomes the Hamiltonian, the wavefunction(s) are then all functions that are unchanged (up to a constant which is called the energy) by the Hamiltonian. Gravity comes into the Hamiltonian and thus tells you what the wavefunction is in the first place, it doesn't come in after the fact and "measure" the wavefunction.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook