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What does Double slit experiment actually mean

  1. Feb 19, 2016 #1
    I'd like to ask what exactly do the results of double slit experiment mean? I must confess that I've read about this mainly in New Age literature where it was used as a "proof" that our consciousness changes reality. I know that Physicists probably don't like such explanations :eek:
    So I'd like to know what this experiment actually means for the science of physics? What exactly has been discovered and why is it considered so important?
    (My knowledge of Physics and Math is about Grade 10)
  2. jcsd
  3. Feb 19, 2016 #2


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    It's not that physicists "probably don't like such explanations" it's that physicists recognize that such explanations are moronic, given what has been known for the last 100 years. Consciousness just doesn't enter into it.

    What the experiment shows is that quantum objects are exactly that. Quantum objects. Photons, for example, are not waves and they are not particles. They are quantum objects. If you measure wave characteristics you will see wave characteristics but that doesn't make a photon a wave. If you measure particle characteristics you will see particle characteristics but that doesn't make a photon a particle.

    If you "observe" (and this does not mean a conscious observer) the particles going through the slits so as to know which slit an object has gone through, you will of necessity be measuring their particle characteristics and they will not then act like waves to give an interference pattern. If you leave them alone, they act like waves, with wave interference, right up until they hit the screen at which time they "register" as particles exciting another particle on the screen. If they acted like particles all the way from source to target there would be no interference pattern.

    Do NOT read "New Age" stuff and believe that it has anything to do with actual science.
  4. Feb 19, 2016 #3
    Thank you Phinds. I know that NA is not science. I used to read such literature in the past but not any more. That's why I was asking here, at the PF, because I wanted to get the right explanation.

    It's quite difficult to understand what quantum objects are. If everything is made of quantum objects than how is it possible that something bigger becomes a solid particle that shows only one characteristic? Like, how large has the particle to be to "stop being" a quantum object and become a particle? Or is there a certain number of QO in an object (atom?) that are needed to lose wave characteristics and form a solid particle? Why are the double characteristics lost as an object becomes bigger? Maybe it is too complicated to explain on this basic level.

    I'm sorry I can't formulate the question properly but I hope that you get the idea.
  5. Feb 19, 2016 #4


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    But it doesn't need to "stop being a quantum object" and in fact it can't stop. It is what it is. What matters is the behavior it exhibits. Atomic and molecular bonding are beyond me so someone else here will have to get into detail on that.
  6. Feb 19, 2016 #5
    I didn't ask correctly. What I meant is where is the boundary between quantum objects and particles. Is it matter of size or the number of quantum objects "glued" together until they reach a state where the thing made of them is a particle.
    Based on your answer I think it will be about bonding.
  7. Feb 19, 2016 #6
    What do you mean by particles? 'Classical' objects?

    In principle QM applies to both micro and macro objects.
  8. Feb 19, 2016 #7


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    There really isn't a fixed boundary. There have been pretty large objects that have been demonstrated to show quantum behavior. I don't mean large by human standards but large by quantum standards. I think a good-sized Bucky-ball was one such item but my recollection is fuzzy on that.
  9. Feb 19, 2016 #8
    I didn't know that QM applies to both micro and macro. I thought there were two different kinds of physics- one for quantum objects and one for "classical" objects. And that we need theory of everything to put them together.
    That's why I was asking what are the factors that determine if a thing behaves according to quantum or classical (newtonian) laws.
    LOL I'm totally confused now o0)
  10. Feb 19, 2016 #9


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    Your question above is addressed exactly in this article. Quoting a line from there:
    This article actually highlights an experimental result devoted to observe interference pattern formed by macromolecules. The result is documented in this paper. In the experiment performed, the author used a beam of fluorous porphyrin, a large molecule consisting of 810 atoms. An interference pattern was successfully observed.
  11. Feb 19, 2016 #10


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    There no hard and fast line. Generally larger and more complicated systems with more internal degrees of freedom and more interactions with the environment will behave more classically. Experiments have successfully demonstrated quantum effects in objects that are (just barely) large enough to be seen with the naked eye, but these experiments are most interesting for the heroic measures that were required. Under any but the most artificial lab conditions, quantum effects become undetectably small for an object as large as a bacterium - small by human standards but still enormous at the subatomic scale.

    You might want to give Bruce Lindley's book "Where does the weirdness go?". There's also Giancarlo Girardi's "Sneaking a look at God's cards", which is a bit more demanding (which is to say worthwhile) but still layman-friendly. Both are far more accurate than any drivel about consciousness affecting reality.
  12. Feb 19, 2016 #11


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    That is not what is meant by a "Theory of Everything". That term usually refers to the joining of General Relativity (GR or gravity) and the Standard Model (Quantum Field Theory). Although "Standard Model" itself can refer to several things too, just to make it really confusing. Regardless, "Theory of Everything" is the unification of Electromagnetic, Weak, Strong and Gravitational forces.
  13. Feb 19, 2016 #12


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  14. Feb 19, 2016 #13


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    Actually there is no boundary - everything is quantum. We are finding quantum effects in macro objects all the time as technology progresses:

    What's going on in the macro world is everything gets entangled with everything else and without going into the technicalities gives objects (usually) a definite position. This is the solution to the Schrodinger's cat paradox (not the only way to resolve it - you will find others - but its the one I like best) the cats constituent parts have definite position because of that entanglement so you can never have a superposition of alive and dead. Alive it breaths, has a beating heart etc so is different to a dead cat that - well doesn't.

  15. Feb 19, 2016 #14
    +1 for "Sneaking a Look at God's Cards". Very good book, learned a great deal about Quantum Mechanics from it.
  16. Feb 20, 2016 #15
    Thank you everyone!
    I'll read the resources you suggested and ask if I have more questions
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