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Science Question: Double Slit Strangeness

Discussion in 'Science and Technology' started by dybmh, May 19, 2022.

  1. dybmh

    dybmh Terminal Optimist

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    Does science have an explanation for this bizzare behavior of a particle shot through double slits?

    "[A] interference pattern remains — accumulating over many particle impacts — even if particles go through the slits one at a time. The particles seem to interfere with themselves. Odder, the pattern vanishes if we use a detector to measure which slit the particle goes through: it’s truly particle-like, with no more waviness. Oddest of all, that remains true if we delay the measurement until after the particle has traversed the slits (but before it hits the screen). And if we make the measurement but then delete the result without looking at it, interference returns."

    source - Nature.com - Two slits and one hell of a quantum conundrum
     
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  2. sayak83

    sayak83 Veteran Member
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    Yes. It's called quantum mechanics. But it's more of a mathematical model. The physical picture that corresponds to the mathematical model remains hotly contested.
     
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  3. dybmh

    dybmh Terminal Optimist

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    Why is the wave behavior retained if the measurement is collected then deleted?
     
  4. Polymath257

    Polymath257 Think & Care
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    In essence, if the interaction of the detector with the particle is strong enough, the interference pattern disappears. This is true as long as the interaction is strong enough to give 'which slit' information.

    If the information about which slit is erased *permanently* (which requires and additional strong interaction with the detector), the interference pattern is seen.

    The explanation is in how the math of the interaction plays out: a strong interaction 'randomizes' a phase, meaning things don't add and subtract in the same way (imagine water waves with randomized sizes).

    My personal view is that much of the paradox arises because we seek to 'explain' things in classical terms: waves and particles that act like classical waves and particles. But, I think. that is a very wrong approach. We should not try to explain the new theory in terms of the old, but rather the old in terms of the new. So, we should be trying to explain why *macroscopic* things show 'classical' properties, not why microscopic things show quantum properties.

    But that is much easier to answer: macroscopic things show classical properties because that is what happens when you average together a large number of quantum properties.

    So, if you roll a dice, you won't be able to predict how it will land on any given roll. But if you roll it a million times, you can predict pretty accurately what the average value for all those rolls will be. That is the difference between quantum randomness and classical determinism.

    One good thing about the quantum world: everything acts the same. There is no distinction between waves and particles: photons, electrons, neutrons, etc ALL act the same, with interference patterns at times and no pattern at other times, always depending on whether 'which path' information is kept.
     
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  5. Polymath257

    Polymath257 Think & Care
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    Because the interference pattern appears because there is a lack of 'which slit' information. If you *actually* delete that information, the pattern will show up.
     
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  6. sayak83

    sayak83 Veteran Member
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    This is too vague. What is the exact procedure being adopted? The link you quoted does not discuss this at all.
     
  7. dybmh

    dybmh Terminal Optimist

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    So it's a factor of the measuring device? If the device were more subtle so that there was much much less interaction would it be expected that the wave behavior would be retained?
    So this is still a function of the properties of the measuring device and what needs to be done to permanently delete the information?
     
  8. Polymath257

    Polymath257 Think & Care
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    Well that is one aspect of quantum mechanics. There is a playoff that is unavoidable between precision and strength of the interaction.

    So, in the double slit experiment, you might want to determine which slit an electron goes through. But the slits are a certain distance apart, which means you need to probe with something having a wavelength smaller than the distance between the slits. But a small wavelength corresponds to a high energy. So if you can distinguish between the slits, you have used something with a high enough energy to destroy the interference pattern.

    Alternatively, if you turn down the amount of interaction, the wavelength gets longer, and you can no longer distinguish between the slits, which means the pattern interference emerges. There is even the possibility of 'sliding' between the two extremes and the interference pattern grows in definiteness or fades depending on the amount of energy (or wavelength ) from the detector.

    Yes, there is an experiment called the 'quantum eraser'. In essence, if you collect the information about which slit, no interference pattern occurs. But, if you change the detector to NOT show which slit, the pattern re-emerges. One subtlety is that the erasure has to be at the quantum level.

    The Quantum Eraser

    And it should be pointed out that ALL of this corresponds precisely to what the quantum theory predicts. There *is* an explanation, just not a classical one.
     
    #8 Polymath257, May 19, 2022
    Last edited: May 19, 2022
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  9. Polymath257

    Polymath257 Think & Care
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  10. Polymath257

    Polymath257 Think & Care
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    I think it is referring to the quantum eraser experiment.

    There is a LOT of bad information about this experiment.
     
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  11. robocop (actually)

    robocop (actually) Well-Known Member
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    I have a theory. It's never been debunked and never been made famous so I don't care to spell it out, but basically the electron is composed of several smaller particles. When they add up on the screen you detect an electron and when you measure a slit there will have to be enough together to measure it there, so you measure the same amount of stuff going through the slit as on the screen.
     
  12. Heyo

    Heyo Veteran Member

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    One of the best answers I have ever heard:

     
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  13. Twilight Hue

    Twilight Hue Twilight, not bright nor dark, good nor bad.

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    Please please please....

    No Dr Quantum videos!
     
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  14. Twilight Hue

    Twilight Hue Twilight, not bright nor dark, good nor bad.

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    That's an understatement for sure.
     
  15. viole

    viole Ontological Naturalist
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    This is bizarre only if we assume the world is classical. Since the world is not classical, the behaviour is not necessarily bizarre.

    So, it could be that it looks bizarre because our natural intuition evolved to survive in a world populated by classical macroscopic objects like predators, food, etc. In other worlds, it looks bizarre only because our mind has a naturalistic origin, and evolved for survival in that kind of world, and not for having a natural intuition about fundamental truths about the universe.

    If that is the case, no explanation is needed. The world is just the way it is, and the weak part is our natural cognition capabilities, which we cannot change.

    IOW: if there any need of an explanation, it would concern only metaphysical things. Like: why didn't God give us a natural intuition to grasp what is actually true about the world?

    Ciao

    - viole
     
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  16. mikkel_the_dane

    mikkel_the_dane Shadow Wolf's Aspie sibling

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    That is also a classical view about the world back to the idea of knowledge as justified true belief.
     
  17. Brickjectivity

    Brickjectivity Turned to Stone. Now I stretch daily.
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    I like that.

    I watched that...or at least part of it. Look at her favorites list. There's a video where she goes over how heisenberg derives the uncertainty formula. Its interesting, and its all because he nearly fails to get his doctorate and is embarrassed.
     
  18. RestlessSoul

    RestlessSoul Well-Known Member

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    The philosophical, and metaphysical, implications of QM are profound. Or not, depending on one's p.o.v. Either way, the philosophers, baffled by infinitely complex calculus, are only just beginning to catch up with the scientists; who, depending on your p.o.v., may just be catching up with the timeless wisdom of ancient philosophers;

    All phenomena are devoid of inherent existence, and are empty.
    - Nagarjuna, 1st Century Indian monk

    We cannot think of the world as if it were made of things, of entities. It simply doesn't work.
    -Carlo Rovelli, 21st Century physicist

    We break things down into smaller and smaller pieces, but the pieces, when they are examined, are not there. Only the arrangements of them are.
    -Anthony Aguirre, Cosmological Koans

    So if the parts of things aren't real, then what is? According to certain perspectives, only the whole;

    The cosmos is in an entangled state
    Entangled systems are fundamental wholes.
    Therefore;
    The cosmos is a fundamental whole.
    -Jonathan Schaffer, Monism - The Priority of the Whole

    To Schaffer and other monists, sub-systems, entities, and objects are less fundamental, less real, than the cosmos itself. The implication here is that galaxies, stars, solar systems, planets, life forms, cells, atoms, sub atomic particles etc, have their existence only as fragments or facets of the whole. Nothing can exists independently of everything. The Buddha, Krishna, and Jesus all knew this, of course. So did Paul Dirac, when he said "pick a flower on earth, and you move the farthest star".

    Some philosophers go further; Don Howard (Notre Dame University) uses the phenomenon of quantum entanglement to support the contention that it isn't simply that quantum wholes are more fundamental than their parts, but rather that it is only the wholes that exist. There are no distinct realities within fundamental wholes, locality is universal, and separation is illusory.

    In the view revealed by this paradigm, relations between, and qualities of, distinct entities are defined only as qualities of the one, the cosmos. Seemingly separate entities, including you and I, have no features or qualities of our own. Our qualities manifest only in relation to the whole, as figures in the dance, defined by the music of the spheres.

    There are wholes, there are parts of wholes, but there are no whole parts.

    There's loads more to be said on this vast subject of the infinitesimally small, and what it can tell us about our low dimensional macroscopic world; but I'll leave the last word here to Carlo Rovelli;

    The interconnectedness of things, the reflection of one in another, shines with a clear light that the coldness of 18th century mechanics could not capture.
    -Rovelli, Helgoland
     
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