Understanding particle/wave duality and the Wave Function

  • #1

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Im just starting to try to break into and understand quantum physics and so this question may be a completely absurd but im curious as to whether or not its been proven that a particle really does act like a wave until observed or if the "spin" of two entangled atoms actually changes opposite of its counterpart or if both of these things can be chalked up to insufficient tools and calculations. Its my understanding that Einstein believed that if we could measure things infinitely better and take into account every factor that probability would cease to exist. Does the WF actually collapse because of the observer or does the WF even exist? Do entangled particles really "snap" to attention when we look at their position, or was the position always as such?
 

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  • #2
Nugatory
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im curious as to whether or not its been proven that a particle really does act like a wave until observed.....
That's not really what quantum mechanics says. This notion of wave-particle duality as it described in popular books and articles dates from early last century and was abandoned after the modern understanding of quantum mechanics was hammered out in the 1920s and 1930s. But with that said.... The experimental evidence in support of what modern QM does claim is overwhelming - even if some as-yet-undiscovered theory were to replace QM, that theory would have to agree with what QM predicts for all the experiments that have already been done, and would necessarily be no less weird than QM itself.

If you are serious about understanding this stuff, you will want to start with a reliable source. If you're not looking for a serious textbook, Giancarlo Ghiarardi's "Sneaking a look at God's cards" is a good layman-friendly explanation requiring minimal math.

the "spin" of two entangled atoms actually changes opposite of its counterpart or if both of these things can be chalked up to insufficient tools and calculations. Its my understanding that Einstein believed that if we could measure things infinitely better and take into account every factor that probability would cease to exist. Does the WF actually collapse because of the observer or does the WF even exist? Do entangled particles really "snap" to attention when we look at their position, or was the position always as such?
It has been decisively settled by experiment that the the entangled particles do not have a preexisting spin that we are just unable to detect because of inadequate tools or calculations. The key here is Bell's theorem, which has been discussed in many previous threads, for example this one is most recent: https://www.physicsforums.com/threads/what-is-the-difference-between-the-lottery-and-qm.950035/
 
  • #3
That's not really what quantum mechanics says. This notion of wave-particle duality as it described in popular books and articles dates from early last century and was abandoned after the modern understanding of quantum mechanics was hammered out in the 1920s and 1930s. But with that said.... The experimental evidence in support of what modern QM does claim is overwhelming - even if some as-yet-undiscovered theory were to replace QM, that theory would have to agree with what QM predicts for all the experiments that have already been done, and would necessarily be no less weird than QM itself.

If you are serious about understanding this stuff, you will want to start with a reliable source. If you're not looking for a serious textbook, Giancarlo Ghiarardi's "Sneaking a look at God's cards" is a good layman-friendly explanation requiring minimal math.


It has been decisively settled by experiment that the the entangled particles do not have a preexisting spin that we are just unable to detect because of inadequate tools or calculations. The key here is Bell's theorem, which has been discussed in many previous threads, for example this one is most recent: https://www.physicsforums.com/threads/what-is-the-difference-between-the-lottery-and-qm.950035/
I appreciate the information and the resource recommendation. Im excited to learn this stuff so definitely serious about it. Even planning on picking up Calculus as I never took it in school. I also appreciate the corrections. As I said im very new to this and just finding what information I can which is why I wanted to start posting here. I must be misunderstanding modern QM as I thought the dual slit experiment showed us that a particle did in fact act like a wave at least until observed. Regardless its mind boggling that entangled particles do not have a preexisting spin. I much thought of the particles as two colored marbles and you had an "either" "or" situation. Not that it was both until observed. Is this the same thing as superpositioning or does that only apply to moving particles and their position? Is superpositioning even still a term?
 
  • #4
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Im just starting to try to break into and understand quantum physics and so this question may be a completely absurd but im curious as to whether or not its been proven that a particle really does act like a wave until observed or if the "spin" of two entangled atoms actually changes opposite of its counterpart or if both of these things can be chalked up to insufficient tools and calculations. Its my understanding that Einstein believed that if we could measure things infinitely better and take into account every factor that probability would cease to exist. Does the WF actually collapse because of the observer or does the WF even exist? Do entangled particles really "snap" to attention when we look at their position, or was the position always as such?
Your question doesn't match the title you created for the thread. This really doesn't deal directly with "wave/particle duality". It is more of an issue of you not understanding quantum superposition.

This is why quantum statistics is different than classical statistics. If you flip a coin but not look at the outcome, the outcome is already determined. You just don't know it. So classical statistics describes not the physical situation, but rather the state of our knowledge, or ignorance, of the outcome. This is different in QM.

In QM, the state will continue to be a "superposition" of all the possible state until an observable is measured. In other words, unlike the classical system, it has not been determined yet until the actual measurement of that observable. In some interpretation, it implies that all of the possible outcome of that observable are there. This led to the infamous Schrodinger Cat analogy where the cat is "simultaneously" dead and alive. It was an attempt to illustrate how QM is very different than the classical situation.

And yes, this superposition is truly verified. There are many instances (bonding-antibonding states, coherence gap in the Delft/Stony Brook experiments, etc.) that are direct outcomes of such superposition phenomena. It is also why the Bell-type experiments that illustrate quantum entanglement are different than just a simple conservation of momentum/spin/etc. experiment.

Zz.
 
  • #5
Your question doesn't match the title you created for the thread. This really doesn't deal directly with "wave/particle duality". It is more of an issue of you not understanding quantum superposition.

This is why quantum statistics is different than classical statistics. If you flip a coin but not look at the outcome, the outcome is already determined. You just don't know it. So classical statistics describes not the physical situation, but rather the state of our knowledge, or ignorance, of the outcome. This is different in QM.

In QM, the state will continue to be a "superposition" of all the possible state until an observable is measured. In other words, unlike the classical system, it has not been determined yet until the actual measurement of that observable. In some interpretation, it implies that all of the possible outcome of that observable are there. This led to the infamous Schrodinger Cat analogy where the cat is "simultaneously" dead and alive. It was an attempt to illustrate how QM is very different than the classical situation.

And yes, this superposition is truly verified. There are many instances (bonding-antibonding states, coherence gap in the Delft/Stony Brook experiments, etc.) that are direct outcomes of such superposition phenomena. It is also why the Bell-type experiments that illustrate quantum entanglement are different than just a simple conservation of momentum/spin/etc. experiment.

Zz.
This was kind of where I was confused because much like the two marble example after flipping a coin the outcome is determined whether you observe it or not. Much like the moon remains in the sky after you stop watching it. The act of observing which statistical outcome comes to be doesnt mean that you changed it by observing it. Thats what led me to ask if superpositioning was even a thing or if a probability wave actually existed. Is the particle really everywhere until its observed or is it in a particular location the entire time. However, hearing that experimentation has proven that entangled particles do not have a predetermined spin before we observe them is very intriguing.
 
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  • #6
Nugatory
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Thats what led me to ask if superpositioning was even a thing....
It is. The state "superposition of A and B" behaves differently than the state "It is A or it is B, but we don't know which". For example: if we take large number of particles and prepare half of them in the state "spin up" and half in the state "spin down", we now have a large number of particles in the state "It is spin-up or spin-down but we don't know which". Now if we measure their spin on the horizontal axis we will get "spin-left" half the time and "spin-right" half the time. However, there are superpositions of "spin-up" and "spin-down" that will give "spin-left" every time.

The words "observation" and "measurement" are somewhat misleading though. They are used interchangeably, and they don't mean what you'd expect from their ordinary English-language meanings. "Interaction" would be better because just about any interaction with any reasonable-sized macroscopic system counts as an observation/detection - a laboratory particle detector is just a particular kind of macroscopic system, one that includes a dial or flashing light or whatever so that we can tell whether the interaction happened.

This confusion is an unfortunate historical accident: the words "observation", "measurement", "particle", and "wave" were all being used before the modern theory was discovered, and they stuck around afterwards and ever since.
Even planning on picking up Calculus as I never took it in school....
Go with the Ghirardi book then. Even an intro QM textbook is going to assume that you're comfortable with multivariable calculus and elementary differential equations, stuff that you won't get until your second year of calculus.
 
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Go with the Ghirardi book then. Even an intro QM textbook is going to assume that you're comfortable with multivariable calculus and elementary differential equations, stuff that you won't get until your second year of calculus.
In addition to the excellent book Nugatory suggested, I can also recommend the following:
1. https://www.crcpress.com/Quantum-Reality-Theory-and-Philosophy/Allday/p/book/9781584887034 (you can ignore the philosophy part of that book, if you want)
2. https://www.worldscientific.com/worldscibooks/10.1142/7965 and
3. https://www.amazon.com/dp/0465062903/?tag=pfamazon01-20
 
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  • #8
In addition to the excellent book Nugatory suggested, I can also recommend the following:
1. https://www.crcpress.com/Quantum-Reality-Theory-and-Philosophy/Allday/p/book/9781584887034 (you can ignore the philosophy part of that book, if you want)
2. https://www.worldscientific.com/worldscibooks/10.1142/7965 and
3. https://www.amazon.com/dp/0465062903/?tag=pfamazon01-20
I would never ignore the philosophy part of anything XD. Thank you for the suggestions. I have purchased a copy of sneaking a look at gods cards and will look these resources you suggested up today. Still very confused by everything im reading and trying to understand but still very intrigued and excited to learn. I just wish as a kid I wouldn't have been so pushed into christianity and would have wanted to learn more about how the universe worked when I was still in school. Now its a matter if trying to teach myself.
 

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