Quantum Behavior As Extreme Classical Behavior

In summary, the conversation discussed the inability of classical mechanics to fully explain quantum behavior, such as superposition and spin values of particles. It was proposed that classical mechanics could account for these behaviors by explaining them as extreme versions of classical behaviors, such as high frequency switching between states and non-locality or tunneling. However, this idea was challenged by concepts like Bell's theorem and the Bose-Einstein and Fermi-Dirac distributions, which are not compatible with classical mechanics. The Stern-Gerlach experiment was used as an example, showing that the quantized spin values of electrons cannot be explained classically. The conversation also touched on the double-slit experiment and the concept of wave-particle duality, with the introduction of a
  • #1
sanman
745
24
Why can't quantum behavior be explained as an extreme version of classical behavior?

For instance, the idea of a small quantum particle being in superposition could be explained by that particle switching between 2 or more states at an extremely high frequency. How high a frequency? Well, on the order of a Planck Length or Planck Unit.

The only addendum to classical behavior that would be required would be non-locality or tunneling (ie. macroscopic objects are too big to tunnel, but quantum-sized objects are small enough to squeeze through the cracks)
 
Physics news on Phys.org
  • #2
How would you explain the Stern-Gerlach experiment as extreme classical behavior?
 
  • #3
Hmm, so I just did a quick read on Stern-Gerlach, and it showed that atoms have spin. So what's the problem? How is that irreconcilable with classical mechanics? In large macroscopic objects, the tiny quantum-scale forces would not be large enough to impart an apparent spin. In quantum-scale objects, those forces would be large enough to impart spin.

A leaf blowing in the breeze can be spun around easily with all the currents and eddies. But a large airplane is too big to be spun around like that so easily. So why can't classical mechanics offer an adequate explanation for this?
 
  • #4
sanman said:
Hmm, so I just did a quick read on Stern-Gerlach, and it showed that atoms have spin. So what's the problem?

Check out Susskinds lectures - he explains it masterfully and clearly:
http://www.newpackettech.com/Resources/Susskind/PHY30/QuantumEntanglementPart1_Overview.htm

But basically you have things like Bells theorem:
http://en.wikipedia.org/wiki/Bell's_theorem

It shows if you assume classical behavior (in this case the very basic property of local realism ie properties are only influenced by local surroundings) then it leads to predictions at variance with what experiments show - but QM is in full agreement with them. The lectures above gives the full detail.

There are other things as well. For example, classically if you have two particles, say particle 1 and particle 2, you can tell them apart so that if you exchange them so you have particle 2 and particle 1 then that is different than before the exchange. If you assume this very obvious classical rule then you can derive a property of gasses called the Maxwell Boltzmann distribution:
http://en.wikipedia.org/wiki/Maxwell–Boltzmann_distribution

But weirdly this doesn't work for quantum particles - when you exchange them there is no difference - you get either the Bose-Einstein distribution:
http://en.wikipedia.org/wiki/Bose–Einstein_statistics

Or the Fermi-Dirac distribution:
http://en.wikipedia.org/wiki/Fermi–Dirac_statistics

Thanks
Bill
 
Last edited:
  • #5
I still don't see why locality and non-locality can't be differentiated for through classical mechanics.

I can't walk through a screen door, but certainly the breeze can move through it. Classical mechanics can explain that just fine.

By the same token, I as a macroscopic entity can't tunnel-jump to some remote location, but a small quantum-scale object can.
I as a macroscopic entity can't influence any other object at a non-local distance, but a small quantum-scale object can. It can do so just like the air particles can pass through the screen door while I can't. I don't see anything in this that inherently thwarts classical ideas, just as Special Relativity doesn't screw up Relativity.
 
  • #6
sanman said:
Hmm, so I just did a quick read on Stern-Gerlach, and it showed that atoms have spin. So what's the problem? How is that irreconcilable with classical mechanics? In large macroscopic objects, the tiny quantum-scale forces would not be large enough to impart an apparent spin. In quantum-scale objects, those forces would be large enough to impart spin.

A leaf blowing in the breeze can be spun around easily with all the currents and eddies. But a large airplane is too big to be spun around like that so easily. So why can't classical mechanics offer an adequate explanation for this?
What's interesting about the Stern-Gerlach experiment is that the spin values are quantized. That's what you would need to explain classically.
 
  • #7
sanman said:
I can't walk through a screen door, but certainly the breeze can move through it. Classical mechanics can explain that just fine.

But can classical mechanics explain these electrons behaving like this?

https://www.youtube.com/watch?v=FCoiyhC30bc&lr
 
  • #8
Yeah, I know, I've seen the double-slit explanation countless times, and it still puzzles me as much today as it did 25 years ago when I first saw it. Here's more kid-friendly video for laymen like me:

https://www.youtube.com/watch?v=DfPeprQ7oGc
So they say that the results of the experiment changed when they introduced a "detector", but they don't say exactly what the detector is or what its mechanism of detection is. Obviously the introduction of the detector changed the experiment. But even before they introduced the detector, weren't they likewise "observing" the electrons when they saw the fringe pattern?

To me, the presence of wave behavior while firing particles would intuitively (classically) indicate that those particles are traveling through a medium. If you fire a bunch of projectiles through a medium - even one at a time - the projectiles will interact with the medium to produce waves.

It's still not clear to me what the detector was doing exactly. Was it intercepting electrons at some point?
 
  • #10
sanman said:
So they say that the results of the experiment changed when they introduced a "detector", but they don't say exactly what the detector is or what its mechanism of detection is. Obviously the introduction of the detector changed the experiment. But even before they introduced the detector, weren't they likewise "observing" the electrons when they saw the fringe pattern?

Susskinds lectures I gave the link to explains this in detail - please view them.

sanman said:
It's still not clear to me what the detector was doing exactly. Was it intercepting electrons at some point?

The detector becomes entangled with the particle localizing it so it goes through one hole only hence you do not get an interference pattern.

In fact its this weird phenomena of entanglement that is the rock bottom thing that distinguishes classical from quantum behavior:
http://arxiv.org/abs/0911.0695

Thanks
Bill
 
Last edited:
  • #11
Okay, so here's an explanation with a little more detail on what the detectors were doing:

https://www.youtube.com/watch?v=LW6Mq352f0E

So leaving the speaker's hokey "consciousness" claims aside, the explanation still says that the electrons "knew" when they were going to end up as a magnetic recording or not, and changed their behavior accordingly. To me, that intuitively implies something like a circuit (ie. electric current doesn't flow unless there's a full circuit path available ahead of it, so in that sense the electrons "know" whether to flow or not)

So why can't a circuit be used as a classical analogy here?
 
  • #12
sanman said:
So leaving the speaker's hokey "consciousness" claims aside, the explanation still says that the electrons "knew" when they were going to end up as a magnetic recording or not, and changed their behavior accordingly. To me, that intuitively implies something like a circuit (ie. electric current doesn't flow unless there's a full circuit path available ahead of it, so in that sense the electrons "know" whether to flow or not)

So why can't a circuit be used as a classical analogy here?

Then you end up with the De Broglie-Bohm pilot wave theory, which is still definitely not classical in any way.
 
  • #14
ajw1 said:
The double slit can be completely explained classically, as is shown here: http://www.youtube.com/watch?v=W9yWv5dqSKk&feature=player_embedded#!

See https://hekla.ipgp.fr/IMG/pdf/Couder-Fort_PRL_2006.pdf for the scientific publication, and http://arxiv.org/pdf/1304.3719.pdf for the results of a computer simulation following the principles exposed by the bouncing droplets experiments.

There is a medium involved. As mentioned in my earlier post, quantum mechanically this would correspond to the pilot wave theory. Unless somehow you think that the idea of photons and electrons emitting guiding waves is classical, I still don't see this "proves" that the double slit experiment with photons and electrons can be explained classically.
 
  • #15
In addition to spin, entanglement, Bell and the double-slit experiment (which are good examples):

The uncertainty principle(s) (relation(s)) is also a nonclassical feature, quite counterintuitive. Here's a nice clip demonstrating it.

I'd also say that antimatter, annihilation & pair production are nonclassical features. Two massive particles (e.g. electron + positron) can annihilate into two photons - who would have expected that in classical physics? :smile:
 
  • #16
sanman said:
Why can't quantum behavior be explained as an extreme version of classical behavior?

For instance, the idea of a small quantum particle being in superposition could be explained by that particle switching between 2 or more states at an extremely high frequency. How high a frequency? Well, on the order of a Planck Length or Planck Unit.

The only addendum to classical behavior that would be required would be non-locality or tunneling (ie. macroscopic objects are too big to tunnel, but quantum-sized objects are small enough to squeeze through the cracks)


read:
Quantum Physics from Classical Physics with an epistemic restriction
https://www.physicsforums.com/showthread.php?t=611383&


and briefly
physics as an interface to underlying structure
https://www.physicsforums.com/showthread.php?t=648636
 
  • #17
Alright, so the rules governing quantum behavior are markedly different than those governing classical behavior. But it's all still happening in the same universe, so it's not like the "quantum world" is truly separate from the "classical world" is it?

So is there a sliding scale of transition between quantum rules of behavior and classical rules of behavior? Or does it transition abruptly? Can we say that classical behavior is an emergent behavior arising from quantum behavior? Is it reasonable to think that what happens on the macro scale is the aggregate result of what happens on the small scale?
 
  • #18
bhobba said:
Susskinds lectures I gave the link to explains this in detail - please view them.

The detector becomes entangled with the particle localizing it so it goes through one hole only hence you do not get an interference pattern.

In fact its this weird phenomena of entanglement that is the rock bottom thing that distinguishes classical from quantum behavior:
http://arxiv.org/abs/0911.0695

Thanks
Bill

Another thing about the double slit experiment that puzzles me.

When the electron(s) passes through the double slit, it only interferes with itself but does not "collapse" by interacting with itself. It's when the electron(s) interact with a detector that its wave "collapses"

You say this collapse is due to entanglement? So no entanglement means no collapse?

And electrons automatically interfere with other electrons, right? So in that case, entanglement is unavoidable? Is there any circumstance where an electron can collapse another electron's wave?
 
  • #19
sanman said:
Alright, so the rules governing quantum behavior are markedly different than those governing classical behavior. But it's all still happening in the same universe, so it's not like the "quantum world" is truly separate from the "classical world" is it?

Everything is quantum - the classical world emerges from entanglement and decoherence.

For example all quantum particles of the same type are indistinguishable - the reason atoms etc can be distinguished at our classical level is entanglement. At a low enough temperature you have what are called Bose Einstein Condensates where the atoms have totally lost their individuality and they behave as one single giant atom with very strange properties. Raising the temperature means you are entangling it with the environment and that's when it starts to behave classically and the constituent atoms/molecules become distinguishable.

Thanks
Bill
 
  • #20
Alright, but if I shoot a basketball at a double slit, it's not going to create an interference pattern. How large an object can I use, and still get the interference pattern?

I've read that it's possible to use C-60 buckyballs and still get the interference pattern.
I've read they've even gone larger than that with even bigger molecules and gotten the interference pattern.

So is it a gradual transitioning of wave propagation to particle model?
 
  • #21
sanman said:
Another thing about the double slit experiment that puzzles me.

When the electron(s) passes through the double slit, it only interferes with itself but does not "collapse" by interacting with itself. It's when the electron(s) interact with a detector that its wave "collapses"

You say this collapse is due to entanglement? So no entanglement means no collapse?

And electrons automatically interfere with other electrons, right? So in that case, entanglement is unavoidable? Is there any circumstance where an electron can collapse another electron's wave?

A few issues here. First the very existence of collapse is interpretation dependent - some interpretations have it - others don't. What all interpretations have is when an observation occurs (here observation means some kind of record appears here in the macro world) then the probability of that is given by the Born rule. It is entirely up to how you want to interpret the math if a wavefunction collapse occurs - see for example the Ensemble Interpretation:
http://en.wikipedia.org/wiki/Ensemble_interpretation

In modern times many believe decoherence (decoherence is a form of entanglement) has something to do with it. But you have to understand what decoherence does. To understand that you need to understand a mixed state:
https://en.wikipedia.org/wiki/Quantum_state

What decoherence does is transform a pure state into an improper mixed state. Here improper means mathematically and observationally it's the same as a proper mixed state but it has not been prepared the same way. A proper mixed state is a pure state that has been randomly selected. If the improper mixed state of decoherence was prepared that way then vola - no measurement problem - what you observe is there prior to observation - its the state that has randomly been selected and you observe it - no change in the state - no collapse - nothing - everything is sweet:
http://en.wikipedia.org/wiki/Quantum_mind%E2%80%93body_problem [Broken]
'Decoherence does not generate literal wave function collapse. Rather, it only provides an explanation for the appearance of wavefunction collapse, as the quantum nature of the system "leaks" into the environment. That is, components of the wavefunction are decoupled from a coherent system, and acquire phases from their immediate surroundings. A total superposition of the universal wavefunction still exists (and remains coherent at the global level), but its fundamentality remains an interpretational issue. "Post-Everett" decoherence also answers the measurement problem, holding that literal wavefunction collapse simply doesn't exist. Rather, decoherence provides an explanation for the transition of the system to a mixture of states that seem to correspond to those states observers perceive. Moreover, our observation tells us that this mixture looks like a proper quantum ensemble in a measurement situation, as we observe that measurements lead to the "realization" of precisely one state in the "ensemble".'

To get around the issue that it just gives the appearance of collapse an extra interpretive assumption is required. Different assumptions lead to different views. Just as an example check out Decoherent Histories:
http://arxiv.org/pdf/gr-qc/9407040v1.pdf

But other ways of handling it are possible - eg Many Worlds. And still others like the Ensemble interpretation claim its not even required.

Welcome to the weird and wacky world of different quantum interpretations.

Thanks
Bill
 
Last edited by a moderator:
  • #22
sanman said:
Alright, but if I shoot a basketball at a double slit, it's not going to create an interference pattern. How large an object can I use, and still get the interference pattern?

I've read that it's possible to use C-60 buckyballs and still get the interference pattern.
I've read they've even gone larger than that with even bigger molecules and gotten the interference pattern.

So is it a gradual transitioning of wave propagation to particle model?

That's an area of active investigation - there are outstanding issues. If you want to get the up to date view of it you need to read the modern literature:
https://www.amazon.com/dp/0691004358/?tag=pfamazon01-20

Thanks
Bill
 
Last edited by a moderator:
  • #23
A wave function is supposed to be fully continuous, and thus infinitely divisible, right? The double slit experiment utilizes Huygens Principle to create the interference pattern, as if produced from 2 point sources. I guess we can assume that if you put 3 slits after the double slit, and then 4 after that, and 5 after that, etc, that conclusions from Young's experiment will still hold true.

But a particle isn't supposed to be infinitely divisible.

As a wavefront spreads out while propagating, its amplitude falls off with distance squared. But particles don't fall off with distance squared. In principle, the particle is still supposed to stay the same no matter how far it travels, right?
I assume that any detector at one of the 2 slits would still detect an electron at full strength, and not some fractional faded out electron.

Furthermore, for a true wave, all points on its wavefront are supposed to be equal. But observation of quantum particle waves shows that's not true, since the wave function can be collapsed to a particular point.
So is that wave being observed really a true wave? How can all points be equal, and yet one point is more equal than others? Why should any collapse be possible at all?

A particle moves in 1 dimension, a straight line. But a wave from a point source moves symmetrically in all dimensions. So if my double slit wasn't directly in front of the electron gun, but was off to the side, or above, shouldn't it still show the same interference pattern?

I'm used to thinking of ballistic travel in terms of cartesian coordinates of x,y,z. But in the case of a wave that collapses into a ballistic trajectory, it seems easier for me to visualize this in terms of polar coordinates, because the wave is advancing along the r coordinate and it's only when it collides with something that the angular component collapses into the particular value. Hmm, so it's only the angular component that's indeterminate during propagation...
 
Last edited:
  • #25
Thanks - so just improving my thoughts here...

The difference between quantum wave motion trajectory and ballistic motion trajectory is that for the former, the radial and angular components are both determined by collision, whereas with the latter just the radial component is determined by the collision. Fair enough?

So isn't that then what separates the quantum world from the classical world? For the trajectories of quantum objects, angular indeterminacy is just as apparent as radial indeterminacy, but for trajectories of classical objects there is no angular indeterminacy but only just radial indeterminacy for ballistic motion.
 
  • #26
sanman said:
The difference between quantum wave motion trajectory and ballistic motion trajectory is that for the former, the radial and angular components are both determined by collision, whereas with the latter just the radial component is determined by the collision. Fair enough?

I have zero idea what you are trying to say.

Classical wave motion is a change in something physical like a field or water height. Quantum waves are simply wavelike solutions of something called a system state which is an abstract thing that allows the calculation of probabilities. That's the basis of my comment that you need to learn QM.

There is really no wave particle duality - its really all the same stuff - quantum stuff:
https://www.physicsforums.com/showthread.php?t=511178
'So there is no duality – at least not within quantum mechanics. We still use the “duality” description of light when we try to describe light to laymen because wave and particle are behavior most people are familiar with. However, it doesn’t mean that in physics, or in the working of physicists, such a duality has any significance.'

Thanks
Bill
 
  • #27
sanman said:
Alright, so the rules governing quantum behavior are markedly different than those governing classical behavior. But it's all still happening in the same universe, so it's not like the "quantum world" is truly separate from the "classical world" is it?

So is there a sliding scale of transition between quantum rules of behavior and classical rules of behavior? Or does it transition abruptly?
Can we say that classical behavior is an emergent behavior arising from quantum behavior? Is it reasonable to think that what happens on the macro scale is the aggregate result of what happens on the small scale?



Quantum incompleteness?
https://www.physicsforums.com/showthread.php?t=692665
 
  • #28
sanman said:
Furthermore, for a true wave, all points on its wavefront are supposed to be equal. But observation of quantum particle waves shows that's not true, since the wave function can be collapsed to a particular point.
Some believe all points are actualized in different universes. This would be the MWI.

So is that wave being observed really a true wave? How can all points be equal, and yet one point is more equal than others? Why should any collapse be possible at all?
The 'particle' lives in an infinitely dimensional space and the act of observation/measurement is associated with its classical behavior.

I think most physicists feel strange about the macro world from the quantum mechanical perspective. Or they altogether avoid thinking about it. My impression is that physics is delving into the very nature of existence, hence the existential problems that spring up from certain experiments. And we know very little about existence, almost nothing at all.
cle moves in 1 dimension, a straight line. But a wave from a point source moves symmetrically in all dimensions. So if my double slit wasn't directly in front of the electron gun, but was off to the side, or above, shouldn't it still show the same interference pattern?
Did you mean 'directions' instead of 'dimensions'?
In practice no. Unless you have a couple of thousand years.

I'm used to thinking of ballistic travel in terms of cartesian coordinates of x,y,z. But in the case of a wave that collapses into a ballistic trajectory, it seems easier for me to visualize this in terms of polar coordinates, because the wave is advancing along the r coordinate and it's only when it collides with something that the angular component collapses into the particular value. Hmm, so it's only the angular component that's indeterminate during propagation...
For an ensemble of states it can be shown that position/momentum and time/energy do not have joint definite values.
 
Last edited:
  • #29
It seems to me that the main intrinsic difference between a tiny quantum particle and macro-scale object like a basketball is really just mass, and that this mass difference is mainly responsible for their different respective modes of travel (ie. the basketball travels classically/ballistically, while the electron travels as a wave)

If I'm firing basketballs at an enlarged double-slit, they of course won't form an interference pattern. The basketballs will travel ballistically, each starting on a particular angular heading (let's say θ and ∅ ) and traveling some distance R before hitting something.

But if I scale down so that I'm now firing electrons at my tiny double-slit, they seem to be traveling some distance R before hitting something, but this time they are not starting out on a particular angular heading (θ and ∅ are indeterminate, at least until the electron hits something). It's this mode of travel through which we observe the electron propagating like a wave.

But of course it's once the electron hits something that suddenly θ and ∅ become determined, so that our end destination has now determined what angular heading we started out on. It's this oddly reversed tail-before-head / effect-before-cause that boggles our classical intuition.
 
Last edited:
  • #30
When I was a little kid 30 years ago, some govt education official visited our classroom, and began philosophizing to us about dimensions. He talked about how in our 3-dimensional world time is the 4th dimension, and about how if we were 2-dimensional creatures living in a 2-dimensional world we might experience time as a 3rd dimension, and if we were 1-dimensional creatures living in a 1-dimensional world we might percieve time as a 2nd dimension. In each, the higher dimension becomes an ordinal axis (aka "time")

But what about experiencing other geometry analogies? What about Polar-to-Cartesian mapping?
What if R was a time-like ordinal axis for θ and ∅, so that as our electron moves along R and hits something, this results in the determination of θ and ∅? And then what if those dynamics were then mapped onto our classical perceptions which use T as their ordinal axis?
Isn't that perhaps what we limited creatures are experiencing and perceiving when we witness Young's double slit experiment?
I only saw the first few minutes of Susskind's lectures which were linked to in this thread, but when he mentioned how our perceptions and intuitions as animals have been shaped by our circumstances, then it reminded me a little of that classroom talk I received 30 years ago.
 
  • #31
As it has already been said, you shouldn't try to derive quantum mechanics with classical intuition. Classical mechanics is quantum mechanics within a limit. In many cases it is straightforward to revive the results of classical mechanics from quantum mechanics.

You keep going to the basketball in a hoop example. The basketball is a wave, but consider its wavelength with respect to the distance it travels and the size of the hoop. Now consider the wavelength of an electron compared to Young's slits.
 

1. What is "Quantum Behavior As Extreme Classical Behavior"?

"Quantum Behavior As Extreme Classical Behavior" is a concept in quantum mechanics that explains how the behavior of particles at the quantum level can sometimes resemble the behavior of classical particles at the macroscopic level.

2. How does quantum behavior differ from classical behavior?

Quantum behavior differs from classical behavior in several ways. At the quantum level, particles can exist in multiple states at once, can be entangled with other particles, and can exhibit wave-like properties. In contrast, classical particles can only exist in one state at a time and do not exhibit these quantum phenomena.

3. What are some examples of quantum behavior as extreme classical behavior?

One example is the phenomenon of superposition, where a particle can exist in multiple states simultaneously. This can be observed in the double-slit experiment, where a single particle can pass through both slits at once. Another example is quantum tunneling, where a particle can pass through a barrier that it classically should not be able to overcome.

4. How is the concept of "Quantum Behavior As Extreme Classical Behavior" useful in scientific research?

This concept is useful in understanding and predicting the behavior of particles at the quantum level, which is crucial in fields such as quantum computing and quantum cryptography. It also helps bridge the gap between classical and quantum mechanics, allowing for a more comprehensive understanding of the universe.

5. Are there any real-world applications of "Quantum Behavior As Extreme Classical Behavior"?

Yes, there are several real-world applications of this concept. For example, the principles of quantum behavior are used in technologies such as transistors, lasers, and MRI machines. Additionally, the study of quantum behavior has led to advancements in fields such as materials science and chemistry.

Similar threads

Replies
7
Views
1K
  • Quantum Physics
7
Replies
232
Views
15K
  • Quantum Physics
Replies
2
Views
921
  • Quantum Physics
Replies
2
Views
1K
  • Quantum Physics
Replies
2
Views
2K
Replies
2
Views
927
  • Quantum Physics
Replies
1
Views
825
Replies
46
Views
2K
  • Quantum Physics
Replies
1
Views
1K
Replies
13
Views
2K
Back
Top