Possible explanation for the wave-particle duality ?

[DevilsAvocado]

Why - its not inconsistent with anything I said.

Maybe you are right, I'm sorry in that case, it’s just that it feels maybe a little bit 'awkward' to put empirically verified theories in the "dustbin of history"... and as you see the "abandoned matter waves" are still in use in today...

 

[bhobba]

Question: What would happen if the world only was made of only "Ballentineists"? Would we have the electron microscope and neutron diffraction then? And would that be a better world??

It would make no difference.

It makes exactly the same predictions.

Thanks
Bill

 

[probert84]

So many things have been said here, unfortunately I still have not had time to read them completely, but I think some of you have not completely understood what my original assumption was. I can't really explain it better, I'd rather show something similar to it:


so I supposed that the mater (or rather energy) may look like this swarm, and the 'shape' of it is determined by a field of probability. The different behavior we experience may come from the different properties of the structure of the examined object, I mean that there are areas where the energy is more dense (like the birds or thee quanta) and this makes energy appear as a particle, but how these 'densities' move together and their path is determined by a constraint on a larger scale (swarm) which results in wave phenomena. You can't look at them at the same time and 'merge' your viewpoints, because these are two different pieces of the puzzle and put one over another because then one will overlie the other, but you have to put them next to each other along the line where they fit.

 

[atyy]

So many things have been said here, unfortunately I still have not had time to read them completely, but I think some of you have not completely understood what my original assumption was. I can't really explain it better, I'd rather show something similar to it:





so I supposed that the mater (or rather energy) may look like this swarm, and the 'shape' of it is determined by a field of probability. The different behavior we experience may come from the different properties of the structure of the examined object, I mean that there are areas where the energy is more dense (like the birds or thee quanta) and this makes energy appear as a particle, but how these 'densities' move together and their path is determined by a constraint on a larger scale (swarm) which results in wave phenomena. You can't look at them at the same time and 'merge' your viewpoints, because these are two different pieces of the puzzle and put one over another because then one will overlie the other, but you have to put them next to each other along the line where they fit.

Yes, there is an interpretation of non-relativistic quantum mechanics called de Broglie-Bohm theory in which each individual particle has a definite trajectory, but the trajectory is guided by a nonlocal wave. In addition to the dynamics of the wave, and how the wave guides a particle, an important point for reproducing quantum mechanics is a postulate about the initial density or distribution of particles. However, the analogy to the swarm is only partial, so take a look at de Broglie-Bohm theory itself.

Although not exactly the same as de Broglie-Bohm theory, this video of droplets guided by a wave is similar in many respects, and can give some intuition for de Broglie-Bohm theory (I learned about this from Bohm2 who posted it on another thread here). http://web.mit.edu/newsoffice/2013/when-fluid-dynamics-mimic-quantum-mechanics-0729.html

 

[Zag]

Well, the Schroedinger equation is precisely a Diffusion equation with a imaginary/complex diffusion constant. Having said thay, try not to push the analogy too far because, after all, analogies always fail at some point.

 

[Jilang]

Well, the Schroedinger equation is precisely a Diffusion equation with a imaginary/complex diffusion constant. Having said thay, try not to push the analogy too far because, after all, analogies always fail at some point.

Yes Zag, it's intriguing! It's also a diffusion equation with real time replaced with imaginary time depending on how you look at it!

 

[probert84]

@atyy :

Yeah this is exactly what I thought. Nevertheless I claimed that this is the consequence of HUP. Because when you launch a 'particle' (a pack of energy), you know (more precisely) where it is, so it must be uncertain that which one of the slits it goes through, because you must know its momentum to be able to predict that. And the same applies to the particles past, not only to its the future, when the particle has already hit the detector screen, we know its place, therefore we shouldn't be able to know where it came from, and the consequence of this: it must have passed both slits by some chance.

 

[DevilsAvocado]

It would make no difference.

I don't agree bhobba, and the paper l quoted in #42 is just one example of experiments that most probably would not have been made if everybody, in their bones, believed that the ensemble interpretation is the "final truth".

 

[DevilsAvocado]

[...] but how these 'densities' move together and their path is determined by a constraint on a larger scale (swarm) which results in wave phenomena. You can't look at them at the same time and 'merge' your viewpoints,

I'm afraid the "scale factor" has nothing to do with QM, neither has any clustering of particles. To understand how far your swarms of birds are from QM, consider this:

You could send one electron for, let's say, every decade, and continue this experiment for ten thousand years, and then gather all the data, and you will still get the interference pattern. Or, you could set up the double-slit experiment in a thousand different laboratories around the globe, to fire one single electron, and then gather all the data = same interference pattern.

Or if we had the technology – we could perform "The One Single Electron Double-Slit Experiment" in different galaxies, and then gather all the data in one place = same interference pattern!

This has nothing to do with 'swarms' or 'scale' (except it's extremely hard to do with bigger objects).

Your birds would be completely lost if they where to perform those beautiful patterns, one by one (in different galaxies! ).


P.S: Entanglement has absolutely nothing to do with.

 

[bhobba]

I don't agree bhobba, and the paper l quoted in #42 is just one example of experiments that most probably would not have been made if everybody, in their bones, believed that the ensemble interpretation is the "final truth".

The reason its called an interpretation is because there is no way to tell the difference from any other interpretation.

I think questions like you pose are best taken up with historians of science - its really got nothing to do with the actual science - merely how it actually came about. That's an interesting thing in its own right, but not really germane to the question asked by the OP.

Thanks
Bill

 

[probert84]

@DevilsAvocado

You still don't understand it. You think that I say that the other electrons affect the trajectory but I don't. The electron has nothing to do with the interference, therefore it doesn't matter how much time or space is between each launch of the particles, and this is why you get the same interference pattern each time.
The swarm means all the paths what a single electron can take. The swarm is not the electron itself, its just the part of it. Just like when it appears as a particle. It is not a particle, but a particle is a manifestation, a realization of that energy, and basically when you are detecting it as a particle you are realizing that manifestation by localizing it. I would say if you localize any kind of energy, it should appear similar to a particle. Otherwise how could it be localized ? The reason why it appears to be a 'solid' object is because you narrowed its possibilities down, while when you do the opposite it looks more like a wave. So its appearance is rather the end result of your process of examination than the real (or so thought) properties of the energy.

And I meant 'scale' in this interpretation, by larger scale (like local vs global scale) I mean more possibility, more options, more values for the same variable, and I was not referring to it in a meaning of a difference in the size of objects.

I think that energy has no form or 'shape' by itself, it is not determined, until you determine it by your own choice.

Think on it as kinetic energy vs potential energy, for ex imagine a spring dropped down and hitting the ground and squeezing together, now would you say that the energy that the spring carries consists of two different energies (the moving and squeezed one), or its the same energy with two appearances ?

The same is true for the electron or whatever particle. When you are localizing the particle you are narrowing your viewpoint from the energy distribution that is behind the object to a particle, and in the moment when you detect it with a detector it turns into a particle. Its like when the spring hits the ground and gets into a squeezed state. So both the particle and the wave are a form of the same energy, an image, and not the object itself.

 

[bohm2]

You could send one electron for, let's say, every decade, and continue this experiment for ten thousand years, and then gather all the data, and you will still get the interference pattern. Or, you could set up the double-slit experiment in a thousand different laboratories around the globe, to fire one single electron, and then gather all the data = same interference pattern.

I haven't looked at the paper referenced in this paper but how would one interpret these results:

In one experiment, Kim et al. controlled the exact interval between independent signal photons emitted in pairs [12]. As the time delay between photons was increased, first-order interference gradually vanished.

Interpreting Negative Probabilities in the Context of Double-Slit Interferometry
http://arxiv.org/pdf/physics/0611043v1.pdf

 

[bhobba]

I think that energy has no form or 'shape' by itself, it is not determined, until you determine it by your own choice.

I think you need to understand what energy is:
http://physwiki.ucdavis.edu/Classic..._Mass_and_Energy/Noether's_Theorem_for_Energy

Thanks
Bill

 

[atyy]

@atyy :

Yeah this is exactly what I thought. Nevertheless I claimed that this is the consequence of HUP. Because when you launch a 'particle' (a pack of energy), you know (more precisely) where it is, so it must be uncertain that which one of the slits it goes through, because you must know its momentum to be able to predict that. And the same applies to the particles past, not only to its the future, when the particle has already hit the detector screen, we know its place, therefore we shouldn't be able to know where it came from, and the consequence of this: it must have passed both slits by some chance.

@DevilsAvocado

You still don't understand it. You think that I say that the other electrons affect the trajectory but I don't. The electron has nothing to do with the interference, therefore it doesn't matter how much time or space is between each launch of the particles, and this is why you get the same interference pattern each time.
The swarm means all the paths what a single electron can take. The swarm is not the electron itself, its just the part of it. Just like when it appears as a particle. It is not a particle, but a particle is a manifestation, a realization of that energy, and basically when you are detecting it as a particle you are realizing that manifestation by localizing it. I would say if you localize any kind of energy, it should appear similar to a particle. Otherwise how could it be localized ? The reason why it appears to be a 'solid' object is because you narrowed its possibilities down, while when you do the opposite it looks more like a wave. So its appearance is rather the end result of your process of examination than the real (or so thought) properties of the energy.

And I meant 'scale' in this interpretation, by larger scale (like local vs global scale) I mean more possibility, more options, more values for the same variable, and I was not referring to it in a meaning of a difference in the size of objects.

I think that energy has no form or 'shape' by itself, it is not determined, until you determine it by your own choice.

Think on it as kinetic energy vs potential energy, for ex imagine a spring dropped down and hitting the ground and squeezing together, now would you say that the energy that the spring carries consists of two different energies (the moving and squeezed one), or its the same energy with two appearances ?

The same is true for the electron or whatever particle. When you are localizing the particle you are narrowing your viewpoint from the energy distribution that is behind the object to a particle, and in the moment when you detect it with a detector it turns into a particle. Its like when the spring hits the ground and gets into a squeezed state. So both the particle and the wave are a form of the same energy, an image, and not the object itself.

Actually, the picture you paint here is not so much like that of de Broglie-Bohm theory. It is more like the standard textbook picture. Both de Broglie-Bohm theory and the standard textbook picture give the same predictions for non-relativistic quantum mechanics, so they are essentially different methods of calculating the same predictions of non-relativistic quantum mechanics.

In the standard textbook picture, the electron is a wave or a field. Since a wave or field is in general spread out over all space, it does not have a definite trajectory. However, if it happens to be very localized, then we say that it has a definite position in space. In contrast, in quantum mechanics, to have a definite momentum means having a well defined sinusoidal wavelength. A wave which has a well defined sinusoidal wavelength is by definition spread out over all space, and so does not have a definite position. This is the essence of the uncertainty principle. And yes, it is correct that when you measure the position of an electron, you force it to become a well-localized field, which indeed does not have a well defined sinusoidal wavelength, and therefore does not have a well defined momentum.

So the uncertainty principle basically comes about because
(1) the electron is a wave
(2) position is position
(3) momentum is related to wavelength

 

[probert84]

Well I think I paint the same picture because in the de Broglie-Bohm theory there is a carrying wave which defines the possible trajectories of the particle and I found this similar to the swarm which defines the trajectory of a bird in it. I think on this as sort of a random path dispatching algorithm.

Let the slits be dices. Each throw of the dice represents a chosen direction from 1-6 for a signal we want to send. If we throw two dices(two open slits = two possibilities) at the same time, we have 21 options, and these are:

11 22 33 44 55 66
12 23 34 45 56
13 24 35 46
14 25 36
15 26
16

Say we throw '25' then x % of the signal will go towards direction #2 and 100-x % towards #5. When we throw the same direction with both dices (for ex '11'), we must throw again, because otherwise 100% of the signal would go in the same direction and this means 100% accuracy, which we assume to be impossible (and this is where HUP comes in). Hence 11,22,33,44,55,66 fall out. Let this signal be light and what do you see in these directions ? Black lines, and the overall picture is an interference.

 

[DevilsAvocado]

The reason its called an interpretation is because there is no way to tell the difference from any other interpretation.

It's good that we agree on the "interpretational status", since earlier in this thread there were a lot of talk about "formalism" and "bog standard", which of course the ensemble interpretation is nothing like.

I think questions like you pose are best taken up with historians of science - its really got nothing to do with the actual science - merely how it actually came about. That's an interesting thing in its own right, but not really germane to the question asked by the OP.

That would make the "Shut up and calculate!" physicist David Mermin a "historian", which we both know is not true.

"[...] the notion that probabilistic theories must be about ensembles implicitly assumes that probability is about ignorance. (The 'hidden variables' are whatever it is that we are ignorant of.) But in a non-deterministic world probability has nothing to do with incomplete knowledge, and ought not to require an ensemble of systems for its interpretation" -- David Mermin​

I don't think we will get any further on this issue, except to agree on disagreement – you did/do claim the statistical ensemble interpretation to represent the bog standard of QM, fait accompli.

I, in company with prominent physicists, do not agree. Let's move on.

 

[Jilang]

It seems to me that we have the maths to describe the physical process, but no real idea do that that physical process is. Any questions raised about what might be the physical process are classed as "interpretation". This appears to be regarded as a type of mysticism or witchcraft. So it's off to the ducking stool, the thread is closed, deleted if you are less lucky. Either way we die.

 

[DevilsAvocado]

The same is true for the electron or whatever particle. When you are localizing the particle you are narrowing your viewpoint from the energy distribution that is behind the object to a particle, and in the moment when you detect it with a detector it turns into a particle. Its like when the spring hits the ground and gets into a squeezed state. So both the particle and the wave are a form of the same energy, an image, and not the object itself.

It's good that you try to visualize and make pictures of the problem (it's basically what I do all the time... ), but you have to realize that QM is nothing like our classical "everyday experience", and sometimes (mostly) – pictures don't make it all the way.

How come??

Well, to begin with, you must have some basic understanding about the mathematics, which is the only foundation of QM. It requires an understanding of complex numbers (and partial differential equations). In our everyday life we use real numbers:

Adding the imaginary unit to a real number forms a complex number:

To make it even 'weirder', the wavefunction does not give any information about the QM particle per se, but only provide the probability of finding the QM particle at a given position:

Left: The real part (blue) and imaginary part (red) of the wavefunction.
Right: The probability distribution of finding the particle with this wavefunction at a given position.
The top two rows are examples of stationary states, which correspond to standing waves.
The bottom row an example of a state which is not a stationary state.

As you see, there are 'imaginary processes' in the calculation of the wavefunction, to make it possible to get the probabilities of a 'real output' in the other end. That is weird!

Therefore, to translate your picture of "energy distribution", we must be able to calculate the energy with complex numbers (i.e. \sqrt{-1}), which don't make a happy end for the resolution of the "energy distribution", i.e. it don't work.

To give you some comfort, Erwin Schrödinger – the genius who formulated the Schrödinger wave equation – did not know what it represented at first. He tried to interpret his wavefunction as "the density" of the stuff of which the world is made. He tried to think of an electron as represented by a wavepacket. But wavepackets diffuse, and become indefinitely extended, but how ever far the wavefunction extends; the detection of an electron remains 'spotty', i.e. localized. Hence Schrödinger's 'realistic' interpretation of his wavefunction did not survive.

Then Born came and said that the wavefunction does not represent "the density of stuff", but gives the density of probability (modulus squared).

And this is the theory we have today.

 

[DevilsAvocado]

I haven't looked at the paper referenced in this paper but how would one interpret these results:

In one experiment, Kim et al. controlled the exact interval between independent signal photons emitted in pairs [12]. As the time delay between photons was increased, first-order interference gradually vanished.

Woowa!

If this is true... that would mean that bhobba is right after all!? ()

Must check it out...

 

[bhobba]

you did/do claim the statistical ensemble interpretation to represent the bog standard of QM, fait accompli.

I never claimed that, and its obviously not true.

I claim the ensemble interpretation was related to the frequentest interpretation of probability, Copenhagen the Baysian view.

QM formalism simply speaks of probability without interpretation, as do most areas of applied math. To be specific probabilities enters into it via Born Rule which says the expected value of an observation O of a system in state P is Trace(OP). Nothing about ensembles there. That comes when you try and give meaning to expected value. Most applied mathematicians do that via Kolmogorov's axioms and a reasonable mapping without actually worrying about specifics. But some want to go further and say it applies to statistical ensembles, while others say it applies to a level of belief which is Copenhagen. But really it doesn't make much difference.

Thanks
Bill

 

[atyy]

Well I think I paint the same picture because in the de Broglie-Bohm theory there is a carrying wave which defines the possible trajectories of the particle and I found this similar to the swarm which defines the trajectory of a bird in it. I think on this as sort of a random path dispatching algorithm.

Let the slits be dices. Each throw of the dice represents a chosen direction from 1-6 for a signal we want to send. If we throw two dices(two open slits = two possibilities) at the same time, we have 21 options, and these are:

11 22 33 44 55 66
12 23 34 45 56
13 24 35 46
14 25 36
15 26
16

Say we throw '25' then x % of the signal will go towards direction #2 and 100-x % towards #5. When we throw the same direction with both dices (for ex '11'), we must throw again, because otherwise 100% of the signal would go in the same direction and this means 100% accuracy, which we assume to be impossible (and this is where HUP comes in). Hence 11,22,33,44,55,66 fall out. Let this signal be light and what do you see in these directions ? Black lines, and the overall picture is an interference.

Here you are controlling the distribution of the initial positions of the particles. de Broglie-Bohm theory has something like that also. However, it does allow all possible initial positions, although they may not all occur with the same probability. To reproduce the interference pattern, the trajectory in space of a particle is nonlinearly guided by the wave function, so that particles do not go straight after passing through a slit. Here is a picture of trajectories in de Broglie-Bohm theory http://scienceblogs.com/principles/2011/06/03/watching-photons-interfere-obs/.

 

[DevilsAvocado]

I never claimed that, and its obviously not true.

I very sorry bhobba, my fault, and I do apologize for my misinterpretation.

Hope it's accepted.

 

[bhobba]

I very sorry bhobba, my fault, and I do apologize for my misinterpretation. Hope it's accepted.

Of course it is, and no apology necessary.

We all glean others views from what they write and its simple human nature that sometimes its not conveyed properly or we interpret it incorrectly. It happens all the time.

Thanks
Bill

 

[DevilsAvocado]

Thanks bhobba! As always, you're a wise and reasonable man!

 

[DevilsAvocado]

I haven't looked at the paper referenced in this paper but how would one interpret these results:

It looks 'strange'... why only photons? When electrons easily could be more controlled? For example afaik, Tonomura could easily have experimented with longer time delay between every single electron, right?

And this looks troublesome:

http://arxiv.org/abs/physics/0611043v1]This[/PLAIN] evidence is sufficient for us to conclude that self-interference did not happen in a context, in which its preconditions were met. Whatever the nature of matter waves, they do not seem to produce quantum interference via self-interaction.

In comparison to this:

Some time before the discovery of quantum mechanics people realized that the connection between light waves and photons must be of a statistical character. What they did not clearly realize, however, was that the "wave function" gives information about the probability of one photon being in a particular place and not the probable number of photons in that place. The importance of the distinction can be made clear in the following way. Suppose we have a beam of light consisting of a large number of photons split up into two components of equal intensity. On the assumption that the beam is connected with the probable number of photons in it, we should have half the total number going into each component. If the two components are now made to interfere, we should require a photon in one component to be able to interfere with one in the other. Sometimes these two photons would have to annihilate one another and other times they would have to produce four photons. This would contradict the conservation of energy. The new theory, which connects the wave function with probabilities for one photon gets over the difficulty by making each photon go partly into each of the two components. Each photon then interferes only with itself. Interference between two different photons never occurs.

Conservation of energy is not easy to ignore...

 

[Cthugha]

In his Nobel prize lecture, Roy Glauber commented on that point. He published a more focused version of that remark in Nucl. Phys. A 774 (2006) 3-13 (free ArXiv version here: http://arxiv.org/abs/nucl-th/0604021).

Allow me to quote it:
"When you read the first chapter of Dirac’s famous textbook in quantum mechanics [8], however, you are confronted with a very clear statement that rings in everyone’s memory. Dirac is talking about the intensity fringes in the Michelson interferometer, and he says,

"Every photon then interferes only with itself. Interference between two different
photons never occurs."

Now that simple statement, which has been treated as scripture, is absolute nonsense."

He goes on to explain it in detail, but it is very obvious that Dirac was all-out wrong. Reading ancient textbooks which were written before the first laser was invented is a bad idea when trying to learn about quantum optics. Dirac's book is especially bad in that respect.

 

[DevilsAvocado]

Now that simple statement, which has been treated as scripture, is absolute nonsense.

OMG

I need a break... I had enough of "physics-fighting" for today... can't handle one more head/bottomless failure...

 

[atyy]

In his Nobel prize lecture, Roy Glauber commented on that point. He published a more focused version of that remark in Nucl. Phys. A 774 (2006) 3-13 (free ArXiv version here: http://arxiv.org/abs/nucl-th/0604021).

Allow me to quote it:
"When you read the first chapter of Dirac’s famous textbook in quantum mechanics [8], however, you are confronted with a very clear statement that rings in everyone’s memory. Dirac is talking about the intensity fringes in the Michelson interferometer, and he says,

"Every photon then interferes only with itself. Interference between two different
photons never occurs."

Now that simple statement, which has been treated as scripture, is absolute nonsense."

He goes on to explain it in detail, but it is very obvious that Dirac was all-out wrong. Reading ancient textbooks which were written before the first laser was invented is a bad idea when trying to learn about quantum optics. Dirac's book is especially bad in that respect.

Presumably the problem is with "only with itself" and "Interference between two different
photons never occurs." I assume it is still ok to say that a single photon interferes with itself? Something like http://falling-walls.com/videos/Alain-Aspect--1216 "single-photon interference"?

 

[Cthugha]

OMG

I need a break... I had enough of "physics-fighting" for today... can't handle one more head/bottomless failure...

When giving talks at major conferences in order to promote my own results, I sometimes added the Dirac quote and the Glauber quote in order to get people interested. At that point you usually hear some laughs and people are indeed interested. In the end it turned out that many of the people in the audience indeed started thinking about that. However, most did that instead of listening to the stuff I tried to get across. :/

Anyhow, it is surprising how much influence such a phrase in an old textbook can have just because it is catchy. However, for the notes: In a simple standard double slit with a simple light source, Dirac is right. However, as soon as you discuss entangled light or other complicated things, Dirac is not a good reference anymore. That should not come as a surprise. All of that stuff was investigated way later. I would not expect deep insights into QM from reading Newton's books either.

I assume it is still ok to say that a single photon interferes with itself?

Sure, within a coherence volume single photon interference happens as expected.

 

[DevilsAvocado]

When giving talks at major conferences in order to promote my own results, I sometimes added the Dirac quote and the Glauber quote in order to get people interested. At that point you usually hear some laughs and people are indeed interested. In the end it turned out that many of the people in the audience indeed started thinking about that. However, most did that instead of listening to the stuff I tried to get across. :/

It is a dangerous quote, it can vaporize any pompous reasoning, trust me!

Anyhow, it is surprising how much influence such a phrase in an old textbook can have just because it is catchy.

Yeah, and the worst thing – it makes perfect sense – you don't even have to check it.

However, for the notes: In a simple standard double slit with a simple light source, Dirac is right.

Phew, you've just saved my day... almost...

However, as soon as you discuss entangled light or other complicated things, Dirac is not a good reference anymore. That should not come as a surprise. All of that stuff was investigated way later. I would not expect deep insights into QM from reading Newton's books either.

Nothing surprises me anymore – not even my own "extraterrestrial brilliance" – here comes the final punch!

[Script draft for sequel "Dumb and Dumber To", Nov 2014 release]
In post #42 I quoted this paper:

http://pra.aps.org/abstract/PRA/v49/i5/p4243_1]-->[/PLAIN] *Two-photon interference* <-- in a standard Mach-Zehnder interferometer

A pair of light quanta with different colors (155.9-nm difference in center wavelength) generated from parametric down-conversion was injected collinearly into one input port of a Mach-Zehnder interferometer. Coincidence interference behavior was studied over a wide range of optical path differences of the interferometer. A measurement of 75% interference visibility with oscillation of the pump frequency for a large optical path difference of the interferometer (43 cm) is the signature of a quantum two-photon entangled state, which reflects both particle and wave nature of the light quanta in one experiment.

DOI: 10.1103/PhysRevA.49.4243

And a few posts later I (and my dear friend Dirac), claimed it completely impossible! Do I get a prize for this achievement? Ig Nobel maybe??




P.S: Thanks for the laughs Cthugha, and here's a cake on your "1,500 posts day".

 

[bhobba]

He goes on to explain it in detail, but it is very obvious that Dirac was all-out wrong. Reading ancient textbooks which were written before the first laser was invented is a bad idea when trying to learn about quantum optics. Dirac's book is especially bad in that respect.

As a person that learned QM from Dirac's and Von-Neumann's books I fully concur.

Both are full of stuff that from our vantage point are downright WRONG.

Both are classics and should be in the library of anyone seriously interested in QM - but do not learn QM from them or you will run into trouble and need to unlearn stuff - just like I did.

Ballentine leaves them for dead.

Thanks
Bill

 

[probert84]

I have been thinking recently and I have a few questions. I wonder if the following thought experiment was valid :

We establish two sources of "perfectly inelastic" particles facing directly to each other, so that they generate particles moving exactly towards the opposite direction than the other. We generate these particles with the same exact speed that we determine beforehand, and so they can't be generated with an arbitrary precision towards the above direction but some % of the particles will still have to move the way we want it, so that they collide and bounce back exactly in the direction where they came from. What I'd like to establish is the this:

We generate two particles (lets call them Alice and Bob) in 'x' and '-x' directions. After they collided, they are going to switch directions, so if Alice moved in 'x' direction, after the collision it will move to '-x', and vice versa.
While the particles are coming back to their sources, we replace one's generator with a detector, so that we can determine when the desired collision has happened. This means that for ex. when the detector of Alice detects that Alice has come back, Bob must be also at its origin, and this means we know both the place and speed of Bob at the same time with an infinite precision. What I'd like to know is that if we let Bob pass through a double slit, would we still see it interfering with itself ?

And another thing, can time be arbitrarily short ?

 

[bhobba]

And another thing, can time be arbitrarily short ?

We don't know. We currently assume it is - but we do not know.

Your collision thought experiment will not work - collide quantum objects and all sorts of strange things happen such as new particles spewing forth and scattering.

Thanks
Bill

 

[manojr]

About slit experiment video in post 50.
As delta X becomes smaller and smaller the delta P becomes larger and larger.
But why does it do so in direction exactly perpendicular to slit? Why not in random directions to form a circular spot on screen?

 

[stevmg]

probert84 - your "answer" is more confusing than your question.

I just think of the "mass" of a wave = E/c^2 and the dimension of the wave is the entire wave front in which the entire energy, E, is spread out over the ENTIRE wavefront (I.e., exists simultaneously - no "probability" involved.)

In truly empty space where there is no mass and no energy, this is immediately disrupted by any particle or energy which imparts mass, curves or displaces space and changes the physics of that region.

 

[Maui]

About slit experiment video in post 50.
As delta X becomes smaller and smaller the delta P becomes larger and larger.
But why does it do so in direction exactly perpendicular to slit? Why not in random directions to form a circular spot on screen?

The slit is vertical so you are only restricting the light path horizontally. Vertically the slit stays the same height, i.e. no shortening and in a sense it's still in the classical domain..

 

[bhobba]

But why does it do so in direction exactly perpendicular to slit? Why not in random directions to form a circular spot on screen?

Because being a vertical slit the position is not localized vertically - only horizontally.

Thanks
Bill

 

[probert84]

We don't know. We currently assume it is - but we do not know.

Your collision thought experiment will not work - collide quantum objects and all sorts of strange things happen such as new particles spewing forth and scattering.

Thanks
Bill

Why do we assume that about time ?

So there is no perfectly inelastic collision at all in the quantum world ?

 

[bhobba]

Why do we assume that about time ?

Why not?

Its made in all areas of physics because its common-sensical, works and allows the powerful methods of calculus to be employed. If you want to develop a version that doesn't assume it go ahead - feel free. And make quantitative predictions with it that experimentally distinguish it from the standard theory. A Nobel prize awaits if you can. But you won't have calculus to help you.

So there is no perfectly inelastic collision at all in the quantum world ?

Collisions in QM are not amenable to such a classification because they are not particles in a classical sense. When, for example, two photons collide, a positron and electron can come out - and that's not all that can happen - its quite complicated. Its described by Feynman diagrams and that mathematically difficult area of QFT.

Thanks
Bill

 

[probert84]

Why not?

Because that would explain why energy is quantized.

 

[bhobba]

Because that would explain why energy is quantized.

Energy is not always quantized.

But aside from that your logic escapes me.

First, before going any further, exactly what do you think energy is and why is it conserved?

Modern physics knows the answer to that, and when you do you realize a statement like you made is nonsensical, but before going any further let's pin down what you think it is.

Thanks
Bill

 

[probert84]

Under which circumstance is it not quantized ?

My definition of energy would be something like this:

<<Personal speculation deleted>>

 

[Dale]

Under which circumstance is it not quantized ?

Typically the energy of bound states are quantized, but the energy of free states are not quantized. So, for example, a hydrogen atom has a whole series of quantized energy levels, but once you add enough energy to separate the electron from the proton (ionization) the energy is no longer quantized.

My definition of energy would be something like this:

<<Personal speculation deleted>>

With that, this thread is closed.