How I Stopped Worrying and Learned to Love Orthodox Quantum Mechanics - Comments

[atyy]

That may well be true, and maybe after all nature is not Poincare invariant at very large scales where we have no observations yet. All this is, of course, wild speculation, which won't be solved by theory alone but one needs some phenomenological hint to the highly desirable "physics beyond the standard model"!

Yes, but if we think the standard model is an EFT (and we don't know whether the theory above the Landau pole is Poincare invariant or not), then it is also wild speculation to say that the standard model is Poincare invariant - unless you can put a cut off that is both Poincare invariant and gauge invariant?

 

[fanieh]

They aren't. That's aether in disguise.

I fast read this message and missed the context. I thought "They aren't" meant the fundamental particles in the Insight article were not related to aether.. but then reading again now. Demystifier meant the fundamental particles could be the aether themselves! (maybe just in jest and not serious or half serious) But then the Aether has already meaning in physics which is a substance that the Morley-Michelson experiment has refuted prior to Einstein's concept of Special Relativity.. in modern form it is revived by Lorentz Aether Theory.. which is another substance devoid of any properties. Therefore I think we must not use the very vague term Aether and ought to choose another term. The word Aether is medieval and may sound elegant but we musn't use it because we may spend half of the time just trying to to fight over or defend the word itself. Therefore we (or at least Demystifer) must invent a new term or substitute for it. I wonder what other ancient words confer the same idea. There's the Fifth Element, Akasha, Plenum of the ancient, what else? oh there was "Koilon"... in ancient literature.. Koilon is described as thus:

"Matter is not koilon, but _the absence of koilon_, and at first sight, matter and space appear to have changed places, and emptiness has become solidity, solidity has become emptiness. The Latin coelum (koilon, a vault) is derived by many from the root of celare "to cover, to conceal" (coelum, "ceiling" "roof of the world"). But now comes the startling part of the investigation: we might expect matter to be a densification of this koilon; it is nothing of the kind. Just as such bubbles are not water, but are precisely the spots from which water is absent, so these units are not koilon, but the absence of koilon -- the only spots where it is not -- specks of nothingness floating in it, so to speak, for the interior of these space-bubbles is an absolute void to the highest power of vision that we can turn upon them."

I think it's an occult work of fiction just like the ancient concept of Aether. This is just to derive the point we mustn't use the word Aether again because it would confuse so many. So does anyone know a better sounding and elegant word to describe the fundamental particles in Demystifier investigation of condense matter phonon quasiparticles (that our relativistic particles may be based on in contrast to the fundamental BM non-relativistic particles)? (btw.. is it possible the fundamental particles are voids or bubbles in the aether? (asked in jest meaning non-serious :) ))

Of course. Nobody ever proved that aether doesn't exist. What has Einstein (and others) demonstrated is that it is merely simpler to describe the observed phenomena without the aether. But simpler doesn't always mean "more correct". For instance, it is simpler to describe a fluid as a continuum, yet today we know that it is more correct to describe it as a discrete set of atoms.

 

[bhobba]

So just cut the theory off at that scale. Is there any problem with that?

Of course - I already said that was the critical issue for current theoretical physics to fix that up.

All I am pointing out is what the critical issue with quantum gravity is - its sometimes forgotten everything is fine up to the Plank scale - the same with the standard model - nobody I am aware of trusts that at the Plank scale either.

Thanks
Bill

 

[bhobba]

Yes, but if we think the standard model is an EFT (and we don't know whether the theory above the Landau pole is Poincare invariant or not), then it is also wild speculation to say that the standard model is Poincare invariant - unless you can put a cut off that is both Poincare invariant and gauge invariant?

Exactly.



Thanks
Bill

 

[atyy]

Of course - I already said that was the critical issue for current theoretical physics to fix that up.

All I am pointing out is what the critical issue with quantum gravity is - its sometimes forgotten everything is fine up to the Plank scale - the same with the standard model - nobody I am aware of trusts that at the Plank scale either.

Thanks
Bill

Yes. I making the analogy between the cut at the Planck scale and the classical-quantum cut. In both theories, you have to cut somewhere. Both theories work great despite the cut - in fact, they work great because of the cut. But the cut suggests an incompleteness, hence there is research in string theory and in Bohmian Mechanics, GRW, MWI etc.

 

[vanhees71]

Yes, but if we think the standard model is an EFT (and we don't know whether the theory above the Landau pole is Poincare invariant or not), then it is also wild speculation to say that the standard model is Poincare invariant - unless you can put a cut off that is both Poincare invariant and gauge invariant?

Well, as an effective theory the Standard Model is Poincare invariant and in accordance with observations. As I said, nobody can know without observations, whether Poincare invariance holds up to higher energies beyond the validity of the effective theory.

 

[atyy]

Well, as an effective theory the Standard Model is Poincare invariant and in accordance with observations. As I said, nobody can know without observations, whether Poincare invariance holds up to higher energies beyond the validity of the effective theory.

What does it mean to be Poincare invariant but not exist at all energies? Doesn't strict Poincare invariance mean the theory exists at all energies?

 

[vanhees71]

Yes, but if we think the standard model is an EFT (and we don't know whether the theory above the Landau pole is Poincare invariant or not), then it is also wild speculation to say that the standard model is Poincare invariant - unless you can put a cut off that is both Poincare invariant and gauge invariant?

Well, as an effective theory the Standard Model is Poincare invariant and in accordance with observations. As I said, nobody can know without observations, whether Poincare invariance holds up to higher energies beyond the validity of the effective theory.

 

[Demystifier]

What does it mean to be Poincare invariant but not exist at all energies? Doesn't strict Poincare invariance mean the theory exists at all energies?

Newtonian mechanics is Galilean invariant. It is only valid for velocities much smaller than c, but we still call it Galilean invariant.

Just because theory is wrong, or even meaningless, when extrapolated too far, does not mean that the theory looses its symmetry in the extrapolation.

 

[atyy]

Newtonian mechanics is Galilean invariant. It is only valid for velocities much smaller than c, but we still call it Galilean invariant.

Just because theory is wrong, or even meaningless, when extrapolated too far, does not mean that the theory looses its symmetry in the extrapolation.

Newtonian theory with perfect Galilean invariance exists as a theory in itself. It is falsified by data.

It is not clear that QED with Poincare invariance exists as a theory in itself - even without data, we seem to need a cutoff to make sense of it. If we take say lattice QED with the lattice spacing near the Landau pole scale, the theory is FAPP Poincare invariant at low energies. But because of the lattice, it is not even true that the theory is Poincare invariant below the cut off - already near the Landau pole there should be huge violations of Poincare invariance. So it is only far, far, far below the cutoff that QED is Poincare invariant.

 

[vanhees71]

What does it mean to be Poincare invariant but not exist at all energies? Doesn't strict Poincare invariance mean the theory exists at all energies?

It's in the same sense Poincare invariant as Newtonian physics is Galilei invariant. Within its range of validity it's in accordance with observations. The only difference is that for the Standard Model we don't know the exact range of validity yet let alone a more comprehensive theory (be it Poincare invariant or not) which tells us in which sense the Standard Model is a good approximation and what it's range of applicability really is.

 

[vanhees71]

Newtonian theory with perfect Galilean invariance exists as a theory in itself. It is falsified by data.

It is not clear that QED with Poincare invariance exists as a theory in itself - even without data, we seem to need a cutoff to make sense of it. If we take say lattice QED with the lattice spacing near the Landau pole scale, the theory is FAPP Poincare invariant at low energies. But because of the lattice, it is not even true that the theory is Poincare invariant below the cut off - already near the Landau pole there should be huge violations of Poincare invariance. So it is only far, far, far below the cutoff that QED is Poincare invariant.

QED exists. It makes predictions, which are testable by experiment and so far it was utmost successful. That there are quibbles a la Haag's theorem is not too relevant from this practical perspective. QED, applicable to real-world observations, is defined as renormalized (and appropriately resummed) perturbation theory. I thought, you are a proponent of the Wilsonian view at QFT?

 

[atyy]

It's in the same sense Poincare invariant as Newtonian physics is Galilei invariant. Within its range of validity it's in accordance with observations. The only difference is that for the Standard Model we don't know the exact range of validity yet let alone a more comprehensive theory (be it Poincare invariant or not) which tells us in which sense the Standard Model is a good approximation and what it's range of applicability really is.

No it is not the same as Newtonian physics.

Newtonian physics exists mathematically as a theory with perfect Galilean invariance. It just turns out the theory is false, even though it is coherent.

But we do not have a coherent theory of QED with perfect Poincare invariance.

 

[atyy]

QED exists. It makes predictions, which are testable by experiment and so far it was utmost successful. That there are quibbles a la Haag's theorem is not too relevant from this practical perspective. QED, applicable to real-world observations, is defined as renormalized (and appropriately resummed) perturbation theory. I thought, you are a proponent of the Wilsonian view at QFT?

Yes, it is the Wilsonian view that says QED need not come from a Poincare invariant theory, ie. the Poincare invariance may exist as an approximation at very low energies.

In other words, one cannot use the low-energy Poincare invariance of QED as an argument against Bohmian Mechanics.

 

[vanhees71]

I'd not say that Newtonian physics is false. It has only a known range of applicability.

I don't understand your statement about QED. It's manifestly Poincare invariant. We know, it breaks down at a large energy scale, where it has a Landau pole, and that's for sure some range of applicability of renormalized perturbative QFT. Whether it exists beyond the perturbative approach is unknown (and perhaps even not very probable). We don't know it's precise range of validity yet, because we don't have observations where it (or better said the Standard Model as a whole) really fails and in which way.

 

[vanhees71]

Yes, it is the Wilsonian view that says QED need not come from a Poincare invariant theory, ie. the Poincare invariance may exist as an approximation at very low energies.

That's what I'm saying all the time!

In other words, one cannot use the low-energy Poincare invariance of QED as an argument against Bohmian Mechanics.

Well, I don't think that de-Broglie-Bohm mechanics (please always mention de Broglie too, he's the originator of the pilot-wave idea!) has any merits beyond (non-relativistic) QM in the minimal interpretation, and it's hard to find a convincing interpretation in the context or relativistic QFT. Why should I adopt an interpretation which is less comprehensive than standard (relativistic) QFT without any additional merit for the description of nature?

 

[Demystifier]

It is not clear that QED with Poincare invariance exists as a theory in itself - even without data, we seem to need a cutoff to make sense of it. If we take say lattice QED with the lattice spacing near the Landau pole scale, the theory is FAPP Poincare invariant at low energies. But because of the lattice, it is not even true that the theory is Poincare invariant below the cut off - already near the Landau pole there should be huge violations of Poincare invariance. So it is only far, far, far below the cutoff that QED is Poincare invariant.

I would like to reformulate the issue in the following way. Classical electrodynamics is Poincare invariant. If the corresponding quantum theory is not Poincare invariant, it should manifest as a quantum anomaly. Quantum anomalies are a well developed subject in QFT, but I never heard of an anomaly related to Poincare invariance. Yes, you need to introduce a cut-off that seems to spoil the invariance, but if there is no anomaly then it looks like a formal nitpicking without direct physical consequences.

 

[Demystifier]

(please always mention de Broglie too, he's the originator of the pilot-wave idea!)

Don't you know about the Stigler’s law?
https://en.wikipedia.org/wiki/Stigler's_law_of_eponymy

 

[stevendaryl]

You are basically asking why the detector in the double slit experiment can only detect one electron and not have multiple hits for only one electron emitted. But isn't it that according to:

1. Bohmian Mechanics.. there is a trajectory for the one electron being emitted so it hits the detector at one point...
2. Many Worlds.. there are multiple hits in the screen.. but we only viewed one of them because we are entangled with only one of them...
3. Copenhagen.. the wave function may pass through both slits but it collapses into one hit when it reached the screen...

Yes, I'm mostly saying why I find the "minimal interpretation" inadequate. Those three have different issues.

 

[name123]

Demystifier submitted a new PF Insights post

How I Stopped Worrying and Learned to Love Orthodox Quantum Mechanics
View attachment 210012Continue reading the Original PF Insights Post.

I can understand why Einstein assumed that a physical universe in which nothing could travel faster than the speed of light would not have the "spooky action at a distance" suggested by Bohmian mechanics. Do you think "spooky action at a distance" is compatible with a physical universe in which nothing could travel faster than light? If so would you mind explaining how you think it would work?

(P.S. my knowledge of physics is pretty poor)

 

[Demystifier]

I can understand why Einstein assumed that a physical universe in which nothing could travel faster than the speed of light would not have the "spooky action at a distance" suggested by Bohmian mechanics. Do you think "spooky action at a distance" is compatible with a physical universe in which nothing could travel faster than light? If so would you mind explaining how you think it would work?

(P.S. my knowledge of physics is pretty poor)

Even with a poor knowledge of physics you may try reading my
https://arxiv.org/abs/1002.3226
because it contains a dialogue with no equations.

 

[name123]

Even with a poor knowledge of physics you may try reading my
https://arxiv.org/abs/1002.3226
because it contains a dialogue with no equations.

Thank you for the link to the article which I found useful. Though I still have some problems in understanding the idea you were suggesting (the answers might have been in the equations (which I do not understand)).

You wrote:
---
O: The theory of relativity implies that nothing can travel faster than light.
R: No, the theory of relativity does not imply that. The best known counterexample is
a tachyon, hypothetical particle with mass squared m² < 0. It is a completely relativistic
object, and yet it travels only faster than light.
---

But when checking up on them in wiki (https://en.wikipedia.org/wiki/Tachyonic_field) I read:
---
The term "tachyon" was coined by Gerald Feinberg in a 1967 paper[7] that studied quantum fields with imaginary mass. Feinberg believed such fields permitted faster than light propagation, but it was soon realized that Feinberg's model in fact did not allow for superluminal speeds.[6] Instead, the imaginary mass creates an instability in the configuration: any configuration in which one or more field excitations are tachyonic will spontaneously decay, and the resulting configuration contains no physical tachyons. This process is known as tachyon condensation. A famous example is the condensation of the Higgs boson in the Standard Model of particle physics.
---

Is this simply a case of different theories different suggestions?

Also I think that non-local effects occur in both QFT and Bohmian Mechanics, but I am not sure of the Bohmian mechanics interpretation of the Alain Aspect experiment (where I think spin states were measured), given Bell's inequality theorem. In Bohmian Mechanics, do the entangled particles not have a spin state prior to measurement, or is it that there is some suggested mechanism for changing the spin state of one dependent on the measurement of the other? If the latter, how is it suggested that the particle that is to have its spin state change singled out so that it is its state that is changed and not some other particle's?

 

[Demystifier]

@name123 one should distinguish classical tachyon particle from classical tachyon field. It is true that classical tachyon field does not propagate faster than light. Nevertheless, classical tachyon particle does travel faster than light.

Concerning the spin measurement in BM, the spin actually never exists in a fundamental sense. That's related to the fact that spin is measured by the Stern-Gerlach apparatus which really measures the position of the particle, while the association of spin with a measured position is just a convenient interpretation.

 

[vanhees71]

The point of the SG apparatus is to entangle the particle's spin-$z$ component (homogeneous part of the magnetic field in $z$ direction) with the particle's position, and thus you can filter out particles with well-determined spin-$z$ values. The association between spin and position is very much straight forward without any reference to pilote-wave or de Broglie Bohm. It's completely understandable and analytically (semi-numerically) calculable from the time-dependent Schrödinger equation alone!

 

[name123]

@name123 one should distinguish classical tachyon particle from classical tachyon field. It is true that classical tachyon field does not propagate faster than light. Nevertheless, classical tachyon particle does travel faster than light.

In the paper you wrote:
"Of course, QFT alone with its standard purely probabilistic interpretation certainly does not describe such superluminal influences, but it does not exclude their existence either (unless, of course, you assume that QFT with its standard interpretation is the ultimate theory of everything)."

When you talk about the standard interpretation of QFT did you mean that all particles are fields?

Concerning the spin measurement in BM, the spin actually never exists in a fundamental sense. That's related to the fact that spin is measured by the Stern-Gerlach apparatus which really measures the position of the particle, while the association of spin with a measured position is just a convenient interpretation.

So regarding the position, in BM do the entangled particles have some associated value which will determine whether they will have their position measured as an up or down spin prior to measurement (perhaps some trajectory), such that if they were measured along the same orientation their measured positions could be interpreted as different spins? Or is it that there is some suggested mechanism for changing the measured position to give an up or down spin interpretation dependent on the measurement of the other? If the latter how is it suggested that the particle that is to have its "spin state"/position changed singled out so that it is its position that is changed and not some other particle's?

 

[Demystifier]

When you talk about the standard interpretation of QFT did you mean that all particles are fields?

Yes.

So regarding the position, in BM do the entangled particles have some associated value which will determine whether they will have their position measured as an up or down spin prior to measurement (perhaps some trajectory), such that if they were measured along the same orientation their measured positions could be interpreted as different spins? Or is it that there is some suggested mechanism for changing the measured position to give an up or down spin interpretation dependent on the measurement of the other? If the latter how is it suggested that the particle that is to have its "spin state"/position changed singled out so that it is its position that is changed and not some other particle's?

For more details about spin in BM see
https://arxiv.org/abs/1305.1280
Even if you skip equations, you have a lot of text to read and pictures to see.

 

[vanhees71]

The problem with tachyons in local QFT is that for the interacting case, as far as I know, one cannot define the S-matrix in the usual way, because it's hard to define Hamiltonian densities that commute at spacelike separated arguments, which is (at least) a sufficient condition for having a Poincare invariant unitary S-matrix fulfilling the linked-cluster principle. See, e.g.,

https://academic.oup.com/ptp/article-pdf/45/5/1646/5399190/45-5-1646.pdf

 

[name123]

Yes.
For more details about spin in BM see
https://arxiv.org/abs/1305.1280
Even if you skip equations, you have a lot of text to read and pictures to see.

Thanks for the link.

It seemed from what I read that it is suggested that the measurement of the first particle would instantaneously change the measured position of the second particle. What I am not clear on is the suggested mechanism for the measurement of the position of the first particle influencing the measurement of the position of the second particle. Perhaps I am simply misunderstanding the basics. I was imagining a non-local guiding wave influencing a population of particles, and the measurement influencing the non-local guiding wave.

If I have not misunderstood the basics, then a couple of points I am not clear on are:

1) If a thousand Bell Tests were done simultaneously (the first particles measured) what ensures that the measurement of second particles will not be influenced by changes to the pilot wave by the other tests (or whatever else is going on in the universe)?

2) How is it explained that the change to the pilot wave will influence the position of the entangled second particle such that it will be measured as having the opposite spin to the entangled first particle no matter whether without the altered guidance the second particle would have have "spun up or down"? I presumed the alteration required to get the effect would depend upon what position the second particle had prior to the alteration being made.

 

[Demystifier]

It seemed from what I read that it is suggested that the measurement of the first particle would instantaneously change the measured position of the second particle.

Yes.

I was imagining a non-local guiding wave influencing a population of particles, and the measurement influencing the non-local guiding wave.

Velocity of each particle is determined by position of that and other particles. But the rule of this determination is not fixed. It is defined by the guiding wave. The guiding wave guides both the measured particles and the particles constituting the measuring apparatus.

1) If a thousand Bell Tests were done simultaneously (the first particles measured) what ensures that the measurement of second particles will not be influenced by changes to the pilot wave by the other tests (or whatever else is going on in the universe)?

It is ensured by the fact that wave functions (i.e. guiding waves) associated with different measurements are not entangled with each other.

2) How is it explained that the change to the pilot wave will influence the position of the entangled second particle such that it will be measured as having the opposite spin to the entangled first particle no matter whether without the altered guidance the second particle would have have "spun up or down"?

It is ensured by the entanglement of the wave function, which is explained by the Schrodinger equation ... but if this looks too abstract for you, well, some aspects cannot be properly understood without the math.

Before asking further questions, read also this:
https://arxiv.org/abs/quant-ph/0611032

 

[name123]

It is ensured by the fact that wave functions (i.e. guiding waves) associated with different measurements are not entangled with each other.

There are multiple guiding waves? I had thought there was one for the universe, and that it appeared random because there was no way to have all the information about all the non-local influences. Are you suggesting each particle has its own guiding wave, and that particle guiding waves can become entangled? If so how do they become entangled and disentangled?

Before asking further questions, read also this:
https://arxiv.org/abs/quant-ph/0611032

On page 7 under the Non-locality section it states:
"Since the wavefunction is defined on the configuration space, the guidance equation of an N-particle system links the motion of every particle to the position of the other particles at the same time". Is this only if the N-particles are entangled?

In the same section it goes onto state:
"Finally does the non-locality of the de Broglie-Bohm theory vanishes if the state is not entangled."

Which seems like a question, but perhaps the "does" can be removed and it would be a statement. Is this how you would read it?

 

[Demystifier]

There are multiple guiding waves? I had thought there was one for the universe, and that it appeared random because there was no way to have all the information about all the non-local influences. Are you suggesting each particle has its own guiding wave, and that particle guiding waves can become entangled? If so how do they become entangled and disentangled?

There is only one wave for the whole system, but when the system consists of non-entangled subsystems the wave can be decomposed into separate waves for each subsystem.

On page 7 under the Non-locality section it states:
"Since the wavefunction is defined on the configuration space, the guidance equation of an N-particle system links the motion of every particle to the position of the other particles at the same time". Is this only if the N-particles are entangled?

Yes.

In the same section it goes onto state:
"Finally does the non-locality of the de Broglie-Bohm theory vanishes if the state is not entangled."

Which seems like a question, but perhaps the "does" can be removed and it would be a statement. Is this how you would read it?

Yes.

 

[name123]

There is only one wave for the whole system, but when the system consists of non-entangled subsystems the wave can be decomposed into separate waves for each subsystem.

If they are entangled how are you suggesting that changes to the wave subsystems influence each other at faster than light speeds, because waves are fields are they not, and you have stated that tachyon fields do not propagate at faster than light speed? Are you suggesting that tachyon particles are involved in the entanglement of the wave subsystems?

 

[martinbn]

If they are entangled how are you suggesting that changes to the wave subsystems influence each other at faster than light speeds, because waves are fields are they not, and you have stated that tachyon fields do not propagate at faster than light speed? Are you suggesting that tachyon particles are involved in the entanglement of the wave subsystems?

They are called waves, but the equation is not a wave equation, it isn't hyperbolic to expect finite speed of propagation. In fact, if I am not wrong, it has infinite speed of propagation.

 

[name123]

They are called waves, but the equation is not a wave equation, it isn't hyperbolic to expect finite speed of propagation. In fact, if I am not wrong, it has infinite speed of propagation.

Yes, I also understand that, the wave in BM has infinite speed of propagation. But earlier Demystifier had given me a link to a paper in which he had seemed to suggest that QFT did not rule out the type of superluminal influences in BM, and I had asked him about it. He wrote that:

@name123 one should distinguish classical tachyon particle from classical tachyon field. It is true that classical tachyon field does not propagate faster than light. Nevertheless, classical tachyon particle does travel faster than light.

But in BM the guiding wave would (I think) be a field (it is not a particle), and so even if imagined to have an imaginary mass (in order to propagate at faster than light speeds and be compatible with relativity), it would be a tachyon field (not a tachyon particle). And, as I understood it, QFT does rule out tachyon fields propagating at faster than light speeds. Which is why I was checking whether it was being suggested that tachyon particles were involved.

 

[vanhees71]

They are called waves, but the equation is not a wave equation, it isn't hyperbolic to expect finite speed of propagation. In fact, if I am not wrong, it has infinite speed of propagation.

Which speed are you referring to? Take a free particle. The dispersion relation is
$$\omega=\frac{\vec{p}^2}{2m},$$
and thus the phase velocity is
$$c_{\text{phase}}=\frac{\omega}{|\vec{p}|}=\frac{|\vec{p}|}{2m},$$
and the group velocity is
$$c_{\text{group}}=\partial_{|\vec{p}|} \omega=\frac{|\vec{p}|}{m},$$
neither of which is infinite.