schroedinger and Bohm

[Rothiemurchus]

The schroedinger equation is an inspired postulate - it cannot be derived
from fundamental principles.The pilot wave of David Bohm's version of quantum mechanics is also postulated.Has anyone tried to derive the
pilot wave and schroedinger equation from physical laws?

[ZapperZ]

The schroedinger equation is an inspired postulate - it cannot be derived
from fundamental principles.

Oh really?

There is a reason why the Schrodinger equation is often called the Hamiltonian of the system. Now, unless you are also claiming that the Hamiltonian/Lagrangian principle of classical mechanics are also an "inspired postulate" (so then why pick on the Schrodinger equation only?), then maybe you should look at the connection between the two and how Schrodinger actually derived his infamous equation[1].

There are several postulates in QM. The Schrodinger equation isn't one of them.

Zz.

[1] E. Schrodinger, Phys. Rev. v.28, p.1049 (1926); or look here: http://fangio.magnet.fsu.edu/~vlad/pr100/100yrs/html/chap/fs2_14001.htm

[marlon]

This is a very nice reference ZapperZ.

It is always nice to see how very well established theories like QM are constructed from "scratch". I always have been interested in the original documents of people like Schrödinger, Dirac, Einstein and so on.

Isn"t there some link available where we could see the original version of the incorporation of magnetic monopoles into the Maxwell-equations...by the hand of Dirac

regards
marlon

[humanino]

Zz ! That is the greatest link ever ! Why did not I ask this before, I can only blame myself. Thank you so much Zz.

[ZapperZ]

Hey, I'm glad you two liked it. If you notice, that link has several other landmark papers in QM. I have been collecting a lot of legitimate physics links over the years, so it doesn't hurt to ask. You might just get it! :)

Zz.

Addendum: If one is questioning something, it is ALWAYS a good idea to see the origin of that "thing" and how it came into being.

[Rothiemurchus]

The Lagrangian, kinetic energy - potential energy - turns up in many classical situations but why, as someone else on this forum has said,
should that energy difference be such an important part of nature, which it clearly is?
Of all the possible combinations such as KE + (PE) ^2, ( KE)^3 + (PE) ^3 etc. why
KE - PE?

[humanino]

If you add two things, make sure they have the same units. You cannot add GeV and GeV^2, that is meaningless.

Why the difference of KE and PE ? The sum is already the total energy. It turns out that, you can perform a mathematical operation called a Legendre transformation... that is not the explanation you want, is it ?

The action is the number nature optimize during a process. Imagine falling in a gravitational potential : to minimize the action, you want to "need a minimum of KE" while "use as much PE as possible". Does that make sens ?

[ZapperZ]

The Lagrangian, kinetic energy - potential energy - turns up in many classical situations but why, as someone else on this forum has said,
should that energy difference be such an important part of nature, which it clearly is?
Of all the possible combinations such as KE + (PE) ^2, ( KE)^3 + (PE) ^3 etc. why
KE - PE?

Again, this is an example on why, if one did not learn from the ground up, things will seem to appear out of nowhere.

We have gone over this in other threads of the importance of calculus of variation, and in particular the principle of least action. This is the only means of understanding the origin of the Lagrangian/Hamiltonian approach to classical mechanics. I strongly suggest you look this up.

Zz.

[Rothiemurchus]

Yes it makes sense.
The action can be maximised or minimised can't it -Hamilton's principle?
Doesn't Feynman's sum over all histories minimise the action?
And is the action minimised in GR ?
But again why should nature favour maximum/minimums?

[ZapperZ]

Yes it makes sense.
The action can be maximised or minimised can't it -Hamilton's principle?
Doesn't Feynman's sum over all histories minimise the action?
And is the action minimised in GR ?
But again why should nature favour maximum/minimums?

For once, let's not stray too far from the tree. Do you still think the Schrodinger equation is an "inspired postulate"?

Zz.

[humanino]

I'm french : Pierre Louis Moreau de Maupertuis' principle :tongue2: one century before
Please follow Zz advice. Otherwise this site would grow indecently. Use the search function. You cannot search more than once in 5 minutes.

Yes the action is stationnary.
Yes.
Yes.
Because Nature is elegant. You can also choose to formulate the laws in terms of optimization.

--------
EDIT : I also want to add that in France, Hamilton is not recognized as the great mathematician he was. It always bothered me.

[Rothiemurchus]

Zapper Z:
For once, let's not stray too far from the tree. Do you still think the Schrodinger equation is an "inspired postulate"?

Rothie M:
When I studied chemistry it was derived for us!
But because I am not a physicist and I read a physics book that said it was "an inspired postulate" I thought maybe I had been mislead on my chemistry course.
However I am currently reading a 500 page book on the maths of QM and will soon be
on the page about Schrodinger's equation.
But Tom Mattson said in reply to one of my questions that the pilot wave of Bohm's theory was a "sourceless differential equation."
Is this why Bohm's theory has less credibility than standard QM?

[bd1976]

Mr.Rothiemurchus, your original post was correct in a sense. Schrödinger’s equation was a kind of inspired postulate.

Well actually to clarify it wasn't so much of a postulate as a differential equation manufactured so that its solutions fit the observed measurements on qm systems. However Schrödinger’s equation was not and currently can not be derived from any known principles. How and why it arises are questions that currently have no answer.

In modern quantum theory the postulate is that each dynamical variable in quantum mechanics (position, momentum etc...) can be represented by quantum mechanical operators. But these once again mysteriously arise they cannot be derived from any know principle - they just are!

This is just one of the reasons why quantum mechanics is viewed so sceptically by so many people.

[humanino]

First of all, welcome bd1976.

Did you read Zz post (#2)
Zz is a professional physicist, taking on his precious time for a noble cause : communicating science. So please, read post #2.

[bd1976]

Thanks for the welcome. Happened to be reading this thread and thought I'd offer a bit of help. First of all I don't claim to be an expert on qm. (thats the goal of a lifetime!) But I have taken four undergraduate courses on the subject and can say that no one can derive the wave equation based on underlying physical principals. And If you can, then you have revolutionised physics as we know it today and should put in for your rightful nobel prize!

As to Bohm theory. I don't know very much about it. From what little I can remember I think its a hidden variable theory proposed to explain some of the conceptual problems with quantum mechanics. However as I remember (this is pretty fuzzy) the theory introduces conceptual problems that are as bad as the ones its trying to solve. Amoung other things I think its non-local and has some problems when you try and integrate relaitivity into the theory. So basically the reason its not widely accepted is that its just as bad as quantum mechanics and its harder to work with!

[humanino]

I see your point of view : nobody knows where QM comes from.

The principles of QM cannot be derived. Yet the wave equation can be derived. Schrodinger equation can be obtained from the classical hamiltonian by using the operator representations for p and E. In turn, those can be derived in the Hilbert space. The only thing you must postulate can be for instance the correspondance between the classical Poisson bracket, and the commutation rules in QM.

Can classical mechanics be demonstrated as well ?

[humanino]

So basically the reason its not widely accepted is that its just as bad as quantum mechanics and its harder to work with!
:rofl:
Please ! Don't :grumpy:

[ZapperZ]

Mr.Rothiemurchus, your original post was correct in a sense. Schrödinger’s equation was a kind of inspired postulate.

Well actually to clarify it wasn't so much of a postulate as a differential equation manufactured so that its solutions fit the observed measurements on qm systems. However Schrödinger’s equation was not and currently can not be derived from any known principles. How and why it arises are questions that currently have no answer.

In modern quantum theory the postulate is that each dynamical variable in quantum mechanics (position, momentum etc...) can be represented by quantum mechanical operators. But these once again mysteriously arise they cannot be derived from any know principle - they just are!

This is just one of the reasons why quantum mechanics is viewed so sceptically by so many people.

I will address that last part first. During the 100 year anniversary of QM in 1999, there was a unanimous proclamation that QM is the most successful theory of mankind so far by the physics community.

So three questions: (1) who are these "so many people" who are viewing QM so sceptically; (2) are they skeptical about the INTERPRETATION of QM or the FORMALISM of QM; and (3) do these skeptical people realize that they are using the application of QM in their modern electronics every single second of the day?

I don't know where this "manufactured" accusation of QM came from. I would think a "manufactured" idea to fit a particular result would have difficulties in fitting other results, especially when they come from wildly different phenomena. How do you manufacture a result that agrees with the band theory of semiconductors used in your modern electronics to also agree with BE condensation in atomic gasses that also describes light diffraction from a single slit?

Let me repeat, the Hamiltonian/Schrodinger equation didn't come out of nowhere! Read that paper! QM has a set of postulates that requires the assignment of PHYSICAL MEANINGS to mathematical formalism. This is not unusual. Look at all of physics and you will see that at some point, there HAS to be a set of postulates that simply cannot be derived via First Principles. That is what made this physics and not mathematics.

I'm also puzzled by another point. If there ARE people who are "skeptical" of QM simply because they (incorrectly) think QM is simply manufactured to fit the results, why aren't you and these people also complaining about classical E&M? Coulomb's law, for example, is PURELY phenomenological. I dare you to open a classical E&M text and find me its derivation.

As I've repeated often in this section of PF, why are people using their prejudice and ignorance against QM and yet, they completely ignore the very same "problem" in other parts?

Zz.

[ZapperZ]

I see your point of view : nobody knows where QM comes from.

The principles of QM cannot be derived. Yet the wave equation can be derived. Schrodinger equation can be obtained from the classical hamiltonian by using the operator representations for p and E. In turn, those can be derived in the Hilbert space. The only thing you must postulate can be for instance the correspondance between the classical Poisson bracket, and the commutation rules in QM.

Can classical mechanics be demonstrated as well ?

That is incorrect. We KNOW where QM comes from. We know where a lot of physics came from. We however have no explanation for why certain things are that way. Physics are not meant to explain. Our understanding of our world is based on our ability to describe with accuracy how things behave.

Unlike people who work in other areas of our society who have no qualms in giving reasons (sometimes with alarming certainty that they are right) why certain things occur, we can only go by what we can test and verify. We dare not go beyond that by offering things that we simply have no business in saying. That is not a weakness, but the strength of physics and well-defined sciences that is unmatched in other areas of study. The fact that something WORKS seems to be sniffed and trivialized at.

When I used to teach intro physics in college many years ago, I came in the first day and wrote on the board "Conservation of Energy (or mass/energy)" and "Conservation of momentum (both linear and angular)".

I then told the students that throughout their undergraduate career, EVERYTHING they will be studying are nothing more than various manifestations of those two principles. Think about it. All the things you will be studying in undergraduate classical mechanics, E&M, QM, Thermo, etc, etc., are nothing more than various manifestation of those two principles!

Now, if you have learn anything about Noether theorem, you would know that for every conservation law, there is a corresponding symmetry principle behind it. So the conservation law is nothing more than a manifestation of that symmetry. The two conservation laws I mentioned above are directly due to the time-symmetry of our physical universe and the translation symmetry/isotropic nature of classical empty space.

These two symmetry principles are NOT DERIVABLE! They are just the way our universe is! These, in fact, are our starting postulates for almost all of our physical description of our universe! [I'll smack anyone with a large boson who brings up the CP violation in some weak decay events :)]

Again, this is why physics is physics and NOT mathematics. One should not confuse between the two and then think that it is why QM, for example, has a problem.

Zz.

[bd1976]

Can classical mechanics be demonstrated as well ?

The problem with these questions is that your talking about pretty deep stuff. I'm fairly sure that I don't have any of the qualifications needed to answer this question but I'll give it a go in the hope of being corrected by someone wiser.

I think the problem is that theories in physics do not (as I think most people believe) attempt to explain the natural world. A physical theory is really just a set mathematical relationships between measurable physical quantities from which predictions can be made. To explain this considers Newtonian mechanics.
Basically here the fundamental concept is that objects interact via forces. The theory then goes on to say that force is related to the rate of change of velocity via the equation f = ma. Now the theory was wildly successful accurately predicting the motion of projectiles, rockets even the planets. However for all that, Newtonian mechanics says nothing about what a force actually is.. how it acts, or what mass actually is! It doesn't explain these things at all. Physics has to start with some principle concepts which can not be derived.
However Newtonian mechanics makes sense conceptually. I think its easy to grasp the concept of force and acceleration because we feel these things all the time in the real world. Also Newtonian mechanics produces real, testable predictions. Quantum mechanics is different because it just doesn't make the same kind of sense conceptually. First of all the fundamental equation arises by an indirect inductive argument and the theory makes no actual predictions rather it can only generate probabilities. And also there’s all the stuff about the collapse of the wave function etc... Suffice it to say Einstein didn’t like quantum mechanics and that’s a good enough reason to think it’s dodgy for me!

(p.s Thinking about that stuff seriously tested by brain and I’m sure it’s probably all very dodgy.)

[bd1976]

oops.. I think I already was corrected by someone wiser! :smile:

[ZapperZ]

oops.. I think I already was corrected by someone wiser! :smile:

No, bd. I think it is a plus to have someone else that also presents the same idea. It indicates that I'm not making this up as I go along. :)

However, as far as Einstein goes, his opposition was based on TASTES, not on any concrete observations. We need to clearly distinguish between an opposition to the INTERPRETATION versus FORMALISM. If you have a phenomenon, and that phenomenon violates the prediction of a theory, that is a problem with the FORMALISM. If you simply say "I don't like the way it looks", then you are challenging something not on solid evidence but on purely a matter of personal preference and taste. This is NOT a valid challenge in physics.

Furthermore, Einstein NEVER said QM was wrong. He had problems with the Copenhagen Interpretation of QM, and based on that, he stated that QM must be "incomplete", the same way classical mechanics is incomplete or an approximation of a more general relativistic theory.

Zz.

[bd1976]

Well. (Better make this quick seeing as I'm only just keeping my head above the water here) No one is going to disagree with the fact the fact that quantum mechainics is a succesful theory in that it dosen't make any predictions that do not fit the observed facts. However I am not alone (or at least I very much hope im not alone :cry: ) in thinking that quantum mechanics as it stands contains some real conceptual problems. For example the only things in the theory that have real world counter parts are measurements. However no one can really say what a quantum mechanical measurement is, or exactly how it affects the wavefunction which in turn dosen't exist physically yet.... arrggg. *brain gives out*

Well anyway suffice it to say that quantum mechanics is differen't to the other physical theories in that, the principle object, "the wavefunction" has no physical significance. I think that the conceptual problems with the theory are so extensive that they point to something being incorrect or something missing from the theory itself.

p.s On a completely differn't note. One thing that I did get from my courses was a sense of depression about physics. It seems that the only real way for physics to advance is for a phenonomen to be discovered that is not currently explained by any theory. However it seems that dispite an ever increasing amount of science we are no closer to finding such a phenonomen than we were 50 years ago! What if such a thing is never found? There's a depressing thought. Hummanity could be stuck at its present level of understanding forever! :eek:

[metacristi]

The schroedinger equation is an inspired postulate - it cannot be derived
from fundamental principles.The pilot wave of David Bohm's version of quantum mechanics is also postulated.Has anyone tried to derive the
pilot wave and schroedinger equation from physical laws?

Well loosely speaking we are entitled to say that Schrodinger's equation is 'invented' (this terminology is widely used in the philosophy of science by the way) though from a strictly logical perspective it can still be deduced from the hamiltonian.But 'derivation' is not the most appropriate term to use here rather Schrodinger equation is equivalent with the equation of the quantum hamiltonian H which is constructed,invented,using an analogy with the classical situation.As about Bohm's equation it is the mere Schrodinger equation but rewritten in a form ressembling classical physics (having an extra term,the so called 'quantum potential').

[Rothiemurchus]

Max Born guessed that the wavefunction amplitude squared was proportional to the probability of finding a particle at a point in space.This guess works but it is not known why.If there is anything about QM that I would like clarified it is why Born's guess works.I prefer Bohm's pilot wave because it is a physical entity that moves particles around.

[marlon]

This idea was adopted from the theory of waves, i think. There you have that the squared amplitudo of the waves yields the intensity. Now in terms of particles one can say that intensity is equal to the number of particles that pass through a surface each second for example...

Once the concept of wave-function was constructed , the idea of intensity was used as the probability of finding a particle on a certain position.

Think also of the double-slit-experiment where the describing theory needed the concept interference of waves in order to fit the measured probabilities of finding a particle when both slits are open !!!

regards
marlon

[ZapperZ]

Well. (Better make this quick seeing as I'm only just keeping my head above the water here) No one is going to disagree with the fact the fact that quantum mechainics is a succesful theory in that it dosen't make any predictions that do not fit the observed facts. However I am not alone (or at least I very much hope im not alone :cry: ) in thinking that quantum mechanics as it stands contains some real conceptual problems. For example the only things in the theory that have real world counter parts are measurements. However no one can really say what a quantum mechanical measurement is, or exactly how it affects the wavefunction which in turn dosen't exist physically yet.... arrggg. *brain gives out*

Well anyway suffice it to say that quantum mechanics is differen't to the other physical theories in that, the principle object, "the wavefunction" has no physical significance. I think that the conceptual problems with the theory are so extensive that they point to something being incorrect or something missing from the theory itself.

Again, this is an objection based on a matter of tastes.

Secondly, when you say something is "conceptually difficult", what does that mean? I know of MANY things which I found to be "conceptually difficult" to comprehend until I actually learned about those things. Then they became conceptually easy to understand! Are we basing it on intuition? If so, then this isn't a valid foundation to use since our intuition changes with our accumulated knowledge! So when you say something is conceptually difficult, how would you know the problem isn't with you or your understanding of it?

Again, this is something that most people either seem to overlook, or dismiss. There has been ZERO experimental observation so far that is inconsistent with QM. Now think about it for a minute. Of all the humongous number of experiments going on throughout the world, we have ZERO experimental observation that is inconsistent with QM. Regardless of anyone's level of education, this has GOT to be an astounding fact! If this does not convince anyone that there is something to QM, then nothing can. People have believed in things with significantly less convincing body of evidence than this!

There is, however, another issue involved here, and that is the a priori belief that our classical notion MUST work everywhere. The "conceptual problem" that you talked about are based on your insistance that things that you accept to be true in the classical sense, such as "position", "momentum", "wave", "particle", etc. MUST all still be true even at the sub-atomic scale. I would assert that THAT point of view is very narrow and prejudicial. I think it is highly arrogant of us to want to force nature to fit within our comfort level. Whether the CI version of QM is valid or not isn't the issue here. Rather, it is our unwillingness to realize that our cherished notion of the classical world may not be valid beyond a certain extent, inspite of the huge number of experimental evidence staring us in our face. I find this more troublesome than the "conceptual problem" of QM.

As far as Bohm's pilot wave formulation of QM, I have mentioned this before in another thread, but anyone who professes to be a fan of such a formulation seem to have swept under the carpet the zoo of problems that come with such formulation. This includes the still troubling inability to formulate a correct QFT-like formalism (meaning no creation/desctruction of particles) and the fact that the first attempt to do that resulted in a non-lorentz invariant form! Is this "conceptually easier" to accept?!

Zz.

[Rothiemurchus]

ZAPPER Z:
Again, this is something that most people either seem to overlook, or dismiss. There has been ZERO experimental observation so far that is inconsistent with QM. Now think about it for a minute. Of all the humongous number of experiments going on throughout the world, we have ZERO experimental observation that is inconsistent with QM. Regardless of anyone's level of education, this has GOT to be an astounding fact! If this does not convince anyone that there is something to QM, then nothing can. People have believed in things with significantly less convincing body of evidence than this!

Rothie M:
I don't doubt for a second that the maths of QM is right because the evidence for it being right is overwhelming.

ZAPPER Z:
As far as Bohm's pilot wave formulation of QM, I have mentioned this before in another thread, but anyone who professes to be a fan of such a formulation seem to have swept under the carpet the zoo of problems that come with such formulation. This includes the still troubling inability to formulate a correct QFT-like formalism (meaning no creation/desctruction of particles) and the fact that the first attempt to do that resulted in a non-lorentz invariant form! Is this "conceptually easier" to accept?!

Rothie M:
Bohm's theory might be Lorentz invariant if the pilot wave was made classical .
The current situation is that the pilot wave can change instantaneously along its length - that does not
go well with general relativity.Perhaps gravity will be quantized successfully when qft for a modified Bohmian QM is sorted.

[humanino]

gravity could not be quantized successfully until qft for Bohmian QM is sorted
I must say I disagree with such a statement. QM is perfectly fine the way it is right now. The axioms are well-defined, and only interpretation is debatable. Besides, loop quantum gravity could be about quantisizing gravity soon, without changing any thing to QM.

Do you really use QM everyday in your calculations ? Because if so, I do not understand where your problem with QM comes from. If you do not use QM, maybe that is the problem.

[Rothiemurchus]

Humanino:
QM is perfectly fine the way it is right now

Rothie M:
I will agree with you when gravity is quantized using standard qft!
Until then there could be a problem with standard QM. Bohmian QM definitely has problems but less work is done on Bohm's theory and solving the problems with that might be the way forward for quantizing gravity.I used to use QM every day in calculations - I don't doubt that it works for just about all practical purposes.
But gravity could be the downfall for standard QM.And bear in mind that Bohm's version of QM gives the same predictions as standard QM.

[Rothiemurchus]

There is a thread I opened on sci.physics.research about "solitons and water waves"
which has a link to the use of the Schrodinger equation in showing how water waves
take energy from one another.Apparently nobody thought the equation would work on this scale.There's not a lot of detail but I think you'll find the thread as a whole interesting.

[humanino]

I will agree with you when gravity is quantized using standard qft!

That is certainly not going to happen !!!
QM & QFT are two things. We know QFT failed with regard to gravity. Still QM must and will hold. You are confusing.

[humanino]

What you don't realize is that QM is a framwork much more general than when applied to a particular field. All the relevant theories attempting to quantize gravity today are very close to success, and none of them ever even tried to change QM. They have to fit in it. Don't tell me that is the reason why they did not successeded yet.

[Rothiemurchus]

The addition of a quantized electromagnetic field to Dirac's theory is qft isn't it?
And isn't Dirac's theory standard QM plus rest mass?

[humanino]

No it is not.

[humanino]

Dirac theory emerge from an attempt to have a relativistic Schrodinger equation, that is describe a (EM) chargeless particle respecting the Klein-Gordon equation, but without the plague of negative probability. You can have a classical Dirac equation, and then quantisize it.

[humanino]

The addition of a quantized electromagnetic field to Dirac's theory is qft isn't it?

It is a QFT. The formalism applies to any field.

[Rothiemurchus]

I should have said rest energy , mc^2.

Marlon:
Once the concept of wave-function was constructed , the idea of intensity was used as the probability of finding a particle on a certain position.

Rothie M:

A water wave would have a greater amount of mass, at one single space co-ordinate (e.g an x co-ordinate), for a bigger wave amplitude.
Can't the wavefunction be like this in reality - can't it represent a lot of particles that exist together simultaneously?
Perhaps an electron likes to surf on these waves - the higher waves
attracting it the most?

[humanino]

But the Schrodinger equation has a mass parameter ! Even : you cannot apply the Schrodinger equation to a massless particle, which is relativist, since the mass term is in a denominator !

[humanino]

The problem was to respect the Klein-Gordon p^2+m^2=E^2

tex is not working girht now !?

[nrqed]

The schroedinger equation is an inspired postulate - it cannot be derived







I agree with you.

Well, it's true that the Schroedinger equation can be "derived" from other considerations but whenever you trace back the steps, you always end up at a point which is an educated (clever) guess. Some start from postulating the quantum brackets starting from classical Poisson brackets, some start from directly replaing E and p by operators acting on this (weird and nonclassical) wavefunction, etc. But there is always an educated guess at the beginning. Quantum mechanics cannot be derived from classical physics so it absolutely require some smart guessing. Of course, it works great so that makes the guess very convincing.

But F=m a could also be said to be an educated guess. As are all fundamental principles of physics. There's nothing wrong with this.

Pat

[humanino]

Rothiemurchus : there is plenty of literature on the web, especially here on this site.
Again :
Please follow Zz advice. Otherwise this site would grow indecently. Use the search function. You cannot search more than once in 5 minutes.

[humanino]

This discussion is becoming ridiculous. Are you guys flattering your ego or what ? You seem not even to listen to the precious informations Zz gave you. This is not fair.

[humanino]

But F=m a could also be said to be an educated guess. As are all fundamental principles of physics.
Pat this is simply wrong ! The law of attraction is an educated guess. F = m a is merely a definition of what a force is !

[marlon]

But gravity could be the downfall for standard QM..

That is very untrue for the simple reason that QM is not trying to describe gravity. Gravitational effects are not included in QM and even the QFT from the Standard Model because at the atomic scale, they are negligible...

regards
marlon

[marlon]

Pat this is simply wrong ! The law of attraction is an educated guess. F = m a is merely a definition of what a force is !

I agree with Humanino.
Just look at history : how did Newton come up with the connection between F and a ??? He just found out experimantally that F = ma, he did not guess this...

regards
marlon

ps : also, indeed I think this discussion is more about personal opinions and so on...Let's stick to the facts QM is the best theory for atomic scaled-events, backed up by many many experimental evidence...POINT FINAL

regards
marlon

[Haelfix]

You know, a lot of this depends on how you want to axiomatize your system. Non relativistic Quantum mechanics does have a rigorous mathematical interpretation that is self consistent, but I does not start from the Schroedinger equation right from the get go, or indeed even where the paper in post #2 starts from.

Von Neumann's text is probably where you want to start.. But ultimately, its the nice properties of the the Wiener measure that makes things work out.

There are still mysteries though, particularly when you jump into relativistic material. There you have to axiomatize completely differently, and in a non intuitive way, in order to have any hope for progress.... And unfortunately, there is still a lot that needs to be done, it is by no means a full theory yet.

I mean, I could just as well take as a postulate that classical Hamiltonian mechanics is correct.. And then, indeed, I can *derive* Newtonian physics as an isomorphism between theories.

[Rothiemurchus]

Marlon:
That is very untrue for the simple reason that QM is not trying to describe gravity.

Rothie M:

In the real world all physical processes take place in the presence of gravity -
qm must depend on gravity and therefore in some sense describe it (gravity can be put into the potential energy term of the schrodinger equation but because it is very weak compared to EM it is not, but that does not describe reality - just a useful approximation to it).

Humanino:
But the Schrodinger equation has a mass parameter ! Even : you cannot apply the Schrodinger equation to a massless particle, which is relativist, since the mass term is in a denominator !

Rothie M:
You are talking about an infinity here?
But even a photon might have a small mass - people are trying to
determine what it is.



I would like to emphasize that the only problem I have with QM is that nobody has ever justified squaring the amplitude of the wavefunction to get a probability.
There could be something fundamental underlying why this is the right thing to do.

Using the rubber sheet analogy for spacetime in GR:
If I stretch the sheet it would gain potential energy.
Could the Schrodinger wavefunction be a measure of the amplitude of the stretching
of spacetime with an electron most likely to be where the stretching is greatest
(which for a hydrogen atom would be close to the proton at 0.52 Angstroms).

[nrqed]

Pat this is simply wrong ! The law of attraction is an educated guess. F = m a is merely a definition of what a force is !

Yes, I agree with you. My mistake.

Pat

[nrqed]

I agree with Humanino.
Just look at history : how did Newton come up with the connection between F and a ??? He just found out experimantally that F = ma, he did not guess this...


I agree with Humanino too and just posted something saying so. But I am surprised by your statement that Newton found F=ma experimentally. I'd love to see something more specific about this (what experiment did he actually use? What was his reasoning?)




ps : also, indeed I think this discussion is more about personal opinions and so on...Let's stick to the facts QM is the best theory for atomic scaled-events, backed up by many many experimental evidence...POINT FINAL


To a certain extent, it's true that there is some subjectivity. It does not mean that it is not a useful and worthwhile line of discussion. Of course, we could all follow the "shut up and calculate" approach but I don't think that's a good attitude. It's good that Einstein did not have this attitude. Or Bell or Feynman etc etc.
Pat

[nrqed]

You know, a lot of this depends on how you want to axiomatize your system. Non relativistic Quantum mechanics does have a rigorous mathematical interpretation that is self consistent, but I does not start from the Schroedinger equation right from the get go, or indeed even where the paper in post #2 starts from.

Von Neumann's text is probably where you want to start.. But ultimately, its the nice properties of the the Wiener measure that makes things work out.

There are still mysteries though, particularly when you jump into relativistic material. There you have to axiomatize completely differently, and in a non intuitive way, in order to have any hope for progress.... And unfortunately, there is still a lot that needs to be done, it is by no means a full theory yet.

I mean, I could just as well take as a postulate that classical Hamiltonian mechanics is correct.. And then, indeed, I can *derive* Newtonian physics as an isomorphism between theories.


Very true and very interesting. Thanks for your input.

Regards

Pat

[ZapperZ]

Marlon:
That is very untrue for the simple reason that QM is not trying to describe gravity.

Rothie M:

In the real world all physical processes take place in the presence of gravity -
qm must depend on gravity and therefore in some sense describe it (gravity can be put into the potential energy term of the schrodinger equation but because it is very weak compared to EM it is not, but that does not describe reality - just a useful approximation to it).

Take note that the quantum effects of gravity HAS been verified for at least a couple of years already![1]

Humanino:
But the Schrodinger equation has a mass parameter ! Even : you cannot apply the Schrodinger equation to a massless particle, which is relativist, since the mass term is in a denominator !

Rothie M:
You are talking about an infinity here?
But even a photon might have a small mass - people are trying to
determine what it is.



I would like to emphasize that the only problem I have with QM is that nobody has ever justified squaring the amplitude of the wavefunction to get a probability.
There could be something fundamental underlying why this is the right thing to do.

Using the rubber sheet analogy for spacetime in GR:
If I stretch the sheet it would gain potential energy.
Could the Schrodinger wavefunction be a measure of the amplitude of the stretching
of spacetime with an electron most likely to be where the stretching is greatest
(which for a hydrogen atom would be close to the proton at 0.52 Angstroms).

This is where I clearly said early in this thread that QM has a set of postulates.[2] Most of these postulates assign a PHYSICAL meaning to certain mathematical operations! However, it is incorrect to think that the wavefunction as a real, physical wave. This is one of the most popular misconception of QM. Other than the fact that the wavefunction itself is complex, the wavefunction sits in a "configuration space", not in real space (except for a single-particle special case).

This hypothesis of assigning a part of the wavefunction to the location of an electron borders on an unverified personal theory. Unless we be careful, that will cause this whole thread to be dumped into the Theory Development section, which will end my participation (that may not be such a bad thing to some people).

Zz.

[1] V.V. Nesvizhevsky et al., Nature v.415, p.297 (2002).
[2] http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/qm.html

[humanino]

Rothie M:
You are talking about an infinity here?
But even a photon might have a small mass - people are trying to
determine what it is.

I am not talking about infinity.

There are not many things we know with such an accuracy as the vanishing of the photon mass. Who is seriously trying to show that it is non-zero ? QED relies on a gauge theory which is not broken and for which the mass of the boson is zero. For all purpose the mass of the real photon is experimentally and theoretically zero in physics today.

Of course, something very nice about this mass, is that although introducing a mass term spoils the gauge invariance, you can still do it in the calcultaions and set it to zero in the end of the day. There are non-trivial reasons for the gauge invariance to be recovered.

We are not having a very constructive discussion here. All of us agree on the fact that QM is mysterious at some point, when you think about it. Yet it is working perfectly fine. All the rest is speculations so far unfortunately. I wish thise speculations could lead somewhere.

[vanesch]

But I am surprised by your statement that Newton found F=ma experimentally. I'd love to see something more specific about this (what experiment did he actually use? What was his reasoning?)


He used an apple tree :rofl: :rofl:
His reasoning went like "aaauw" :tongue:

cheers,
patrick.

[nrqed]

He used an apple tree :rofl: :rofl:
His reasoning went like "aaauw" :tongue:

cheers,
patrick.

:biggrin: You are right but that's the "experiment" he used to discover the universal law of gravitation, not F=ma....

Pat

[Rothiemurchus]

Humanino:
We are not having a very constructive discussion here. All of us agree on the fact that QM is mysterious at some point, when you think about it. Yet it is working perfectly fine.

Rothie M:
Yes it works fine.But perhaps finding out why it works could be a useful thing to know.

ZAPPER Z:
it is incorrect to think that the wavefunction as a real, physical wave. This is one of the most popular misconception of QM. Other than the fact that the wavefunction itself is complex, the wavefunction sits in a "configuration space", not in real space (except for a single-particle special case).

Rothie M:
In Bohm's theory it is not incorrect to think of the pilot wave as a physical wave.

The magnitude of the wavefunction squared in standard qm is real even if the wavefunction itself is complex.This is of interest because in the analogy with the intensity of a light wave both the amplitude squared and the amplitude are real numbers.The analogy isn't that good is it?

[bd1976]

Again, this is an objection based on a matter of tastes.

Secondly, when you say something is "conceptually difficult", what does that mean? I know of MANY things which I found to be "conceptually difficult" to comprehend until I actually learned about those things. Then they became conceptually easy to understand! Are we basing it on intuition? If so, then this isn't a valid foundation to use since our intuition changes with our accumulated knowledge! So when you say something is conceptually difficult, how would you know the problem isn't with you or your understanding of it?

First of all I think that quantum mechanics as a theory is fundamentally different to other physical theories. Yes its true that sometime you gain knowledge ideas become easier to understand, however I think that qm is an example of completely the opposite the more knowledge you gain the more challenging the conceptual problems become. I'm sure there’s a quote from Schrödinger that goes something like - anyone who claims to have understood qm hasn't understood it at all!

First of all there's the problem of measurement. QM is a theory based around "measurements". However what a "measurement" actually is not understood!

Secondly there is the problem of instantaneous information exchange - violating the principle of relativity! Now since there is no experiment which can preformed that violates relativity it has to be said that such a conflict is a serious cause for alarm.

Finally there is the problem of complex numbers. Now don't get me wrong complex number theory is (in my humble opinion) the most beautiful piece of mathematics I have ever encountered. However that doesn't get over the "pie" problem. Integers are whole pies, rational numbers allow for slices of pies.. but what is a complex pie? The answer is that there is no such thing! Complex numbers have no physical correspondence. So here we have a theory where the main object - "the wave-function" has no physical meaning at all and that does separate qm from the other theories in physics.

Please address any comments on complex numbers inthis thread (http://www.physicsforums.com/showthread.php?t=44648) Integral

[humanino]

You guys are addressing here questions which we would like to have an answer to. So please, discuss here and find it. I don't have it. In the meantime, if you could find a simple geometrical TOE, don't hesitate, I'd be glad too. Ho, and elixir of long life would be fine as well.

[ZapperZ]

First of all there's the problem of measurement. QM is a theory based around "measurements". However what a "measurement" actually is not understood!

But we CONTINUE to study it. However, this doesn't detract from the validity of QM because it only states what CAN be measured. The mechanism of a measurement (if there is any) is part of something QM can't say unless one has a clear definition and idea of what to look for. QM can't make up things out of the air simply to satisfy something that may or may not be there.

And lest we ignore one important thing: there is ALSO a measurement problem in classical mechanics. Think about it. What you measure will depend on how accurately you measure it. At some point, the accuracy of your measurement will bump into the quantum regime. If you don't believe me, look at the diffraction from a single slit. It only APPEARS that what you measured gave you a "good" value because of the coarseness of your measurement.

Secondly there is the problem of instantaneous information exchange - violating the principle of relativity! Now since there is no experiment which can preformed that violates relativity it has to be said that such a conflict is a serious cause for alarm.

Strangely enough, EVERYONE who works in the field that does this EPR-type study, finds no such alarm. This is because for there to be a violation of SR, there has to be a TRANSFER of information via a continuous displacement over space from one location to another. QM indicates that there is no such thing! There is no info flowing from one location to another in an entanglement measurement. If there is, wouldn't you think this is widely mentioned in physics journals already and highly debated, considering this would cause two MAJOR physics principles (Relativity and QM) to be at odds with each other? If you read ALL the EPR-type papers, be it theoretical or experimental (any paper by Anton Zeilinger would suffice), in NONE of them are there any claims of superluminal transfer of information.

Finally there is the problem of complex numbers. Now don't get me wrong complex number theory is (in my humble opinion) the most beautiful piece of mathematics I have ever encountered. However that doesn't get over the "pie" problem. Integers are whole pies, rational numbers allow for slices of pies.. but what is a complex pie? The answer is that there is no such thing! Complex numbers have no physical correspondence. So here we have a theory where the main object - "the wave-function" has no physical meaning at all and that does separate qm from the other theories in physics.

Then you must also have major problems in accepting electrical engineering, classical E&M, etc. So why are we picking on QM alone?

Zz.

[nrqed]

....
Strangely enough, EVERYONE who works in the field that does this EPR-type study, finds no such alarm. This is because for there to be a violation of SR, there has to be a TRANSFER of information via a continuous displacement over space from one location to another. QM indicates that there is no such thing! There is no info flowing from one location to another in an entanglement measurement. If there is, wouldn't you think this is widely mentioned in physics journals already and highly debated, considering this would cause two MAJOR physics principles (Relativity and QM) to be at odds with each other? If you read ALL the EPR-type papers, be it theoretical or experimental (any paper by Anton Zeilinger would suffice), in NONE of them are there any claims of superluminal transfer of information.


Zz.



First, let me thank you for your input in this thread.

I agree with what you are saying, but I must still admit that I do feel very uneasy about this entanglement stuff. I know that no information, in the ordinary sense, is transfered, but still there *is* a correlation between the measurements. I know that my position is not a popular one among physicists but I am deeply dissatisfied with the conventional point of view that there is nothing bothersome there and that if one is wondering about whether "something" is exchanged (maybe in some way that would require a rethinking of spacetime), then that person either does not understand the formalism or is a crackpot.



I guess that maybe we should simply say "our formalism is consistent and it agrees with experiments so let's just accept that our comprehension has reached its limits (as opposed to our ability to do calculations) and let's stop asking certain types of questions". But it's hard for me to accept. These EPR type experiments are, imho, the most intriguing and mind blowing aspects of modern physics and I am suprised that most physicists just go "that's neat and strange but we "understand" what's going on, it's all in the formalism. let's move on to other things". I, on the other hand, can't help feeling that I am missing something. That's there something more to the story. Of course, I am not saying that I'll be coming up with a new revolutionary theory, I am just saying that I find it amazing how other people find it easy to accept this aspect of the theory.


Regards,

Pat


(PS:In his book on QFT, Weinberg defines the cluster decomposition principle as the principle that says that "distant experiments yield uncorrelated results. " Well, one should probably define more clearly what "uncorrelated results" means but it would seem that Bell type experiments would violate this principle!)

[vanesch]

I, on the other hand, can't help feeling that I am missing something. That's there something more to the story. Of course, I am not saying that I'll be coming up with a new revolutionary theory, I am just saying that I find it amazing how other people find it easy to accept this aspect of the theory.


I have exactly the same feeling. In fact, I came to a peace of mind with this by considering very seriously solipsism.
(look at http://www.iep.utm.edu/s/solipsis.htm)

I cannot help but relate the quantum measurement problem to the hard problem of consciousness. I discussed this a while ago in the philosophy forum.

However, I don't take myself very seriously there :-)

cheers,
Patrick.

[humanino]

So according to solipsism, I am the cause of all those annoying people in my neighborhood. :bugeye: I must be pretty masochist :rolleyes:

... sorry :shy:

[vanesch]

So according to solipsism, I am the cause of all those annoying people in my neighborhood. :bugeye: I must be pretty masochist

It doesn't matter. You don't even exist :rofl: :rofl:

cheers,
patrick.

[humanino]

Yourself ! :mad:

:rofl: :rofl:

[Rothiemurchus]

nrqed:
These EPR type experiments are, imho, the most intriguing and mind blowing aspects of modern physics and I am suprised that most physicists just go "that's neat and strange but we "understand" what's going on,

Rothie M:

Einstein certainly thought that instantaneous action at a distance was a problem.
I think most physicists would be delighted if it is shown that a signal can travel faster than light because it would make the world more interesting and it would restore causality to it.

[bd1976]

I think most physicists would be delighted if it is shown that a signal can travel faster than light because it would make the world more interesting and it would restore causality to it.

I for one very much like the idea that the universe can not be understood. One of the quantum principles is that our knowedege of the universe will always be limited and I think thats strangely appealing. We are not God and shouldn't believe that we can ever approach the divine! (sounds catchy hey!)

Anyway can someone have a crack at explaining why quantum mechanics is more dodgy fundamentally than say classical E.M. I have thought a bit about it but I'm worried that if I am the first one to put my toe in the water I might be the who is drowned! :tongue2:

[humanino]

QM is a framework. It defines a general formalism into which observable are operators. EM is a physical interaction. As other interactions, when requiring a high accuracy or more precisely when dealing with phenomena involving a small action, it must conform to QM.

[nrqed]

I for one very much like the idea that the universe can not be understood. One of the quantum principles is that our knowedege of the universe will always be limited and I think thats strangely appealing. We are not God and shouldn't believe that we can ever approach the divine! (sounds catchy hey!)


The thing is that up until now, this has never been the correct approach. I mean what if Newton had said "well, there are these Kepler laws and maybe we can not understand them, we have reached the limit of our comprehension so let's just accept them as empirical laws. That's the way Nature is. They work well and that's all we should care about"

Instead he went "I'm sure I can figure this out".... and he did, to a certain extent.

We could repeat this pattern for many major discoveries. And so on.

So why somehow should we reach this point now and say "we can't understand this correlation business. That's just the way things are. It works well and that's all that matters" ?

Maybe QM is the end of the road. Maybe QM is fundamental the way it is and we'll never uncover a deeper principle. But I would not bet on it.



Anyway can someone have a crack at explaining why quantum mechanics is more dodgy fundamentally than say classical E.M. I have thought a bit about it but I'm worried that if I am the first one to put my toe in the water I might be the who is drowned! :tongue2:


Well, classical E&M can be recovered from QED so this is clear.

But, if you are asking "why is QM fundamental", I would have to say that there is no reason to be sure of that! It might well be a kind of approximate theory to something else (maybe even more weird). Im my opinion (and that's just that, a very personal opinion), the nonlocality exhibited in Bohm-Aharonov, Bell's inequality type of experiments, which way experiments, etc are the strongest hints that we should think about some more fundamental principle. I am apparently almost alone in this :devil: . It sounds as if most people just say "well, no information (in the usual sense) is transmitted, no energy is transmitted so everything is fine. End of story. Whereas I think that a more fundamental theory would present a more clear picture of the measurement process, of the collapse of the wavefunction, etc.

But it seems that people have got so used to the weirdness of QM that it does not elicit much desire to dig deeper.

Pat

[ZapperZ]

The thing is that up until now, this has never been the correct approach. I mean what if Newton had said "well, there are these Kepler laws and maybe we can not understand them, we have reached the limit of our comprehension so let's just accept them as empirical laws. That's the way Nature is. They work well and that's all we should care about"

Instead he went "I'm sure I can figure this out".... and he did, to a certain extent.

We could repeat this pattern for many major discoveries. And so on.

So why somehow should we reach this point now and say "we can't understand this correlation business. That's just the way things are. It works well and that's all that matters" ?

Maybe QM is the end of the road. Maybe QM is fundamental the way it is and we'll never uncover a deeper principle. But I would not bet on it.




Well, classical E&M can be recovered from QED so this is clear.

But, if you are asking "why is QM fundamental", I would have to say that there is no reason to be sure of that! It might well be a kind of approximate theory to something else (maybe even more weird). Im my opinion (and that's just that, a very personal opinion), the nonlocality exhibited in Bohm-Aharonov, Bell's inequality type of experiments, which way experiments, etc are the strongest hints that we should think about some more fundamental principle. I am apparently almost alone in this :devil: . It sounds as if most people just say "well, no information (in the usual sense) is transmitted, no energy is transmitted so everything is fine. End of story. Whereas I think that a more fundamental theory would present a more clear picture of the measurement process, of the collapse of the wavefunction, etc.

But it seems that people have got so used to the weirdness of QM that it does not elicit much desire to dig deeper.

Pat

That last part is clearly incorrect. The fact that there are still experiments being done, both in testing the violation of Bell inequality up to higher sensitivity, the continuing increase in size of detecting quantum superpostion as done by SQUID experiments, and especially the study of decoherence of a quantum state into classically familiar values, all these point to the fact that the validity of QM are continually being tested. So to argue that physicists especially are satisfied or "done" with testing QM is simply absurd based on such evidence. The same can be said with the continuing tests on the various postulates of Special Relativity, including more accurate determination of the upper limit of the photon mass (if any).

However, note that in these cases, we have CONCRETE stuff to test and to measure! In none of these are we testing something vague and ambiguous such as "it doesn't feel right" or "it is conceptually difficult". To argue that QM is incomplete or incorrect because it doesn't feel or look right makes it sound as if this is a beauty contest. This is what I have been arguing against. I am NOT insisting that we stop testing and prodding QM to see if and where it might fail! Being an experimentalist, that's what I do and in the end, that is the ONLY thing that will convince me one way or the other.

Zz.

[vanesch]

To argue that QM is incomplete or incorrect because it doesn't feel or look right makes it sound as if this is a beauty contest. This is what I have been arguing against.

Well, although I agree of course that the final judge is and should be experiment, using beauty contest arguments in order to find inspiration for new ideas is something that has been successfully used in the past. Dirac even went to say that he preferred a beautiful equation over a correct one :eek:

cheers,
Patrick.

[Haelfix]

Look, I think we all agree QM is correct in producing calculations and correct results, at least in the domain of validity that has been probed experimentally.

The correct interpretation however is still up in the air IMO, and there are theoretical and consistency problems with *ALL* interpretations that simply won't go away. In fact, depending on the interpretation, some things in the actual mechanics of the theory could change, so again the whole story is not known entirely.

I don't understand why some people must insist that the theory is 100% complete, its not, and indeed serious people are still working on it years after the initial formulations.

Again, I don't expect quantum mechanics to be entirely solved for quite some time still, as I suspect there are still some fundamental pieces deep down in the chain that elude us. But you know what... They *have* to be there, if we subscribe to the tenets of logic.

[Rothiemurchus]

NRQED:

Im my opinion (and that's just that, a very personal opinion), the nonlocality exhibited in Bohm-Aharonov...

Rothie M:

It is Bohm-Aharonov that convinces me that there is a significant piece of
a jigsaw to be found.The results of toroid experiments could be due to some kind of particles passing through the toroid material and then interacting with electrons and changing the phase of electron interference patterns.
We know that at least 95 per cent of the mass of the universe is unaccounted for,so this is not such an unreasonable proposition.

[ZapperZ]

Well, although I agree of course that the final judge is and should be experiment, using beauty contest arguments in order to find inspiration for new ideas is something that has been successfully used in the past. Dirac even went to say that he preferred a beautiful equation over a correct one :eek:

cheers,
Patrick.

But you also have to admit that what Dirac and Einstein termed to be "beautiful" is distinctly different than what is being used within the context of this thread here. Logical consistency of a theory is beautiful. I find QM that is filled with that! However, as you said, this also cannot be the definitive "proof" that such a theory is valid. There are many gorgeous idea and theories that went nowhere.

Zz.

[humanino]

Evo's signature lastly :
"The great tragedy of Science - the slaying of a beautiful hypothesis by an ugly fact." - Thomas H. Huxley

[nrqed]

That last part is clearly incorrect. The fact that there are still experiments being done, both in testing the violation of Bell inequality up to higher sensitivity, the continuing increase in size of detecting quantum superpostion as done by SQUID experiments, and especially the study of decoherence of a quantum state into classically familiar values, all these point to the fact that the validity of QM are continually being tested. So to argue that physicists especially are satisfied or "done" with testing QM is simply absurd based on such evidence. The same can be said with the continuing tests on the various postulates of Special Relativity, including more accurate determination of the upper limit of the photon mass (if any).


Thanks for your feedback.

I never meant to imply that people are not testing QM anymore!! I was talking about the *conceptual* foundations of the theory. See below please.


However, note that in these cases, we have CONCRETE stuff to test and to measure! In none of these are we testing something vague and ambiguous such as "it doesn't feel right" or "it is conceptually difficult". To argue that QM is incomplete or incorrect because it doesn't feel or look right makes it sound as if this is a beauty contest. This is what I have been arguing against. I am NOT insisting that we stop testing and prodding QM to see if and where it might fail! Being an experimentalist, that's what I do and in the end, that is the ONLY thing that will convince me one way or the other.

Zz.


I think this is where we might have different points of view. To paraphrase, you are saying that if a theory is mathematically consistent, the only worthwhile questions to focus on are the things that can be tested experimentally. All other considerations are vague, ambiguous and a waste of time.

That's where I would disagree. I think that even though it is indeed vague and somewhat ambiguous, being guided by notions of "beauty", "naturalness" etc is still a worthwhile direction. In other words, you would probably say: unless there is an internal mathematical inconsistency in a theory (this is still subjective since it assumes that the mathematics we have developped are appropriate to undertsand the universe!! But I digress), or unless there is an experiment disproving a theory, then we should not waste our time trying to undercover something deeper. If it ain't broke, don't fix it!



That's where I would disagree. Again, there were no experimental contradictions to Kepler's laws (at the time of Newton), so why the need to develop a theory of gravity? Only the need for something deeper that would explain in a "unified" way all three laws of planetary notion. If that's not a consideration of beauty and naturalness I don't know what is.

If I understand your point of view, you would have said: let's focus on experiments to test the validity of Kepler's laws. Let's measure the positions of the planets with ever increasing precision. Talking about new principles without experimental discrepancies would have been misdirected. It's only when discrepancies with the Kepler's laws that you would have felt warranted the search for a new theory.

On the other hand, just the feeling that "there must be something that we are missing" was enough for Newton. And it turned out he was right.

Of course, it's not enough to simply say "I feel something's wrong". One should come up with alternatives or gedanken experiments, etc. But on such an informal forum (it's not the lanl archives, after all), I think it's at least important to say that QM might not be the final word and that people should keep thinking about what could be deeper principles. I think we should not wait for discrepancies in experimental results to consider new conceptual ideas. This is where maybe we should agree to disagree.

Maybe QM could be the final word. But I find this whole business of nonlocality and measurement very disturbing. It seems to me that it is in conflict with the entire machinery of mathematical physics we have been developping over almost 400 years. Locality is a key element of almost all of our equations, and it's easy to just say, well no information (in the conventional sense) is exchanged so there is no problem. But I still feel that that it's not a satisfactory answer. I agree, though, that it's very subjective.


So maybe we should agree to disagree. But I still think that we should not wait for experimental discrepancies to consider new physical principles.

My sincere regards

Pat

[nrqed]

Look, I think we all agree QM is correct in producing calculations and correct results, at least in the domain of validity that has been probed experimentally.

The correct interpretation however is still up in the air IMO, and there are theoretical and consistency problems with *ALL* interpretations that simply won't go away. In fact, depending on the interpretation, some things in the actual mechanics of the theory could change, so again the whole story is not known entirely.

I don't understand why some people must insist that the theory is 100% complete, its not, and indeed serious people are still working on it years after the initial formulations.

Again, I don't expect quantum mechanics to be entirely solved for quite some time still, as I suspect there are still some fundamental pieces deep down in the chain that elude us. But you know what... They *have* to be there, if we subscribe to the tenets of logic.

Thanks for your input. I totally agree with what you wrote. Especially your sentence "I suspect there are still some fundamental pieces deep down in the chain that elude us". I feel the same exactly the same way. And this is all I was trying to say in this thread.

Personally, what especially makes me feel this way is the nonlocality issue. I know that people say "no information is exchanged, no energy is transferred, so there is no problem to it. End of story".... But *there* is correlation between the measurements and either we are missing some principle that will clarify this or we have to change our understanding of the physical laws in a deeper way. For example, we would need to rewrite SR in a way that would make clear when two light-like events cannot be correlated and when they can be correlated. But people keep repeating "no energy is transferred, information in the usual sense can't be transmitted so ther is no problem"!!! And this bothers me.

Anyway, just my two cents.

I don't think I can add to the discussion anything constructive so I'll stop posting.

Thanks to all for their input!!!

Pat

[ttn]

As far as Bohm's pilot wave formulation of QM, I have mentioned this before in another thread, but anyone who professes to be a fan of such a formulation seem to have swept under the carpet the zoo of problems that come with such formulation. This includes the still troubling inability to formulate a correct QFT-like formalism (meaning no creation/desctruction of particles) and the fact that the first attempt to do that resulted in a non-lorentz invariant form! Is this "conceptually easier" to accept?!
Zz.

I don't think it is at all fair to suggest that fans of Bohm's theory "have swept under the carpet the zoo of problems that come with such formulation." In fact, if anyone is guilty of such sweeping, it is the advocates of the standard interpretation of QM. This is known to be plagued by the measurement problem, for example, yet most of the advocates of the standard interpretation simply ignore this. John Bell described the reliance of the standard interpretation on the concept of "measurement" as "unprofessionally vague and ambiguous." Why? Because the theory contains two different rules for how wave functions evolve in time, but fails to give any coherent account of when the rules apply. (The two rules are of course Schroedinger's equation and the collapse postulate.) And for a theory which claims to provide a complete description of physical reality, that is a serious problem.

It also frustrates me to hear the argument that Bohm's theory cannot be made consistent with relativity (i.e., put in a lorentz invariant form). It's true that consistency with relativity is a major issue for Bohm's theory, but it is no more and no less an issue for Bohm than for the standard interpretation of QM. After all, that standard interpretation includes a postulate about the "collapse of the wave function" which is supposed to occur instantaneously (presumably across some space-like hypersurface, though this is not typically even mentioned as an issue) when a measurement is made. So if one regards the wave function as a complete description of the physical system, the wave function collapse process evidently describes a kind of relativity-violating action at a distance no more and no less spooky than the non-local effects in Bohm's theory.

On the other hand, if one rejects the claim that the description provided by the wave function is complete, one immediately finds oneself in the company of Bohm fans and other "hidden variable theory" advocates. And since Bell proved that any experimentally viable hidden variable theory must include non-local effects, the lesson is that non-local effects must be included in any experimentally viable formulation of QM, period. Bell said this quite clearly and quite explicitly, but people seem to have a difficult time hearing and understanding him. See, for example, quant-ph/0408105 at www.arxiv.org.

One can of course say what one wants about the strange features of Bohmian mechanics. But it cannot be reasonably asserted that the advocates of that theory deliberately blind themselves to its problems. Indeed, to again cite the great John Bell (who was, by the way, the principal advocate of Bohm's theory for several decades!), it is to the great credit of Bohm's theory for bringing out in a clear way some strange features (such as non-locality) that had been inside QM all along, but which had been hidden away behind the "unprofessionally vague and ambiguous" fuzz of the standard interpretation.

[ttn]

Strangely enough, EVERYONE who works in the field that does this EPR-type study, finds no such alarm. This is because for there to be a violation of SR, there has to be a TRANSFER of information via a continuous displacement over space from one location to another. QM indicates that there is no such thing! There is no info flowing from one location to another in an entanglement measurement. If there is, wouldn't you think this is widely mentioned in physics journals already and highly debated, considering this would cause two MAJOR physics principles (Relativity and QM) to be at odds with each other? <snip>
Zz.

Ummm, does John Bell count as someone "who works in the field that does this EPR-type study"? Because he DEFINITELY found the kind of alarm you refer to here, namely, a reason to worry that the non-locality of quantum theory was in conflict with relativity. Here are his words:

"For me then this is the real problem with quantum theory: the apparently essential conflict between any sharp formulation and fundamental relativity. That is to say, we have an apparent incompatibility, at the deepest level, between the two fundamental pillars of contemporary theory..." (from J.S. Bell, "Speakable and Unspeakable...", page 172.)

Note also that it represents a confusion to discuss "information transfer" in this context. Do we really want to commit to the idea that the only thing relativity says can't go faster than light is "information"? For one thing, this would make orthodox QM and Bohmian mechanics equally consistent with relativity. For another thing, what the heck is "information"? Whose information, and information about what? Put bluntly, "information" is just not the kind of "stuff" that relativity or any other physical theory ought to be talking about. It is just way too mental. At least, that's what most of the people who have scrutinized these questions carefully believe.

At this point, it probably won't surprise anyone that Bell was among these careful scrutinizers:

"Do we then have to fall back on 'no signaling faster than light' as the expression of the fundamental causal structure of contemporary physics? That is hard for me to accept. ...the 'no signaling' notion rests on concepts which are desperately vague, or vaguely applicable. The assertion 'we cannot signal faster than light' immediately provokes the question:

Who do [I]we think we are?

We who can make 'measurements', we who can manipulate 'external fields', we who can 'signal' at all, even if not faster than light? Do we include chemists, or only physicists, plants, or only animals, pocket calculators, or only mainframe computers?" (from Bell's article "La Nouvelle Cuisine", reprinted in the 2nd edition of "Speakable and Unspeakable...")

[vanesch]

Who do we think we are?

We who can make 'measurements', we who can manipulate 'external fields', we who can 'signal' at all, even if not faster than light? Do we include chemists, or only physicists, plants, or only animals, pocket calculators, or only mainframe computers?" (from Bell's article "La Nouvelle Cuisine", reprinted in the 2nd edition of "Speakable and Unspeakable...")

This is indeed exactly the kind of reasoning that lead me (only half jokingly) to say that QM with the projection postulate leads to a kind of solipsism. The only "measurement" that is undeniable and necessary is my conscious observation. Only mine, because I'm not sure whether yours gives rise to a true measurement or simply a decoherence, in the same way as I'm not sure a measurement device has applied the projection postulate or is just correlated with the environment in such a way that when *I* observe it, it collapses into a state which has a recorded history compatible with the Born rule.
So the only true, necessary "collapse of the wave function" is introduced by my consciousness.
The problem with the above statements is that it will for sure trigger reactions such as: "come on, a postulate in a fundamental physical theory cannot have anything to do with the existence or not of a consciousness", or "this is not science" or...
However, if you think about the measurement problem as formulated in standard QM, together with decoherence that confirms Born's idea that we can put the "cut" anywhere in between the observed system and the human observer, will lead you in one way or another to considerations of the kind I mention. It solves also the problem of the vague definition of what is a measurement: it is *my conscious observation*, period. ALL the rest is unitary quantum theory. And it solves, in a way, the non-local aspects: after all, my consciousness can only observe locally.

As I said before, I'm the first one to say that these metaphysical considerations on a purely scientific question make me feel uneasy ; one shouldn't be forced into such considerations in order to try to make sense of a theory, no ?

cheers,
Patrick.

[ZapperZ]

I don't think it is at all fair to suggest that fans of Bohm's theory "have swept under the carpet the zoo of problems that come with such formulation." In fact, if anyone is guilty of such sweeping, it is the advocates of the standard interpretation of QM. This is known to be plagued by the measurement problem, for example, yet most of the advocates of the standard interpretation simply ignore this. John Bell described the reliance of the standard interpretation on the concept of "measurement" as "unprofessionally vague and ambiguous." Why? Because the theory contains two different rules for how wave functions evolve in time, but fails to give any coherent account of when the rules apply. (The two rules are of course Schroedinger's equation and the collapse postulate.) And for a theory which claims to provide a complete description of physical reality, that is a serious problem.

But notice above that the way you present your argument against my assertion that Bohm's theory problem have been swept under the carpet is to blast away against CI. You didn't present anything to show that my original assertion about Bohm's theory isn't true.

It also frustrates me to hear the argument that Bohm's theory cannot be made consistent with relativity (i.e., put in a lorentz invariant form). It's true that consistency with relativity is a major issue for Bohm's theory, but it is no more and no less an issue for Bohm than for the standard interpretation of QM. After all, that standard interpretation includes a postulate about the "collapse of the wave function" which is supposed to occur instantaneously (presumably across some space-like hypersurface, though this is not typically even mentioned as an issue) when a measurement is made. So if one regards the wave function as a complete description of the physical system, the wave function collapse process evidently describes a kind of relativity-violating action at a distance no more and no less spooky than the non-local effects in Bohm's theory.

This is NOT what I meant when I said it can't be put in a lorentz invariant form. This is in reference to a recentely published PRL paper that tried to formulate a QFT-equivalent form of Bohm's theory.[1] The lack of a QFT-equivalent form is a major drawback of Bohmian mechanics - everyone who works in that field acknowledged this. The authors of this paper basically tried to show how Bohmian mechanics can be extended to QFT. There are still problems, though. The theory isn't Lorentz invariant, so there is a "preferred" reference frame. But they claim that there can be no experiment that would determine which frame is the preferred one. (Oy vey!) THIS is what I meant as a non-lorentz invariant problem!

On the other hand, if one rejects the claim that the description provided by the wave function is complete, one immediately finds oneself in the company of Bohm fans and other "hidden variable theory" advocates. And since Bell proved that any experimentally viable hidden variable theory must include non-local effects, the lesson is that non-local effects must be included in any experimentally viable formulation of QM, period. Bell said this quite clearly and quite explicitly, but people seem to have a difficult time hearing and understanding him. See, for example, quant-ph/0408105 at www.arxiv.org.

One can of course say what one wants about the strange features of Bohmian mechanics. But it cannot be reasonably asserted that the advocates of that theory deliberately blind themselves to its problems. Indeed, to again cite the great John Bell (who was, by the way, the principal advocate of Bohm's theory for several decades!), it is to the great credit of Bohm's theory for bringing out in a clear way some strange features (such as non-locality) that had been inside QM all along, but which had been hidden away behind the "unprofessionally vague and ambiguous" fuzz of the standard interpretation.

Let's be clear about one thing here. I referred to "fans of Bohmian mechanics" as the people in this forum who continuously advocated this version of QM. Practically all the postings I've seen regarding this on here has been devoid of the glaring problems with this version of QM. I am NOT refering to people, some of whom I know of personally, who work and advocate this formulation. In fact, I have been avidly studying this for the past 4 years ever since I became seriously interested in it, and thus my contact with people who are actively involved in it.

If this forum is full of CI fans who does nothing but tout its "superiority", I would also stand up and start rattling off a bunch of problems with it. But I don't need to do that. There's enough CI bashing going on without my help. So please, try not to equate my pointing out the problems with Bohm theory as an indication that I dislike it. If I dislike it THAT much, I wouldn't have followed and read almost every single paper on it that I can find.

Zz.

[1] D. Durr et al., PRL v.93, p.090402 (2004).

[ZapperZ]

Ummm, does John Bell count as someone "who works in the field that does this EPR-type study"? Because he DEFINITELY found the kind of alarm you refer to here, namely, a reason to worry that the non-locality of quantum theory was in conflict with relativity. Here are his words:

"For me then this is the real problem with quantum theory: the apparently essential conflict between any sharp formulation and fundamental relativity. That is to say, we have an apparent incompatibility, at the deepest level, between the two fundamental pillars of contemporary theory..." (from J.S. Bell, "Speakable and Unspeakable...", page 172.)

Note also that it represents a confusion to discuss "information transfer" in this context. Do we really want to commit to the idea that the only thing relativity says can't go faster than light is "information"? For one thing, this would make orthodox QM and Bohmian mechanics equally consistent with relativity. For another thing, what the heck is "information"? Whose information, and information about what? Put bluntly, "information" is just not the kind of "stuff" that relativity or any other physical theory ought to be talking about. It is just way too mental. At least, that's what most of the people who have scrutinized these questions carefully believe.

At this point, it probably won't surprise anyone that Bell was among these careful scrutinizers:

"Do we then have to fall back on 'no signaling faster than light' as the expression of the fundamental causal structure of contemporary physics? That is hard for me to accept. ...the 'no signaling' notion rests on concepts which are desperately vague, or vaguely applicable. The assertion 'we cannot signal faster than light' immediately provokes the question:

Who do [I]we think we are?

We who can make 'measurements', we who can manipulate 'external fields', we who can 'signal' at all, even if not faster than light? Do we include chemists, or only physicists, plants, or only animals, pocket calculators, or only mainframe computers?" (from Bell's article "La Nouvelle Cuisine", reprinted in the 2nd edition of "Speakable and Unspeakable...")

1. What exactly does Bell theory (or that infamous inequality) tell us? Is it really that there are NO hidden variables of all kind, or a test of what is now known as local realism, as defined within the CHSH[1] reformulation of Bell's theory? The violation of Bell's (or more accurately, CHSH's) inequality can only rule out, at best, local realism scenario. This is as far as what those EPR-type experiments can tell us! We have no clue if there is such a thing as non-local hidden variables, which would then make SR, not QM, to be the one in deep doo doo.

2. Consider the following CLASSICAL scenario. A body is at rest in a reference frame, and no net angular momentum. At time t=0, it explodes into 2 separate pieces. The 2 pieces fly off in opposite direction. Piece A reaches a detector on the other side of the galaxy and its angular momentum was measured. Instantaneously, the measurer automatically knows the angular momentum of Piece B that is on the opposite side of the galaxy because he/she was told of the original set up. Was there any "signal" or "information" travelling between the two?

The difference between this classical scenario and the EPR-type experiment is the existence of the superposition of various states before a measurement. So while the classical scenario has a "predermined" orientation before a measurement, the QM scenario does not! The orientation for both pieces are still in an undetermined superposition of states. But in both cases, when a measurement is made, it is a "joint" measurement, meaning the orientation of both pieces are instantaneously determined. They are not separable, both semanticly (is this a word?) and mathematically. If there are no obvious problem with the classical scenario, why would there be with the QM scenario?

3. I have gone back and double checked all the papers by Aspect, Zeilinger, etc., and in NONE of them were there any claims of violation of SR. I will continue to look some more and see if I can come up with a few things I can quote.

Zz.

[1] J.F. Clauser et al., PRL v.23, p.880 (1969).

[ttn]

This is indeed exactly the kind of reasoning that lead me (only half jokingly) to say that QM with the projection postulate leads to a kind of solipsism.



I can sympathize with the reasoning here, though not the conclusion. I mean, you're certainly right that one way to solve the measurement problem is to come up with a clear, physically-grounded definition of what is and isn't a "measurement" (and hence, a clear definition of when wf's evolve by the Sch eq and when they undergo collapse). And since everything on the "outside" of consciousness appears to be essentially the same in terms of its being constructed from the same electrons, protons, etc., the only semi-plausible place to hypothesize there might be a real difference is between matter and consciousness.

But I also agree with what you said about this being pretty crazy and being, probably, the kind of thing that reasonable physicists shouldn't even be taking seriously. (I would only add this spin: since the standard interpretation of QM seems to almost inevitably lead here, perhaps it's that interpretation itself that reasonable people shouldn't take seriously.)

Let me also note that Bohm's theory provides a completely different (and in my opinion far superior and eminently scientific) answer to the measurement problem. Since, in that theory, there is a fact of the matter about where particles are at all times, there is no need to postulate a mysterious collapse process. We simply find particles where they are when we look, period. I can't go into too much detail here, but I would encourage people to look at some of the literature on Bohmian Mechanics to find out more about exactly how the theory unambiguously solves the measurement problem. See, for example the wonderful article by Sheldon Goldstein at:

http://plato.stanford.edu/entries/qm-bohm/

[ttn]

But notice above that the way you present your argument against my assertion that Bohm's theory problem have been swept under the carpet is to blast away against CI. You didn't present anything to show that my original assertion about Bohm's theory isn't true.


Fair enough. And, being new to this forum, I don't know much about the context of your remarks (e.g., the fact that maybe there are some ignorant bible-thumping Bohmians here!). So I apologize if my earlier post had an unjustly confrontational tone. I didn't mean for it to come across that way, and I'm delighted to hear that you are sincerely interested in the Bohm theory since you are obviously a knowledgable and thoughtful physicist.

But given your interest in Bohmian mechanics, I think your critical comments about Bohm's theory are potentially misleading. Here's the best analogy I could come up with: suppose someone criticized G.W. Bush for being inconsistent and dancing around all sides of every issue and never really taking a definite stand on anything. Now, that *is* true of Bush to some extent, so it's not, strictly speaking, an invalid criticism. But unless the person specifically states otherwise, every person reading the criticism will infer that the person supports Bush's opponent, Kerry. And to support Kerry *on those grounds* would be, I think, quite preposterous.

The fact is, people have been dismissing Bohm's theory on the sorts of grounds you raised (it isn't lorentz invariant, it requires a preferred reference frame that is unobservable, there's no clean Bohmian version of QFT, etc.) for decades. Yet every single one of these criticisms, I maintain, is equivalent to the Bush/Kerry analogy. So it is simply misleading to criticize Bohm's theory *on these grounds* unless one simultaneously and explicitly makes crystal clear that, despite these issues, Bohm's theory is *no worse off on precisely these grounds* than any other formulation of QM. And when you throw into the mix the fact that Bohm's theory unambiguously solves the measurement problem (and provides a wonderful, visualizable, intuitive picture of quantum phenomena to boot) it seems downright bizarre to be criticizing Bohm's theory in this way.



This is NOT what I meant when I said it can't be put in a lorentz invariant form. This is in reference to a recentely published PRL paper that tried to formulate a QFT-equivalent form of Bohm's theory.[1] The lack of a QFT-equivalent form is a major drawback of Bohmian mechanics - everyone who works in that field acknowledged this. The authors of this paper basically tried to show how Bohmian mechanics can be extended to QFT. There are still problems, though. The theory isn't Lorentz invariant, so there is a "preferred" reference frame. But they claim that there can be no experiment that would determine which frame is the preferred one. (Oy vey!) THIS is what I meant as a non-lorentz invariant problem!


There are lots of preliminary attempts to formulate a Bohm-like theory of relativistic particle phenomena; the paper you mentioned being merely one recent one. I agree with you that there is no single, clean theory here yet. But I don't think it's legitimate to dismiss Bohmian mechanics (considered as a theory of non-relativistic quantum phenomena) on these grounds. For the same objection would have applied in the 30's to orthodox QM. How did the standard theory in fact achieve a relativistic (particle / field theory) extension? Through lots of hard work by lots of very talented physicists. I believe that it is confusing cause and effect to reject Bohmian mechanics on the grounds that a fully-worked-out relativistic extension does not yet exist. Perhaps it is precisely *because* the community has (in my opinion, unjustifiably) rejected Bohm's theory for 50 years that more progress in this direction hasn't been made.

[ZapperZ]

There are lots of preliminary attempts to formulate a Bohm-like theory of relativistic particle phenomena; the paper you mentioned being merely one recent one. I agree with you that there is no single, clean theory here yet. But I don't think it's legitimate to dismiss Bohmian mechanics (considered as a theory of non-relativistic quantum phenomena) on these grounds. For the same objection would have applied in the 30's to orthodox QM. How did the standard theory in fact achieve a relativistic (particle / field theory) extension? Through lots of hard work by lots of very talented physicists. I believe that it is confusing cause and effect to reject Bohmian mechanics on the grounds that a fully-worked-out relativistic extension does not yet exist. Perhaps it is precisely *because* the community has (in my opinion, unjustifiably) rejected Bohm's theory for 50 years that more progress in this direction hasn't been made.

But then again, I don't think I've ever said anything about rejecting Bohmian mechanics. The very reason I studied it was because of the potential of using it for certain cases when it is more convenient than using the straightforward propagator method in many-body physics.

Dan Styer has a very useful paper on the 9 different formulations of QM.[1] His most important comment, to me, is that fact that no one formulation is convenient all the time. I shift quite often between 2nd quantization and path integral whenever one sucks and the other becomes more useful. I have yet to adopt Bohmian mechanics seriously enough to actually use it in my work, because using it simply because it is "conceptually easier" doesn't cut it, especially when other formulations are well-tested. There simply aren't many application of it yet to describe complex phenomena that we study, even non-relativistic ones.

Zz.

[1] D. Styer et al. Am. J. Phys., v.70 p.288 (2002).

[ttn]

1. What exactly does Bell theory (or that infamous inequality) tell us? Is it really that there are NO hidden variables of all kind, or a test of what is now known as local realism, as defined within the CHSH[1] reformulation of Bell's theory? The violation of Bell's (or more accurately, CHSH's) inequality can only rule out, at best, local realism scenario. This is as far as what those EPR-type experiments can tell us! We have no clue if there is such a thing as non-local hidden variables, which would then make SR, not QM, to be the one in deep doo doo.


The issue of "realism" is a complete red-herring. Violations of Bell's inequality shows that hidden variable theories (i.e., theories according to which the quantum description of reality is incomplete) cannot be local. And the EPR argument shows that if quantum mechanics itself is complete (as Bohr claimed) than it is non-local. So pick your poison. You must face non-locality (i.e., the "deep doo doo" of conflicting with SR) no matter what.



2. Consider the following CLASSICAL scenario. A body is at rest in a reference frame, and no net angular momentum. At time t=0, it explodes into 2 separate pieces. The 2 pieces fly off in opposite direction. Piece A reaches a detector on the other side of the galaxy and its angular momentum was measured. Instantaneously, the measurer automatically knows the angular momentum of Piece B that is on the opposite side of the galaxy because he/she was told of the original set up. Was there any "signal" or "information" travelling between the two?

I don't know exactly what "signals" and "information" are, but the answer is almost certainly: no. More importantly, there was surely no physical, causal influence exerted on Piece B by the observation event on Piece A.

The difference between this classical scenario and the EPR-type experiment is the existence of the superposition of various states before a measurement. So while the classical scenario has a "predermined" orientation before a measurement, the QM scenario does not! The orientation for both pieces are still in an undetermined superposition of states.


Excellent. So, after the measurement at A, the piece at B suddenly does have a definite state. If it had it all along, the pre-measurement quantum description (a "superposition of various states" as you said) was an incomplete description of the state of particle B, i.e., some hidden variable theory is true. If, on the other hand, the state of Piece B changed, because of the measurement at A, to a state with a definite angular momentum value, then quantum mechanics is non-local. That's the EPR dilemma. QM is either incomplete, or it's non-local.

Which do you think it is? Or do you think the argument for the dilemma is flawed?

But in both cases, when a measurement is made, it is a "joint" measurement, meaning the orientation of both pieces are instantaneously determined. They are not separable, both semanticly (is this a word?) and mathematically. If there are no obvious problem with the classical scenario, why would there be with the QM scenario?

Because the standard interp of QM asserts that the quantum description of reality is complete!


3. I have gone back and double checked all the papers by Aspect, Zeilinger, etc., and in NONE of them were there any claims of violation of SR. I will continue to look some more and see if I can come up with a few things I can quote.

The conflict with SR is sufficiently subtle that it's possible for people to fail to see it for a variety of reasons. A careful reading of "Speakable and Unspeakable" will, I think, clear up any doubts. Tim Maudlin's book ("Quantum NonLocality and Relativity") is also an excellent, and highly accessible, text.

[ZapperZ]

The issue of "realism" is a complete red-herring. Violations of Bell's inequality shows that hidden variable theories (i.e., theories according to which the quantum description of reality is incomplete) cannot be local. And the EPR argument shows that if quantum mechanics itself is complete (as Bohr claimed) than it is non-local. So pick your poison. You must face non-locality (i.e., the "deep doo doo" of conflicting with SR) no matter what.

Ah, but now I think that "non-locality" is also a red herring. This is because it is uncertain if we mean superluminal motion or the "spooky action at a distant", or other beasts. I think I am being consistent with my other stance by only restricting to only what can be determined. The CHSH refinement of Bell's theorem indicates, by people who are experts in this field, that all the experimental results so far have been inconsistent with local realism. Unlike you, I don't think that just because someone criticizes Bush, he/she is automatically for Kerry. The logical path has not been established the way Bell did that this is an "either-or" situation.

I don't know exactly what "signals" and "information" are, but the answer is almost certainly: no. More importantly, there was surely no physical, causal influence exerted on Piece B by the observation event on Piece A.

Excellent. So, after the measurement at A, the piece at B suddenly does have a definite state. If it had it all along, the pre-measurement quantum description (a "superposition of various states" as you said) was an incomplete description of the state of particle B, i.e., some hidden variable theory is true. If, on the other hand, the state of Piece B changed, because of the measurement at A, to a state with a definite angular momentum value, then quantum mechanics is non-local. That's the EPR dilemma. QM is either incomplete, or it's non-local.

Which do you think it is? Or do you think the argument for the dilemma is flawed?

Because the standard interp of QM asserts that the quantum description of reality is complete!

The conflict with SR is sufficiently subtle that it's possible for people to fail to see it for a variety of reasons. A careful reading of "Speakable and Unspeakable" will, I think, clear up any doubts. Tim Maudlin's book ("Quantum NonLocality and Relativity") is also an excellent, and highly accessible, text.

Bell's book is well read and well cited by these EPR papers. I am very skeptical that these prominent people simply ignored such clear contradiction between QM and SR. And I have no problem with QM being non-local without violating SR. There is simply no evidence that I know of of any superluminal effects of any kind.

Here's a question: do you think this has deteorated into simply an argument based on a matter of taste? If it has, I see it going nowhere.

Zz.

[selfAdjoint]

So, after the measurement at A, the piece at B suddenly does have a definite state. If it had it all along, the pre-measurement quantum description (a "superposition of various states" as you said) was an incomplete description of the state of particle B, i.e., some hidden variable theory is true. If, on the other hand, the state of Piece B changed, because of the measurement at A, to a state with a definite angular momentum value, then quantum mechanics is non-local. That's the EPR dilemma. QM is either incomplete, or it's non-local.

There's a third altrnative: Piece B DIDN'T HAVE the property in question until a measurement took place. The superposition wasn't just a combination of properties but a complex propensity for Piece B to have property 1 if Piece A had property 2 and vice versa. This complex propensity was created before the two particles separated and has spread, quite causally, with them. When a measurement takes place, no matter at which particle, it gives the other particle the appropriate property, just as quantum states always project into the properties in the real world.

You say that if Piece B didn't have its property all along then QM is incomplete. But that's just the point. QM is complete and it is NOT realist, either local or otherwise. It's not a bug, it's a feature!

[ZapperZ]

There's a third altrnative: Piece B DIDN'T HAVE the property in question until a measurement took place. The superposition wasn't just a combination of properties but a complex propensity for Piece B to have property 1 if Piece A had property 2 and vice versa. This complex propensity was created before the two particles separated and has spread, quite causally, with them. When a measurement takes place, no matter at which particle, it gives the other particle the appropriate property, just as quantum states always project into the properties in the real world.

You say that if Piece B didn't have its property all along then QM is incomplete. But that's just the point. QM is complete and it is NOT realist, either local or otherwise. It's not a bug, it's a feature!

Er... selfadjoint, your posting quoted me. But what you quoted didn't come from me at all. :)

Zz.

P.S. Er.. it was probably my fault. I messed up the quote commands in my previous posting.

[ttn]

Bell's book is well read and well cited by these EPR papers. I am very skeptical that these prominent people simply ignored such clear contradiction between QM and SR.

Fair enough. I'd be very skeptical too if I didn't know this field very well for myself.

But I'm curious what you think of the Bell quote I gave earlier, the one where he says quite explicitly that, in his opinion, there is a fundamental conflict between relativity and quantum theory. Surely Bell understood Bell at least as well as all the folks writing papers on EPR. Are you also "very skeptical" that Bell himself could fundamentally misunderstand his own result?

I know both possibilities are difficult to believe. But either Bell himself didn't understand the significance of Bell's theorem, or a bunch of the subsequent commentators didn't understand it. (Of course, many others *do* understand it: David Albert, Tim Maudlin, Sheldon Goldstein, etc.) It's one or the other (or, I suppose, both) since Bell believed his theorem proved a deep inconsistency between QM (in any formulation) and relativity.


And I have no problem with QM being non-local without violating SR.

I don't understand this. Could you clarify what you take SR to require or prohibit... and what you take "non-locality" to mean?

There is simply no evidence that I know of of any superluminal effects of any kind.

How to you account for Bell's belief to the contrary?



Here's a question: do you think this has deteorated into simply an argument based on a matter of taste? If it has, I see it going nowhere.

A matter of taste? No way. Absolutely not. It's a matter of replacing the "unprofessionally vague and ambiguous" interpretation that is currently dominant with something that is clear and consistent. I mean, I guess you can call that a matter of taste. But I would say anyone who prefers the taste of subjectivity and vagueness and inconsistency, doesn't deserve to be called a scientist.

[ttn]

There's a third altrnative: Piece B DIDN'T HAVE the property in question until a measurement took place.

So the transition from a state in which it doesn't have the property in question, to a state in which it does, isn't a change in the state of the piece?

It's a simple yes/no question. And it's precisely the EPR dilemma.


When a measurement takes place, no matter at which particle, it gives the other particle the appropriate property...

Sounds like a non-local action at a distance to me.


You say that if Piece B didn't have its property all along then QM is incomplete. But that's just the point. QM is complete and it is NOT realist, either local or otherwise. It's not a bug, it's a feature!

Here's a question: if QM denies realism (which I assume means the idea that there is some real, objective world "out there" which is referred to by the theory) then what does it mean to claim, as you did, that "QM is complete"? I always thought completeness meant that the theory provided a complete account of the physical state of the real, objective system. If there is no such real system, then there would seem to be nothing for QM to provide a complete description *of*.

[ZapperZ]

Fair enough. I'd be very skeptical too if I didn't know this field very well for myself.

But I'm curious what you think of the Bell quote I gave earlier, the one where he says quite explicitly that, in his opinion, there is a fundamental conflict between relativity and quantum theory. Surely Bell understood Bell at least as well as all the folks writing papers on EPR. Are you also "very skeptical" that Bell himself could fundamentally misunderstand his own result?

I know both possibilities are difficult to believe. But either Bell himself didn't understand the significance of Bell's theorem, or a bunch of the subsequent commentators didn't understand it. (Of course, many others *do* understand it: David Albert, Tim Maudlin, Sheldon Goldstein, etc.) It's one or the other (or, I suppose, both) since Bell believed his theorem proved a deep inconsistency between QM (in any formulation) and relativity.

I have no response against what Bell has mentioned, the very same way that I have no response against Einstein when he claim that QM is incomplete. This is because these were not based on any physical findings. I have not seen, nor has Bell indicated, of any observables that has superluminal transmission. This comes back again to the very argument of information transfer - is there anything being transfered from one location to another? The very same way that the phase velocity of light can be of ANY speed but carries no information, a measurement made in an EPR type experiment transfers no info about a measurement in one location to the other EPR pair. If there is, then this will be a clear violation of SR. In ALL of the EPR experiments, there has been no insistance that this is the case.

I don't understand this. Could you clarify what you take SR to require or prohibit... and what you take "non-locality" to mean?

How to you account for Bell's belief to the contrary?

A matter of taste? No way. Absolutely not. It's a matter of replacing the "unprofessionally vague and ambiguous" interpretation that is currently dominant with something that is clear and consistent. I mean, I guess you can call that a matter of taste. But I would say anyone who prefers the taste of subjectivity and vagueness and inconsistency, doesn't deserve to be called a scientist.

But if it is subjective, vague, and inconsistent, it should not work. And it should not work this spectacularly. However, I'm a bit confused. You appear to have completly accepted Bohmian mechanics, even when faced with the problem of non-lorentz invariant. I know you have argued that, hey, it is only the beginning, they'll work this out, but aren't you a bit too certain about it? The Dirac/Klein-Gordon equation has successfully dealt with the relativistic aspect of the Schrodinger equation, so to argue that this is still a problem with the conventional QM that is being ignored is highly inaccurate. And yet, you think it is perfectly OK to abandon what HAS worked, and jump onto a bandwagon that is still untested and struggling to plug a lot of unsolved problems. And we're not just talking about conceptual problems either such as the "measurement" problem.

I like the way Bohm's idea has evolved, and continue to evolve. But is it actually read for Prime Time? I hardly think so. I have one test I use to see if a certain formulation is ready to be used - deriving the BCS theory of superconductivity. As a punishment to myself, I have derived this via variational method, field-theoretic method, and even "fudged" perturbation method. I have presented this as a challenge to a couple of people who are big advocates of Bohmian mechanics. Until this can be shown to work, I have no confidence in using it as a tool to solve real research problems.

Zz.

[ttn]

I have no response against what Bell has mentioned, the very same way that I have no response against Einstein when he claim that QM is incomplete. This is because these were not based on any physical findings.

What do you mean by "physical findings"? Direct experimental results? Well, OK, but then aren't you essentially saying that all of theoretical physics is hot air, and all that matters or is meaningful is the "raw" uninterpreted data of experiment? I think this attitude is mistaken; for example it would leave one unable to prefer the Copernican model of the solar system to the old Greek Ptolemaic theory. Moreover, I find it a bit offensive to essentially accuse two of the greatest physicists of the last century as basically being full of hot air.


This comes back again to the very argument of information transfer - is there anything being transfered from one location to another? The very same way that the phase velocity of light can be of ANY speed but carries no information, a measurement made in an EPR type experiment transfers no info about a measurement in one location to the other EPR pair. If there is, then this will be a clear violation of SR. In ALL of the EPR experiments, there has been no insistance that this is the case.

You're certainly right that none of the experiments literally saw a physical thing flying faster than c. No doubt. Yet despite this, Bell still firmly believed that there was a fundamental conflict between QM and relativity. Why do you think he believed this? And why do you think all the other smart people I mentioned earlier agree with Bell on this point?


But if it is subjective, vague, and inconsistent, it should not work. And it should not work this spectacularly.

What's subjective, vague, and inconsistent is the orthodox interpretation of the quantum formalism. It's the formalism itself which has demonstrated spectacular success. But nobody thinks the equations are wrong. I just think Bohr was dead wrong in virtually everything he said about what those equations *meant* about the way the world works.


However, I'm a bit confused. You appear to have completly accepted Bohmian mechanics, even when faced with the problem of non-lorentz invariant. I know you have argued that, hey, it is only the beginning, they'll work this out, but aren't you a bit too certain about it?

That wasn't my argument at all. I agree with Bell that *any* -- that is, *every* -- sharp formulation of quantum theory suffers from non-locality. So the non-locality of Bohm's theory isn't a problem to be worked out. It is a feature that must be present in any theory which accurately describes nature -- i.e., non-locality is a fact of nature. And (again like Bell) I believe non-locality and relativity are at odds. If nature is non-local, then relativity is wrong or broken or needs to be re-interpreted or something like that. So the fact that, e.g., attepts to formulate Bohmian versions of QFT require a preferred frame, does not appear to me to be a problem. It is just one of the possible ways of fixing up whatever it is that's broken with relativity. (Incidentally, at the risk of sounding like a broken record, this is the "fix" that Bell himself preferred, at least at times: see his wonderful article on "How to Teach Special Relativity" for example.)



The Dirac/Klein-Gordon equation has successfully dealt with the relativistic aspect of the Schrodinger equation, so to argue that this is still a problem with the conventional QM that is being ignored is highly inaccurate.

Wait, now you're the one failing to distinguish equations from interpretation. (If I recall, you stressed the importance of that distinction at the beginning of this thread.) The Dirac or KG equations are fine, and the usual recipes for using them are obviously correct. But the standard "story" that goes along with the use of these equations contains all the same vagueness about measurement and wave function collapse as is present in regular old non-relativistic QM. The equations are lorentz covariant, but the conceptual problems remain. Turning it around, the mere fact that the equations work doesn't prove that the currently dominant interpretation is correct (any more or any less than it proves any other interpretation is correct).


And yet, you think it is perfectly OK to abandon what HAS worked, and jump onto a bandwagon that is still untested and struggling to plug a lot of unsolved problems.

That's not true. The equations work great, and I'm all for keeping them. It's mostly Bohr's verbiage about completeness and measurement and collapse that I want to abandon -- precisely because those things haven't "worked" at all!


And we're not just talking about conceptual problems either such as the "measurement" problem.

Did you intend these as scare quotes? I don't follow you. Are you denying that the measurement problem is a real problem? You think it's just semantics or metaphysics or something?

I like the way Bohm's idea has evolved, and continue to evolve. But is it actually ready for Prime Time? I hardly think so.

I do. I have all sorts of questions about it -- there's lots of work left to be done, lots of interesting paths to pursue. But in my opinion it's the best thing available at present. So it's ready for prime time, baby. =)



I have one test I use to see if a certain formulation is ready to be used - deriving the BCS theory of superconductivity. As a punishment to myself, I have derived this via variational method, field-theoretic method, and even "fudged" perturbation method. I have presented this as a challenge to a couple of people who are big advocates of Bohmian mechanics. Until this can be shown to work, I have no confidence in using it as a tool to solve real research problems.

The various formulations you mention here aren't different interpretations of the quantum formalism, they're just different mathematical tools or perspectives on that formalism. So I don't see the point of your challenge. Any valid quantum mechanical derivation of the BCS theory could be understood from a Bohmian point of view, or a Copenhagen point of view (to the extent that's possible), or a MWI point of view, or whatever. They all share the same core formalism.

[ZapperZ]

Then I'm COMPLETELY confused. I could have sworn that I read a while back of your criticism of the "conventional" QM by pointing out the fact that the Schrodinger eqn. is also not covariant under lorentz transformation. When you said that (unless I imagined it), then I took it that you were disagreeing with the formalism of QM as presented in the conventional manner, NOT the interpretation.

Honestly, and I've said this a long time ago on here so someone else can verify this, I have little patience for "interpretation" philosophy. I view it as part of a necessary evil (inconvenience?). And the fact that people often confuse the interpretation with the formalism makes this even more annoying.

If you are unhappy with CI, then be my guest. I have absolutely ZERO problem with that unhappiness. However, the Schrodinger wavefunction approach is a different formulation of QM with compared to the Bohmian pilot wave formulation, which is then different then Feynman path integral approach, which is then different than the Heisenberg Matrix formulation, etc...etc. (Ref. to Dan Styer's paper). I thought that these difference in formulations are what we're debating on, not interpretation. It is why I used the BCS theory as the test case of any of these formulations to be shown as workable.

Zz.

[Rothiemurchus]

A slight diversion:

Could the Pauli exclusion principle be due to superconductivity -
assuming space around electrons in atoms is occupied by some highly ordered arrangement of charged particles?

The hyperphysics website repeats the assertion that Schrodinger equation cannot be
derived.It says:

"Though the Schrodinger equation cannot be derived, it can be shown to be consistent with experiment. The most valid test of a model is whether it faithfully describes the real world. "

[humanino]

The hyperphysics website's statement is not very precise : it cannot be derived outside the axioms of QM.

The Pauli principle is more fundamental. Besides, why would other states outside the the atom explain statistics ?

[ZapperZ]

A slight diversion:

Could the Pauli exclusion principle be due to superconductivity -
assuming space around electrons in atoms is occupied by some highly ordered arrangement of charged particles?

Not that I know of, and I've studied superconductivity for almost all of my college student years. Note that if it is due to superconductivity, then it shouldn't occur in atoms, in light, in the deBoer effect of Nobel gasses, etc., where there are no superconductivity.

The hyperphysics website repeats the assertion that Schrodinger equation cannot be
derived.It says:

"Though the Schrodinger equation cannot be derived, it can be shown to be consistent with experiment. The most valid test of a model is whether it faithfully describes the real world. "

I love the hyperphysics site and cite it regularly. However, they have made several inaccurate statements before and this would be one of them. [The other being that the energy gap in a superconducting density of states leads to the zero resistivity property. This is not correct - these two are correlated, but the gap is not the cause of zero resistance].

Zz.

[ttn]

Then I'm COMPLETELY confused. I could have sworn that I read a while back of your criticism of the "conventional" QM by pointing out the fact that the Schrodinger eqn. is also not covariant under lorentz transformation. When you said that (unless I imagined it), then I took it that you were disagreeing with the formalism of QM as presented in the conventional manner, NOT the interpretation.

No, I'm sorry, maybe I wasn't very clear before. The non-locality in the orthodox formulation of QM is not to be found in the Schroedinger equation. That has just the right sort of relativity (namely, Galilean invariance) to be a good non-relativistic dynamical equation (just as the Dirac and KG equations have the correct sort of invariance to be good relativistic dynamical equations). The non-locality is to be found, rather, in the collapse postulate. It's the collapse of the wave function which I believe violates the prohibitions of relativity (if we regard QM as complete).

Of course, one could get rid of the non-locality (and lots of the vague talk about "measurement") by simply jettisoning the collapse postulate. But then one's theory simply predicts the wrong thing, e.g., that the pointers on (what we call) measuring instruments end up pointing in definite directions at the ends of experiments.

So... just to clarify, I'm not at all against the formalism of QM. Of course that is correct -- it's been verified to an amazing degree by decades of experiments, many of which were specifically designed to test what people thought might be its weak points. My main goal in this discussion was simply to object to using the non-locality in Bohmian mechanics as an argument against Bohmian mechanics. I don't think this is a valid objection, since all other interpretations of QM (leaving aside many worlds, which has plenty of other problems to contend with) are non-local too.

(That was the point of the Bush/Kerry analogy. It's not that I think anyone who hates Bush must love Kerry. I just don't think it's appropriate to criticize Bush for a characteristic he shares with the other contenders in the ring -- at least, not without making it clear that one is aware of that fact.)


Honestly, and I've said this a long time ago on here so someone else can verify this, I have little patience for "interpretation" philosophy. I view it as part of a necessary evil (inconvenience?). And the fact that people often confuse the interpretation with the formalism makes this even more annoying.

I agree with the last part, but I guess, unlike you, I see interpretation as an absolutely central and essential part of the progression of science. Where would astronomy be without Copernicus' interpretation of the data about the solar system (or, if you like, the proto-equations that summarized all this data)? Where would physics be without Boltzmann's interpretation of the physical basis for the laws of macroscopic thermodynamics?

If you are unhappy with CI, then be my guest. I have absolutely ZERO problem with that unhappiness. However, the Schrodinger wavefunction approach is a different formulation of QM with compared to the Bohmian pilot wave formulation, which is then different then Feynman path integral approach, which is then different than the Heisenberg Matrix formulation, etc...etc.

Probably this is mostly just a dispute over terminology. But I don't think the difference between Standard QM and (say) Feynman Path Integrals, is the same as the difference between Standard QM and Bohmian mechanics. Path Integrals are just another mathematical tool for evolving wave functions forward in time (or, if you like, calculating matrix elements). They are mathematically equivalent to the Sch equation (or whatever the basic dynamical equation is of whatever type of quantum theory one is talking about) but they are sometimes computationally more elegant or more practical. Bohm's theory, on the other hand, provides a physical interpretation of the meaning of the equations -- one very different from the "standard" interpretation due to some superposition of Bohr, Heisenberg, and von Neumann.


(Ref. to Dan Styer's paper).

I know the paper you mean. I wouldn't recommend Styer as an expert on these issues, however. In his paper on "common misconceptions regarding quantum mechanics" (AmJPhys 64, 31-34) he basically dismissed Bohm's theory (and all other hidden variable type theories) by saying that the whole idea that the wave function represents an incomplete description of reality "was rendered untenable by tests of Bell's theorem which show that no deterministic model, no matter how complicated, can give rise to all the results of quantum mechanics."

This is really a terrible and false statement about what Bell's theorem shows. It's just not right at all. Indeed, Bohm's theory is an explicit counterexample to his claim, for it is a deterministic model (not even all that complicated) which gives rise to all the results of QM.

[humanino]

I am not saying the discussion is useless.

I see interpretation as an absolutely central and essential part of the progression of science.
I agree very much with that statement for instance.
But when it comes to
I think anyone who hates Bush must love Kerry
that kind of analogy, I must say I feel the discussion is not very scientific.

The EPR "paradox" has been discussed many times. QM is not intuitive, but it is rigorous.


Path Integrals are just another mathematical tool for evolving wave functions forward in time (or, if you like, calculating matrix elements). They are mathematically equivalent to the Sch equation (or whatever the basic dynamical equation is of whatever type of quantum theory one is talking about) but they are sometimes computationally more elegant or more practical.
The all mystery of the quantum world is in the path integral. Is it not ?

[wm]

Here's what I know: Every version of Bell's theorem (BT) known to me is flawed. The probabilistic versions are based on BE (Bell's error); non-prob versions are based on ME (Mermin's error). These errors may be associated with the EPRCM (EPR's category mistake) but are (imo) best named as above for clarity.

Here's what follows: A local realistic QM is valid, in full accord with Einstein's ideas re relativity, locality & separability, and a commonsense view of reality; a reality that justifies the term "hidden variables" because the sub-stratum reality is (often) "hidden" or "veiled" from us due to perturbative measurement effects.

Here's what I suspect: That the quantum potential in Bohm's work might be re-interpretable as a logical consequence of the initial conditions. This suspicion arises from (so-called) "non-local effects" in other theories being replaced by logical consequences in a fully local-realistic theory. PS: I have little interest in this direction (wanting to focus elsewhere), but am sure that my refutation of BT (with little more than highschool maths and logic) will encourage others to dig a little deeper with Bohm.

If anyone's interested, I suggest we start four new threads (to provide focus): EPRCM: EPR's category mistake? BE: Bell's error? ME: Mermin's error? BTR: Bell's theorem refuted? Could be fun.

[ttn]

Here's what I know: Every version of Bell's theorem (BT) known to me is flawed.

I would be interested to hear what you think the flaw is. But let's just say I'm not holding my breath.

Here's what follows: A local realistic QM is valid, in full accord with Einstein's ideas re relativity, locality & separability, and a commonsense view of reality; a reality that justifies the term "hidden variables" because the sub-stratum reality is (often) "hidden" or "veiled" from us due to perturbative measurement effects.

A local hidden variable theory that agrees with QM's predictions?! Let's see it!

[vanesch]

When do complex numbers arise?
Is there a well established theory already for what type of equations produce complex numbers as solutions?

One should study things in order :bugeye:
You talk about quantum gravity and then you ask the above question ; I don't want to sound offending, but it is a bit as if you subscribed to Formula 1 contests, and ask the technician on the starting line, what do people mean by "changing gears" ?
But I can understand that this comes from reading lots of popular science books. There is a not to be underestimated pleasure to be gained in doing things in the right order. Do you know real calculus ? (integrals, differentials etc...) We can take that maybe as a starting point.

cheers,
Patrick.

[Rothiemurchus]

vanesch:
But I can understand that this comes from reading lots of popular science books. There is a not to be underestimated pleasure to be gained in doing things in the right order. Do you know real calculus ? (integrals, differentials etc...) We can take that maybe as a starting point.

Rothie M:
It might surprise you to know that I know calculus of variations, Hamilton's principle,
how to solve differential equations and just about any useful mathematical procedure you can think of that relates to classical mechanics.I also know much of the maths of relativity - general and special relativity.I have studied complex numbers in detail - years ago - but I do not think they provide a reasonable or satisfactory description of reality.Physics is about ideas - not mathematics.Einstein said the maths will always follow from a good idea.
A mastery of mathematics does not guarantee an understanding of anything.
The trouble with quantum mechanics is this -
It has taken causality away from the world.It is de a defeatist point of view:it says " there are some things that just can't be understood in terms of the commonsense world."
Where is the proof of this? The most important question to ask about qm - in my opinion - is this:why is Max Born's guess ( that the wavefunction x complex conjugate of wavefunction is proportional to the probability of finding a particle at a certain position in space) so useful - what is a wavefunction? It must be something physical like Bohm's pilot wave.
There is a way to resolve the problem's associated with Bell's Theorem
and to restore causality to the world and that is to assume a signal exists that travels faster than light.But because such an idea shakes the foundations of relativity people will not get their heads around it.
But there was a time when nobody would have believed that the speed of a light wave catching up with the Earth equals the speed of a light wave approaching the Earth.

[vanesch]

Rothie M:
It might surprise you to know that I know calculus of variations, Hamilton's principle,
how to solve differential equations and just about any useful mathematical procedure you can think of that relates to classical mechanics.I also know much of the maths of relativity - general and special relativity.I have studied complex numbers in detail - years ago - but I do not think they provide a reasonable or satisfactory description of reality.

Well I then offer my apologies, but you have to understand that it is somehow contradictory to read the above, and:


When do complex numbers arise?
Is there a well established theory already for what type of equations produce complex numbers as solutions?


Do you see what I mean ?

cheers,
Patrick.

[ZapperZ]

The trouble with quantum mechanics is this -
It has taken causality away from the world.It is de a defeatist point of view:it says " there are some things that just can't be understood in terms of the commonsense world."

But you see nothing wrong in demanding that the world behaves only in ways that you approve DESPITE of all the experimental observations?

Where is the proof of this? The most important question to ask about qm - in my opinion - is this:why is Max Born's guess ( that the wavefunction x complex conjugate of wavefunction is proportional to the probability of finding a particle at a certain position in space) so useful - what is a wavefunction? It must be something physical like Bohm's pilot wave.
There is a way to resolve the problem's associated with Bell's Theorem
and to restore causality to the world and that is to assume a signal exists that travels faster than light.

I can play the same game as you do and ask you "Where is the proof of this"?

We didn't just make things up just so we can feel good about it and sleep comfortably at night. If you insist that there ARE signals travelling faster than light, then describe the nature of the signal so that it can be measured and proven to exist, and then be proven that it DOES travel faster than c. Till then, you're just making things up as you go along.

But because such an idea shakes the foundations of relativity people will not get their heads around it.
But there was a time when nobody would have believed that the speed of a light wave catching up with the Earth equals the speed of a light wave approaching the Earth.

The difference being that there were existing TANGIBLE, experimental observations that simply did not fit the old notion of how light speed behave. These were not based on simply a matter of tastes, which is all you have stated. There have been NOTHING, no clear experimental observation, to indicate violation of any of SR's postulates so far. You should not equate what have been done to advance our knowledge of light with what you are trying to do here, because they are not even close to being the same.

Zz.

[Rothiemurchus]

Zapper Z:
But you see nothing wrong in demanding that the world behaves only in ways that you approve DESPITE of all the experimental observations?


Rothie M:

I do not doubt that the mathematical predictions of qm match experiment and
that any theory challenging qm must explain why.
As for my piece on superluminal signals:are we left with any alternative to them to
explain what Einstein called " ghostly action at a distance."
Everything else seems to have been tried.
I would say that your attitude is "I think that unfortunately the world is just
incomprehensible at some level."
That could be true but there is no harm in challenging it.
And as you have said previously people test qm all the time - just in case.
And people were very surprised by the results of Michelson and Morley
on the speed of light relative to the Earth.

Vanesch:
No need to apologise, I do have a habit of asking what people call
"naive" questions.

[selfAdjoint]

There are no signals, according to QM. The particle is not "told" what attribute to assume from afar; the projection of its state to an eigenvalue tells it just as with any particle. The fact that the state was complicated and the projection contingent doesn't change this.

[ZapperZ]

I do not doubt that the mathematical predictions of qm match experiment and
that any theory challenging qm must explain why.
As for my piece on superluminal signals:are we left with any alternative to them to
explain what Einstein called " ghostly action at a distance."
Everything else seems to have been tried.
I would say that your attitude is "I think that unfortunately the world is just
incomprehensible at some level."
That could be true but there is no harm in challenging it.
And as you have said previously people test qm all the time - just in case.
And people were very surprised by the results of Michelson and Morley
on the speed of light relative to the Earth.

And you're forgetting that for the MM expt. to be designed, we must first know WHAT it is that we're trying to measure. The old ether theory CLEARLY stated the kinds of influences it exert on light and how it should change. In other words, it had something CONCRETE that we can measure. It didn't just say "oh, there must be an ether", and left it at that, the way YOU did. You can't just say "oh, there must be something moving faster than c" without describing WHAT it is that is moving, and what property does it have for us to be able to measure AND detect its speed.

As an experimentalist, I am SELDOM satisfied with being told "oh, that's just the way it is". However, I have no qualm in settling for the POSSIBILITY that the quantum world is NOTHING like what we are familiar with. I make NO DEMANDS that it should. Unfortunately, from your complaints, you WANT and insisit that it must conform to your classical perception of the world. I find that highly irrational.

Zz.

Vanesch:
No need to apologise, I do have a habit of asking what people call
"naive" questions.[/QUOTE]

[Rothiemurchus]

Zapper Z:
You can't just say "oh, there must be something moving faster than c" without describing WHAT it is that is moving, and what property does it have for us to be able to measure AND detect its speed.

Rothie M:
I will set up a website sometime for you to look at the details of what I had in mind.
They are the kind of details you want!

[humanino]

I know (...) any useful mathematical procedure you can think of that relates to classical mechanics
:bugeye:
You need humility Rothie. I seriously doubt. You just demonstrated that you are not aware of the gigantic field of mathematics. I know some, and I am aware that is so few.

The last person considered to know all mathematics at his time is Poincare. That is what we say in France. Today, it simply impossible, even in a narrow field.

If I am wrong about you needing humility, you are a authentic genius in math. Above any in history.

[ZapperZ]

Zapper Z:
You can't just say "oh, there must be something moving faster than c" without describing WHAT it is that is moving, and what property does it have for us to be able to measure AND detect its speed.

Rothie M:
I will set up a website sometime for you to look at the details of what I had in mind.
They are the kind of details you want!

Oh no! Not one of those!

If you think you have anything authentic and valid, then please send it for publication in a peer-reviewed journal. If you don't, then you are no better than the tons of quackery we find on Crank Dot Net.

I don't read, nor do I pay any degree of emphasis on stuff that can only see the light of day on someone's website.

Zz.

[nrqed]

There are no signals, according to QM. The particle is not "told" what attribute to assume from afar; the projection of its state to an eigenvalue tells it just as with any particle...

But the particle *is* "told" in what state to collapse even though the measurement might have been made on the other side of the universe.

I am not saying that QM is wrong or that Nature should obey rules that are intuitive.

What I *am* saying is that it seems to me that the standard presentations of QM and SR can't be the whole story. For example, the measurement problem. We say "take the measurement of that particle here and *then* the wavefunction collapses. There is , imho, something obviously flawed here. In the case of two entangled photons separated by timelike intervals, the order of the measurements is frame dependent. So in one frame it's observer A which makes the wavefunction collapse, in another frame it's observer B. So it does not make sense to talk about a measurement making the wavefunction collapse. That means that, imho, the standard picture can't be right. The usual way used to describe QM measurements would have to be changed.


Just one example to be more specific: You have two entangled photons separated by timelike intervals. Their polarizations are measured by two observers.

Question 1: you are in a frame where measurement A is taken first. Compute the probabibilities of each measurement of A and then the proabilities of each measurement obtained by B. In the standard presentations, the results of A would be 50/50 and then the result of B would be determined at 100%.

Question 2: Now you are in another frame where B is measured first. Then the standard answer would be quite different than the first, it would be 50/50 for B, then entirely determined for A.

Obviously, there is no way to distinguish one interpretation from the other experimentally. But still, I think it would be important to rephrase the standard interpretation. It sounds to me that the correct phrasing would be to abandon completely the collapse part and to phrase things in a way that is from the start symmetric between the two cases. One should consider the measurements grouped together, with no notion of time delay between the two or of collapse of the wavefunction for that matter. One should then say:

A and B make measurements. There are two possible outcomes: A measures this type of polarization and B measures this other type of polarization, with a probability of 50%. OR the other way around with prob 50%.

That's it, no mention of spacetime interval, no collapse, no time delay, no space separation.

I guess that most people already think that way and see no big deal to it. But if we take his seriously, we should apply the same point of view to all QM measurements. For example, you measure the position of a particle, and then 10 hours later you measure its momentum. In the standard approach, the first measurement caused a collapse of the wavefunction. Then we time evolve the state to find the prob of different momentum measurements 10 h later. But maybe we whould never think of it that way and use the above, symmetric prescription. Then we should say that it's also equivalent to see the second measurement (the momentum one) as causing the collapse and specifying, back in time, the possible results of the x measurement.

My point is : if we adopt a point of view for some measurements, we should adopt the same point of view for all. It feels to me that people treat implicitly treat differently EPR type measurements then other types of measurements. That's what bothers me.

Pat

[vanesch]

So it does not make sense to talk about a measurement making the wavefunction collapse. That means that, imho, the standard picture can't be right. The usual way used to describe QM measurements would have to be changed.


Hi Pat,

What you write here bothered me also quite a while, until I realised that collapse of the wavefunction does make sense as long as it is an observer-bounded concept. This is a viewpoint which is somewhat intermediate in between the standard interpretation and MWI. Indeed, thanks to decoherence, you cannot distinguish between a measurement that gives rise to a true collapse, and one that just "decoheres".
So if you have two entangled particles, A and B, and you have two observers, P and Q, P which observes A and Q which observes B (and we assume these observation interactions to be spacelike separated - you write everywhere timelike but I suppose you mean spacelike), let us then take the point of view of P.
When P observes A, this is a true observation for P. But at that point, he doesn't know anything about B or Q, so it doesn't make sense for P to talk about a collapse of the state at Q. When Q travels to P to tell him the result of his measurement, P just considers this message from Q as another measurement (P makes a measurement on Q). All this is completely local at P, and his successive measurements (with collapse) make completely sense.
Q can do exactly the same, but then of course we have different quantum discriptions according to the observers.
I didn't work this out, maybe one can think of a propagating collapse wavefront going out from each observer ; or one considers that there is only one true observer in the universe, namely me :-)

cheers,
Patrick.

[selfAdjoint]

Patrick, it seems you have the esssence of a sound view here, if you will just lose the "propagating wavefront". Necessarily such a wavefront would be unphysical, since experiment has proved that the time between observations P and Q can be less than the distance between them in light units, i.e. the events showing the correlation can be spaclike. What I think is correct is that the correlation was born, though not yet physical, when the particles were produced entangled, and has spread with the particles; so the cause of the correlation lies in the past light cones of both particles. The only thing that happens at the later time is that the correlation becomes physically manifest at the first measurement; and if the measurements are spacelike related it is impossible to say meaningfully which one came first, since no one can view both of them, except historically.

[cepheid]

Again, this is an example on why, if one did not learn from the ground up, things will seem to appear out of nowhere.

We have gone over this in other threads of the importance of calculus of variation, and in particular the principle of least action. This is the only means of understanding the origin of the Lagrangian/Hamiltonian approach to classical mechanics. I strongly suggest you look this up.

Zz.

Cool, I'm learning this stuff just now, in a course called PHYS 350...Applied Classical Mechanics. My prof said the formulation is far more fundamental than the Newtonian formulation of mechanics in that it applies more universally and draws together many branches of physics. We've already seen things like Fermat's Principle of Least Time in optics. But both that course and this one are very difficult to understand. :frown:

Another funny anecdote. When the same prof (the 350 one) tried to show how the Hamiltonian/Lagrangian approach applied more broadly, he asked our class, "Have you studied quantum mechanics?" When he eventually got the sense that our sole exposure to QM in a previous course (Intro to Modern Phys.) consisted of being dumped with the Schrodinger Equation, and shown how to solve certain problems with it, his exact words were:

"You mean to say they never even went over the history of how the theory arose?" That's pathetic!!"

I couldn't have agreed more. It was pathetic. I'm starting to realise that some of the treatment of physics for us in Engineering Physics might be lacking compared to the treatment in the pure physics programme. Still...*hopes fervently that QM makes more sense the second time 'round*

EDIT: Thanks for that link you gave us back on the 1st page Zz! That should help...

[ttn]

What I think is correct is that the correlation was born, though not yet physical, when the particles were produced entangled, and has spread with the particles; so the cause of the correlation lies in the past light cones of both particles. The only thing that happens at the later time is that the correlation becomes physically manifest at the first measurement; and if the measurements are spacelike related it is impossible to say meaningfully which one came first, since no one can view both of them, except historically.

Actually, if I understand you correctly, your view here is precisely what is shown by Bell's theorem to be impossible. If you assume that "the correlation lies in the past light cones of both particles" (i.e., that the particles get their properties correlated at birth) and if you assume that the outcomes of the two measurements depend only on that total, joint two-particle state (and not on the setting or outcome of the distant experiment) then you get Bell's inequality, which is violated by experiment. So the quantum correlations cannot be explained by any (local) model like the kind (I think) you have in mind.

But then, I'm not entirely sure what you meant by saying that "the correlation becomes physically manifest at the first measurement." If this allows for the first measurement to causally affect the state of the distant particle (or, more generally, the probability distribution for possible outcomes of the distant measurement) then this would be consistent with experiment. But it would of course be non-local.

[selfAdjoint]

I didn't mean to suggest classical movement of the correlation, or the quantum state. They evolve outside of spacetime. But the state _mmmm_, "pro-exists" where the two particles are, in the sense that it is available to provide probabilities to the experimenters. All of this - the essence of QM - is outside classical physics, and it is classical physics that yields the Bell inequality. It is nevertheless true that the extended state carries the information "If one of the particles is found to be in the "DOWN" state, the other will be in the "UP" state, and vice versa". And that state subsists in spite of separation, until a measurement is made. The collapse of the state, or its projection onto its spacetime eigenvalues, conveys the values appropriate value to both particles and doesn't need to travel from one to the other because it is available at both and its link is outside of spacetime, as all states are in QM.

[ttn]

I didn't mean to suggest classical movement of the correlation, or the quantum state. They evolve outside of spacetime. But the state _mmmm_, "pro-exists" where the two particles are, in the sense that it is available to provide probabilities to the experimenters. All of this - the essence of QM - is outside classical physics, and it is classical physics that yields the Bell inequality. It is nevertheless true that the extended state carries the information "If one of the particles is found to be in the "DOWN" state, the other will be in the "UP" state, and vice versa". And that state subsists in spite of separation, until a measurement is made. The collapse of the state, or its projection onto its spacetime eigenvalues, conveys the values appropriate value to both particles and doesn't need to travel from one to the other because it is available at both and its link is outside of spacetime, as all states are in QM.

So... when Alice makes a measurement on one side, Bob's particle is affected -- but the "information" that lets Bob's particle "know" to do this doesn't propagate through regular space, instead taking a detour outside of space and time on its way there?

Is this supposed to be consistent with relativity?! Or maybe you didn't intend it to be. But surely if it's really true that, according to QM, all states are "outside of spacetime", then QM is simply not consistent with relativity. This is a nice illustration of the point I made earlier in this thread: it's wrong to criticize Bohmian mechanics on the basis of its violating relativity's prohibition on superluminal causation, if one's favored alternative is to reject altogether the idea of micro-physical events unfolding on a space-time stage. The fact is, *no* sharp formulation of quantum mechanics is consistent with relativity. It's not just true because Bell said it, but he did say it, and it is true... and it seems like it's time people started recognizing this.

Also, what you said about the inputs to Bell's theorem isn't correct. The inequality is in no way based on "classical physics." I challenge you to point out any place in any of Bell's papers where he brings in something from classical physics. In fact, the inequality isn't based on *any* kind of physics. It's just pure statistics (plus some assumptions about what's allowed to depend on what, i.e., a locality assumption).

[vanesch]

Patrick, it seems you have the esssence of a sound view here, if you will just lose the "propagating wavefront". Necessarily such a wavefront would be unphysical, since experiment has proved that the time between observations P and Q can be less than the distance between them in light units, i.e. the events showing the correlation can be spaclike.

Yes I understood that of course. What I'm saying is that from P's point of view, Q doesn't make a measurement. It is only P who makes two measurements: first on particle A and second on "pseudoobserver Q" which remains itself in a decohered superposition until P (the only true observer in the universe) observes Q. P can only start to observe Q's results (Q's entanglement with B) when Q is in the past lightcone of P after the entanglement took place at Q.

So my point is that there is not necessarily a collapse at Q when P makes his first measurement. It is only when Q is in the past lightcone of P after the entanglement with B that potentially P can observe Q's results and hence that there must be a projection.

You can ask: and what about Q ? Well, Q is a different observer, and hence lives in a different quantum observer world. So he can observe completely different things, P can never find out. P can only make measurements on Q, and then P's measurements will be coherent with other measurements P made in his history record. This is the same issue as how different people perceive the color blue. When presented with something blue, both say that it is blue because told so since they were a child. But you'll never find out if what you perceive as "blue" isn't perceived as "orange" by the other person.

As I said before, this is very strange to me too! But it is the only way I found to have peace of mind with SR and QM, the way they are formulated.

cheers,
Patrick.

[Rothiemurchus]

Humanino:
You need humility Rothie. I seriously doubt. You just demonstrated that you are not aware of the gigantic field of mathematics. I know some, and I am aware that is so few.

Rothie M:
I was just emphasising that I am not completely ignorant of mathematics used in physics! You are right to say it is hard for anyone to know
all mathematics .In fact Feynamn went out of his way to learn only maths he thought would be useful.

Zapper Z:
Oh no! Not one of those!

If you think you have anything authentic and valid, then please send it for publication in a peer-reviewed journal.

Rothie M:
There is no real opportunity for alternative theories on this website
that is why I suggested setting up my own.A journal is the right place though.

[Rothiemurchus]

Photon correlations have been determined over a distance of 10 km.
If a particle or wave of some sort travelled from one photon to another,
then perhaps at a greater distance the second photon would be absorbed by the detecting apparatus before the correlating signal reached it.I think that it is important
to keep testing these correlations over greater distances.No doubt people will.

[Roberth]

I am apparently almost alone in this :devil: . It sounds as if most people just say "well, no information (in the usual sense) is transmitted, no energy is transmitted so everything is fine. End of story. Whereas I think that a more fundamental theory would present a more clear picture of the measurement process, of the collapse of the wavefunction, etc.

But it seems that people have got so used to the weirdness of QM that it does not elicit much desire to dig deeper.

Pat

You almost said exactly the same thing that I said at the General Physics about "Speed of Gravity".

Here is an extract:

My point is this: Quantum entanglement shows non-locality, hence there is something that is not bound by the speed of light. This 'something' causes entanglement. I believe that our known "Physics" is only a subpart of a larger structure and entanglement or the Aharanov-Bohm effect are evidence of that structure.

The fact that you cannot transmit information via entanglement is always used to 'save' locality (ie. the speed of light barrier). However, it does not matter whether you can use it to send meaningful information. The fact remains that there is an action that has a physical effect which acts faster than the speed of light.

Roberth

[selfAdjoint]

No I keep saying that in orthodox QM there is no signal between the particles, non3e at all, let alone an FTL one. In QM the correlation is caused by the extended entangled state, which does not exist in spacetime, and so does not have anything to do with relativity or "sending". What the state "is" truly is of course problematical, but that doesn't affect the truth of this statement.

[Roberth]

No I keep saying that in orthodox QM there is no signal between the particles, non3e at all, let alone an FTL one. In QM the correlation is caused by the extended entangled state, which does not exist in spacetime, and so does not have anything to do with relativity or "sending". What the state "is" truly is of course problematical, but that doesn't affect the truth of this statement.


I am not saying that there is a 'signal' as such in the conventional way. Your comment about spacetime is exactly what I meant in this other post.

Most likely, there is a higher dimensional (5-dimensional or higher) space above Minkowsky space where symmetry considerations are observed and they act instantly. Minkowsky space is then a sub-space of this higher dimensional 'order'.

You can think of it as something like a Hawking´s wormhole, if you like (although I do not believe that it is a wormhole). The 'information of the entanglement' does not go through our spacetime but ' cuts' through it.

Now, how could one start with a more 'flesh on the bone' theory? A candidate would be a group theoretical approach and see if there is a symmetry that must be observed in order to explain the result of the spin entanglement. The problem with that is, however, that group theory is also an epistemological and not ontological approach, similarly to the major parts of QM.

Bohm at least tried to acknowledge that there is something, ie. his quantum potential. This could be in the right direction but must probably be explained from an upper-dimensional level to forecast new physics.

Roberth

[nrqed]

Hi Pat,

What you write here bothered me also quite a while, until I realised that collapse of the wavefunction does make sense as long as it is an observer-bounded concept. This is a viewpoint which is somewhat intermediate in between the standard interpretation and MWI. Indeed, thanks to decoherence, you cannot distinguish between a measurement that gives rise to a true collapse, and one that just "decoheres".
So if you have two entangled particles, A and B, and you have two observers, P and Q, P which observes A and Q which observes B (and we assume these observation interactions to be spacelike separated - you write everywhere timelike but I suppose you mean spacelike),

Yes, sorry about that. For some reason I was thinking "spacelike" and typed timelike throughout the post

let us then take the point of view of P.
When P observes A, this is a true observation for P. But at that point, he doesn't know anything about B or Q, so it doesn't make sense for P to talk about a collapse of the state at Q. When Q travels to P to tell him the result of his measurement, P just considers this message from Q as another measurement (P makes a measurement on Q). All this is completely local at P, and his successive measurements (with collapse) make completely sense.
Q can do exactly the same, but then of course we have different quantum discriptions according to the observers.



Very interesting, Patrick. That's the kind of ideas that Iwould like to see people discussing more, instead of just saying "well, no energy is transferred and the setup can't be used to transmit the results of a baseball game faster than the speed of light so there is no problem. End of story". I find it hard to understand how anybody could feel satisfied with the present status of QM and SR in light of Bell type experiments. Anyway, sorry for the rant...

You idea is a very very interesting one. But it brings up tricky issues....See below.


I didn't work this out, maybe one can think of a propagating collapse wavefront going out from each observer ; or one considers that there is only one true observer in the universe, namely me :-)

cheers,
Patrick.

hehehe...

Patrick added, in a later post:

What I'm saying is that from P's point of view, Q doesn't make a measurement. It is only P who makes two measurements: first on particle A and second on "pseudoobserver Q" which remains itself in a decohered superposition until P (the only true observer in the universe) observes Q. P can only start to observe Q's results (Q's entanglement with B) when Q is in the past lightcone of P after the entanglement took place at Q.

So my point is that there is not necessarily a collapse at Q when P makes his first measurement. It is only when Q is in the past lightcone of P after the entanglement with B that potentially P can observe Q's results and hence that there must be a projection.

You can ask: and what about Q ? Well, Q is a different observer, and hence lives in a different quantum observer world. So he can observe completely different things, P can never find out. P can only make measurements on Q, and then P's measurements will be coherent with other measurements P made in his history record. This is the same issue as how different people perceive the color blue. When presented with something blue, both say that it is blue because told so since they were a child. But you'll never find out if what you perceive as "blue" isn't perceived as "orange" by the other person.

As I said before, this is very strange to me too! But it is the only way I found to have peace of mind with SR and QM, the way they are formulated.



Ok, but here's a question: what is "observer Q" is a piece a paper on which the results of a polarization measurement are printed out. No human consciousness is involved there. So when P (who is human, let's say!) receives paper Q, what happens to the results printed on the paper? Would you say that the numbers on the paper are not well-defined before P reads it? It almost starts to sound like the question: if there is nobody in the forest, does a falling tree make any noise......

In any case, at least I appreciate the fact that you are struggling with these issues and trying to make sense of them, which seems to be th eexception rather than rule in the physics community.


Regards

Pat

[vanesch]

Would you say that the numbers on the paper are not well-defined before P reads it? It almost starts to sound like the question: if there is nobody in the forest, does a falling tree make any noise......


Well, if you take unitary evolution literally, such as MWI proponents do, then your piece of paper (and everything it potentially interacted with, so the whole universe within it's past lightcone) is in a superposition in exactly the same way as the original system was ; the "measurement" at Q is nothing else but an entanglement:

Piece of paper state |empty> (there exists 2 other states |+> and |->, when we've written respectively "+" and "-" on the paper)
System: |s0> = a |spin up> + b |spin down>

"measurement hamiltonian" gives rise to:
|spin up> x |empty> ----> |spin up> x |+>
|spin down> x |empty> ---> |spin down> x |->

so: |s0> x |empty> ----> a |spin up> x |+> + b |spin down> x |->

So the state of the paper simply entangled with the spin state, and it is only P who did the measurement with collapse:
probability |a|^2 to find a + sign and probability |b|^2 to find a - sign, and at this point, you can also say that the spin state is determined: because in the first case, the state is |spin up> x |+> ; remember that this collapse only happens when the paper arrives at P, so causality for the collapse of the (past) spin state at Q is preserved.

cheers,
Patrick.

[Rothiemurchus]

Vanesch:
When presented with something blue, both say that it is blue because told so since they were a child. But you'll never find out if what you perceive as "blue" isn't perceived as "orange" by the other person.

Rothie M:
Unless one day it is shown that perceiving a particular colour in the brain uses quanta of energy and that everyone's brain gets stimulated to use the same number of quanta.