Questions About Quantum Theory: What's Wrong?

[reilly]

After 75 or so years of phenomenal success, some folks have apparently severe problems with Quantum Theory. In fact, this physics forum would not, could not exist without the fruits of QM -- semiconductors and all that.

Granted, at the margins there are formal issues about measurements. But the plain fact is that we understand measurements well enough to do them and interpret them with substantial success. Many say, and I agree, that QM is the most successful and tested physics theory ever.

So what's the problem?

Regards,
Reilly Atkinson

 

[ZapperZ]

After 75 or so years of phenomenal success, some folks have apparently severe problems with Quantum Theory. In fact, this physics forum would not, could not exist without the fruits of QM -- semiconductors and all that.

Granted, at the margins there are formal issues about measurements. But the plain fact is that we understand measurements well enough to do them and interpret them with substantial success. Many say, and I agree, that QM is the most successful and tested physics theory ever.

So what's the problem?

Regards,
Reilly Atkinson

You missed it by about 25 years, Reilly! :) 1999 was the Centenial year of QM.

The people that you are complaining about confuse the issue between "interpretation" and "formalism". They seem to think that "Ah, we find so-and-so puzzling and in contradiction to what we believe" as "proof" that QM is wrong. They are confusing "tastes" with valid observation. Often, they do not understand, or have never worked though, the QM formalism in detail.

As I've said elsewhere, the most convincing evidence of the validity of QM comes from the very devices we use every single day. Condensed matter physics/solid state physics/material science would not be what they are today without QM.

Zz.

 

[reilly]

ZapperZ--We are on the same page. For better or for worse, I started with the development of wave and matrix mechanics, but you are quite correct about more than 100 years for the whole package.

As I've said, you learn QM by doing it.

Regards,
Reilly

 

[Crosson]

QM has a dirty, empirical history. Using QM to predict results is similar to using Keplers 3 observations to track the motion of the planets. Of course, the tracks have been erased and the logical presentation is now quite slick; but the fact is that QM was guided more in its development by experiment than by actual physics.

What we really need is someone (It was Newton in the Kepler analogy) to find some real physics that explains why we observe what we do. Instead we have a bunch of Keplers, happy to chart the stars, that have given up finding the cause of their observations,

Another problem (not with the theory itself) is that it is common for people to talk as if there was "a quantum world" where motion is not continuous, and funny things happen. Then there is the asinine copenhagen interpretation, which says that electrons and such are not even in a particular state until we observe them! Shrodingers cat paradox disproves the copenhagen interpretation, but many QM zombies continue to tell the Shrodingers cat story not as a paradox, but as a "spooky story about the quantum world". All this stuff bothers me because it is not supported by QM.

Another irritating point is that people think QM events are ontologically (really) random, which they are not (simply observationally indeterminate like a coin flip). QM has no impact what so ever on the philosophical doctrine of Causal Determinism, but it is often brought up in such a discussion.

 

[Nylex]

QM is just so confusing, it doesn't make much sense to me.

 

[ZapperZ]

QM has a dirty, empirical history. Using QM to predict results is similar to using Keplers 3 observations to track the motion of the planets. Of course, the tracks have been erased and the logical presentation is now quite slick; but the fact is that QM was guided more in its development by experiment than by actual physics.

And this is BAD?

What area of physics was NOT guided by experiments? String, superstring, and M-Theory? And we know how "valid" those are, don't we?

I've just finished listening to a seminar by Harry Lipkin, who himself is a quite well-known theorist. He, of all people, questioned the need for "theorists" in his rather amusing essay "Who Ordered The Theorist" in an issue of Physics Today.[1] The majority of major advancement and new physics have come out of experimental discovery that no theory has predicted. This includes superconductivity, fractional quantum hall effect, and even CP violation. So being "guided" by experiments is not a drawback, but rather a NECESSITY!

What we really need is someone (It was Newton in the Kepler analogy) to find some real physics that explains why we observe what we do. Instead we have a bunch of Keplers, happy to chart the stars, that have given up finding the cause of their observations,

I'm sorry, but Newtonian laws actually "explain" the physics that we observe? Since when? Every time we are able to describe an even lower level of a phenomenon, someone is going to come in and ask "why?". This is not unique to QM only, thankyouverymuch.

Another problem (not with the theory itself) is that it is common for people to talk as if there was "a quantum world" where motion is not continuous, and funny things happen. Then there is the asinine copenhagen interpretation, which says that electrons and such are not even in a particular state until we observe them! Shrodingers cat paradox disproves the copenhagen interpretation, but many QM zombies continue to tell the Shrodingers cat story not as a paradox, but as a "spooky story about the quantum world". All this stuff bothers me because it is not supported by QM.

Another irritating point is that people think QM events are ontologically (really) random, which they are not (simply observationally indeterminate like a coin flip). QM has no impact what so ever on the philosophical doctrine of Causal Determinism, but it is often brought up in such a discussion.

How does the Schrodinger cat disproves CI? Not that I'm that much of a fan of CI, but it "disproves" it? You mean that an electron is not in two simultaneous location in an H2 molecule to produce those bonding-antibonding bonds? Or that the Stony Brook SQUID experiment did not really measure a supercurrent simultaneously going in BOTH directions to produce that energy gap?

Again, as I've stated earlier, none of these objections have anything to do with experimental evidence. Rather they have everything to do with a matter of tastes and preferences. Nothing has changed or is new here.

Zz.

[1] http://www.physicstoday.org/vol-53/iss-7/p15.html

 

[ZapperZ]

QM is just so confusing, it doesn't make much sense to me.

Then maybe you need to consider the words of one Albert Einstein who said:

"Common sense is the collection of prejudices acquired by age eighteen."

Zz.

 

[Crosson]

What area of physics was NOT guided by experiments?

Special Relativity is the best example of this. Another good example is Maxwell's addition of the displacement current to Ampere's law; this term is necessary to predict EM waves.


I believe that nothing is more relevant to this case than the analogy of Kepler, or else maybe Lorentz.

Keplers laws are based on observation. The lorentz transformations are based on the Michelson Morely experiment. Newton created Universal Gravitation to explain kepler's laws. Einstein created Special Relativity to explain the observed length contraction.

Is it obvious the distinction that I am trying to draw? Einstein and Newton are the ones who saw through the dark, Kepler and Lorentz just played with puzzle pieces.

Again, as I've stated earlier, none of these objections have anything to do with experimental evidence. Rather they have everything to do with a matter of tastes and preferences. Nothing has changed or is new here.

...rather amusing essay "Who Ordered The Theorist"

It is obvious why we disagree on this point. Your heroes are the ones who found it first; Kepler, Lorentz, Rydberg. My heroes are the ones who explained what was found: Newton, Einstein, Bohr.

It seems to me that physics, and history in general, have remembered Newton, Einstein and Bohr much more than Kepler, Lorentz and Rydberg.

It is not simply a matter of taste, physics is about explaining things.

I'm sorry, but Newtonian laws actually "explain" the physics that we observe? Since when? Every time we are able to describe an even lower level of a phenomenon, someone is going to come in and ask "why?". This is not unique to QM only, thankyouverymuch.

Listen to yourself! Of course Newton's laws explain Keplers Observations, don't play naive. It sounds like your attitude is: we can't explain anything so let's not try, physics is only about predicting observables.

Schrodingers cat disproves the CI because it is absurd to say that the cat is both alive and dead until it is observed! Because of this contradiction, CI is false. I admit "proof" is too strong of a word, and that your experiments will have to be explained some other way.

QM is just so confusing, it doesn't make much sense to me.

Take comfort in Feynman's quote, which sums up all of the problems with QM:

Nobody understand quantum mechanics.

 

[jtbell]

Another irritating point is that people think QM events are ontologically (really) random, which they are not (simply observationally indeterminate like a coin flip).

Is there any experimental evidence for your position, or do you just "know" it to be true?

 

[Antiphon]

If I undertand the original poster, what's wrong with it is that it's difficult for
people to accept and understand a theory which is so radically at odds with
everyday experience.

There's nothing wrong with it as an emperical prediction tool- in fact its quite
spectacular.

 

[Crosson]

Is there any experimental evidence for your position, or do you just "know" it to be true?

Your right, I stated my position too strongly. What I mean to say is:

"Another irritating point is that people think QM events are ontologically (really) random, which there is absolutely no reason to believe. "

If I undertand the original poster, what's wrong with it is that it's difficult for people to accept and understand a theory which is so radically at odds witheveryday experience.

To clarify my position (since I seem to be the antagonist), this is not my problem with QM. My problem is that it is lacking in real explanative power and is likely to be superceded by a physical theory, just as Newton superceded Kepler.

 

[inha]

If I undertand the original poster, what's wrong with it is that it's difficult for
people to accept and understand a theory which is so radically at odds with
everyday experience.

To understand: I don't think reilly thinks there's anything wrong with not understanding everything under QM.

To accept: I as well find it weird that QM gets such zealous opposition. A theory is to explain and predict, QM has done both and done them well. I don't see a reason for the amount of opposition QM receives from some people. At times this forum seems to be a place for desperate attempts to disprove QM rather than a way to learn about it.

 

[dextercioby]

Your right, I stated my position too strongly. What I mean to say is:

"Another irritating point is that people think QM events are ontologically (really) random, which there is absolutely no reason to believe. "



To clarify my position (since I seem to be the antagonist), this is not my problem with QM. My problem is that it is lacking in real explanative power and is likely to be superceded by a physical theory, just as Newton superceded Kepler.

Untill u give an example of an experiment in the "range" of QM which the latter cannot account for,i disagree.

And about "likely",how come that in the last 80 yrs,(almost) nothing has changed...?We still have to quantize theories.Which means applying the formalism of QM (either Dirac or Feynman) to all sorts of models culminating with superstrings.


Daniel.

 

[caribou]

Despite recent progress in taming the problems of the pardoxes of wave function collapse, EPR, Schrodinger's cat, etc. in quantum theory, a fundamental question which still remains is the "objectification problem" in that, from the possibilities, why does one event occur and not another?

We don't know if apparently chance events actually have something behind them. As Murray Gell-Mann says, it's just easier to believe that they are random.

 

[dextercioby]

Despite recent progress in taming the problems of the pardoxes of wave function collapse, EPR, Schrodinger's cat, etc. in quantum theory, a fundamental question which still remains is the "objectification problem" in that, from the possibilities, why does one event occur and not another?

We don't know if apparently chance events actually have something behind them. As Murray Gell-Mann says, it's just easier to believe that they are random.

Because,at microscopical level,even for very simple systems,NATURE has chosen to be PROBABILISTIC and simply follow blindly the 6 axioms of Dirac's formulation.
It's like asking why the speed of the car u're in is 60Kmph and not other value.The answer is that NATURE behaves in such a way that,each time u measure the speed,the # u get is 60Kmph.

Daniel.

P.S.WHY WAS THE UNIVERSE (assuming it is only one) CREATED AND BY WHOM??(if u're really interested in phylosophical questions).

 

[Crosson]

Because,at microscopical level,even for very simple systems,NATURE has chosen to be PROBABILISTIC and simply follow blindly the 6 axioms of Dirac's formulation.

Maybe you are not speaking english very well, but this statement is ludicrous! Imagine the young Newton being taught:

"Because when it comes to the planets, NATURE has chosen to be ELLIPTICAL and simply follow blindly the 3 axioms of Keplers formulation."

Rubbish! Quantum theory itself is acceptable, but the terrible thing is that many professional physicists see no need to progress beyond it!

 

[dextercioby]

We have no theory in which Dirac's axioms are theorems.If we did,it's just the same theory,but in von Neumann's formulation or Feynman's...

So,i'm looking forward till the day QM's axioms would become theorems/consequences of other axioms...

I may not live that day.Maybe your grand-grand-grandnephews would tell mine that their grand-grand-granddaddy was wrong 200 yrs before.

Daniel.

 

[reilly]

There's one thing I've never understood about the Schrodinger cat problem. It has nothing to do with QM, and everything to do with standard probability matters. A horse in a horse race certainly is not simultaneously winning and losing. When my kids were born, we did not know the sex of the kid until actual birth. It is absurd to say that throughout the gestation period the child was both male and female. The point is in anything that is described by probability -- or not-- that you don't know until you look. Indeed anybody can claim the cat is simultaneously dead and alive, but why do so? To the best of my knowledge, no one has ever seen a dead/alive cat. It seems to me that the justly famous Occam would say: it's either dead or alive, as we know cats to be, and when we look we'll find out what its state is. Any other view just complicates the matter.

Copenhagen? What that means to most of us is that the absolute square of a normalized wave function is a probability density, as Born suggested. As far as I can figure out, classical probability is as subject to collapse as QM. That is, measurement simply tells us at that moment what is, whether an electron in a scattering experiment, or the price of IBM stock, a sales forecast, or what you will have for dinner in two weeks.

If you work with QM, you develop physical intuition about how it works, you learn that it is good physics with immense explanatory power. Use scattering theory, the Lippman-Schwinger Eq., compute the coherent field that a classical electric current produces, compute nuclear decay rates. For a particularly intuitive physical approach to QM, study all the work behind the theory of chemical bonding -- Linus Pauling's book on bonding is absolutely brilliant, and there are many physically based arguments about the QM involved. Work through the BCS theory of supercoductivity, Cooper pairs, etc, etc. etc. I suspect that many who seem offended by the precepts of QM have not worked with it much. The claim that QM has no explanatory power is absurd.

Further, why do any of Newton's Laws work? People during the Greco-Roman times or during the Dark Ages would have felt Newton's work was preposterous; they had an enormously different world view. If QM is strictly empirical, simply a tool to compute, then the same must be said about Newtonian mechanics. In the final analysis why are Newton's Laws, in practice, different than the Schrodinger Eq. After all our acceptance and comfort with Newton comes simply from years of experience -- Aristotle, brilliant as he was, would have had an equally difficult time making any sense of Newton or Schrodinger.

So it goes. But I'll say again: you learn QM by doing it.

Regards,
Reilly Atkinson

 

[ZapperZ]

Special Relativity is the best example of this. Another good example is Maxwell's addition of the displacement current to Ampere's law; this term is necessary to predict EM waves.

I'm sorry, but SR is NOT guided by experimental observation? Einstein was very troubled (as were the rest of the physics community) with the non-covariant form of Maxwell Equation under galilean transformation. This is simply contradictory to ALL experimental observations. And Maxwell Equations themselves came out of experimental phenomenology. Coulomb's law was certainly NOT derived out of First Principles, and neither did the rest. They are certainly very strongly guided by experiments.

I believe that nothing is more relevant to this case than the analogy of Kepler, or else maybe Lorentz.

Keplers laws are based on observation. The lorentz transformations are based on the Michelson Morely experiment. Newton created Universal Gravitation to explain kepler's laws. Einstein created Special Relativity to explain the observed length contraction.

Is it obvious the distinction that I am trying to draw? Einstein and Newton are the ones who saw through the dark, Kepler and Lorentz just played with puzzle pieces.

Newton didn't "explain" anything. Newtonian laws are phenomenology. They connect seemingly unconnected phenomena, but it still doesn't explain why things are "attracted" or the nature of forces. It is simply one "level" down from Kepler. I could say the same about QM, where it "explains" HOW certain things work that classical mechanics could not. However, I won't, because if one were to examine it closely, all we have in physics are just descriptions.

It is obvious why we disagree on this point. Your heroes are the ones who found it first; Kepler, Lorentz, Rydberg. My heroes are the ones who explained what was found: Newton, Einstein, Bohr.

My heroes? You mean I don't get to choose my heroes, but rather get assigned to them by you?

My "hero", if there ever is one, is John Bardeen.

It seems to me that physics, and history in general, have remembered Newton, Einstein and Bohr much more than Kepler, Lorentz and Rydberg.

It is not simply a matter of taste, physics is about explaining things.

Listen to yourself! Of course Newton's laws explain Keplers Observations, don't play naive. It sounds like your attitude is: we can't explain anything so let's not try, physics is only about predicting observables.

Look carefully. Newton Laws only goes one level deeper than Keplers. It still "explained" nothing! Newton laws left large holes in terms of explanation. It still only describes things. There is a huge difference between "explanation" and "accurate description". Just because you can come up with a theoretical model to describe a set of observation, doesn't mean you have explained it.

Schrodingers cat disproves the CI because it is absurd to say that the cat is both alive and dead until it is observed! Because of this contradiction, CI is false. I admit "proof" is too strong of a word, and that your experiments will have to be explained some other way.

It is absurb because you are trying to force a square object through a round hole, and then blaming the hole for not fitting with your square object. If SR has taught us anything, it is that our cherised prejudices may not fit when we go beyond the boundary of classical physics. Why can't the same thing happen at the QM scale? Why would "position", "momentum", "energy" etc the way we defined it classically make any sense at the QM scale? It seems that we are forcing nature to accept those concepts, and then when she spits out things that simply don't gell with our classical concept, we blame her instead of the fact that those concepts simply do not fit!

Superposition principle is alive and well (simultaneously). Chemists have seen these effects WAY before QM was formulated, and have been unable to figure out a rational description for them. Material scientists make use of various bonding-antibonding bands in looking at band structure of materials all the time (example: the split bands in dual-layer Bi2212 high Tc superconductors). You simply cannot brush this aside and hope to explain this "some other way". There has been no "other way".

Again, physics has never been challenged by "preferences" or tastes. Every single challenge to expanding it into new areas have always been done by valid experimental observations. There have been none, no experimental observations that so far have contradicted QM. I would LOVE to find one! As an experimentalist, I love nothing better than to find something that squish a theory or idea.

Again, what you have brought up is nothing new. Search PF if you don't believe me. We periodically get this all the time on here where someone either question the validity of QM, or not happy with what it does (or doesn't do). So far, all of them have accomplished nothing but tired fingers.

Zz

 

[Crosson]

So,i'm looking forward till the day QM's axioms would become theorems/consequences of other axioms...

Thank you for admitting this, it is my main point. We would all like to see a theory which supercedes quantum mechanics. Except for ZapperZ, who would like to discourage any progress in physics:

So far, all of them have accomplished nothing but tired fingers.

If at first you don't succeed, try try again. Because giving up is not winning.

 

[ZapperZ]

Thank you for admitting this, it is my main point. We would all like to see a theory which supercedes quantum mechanics. Except for ZapperZ, who would like to discourage any progress in physics:

I always snicker whenever someone tells me this. At the APS Centenial March Meeting in Atlanta, I presented a result from my work which I stressed, was consistent with signatures of spin-charge separation in a 2D system strongly-correlated system. A prominent physicst in the field commented at the end that I was pushing the envelope too far and should wait until more evidence come in. We had the same comment for the paper that we submitted for publication.

.. and here, I get accused of discouraging progress in physics! :)

If at first you don't succeed, try try again. Because giving up is not winning.

The difference being that, unless you have completely thrown out the history of physics, LEGITIMATE challenges to existing ideas can only come from, not from personal preferences, but valid experimental observations. You do not make any progress in physics by citing personal TASTES in how the universe should behave. That's just plain arrogant. You can't dictate that a neutrino should not change flavor just because you have a problem with things transforming itself into different "genders". The ultimate arbiter of what is valid is still experimental verifications. So far, there has been NONE that would challenge the validity of QM.

I know I've said this before, but it appears that people seem to trivialize the fact that it works! I don't know whether these people are aware of the breath and range of area that QM has been applied to. If one considers this, it is astounding how well it works in such a diverse area of physics!

Having said that, I still would love to see indications that QM may be "generalized" by something else. However, it will be in the form of an experimental discovery that offer tantalizing hints that QM may fall short of describing such phenomenon. It certainly will NOT come out of someone's personal preference or discomfort of QM. Such things have never been used to justify publication of any physics papers in respected journals.

Zz.

 

[juvenal]

As I mentioned in another thread - this is really a debate about philosophy rather than science. There will almost certainly never be a perfect theory out there. Only effective theories that work under certain conditions and energy scales. If string theory turns out to be right - it will still be only as right as we can test with our experimental apparatus.

Is it nice to come up with better and better effective theories that encompass higher energy scales (like string theory)? Yes - but at the same time - these theories tend to be only practically useful in very limited circumstances. Even if string theory turned out to be right, Newtonian mechanics would still far more useful even though it is only effective under certain conditions (the conditions that apply to everyday life).

So to complain about QM being flawed or not being the theory of everything is completely missing the point. It is a great effective theory at atomic distance scales, and it's not clear that we need a better theory at those scales, any more than we need an improvement in classical mechanics to solve standard problems at larger distance scales like billiard ball collisions.

 

[Dr Transport]

After 75 or so years of phenomenal success, some folks have apparently severe problems with Quantum Theory. In fact, this physics forum would not, could not exist without the fruits of QM -- semiconductors and all that.

Granted, at the margins there are formal issues about measurements. But the plain fact is that we understand measurements well enough to do them and interpret them with substantial success. Many say, and I agree, that QM is the most successful and tested physics theory ever.

After reading all of the posts in this starting with the original above, I agree QM is a wonderful theory, but my old E&M Prof would claim that Electromagnetics/dynamics is the most tested and exact field theory out there. We can split hairs, but QM has had to be modified from the original to include other effects, whereas E&M is valid until you hit the QED. After the hydrogen atom, QM breaks down pretty quickly for getting exact solutions.

 

[Crosson]

You do not make any progress in physics by citing personal TASTES in how the universe should behave.

"The laws of physics should be able to be written in a covariant manner..."

This is the statement which led to the Einstein Field Equations, along with the prediction that gravity bends light (predicted by theory before it was observed) and that the universe is non-static (predicted by theory before observation, but too radical to publish).

 

[Andrew Mason]

After 75 or so years of phenomenal success, some folks have apparently severe problems with Quantum Theory. In fact, this physics forum would not, could not exist without the fruits of QM -- semiconductors and all that.

Granted, at the margins there are formal issues about measurements. But the plain fact is that we understand measurements well enough to do them and interpret them with substantial success. Many say, and I agree, that QM is the most successful and tested physics theory ever.

So what's the problem?

One could ask: what's the problem with having a problem with it?

QM may be the most successful and accurate constructive theory in the history of science. Its power is remarkable. But its rules appear to be ad hoc and cannot be derived from some underlying kernal of truth. Some seek that elusive 'kernal', which is the basis for other successful theories (e.g Relativity).

The student in search for that 'kernal' is told: "there is no reality". Or, "there are many equivalent and equally valid truths. Take your pick." I don't see that there is anything wrong with a student who thinks there should be a better answer.

AM

 

[quantumdude]

After the hydrogen atom, QM breaks down pretty quickly for getting exact solutions.

May I ask, what's your definition of "breaking down"? I always thought that for a theory to break down, it had to yield a false prediction. Correct me if I'm wrong, but it seems to me that you are implying that QM "breaks down" for atoms that are more complex than hydrogen. Is that a fair characterization of what you are saying?

 

[quantumdude]

One could ask: what's the problem with having a problem with it?

It's not that one should be criticized for wanting to know what lies beneath QM. It's that there are a number of people on the internet (some of whom have come to PF) who advocate a return to classical physics over QM, which is a move in the wrong direction.

 

[ZapperZ]

After reading all of the posts in this starting with the original above, I agree QM is a wonderful theory, but my old E&M Prof would claim that Electromagnetics/dynamics is the most tested and exact field theory out there. We can split hairs, but QM has had to be modified from the original to include other effects, whereas E&M is valid until you hit the QED. After the hydrogen atom, QM breaks down pretty quickly for getting exact solutions.

I'm not sure QM had to be "modified". Rather, it evolved!

And as far as the description of heavier atoms, QM certainly does NOT break down. It simply doesn't give you a closed solution because it has now become a many-body problem (or N-body problem). After all, you don't say classical mechanics breaks down simply because it cannot give you a closed solution to the most general situation beyond the 3-body problem, do you? With DFT and QMC, QM can certainly come up with a darn fine job in quantum chemistry.

Zz.

 

[ZapperZ]

One could ask: what's the problem with having a problem with it?

QM may be the most successful and accurate constructive theory in the history of science. Its power is remarkable. But its rules appear to be ad hoc and cannot be derived from some underlying kernal of truth. Some seek that elusive 'kernal', which is the basis for other successful theories (e.g Relativity).

Eh?

Relativity is built on a number of POSTULATES! These postulates are not derivable! What's different about this then with QM?

Do you want something even MORE ad hoc? Try translation/rotation symmetry of space! I challenge you to DERIVE this. It is pure observation! Yet, it is the foundation of the conservation laws of momenta that we have today. We put it in because it is the nature of our universe. We certainly did not derive it!

This happens repeatedly. People pick on QM, and yet, they ignore the identical thing happening elsewhere and you see no complaints about those! Again, you cannot challenge physics this way! Our gut instincts and intuition have been wrong MORE OFTEN than physics. Complaint like this gives the rest of us who are REALLY working in trying to push the boundaries of physics a bad smell.

Zz.

 

[Andrew Mason]

Relativity is built on a number of POSTULATES! These postulates are not derivable! What's different about this then with QM?

There are only two postulates of Special Relativity and those two are essentially one: The speed of light is the same in all intertial frames. SR follows mathematically from that postulate. What is the essential postulate from which one can derive all of QM? I must have missed that class.

Eh?

Spoken like a true Canadian!?

AM

 

[ZapperZ]

There are only two postulates of Special Relativity and those two are essentially one: The speed of light is the same in all intertial frames. SR follows mathematically from that postulate. What is the essential postulate from which one can derive all of QM? I must have missed that class.

You are welcome to google those - even the mathpages link that you have used to refer others to might have them.

It is still besides the point. There are postulates and none-derivable axioms in ALL of physics. I do not understand why you pick on QM and ignore everything else.

Spoken like a true Canadian!?

AM

I also frequently say "oy vey". Does that make me jewish? Even better, I sometime say "oy vey" and "masha'allah" in the same sentence. Does that make me a muslim jew? Hey, I could be a quantum person with a superposition of two orthorgonal "states"!

Try and predict my "heroes", and you'll be wrong (as has been proven earlier in this thread). Try and predict my "nationality", and you'll be wrong too. Even I don't try to categorize me, so don't presume that you can.

Zz.

 

[dextercioby]

There are only two postulates of Special Relativity and those two are essentially one: The speed of light is the same in all intertial frames. SR follows mathematically from that postulate. What is the essential postulate from which one can derive all of QM? I must have missed that class.


AM

Either that,or the QM teacher didn't say the 6 axioms are equally important...

Daniel.

 

[reilly]

Special Relativity is the best example of this. Another good example is Maxwell's addition of the displacement current to Ampere's law; this term is necessary to predict EM waves.

My suggestions to read some history and get the facts apparently fall on deaf ears. Einstein himself said about SR, "I took into consideration Fizeau's experiment, and then attempted to deal with the problems on the assumption that Lorentz's equations concerning the electron should hold as well in the case of our system of coordinates being defined on the moving bodies as well as defined in vacuo." (p 139 in 'Subtle is the Lord... The Science and Life of Albert Einstein by Abraham Pais. This book is absolutely essential reading for anyone who wants to understand what Einstein did, and how he did it. It is a wonderful book, made particulalry special because Einstein and Pais were friends and colleagues at the Advanced Institute.) If you read, you will discover more about the empirical basis of SR, along with theoretical pushes from Poincare and Lorentz.

I'll also say again, that QM has remarkable explanatory power. With all due respect, to suggest that QM has no explanatory power is to demonstrate a considerable lack of knowledge about QM -- see, for example, Pauling's book on chemical bonds.

You are wrong about Einstein and wrong about QM. Again, profit from reading and the facts. If you read Einstein's great little book, Relativity, you'll find that the two primary pillars of SR are supported by some more subtle assumptions. They are there for the discovery.

Regards,
Reilly Atkinson

 

[reilly]

To understand: I don't think reilly thinks there's anything wrong with not understanding everything under QM.

To accept: I as well find it weird that QM gets such zealous opposition. A theory is to explain and predict, QM has done both and done them well. I don't see a reason for the amount of opposition QM receives from some people. At times this forum seems to be a place for desperate attempts to disprove QM rather than a way to learn about it.

Hear, hear.
Regards,
Reilly Atkinson

 

[Dr Transport]

I'm not sure QM had to be "modified". Rather, it evolved!

I retract the "modified", it should have been "evolved". I never meant to imply that QM yielded incorrect results, but to imply that you make approximations in the form of perturbations etc for most problems at hand. In E&M you do not have to approximate to get an answer, maybe the solutions are not exactly tractable, but the basic equations have not been modified since Maxwell.

I spend about half my time working classical problems (Optics etc...) and the other half working in Optical Properties of Semiconductors and am truly amazed after all the years I have been doing this type of thing that QM gives reasonably correct answers that are verified experimentally. Devices I design work and the basic principles behind them are derived from the quantum mechanics of solids how do we do better?

 

[juvenal]

I retract the "modified", it should have been "evolved". I never meant to imply that QM yielded incorrect results, but to imply that you make approximations in the form of perturbations etc for most problems at hand. In E&M you do not have to approximate to get an answer, maybe the solutions are not exactly tractable, but the basic equations have not been modified since Maxwell.

I spend about half my time working classical problems (Optics etc...) and the other half working in Optical Properties of Semiconductors and am truly amazed after all the years I have been doing this type of thing that QM gives reasonably correct answers that are verified experimentally. Devices I design work and the basic principles behind them are derived from the quantum mechanics of solids how do we do better?

Right - but classical E&M does not work at the atomic level. It is wrong.

There is the modern notion of "effective theory" which explains why our theories work as well as they do.

http://arxiv.org/PS_cache/cond-mat/pdf/9502/9502052.pdf

http://arxiv.org/PS_cache/gr-qc/pdf/0311/0311082.pdf

provide some background on this notion. There are other similar sorts of papers out there.

 

[quantumdude]

Right - but classical E&M does not work at the atomic level. It is wrong.

That's what I was driving at. QM may not yield exact solutions for atoms more complex than hydrogen, but the classical electrodynamics of charged particles doesn't even buy you that much.

 

[Andrew Mason]

I spend about half my time working classical problems (Optics etc...) and the other half working in Optical Properties of Semiconductors and am truly amazed after all the years I have been doing this type of thing that QM gives reasonably correct answers that are verified experimentally. Devices I design work and the basic principles behind them are derived from the quantum mechanics of solids how do we do better?

Models don't have to be correct to be useful. The model of magnetic field consisting of little lines of force works really well. The model of electricity being a fluid passing through wires under pressure has some limited usefulness as well. Treating current flow in semiconductors as electrons and holes moving through a junction works too. Kepler's nested spheres could be used to work out orbits of the planets.

Usefulness in predicting results is important. But if one wants to understand what the 'reality' is, one needs a theory that does more than usefully predict results.

AM

 

[ZapperZ]

Models don't have to be correct to be useful. The model of magnetic field consisting of little lines of force works really well. The model of electricity being a fluid passing through wires under pressure has some limited usefulness as well. Treating current flow in semiconductors as electrons and holes moving through a junction works too. Kepler's nested spheres could be used to work out orbits of the planets.

Usefulness in predicting results is important. But if one wants to understand what the 'reality' is, one needs a theory that does more than usefully predict results.

AM

Whoa!

There is a difference between a "physics model" and "visualization"! You are confusing those two! Magnetic field lines are NOT a "model", it is a visualization! I challenge you to show me there there are "magnetic lines" in the Maxwell equations.

Usefully predicting result IS a part of reality! In fact, it is ALL that we have! Again, show me a "theory" that does MORE than this. Till then, what you have said is all hypothetical.

Zz.

 

[Dr Transport]

Right - but classical E&M does not work at the atomic level. It is wrong.

Didn't I mention that exact fact in my original post, E&M works down to the point where QED takes over. There isn't a theory to my knowledge that takes into account everything. I took a Relativity course from a guy (Mendel Sachs) who claimed that after rewriting Einsteins equations in terms of quaterians and taking the linear limit he reproduced Quantum Mechanics and for a time had the best calculation of the Lamb shift. One of his students calculated the mass of the tau lepton to within an order of magnitude without using QM at all using Reletivity theory only.

Now Reletivity is about as close as I have ever seen a theory accounting for a the very large to the very small.

I still maintain that E&M is a very good, if not excellent field theory and QM is a close second.

 

[jtbell]

Usefulness in predicting results is important. But if one wants to understand what the 'reality' is, one needs a theory that does more than usefully predict results.

But how does one judge how well a theory corresponds to "reality," if not by its ability to usefully predict results?

 

[binarybob0001]

The problem we are discussing is written in Aristotles meditations. Essentially, the only thing I know for certain is that I exist. I may be writing this letter to nothing or something non-human or to a human or for nothing, but I do not know answer. The problem is we cannot reach out past our own experience. Some people argue that we can learn without experience(a priori), but I am trying to make a simple explanation, so I will only talk about learning from experience(a posteriori).
The complaint is that QM is taken from observation with no axioms to back it up. Newton was wrong. Einstein may be really close to the right answer or right on. QM may be right or close.
Newton based his theory off of experiences with the world. Newton could not see the whole structure of reality(If he could, would he know he was observing all reality?); therefore, he could not know if his theory was right or wrong. An old textbook will list Newtons theory as fact(a law), but we know that to be wrong. The point is, there cannot be axions about reality because we cannot go beyond our experience. Therefore, we cannot know what theories are right and what theories are wrong. We know that a theory explains our experiences with the world, and that is all. Whether the world really works that way, we can never know. Unless as I said before, learnig fully about the universe is possible a priori. I will let you guys decide whether or not that is possible.
QM, like or not, is a theory that explains much of the observable phenomenon in the universe. People may say that it is counter intuitive, and I understand. People should understand though that there will never be a truly provable TOE(theory of everything), only a TOE that explains all we observe. We can always ask the question is there something else? And we will never be able to answer it.

 

[ZapperZ]

People should understand though that there will never be a truly provable TOE(theory of everything), only a TOE that explains all we observe. We can always ask the question is there something else? And we will never be able to answer it.

Even that part is debatable. Condensed matter physicists like Anderson, Laughlin, and Pines would argue that the so-called TOE that is the result of a unified theory is simply a TOE for REDUCTIONISM, not a TOE of physics. I have described this at length with appropriate references elsewhere and won't bore long-time readers with this point again.

Zz.

 

[DrChinese]

But if one wants to understand what the 'reality' is, one needs a theory that does more than usefully predict results.

AM

It is very debatable that any good theory does more than provide utility, or that there is an objective reality that can be understood in any meaningful sense.

(For example, tell me ANY physical theory that explains reality in a way that folks will say, hmmm, now I completely understand that. GR gives us a nice pretty picture, for example, but how does it explain reality any more than QM does?)

 

[Stingray]

The problem with QM is that it is basically two theories stuck together in an incomplete way. You have the usual unitary evolution of states, which is nice and elegant. But you also have a completely separate process of measurement, which cannot be applied in an unambiguous way. It is certainly true that for a large class of experiments, people have learned what a measurement is (i.e. how to apply the formalism in a way that matches experiments). This has obviously been extremely useful, but is also incomplete.

The measurement postulates cannot be applied uniquely in any imaginable situation. If QM is a fundamental theory of physics, it should describe everything. In principle, it should be possible to remove any external "classical experimenter." Does the whole system then evolve unitarily? How would that be reconciled with the fact that we seem to need the projection postulate experimentally? Is that just an approximation when a large number of degrees of freedom are involved?

The resolutions of these problems will (probably) not have any profound influence on "practical" physics, but that doesn't remove their importance.

 

[ZapperZ]

The problem with QM is that it is basically two theories stuck together in an incomplete way. You have the usual unitary evolution of states, which is nice and elegant. But you also have a completely separate process of measurement, which cannot be applied in an unambiguous way. It is certainly true that for a large class of experiments, people have learned what a measurement is (i.e. how to apply the formalism in a way that matches experiments). This has obviously been extremely useful, but is also incomplete.

The measurement postulates cannot be applied uniquely in any imaginable situation. If QM is a fundamental theory of physics, it should describe everything. In principle, it should be possible to remove any external "classical experimenter." Does the whole system then evolve unitarily? How would that be reconciled with the fact that we seem to need the projection postulate experimentally? Is that just an approximation when a large number of degrees of freedom are involved?

I disagree. This is because the quantities we measure are classical! Position, momentum, energy, etc. are all "classical" quantites that we inherited out of classical mechanics. QM is simply telling us what they are if we insist on using these quantities. (Again, square objects being forced through round holes).

Unless we want to invent a new set of quantites and concepts, we're stuck with these classical ideas. If you have followed this thread, you'll know how DIFFICULT it is to make some people part with their beloved classical quantities.

Tony Leggett recently wrote a terrific article summarizing the so-called "measurement problem" of QM, and in particular, the Schrodinger Cat-type phenomenon (it is no longer a "paradox").[1] I strongly suggest people who insist that there is a "measurement problem" to read this, and his other paper in J. Phys. Cond. Matt. to look at the wealth of experimental observations and how they compare to what we know about what QM is saying.

Zz.

[1] A.J. Leggett, Science v.307, p.871 (2005).

 

[Andrew Mason]

It is very debatable that any good theory does more than provide utility, or that there is an objective reality that can be understood in any meaningful sense.

(For example, tell me ANY physical theory that explains reality in a way that folks will say, hmmm, now I completely understand that. GR gives us a nice pretty picture, for example, but how does it explain reality any more than QM does?)

Good point. A theory simply reduces a lot of little things that we didn't understand to fewer bigger things that we still don't understand: like Newton's laws which explained why things move the way they do in terms of forces and inertia.

And no doubt about it: QM does reduce a lot of little things to fewer rules and principles. The problem is that, unlike force and inertia, people lack an intuitive grasp of what these rules and principles mean physically. I long ago concluded that one should not expect to have that intuitive grasp of QM as the world at that level is quite beyond our experience.

But I don't think it is wrong for people to find QM's explanations unsatisfying. I should think that any good physicist would always want to improve understanding of the physical world. One can't do that if one is completely happy with all the current explanations of things. So that is why I complain about people who complain about people complaining about the 'unsatisfactory' explanations that QM provides.

AM

 

[ZapperZ]

Good point. A theory simply reduces a lot of little things that we didn't understand to fewer bigger things that we still don't understand: like Newton's laws which explained why things move the way they do in terms of forces and inertia.

And no doubt about it: QM does reduce a lot of little things to fewer rules and principles. The problem is that, unlike force and inertia, people lack an intuitive grasp of what these rules and principles mean physically. I long ago concluded that one should not expect to have that intuitive grasp of QM as the world at that level is quite beyond our experience.

But I don't think it is wrong for people to find QM's explanations unsatisfying. I should think that any good physicist would always want to improve understanding of the physical world. One can't do that if one is completely happy with all the current explanations of things. So that is why I complain about people who complain about people complaining about the 'unsatisfactory' explanations that QM provides.

AM

But then you miss the point of my complaint about people who complain about QM. There are ways to "complain", and just saying it based on a matter of tastes is NOT the way to complain about ANYTHING in physics, and not just QM. If you complain about E&M based simply because you dislike the idea of "fields", I would complain about your complaints too. This has nothing to do with QM. It has everything to do with how one challenges ideas in physics.

You cannot base it on "intuition", or "intuitively easy". Your intuition changes all the time as you gain more knowledge. What was intuitively difficult when you were 18 can be intuitively obvious when you're 30. So just saying QM is intuitively difficult (especially for the masses) should be completely irrelevant. Nature owes none of us any explanation on why she behaves that way. To force her to fit into our "intuition", as limited as it is, is plain arrogant. As scientists, that's the worst mistake we can ever do.

Zz.

 

[reilly]

Classical theory leaves a lot of open questions, which, typically, we don't consider often:

Whence electric charge? Why is it quantized? Why do protons and electrons have charge that is equal and opposite?


Why is the speed of light what it is?

Why is gravity, under normal human conditions, weaker than the other forces in nature?

Why does F = dP/dt?

Why are so many repeated measurements the same, relative to standard measurement error?

Why does the sun come up every day?

What is mass?

Does the elecromagnetic spectrum include arbitrarily large frequencies?

Relative to human scales, why are stars and galaxies generally so widely spread?

How, albeit under extreme circumstances, can a single person lift a car?

Why does probability work?

Why is there regression to the mean? (That is, why does statistics work?)

Why do some heavy smokers not get lung cancer?

Why is there so much nonlinearity in the world?

Why don't our children follow our superb advice?

And, on and on.

Life is full of mysteries. To suggest QM is inadequate because we do not understand the measurement process is to miss the point. Classical probability and statistics, as used in practice, suffer from the same problem, that is collapse. Prior to a coin toss the probability of a heads is 1/2. If the toss comes up tails, then the probability of tails is 1, and he probability of heads is 0. Looks like collapse of the probability to me -- not much different from measuring whether spin up or spin down.

Classical or quantum, science and physics are imperfect, but they do give us a beacon of light into the void -- and, from my own experience, that is a great gift as one gets older. Life is full of mysteries. You do the best you can with what you've got.

Regards,
Reilly Atkinson

 

[Locrian]

but the fact is that QM was guided more in its development by experiment than by actual physics.

What?? Physics by definition develops by experiment. Saying Einstein didn't use experiment is rediculous - he just wasn't the one doing the experiments. The first page of his paper on special relativity are the Lorentz transformation equations, which are based on maxwell's equations, which are 100% experimentally derived.

There is no part of physics that does not rely on experimentation, whether before or after, and without experimentation we'd still be in the dark ages. Assumptions and hypothesis are all well and good, but they require experiment to verify them. Einstein had the habit of guessing first and testing later (with exception maybe of his experiments in photon absorption), and this ended up making him wrong very, very often, and right very, very rarely. I guess if we remember his hits and forget his misses we are to be impressed?

Saying that zapperz is impeding physics is amusing, given his employment and the hard work he does on these forums. I would love to see who had contributed more to physics, Crosson or Zapperz.