I The typical and the exceptional in physics

[atyy]

The observables are defined operationally by real-world measurement processes.

Are there measurement processes without human beings?

 

[vanhees71]

Sure, the data from the LHC, e.g., are taken by detectors and stored on hard disks. No human being could ever take these vast amount of data coming in a very short time.

 

[atyy]

Sure, the data from the LHC, e.g., are taken by detectors and stored on hard disks. No human being could ever take these vast amount of data coming in a very short time.

So you claim that if we have a wave function describing the LHC, it will evolve unitarily?

 

[Demystifier]

Whether even a classical abstraction as the electromagnetic field has an ontic meaning, is completely outside of science.

Maybe, but then I would say that it is impossible for a human being to do science without combining it with some elements of meta-science (things outside of science). Meta-science is relevant for science.

Or let me ask you a personal question. Obviously, you are interested in some meta-science and you spend some time for thinking about meta-science and discussing meta-science. Do you think that it makes you a better scientist?

 

[Demystifier]

So you claim that if we have a wave function describing the LHC, it will evolve unitarily?

I think he would say that there is no such thing as a wave function describing the whole LHC.

 

[Demystifier]

I agree that it is nonsense to believe that physics depends on human observers.

I think the word "physics" is used with two different meanings.

Physics 1 - the laws obeyed by Nature itself

Physics 2 - a science invented by humans to describe their knowledge about nature

Presumably, Physics 1 does not depend on human observers. But Physics 2 certainly does. So one should specify what does one mean by "physics".

 

[vanhees71]

Physics 1 is not part of physics since it cannot be observed. We can only observe what we can observe. But now, we really start philosophical gibbering (in German we have the very adequate word "Geraune" for it; I don't know whether there is a literate translation to English ;-)) rather than exchanging sound and solid scientific arguments. Indeed, you are right, concerning the "wave function of CERN". I guess, the entire universe wasn't large enough to store the corresponding information.

 

[atyy]

Physics 1 is not part of physics since it cannot be observed. We can only observe what we can observe. But now, we really start philosophical gibbering (in German we have the very adequate word "Geraune" for it; I don't know whether there is a literate translation to English ;-)) rather than exchanging sound and solid scientific arguments. Indeed, you are right, concerning the "wave function of CERN". I guess, the entire universe wasn't large enough to store the corresponding information.

But if there is no wave function of CERN, then you are treating CERN as a "classical measuring apparatus", which is the Heisenberg cut.

 

[Simon Phoenix]

The paradox is equally avoided if you suppose they're both real, but qua scientist it's best to have no opinion on the issue, which is the province of philosophy.

Here's how Matt Leifer describes the terms in his review paper

"In the present context, an ontic state refers to something that objectively
exists in the world, independently of any observer or agent. In other words, ontic states are the things that
would still exist if all intelligent beings were suddenly wiped out from the universe. On the other hand,
"epistemology" is the branch of philosophy that studies of the nature and scope of knowledge. An epistemic
state is therefore a description of what an observer currently knows about a physical system. It is something
that exists in the mind of the observer rather than in the external physical world."

It would seem, especially for QM, that it is largely a philosophical distinction since one can perform calculations using an ontic or epistemic perspective and get the same answers. However, the PBR theorem purports to rule out a class of epistemic interpretations - in much the same way that Bell's theorem rules out certain hidden variable interpretations.

So I would say that, currently, the matter of ontology vs epistemology with regards to QM (and maybe science) is somewhat philosophical, but I don't think that should dissuade us from attempting to settle the matter scientifically, or to at least put bounds on possible interpretations in the way that PBR claims to do.

 

[secur]

It would seem, especially for QM, that it is largely a philosophical distinction since one can perform calculations using an ontic or epistemic perspective and get the same answers. However, the PBR theorem purports to rule out a class of epistemic interpretations - in much the same way that Bell's theorem rules out certain hidden variable interpretations. So I would say that, currently, the matter of ontology vs epistemology with regards to QM (and maybe science) is somewhat philosophical, but I don't think that should dissuade us from attempting to settle the matter scientifically, or to at least put bounds on possible interpretations in the way that PBR claims to do.

Well, it's in the nature of categorization to draw sharp delineations. Actually things are always fuzzy. For instance math and science are distinct entities but you can't do science without math. And, you can't do science without some sort of philosophy. The only reason to try to draw the boundary is to eliminate - at least reduce - the huge waste of brainpower when the two get confused. For example, Copenhagen and thermal interpretations are, AFAIK, both valid ways to picture what the math describes. Sure, you can prefer one or the other, and debate them - a bit. But at some point realize it just doesn't matter, and let the other guy picture it however he wants.

That's assuming they really are both valid interpretations, or ontologies. It may be possible to prove, rigorously, that what appears valid really isn't. If reality were that way, it couldn't give the experimental results. That's what Bell's inequality (and related experiments) successfully does: rules out a type of at-first-glance plausible model, by clever mathematical and scientific reasoning.

Go ahead and do science using all necessary auxiliaries: philosophy, math, language, logic, classrooms, conferences, grants, salaries, food, water, and many other things which aren't science per se. But whenever you get into one of these endless arguments, it's time to step back a moment. Is it really about science? In that case, argue away, since it's actually decidable. Or, is it really about philosophy? In that case shrug, and agree to disagree. Or, go argue about it (if you must) on a philosophy board, not PF :-)

In other words, ontic states are the things that would still exist if all intelligent beings were suddenly wiped out from the universe.

A quibble: I see no reason to limit it to intelligent beings, rather any conscious beings with some rudimentary mind. And, BTW, it's possible nothing would still exist if all consciousness were wiped out: that ontology is an artifact of epistemology. That's a key point in this discussion.

 

[Simon Phoenix]

That's what Bell's inequality (and related experiments) successfully does: rules out a type of at-first-glance plausible model, by clever mathematical and scientific reasoning.

Yes - and that's really one of the main thrusts of Leifer's article - to examine whether it's possible to rigorously rule out certain ways of looking at things and to lift the debate out of the murky philosophical waters and into the crystal clarity of the light of science

(only slightly tongue-in-cheek there)

 

[Demystifier]

But if there is no wave function of CERN, then you are treating CERN as a "classical measuring apparatus", which is the Heisenberg cut.

There is no problem with the Heisenberg cut, provided that you don't take it too seriously, but merely use it as a practical operational tool. (Perhaps this is not what Bohr would say, but probably something what Peres would agree with.)

 

[Ken G]

This was not my point. My point was more modest, that when two theories are mutually inconsistent at least one of them is wrong.

But your point is more than that-- you are saying that it would not be true that one of them had to be wrong unless there was a reality that the theories were attempting to model. I see it simply as a logical requirement that both theories cannot be completely correct if they disagree, like saying that if 2+2=4 it cannot also equal 5 unless 4 and 5 are equivalent. We don't need a reality to enforce that mathematical truth, so why do we need it in physics? There is no part of physics that says "this only works if there is a reality", there is only "model, test, repeat, all the while using mathematical logic." We set it up that way because it appears to work, and for no other reason. Certainly not "because there is a reality," no such requirement exists. It's not that there isn't a reality, it's that science doesn't need what it never uses.

 

[Ken G]

Actually I am trying to figure out reality - but not qua scientist. Indeed the only reason I'm interested in science - these days, since I no longer need a job - is to help me understand what reality "really is". That's the job of philosophy, which uses scientific facts as raw material.

Fair enough, I really only mean that the scientist is not trying to do that. As a kind of subroutine invoked by a philosopher, science can be used for that goal, going outside the subroutine. I agree with you that the paradoxes only occur when the "program" being used cannot distinguish the inside from the outside of that subroutine. A computer programmer would instantly notice a problem if there was a specific goto statement within a subroutine that referred to the main program, so why don't physicists notice that same thing when they take scientific ontology seriously in the process of solving physics equations?

Premises:

1) Only scientific reasoning is valid.
2) But I want to know what reality is.

Conclusion: Therefore the ontological question - what is real - must be scientific, or I can't address it.

This is a problem, because the reasoning you just applied is not scientific, it is philosophical. Philosophical reasoning obeys the rules of logic, and uses premises and axioms as you are doing, but it's not scientific reasoning until it looks like "model, test, repeat." So for a set of premises to be part of scientific reasoning ,they can never be taken as axioms of truth, they must always be hypotheses to be tested. It doesn't sound like your goal is to test those premises, it sounds like your goal is to take them as given and go from there. But as soon as you do that, you are not doing scientific reasoning. Thus, this program is incompatible with premises that assert that only scientific reasoning is valid. The program is internally inconsistent, which is the problem with logical positivism, which essentially embodies the subjective philosophy of replacing subjective philosophy with science, which doesn't make sense. It can be fixed either by treating the reliance on scientific reasoning as the hypothesis being tested (which will never close the process because the tests of science never end), or by accepting that other forms of reasoning than science are valid (which opens the problem to what forms of reasoning that includes). Either way, it's a program that does not complete in a finite number of steps, but like science itself, this need not be viewed as a problem if one focuses on the lessons of the journey rather than some final destination.

There's no problem if one also says that science's idea of a rock (for instance) is "merely descriptive of our 'state of knowledge'". Paradox occurs only when you say a rock is ontologically real but a wavefunction (or at least, some aspect of QM) isn't. Something real can't be composed of a bunch of things that aren't real!

Yes, that's right on. In fact, we could view it as rather bizarre that most people regard rocks as ontologically real without doubt, but the wavefunction of an isolated hydrogen atom as an epistemological abstraction, when the wavefunction is much simpler and more precise, and is used in a much more tightly constrained way. I think all that is happening there is that the concept of a "rock" is so much more vague that its epistemological character is more difficult to see. Ironically, this means we only regard wavefunctions as abstractions and rocks as fundamental entities because we understand the former so much better than the latter.

 

[Simon Phoenix]

We set it up that way because it appears to work, and for no other reason. Certainly not "because there is a reality," no such requirement exists. It's not that there isn't a reality, it's that science doesn't need what it never uses.

When did science become so defeatist?

My primary motivation is to understand "why the world is as it is", so to speak. I'll settle for the secondary goal of being able to predict stuff - but ultimately I'm really wanting something a bit more than some set of techniques that 'work' - and when those techniques are said not to be descriptive of some underlying reality but, rather, descriptive of what's going on in my noggin - then I do have to do the occasional sanity check

Before QM came along I suspect that very few scientists would have held that it is the job of science just to predict stuff, and not to say anything about 'reality'. Of course after QM, when it became awkward (to say the least) to ascribe some 'reality' to the state, I get the impression it was as if there was some collective decision to 'redefine' what science is about.

 

[Ken G]

Now everything gets mixed up. Of course quantum theory is there because humans have discovered it as a description of what's observed but not more, particularly it doesn't provide ontology (neither does classical physics). The observables are defined operationally by real-world measurement processes. Whether even a classical abstraction as the electromagnetic field has an ontic meaning, is completely outside of science. It is a mathematical description that describes successfully what we observe in the corresponding realm of nature, including phenomena from electrostatic and magnetic forces to light (electromagnetic waves). Whether the field is ontic or not, cannot be clarified in any way but is a matter of personal world view. What can be stated scientifically is that it's a mathematical picture which fits to all observations.

Surely this must be something no scientist can disagree with, can this not be considered a consensus view? All it does is enforce the distinction between how science is defined, and what people sometimes choose to use it for that goes beyond that definition.

 

[Ken G]

When did science become so defeatist?

This is a crucial point-- is it really defeatist to notice that science doesn't do ontology because what it actually does is challenge hypotheses? I don't see that as giving up on science, I see it as empowering science. It is the wings that let science fly, that it does not pin itself down to one doomed ontology after another (though that does seem to be how many people seem compelled to use it.) Look at all the doomed ontologies of history, and how effortlessly science abandoned them without a hitch. Is it defeatist to notice science's greatest strength?

My primary motivation is to understand "why the world is as it is", so to speak.

Then let me suggest a minor but crucial reframing of that which is more compatible with science: your primary motivation is to generate a working picture of why the world is as it is. Your working picture should pass a bunch of tests, and offer considerable conceptual unification. And it should contain valuable lessons, not the least of which is that you should expect it to one day be replaced by something almost completely different-- likely after you and I are long gone.

I'll settle for the secondary goal of being able to predict stuff - but ultimately I'm really wanting something a bit more than some set of techniques that 'work' - and when those techniques are said not to be descriptive of some underlying reality but, rather, descriptive of what's going on in my noggin - then I do have to do the occasional sanity check

We all want more than successful predictions. Nobody ever "shuts up and calculates", we are not adding machines. The pictures we create are wonderful, exquisite, and fascinating, all without the impossible requirement of being some true reality. What's so wrong about freeing the constraints from what science has never been, and let it be what it demonstrably actually is?

Of course after QM, when it became awkward (to say the least) to ascribe some 'reality' to the state, I get the impression it was as if there was some collective decision to 'redefine' what science is about.

I suspect that our modern fascination with the spookiness of quantum mechanics, and the challenges it presents to our concepts of reality, is actually nothing new at all-- it's simply the modern version of what science has constantly encountered. Could going from trajectories to superpositions of wavefunctions be any more shaking to one's world view than going from a stationary Earth at the center of a lofty and exalted heavens, to a random rock at a random location of a vast cosmos of seemingly arbitrary interactions? Every new theory shatters the old ontology, and every generation thinks their own version is the one that is a crisis. I think Feynman's sage words are more the norm than the exception:
"We have always had a great deal of difficulty understanding the world view that quantum mechanics represents. At least I do, because I'm an old enough man that I haven't got to the point that this stuff is obvious to me. Okay, I still get nervous with it... You know how it always is, every new idea, it takes a generation or two until it becomes obvious that there's no real problem. I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem."

 

[zonde]

But your point is more than that-- you are saying that it would not be true that one of them had to be wrong unless there was a reality that the theories were attempting to model. I see it simply as a logical requirement that both theories cannot be completely correct if they disagree, like saying that if 2+2=4 it cannot also equal 5 unless 4 and 5 are equivalent. We don't need a reality to enforce that mathematical truth, so why do we need it in physics?

First let me make my statement more general by stating that "when two descriptions are mutually inconsistent at least one of them is wrong" as single theory can implement alternative descriptions.
Now let me give you two examples.
In special relativity you can describe physical situation from different inertial reference frames. These descriptions are mutually consistent.
In orthodox quantum theory it is common to say that say quite large complex object (buckyball) can be in superposition of going through left or right slit. These two descriptions are not mutually consistent because both options are required to predict result.
In second case proposed explanation contradicts realism. Now the question is - can we come up with model that gives correct prediction but does not contradict realism? And pilot wave theory does that.

There is no part of physics that says "this only works if there is a reality", there is only "model, test, repeat, all the while using mathematical logic." We set it up that way because it appears to work, and for no other reason. Certainly not "because there is a reality," no such requirement exists. It's not that there isn't a reality, it's that science doesn't need what it never uses.

We evaluate models, if they are scientifically acceptable. For example we require that predictions of model are unequivocal.

 

[zonde]

The pictures we create are wonderful, exquisite, and fascinating, all without the impossible requirement of being some true reality. What's so wrong about freeing the constraints from what science has never been, and let it be what it demonstrably actually is?

This is strawman argument. We do not require that our ontologies are true reality. Ontolgies are only good approximations of reality that simplify our current and future models as they are reusable in different models.

 

[atyy]

The big problem with ignoring ontology is that people who claim to ignore it actually promote it: eg. Ballentine, Peres and vanhees71.

If they truly did not care about ontology, they would have no problems with collapse.

There are well respected positions that ignore ontology, eg. Bohr, Landau and Lifshitz, Copenhagen as described by Weinberg - but all of these have things which are disavowed by vanhees71, eg. collapse and the Heisenberg cut.

 

[Ken G]

Now the question is - can we come up with model that gives correct prediction but does not contradict realism? And pilot wave theory does that.

It is impossible to contradict realism, because realism is untestable. All one could ever contradict is a prediction, and pilot wave theory does not contradict any predictions that quantum mechanics does not contradict. I agree that when our technology becomes able to test predictions that pilot theory makes that go beyond quantum theory, then it becomes an interesting physical theory, but that it doesn't contradict realism is of no interest within the "science" subroutine. It does not surprise me at all that any scientific theory can be dressed up suitably to get it to satisfy any philosophical doctrine, what bothers me is that dressing up our science to get it to fit preconceived notions seems very opposite to the spirit of science. But if someone says "I like to picture a pilot wave when I do quantum mechanics because it allows me to picture a classical world", then there can be no objection whatsoever.

 

[Ken G]

This is strawman argument. We do not require that our ontologies are true reality. Ontolgies are only good approximations of reality that simplify our current and future models as they are reusable in different models.

So you are fine with saying "one can picture that matter is made of atoms to help motivate the correct application of our theory of matter" instead of saying "matter is made of atoms"? Because that's what I'm talking about.

 

[vanhees71]

If it comes to ontological interpretations of quantum theory, you cannot scientifically disproof the one or the other by observation/experiment, and that's why this question is not science but philosophy. There are many things in philosophy, very important for our existence, that cannot be scientifically evaluated like ethics. Science is not comprehensive concerning human experience. This one shouldn't forget as a scientist both concerning science and all the other realms of the human endeavors. It is important to know the restrictions and the strengths of science. The restriction is that science only deals with the description of phenomena that are reproducible and can be objectively observed, i.e., that are not due to some errorneous experiences of our brain like dreams or conscious prejudices. All that counts for science is observable by anybody leading to the same (often even accurate quantitative) results given (with sufficient precision) a certain situation. This situation can just be found in nature (as is the case for all astronomical observations, where we just observe "what's out there" without the possiblity for us to manipulate anything) or it can be "men made" in the sense that we can setup particularly simple situations (sometimes with an astonishing precision), and this we call an experiment.

In this way one finds patterns in the phenomena, which can be described mathematically in models or even theories (there are many models but a very few theories; fundamental theories in common use in contemporary physics are just general relativity and quantum theory and effective theories valid in restricted realms of applicability like relativistic and non-relativistic classical mechanics and field theories). That this is the case is already a remarkable observation and one of the key results of physics. These theories lead to the development of technologies and with them new possibilities to measure things which are far away from the everyday experience of the environment around us, and it is not surprising that many things, particularly concerning quantum theory, seem to be quite bizarre to us, because they refer to things outside of our everyday experience (like single elementary particles like electrons interacting with other particles or superfluid helium etc.).

That seems to trigger all kinds of speculation concerning the "ontology", and there are as many ontic interpretations of QT as there are physicists, and of course these must be in accordance with the observational facts, which are in a sense summarized in the fundamental theory of QT. These interpretations can thus not be scientifically distinguished and are thus not part of science. The only thing you need for a physical theory not to be just an abstract mathematical game but a "summary of observed phenomena" is a connection between the mathematical formalism and what's observed in the lab or elsewhere in nature. In this sense the mathematical objects of the theory are only epistemic, i.e., mere descriptions of what's observable given the information about the situation in which you make these observations. There is not more but also not less to science than that.

 

[Simon Phoenix]

What's so wrong about freeing the constraints from what science has never been, and let it be what it demonstrably actually is?

Well, when I'm describing my primary goal as one of 'understanding' why the world as it is - of course I'm not suggesting that one should mindlessly fixate on one particular ontology :-)

I guess the philosophical question is whether there is some 'underlying' reality to which our theories (and pictures, if you like) get closer and closer as we develop them. In terms of QM we don't even have a good way of describing that underlying reality (if it does indeed exist) and as far as predictions go we don't even 'need' to develop such a picture.

Let's just assume a classical world view, for the moment. There is something we call an electric field and we have a very good mathematical framework for describing this. Is it just fancy maths or is there really something there? Well whenever we put a test charge in this field we can see it responds to 'something' - it feels a pull or a push. Furthermore, this pull or push is precisely described by this mathematical model. The mathematical model is a very faithful model of something that actually happens. I think it's stretching things a bit to describe the maths as being essentially divorced from the reality here. There really is something that behaves to all intents and purposes as if it were the physical analogue of our mathematical model.

Of course we may need to adjust that picture in the light of new evidence (Newton's gravitational 'force' being replaced by a bending of the fabric of spacetime is a prime example of a very radical revision of our picture of things).

I just don't think 'science' is only about building successful epicycles.

 

[atyy]

If it comes to ontological interpretations of quantum theory, you cannot scientifically disproof the one or the other by observation/experiment, and that's why this question is not science but philosophy. There are many things in philosophy, very important for our existence, that cannot be scientifically evaluated like ethics. Science is not comprehensive concerning human experience. This one shouldn't forget as a scientist both concerning science and all the other realms of the human endeavors. It is important to know the restrictions and the strengths of science. The restriction is that science only deals with the description of phenomena that are reproducible and can be objectively observed, i.e., that are not due to some errorneous experiences of our brain like dreams or conscious prejudices. All that counts for science is observable by anybody leading to the same (often even accurate quantitative) results given (with sufficient precision) a certain situation. This situation can just be found in nature (as is the case for all astronomical observations, where we just observe "what's out there" without the possiblity for us to manipulate anything) or it can be "men made" in the sense that we can setup particularly simple situations (sometimes with an astonishing precision), and this we call an experiment.

In this way one finds patterns in the phenomena, which can be described mathematically in models or even theories (there are many models but a very few theories; fundamental theories in common use in contemporary physics are just general relativity and quantum theory and effective theories valid in restricted realms of applicability like relativistic and non-relativistic classical mechanics and field theories). That this is the case is already a remarkable observation and one of the key results of physics. These theories lead to the development of technologies and with them new possibilities to measure things which are far away from the everyday experience of the environment around us, and it is not surprising that many things, particularly concerning quantum theory, seem to be quite bizarre to us, because they refer to things outside of our everyday experience (like single elementary particles like electrons interacting with other particles or superfluid helium etc.).

That seems to trigger all kinds of speculation concerning the "ontology", and there are as many ontic interpretations of QT as there are physicists, and of course these must be in accordance with the observational facts, which are in a sense summarized in the fundamental theory of QT. These interpretations can thus not be scientifically distinguished and are thus not part of science. The only thing you need for a physical theory not to be just an abstract mathematical game but a "summary of observed phenomena" is a connection between the mathematical formalism and what's observed in the lab or elsewhere in nature. In this sense the mathematical objects of the theory are only epistemic, i.e., mere descriptions of what's observable given the information about the situation in which you make these observations. There is not more but also not less to science than that.

But you are the one promoting ontology! If you don't care about ontology, you would not object to collapse.

 

[vanhees71]

I object to collapse because it violates fundamental principles, but we have discussed this again and again. There's no value of repeating the obvious argument again and again.

 

[atyy]

I object to collapse because it violates fundamental principles, but we have discussed this again and again. There's no value of repeating the obvious argument again and again.

Your fundamental principles are ontological. Collapse clearly does not affect the locality of the Hamiltonian, nor does collapse allow superluminal signalling.

 

[Ken G]

What I mean that science doesn't do ontology goes well beyond the strawman argument that science only approximates, it questions what an approximation even is. If I approximate curvature of spacetime near the Earth by invoking Newton's force of gravity, I have two schemes that make very closely the same predictions, but their ontologies are not even remotely close. So that's what "approximation" means in science, it never means that our ontologies are nearly the correct ones-- I wouldn't even know how to give that phrase meaning.

So for example, when Galileo challenged Ptolemy's ontology, he really should have said words to the effect that "by invoking the Copernican model, we better predict the following observations, and we also achieve the following conceptual unifications. Hence, we achieve greater predictive and conceptual power in the framework of the Copernican picture than the Ptolemaic picture." It's much more memorable to say "Eppur si muove", but it's really not good science-- as we discovered a few hundred years later with the next revolution in thought about motion.

 

[Simon Phoenix]

If it comes to ontological interpretations of quantum theory, you cannot scientifically disproof the one or the other by observation/experiment

I would certainly say that we can't currently distinguish between the various interpretations (any of the various ontic, epistemic or some mix of the two). But is it true to say that in principle we cannot? Maybe there's something in the structure of QM, some future Bell that will ring, that will allow us to subject some of the different interpretations to experimental test. I'd like to think so - but in the meantime it's "keep the philosophy quiet whilst I do this calculation".

 

[zonde]

So you are fine with saying "one can picture that matter is made of atoms to help motivate the correct application of our theory of matter" instead of saying "matter is made of atoms"? Because that's what I'm talking about.

Sort of. I would say that "one can picture that matter is made of atoms to greatly simplify different theories about matter (in chemistry and physics)".
Hmm, how would look alternative formulations of these theories without some element that takes place of atoms. Just thinking.