Why is anything measurable?

[ConradDJ]

I want to argue that there’s something very basic about the structure of the physical world that’s taken for granted everywhere in physics, but isn’t actually described in any theory. The argument goes like this –

What does it take for any physical parameter to be observable? Take the mass of a particle – there are several ways to measure that. For example, if we know its charge, we can watch how the particle’s path gets deflected as it moves through a magnetic field. To do that we have to measure its charge and observe its position at certain times, so we have to be able to measure distances and time-intervals, as well as the strength and orientation of the field.

Very generally, every way that any physical parameter can be measured will always involve the measurement of several other parameters. There is no such thing as a simple isolated measurement. So the question is – in what kind of system is any kind of measurement possible?

What I want to get at here has nothing to do with whether a human being is involved. It’s a question of what’s needed in the physical situation itself so that the value of a certain parameter can be meaningfully defined, in that situation. The mass of the particle can’t be meaningfully defined except by reference to other parameters, whose values must also be meaningfully defined.

Now in the world we live in, there are obviously many observable parameters. For every one of them there are certain interaction-contexts through which they can be measured, all of which involve the measurement of other parameters, in other interaction-contexts. It’s not important to this argument exactly what a “measurement” or “observation” is. It’s enough that we know they’re possible... and that for anything to be in any way observable, there have to be other things that are also observable, in terms of still other things that are also observable.

This isn’t an infinite regress – I assume there are only a finite number of basic physical parameters defining each other. But there has to be a certain closure or completeness to the structure of the observable world, as a self-defining system. It seems to me that this inter-referential completeness is a very remarkable characteristic of our universe, and one that no theory I know of takes into account.

We tend to take it for granted that if something is real, then of course there will be some way to measure it. After all, if a particle has a certain property X that can’t be observed in any way, then it makes no difference to anything whether that property exists or not – it’s simply meaningless. That makes sense, but I don’t think it undercuts my argument.

It’s easy to see that not just any physical system supports the measurement of its own parameters. Imagine a Minimal Newtonian Cosmos consisting of simple point-particles scattered through Euclidean space and time. Say each particle has a certain mass, and no other characteristics, and that they interact with each other only through Newton’s gravity.

This seems like a mathematically well-defined system – but there’s no way actually to measure the distance between two particles, or how they move, or what their respective masses are. Interaction in this system may be lawful, but it doesn’t communicate any information about anything, since none of the parameters of the law are defined by the system itself.

My point is that in physics, we don’t require that our theoretical models define all their own parameters in terms of each other. We try not to introduce parameters that are – in our universe – unobservable. But we don’t try to model what it is about the structure of our universe that lets anything be observable.

I think this is probably why we haven’t come to any clear understanding about Relativity and Quantum theory, and the relationship between them. These theories both (in different ways) make measurement central, but we’re still building models that don’t consider what it takes to make any measurement possible.

[kote]

I like it, but I'm a little confused. I see the underline - can you clarify what you are asking though?

I will say that it all reminds me of arguments concerning language. How can we precisely define any word when we must use other undefined words to do so? Are we doomed to circular references and ambiguity? Is precision even possible?

Anyways I don't want an answer. I just thought it was interesting parallel. But what exactly are you asking? Are you looking for a grounding to the circular definitions of properties in terms of other properties?

[kote]

See http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/MentalSemanticHolism.html#anchor822217 (It's just a passing overview, so I'm sure there's better literature to find)
One doesn't learn definitions of 'force', 'mass', 'kinetic energy', or 'momentum' in terms that are understood beforehand, for there are no such definitions. Rather, these terms are learned together (in conjunction with procedures for solving problems. As Quine and Putnam argued, local "definitions" in a scientific theory tend to be mere passing expository devices of no lasting importance for the theory itself. And this is quite ubiquitous in theories--a circle of interdefined theoretical terms none of which are definable in terms outside the theory. This fact motivates Lewis' proposal that scientific terms can be defined functionally in terms of their roles in a whole theory (see FUNCTIONALISM; SEMANTICS, CONCEPTUAL ROLE).

Also:

http://en.wikipedia.org/wiki/Confirmation_holism
http://en.wikipedia.org/wiki/Semantic_holism

[rewebster]

in what kind of system is any kind of measurement possible?


Those things which are known, and that we are capable of measuring through 'standards' we have set with the measuring tools we have created.

[brainstorm]

The OP started with a empirical approach to measurement and then degenerated (in my evaluative opinion) into a philosophical discussion of logical propositions and necessary conditions/consequences.

When I want to understand what measurement is and what makes it possible, I would start with a sample of concrete examples. To measure the mass of something, you place it on a scale where the fulcrum is exactly in between the end-points. Then you balance the scale with an certain amount of standardized mass-units on the other end, such as 1g weights. Measuring mass, thus, requires comparison based on the principle of a lever suspended in a homogeneous gravity context. One object going down is presumed to exert equivalent force to the opposite object being pushed up, hence the comparison becomes possible.

So things are measurable not because they exist, but because they are manipulated to generate results according to the logic of certain assumptions, which may also be verified through repeatable testing. If you don't believe a scale works, you can measure one object and then another of the same mass and then balance the two objects with each other instead of counterweights. This demonstrates generalizability among different instances of applying the same comparative logic.

If different things couldn't be compared in terms of the same comparative reference, they would not be measurable; or you would have to experiment until a stable reference was found.

Measurement is based on the logic of regularity and comparability.

Now my question is what the empirical facts are about this magnetic field used to measure particles. What is measured exactly and how?

[humanino]

If I want to measure a length with a 1 mm accuracy, I need a stick 1 mm long, and I will count how many of those sticks will cover the length I want to measure. So all I need is a reference stick. In the past, the reference stick was defined by an actual physical stick. Today, the definition of length is a spectral one, from quantum mechanics. In principle, it does not require anything to be previously defined. It is a (pure) number times the wavelength of an atomic transition. We can have experimental definitions for units which are purely spectral, and only require a pure integral number times a fundamental constant throughout the universe. This is not done yet for every unit, in particular, the mass is still defined from a physical object (IIRC).

On the theoretical side, we know the exact lists of parameters for our standard models of particle physics or cosmology for instance. Particle physics has 20 or so parameters. Speculations beyond the standard model amount to reducing this number of parameters, and this requirement is something explicit and well-understood in any serious research beyond the standard model of particle physics.

Magnetic fields can be used to measure the ratio of charge to momentum for a particle. This ratio is directly related to the curvature radius of the trajectory of the particle in the magnetic field.

[rewebster]

Now my question is what the empirical facts are about this magnetic field used to measure particles. What is measured exactly and how?

well, you're going to have to wait just for a while until the 'magnetic field' is explained

[brainstorm]

Empiricism and critical reason seems to be absent in these explanations of measurement. Are people capable of breaking these things down to the level of reviewable observations and reasoning, or is that too basic a level?

[rewebster]

Empiricism and critical reason seems to be absent in these explanations of measurement. 1) Are people capable of breaking these things down to the level of reviewable observations and reasoning, or 2) is that too basic a level?


1) yes

2) no

[brainstorm]

1) yes

2) no

Wonderful, but you don't provide an example to go with it.

[rewebster]

Wonderful, but you don't provide an example to go with it.

what kind of example were you looking for?

If your question is about the magnetic field, refer back to post #7

[kote]

To address a little more of the original question...

In your minimal universe, if the only force is gravity, then that is what must be used for measurement. Introduce a third low-mass particle and see how it behaves. You can see the mass and location of the first two particles by observing what happens to your measuring device, the third particle.

I know you wanted to avoid questions of measurement, but barring discussions of subjective knowledge, measurement just is interaction. Any system that undergoes an effect can be said to have measured whatever system it was that caused that effect. Measuring devices are physical systems designed to amplify effects to give us information about their causes.

And units, of course, are arbitrary in terms of any underlying framework. We pick units that are useful because of their relationship to certain aspects of nature that we observe (or to other units that we decide are more basic).

As to what generates observables from the void... who knows. In your example system, mass and location actually are observable because information about them can be communicated through gravity, which you allow for. Say your universe also has charge, though, but with no EM fields. Then you really would have a mathematically defined parameter with absolutely no method of being measured. There's no way to tell that there aren't such properties.

From QM we know that things like mass and spin are not consistently defined properties belonging to particles. It is very reasonable to question whether these properties can even be said to exist, or if there is some other basic layer that these manifest out of. The properties we have probably aren't even basic, but because they are measurable, they are all we have to work with. Since we can't investigate anything beyond the observable, we're really just stuck here. I think at this point the question reduces to why is there something rather than nothing? - what reason is there for anything to appear as an observable. That's a tough question, but at least there's been a lot of investigation into it.

So to answer why is anything measurable? I would refer to discussions of why is there something rather than nothing? I really think they reduce to the same question of why observables exist, or rather, why anything is observable. There is a technical difference on the matter of unobservable properties, but unobservable properties aren't what anyone is asking about when they ask why there's something rather than nothing. That technicality isn't a concern for any of the arguments.

Unless, of course, your issue is with the holism of scientific theories and properties. Then see above :smile:.

[brainstorm]

what kind of example were you looking for?

If your question is about the magnetic field, refer back to post #7

What I'm looking for? You answered my question that "yes, people are capable of breaking these things down to the level of reviewable observations and reasoning."

You shouldn't have to explain how a magnetic field works to explain how it can be applied to measure something else. You don't have to explain how gravity works to postulate that downward movement on one side of a scale is equal to upward movement on the other, and that the two balancing each other out means mass-equivalency.

[rewebster]

You shouldn't have to explain how a magnetic field works to explain how it can be applied to measure something else. You don't have to explain how gravity works to postulate that downward movement on one side of a scale is equal to upward movement on the other, and that the two balancing each other out means mass-equivalency.

well, if you don't explain how a magnetic field works or you don't explain how gravity works, then any results will be flawed to some extent, in the same way as if you don't know how a yardstick works (how to use it), it can only be used in a comparative sense, like the balance beam scale.

[humanino]

From QM we know that things like mass and spin are not consistently defined properties belonging to particles.Mass and spin are precisely the constants required to define a particle in modern QM. Mass and spin define the representation of the proper orthochronous Lorentz group to which the particle belong.

[kote]

Can I ask if you agree with the argument that "why is anything measurable?" is functionally equivalent to "why is there something rather than nothing?" See above, but to recap, it's something like:

Why is anything measurable?
Why is anything observable?
Why is anything an observable?
Why do observables exist?
Why do observables exist rather than not existing?
Why is there something rather than nothing?

If you disagree that the above are equivalent, or at least equivalently motivated (and therefore analyzed), at which step do you think they differ and why?

[kote]

Mass and spin are precisely the constants required to define a particle in modern QM. Mass and spin define the representation of the proper orthochronous Lorentz group to which the particle belong.

And neither mass nor spin are persistently defined on a particle. There are particles with indefinite mass. There are particles with indefinite spin. Neither mass nor spin can therefore be an essential property of a particle, so the argument goes.*

If there are basic properties essential to the existence of particles, we haven't found them yet.

This conversation probably belongs somewhere else though. It wasn't terribly important to my argument.

(*Similarly, no other properties that we use in physics can be essential properties of particles.)

[brainstorm]

well, if you don't explain how a magnetic field works or you don't explain how gravity works, then any results will be flawed to some extent, in the same way as if you don't know how a yeardstick works (how to use it), it can only be used in a comparative sense, like the balance beam scale.

the comparative sense is all that is entailed in measurement. Measurement is nothing more than comparison of comparable things in terms of standardized units. You can measure length in terms of anything else, if you can keep moving one across the other without losing track of where the end of it was before you put it at the point again as a beginning. You can measure volume using any comparison if both can be submerged in the same fluid. The foundation of measurement is to understand the mechanics of the instrumentation.

[brainstorm]

Can I ask if you agree with the argument that "why is anything measurable?" is functionally equivalent to "why is there something rather than nothing?" See above, but to recap, it's something like:

Why is anything measurable?
Why is anything observable?
Why is anything an observable?
Why do observables exist?
Why do observables exist rather than not existing?
Why is there something rather than nothing?

If you disagree that the above are equivalent, or at least equivalently motivated (and therefore analyzed), at which step do you think they differ and why?

The title of the thread is "why is anything measurable," but it sounds like it should be "is measurability proof of existence?"

It's not. You can measure an imaginary unicorn with an imaginary yardstick and arrive at an imaginary length, but it doesn't mean the unicorn or the yardstick existed outside of your imagination.

[kote]

You can measure an imaginary unicorn...

Yeah, you can't measure imaginary things. You can pretend to, but that's totally irrelevant to anything we're discussing.

I'm trying to keep this on track here. I think we'd all appreciate a little effort.

[rewebster]

The 'knowns' that we use are 'accepted' for applied use.

---this is one reason why a lot of debates arise in these forums. The people that profess the accepted knowledge will present it to explain a question that arises. When the debate goes into the 'unknown' realm, like where this is, it can go more into what one believes.


Measurement seems to be limited down (or out) to the point where it stops at the 'next' assumed 'unknown'.



(PS---this thread is in philosophy)

[brainstorm]

The 'knowns' that we use are 'accepted' for applied use.

---this is one reason why a lot of debates arise in these forums. The people that profess the accepted knowledge will present it to explain a question that arises. When the debate goes into the 'unknown' realm, like where this is, it can go more into what one believes.

Somewhere in between what is known because it is received from a trusted authority and what is unknown but believed, there is what can be established through critical reason.

You don't have to "accept" "knowns" on the basis of applied use, although it can be helpful to for instrumental/practical purposes. You can also dissect why or how something can be known or applied. As you said, this is the philosophy forum - so philosophize.

[humanino]

And neither mass nor spin are persistently defined on a particle.Yes, they are defined. There are particles with indefinite mass.No there is not. There are particles with indefinite spin.No there is not.
Neither mass nor spin can therefore be an essential property of a particle, so the argument goes.This is basically chapter 1 of any good book on quantum field theory, the definition of a particle from the representation of Lorentz group it belongs to. You obviously have no idea what you are talking about. Do you know what a group representation is ? Do you know what the Lorentz group is ? Have you heard of Casimir operators ? For Pete's sake, look up "standard model" on wikipedia and you will find a list of particles, defined by their masses, spins, and a few other discrete quantum numbers such as parity.

Can you please name a particle whose spin would not be defined ? There is a basic superselection rule in quantum mechanics that we can not have coherent superpositions of states with different angular momenta.

[brainstorm]

Why doesn't anyone posting on this thread just provide some example of exactly how something is measured instead of jumping into discursive references to complex phemonena or other texts?

If you would just pick some particle with definite mass and definite spin, and explain how these are measured - the issue would be empirically clarified.

[rewebster]

Somewhere in between what is known because it is received from a trusted authority and what is unknown but believed, there is what can be established through critical reason.

You don't have to "accept" "knowns" on the basis of applied use, although it can be helpful to for instrumental/practical purposes. You can also dissect why or how something can be known or applied. As you said, this is the philosophy forum - so philosophize.

and I thought I was---my, my, my...



As far as any 'magnetic' anything to measure anything/something very, very small, we may know some about what a magnetic field can do, but it is an 'accepted' unknown in what it really is. So, doing anything with it is that last step in the 'accepted' unknown measurement.

[brainstorm]

As far as any 'magnetic' anything to measure anything/something very, very small, we may know some about what a magnetic field can do, but it is an 'accepted' unknown in what it really is. So, doing anything with it is that last step in the 'accepted' unknown measurement.

Why can't you just say what it is supposed to be doing when you're using it?

[rewebster]

Why can't you just say what it is supposed to be doing when you're using it?

well, (its a lot better if) you have to know what it is doing, before you can say what it's supposed to be doing.

[brainstorm]

well, 'its a lot better if' you have to know what it is doing, before you can say what it's supposed to be doing.

you didn't say either in your post. what is it doing? what is it supposed to be doing? what do you think it is doing? answers to any of these question would be a substantive starting point.

[rewebster]

you didn't say either in your post. what is it doing? what is it supposed to be doing? what do you think it is doing? answers to any of these question would be a substantive starting point.

yes, they would (were)

[brainstorm]

yes, they would (were)

ok, I didn't get you were purposefully trolling until now. You never intended to do anything more than circumvent substance did you?

[rewebster]

ok, I didn't get you were purposefully trolling until now. You never intended to do anything more than circumvent substance did you?

its against forum rules to post one's theories


if you think that thinking about these things are a good 'starting point' , I agree totally with you

[kote]

Can you please name a particle whose spin would not be defined ?

Huh? It's simple HUP. When particles have a defined location, they don't have a defined momentum... all that good stuff. I suppose I should clarify spin in a certain direction rather than just spin in general, but that's beside the point. Unless you are arguing that particles always have a defined spin in every direction, I don't see how you could disagree with the statement that some particles have undefined spin (in a given direction).

See http://arxiv.org/abs/quant-ph/0110102 for some published rigor on complementarity. Also http://arxiv.org/abs/quant-ph/9905042. As for particles in QFT: http://arxiv.org/abs/quant-ph/0103041. I don't claim to be a QFT expert, but I thought we were pretty set on HUP when it comes to particle properties, no? If it's about "essential properties," fine, that's a philosophical concept that my claim relies on. Hence the "so the argument goes" above.

I'd be happy to follow to the QM forum if you'd care to explain where I'm wrong here.

[brainstorm]

Huh? It's simple HUP. When particles have a defined location, they don't have a defined momentum... all that good stuff. I suppose I should clarify spin in a certain direction rather than just spin in general, but that's beside the point. Unless you are arguing that particles always have a defined spin in every direction, I don't see how you could disagree with the statement that some particles have undefined spin (in a given direction).

See http://arxiv.org/abs/quant-ph/0110102 for some published rigor on complementarity. Also http://arxiv.org/abs/quant-ph/9905042. As for particles in QFT: http://arxiv.org/abs/quant-ph/0103041. I don't claim to be a QFT expert, but I thought we were pretty set on HUP when it comes to particle properties, no? If it's about "essential properties," fine, that's a philosophical concept that my claim relies on. Hence the "so the argument goes" above.

I'd be happy to follow to the QM forum if you'd care to explain where I'm wrong here.

how is spin-direction observed? How is the particle identified in the first place, for that matter?

[humanino]

I suppose I should clarify spin in a certain direction rather than just spin in general, but that's beside the point.Yes you should have clarified it because it is quite different. So particle still have a well defined spin, although they can have different spin components, good.

Now can you describe a situation where a particle has a undefined mass ? I suppose you are going to invoke the HUP again. That would not be a measurable particle then, but a virtual particle. Real particles always have a well-defined mass.

[brainstorm]

Yes you should have clarified it because it is quite different. So particle still have a well defined spin, although they can have different spin components, good.

Now can you describe a situation where a particle has a undefined mass ? I suppose you are going to invoke the HUP again. That would not be a measurable particle then, but a virtual particle. Real particles always have a well-defined mass.

Why does every post in this thread address theory instead of empirical methodology? Why can't people just explain how their observables are empirically observed and measured?

[ZapperZ]

Huh? It's simple HUP. When particles have a defined location, they don't have a defined momentum... all that good stuff. I suppose I should clarify spin in a certain direction rather than just spin in general, but that's beside the point. Unless you are arguing that particles always have a defined spin in every direction, I don't see how you could disagree with the statement that some particles have undefined spin (in a given direction).

See http://arxiv.org/abs/quant-ph/0110102 for some published rigor on complementarity. Also http://arxiv.org/abs/quant-ph/9905042. As for particles in QFT: http://arxiv.org/abs/quant-ph/0103041. I don't claim to be a QFT expert, but I thought we were pretty set on HUP when it comes to particle properties, no? If it's about "essential properties," fine, that's a philosophical concept that my claim relies on. Hence the "so the argument goes" above.

I'd be happy to follow to the QM forum if you'd care to explain where I'm wrong here.

This is a common misunderstanding of the HUP.

If I have ONE particle, and I measure it's position to the precision that's allowed by my instrument, I can then determine its momentum with arbitrary precision, again, that's allowed by my instrument. The accuracy of each of those measurement, one after the other, has nothing to do with the HUP. This is NOT the HUP.

I've described an example of this using the single-slit example a few times. The HUP says nothing about the accuracy of one measurement of position and one measurement of momentum. The uncertainty in each of those measurement is the instrumentation uncertainty, not the HUP. So to say that "... particles have a defined location, they don't have a defined momentum... " is incorrect. Each of those particle can have well defined position and well-defined momentum. It is the spread in the values of the positions and the values of the momentum, measured under identical conditions, that is governed by the HUP. If the spread in the values of the position is small, then the spread in the values of the momentum will be big. This means that your ability to predict what the next value of the momentum is is not very accurate.

One needs to carefully look at the mathematical expression for the HUP. This is not some handwaving argument. It is deeply rooted (as is with the rest of physics) in some underlying mathematical description. And if one does that, one can see the statistical nature of the HUP.

Zz.

[ZapperZ]

Why does every post in this thread address theory instead of empirical methodology? Why can't people just explain how their observables are empirically observed and measured?

My avatar shows where electrons hit a CCD screen. Due to the nature of the instrument (a hemispherical electron analyzer), the vertical axis corresponds to the energy that that electron has (very much like a mass spectrometer), while the horizontal axis is the momentum along a particular direction of the analyzer corresponding to the direction of the slit.

The justification for being able to designate those position are covered in any text on angle-resolved photoemission spectroscopy. In other words, these are extensively covered and well-established to allow us to deduce those "spots" on the screen to correspond to a particular set of observables, in this case, E and k.

It is strange that this is in the Philosophy forum.

Zz.

[brainstorm]

If I have ONE particle, and I measure it's position to the precision that's allowed by my instrument, I can then determine its momentum with arbitrary precision, again, that's allowed by my instrument.
How does the instrument measure position and momentum exactly?

[brainstorm]

The justification for being able to designate those position are covered in any text on angle-resolved photoemission spectroscopy. In other words, these are extensively covered and well-established to allow us to deduce those "spots" on the screen to correspond to a particular set of observables, in this case, E and k.

Why do you cite a text instead of just saying how it works?

[humanino]

How does the instrument measure position and momentum exactly?I have already said how one can measure the momentum of a charged particle, using magnetic fields and trackers.

Take a photon now. An optical lens will select for a given deviation a given momentum. The position can simply be registered by a photographic plate. The slit or simply a punched hole will select a position without destroying the photon.

Alternatively, one could measure energy and position for an electron or a photon using a calorimeter. A calorimeter is simply a segmented stack of individual cells, each of which absorbing a certain amount of energy in the electromagnetic shower, usually recorded by collecting the amount of light out of the material. Typically for instance, one could use crystals. Alternatively one could use a stack of heavy material, such a lead, and scintillators, such as plastic. Then we call it a sandwich calorimeter.

Your question is very vague.

[brainstorm]

This seems to be getting closer, but it's still not at the level of the instrument's methodology and how one observation is linked to another to relate the unit to what is measured.

I have already said how one can measure the momentum of a charged particle, using magnetic fields and trackers.
You did? When?

Take a photon now. An optical lens will select for a given deviation a given momentum.
How? Because momentum determines the angle/path the light takes through the lens? Many things are being left implicit.

The position can simply be registered by a photographic plate. The slit or simply a punched hole will select a position without destroying the photon.
For what purpose? What is being measured exactly this way?

Alternatively, one could measure energy and position for an electron or a photon using a calorimeter. A calorimeter is simply a segmented stack of individual cells, each of which absorbing a certain amount of energy in the electromagnetic shower, usually recorded by collecting the amount of light out of the material.
How is an amount of light collected out of a material? Is this a measurement of units of a particular chemical change that represents a given amount of light energy? What is light affecting exactly in these "cells?"

Typically for instance, one could use crystals. Alternatively one could use a stack of heavy material, such a lead, and scintillators, such as plastic. Then we call it a sandwich calorimeter.

What would change in each or any of these materials that could be measured in terms of units?

Your question is very vague.
My question? Have you been reading how all the posts in this thread avoid actually describing the logic behind measurement by spouting off about the complexities?

[apeiron]

So to answer why is anything measurable? I would refer to discussions of why is there something rather than nothing? I really think they reduce to the same question of why observables exist, or rather, why anything is observable. There is a technical difference on the matter of unobservable properties, but unobservable properties aren't what anyone is asking about when they ask why there's something rather than nothing. That technicality isn't a concern for any of the arguments.

Unless, of course, your issue is with the holism of scientific theories and properties. Then see above :smile:.

The issue at the heart of this is the difference between treating reality as a system and reality as a construction.

Yes, we can model reality as a construction - a bunch of small localised stuff (events, substance, atoms, information) glued together to create additive effects. That works. Although it then introduces paradoxes, such as how did that local stuff get created in the first place? And oh, we also seem to need a global spacetime, a void, a vacuum, a dimensionality, for the stuff to do its constructing in.

So the success of mechanical modelling - gluing together particles, or masses, or energies, or force vectors, or even microstates - is undeniable. But it leaves unanswered some basic metaphysical questions. Which is why it can be such a puzzle over, well, how can we have the measured without also having a measurer?

You will say, I want to be a good mechanist, a good reductionist, and do away with everything but the measured local stuff. Yet I cannot get away from the nagging realisation that a measurer, a global context that makes a measurement meaningful, is also always required.

The best recent philosopher on these issues I believe is CS Peirce. And his theory of semiosis is exactly about this issue. What gives meaning to a sign?

The radical step he made (or was trying to make) was to frame things so that he was talking simultaneously about epistemology and ontology.

Semiosis is how we (as reality modelling creatures) dichotomise the world into our formal models and the measurements they entail.

And then pan-semiosis would be saying well, the world has that logic itself. The world self-organises into a model (the classical, decohered, prevailing state of the universe) and its measurements (the acts of decoherence that create the events, or particles, or bits, or however you chose to think about the local stuff, out of which the whole is being created).

So if Conrad's question is why is anything measurable? The answer would be that systems are measuring devices. The local stuff out of which they are constructed is also the local stuff which they are creating (via the causality of downward "observational" constraint).

It is all about reality modelled as a self-organising system. And to do that properly, you require Peirce's firstness, secondness and thirdness. Or what I normally talk about as vagueness, dichotomies and hierarchies (as Peircean terminology is even more opaque, and I also prefer to connect to the larger bodies of thought on these matters).

[apeiron]

Real particles always have a well-defined mass.

Do you mean a well-defined average mass? That would seem to be the more accurate statement in a QM context.

There would also be the GR view of "well-defined". We would be talking there about rest-mass? And so the local definite status flows from the fixed global measurement frame.

[brainstorm]

Interesting post, but I'm bracketing it in favor of getting to the empirical specifics of specific measurement instruments/techniques to see if people actually understand the basic logical principles their tools are based on.

So if Conrad's question is why is anything measurable? The answer would be that systems are measuring devices. The local stuff out of which they are constructed is also the local stuff which they are creating (via the causality of downward "observational" constraint).
Is this not vague to you? How can any or every "system" be a measuring device? Is such a "system" knowable according to you, or does that transcend the dichotomy of the system/construction approach where only in the mindset of constructionism can a system actually be dissected to its mechanics - and presumably you have some reason that you should not engage in such constructionist mechanical dissections. It's a clever cop out, but still a cop out, imo.

It is all about reality modelled as a self-organising system. And to do that properly, you require Peirce's firstness, secondness and thirdness. Or what I normally talk about as vagueness, dichotomies and hierarchies (as Peircean terminology is even more opaque, and I also prefer to connect to the larger bodies of thought on these matters).
Is "reality as a self-organizing system" the reason why any measurement instrument generates valid measurements without having any logic for how it measures what it is supposedly measuring?

[apeiron]

If there are basic properties essential to the existence of particles, we haven't found them yet.


The best candidate could be local gauge symmetries. In general, like me, you would seem to be taking a constraints-based soliton approach to concieving of particles. Well, what the wider observing system cannot constrain, is then by definition able to exist locally as a degree of freedom.

This is how intrinsic spin and inertial motion would have to arise - as properties that the system cannot see directly. They can only be measured intermittently as events - collisions or polarisations and other kinds of systems measurement.

But in general, properties would arise contextually in a systems (as in condensed matter approaches to particles) rather than being intrinsically existing. And so in existence even in the absence of a measuring context.

[kote]

The HUP says nothing about the accuracy of one measurement of position and one measurement of momentum. The uncertainty in each of those measurement is the instrumentation uncertainty, not the HUP.

Agreed.

So to say that "... particles have a defined location, they don't have a defined momentum... " is incorrect. Each of those particle can have well defined position and well-defined momentum.

Each particle can have a well defined position or a well defined momentum. Not both at the same time. You left out a critical "when" at the beginning of quoting me here.

It is the spread in the values of the positions and the values of the momentum, measured under identical conditions, that is governed by the HUP. If the spread in the values of the position is small, then the spread in the values of the momentum will be big. This means that your ability to predict what the next value of the momentum is is not very accurate.

It's not just about accuracy of predictions though. There are metaphysical implications. As you know, it's not just about our knowledge of position and momentum, it's about their existence as well defined properties. A particle with a well defined momentum does not exist at any specific location. I think it's misleading to talk about small vs larger spreads in this context. There is no reason to assume that during measurement properties have anything but sharp values ontologically. In practice, of course, you'll always have uncertainty. But as you mentioned, it doesn't need to be the HUP variety of uncertainty when just considering a single property by itself.

See http://arxiv.org/abs/quant-ph/0003074 for the math on properties having sharp values. From the abstract: "I shall show that the same subtle issues arise with respect to continuous quantities in classical and quantum mechanics; and that it is, after all, possible to describe a particle as possessing a sharp position value without altering the standard formalism of quantum mechanics." Notice that it was written by a philosopher (with tenure at Princeton) - these are the details philosophers care about.

I'll concede that mentioning mass didn't help my case any. It is clear, though, that (defined) location is a property that particles may lack. Per http://plato.stanford.edu/entries/essential-accidental/, if something can lack a property and still be the same thing, that property is said to be accidental and not essential. You could make a case against this distinction. As it's currently understood however, existing at a defined location is not an essential property of a particle.

[apeiron]

Each of those particle can have well defined position and well-defined momentum. It is the spread in the values of the positions and the values of the momentum, measured under identical conditions, that is governed by the HUP. If the spread in the values of the position is small, then the spread in the values of the momentum will be big. This means that your ability to predict what the next value of the momentum is is not very accurate.


What Kote said was:

Huh? It's simple HUP. When particles have a defined location, they don't have a defined momentum... all that good stuff.

And I can't see any real difference to what Kote meant.

Both Zapper and Humanino seem to be saying that well-defined uncertainty is the same, philosophically, as well-defined existence. Plainly it is not, otherwise QM would not be a challenge to classical conceptions of reality.

[ZapperZ]

Why do you cite a text instead of just saying how it works?

Because I will have to teach you the physics of photoemission spectroscopy, and I'm not good enough (nor do I have the patience) to do that on a public forum, when it took me 2 years to learn it myself. Furthermore, I believe that I HAD given you ample example of how the quantity is measured. What I said what the exact details of how the location on the detector corresponds to these quantities will require further digging into the physics.

I don't know why this is so difficult. When you look at the interference pattern on a screen, and then arrive at the frequency based on the location of the peaks, it is the same thing. So why is this that mysterious?

And why do you want everyone to spoodfeed you?

Zz.

[ZapperZ]

What Kote said was:


And I can't see any real difference to what Kote meant.

Both Zapper and Humanino seem to be saying that well-defined uncertainty is the same, philosophically, as well-defined existence. Plainly it is not, otherwise QM would not be a challenge to classical conceptions of reality.

Er.. this is what I said? I have no clue what you just said here.

Zz.

[ZapperZ]

Agreed.



Each particle can have a well defined position or a well defined momentum. Not both at the same time. You left out a critical "when" at the beginning of quoting me here.

I construct a single slit with width \Delta(x) So any particle that passes through that slit has an uncertainty in position equal to the width of that slit. Now, after the slit, the particle hits a detector at a position x1 measured from the centerline of the slit. The uncertainty of this measurement depends on the resolution of the detector. This is not the HUP. Knowing the distance from the slit to the detector, I can use the x1 position to arrive at the value of momentum along the x direction, i.e. p_x1. The uncertainty of this corresponds to the resolution of the detector. I can make the width as small as I want, it would not affect the uncertainty of the momentum.

Each of the measurement of the position (at the location of the slit) and the measurement of the momentum, has been made with arbitrary accuracy independent of each other. How are they not well defined "at the same time"? Besides, what is this "at the same time" business? In QM, there is an order of the operation of the operator. That's the whole point of non-commutativity. You operate first on one, and then the other. You never operate them "at the same time", so this issue here is non-existent. In this case, I operate my position operator first (by imposing the slit) and then I do the momentum measurement when it hits the screen. How soon or how late I do that doesn't matter, as long as I do one after the other.

It's not just about accuracy of predictions though. There are metaphysical implications. As you know, it's not just about our knowledge of position and momentum, it's about their existence as well defined properties. A particle with a well defined momentum does not exist at any specific location. I think it's misleading to talk about small vs larger spreads in this context. There is no reason to assume that during measurement properties have anything but sharp values ontologically. In practice, of course, you'll always have uncertainty. But as you mentioned, it doesn't need to be the HUP variety of uncertainty when just considering a single property by itself.

You need to be careful here. AFTER the particle passes through the slit, BEFORE it hits the detector that determines its momentum, it is fine to say that it has no specific momentum. This is because it can acquire a range of momentum, depending on how small the width is. The smaller the width of the slit, the larger the range of momentum it can have, and thus, you are not able to say with greater certainty of what momentum it will be WHEN you measure! However, if you look at my example, AFTER it hits the screen, it has a definite momentum!

But here's the next thing. If I do this only ONCE, i.e. one particle passes through the slit, and that one particle then hits the detector, where is the HUP here? I have, in my possession, a definite position and definite momentum values of that particle. Where, in all of this, is the HUP? Can you use the values that I've just obtained to find \Delta(x) and \Delta(p_x)?

Zz.

[kote]

AFTER the particle passes through the slit, BEFORE it hits the detector that determines its momentum, it is fine to say that it has no specific momentum.

All I'm saying is that it's possible for a particle to not have a defined momentum while still being a particle. Similarly, it's possible for a particle to not have a defined location while still being a particle. Therefore, location and momentum are not essential properties of particles.

I agree with you on everything else you said.

[ZapperZ]

All I'm saying is that it's possible for a particle to not have a defined momentum while still being a particle. Similarly, it's possible for a particle to not have a defined location while still being a particle. Therefore, location and momentum are not essential properties of particles.

Show me the exact phenomenon where this is occurring. You'd notice that I gave you a specific illustration on what I was trying to emphasize.

Zz.

[brainstorm]

Because I will have to teach you the physics of photoemission spectroscopy, and I'm not good enough (nor do I have the patience) to do that on a public forum, when it took me 2 years to learn it myself. Furthermore, I believe that I HAD given you ample example of how the quantity is measured. What I said what the exact details of how the location on the detector corresponds to these quantities will require further digging into the physics.

I don't know why this is so difficult. When you look at the interference pattern on a screen, and then arrive at the frequency based on the location of the peaks, it is the same thing. So why is this that mysterious?

And why do you want everyone to spoodfeed you?

Zz.

This post wasn't about spoonfeeding or learning photoemission spectroscopy. It was about why things are measurable. I have been trying to get people to provide clear reasoning about how their instrumentation measures at the level of direct empirical data.

When you look at the interference pattern on a screen, and then arrive at the frequency based on the location of the peaks
Take this sentence, for example. What generates the interference pattern you speak of? What is interfering with what and how do you know that it is?

I'm trying to get at the precise comparison taking place in measurement and what the medium/media are linking the different empirical observations. For example, when volume is measured by displacement of fluid, the fluid is the medium and the level of the fluid in the container is measured in increments of length. So when one object submerged causes the water-level to rise 1cm, its volume is half that of an object that causes the water-level to rise 2cm. The comparison is made between the two volumes of water displaced by the different objects, not by comparison of the objects themselves directly. It is reasoned that the water will not dissolve into the water, and as such all displaced water will correspond to the volume of the submerged object. Likewise it is assumed that no more water will be displaced than the volume of the object. As such, comparing the volumes of displaced water is regarded as analogous to comparing the volumes of the objects themselves.

[kote]

Show me the exact phenomenon where this is occurring. You'd notice that I gave you a specific illustration on what I was trying to emphasize.

Zz.

Apologies - I thought you agreed that particles don't always have defined momentum. We know that when a particle has a sharp momentum, its position isn't just hidden by uncertainty, it's undefined... right? I'd feel a little silly walking through Bell to show that there is no defined momentum when you define location.

Can I show you a positive situation which demonstrates that this is the case? No, I'm not sure that's possible. We have indirect mathematical proof from Bell though. This is all assuming, of course, that QM is valid.

http://arxiv.org/abs/quant-ph/0603277 (Foundations of Physics) is another more recent and concise version of the same argument:

A very simple illustration of the Bell-Kochen-Specker contradiction is presented using continuous observables in infinite dimensional Hilbert space. It is shown that the assumption of the existence of putative values for position and momentum observables for one single particle is incompatible with quantum mechanics.

...

If the predictions of quantum mechanics are correct, then we have proved that position and momentum observables can not be assigned any context independent value. The proof presented here involves elementary observables of one single particle and provides a very simple illustration of the Bell-Kochen-Specker contradiction.

Context dependent putative values are not prohibited and all attempts to replace standard quantum mechanics by some form of hidden variables theories must necessarily include the context dependence in the deterministic assignment of values to the observables. This necessity makes such deterministic theories less appealing. One of the main reasons for developing hidden variables theories was to bring the quantum world closer to the classical expectations but the necessary contextuality goes in the other direction.

So the specific situation in which a particle doesn't have a location, is any time context isn't being created for it. Any time position isn't being measured, it doesn't exist in a well defined way.

This is even a much stronger claim than is required to show that location (or momentum) isn't essential. All that is required for location to be accidental is that it is possible that at one point in time, anywhere in the universe, there might exist a particle without a well defined location.

[kote]

The above uses http://arxiv.org/abs/quant-ph/9912108.However, we shall show here how direct Kochen-Specker arguments for complementarity between position and momentum can be given that are entirely independent of the uncertainty relation and its interpretation.

[apeiron]

Each of the measurement of the position (at the location of the slit) and the measurement of the momentum, has been made with arbitrary accuracy independent of each other. How are they not well defined "at the same time"? Besides, what is this "at the same time" business? In QM, there is an order of the operation of the operator. That's the whole point of non-commutativity. You operate first on one, and then the other. You never operate them "at the same time", so this issue here is non-existent.


It is the impossibility of measuring both aspects of a particle at a single point of spacetime which does make a particle not well-defined in this argument about measurement. It is what puts a theoretical limit on measurement itself.

I'm not sure what you motivation can be here, but you are trying to dodge behind semantics.

Just focus on answering the question for a point in spacetime, not a point in space, or a point in time. Or does the difference need further explaining?


You need to be careful here. AFTER the particle passes through the slit, BEFORE it hits the detector that determines its momentum, it is fine to say that it has no specific momentum. This is because it can acquire a range of momentum, depending on how small the width is. The smaller the width of the slit, the larger the range of momentum it can have, and thus, you are not able to say with greater certainty of what momentum it will be WHEN you measure! However, if you look at my example, AFTER it hits the screen, it has a definite momentum!

And quite clearly the discussion was about a single measurement at a single point in spacetime, not a measurement at one time, then a second measurement at another.

After it hits the screen, you could retrospectively impute that the particle had a definite momentum. And using a single slit apparatus, you would know what it managed to squeeze through (and so that it did not get deflected before passing the screen).

It seems strangely evasive of you that you are even using the single slit story here rather than the twin slit one. Although it does help to conceal the QM issues that were being discussed of course.

[GeorgCantor]

I construct a single slit with width \Delta(x) So any particle that passes through that slit has an uncertainty in position equal to the width of that slit. Now, after the slit, the particle hits a detector at a position x1 measured from the centerline of the slit. The uncertainty of this measurement depends on the resolution of the detector. This is not the HUP. Knowing the distance from the slit to the detector, I can use the x1 position to arrive at the value of momentum along the x direction, i.e. p_x1. The uncertainty of this corresponds to the resolution of the detector. I can make the width as small as I want, it would not affect the uncertainty of the momentum.



Wouldn't this cause an interference pattern(i.e. uncertainty about position, essentially what kote was implying)?


Each of the measurement of the position (at the location of the slit) and the measurement of the momentum, has been made with arbitrary accuracy independent of each other. How are they not well defined "at the same time"?



It's not at the same time. The particle didn't pass the slit and hit the detector at the same time.

Besides, what is this "at the same time" business? In QM, there is an order of the operation of the operator. That's the whole point of non-commutativity. You operate first on one, and then the other. You never operate them "at the same time", so this issue here is non-existent.


You don't operate them at the same time, because it's impossible, as per HUP.


In this case, I operate my position operator first (by imposing the slit) and then I do the momentum measurement when it hits the screen. How soon or how late I do that doesn't matter, as long as I do one after the other.


I am sure kote agrees with this but he was talking about a particle having a definite position and momentum at the same time(not measuring them one after another).





But here's the next thing. If I do this only ONCE, i.e. one particle passes through the slit, and that one particle then hits the detector, where is the HUP here? I have, in my possession, a definite position and definite momentum values of that particle. Where, in all of this, is the HUP? Can you use the values that I've just obtained to find \Delta(x) and \Delta(p_x)?

Zz.


Make the slit opening small enough and you'll start seeing interference(the electron/photon will start interferening with itself, even though you'd need more particles to be sent one after another to make it visible). That's where the HUP is shown experimentally, but you know this stuff better than myself.

[GeorgCantor]

Now can you describe a situation where a particle has a undefined mass ? I suppose you are going to invoke the HUP again. That would not be a measurable particle then, but a virtual particle. Real particles always have a well-defined mass.



This is misleading. You should have said "Real particles always have a well-defined mass"... from a particular frame of reference. Otherwise, mass is not a defined property and since we are discussing the philosophical implications, this is not a minor point.

[apeiron]

This seems a pretty unambiguous statement.......


Heisenberg Uncertainty Relation

The term Heisenberg uncertainty relation is a name for not one but
three distinct trade-off relations which are all formulated in a more or
less intuitive and vague way in Heisenberg’s seminal paper of 1927 [1].
These relations are expressions and quantifications of three fundamental
limitations of the operational possibilities of preparing and measuring
quantum mechanical systems which are stated here informally
with reference to position and momentum as a paradigmatic example
of canonically conjugate pairs of quantities:

(A) It is impossible to prepare states in which position and momentum
are simultaneously arbitrarily well localized. In every state,
the probability distributions of these observables have widths that
obey an uncertainty relation.

(B) It is impossible to make joint measurements of position and momentum.
But it is possible to make approximate joint measurements
of these observables, with inaccuracies that obey an uncertainty
relation.

(C) It is impossible to measure position without disturbing momentum,
and vice versa. The inaccuracy of the position measurement
and the disturbance of the momentum distribution obey
an uncertainty relation.

http://philsci-archive.pitt.edu/archive/00004112/01/HUR_Busch_Falkenburg_philsci.pdf

[apeiron]

Experimental verification of HUP with fullerene molecules and single slit diffraction....


The Heisenberg uncertainty principle for material objects is an essential corner stone of quantum mechanics and clearly visualizes the wave nature of matter. Here, we report a demonstration of the Heisenberg uncertainty principle for the fullerene molecule C70 at a temperature of 900 K. We do this by showing the increase in molecular momentum spread after passage through a narrow slit with a variable width down to 70 nm. We find good quantitative agreement with the theoretical expectation.

http://agnes.dida.physik.uni-essen.de/~backhaus/Quanten/Arndt/PRAHeisenberg.pdf

[ZapperZ]

This post wasn't about spoonfeeding or learning photoemission spectroscopy. It was about why things are measurable. I have been trying to get people to provide clear reasoning about how their instrumentation measures at the level of direct empirical data.

And I thought I did. My avatar was taken exactly from the raw output of an instrument.

Take this sentence, for example. What generates the interference pattern you speak of? What is interfering with what and how do you know that it is?

This is why we have to know the physics of not only the phenomenon (interference), but also the physics of the instrumentation. I've described the physics of the instrumentation (i.e. the spectrometer). The physics of the phenomenon (photoemission) is covered in books.

As far as I can tell, I've given you exactly what you wanted. Short of you actually doing the experiment yourself (which frankly I think everyone should), I'm not sure what else you would want.

Zz.

[ZapperZ]

Apologies - I thought you agreed that particles don't always have defined momentum. We know that when a particle has a sharp momentum, its position isn't just hidden by uncertainty, it's undefined... right? I'd feel a little silly walking through Bell to show that there is no defined momentum when you define location.

Can I show you a positive situation which demonstrates that this is the case? No, I'm not sure that's possible. We have indirect mathematical proof from Bell though. This is all assuming, of course, that QM is valid.

http://arxiv.org/abs/quant-ph/0603277 (Foundations of Physics) is another more recent and concise version of the same argument:



So the specific situation in which a particle doesn't have a location, is any time context isn't being created for it. Any time position isn't being measured, it doesn't exist in a well defined way.

This is even a much stronger claim than is required to show that location (or momentum) isn't essential. All that is required for location to be accidental is that it is possible that at one point in time, anywhere in the universe, there might exist a particle without a well defined location.

Let's go back to the basics, shall we? This is covered in standard intro QM that everyone has to take as a physics major.

The definition of the HUP of an observable is (drum roll):

\Delta(A) = \sqrt{<A>^2 - <A^2>}

I claim that, for the HUP, a single measurement of ANY observable has an uncertainty of ..... ZERO!

Can you tell me where this is wrong?

Now, after you consider that, you might want to start considering that you are missing the key aspect of what I've said, which is the quantity one gets IN A MEASUREMENT. From what I've been reading, it appears that you are think of the superposition of all possible outcome before a measurement that has the effect of contradicting classical realism. This isn't the issue and this isn't what I'm arguing against (heaven knows I've been trying so hard to describe all the Schrodinger Cat states experiment that clearly shows such violation of realism).

Now, as far as having some observables simultaneously, can you please tell me, when I find the commutator of two non-commuting observables, such as [A,B], what exactly does that tell you about the sequence of measurement of those observable? Are you able to show me an example of two non-commuting observables that are measured simultaneously in a single measurement?

Zz.

[ZapperZ]

Make the slit opening small enough and you'll start seeing interference(the electron/photon will start interferening with itself, even though you'd need more particles to be sent one after another to make it visible). That's where the HUP is shown experimentally, but you know this stuff better than myself.

I'm not sure how this answered my question. The "interference" is part of the description of QM. The SPREAD in the available values of the momentum increase according to the HUP. The HUP itself doesn't contain all the details of the pattern that one can see if one does this with many photons. All the HUP does is give a rough idea of how well one can predict the next one, or how much of a spread in values one will get. This is why the HUP has been elevated by some people to a stature that it doesn't deserve. It isn't a "principle" at all, but rather a consequence of the wavefunction and the observable.

Zz.

[ZapperZ]

It seems strangely evasive of you that you are even using the single slit story here rather than the twin slit one. Although it does help to conceal the QM issues that were being discussed of course.

But we're talking about the HUP at the SIMPLEST level. I can talk about the 2-slit as well, but it is no longer as easy because now, you have two locations of x, and each of them has its own slit width, etc. It confuses those who are trying to follow the HUP applied to it, but if you notice, the envelop of the interference pattern remains identical to that of the single slit (this is a popular undergraduate optics question). So I lose no generalities by tackling the single slit as an example.

And quite clearly the discussion was about a single measurement at a single point in spacetime, not a measurement at one time, then a second measurement at another.

After it hits the screen, you could retrospectively impute that the particle had a definite momentum. And using a single slit apparatus, you would know what it managed to squeeze through (and so that it did not get deflected before passing the screen).

Then show how you are able to perform [A,B] operation if A and B are non-commuting.

Zz.

[apeiron]

But we're talking about the HUP at the SIMPLEST level. I can talk about the 2-slit as well, but it is no longer as easy...

The simplest example for demonstrating the essential weirdness of QM is the twin slit experiment (or so Feynman said). That is where you are compelled to adopt a non-classical model such as the path integral.

You can reason from twin slits that the path integral also applies to the single slit case. But I have never seen anyone try to demonstrate that the path integral approach arises in single slit experiments, then derive the more "complicated" twin slit case from it.

Perhaps you can provide cites to support your argument here?

[ZapperZ]

The simplest example for demonstrating the essential weirdness of QM is the twin slit experiment (or so Feynman said). That is where you are compelled to adopt a non-classical model such as the path integral.

You can reason from twin slits that the path integral also applies to the single slit case. But I have never seen anyone try to demonstrate that the path integral approach arises in single slit experiments, then derive the more "complicated" twin slit case from it.

Perhaps you can provide cites to support your argument here?


The simplest demonstration of the SUPERPOSITION concept is the 2-slit experiment. The simplest demonstration of the HUP is the single-slit experiment. You can't use the same phenomenon to demonstrate ALL of the weirdness of QM. Try using the 2-slit experiment to demonstrate a bipartite quantum entanglement, for example.

I've described how the single-slit shows the HUP clearly in this thread, i.e. in how the lateral momentum RANGE increases as the slit becomes smaller. I thought this is a clear example already? If you wish for a QM derivation of the single-slit phenomenon, the Marcella paper that I've cited several times (I'll find the exact reference again if you haven't heard about it) in the QM forum has it in painful detail. You can apply the HUP using the wavefunction used in that formulation.

Zz.

[ConradDJ]

Thanks for all your comments!... I had no idea this thread would go to four pages before I could get back to my computer a mere 24 hours later.

First, this was posted in the philosophy forum because the argument is independent of the specifics of physical measurement processes. If the argument has merit, then I think it is important to look at how actual measurements are made. But as a starting-point, I only want to emphasize the obvious fact that the measurement of any parameter depends on the measurement of others.

I will say that it all reminds me of arguments concerning language. How can we precisely define any word when we must use other undefined words to do so? Are we doomed to circular references and ambiguity? Is precision even possible?

There is a parallel with language, as an inter-referential system, but with an important difference. In human language words refer not only to other words but also to all the stuff we talk about, out there in the world. When I say “tree” I can point to a tree. In physics there is no “outside world” – the observational meaning of any physical parameter has only the observation of other physical parameters to refer to. So there is a closed / complete inter-referential system here in a much stronger sense.

My purpose in emphasizing this is not to cast any doubt on what we can measure. It’s that we know something very remarkable about the structure of the physical world – namely that it provides measurement-contexts for all its own parameters. So, we should take this into account in trying to work out a fundamental physical theory. We should figure out how to construct a model whose parameters can all be defined in terms of each other.

I don’t think this will be easy, and to begin with it’s not very clear what it involves. The good news is that we have a working example of a self-defining system right in front of us, and we know an incredible amount about how it works. In other words, if we can clarify the question – which I take to be a philosophical issue – we have a whole lot of very detailed information about the physics of measurement to help us get to the answer.

Right now, the purpose of physics is to construct an elegant mathematical model that duplicates the structure of what we observe – that gives us all the right particles with their masses and charges and spin, etc. That's completely right. My point is that the model should also eventually duplicate the aspect of physical structure that makes every one of these things observable.

[ConradDJ]

In your minimal universe, if the only force is gravity, then that is what must be used for measurement. Introduce a third low-mass particle and see how it behaves. You can see the mass and location of the first two particles by observing what happens to your measuring device, the third particle.

... barring discussions of subjective knowledge, measurement just is interaction. Any system that undergoes an effect can be said to have measured whatever system it was that caused that effect.

But since we have no electromagnetic field in this model, we can not “see” the location of our particles. From the standpoint of any particle in this system, the most that can be observed is an acceleration in some direction. Even if we were to assume the particle has memory and an internal clock and inertial reference-frame, and so can track how this acceleration-vector changes over time, there’s no way that information could be used to determine the locations and masses of any other particles. That was the point of his illustration -- even though we can "stand outside" it and define the locations of the particles from an absolute standpoint, from inside the system itself, nothing is observable.

So I agree with you that “measurement just is interaction.” In the right context, any physical interaction constitutes a measurement. But we know from QM that interactions occur all the time (in entangled superpositions) without “measuring” anything – just because the “right context” of other interactions is missing.

So the question I'm raising is -- what makes our universe different from the minimal one? How is it that in our universe adequate information is in fact physically available to determine so much about what's in the world?

I think in the big old Misner/Thorne/Wheeler book on Gravitation there’s a construction that shows how to define spacetime intervals observationally using only gravity and light. Of course, you also need something that can detect gravity and light, but leaving that aside – the point is that if you have only gravity or only light, it’s impossible in principle to measure a spacetime interval.

If so, then space and time are only measurable in our universe, because we have these two essentially different kinds of long-distance interaction. We can use light to observe the motions of the planets, and we can measure gravity locally and use that information to interpret our visual information on how the planets move.

The traditional way physics is done, ideally we want a “unified” model in which gravity and electromagnetism turn out to be the same thing. But if measurement is actually a basic feature of our world, then the difference between gravity and light is important. Instead of eliminating this difference in our fundamental theory, we would want to explain exactly what role this difference plays in the referential structure of physics.

[ZapperZ]

Thanks for all your comments!... I had no idea this thread would go to four pages before I could get back to my computer a mere 24 hours later.

First, this was posted in the philosophy forum because the argument is independent of the specifics of physical measurement processes. If the argument has merit, then I think it is important to look at how actual measurements are made. But as a starting-point, I only want to emphasize the obvious fact that the measurement of any parameter depends on the measurement of others.

But with all due respect to philosophers, have they measured anything as a standard practice?

I'm a firm believer that you can't simply read about things to know what it is. You actually have to DO and practice it. I'm an experimentalist, so knowing what I'm measuring, and how I'm able to deduce that it is what it is, is extremely important. In a previous part of my career, a central issue of what I measure (related to my avatar) is whether an 'electron' that we measure in a solid is truly a well-defined particle, or weather such a concept (i.e. quasiparticle) is valid when there is a huge electron-electron interaction the that solid. So knowing what we measure and what that quantity represents is, and has always been, a central issue in physics, especially experimental physics. So that's why I am very puzzled that this is asked in the philosophy forum.

Zz.

[rewebster]

But with all due respect to philosophers, have they measured anything as a standard practice?

I'm a firm believer that you can't simply read about things to know what it is. You actually have to DO and practice it. I'm an experimentalist, so knowing what I'm measuring, and how I'm able to deduce that it is what it is, is extremely important. In a previous part of my career, a central issue of what I measure (related to my avatar) is whether an 'electron' that we measure in a solid is truly a well-defined particle, or weather such a concept (i.e. quasiparticle) is valid when there is a huge electron-electron interaction the that solid. So knowing what we measure and what that quantity represents is, and has always been, a central issue in physics, especially experimental physics. So that's why I am very puzzled that this is asked in the philosophy forum.

Zz.

you do lean toward the idea that just THINKING about things can be unproductive.


So, from that perspective, Einstein didn't know what he was doing and shouldn't have any attention paid to his ideas because HE didn't measure anything.

From your perspective, as an applied/experimental physicist, can you see that IDEA of anything most often comes first, rather than the experiment?----a lot of people HAVE ideas and CAN'T do experiments. Are they to be discounted for that reason?

[rewebster]

So the question I'm raising is -- what makes our universe different from the minimal one? How is it that in our universe adequate information is in fact physically available to determine so much about what's in the world?

...

The traditional way physics is done, ideally we want a “unified” model in which gravity and electromagnetism turn out to be the same thing. But if measurement is actually a basic feature of our world, then the difference between gravity and light is important. Instead of eliminating this difference in our fundamental theory, we would want to explain exactly what role this difference plays in the referential structure of physics.

The 'physics' of a lot of things are still unknown. Even when a 'theory of everything' comes out, there will still be questions and doubts.

We assign names and measures on things first to things that are most concrete and available to us for inspection that we have an interest. After that, its a guessing game (until the right 'guess' makes it a little more concrete).

[ConradDJ]

If different things couldn't be compared in terms of the same comparative reference, they would not be measurable; or you would have to experiment until a stable reference was found. Measurement is based on the logic of regularity and comparability.

the comparative sense is all that is entailed in measurement. Measurement is nothing more than comparison of comparable things in terms of standardized units.

This makes sense. Traditionally we just assume that things exist with certain definite properties, and that there are ways to observe each of these properties. So then, the only issue with measurement is that of finding a consistent way to compare observed properties with each other.

In the context of quantum physics, measurement takes on a different meaning, because the traditional assumptions are at best questionable. It turns out that physical properties generally do not have determinate values except when an interaction occurs that can communicate information about the property in question. Further, it’s not enough that an interaction occur – because in QM, interactions generally result in the entanglement of the two interacting systems, not in the so-called “collapse of the superposition”.

Exactly what is “enough” to constitute a measurement is the great difficulty with QM, and of course there’s a vast literature on this. I think probably the reason this has been so hard to resolve is that the “inter-referential” aspect of measurement I’m trying to focus on here hasn’t been taken seriously.

My argument doesn’t depend on QM. Even if the world were really as classical physics imagined it, any measurement of a physical quantity would still depend on a context of measurements of other physical quantities. And the ability of the universe to make some parameters observable would still be something remarkable.

However, QM does change this picture. Basically, QM provides strong evidence that ALL determinate physical quantities are observable (no “hidden variables”). To me this very strongly suggests that the inter-referential aspect of the structure of physics is in some way fundamental.

It’s not just that our universe happens to be built in such a way that some of its parameters are measurable in terms of others. Instead, it appears that the physical reality of our world in some way depends on measurement. Things only have definite characteristics to the extent that information about those characteristics is communicated to other things. So the physical structure that supports communication-contexts seems to be one of the most basic things we need to understand.

[brainstorm]

And I thought I did. My avatar was taken exactly from the raw output of an instrument.
The image seems to be an expression of some instrument being affected by some physical phenomenon, but it is not clearly defined what, how, and why. Maybe there are too many layers of complexity to provide direct sequences of actions and the logic of what is being measured and how.

This is why we have to know the physics of not only the phenomenon (interference), but also the physics of the instrumentation. I've described the physics of the instrumentation (i.e. the spectrometer). The physics of the phenomenon (photoemission) is covered in books.
I have little doubt that anything discussed on any website is not also covered in books. I'm just trying to get simple direct explanations of what is empirically observed and how it is measured. That way I can analyze why the thing measured is measurable, a la the thread title.

[quote]As far as I can tell, I've given you exactly what you wanted. Short of you actually doing the experiment yourself (which frankly I think everyone should), I'm not sure what else you would want./QUOTE]

I've given examples by describing the logic of measuring mass with a scale and that of measuring volume through water-displacement. I would like the same level of explanation for any other measurement process. I suspect the reason I'm asking a lot is because there's a lot of philosophy and mediality between what is directly empirically observable and what is believed to be measured by the process.

That basically proves my point that reasoning and logic the basis for measurement, but I like to see the connection with actual empirical observations of the phenomena and how the instruments work. Only at that level of dissection am I satisfied that I can trace the exact sequence of events that lead one thing to be compared and comparable with another in terms of standardized units, i.e. measured.

[ConradDJ]

From QM we know that things like mass and spin are not consistently defined properties belonging to particles. It is very reasonable to question whether these properties can even be said to exist, or if there is some other basic layer that these manifest out of. The properties we have probably aren't even basic, but because they are measurable, they are all we have to work with. Since we can't investigate anything beyond the observable, we're really just stuck here. I think at this point the question reduces to why is there something rather than nothing? - what reason is there for anything to appear as an observable.

Kote -- I don’t agree that mass and spin are not “consistently defined” – but apparently what you mean is that they can’t be defined precisely as absolute, intrinsic properties of particles, since they’re subject to quantum indeterminacy. What you’re looking for as “basic” would be underlying properties that are absolutely definite in the nature of particles (or fields or whatever) “in themselves”.

Traditionally this is what philosophers and scientists have understood to be “basic”. What we observe is complex and seemingly chaotic – the goal has been to reduce it to a minimal set of simple, changeless facts. The ideal theory would describe an underlying reality that is not observable, but which accounts for everything we observe.

Against this traditional approach I would argue – even if there exists at the bottom of things a precisely well-defined reality, which precisely determines all the phenomena we observe, there is still an important aspect of the world that it can not account for – namely, that things are observable.

As argued above, for any particular physical parameter to be observable, there needs to be a context consisting of observations of several other parameters. It’s not clear exactly what is required in the structure of this observation-context, but one thing we know is not required is the “underlying reality”. Because this is not something that can be observed, it can make no contribution to the observational context.

To put it another way – the structure of observable phenomena has to be able to define itself whether or not there exists any underlying determinative “basis”. In principle, anything measurable has to be able to be defined exclusively in terms of other things that are measurable. We know that’s true because we can in fact measure things, and in doing so we do not have access to a non-phenomenal reality beyond what we can measure.

Now QM at least suggests that there may be no intrinsically well-defined reality at the bottom of things. That would mean that the inter-referential structure of observable phenomena is itself what’s “basic” in the physical world.

I think this puts a different spin on your question about “why something rather than nothing” – but I can’t take it any further today.

Thanks again -- Conrad

[GeorgCantor]

For me the most important idea behind the developments of twentieth-century physics and cosmology is that things don't have intrinsic properties at the fundamental level; all properties are about relations between things.

[brainstorm]

For me the most important idea behind the developments of twentieth-century physics and cosmology is that things don't have intrinsic properties at the fundamental level; all properties are about relations between things.

That sounds very grand, but it is also very vague. What is an intrinsic property except something's relation to itself or an observer? How can an intrinsic property be distinguished from a relational one? Without examples these are fruitlessly abstract issues.

[GeorgCantor]

But with all due respect to philosophers, have they measured anything as a standard practice?

Zz.


There is the measurement part and the interpretational part. I believe philosophers and philosophy-minded physicists are much better at the latter than intrumentalists. In fact, i and probably most philosophers, find instrumentalism dull and unrewarding.

[GeorgCantor]

That sounds very grand, but it is also very vague. What is an intrinsic property except something's relation to itself or an observer? How can an intrinsic property be distinguished from a relational one? Without examples these are fruitlessly abstract issues.



They are not vague in the slightest to those who understand the important lessons of quantum theory and general relativity.

[baywax]

My question when it comes to measurement is... where do you stop? I mean, firstly, in incremental measurements the increments continue between increments.... so that between every increment there is an infinite amount of increments. These steps may not be observable to our instruments of measurement but, logically and numerically speaking they are there. So, as I said... where do you stop... there's always a "rounding off" of a measurement... but that could be the difference between reality and some imaginary measurement.

[brainstorm]

There is the measurement part and the interpretational part. I believe philosophers and philosophy-minded physicists are much better at the latter than intrumentalists. In fact, i and probably most philosophers, find instrumentalism dull and unrewarding.

The empiricism of measurement is only instrumental in the sense that you bracket the reality of what your measuring in order to analyze the logical connection between observations and synthesis.

What is much duller and unrewarding to me is when discussions of observability and measurement degenerate into insistence that the existence of reality is either a necessary precondition or a proven fact of empiricism. It is irrelevant whether anything is real or not. Access to data and reason is what it is, regardless of reality-status.

[brainstorm]

My question when it comes to measurement is... where do you stop? I mean, firstly, in incremental measurements the increments continue between increments.... so that between every increment there is an infinite amount of increments. These steps may not be observable to our instruments of measurement but, logically and numerically speaking they are there. So, as I said... where do you stop... there's always a "rounding off" of a measurement... but that could be the difference between reality and some imaginary measurement.

Precision is relative to practical application. You're not measuring something to establish absolute truth about its traits. You are trying to answer questions or make predictions about its behavior.

This is what makes science inherently philosophical. Without theoretical reasoning about how a certain methodology addresses a certain question, you're just processing data or generating descriptive imagery (art).

A rounded-off measurement is not necessarily imaginary. It is just a question of sufficiency for the particular practical application. Good, clear scientific questions can be answered with relatively imprecise measurements. Where greater precision is relevant, it must be applied for the question to be answered.

[humanino]

I believe philosophers and philosophy-minded physicists are much better at the latter than intrumentalists.Interesting personal opinion, but how informed ? How many "instrumentalists" do you know ? From what I read in this very subforum, self-appointed philosophers generally have a much poorer understanding of science than the average instrumentalist.

[Freeman Dyson]

In a word, patterns. Why are there patterns? I don't know... Einstein thought this the weirdest thing about the universe. That it was comprehensible. It could be made sense of. To a degree at least..

We can't define anything precisely. If we attempt to, we get into that paralysis of thought that comes to philosophers… one saying to the other: "you don't know what you are talking about!". The second one says: "what do you mean by talking? What do you mean by you? What do you mean by know?"

-Feynman

[brainstorm]

In a word, patterns. Why are there patterns? I don't know... Einstein thought this the weirdest thing about the universe. That it was comprehensible. It could be made sense of. To a degree at least.
Since when is science about recognizing or describing patterns? Patterns may be the basis for recognizability of observables, but science itself is about asking critical questions about what is observed and applying systematic investigation to answering them.

Theory and methodology are critical open processes that are subject to reason the same as any other part of scientific processes. The correct answer to "why does the instrument generate measurement X?" is never, "because it's accurate." Measurement processes have to be predicated on sound reasoning about the relationship between observations and instrumentation. Without that reasoning, you could be measuring the average girth of unicorns by interpreting the patterns on your itunes visualizer.

[ZapperZ]

The image seems to be an expression of some instrument being affected by some physical phenomenon, but it is not clearly defined what, how, and why. Maybe there are too many layers of complexity to provide direct sequences of actions and the logic of what is being measured and how.

If you look at T. Valla et al., Science 285, 2110 (1999), you'll have a complete explanation for the energy and momentum represented in the figure. This 2D images are now quite common in ARPES measurement that allows us to make a direct measurement of both the dispersion of a solid.

I have little doubt that anything discussed on any website is not also covered in books. I'm just trying to get simple direct explanations of what is empirically observed and how it is measured. That way I can analyze why the thing measured is measurable, a la the thread title.

[quote]As far as I can tell, I've given you exactly what you wanted. Short of you actually doing the experiment yourself (which frankly I think everyone should), I'm not sure what else you would want./QUOTE]

I've given examples by describing the logic of measuring mass with a scale and that of measuring volume through water-displacement. I would like the same level of explanation for any other measurement process. I suspect the reason I'm asking a lot is because there's a lot of philosophy and mediality between what is directly empirically observable and what is believed to be measured by the process.

That basically proves my point that reasoning and logic the basis for measurement, but I like to see the connection with actual empirical observations of the phenomena and how the instruments work. Only at that level of dissection am I satisfied that I can trace the exact sequence of events that lead one thing to be compared and comparable with another in terms of standardized units, i.e. measured.

But at some point, things does not stay that simple. For example, the deduction of the mass of a neutrino, for example. This comes in via a very interesting and non-trivial process of flavor mixing. In other words, you don't really "weigh" the mass of a particle. There's a whole lot of physics involved in such a deduction.

But even using a mass spectrometer, for example, to deduce the mass of something, will require you to know some basic classical E&M. A very common experiment in an undergraduate physics laboratory is the measurement of the ratio of e/m using some thermionic source in a uniform magnetic field. Again, the "location" of where the particle hits the screen corresponds to some mass, the same way it is done in my avatar, and the same way one deduces the frequency of the light based on the location of maxima/minima of the interference pattern.

So I'm not sure why you have an issue with all this, assuming that you are well-aware of such things already.

Zz.

[brainstorm]

Again, the "location" of where the particle hits the screen corresponds to some mass, the same way it is done in my avatar, and the same way one deduces the frequency of the light based on the location of maxima/minima of the interference pattern.

So I'm not sure why you have an issue with all this, assuming that you are well-aware of such things already.

You call it "an issue" as if you are defensive about something being questioned.

I am just trying to get the descriptions of measurement instruments and reasoning/deductions down to the level where they are falsifiable. I'm not doing this because I want to falsify them, per se, although shouldn't I want to if they are in fact falsifiable?

The reason is that as long as the description remains at the level of complexity and avoidance of putting the critical details on the table, there's no way to falsify or verify that what is presumed to be measured is actually being measured and how. Instead it's like a game of, "how long are you going to keep asking questions until you give up and accept this as the truth?"

That's not science.

[ZapperZ]

You call it "an issue" as if you are defensive about something being questioned.

I am just trying to get the descriptions of measurement instruments and reasoning/deductions down to the level where they are falsifiable. I'm not doing this because I want to falsify them, per se, although shouldn't I want to if they are in fact falsifiable?

The reason is that as long as the description remains at the level of complexity and avoidance of putting the critical details on the table, there's no way to falsify or verify that what is presumed to be measured is actually being measured and how. Instead it's like a game of, "how long are you going to keep asking questions until you give up and accept this as the truth?"

That's not science.

Science also involves the meticulous study of all the available knowledge. I gave you an exact reference. There's nothing to hide here. You're welcome to read it and learn from it if you wish, or not. You continue to ask for things that have been given.

Many of us have to put in a lot of effort to understand these things. There are no shortcuts. I spent at least one whole year as a postdoc just simply learning about the electron analyzer that are used in those ARPES experiments. None of these were handed to me in a platter, and they can't be. The process of learning and using these things is crucial in one's understanding of it.

So if you want to see if such a thing is falsifiable, you have to have an intimate understanding of it in the first place. What's wrong with such a concept?

Zz.

Zz.

[apeiron]

...the point is that if you have only gravity or only light, it’s impossible in principle to measure a spacetime interval.

Does a universe have to be measurable to exist? My answer, based on Peircean philosophy and systems science, is yes. A system could be considered a self-measuring device. Another way of saying self-organising. A system has to be self-consistent to persist as a dissipative process.

This approach also makes specific claims about the nature of that measurement structure. In particular here, there has to be emergently a dichotomisation of scale. You need a context to measure an event (and synergistically, many measured events add up to construct your measuring context - this second fact is also what the total theory has to capture, and what makes QM incomplete).

Now you highlight here a dichotomy between gravity and EM. You need one to be of different scale to the other to offer a realm in which measurement can take place. And I would argue further, that the two scales must be as far apart as possible. They must be the actual local~global limits of the system in question. You cannot stand in the middle of things and measure them properly. You have to stand right at the edge.

The obvious local~global dichotomy is then absolute rest~lightspeed. You cannot go any slower than absolute rest (QM uncertainty intrudes of course, so the value of absolute rest is asymptotic). And you cannot go faster than lightspeed (again an asymptotic story for massive particles).

So where you are talking about a difference between gravity and EM as being the contrast that allows measurement, I believe what is really at the back of your thinking is the scale contrast between restmass and lightspeed interactions.

Clearly, gravity is a lightspeed interaction itself. But measurable changes in gravitational potential are due to the local motions of masses - so tied to their capacity to be at rest and unchanging.

However, while this restmass~lightspeed dichotomy is essential to the kind of complex universe we find ourselves in, is it still possible to imagine a simpler case that is still a self-measuring system?

I think this is so (though I am happy to hear arguments otherwise). If we imagine a universe in which there was no CP asymmetry to prevent all massive particles radiating away into a pure bath of lightspeed photons, then could this universe exist? Is there anything in theory to prevent it?

I am presuming there would be no gravity fields, no measurable localised gravitational potential differences, because there would be no localised concentrations of mass. The radiation would have a gravity associated with it, but it would be all evenly spread out and so flat - a featureless field and so not observable.

Charley Lineweaver talks about this kind of thing....see p71 on the blackbody radiation that would arise just simply due to residual QM considerations in a de sitter universe with cosmological event horizons.

http://www.mso.anu.edu.au/~charley/papers/LineweaverChap_6.pdf

What would be the measurable here, as I understand it, is any lingering differences in local temperature. Lineweaver says if you have a cosmological constant (a global or general action) then you also have a minimal residual temperature that would be measureable at locales.

So rather than using EM to measure gravity (or whatever), the minimal measurement in this view of the heat death universe would be the global continued expansion (the cosmological constant and the event horizons it creates) vs the locally cooling residual action of photons "the wavelength of the visible universe".

This is the most minimal concept of the universe as a system that I have come across. Lineweaver seems to be developing the idea quietly with Davies (who is the most systems-sympathetic thinker among prominent cosmologists also I feel). It has not been published in an upfront way as cosmological theory yet. So perhaps it does not really fly.

This is why it would be nice to get some other opinions here.

But Conrad, if you are seeking a toy model of what minimal self-measurement would look like, the heat death universe would seem to be it. Especially if CP asymmetry and the persistence of mass is taken as an arbitrary feature of possible universes (it may always be inevitable for some reason - such as gauge symmetry breaking principles - of course).

[kote]

Let's go back to the basics, shall we? This is covered in standard intro QM that everyone has to take as a physics major.

The definition of the HUP of an observable is (drum roll):

\Delta(A) = \sqrt{<A>^2 - <A^2>}

I claim that, for the HUP, a single measurement of ANY observable has an uncertainty of ..... ZERO!

Can you tell me where this is wrong?

Have you read anything I posted? I was very clear in making this exact claim. This has absolutely nothing to do with the status of observables when they aren't actively being measured, which is what we are talking about.

I have no idea why you're asking me for an example of two non-commuting observables measured simultaneously. I've been saying all along that it's impossible to do this. That's the entire point. Who are you trying to argue with?

Do you claim that all particles have, at all times, a well defined position? If not, I can't find anything I've actually said that you should be disagreeing with.

[apeiron]

But at some point, things does not stay that simple. For example, the deduction of the mass of a neutrino, for example. This comes in via a very interesting and non-trivial process of flavor mixing. In other words, you don't really "weigh" the mass of a particle. There's a whole lot of physics involved in such a deduction.

Yes, another good example of a soliton-inspired, constraints-based, approach. The universe as the measuring device does not have the resolution to limit the neutrino's existence to its minimal configuration. It "exists" as a mixture.

I like the kind of approach suggested by Carl Brannen.


Abstract: The spin of a free electron is stable but its position is not. Recent
quantum information research by G. Svetlichny, J. Tolar, and G. Chadzitaskos
have shown that the Feynman position path integral can be mathematically
dened as a product of incompatible states; that is, as a product
of mutually unbiased bases (MUBs). Since the more common use of MUBs is
in nite dimensional Hilbert spaces, this raises the question \what happens
when spin path integrals are computed over products of MUBs?" Such an
assumption makes spin no longer stable. But we show that the usual spin-1/2
is obtained in the long-time limit in three orthogonal solutions that we associate
with the three elementary particle generations. We give applications to
the masses and mixing matrices of the elementary fermions.

http://www.brannenworks.com/Gravity/EmergSpin.pdf


Yes, he is an amateur and the paper is not yet into publication. But it is the kind of reasoning that I am endorsing. He also has support from respectable sources...

http://dorigo.wordpress.com/2007/10/30/guest-post-carl-brannen-four-magnificent-papers-by-authors-who-think-im-a-complete-idiot/

[rewebster]

Clearly, gravity is a lightspeed interaction itself. But measurable changes in gravitational potential are due to the local motions of masses - so tied to their capacity to be at rest and unchanging.


I believe that's an assumption/hypothesis which hasn't any data to support it.

[apeiron]

I believe that's an assumption/hypothesis which hasn't any data to support it.

OK, the experimental verification is still in question (http://www.space.com/scienceastronomy/gravity_speed_030116.html).

But it is a reasonable assumption in most eyes. And there is some data, even if it is being questioned.

Or are you offering an argument that it has some different value? I would be interested in the shape of that argument.

[rewebster]

OK, the experimental verification is still in question (http://www.space.com/scienceastronomy/gravity_speed_030116.html).

But it is a reasonable assumption in most eyes. And there is some data, even if it is being questioned.

Or are you offering an argument that it has some different value? I would be interested in the shape of that argument.

Can't...

the forum doesn't allow personal theories to be posted

[Evo]

Locked pending moderation.