Is Quantum Entanglement Just Correlation or a Real Physical Process?

[WaveJumper]

I'm not assuming it. I'm looking at it..

I'm not sure I understand your point. Can you elaborate?

May i elaborate instead of DrChinese?

That you have seen an image of atoms does not mean that they are there when you aren't probing/measuring them with a scanning tunneling microscope. In fact, the multiple double slit experiments all show the opposite(including the one done with atoms).

 

[zenith8]

May i elaborate instead of DrChinese?

That you have seen an image of atoms does not mean that they are there when you aren't probing/measuring them with a scanning tunneling microscope. In fact, the multiple double slit experiments all show the opposite (including the one done with atoms).

Read my post again. It's not just about seeing a photo of atoms once. I said:

"Single atoms and even electrons can be isolated and trapped in containment vessels for long periods. You can repeat the examination over and over again and get the same data. Individual atoms can be 'pushed around', arranged into patterns (which can also be imaged) and otherwise manipulated. These experiments all yield consistent results and information about quantum entities using a variety of techniques and under different conditions."

So the point is that you can now explore the same individual quantum system over and over again and get the same data each time. Not only can we trap a quantum particle, we find that it is still in its trap after intervals of time where there have been no interactions. Single atoms can be imaged and re-imaged with the same results. This is only possible because quantum systems and elementary particles exist whether we observe them, conduct experiments with them, or not.

Note also the stuff about matter wave optics.

How exactly do multiple double slit experiments show the opposite?

 

[WaveJumper]

Read my post again. It's not just about seeing a photo of atoms once. I said:

"Single atoms and even electrons can be isolated and trapped in containment vessels for long periods. You can repeat the examination over and over again and get the same data. Individual atoms can be 'pushed around', arranged into patterns (which can also be imaged) and otherwise manipulated. These experiments all yield consistent results and information about quantum entities using a variety of techniques and under different conditions."

So the point is that you can now explore the same individual quantum system over and over again and get the same data each time. Not only can we trap a quantum particle, we find that it is still in its trap after intervals of time where there have been no interactions. Single atoms can be imaged and re-imaged with the same results. This is only possible because quantum systems and elementary particles exist whether we observe them, conduct experiments with them, or not.

Note also the stuff about matter wave optics.

How exactly do multiple double slit experiments show the opposite?

While it's obviously true that particles can be confined/trapped, all those quantum objects can't be localised(objectified) until they are measured, due to the wave nature of matter. No one knows where they are until they are measured, all we can say about them is a probability that they might be somewhere.

Why they appear the way they do and maintain the order we see in our macro world is the problem of outcomes which is unsolvable at this time.

 

[zenith8]

While it's obviously true that particles can be confined/trapped, all those quantum objects can't be localised(objectified) until they are measured, due to the wave nature of matter. No one knows where they are until they are measured, all we can say about them is a probability that they might be somewhere.

Why they appear the way they do and maintain the order we see in our macro world is the problem of outcomes which is unsolvable at this time.

Not so. That's just what you've been led to believe.

Atoms stay where they are put. The IBM guys could repeatedly re-image the xenon atoms spelling IBM on the nickel surface, and see that they remained undisturbed between observations. The idea that the atoms take a quick trip around the universe when you're not looking at them and then fly back into precisely the same configuration when you do is no more believable than saying the world ceases to exist when you close your eyes. Read what the experimentalist guys themselves say about this - especially the more modern stuff that has been done in the last few years..

 

[DrChinese]

While it's obviously true that particles can be confined/trapped, all those quantum objects can't be localised(objectified) until they are measured, due to the wave nature of matter. No one knows where they are until they are measured, all we can say about them is a probability that they might be somewhere.

I don't think the question is so much whether the particles exist or not, when not observed. The question is whether they have all possible observable-attributes at times when no observation is occurring. And further, whether those observable-attributes have specific well-defined values at all times.

The answer to that question appears to be NO per many recent experiments (not just Bell, also GHZ, Hardy, etc.). So you would want to accept non-realism and reject non-locality to be consistent with experiment. On the other hand, non-realism is a weird concept and non-locality is easier to imagine as a mechanism. Thus explaining its popularity.

 

[WaveJumper]

Not so. That's just what you've been led to believe.

Atoms stay where they are put. The IBM guys could repeatedly re-image the xenon atoms spelling IBM on the nickel surface, and see that they remained undisturbed between observations. The idea that the atoms take a quick trip around the universe when you're not looking at them and then fly back into precisely the same configuration when you do is no more believable than saying the world ceases to exist when you close your eyes. Read what the experimentalist guys themselves say about this - especially the more modern stuff that has been done in the last few years..

Did someone observe the wave properties of matter?

I did not say that IBM could not repeatedly re-image the same atoms. I specifically said that this fact, that atoms appear in classical matter the way they do, is the problem of outcomes(objectification). The problem of outcomes seeks the answer to the question - why is a particular eigenstate selected out of all other(to maintain our classical predictability and order, aka deterministic world).

 

[zenith8]

Did someone observe the wave properties of matter?

Read my post again - I devoted several paragraphs and one picture to it. There is a whole field of physics called matter wave optics which does precisely that.

I did not say that IBM could not repeatedly re-image the same atoms. I specifically said that this fact, that atoms appear in classical matter the way they do, is the problem of outcomes(objectification). The problem of outcomes seeks the answer to the question - why is a particular observable selected out of all other(to maintain our classical predictability and order)

Look, they're just atoms, with a position. You've been conditioned to believe that something weird is going on in such a situation. There (almost certainly) isn't.

Let's say it like this: the methods of physics have yielded compelling evidence for accepting the existence of the quantum realm. We might take a leaf out of the pages of the history of science and say that it now remains a matter of how much evidence is required to convince the sceptics. Whether it be the acceptance of a heliostatic over an Earth-centred solar system or the Einsteinian over the Newtonian worldview, it was the weight of the evidence which finally decided the question.

So answer me this: what evidence would be needed to convince you of the reality of atoms?

 

[WaveJumper]

Read my post again - I devoted several paragraphs and one picture to it. There is a whole field of physics called matter wave optics which does precisely that.
Look, they're just atoms, with a position. You've been conditioned to believe that something weird is going on in such a situation. There (almost certainly) isn't.

Let's say it like this: the methods of physics have yielded compelling evidennce for accepting the existence of the quantum realm. We might take a leaf out of the pages of the history of science and say that it now remains a matter of how much evidence is required to convince the sceptics. Whether it be the acceptance of a heliostatic over an Earth-centred solar system or the Einsteinian over the Newtonian worldview, it was the weight of the evidence which finally decided the question.

So answer me this: what evidence would be needed to convince you of the reality of atoms?

I never said or implied that they aren't real, i was merely opposed to the way you were trying to prove that atoms were real(by showing an image of atoms). My whole statement during the debate has been:

It's meaningless to talk about observables before we measure them. (i.e. from this we cannot infer if there is or is not an objective reality, an image of atoms is not enough)

 

[zenith8]

I never said or implied that they aren't real, i was merely opposed to the way you were trying to prove that atoms were real(by showing an image of atoms). My whole statement during the debate has been:

The image of atoms was not the main point - it was just meant to be a helpful visual addition to the text. I apologize if you took it otherwise.

It's meaningless to talk about observables before we measure them. (i.e. from this we cannot infer if there is or is not an objective reality, an image of atoms is not enough)

In general, no. In the Copenhagen interpretation, yes - but this is a circular argument, since Copenhagen defines itself to be only concerned with the results of measurements.

 

[WaveJumper]

In general, no. In the Copenhagen interpretation, yes - but this is a circular argument, since Copenhagen defines itself to be only concerned with the results of measurements.

It's not about CI, it's about superposition of states.

 

[zenith8]

It's meaningless to talk about observables before we measure them.

It's not about CI, it's about superposition of states.

Basic Logic:

(A) If you take an interpretation prepared to make a statement about what exists (e.g. the Bohm interpretation) then it is perfectly reasonable to talk about observables before we measure them.

(B) The Bohm interpretation uses precisely the same mathematics as the Copenhagen interpretation.

(A) + (B) --> It cannot be about superposition of states, it must be about CI.

 

[WaveJumper]

Basic Logic:

(A) If you take an interpretation prepared to make a statement about what exists (e.g. the Bohm interpretation) then it is perfectly reasonable to talk about observables before we measure them.

(B) The Bohm interpretation uses precisely the same mathematics as the Copenhagen interpretation.

(A) + (B) --> It cannot be about superposition of states, it must be about CI.

That's the whole point - you cannot pick ONE interpretation(e.g. the realistic MWI) and pull out an image of atoms and claim - Hey look, atoms are real!

Atoms are in superposition of states when they aren't observed/measured. What is the true nature of wavefunction is a subject of interpretaion and there are a multitude of them to suit all tastes(all of them untestable). You cannot base your logic on the validity of one of them, because they aren't falsifiable(i.e. circular logic). The hard data you have is an image, evidenced by an assumption(interpretation). Based on just these 2 you are not justified to claim with the certainty you did, that the atoms are real or not, which is what i objected to.

 

[zenith8]

That's the whole point - you cannot pick ONE interpretation(e.g. the realistic MWI) and pull out an image of atoms and claim - Hey look, atoms are real!

Again, not so. I wasn't talking about quantum interpretations in the post you are referring to - I was talking about experiments.

And as I keep saying, forget the image - that was just for fun. Read what I said in the text.

Atoms are in superposition of states when they aren't observed/measured. What is the true nature of wavefunction is a subject of interpretaion and there are a multitude of them to suit all tastes(all of them untestable).

You're completely missing the point. Because - in the matter-wave optics experiments - we find that it is possible to diffract, reflect, focus, interfere, do stimulated emission with the wave field in question (that is mathematically represented by the wave function) then that is experimental evidence for the objective existence of the wave. If the wave can be subject to and utilized in such a process, it logically follows that the wave field must exist in order to act and be acted upon.

You cannot base your logic on the validity of one of them, because they aren't falsifiable(i.e. circular logic).

I'm not basing my logic on the validity of one of them. You've just misunderstood (again):

We are trying to falsify your sweeping generalization that it is 'always meaningless to talk about observables before we measure them'. That is (because it's defined that way) a correct statement in the Copenhagen interpretation. It is an incorrect statement in the Bohm interpretation, where we make an ontological commitment as to what exists. Both interpretations are currently in complete accord with experiment. It is therefore not necessarily (and probably not, because it's bizarre) a correct statement in the real world, which is what we are talking about.

Therefore your statement is false.

because [interpretations] aren't falsifiable

That's probably because so many people have such a dogmatic insistence on this point that most don't bother looking how to falsify them. I know at least three possible experimental tests of the Bohm interpretation, for instance. Here's an interesting one I read the other day, due to P. Rigg (relevant to the current discussion):

An infinite potential well is an example of a situation that would offer different predictions for the same phenomenon by Copenhagen and Bohm. They do not give the same answer to the question of what a quantum particle with zero net intrinsic angular momentum is doing within the well. According to CI, it must be in motion, that is, measurements of the momentum would always give values bigger than some threshold (or the uncertainty principle would be violated). According to Bohm (let's not bother why), the particle has zero velocity. Is it possible to test this? Probably, yes:

Let's look at matter wave optics again, where suitable approximations to an infinite well are feasible. In the case of an atom trapped in such a cavity it is possible to ascertain the atom's trajectory by looking at how laser light leaving a cavity is modulated. If we only want to ascertain whether an atom is in motion or not then we can do measurements of the atom's momentum. Imagine a horizontal containment vessel (so that gravity will not affect the atom's motion along the length of the vessel) with evanescent light wave reflectors at each end (produced by a laser beam). The evanescent wave will reflect the atom if it is incident at the ends of the vessel without the atom touching the containment vessel's wall. Skipping the practical details, if the Bohm interpretation is correct, one would expect to detect no phase shift in the reflected laser light (i.e. no motion of the atom). If this proves not technically feasible, then one ought to be able to see phase shifts which consistently indicate values of momenta smaller than the minimum value predicted by orthodox QM. This experiment is very difficult, but probably not impossible to do.

I quote S. Manisalco:

"Quantum mechanics is a theory peppered with counterintuitive and bizarre aspects. For this reason, since its very early days, it has given rise to a heated debate - still far from being concluded - on its interpretation and consequences. ... During the last two decades, extraordinary experimental advances in the control and manipulation of single or small numbers of atoms have made it possible to realize experiments which have been considered for a long time as 'gedanken experiments and potentially test what was previously considered untestable."

I don't want this thread to turn into discussions of testing Bohm's interpretation (and I'm sure it won't), but I mention it merely so we understand that is not in principle impossible to distinguish between interpretations. A dogmatic insistence otherwise is just counterproductive.

21st century now, guys..

 

[zenith8]

Moved to Philosophy? How utterly ridiculous.

 

[zenith8]

Seriously, a lot of people have invested a lot of time in writing posts for this thread, and now some anonymous moderator feels he can just banish it to the Philosophy forum where no-one will read it, just on the basis of his personal prejudice that mention of the word 'interpretation' means 'philosophy'.

This thread is about Bell's theorem, non-locality, and action at a distance in quantum physics - these are topics worked on by a great many of the world's leading physicists, both experimental and theoretical. It is not, by any definition, philosophy.

Can the anonymous moderator who did this please post to justify his reasoning?

Thank you.
Zenith

 

[fleem]

So if you want a thread moved to philosophy, simply add a troll post and BOING its in the philosophy forum. My how kind of the moderators to give trolls such power!

 

[zenith8]

So if you want a thread moved to philosophy, simply add a troll post and BOING its in the philosophy forum. My how kind of the moderators to give trolls such power!

Where's the troll post?

If you're referring to the experiment I suggested at the end of my last technical post - then it is a real experiment suggested in a peer-reviewed journal - see p. 3072 of the article "Quantum phenomena in terms of energy-momentum transfer" in J. Phys. A: Math. Gen. 32, 3069 (1999) and many subsequent follow-ups.

See also "Manipulating atoms with photons", Cohen-Tannoudji and Dalibard in "The new physics of the 21st century" ed. G Fraser, Cambridge University Press (2005).

 

[fleem]

Where's the troll post?

If you're referring to the experiment I suggested at the end of my last technical post - then it is a real experiment suggested in a peer-reviewed journal - see p. 3072 of the article "Quantum phenomena in terms of energy-momentum transfer" in J. Phys. A: Math. Gen. 32, 3069 (1999) and many subsequent follow-ups.

See also "Manipulating atoms with photons", Cohen-Tannoudji and Dalibard in "The new physics of the 21st century" ed. G Fraser, Cambridge University Press (2005).

My point is that even if a moderator believes some posts are philosophizing, the moderator should still be hesitant to move the thread to the philosophy forum, because otherwise trolls can easily manipulate the forums. This point is important because it proves the mistake of moving this thread to philosophy without having to debate how much philosophizing was actually occurring within this thread (since surely no one believes it was excessive... I hope). Certainly a thread with obvious excessive philosophizing and little or no science, should be moved. That wasn't the case here.

 

[zenith8]

My point is that even if a moderator believes some posts are philosophizing, the moderator should still be hesitant to move the thread to the philosophy forum, because otherwise trolls can easily manipulate the forums. This point is important because it proves the mistake of moving this thread to philosophy without having to debate how much philosophizing was actually occurring within this thread (since surely no one believes it was excessive... I hope). Certainly a thread with obvious excessive philosophizing and little or no science, should be moved. That wasn't the case here.

I agree completely. So how come a thread with little or no philosophizing and no trolls has ended up here? Someone has made a mistake. Can it be rectified please?

 

[ajw1]

This is incredible! How to discourage an interesting discussion.

Please moderators, reevaluate this action.

 

[WaveJumper]

You're completely missing the point. Because - in the matter-wave optics experiments - we find that it is possible to diffract, reflect, focus, interfere, do stimulated emission with the wave field in question (that is mathematically represented by the wave function) then that is experimental evidence for the objective existence of the wave. If the wave can be subject to and utilized in such a process, it logically follows that the wave field must exist in order to act and be acted upon.

Yes, i concede that it appears you are right. The problem with the cat(or should i say cats) re-surfaces and is back in full swing.

 

[zenith8]

Yes, i concede that it appears you are right. The problem with the cat(or should i say cats) re-surfaces and is back in full swing.

No, it isn't. If - as you say - you now accept that the wave exists, and you (just temporarily) grant me some license with my experimental evidence that particles exist (remember particles are all you actually detect in, say, a two-slit experiment with electrons), then one resolves the cat paradox as follows:

The cat is made of particles. There is also an accompanying objectively existing wave field (represented mathematically by the wave function evolving according to the Schroedinger equation). The wave guides the particles along particular trajectories according to the standard de Broglie-Bohm prescription. The wave - for whatever reason - splits up into non-overlapping branches, which (by decoherence arguments for a macroscopic body) can effectively never overlap again. The particles - which cannot pass through nodes in the many-body wave field - just deterministically end up in one of the branches (which one depends on the particular initial conditions, with a probability that depends on the fraction of initial trajectories that end up in a particular branch).

Thus the particles effectively select one of the branches to be the one that actually happens. This saves us from having to say that each branch forms a whole separate new universe, or (and this is really funny) when we look at the cat the wave suddenly decides to stop evolving according to the Schroedinger equation and er.. instantaneously collapses to a point - no matter how widely distributed over the universe it is - then starts evolving according to the Schroedinger equation again (as implied in orthodox QM).. In the Bohm picture the 'empty waves' just disperse and eventually become part of the background noise.

Simple, isn't it?

P.S. Can we invite you to join our protest in ending up in the Philosophy forum?

 

[pallidin]

Very interesting thread! At the very least, the way this thread evolved should take it out of the Philosophy section of PF.
Just my opinion.

 

[ThomasT]

I assume you mean that no proven physical process has been found for the nonlocal effects and the 'spooky action at a distance'.

I mean that "spooky action at a distance" exists solely as a speculative metaphysical explanation for quantum entanglement correlations.

'Nonlocal effects' regarding any given pair of detection attributes are inferred only when joint filter settings are parallel or perpendicular. But nonlocal effects or actions at a distance aren't necessary to understand why these joint settings produce the results that they do.

At joint settings other than parallel or perpendicular, individual detections at both ends remain random.

In my opinion if one accepts that the Bell experiment supports the standard QM interpretation then both 'Nonlocality' as well as 'spooky action at a distance' have been proven experimentally. For me these words refer to the same process that is called 'collapse of wave function forcing entangled particles to take a stand' in classic QM. In this sense 'spooky action at a distance' is also just a name, no explanation at al.

Afaik, standard QM doesn't use 'collapse of the wavefunction' to refer to speculative occurances in the quantum realm underlying instrumental behavior. It refers to changes in the objective experimental situation following qualitative instrumental results.

The objective situation is what has been instrumentally recorded -- and as far as the objective situation is concerned, neither ftl propagations nor actions at a distance have been demonstrated in entanglement experiments.

I think the important conclusion is that one should not suggest that this problem has been solved, as some of the earliest posts in this topic did. It is only solved by ignoring ontological questions or taking one of the (unproved) interpretations for granted.

Nonlocality, like any metaphysical speculation, is only a consideration if one assumes that the possibility of its existence is well supported. In my view, it isn't.

The point of departure for speculations on the existence of nonlocality is a certain take on the meaning of Bell's theorem. If, as has been suggested, Bell's theorem doesn't pertain to nonlocality, then what other reason is there to entertain the possibility of its existence?

 

[ThomasT]

So you're a fundamentalist instrumentalist (far too many syllables for a job description).

It has a nice ring to it, however I believe in and like to speculate about the deeper reality underlying instrumental behavior. While science is limited to the sensory realm, instrumental behavior provides the basis for many good assumptions about deeper reality which might then become the basis for more realistic theories.

... I fail to see why you are using the instrumentalist Orthodox interpretation of QM to make sweeping statements about the physical reality of 'action at a distance', and to justify writing 'Incorrect. Incorrect.' next to perfectly correct statements of fact in my original post #36.

The assumption of nonlocality in nature isn't warranted vis standard qm -- and the passage from the Stanford Encyclopedia of Philosophy (concerning standard qm) that you quoted supports this.

Note that in post #77 of this thread I retracted my statement that quantum nonlocality is acausal. It's causal, but nonlocality isn't part of or implied by standard qm.

Here's the argument against the assumption of nonlocality:

Statistical dependence of the separate data sets is what causes violation of Bell inequalities. The statistical dependence has a local causal explanation vis experimental design and execution.

Hence, as I outlined in post #77, violation of Bell inequalities does not require superluminal causal connections, nor does it require superluminal info transmission.

Where does this leave us wrt nonlocality? It's an open question, of sorts. But there's no 'nonlocality problem' because there's no good reason to assume that nonlocality is a realistic possibility.

I agree with you that physics can benefit from exploring inferences about the deeper reality. However, I don't think that the existence of a deeper wave and particle reality implies nonlocality. Our universe might be local or nonlocal. I think it's, presently, more reasonable to suppose that there's a propagational speed limit equivalent to the speed of light.

The main difference of opinion seems to be that you think that 'realistic' means 'engaging in speculative metaphysics' rather than 'objectively existing' ...

There are levels of reality. Our mode of existence is somewhat limiting. We all agree that there's a deeper reality. When we offer qualitative descriptions of that deeper reality, then we're engaging in speculative metaphysics because there's no way to completely objectify the descriptions themselves. The only things that are amenable to objectification are the instrumental behaviors predicted by the quantitative theory.

... and that 'metaphysics' appears to be some sort of term of abuse.

It is, somewhat. Speculative physics involves formulating testable hypotheses. Metaphysical speculations are, by definition, nontestable -- though they can still be evaluated as more or less reasonable.

Anyway, it seems that a certain amount of metaphysical speculation will always be part of theoretical physics -- and both despite and because of this, physics will continue to progress.

We cannot accept, as a legitimate argument form, inferences from the unobservability of a distinction to the unreality of the distinction.

FAPP we can. If the level of reality wrt which objective distinctions are made (instrumental predictions) produces no distinction, then as far as the science is concerned there's no distinction.

It's mostly just a matter of taste as to which of several competing nonverifiable descriptions of deep reality is adopted. I say mostly, because some metaphysical speculations are more reasonable than others.

Given what we know, the assumption that our universe is local is the more reasonable alternative.

 

[fleem]

We find nothing spooky about a pair of local particles transferring information (energy, particles, virtual photons) without regard to causality because we consider such interactions as occurring instantaneously, and we learned from the classical world that where there is no time there is no "sequence of events", and where there is no sequence of events there is no causality. In studying entanglement we've discovered the exact same thing can apply to particles that we presume through classical laws are some distance apart from each other, as long as we do not attempt to measure the space-time interval between them. Specifically, it can happen as long as there are no events at each end of that presumed space-time interval. So this should lead us to realize that a space-time interval doesn't exist unless there are events at each end. Specifically, it is those events that define the space-time we're so used to measuring classically (macroscopically).

 

[ThomasT]

As for this particular thread being moved to the (general) Philosophy forum, I don't care. The issues of nonlocality and spooky action at a distance involve certain experimental techniques, results, etc., as well as logical analysis. Sorting it all out is doing philosophy, but it's also an integral part of the whole scientific enterprise.

It's a coin flip. In the absence of some compelling reason to stick it in the Philosophy forum, why not just leave it where it was?

I think it might be a good idea to consider adding a few new sub-forums. Foundational and other, more or less philosophical, issues surrounding quantum theory could branch from the Quantum Physics forum.

 

[ThomasT]

We find nothing spooky about a pair of local particles transferring information (energy, particles, virtual photons) without regard to causality because we consider such interactions as occurring instantaneously, and we learned from the classical world that where there is no time there is no "sequence of events", and where there is no sequence of events there is no causality. In studying entanglement we've discovered the exact same thing can apply to particles that we presume through classical laws are some distance apart from each other, as long as we do not attempt to measure the space-time interval between them. Specifically, it can happen as long as there are no events at each end of that presumed space-time interval. So this should lead us to realize that a space-time interval doesn't exist unless there are events at each end. Specifically, it is those events that define the space-time we're so used to measuring classically (macroscopically).

I don't understand what you're saying here.

 

[fleem]

I don't understand what you're saying here.

We learned about space-time by observing the average behavior of many interacting particles. Specifically, we created the idea of space-time to explain the average behavior of particles. A theory designed solely to explain the average behavior of many simple machines, without any regard whatsoever to the behavior of one of those machines, will not likely be very useful in explaining the behavior of a single machine. It will far more likely prevent us from understanding the machine. Space-time is a strictly classical theory. In fact, even the idea of continuums and manifolds is a strictly classical theory in the same way. Yet scientists the world round continue to blindly presume that the very concepts we designed strictly to predict the average behavior of many particle interactions must unequivocally be used as the foundational axioms in a theory designed to predict the behavior of just one of those interactions. Its rather silly when you think about it.

 

[Doc Al]

Moderator's Note: I'm returning this thread to Quantum Physics, with the proviso that the discussion remain focused on the physics. I think there's some good physics being discussed and that the discussion should continue as long as it doesn't drift off course.

- Doc