A night with the stars (Brian Cox on telly)

[Q-reeus]

While the example given in #59 obeyed BE statistics (in particular a BE condensate), not FD stats as per becox's rubbed diamond. the issue is whether a commonly shared wavefunction changes instantly in any physically real manner. Suppose the exciting coil at A received a step current; then the superconducting TL is obliged to *finally* exhibit a reverse current that exactly cancels any magnetic flux linkage from the coil. Although all Cooper pairs will then continue to occupy the ground state following magnetic linkage with the coil at end A, the wavefunction state is different before vs after - a magnetically linked SQUID detector at B will indicate a change in phase etc. Point was the system as a whole surely settles into the new configuration no differently than a notionally classically perfectly conducting TL - there is a continuous train of reflected pulses that typically decays quasi-exponentially with time. I see no possibility of any instantaneous linkage of any kind between ends A and B - despite the shared single wavefunction.

In #60 Ken G argues that the answer is to see the universe as a kind of "Bohmian whole" (my interpretation!) where electrons have no independent existence - yet the final upshot being yes, there is instantaneous linkage but no instantaneous signalling results. Cannot see that thinking in terms of state occupancy rather than electrons occupying states changes the issue materially - we are still left with an untestable hypothesis of instantaneous linkage (akhmeteli's comments in #44 and #57 are relevant to the notion of 'instantaneous'). In what way exactly is the scenario in #59 and elaborated above an invalid counterexample? Seems to me that change to that single supercurrent wavefunction has to be negotiated among the constituent Cooper pairs over an extended time interval, in accordance with SR causality.

 

[md2perpe]

instead of thinking about a bunch of electrons, and ask what states they are in, let's start by thinking about a bunch of states, and asking whether or not they are occupied by an electron.

That's how I think about it.

 

[Q-reeus]

Ken G: "instead of thinking about a bunch of electrons, and ask what states they are in, let's start by thinking about a bunch of states, and asking whether or not they are occupied by an electron."
That's how I think about it.

Hmm...two gamma ray photons anti-annihilate to create an electron-positron pair. So am I to believe the wavefunctions of said freshly created pair instantly span the entire universe - which btw some cosmologists believe to be many orders of magnitude larger than the horizon limited ~ 13.7 bly portion visible to us. If not, how exactly can the totality of all states be truly universal and instantaneously adjustable? Such questions probably just shows how little I know of QM.

 

[sheaf]

... how exactly can the totality of all states be truly universal and instantaneously adjustable? ...

Is there any reason we shouldn't think of it in the same way that a state for an entangled EPR-style pair of particles can span vast distances, but still lack the capability for FTL signalling ?

 

[Q-reeus]

Is there any reason we shouldn't think of it in the same way that a state for an entangled EPR-style pair of particles can span vast distances, but still lack the capability for FTL signalling ?

This is heading into territory I tend to avoid. Whatever the nature of entanglement truly is, it is integral to such Bell type tests and typically involves just two particles. A far cry surely from the scenario of instantaneous adjustment of all FD electron states throughout the universe - there is afaik no suggestion of universal entanglement. We know that the still dream of quantum computing is plagued with the problem of just how delicate entanglement is and how exponentially sensitive it is to the number of entangled states. Anyway would like some expert feedback on the superconducting TL scenario - I remain sceptical to 'instantaneous' in general.

 

[sheaf]

This is heading into territory I tend to avoid. Whatever the nature of entanglement truly is, it is integral to such Bell type tests and typically involves just two particles. A far cry surely from the scenario of instantaneous adjustment of all FD electron states throughout the universe - there is afaik no suggestion of universal entanglement. We know that the still dream of quantum computing is plagued with the problem of just how delicate entanglement is and how exponentially sensitive it is to the number of entangled states. Anyway would like some expert feedback on the superconducting TL scenario - I remain sceptical to 'instantaneous' in general.

Yes, most discussions of entangled states are concerned with EPR scenarios and involve just a pair of particles. But isn't it true that multiparticle states, for example states describing a system with many electrons, are antisymmetrized products of single particle states, and these are entangled. I'm assuming that the definition of an entangled state is something I can't separate into a tensor product of single particle states. That certainly applies to the multi-electron state doesn't it ?

I guess the question is - would you always describe a multi electron system by an antisymmetric product like that ? If I create an electron at x1 and create a second electron at x2 and have (maybe effectively) an infinite barrier such that they can't interact (i.e. their wavefunctions can't overlap), then I wouldn't describe the system by an antisymmetric state - it would be a separable system. But if they're not separated, they can interact in principle, and then I do have to use the entangled state.

What I'm not sure is how relativity comes into this. I guess it's something to do with cluster decomposition, which someone mentioned earlier - I'll have to read up on that.

 

[Q-reeus]

Yes, most discussions of entangled states are concerned with EPR scenarios and involve just a pair of particles. But isn't it true that multiparticle states, for example states describing a system with many electrons, are antisymmetrized products of single particle states, and these are entangled. I'm assuming that the definition of an entangled state is something I can't separate into a tensor product of single particle states. That certainly applies to the multi-electron state doesn't it ?

Well I know of that definition re tensor product inseparability, but was unaware it applied to say electronic states in the metallic state in general. However your view appears to be backed up by the following passage from: 'Spin Entangled Systems' http://www.google.com.au/url?sa=t&rct=j&q=spin-entangled%20electrons%20in%20solid-state%20systems&source=web&cd=5&ved=0CD0QFjAE&url=http%3A%2F%2Ftheorie.physik.uni-konstanz.de%2Fburkard%2Fsites%2Fdefault%2Ffiles%2Fpdf%2Feent_web.pdf&ei=Zzr_TuaMAq-QiQfu6_GhAQ&usg=AFQjCNGQvkNSUYRhPPjrhu7SUe_3sN1CCA&cad=rja
"Entanglement is not uncommon in solid-state systems. On the contrary, entanglement is the rule rather than the exception in the low-energy states (say, the ground state) of inter-acting many-particle systems. However, such “generic” entangled states are not necessarily useful for quantum information processing. A criterion for the usefulness as a resource is that there must be a realizable physical mechanism to extract and separate a “standard” pair of entangled particles such as the EPR pair in Eq. (1) from the many-body system in such a way that the two particles can be used for quantum communication. This is often complicated by the indistinguishability of the particles: in this case, a state that “looks entangled” when written out in first quantized notation might not be entangled in an operational sense (i.e., there may not be any physical procedure that separates the particle while maintaining their entanglement). Mathematically, this is related to the fact that the Hilbert space for several identical particles is not a tensor product when proper antisymetrization is taken into account. Measures of entanglement which take into account the indistinguishability of particles have been introduced"

Given the role of environmental decoherence, I can only imagine such condensed matter entanglements are fleetingly made and broken, but will leave it to the experts.

 

[Naty1]

So far I'm not sure just what conclusions to reach, so
A few questions:

1]What is the 'proof' that becox refers to in the film segment: That in 1967 a consequence of the Pauli exclusion principle was proved that no two electrons anywhere in the universe can be in precisely the same energy levels….

2] Why should we believe the model referenced by becox actually applies to the universe? For example, does an infinite potential well correctly model our universe?

3] Someone said this is a non relativistic QM model? Is that important? How would a relativistic version differ?

4] I thought that there are problems with defining the energy of the gravitational field in general relativity, as one complicating factor [so many physicists prefer to say that energy is not globally conserved in GR]...given that, how can anyone conclude there is any likelihood of electrons being in the same energy state throughout the universe.

As a side observation, I do like models such as this because they do cause us to think about thing in new ways. So even if a particular model doesn't pan out, the thinking accompanying it could well lead to new insights and new approaches.

 

[Ken G]

In what way exactly is the scenario in #59 and elaborated above an invalid counterexample? Seems to me that change to that single supercurrent wavefunction has to be negotiated among the constituent Cooper pairs over an extended time interval, in accordance with SR causality.

I can agree that no wavefunction can change instantaneously if it would allow FTL communication if it did so. But there are many types of wavefunctions that can change instantaneously without allowing FTL communication. I don't see the wavefunction as a unique entity, I see it as a tool in the head of a physicist. Thus, two physicists can use two different wavefunctions in the same situation and still both be "correct", in the limited sense that "correctness" appears in physics. So one physicist's wavefunction might change instantaneously everywhere, even when a physicist outside their light cone might use the previous wavefunction, and both might get consistent results. So the rule for objectivity is not that everyone lives in the same reality, it is that no two observers' realities can be inconsistent with each other. This also means that "complete information" does not imply a unique description of the reality, it merely implies access to all the information that is locally available to that observer in principle. The locality of the information is what preserves causality.

 

[Q-reeus]

I can agree that no wavefunction can change instantaneously if it would allow FTL communication if it did so. But there are many types of wavefunctions that can change instantaneously without allowing FTL communication. I don't see the wavefunction as a unique entity, I see it as a tool in the head of a physicist. Thus, two physicists can use two different wavefunctions in the same situation and still both be "correct", in the limited sense that "correctness" appears in physics. So one physicist's wavefunction might change instantaneously everywhere, even when a physicist outside their light cone might use the previous wavefunction, and both might get consistent results. So the rule for objectivity is not that everyone lives in the same reality, it is that no two observers' realities can be inconsistent with each other. This also means that "complete information" does not imply a unique description of the reality, it merely implies access to all the information that is locally available to that observer in principle. The locality of the information is what preserves causality.

This may be a consistent worldview but leaves me dissatisfied. At the end of the day, we are still left with the need for instantaneous influence no matter how spatially separated (or does a cosmic horizon set the limit?). If it can be shown transistors would not work without truly instantaneous state adjustments, then perhaps there is no choice but to accept. Decided to actually watch becox's expose tonight - especially the bit about instant adjustment of energy levels universe wide. There is no way known such a claim/theory can ever be observationally confirmed to that level. Assuming though for the moment it is actually correct, the only half-way rational worldview I'm familiar with that then makes sense is the Cramer transactional interpretation. If I have it right it implies basically a kind of grand conspiracy where every single interaction is prenegotiated from the very beginning (how much information can be crammed into a 'point singularity' again?). Which presumably also tallies with the block universe concept. Not my cup of tea.
Anyway - best for new year to all.

 

[Q-reeus]

1]What is the 'proof' that becox refers to in the film segment: That in 1967 a consequence of the Pauli exclusion principle was proved that no two electrons anywhere in the universe can be in precisely the same energy levels….

A small piece here, 3rd paragraph under 'Stability of matter': http://en.wikipedia.org/wiki/Pauli_exclusion_principle#Stability_of_matter , but nothing said about universal reach.

2] Why should we believe the model referenced by becox actually applies to the universe? For example, does an infinite potential well correctly model our universe?

As pointed out in #66, an infinite potential well would kill universal linkage - the usual assumption is a finite potential well of infinite extent (but as per #58, ultra feeble at large r).

3] Someone said this is a non relativistic QM model? Is that important? How would a relativistic version differ?

Do you mean PEP itself? The above Wiki has something to say here under 'The Pauli principle in advanced quantum theory': http://en.wikipedia.org/wiki/Pauli_...he_Pauli_principle_in_advanced_quantum_theory

4] I thought that there are problems with defining the energy of the gravitational field in general relativity, as one complicating factor [so many physicists prefer to say that energy is not globally conserved in GR]...given that, how can anyone conclude there is any likelihood of electrons being in the same energy state throughout the universe.

This article may be of interest: http://www.physorg.com/news200060488.html

 

[Ken G]

There is no way known such a claim/theory can ever be observationally confirmed to that level. Assuming though for the moment it is actually correct, the only half-way rational worldview I'm familiar with that then makes sense is the Cramer transactional interpretation.

I don't think CI would have any trouble with it, because CI asserts that the wave function is merely a calculational tool, so can change instantaneously as information about the system changes.

 

[classicpk]

In accord with many other postings, the extension of Pauli's exclusion principle form 'atom' to 'universe' was quite an alien concept to me in Brian Cox's TV 'show'. Although a scientist, I am not a theoritical physicist, but it strikes me that in none of the subsequent postings to this thread does it appear to be have been considered just what the consequences are/might be (from a quantum viewpoint) of: what if he is wrong? Would it imply total (instantaneous) collapse of the 'universe' to a 'singular' state, because everything, potentially, was equal? Conversely, might it be because no energy state of any conceivable 'particle' can be replicated absolutely within the universe, that the universe as we know/understand it does in fact exist? I think there are some fundamental issues here that might require theoretical considerations beyond my wit to comprehend!

 

[bm0p700f]

There is a post on the first page which clarifies the argument above quite clearly. Well it did for me anyway. The change in states are inmeasurable so no evidence can ever be gathered to prove it happens but the idea follows as a consequence of the exclusion principle. Read the article it might clarify the situation for you as well.

 

[gibbson_e]

There is a post on the first page which clarifies the argument above quite clearly. Well it did for me anyway. The change in states are inmeasurable so no evidence can ever be gathered to prove it happens but the idea follows as a consequence of the exclusion principle. Read the article it might clarify the situation for you as well.

Immeasurable to what degree? Within a single atom, can the change of electrons be measured? How about for the other atoms in near touching proximity?

 

[bm0p700f]

have you read the article?

 

[Ken G]

I think an important thing to clarify is the difference between statements like "this is true about the world" versus statements like "this follows from the most literal interpretation of theory X." I believe Brian Cox's statement about the effects on the states of all electrons when one rubs a diamond has the latter flavor, but can sound like it has the former flavor, and this may be the source of much of the difficulty here. Dr. Cox may himself even believe the former flavor, I wouldn't speak for him, but I think only the latter type can be correctly asserted.

 

[Naty1]

Q-reeus: thanks for the attemopt to clarify things in post #71..,
not very encouraging as far as becox claims are concerned...

...As pointed out in #66, an infinite potential well would kill universal linkage...

yes but as I understand things, that's an infinite potential between systems, not two systems within the same potential well...so it doesn't seem to apply to the becox scenario of one well for the entire universe.

I had already seen the wiki comment about "advanced quantum theory"...multiplying by 'i' fails to inspire as well when I went looking for anything on "relativistic quantum theory"...I know nothinmg about it...I still wonder what it means when we don't have a unified theory...

 

[Naty1]

The underlying idea is that close approach of an electron to the nucleus of the atom necessarily increases its kinetic energy, an application of the uncertainty principle of Heisenberg.[3] However, stability of large systems with many electrons and many nuclei is a different matter, and requires the Pauli exclusion principle.[4]

http://en.wikipedia.org/wiki/Pauli_exclusion_principle#Stability_of_matter

I read the above a few days ago and did not stop to consider "uncertainty"...If the difference in energy states is an issue among electrons worrying about what energy they are allowed, how do they get beneath Heisenberg uncertainty? Seems rather moot.

 

[Q-reeus]

Q-reeus...As pointed out in #66, an infinite potential well would kill universal linkage...

yes but as I understand things, that's an infinite potential between systems, not two systems within the same potential well...so it doesn't seem to apply to the becox scenario of one well for the entire universe.

Naty1 - I don't think he's talking about a single well though. The diamong is basically one system with it's own 'well' (with something like 3 million billion billion well levels as I recall the piece), and the rest of the universe is a conglomerate of everything with their own 'well complexes' - and much which is entirely free of a potential well in the usual sense (interstellar plasma etc).

The first link given in #20 is worth reading over again: http://physics.stackexchange.com/questions/18527/does-the-pauli-exclusion-principle-instantaneously-affect-distant-electrons There are enough points raised there, especially the 3rd last entry, to invalidate the notion of meaningfully discrete state shifts 'from afar' even assuming instantaneous influence. Further, on the theoretical justification for instantaneous connection, Lubos Motl has something interesting to say in entry 5 at: http://physics.stackexchange.com/questions/11003/what-causes-the-pauli-exclusion-principle-and-why-does-spin-1-2-fermion/11013#11013 - especially 3rd paragraph. Maybe some here will disagree with Motl, but those remarks seem clear enough.

 

[geordief]

action at a distance

I was listening to the lecture by Brian Walsh on the BBC over the New Year and was taken aback by one of his statements.
Is this really true?

I think he was saying that ,if you have any object in a system, then it has a characteristic that is completely unique to it (can't recall the terminology...)
If one of these objects (an electron , for example) absorbs energy then every other object in the universe is affected instaneously because each object is required to be unique.

This means (in my mind ) that if we strike a match in Manchester that something happens simultaneously on the Moon.

Can anyone tell me if I have got the wrong end of the stick here?
I know Quantum Theory is meant to be ridiculous but does that go too far?

 

[ThomasT]

I was listening to the lecture by Brian Walsh on the BBC over the New Year and was taken aback by one of his statements.
Is this really true?

Do you mean Brian Cox?

I think he was saying that ,if you have any object in a system, then it has a characteristic that is completely unique to it (can't recall the terminology...)
If one of these objects (an electron , for example) absorbs energy then every other object in the universe is affected instaneously because each object is required to be unique.

This means (in my mind ) that if we strike a match in Manchester that something happens simultaneously on the Moon.

I would guess that, wrt a god's eye view of things, that if you strike a match in Manchester that something happens simultaneously on the Moon, or the Sun, or Jupiter, etc. But I would suppose that none of it has anything to do with your stiking a match in Manchester.

Can anyone tell me if I have got the wrong end of the stick here?
I know Quantum Theory is meant to be ridiculous but does that go too far?

Yes, I think you've got the wrong end of the stick. Quantum theory isn't meant to be riduculous, but it can be made so by unwarranted interpretations. Brian Cox's stuff is meant to entertain, not inform. So don't take it literally.

 

[atyy]

I was listening to the lecture by Brian Walsh on the BBC over the New Year and was taken aback by one of his statements.
Is this really true?

I think he was saying that ,if you have any object in a system, then it has a characteristic that is completely unique to it (can't recall the terminology...)
If one of these objects (an electron , for example) absorbs energy then every other object in the universe is affected instaneously because each object is required to be unique.

This means (in my mind ) that if we strike a match in Manchester that something happens simultaneously on the Moon.

Can anyone tell me if I have got the wrong end of the stick here?
I know Quantum Theory is meant to be ridiculous but does that go too far?

Yes. It is technically true. In technical terms, this simply reflects the requirement that the wavefunction of a system of fermions must be antisymmetric, and the assumption that there is at any particular time a single wavefunction that contains all fermions in the universe. However, of course when we write a wavefunction for a solid on the earth, we don't expect to have to take account of the fermions on the moon to get a really good approximation. I cannot remember the argument that the fermions on the moon can be neglected for all practical purposes, but it is found in Shankar's QM text http://books.google.com/books?id=2zypV5EbKuIC&source=gbs_navlinks_s (around p275, search for "moon"!).

 

[jtbell]

Theads merged.

 

[geordief]

Do you mean Brian Cox?

.

yes - that was a silly mistake.Brian Walsh is my local garage man.
I don't think there is any connection.

 

[Ken G]

What's more, even technically we should probably avoid language like something "happening simultaneously" on the Moon. Relativistic quantum mechanics must respect the limit of causal effects to propagate at less than c, so it is only what we regard as happening on the Moon that is altered simultaneously to the change in what we regard as happening in Manchester. What is "actually" happening on the Moon is a matter for people on the Moon to decide authoritatively, given the local limitations on the act of doing observations. I guess you can call me a positivist!

 

[ThomasT]

yes - that was a silly mistake.Brian Walsh is my local garage man.
I don't think there is any connection.

Apparently, according to Brian Cox, your mistake might not (in some sense) really be a mistake. And anyway Brian Walsh is a lot closer to any of us than the moon (not that that matters). As atyy and others have pointed out, what Brian Cox said can be considered technically correct. But as Ken G and others have pointed out, it's important how formal QM is translated into ordinary language, because its precise relationship to nature is very much a matter of interpretation.

I'm still of the opinion that Brian Cox's popular presentations are meant to entertain, and not necessarily to inform or clarify -- and that it remains for each of us to learn enough of the technical theory to decide for ourselves when and if the mathematical formalism might be translated literally into ordinary language statements about nature.

So, there you have it. Brian Cox's (and anybody else's) popularizations can be taken to be correct statements about reality or nature ... or not, depending on how one chooses to interpret the mathematical formalism.

 

[SecularSanity]

Seems to be some confusion here about the Pauli Principle.

http://www.hep.manchester.ac.uk/u/forshaw/BoseFermi/Double Well.html

Brian

Seems to be some confusion here about far apart and isolated atoms. Personally, I think it was intentional, to push a new book.

“When they are far apart and isolated, the atoms have identical energy levels. However, as the spacing between the two atoms becomes smaller, the electron wave functions begin to overlap. Antibonding orbital are repulsive and act to destabilize the molecule as a whole..”

http://en.wikipedia.org/wiki/Antibonding

Lec 14 | MIT 5.111 Principles of Chemical Science

Double Twit Experiment – What Brian Cox Gets Wrong

 

[Ken G]

In my opinion, that last link is unpleasant and unjustified. If framed as a list of constructive criticisms for Cox to consider in his next presentation, it would only have been presumptuous. As it is, it is a vitriolic diatribe with no apparent reason for existing other than to express a very large chip that the author seems to carry for Dr. Cox. It makes one wonder if Brian kicked sand in his face when they were kids! I only found it interesting for the nice clips it gives of other lecturers, but it is no kind of critique of Dr. Cox that people like Feynman give great lectures. They can all have their own style, and the audience can be allowed to decide their preferences.

 

[James_Sheils]

In my opinion, that last link is unpleasant and unjustified. If framed as a list of constructive criticisms for Cox to consider in his next presentation, it would only have been presumptuous. As it is, it is a vitriolic diatribe with no apparent reason for existing other than to express a very large chip that the author seems to carry for Dr. Cox. It makes one wonder if Brian kicked sand in his face when they were kids! I only found it interesting for the nice clips it gives of other lecturers, but it is no kind of critique of Dr. Cox that people like Feynman give great lectures. They can all have their own style, and the audience can be allowed to decide their preferences.

Hello,

I am the author of the review "Double Twit Experiment – What Brian Cox Gets Wrong", as linked by others.

I came across this thread after Cox's BBC show and linked to it in the blog article. I was surprised to notice a few days later that someone on the forum had linked back to what I had written, and that many people are reading it via this thread.

For Ken G and others who may find my comments 'unjustified', allow me to elaborate a little.

I am a maths and physics graduate who has taught physics in secondary schools in the UK for around 6 years. During this time, I've thought quite carefully about which parts of scientific inquiry are worth teaching - which ideas and skills are valuable.

For classroom teaching, there is inevitably a conflict of interested when we consider how long a student might stay in science education. Some, who will go onto further study, need to be equipped with particular skills and informed of specific ideas. Those who will go on to do other things after high-school will likely find little benefit from these skills. I'm talking about learning how to use a micro-metre, or learning which of Newton Laws is which.

However, there is much of scientific inquiry that is valuable to everyone, regardless of specialisms. Most important of all, any citizen will benefit from understanding the process of scientific thinking. The role of evidence in falsification, what constitutes a scientific theory, how logic is utilized to determine consequences of a theory, the imaginative guesses that bring about new theories. All of this equips a person with thinking skills and understanding they can apply to enrich their lives, and their understanding of the latest research.

Values to extract from this include: anti-authoritarianism, fallibilism, logical analysis, philosophical reflection and courageous imaginations.

Let's suppose you think this is too abstract or challenging. Which parts of physical theory might be valuable knowledge to everyone? Some basic knowledge of Newtonian mechanics, descriptive optics, electrical circuits would be a good start. Sure, they approximations for theories we now know to be closer to the truth, but if taught well they will not impede possible future study.

So what to do with a 1 hour presentation? Now, I'm sure there will be much noise about how producers won't agree to programs that present these 'old' ideas. But Cox seems to command a lot of respect - they have already agreed to let him give a one hour lecture with a blackboard.

It is disappointing that he has decided to present something so esoteric, yet mostly rely on intellectual intimidation and argument from authority to establish the results. Sure, he tried some underrehearsed explanations and demonstration, but the material was far too broad for even the greatest of educators to do a good job.

So what is the result? We have people who think they are interested in science, credulously parroting the latest scientific ideas to each other at the dinner table.

Most dangerous of all, it encourages already arrogant students to presume they have understood an idea, when they have merely remembered some impressive words. I have met many students who have tried to explain black holes to me, or something about string theory. I always fell a sympathy that these curious minds have been duped by yet another shallow presentation of scientific inquiry.

Or, there are the adults I meet who tell me they are 'really interested in science' and then ask me about m-theory, or black-holes.

"Why do some object float in water?" I ask them. Most of them have nothing to say about this. Now I ask you, if a person cannot connect the perceptions of their experience with scientific patterns, what is the possible value in describing the theoretical intricacies of the latest research?

In short, I think presentations like Cox's contributes to a social game that people play, to impress and stupefy. But not to understand.