In the beginning was the bit

[Jonti]

... these successes have encouraged Zeilinger to search for the essence of quantum mechanics--the irreducible kernel from which everything else flows. He believes that he has found it. If he is right, all the mysteries of the quantum world will turn out to be inescapable consequences of a single, simple idea.

source: http://www.quantum.univie.ac.at/links/newscientist/bit.html

Don't worry, read the New Scientist article, and all will be revealed. Enjoy

 

[In Bloom]

I haven't quite finished the article yet, but hasn't physics had more than it's fair share of "Irreducible kernals" that turn out not to be so irreducible after all already?

 

[xenon]

If everything stems from one singular thing. Where is it going? At what point if at all, does it retract?

In essence, is there any point in getting up for work tomorrow?

 

[laptop]

hasn't physics had more than it's fair share of "Irreducible kernals" that turn out not to be so irreducible after all already?

I defy anyone to come up with kernels more fundamental than the, er, thingies out of which Loop Quantum Gravity constructs space-time.

The article doesn't give me much.

It seems these guys have a decent intuition about observations being quantised.

And what they are doing is rewriting the Hilbert space formalism (that's, loosely, a matrix containing the properties of a quantum object, whether that be an electron or, in principle, you, or the unverse).

But when the article told me the Hilbert space was two-dimensional, I realised what they're doing had gone over the head of the writer and the editor and I wasn't going to get anything more.

I just had a quick look and my favourite mathematical physicist, John Baez, hasn't mentioned Zeilinger - and he publishes notes on practically everything.

Time to go away and ponder the connection between that intuition and LQG. Anyone got any weed?

 

[Jonti]

I haven't quite finished the article yet, but hasn't physics had more than it's fair share of "Irreducible kernals" that turn out not to be so irreducible after all already?

I should've striped the journalese out of the article -- Zeilinger's principle is not an Irreducible kernal of all physics. It is a way of looking at things which makes the fundamental phenomena of QM (the quantum nature of reality; indeterminacy; and entanglement) look no more magical or spooky than, well, anything else in physics. It connects those undeniable, but counter-intuitive, phenomena to what we know and feel. After all, other fundamental physical ideas can be made sensible by pithy, comprehensible maxims that anchor the formulae in the everyday world.

Take the science of heat. Though highly mathematical and abstract, thermodynamics is based on two basic principles that can be described in colloquial terms. The first law of thermodynamics is just the conservation of energy: it means that there are no perpetual motion machines. The second law of thermodynamics is simply the statement that heat tends to flow from warm objects to cooler ones. When the stuff called energy was invented to quantify these laws, it was strange and undefinable, and even today we don't know what energy is. Yet energy quickly became a robust term in daily conversation and government policy.

The special theory of relativity is also based on two principles, namely, "Inside a speeding transatlantic jet, you have no way of knowing how fast you are going," and "The speed of light shone from this jet is the same as the speed of light from a stationary source." That second statement is counterintuitive, but it is simple to understand and turns out to be a stubborn experimental fact. And general relativity, Einstein's theory of gravity, is based on the thought that a freely falling person feels no weight. None of these theories suffer from the confusions of quantum mechanics.

In the same way, Zeilinger's principle, an elementary system carries one bit of information makes it easy to explain the three corner stones of QM. In the case of an electron's spin (an example of an elementary system) the argument goes like this

... Consider the spin of an electron. Say it is measured along a vertical axis (call it the z axis) and found to be pointing up. Because one bit of information has been used to make that statement, no more information can be carried by the electron's spin. Consequently, no information is available to predict the amounts of spin in the two horizontal directions (x and y axes), so they are of necessity entirely random. If you then measure the spin in one of these directions, there is an equal chance of its pointing right or left, forward or back. This fundamental randomness is what we call Heisenberg's uncertainty principle.

In order to progress beyond a single elementary system, Zeilinger's principle has to be generalised. He proposes simply that two elementary systems carry exactly two bits of information, and N systems carry N bits. This gives us a natural explanation for one of the most fundamental and puzzling features of quantum mechanics--entanglement.

When, say, two electrons are entangled, it is impossible even in principle to describe one without the other. They have no independent existence. This seems bizarre until you use Zeilinger's principle. Concentrating on their spins, a two-electron system contains two bits. For example, they might be "The spins in the z direction are parallel," and "The spins in the x direction are antiparallel". The two bits are thereby used up, and the state is completely described--yet no statement is made about the direction of spin of one electron or the other. The entire description consists of relative statements, or correlations. This means that as soon as one spin is measured along a certain direction, the other one is fixed, even if it happens to be far away.

Zeilinger's single, simple principle leads to these three cornerstones of quantum mechanics: quantisation, uncertainty and entanglement.

That's a considerable achievement

 

[Jonti]

... when the article told me the Hilbert space was two-dimensional, I realised what they're doing had gone over the head of the writer and the editor and I wasn't going to get anything more.

Best just to skip that bit, I think . It would be a shame to miss this ...

The number of classical bits in a system has traditionally been evaluated using a formula derived by the American engineer Claude Shannon. Say your system is a hand of cards. If you wanted to e-mail a friend to describe your hand, Shannon's formula gives the minimum amount of information you'd need to include. But Zeilinger and Brukner noticed that it doesn't take into account the order in which different choices or measurements are made.

This is fine for a classical hand of cards. But in quantum mechanics, information is created in each measurement--and the amount depends on what is measured when--so the order in which different choices or measurements are made does matter, and Shannon's formula doesn't hold. Zeilinger and Brukner have devised an alternative measure that they call total information, which includes the effects of measurement. For an entangled pair, the total information content in the system always comes to two bits.

You may enjoy reading Zeilinger's own words On the Interpretation and Philosophical Foundation of Quantum Mechanics.

 

[In Bloom]

I should've striped the journalese out of the article -- Zeilinger's principle is not an Irreducible kernal of all physics. It is a way of looking at things which makes the fundamental phenomena of QM (the quantum nature of reality; indeterminacy; and entanglement) look no more magical or spooky than, well, anything else in physics. It connects those undeniable, but counter-intuitive, phenomena to what we know and feel. After all, other fundamental physical ideas can be made sensible by pithy, comprehensible maxims that anchor the formulae in the everyday world.
In the same way, Zeilinger's principle, an elementary system carries one bit of information makes it easy to explain the three corner stones of QM. In the case of an electron's spin (an example of an elementary system) the argument goes like this That's a considerable achievement

I got all that, I just find the way journalists herald every new discovery as the final and absolute answer to everything a little irritating. It's bad enough when you see it in newspapers, but I'd have though the New Scientist would have some standards.

 

[Jonti]

Yeah, that would be irritating alright. But with respect, the piece does not herald (Zeilinger's principle) as the final and absolute answer to everything. It claims the idea captures the essence of quantum mechanics, a rather more modest, but still significant achievement.

The principle does this by deriving quantisation, uncertainty and entangement from a simple definition or principle that is intuitively acceptable. And it certainly does show considerable promise, as your comment that "I got all that" shows

 

[Knotted]

I defy anyone to come up with kernels more fundamental than the, er, thingies out of which Loop Quantum Gravity constructs space-time.

The article doesn't give me much.

It seems these guys have a decent intuition about observations being quantised.

What I worry about is the fact that all scientific observations are 'quantised'. An experiment involves some sort of preparation (ie. a set of discete instructions) some sort of process (ie. the phenonmenon you are studying) and some results (ie. a set of discrete data). This has nothing to do with quantum mechanics.

The point is that at any point during the last few centuries science could have given up its claim that it is studying reality and just claimed that it is studying information processing. Indeed George Berkeley claimed something very similar - except that he couched it in terms of sensuous experience.

And what they are doing is rewriting the Hilbert space formalism (that's, loosely, a matrix containing the properties of a quantum object, whether that be an electron or, in principle, you, or the unverse).

Yes. I don't know how the formalism works but it seems to be an attempt to describe quantum information (qubits) in terms of classical information (bits).

But when the article told me the Hilbert space was two-dimensional, I realised what they're doing had gone over the head of the writer and the editor and I wasn't going to get anything more.
[\QUOTE]

Try to be more generous! The article does not claim such a thing. It just talks about 2D Hilbert space - which is reasonable enough especially considering that it had just been discussing the spins of 2 entangled electrons.

The only criticism I have of the article is the sensationalist title - which is unfortunately typical of New Scientist. Its not clear to me that Zeilinger really is claiming that reality is just information as the title suggests (which I would catagorise as form of Berkleyian idealism) or whether he is claiming that science is just concerned with information processing (which I would catagorise as a form of Humian agnosticism) .

I just had a quick look and my favourite mathematical physicist, John Baez, hasn't mentioned Zeilinger - and he publishes notes on practically everything.

The work seems to be more about the philosophy than physics. I'm very sceptical of the claim that there is anything new here. There already is an extension of Shannon entropy to quantum information for example. Does this new formalism have any actual formal differences with the old one? That's a genuine not a rhetorical question by the way.

 

[Knotted]

I got all that, I just find the way journalists herald every new discovery as the final and absolute answer to everything a little irritating. It's bad enough when you see it in newspapers, but I'd have though the New Scientist would have some standards.

If you ignore the headlines New Scientist is still very good in my opinion.

 

[laptop]

If you ignore the headlines New Scientist is still very good in my opinion.

Still has a tendency to declare "and this week, the final answer is..."

Until next week, when...

And that's the view from the more sceptical inside the office

 

[Knotted]

Zeilinger:
"I have purposely not dealt with questions like: Is there a border between micro- and macro physics? Is a new form of logic necessary for quantum processes? Has one's awareness an active, dynamic influence on the wave function? Such or similar positions were proposed by several physicists, but in my opinion they would all fall victim to Occam's razor: Entia non sunt multiplicanda praeter necessitatem."

I thought this quote was very odd. Occam's razor proscribes against overly elaborate answers, not overly difficult questions. The fact that Zeilinger is not concerned with these sorts of questions seems to underscore that there is no new explanatory value in these theories.

 

[Knotted]

Still has a tendency to declare "and this week, the final answer is..."

Until next week, when...

And that's the view from the more sceptical inside the office

Worse than that many of the 'final answers' are reports of some very obscure work. However this seems to me to only be a problem with the theoretical physics/cosmology articles. Perhaps that says something about the current state of physics...

 

[Jonti]

The work seems to be more about the philosophy than physics ... Does this new formalism have any actual formal differences with the old one? That's a genuine not a rhetorical question by the way.

If I've read him right, the answer is "No." Zeilinger notes that the numerical predictions of QM are awesome in their accuracy; that the math is right.

So yes, he is talking philosophy, or, more precisely, Natural Philosophy, rather than physics. It is the interpretation of QM that is his concern. He's solidly Copenhagen, and seeking a way of rooting the Copenhagen Interpretation on a simple underlying principle. Looks to me as if he's cracked that one. No magic or mystery or malice involved. But it is wonderfully subtle

He's also an experimental physicist. He's found a charactarisation of QM that avoids the, ahh, philosophically difficult consequences of interpretations that involve multiple universes, or (with Bohm) unknowable determinate processes. If I understand the New Scientist article correctly, he's now working on recasting the formalism of QM by working forward from that principle. In his own words (source)

As an interesting case from the history of physics I would like to mention Einstein's development of the special theory of relativity. It so happened that almost all relativistic equations which appear in Einstein's publication of 1905 were known already before, mainly through Lorentz, Fitzgerald and Poincaré - simply as an attempt to interpret experimental data quantitatively. But only Einstein created the conceptual foundations, from which, together with the constancy of the velocity of light, the equations of the theory of relativity arise. He did this by introducing the principle of relativity, which asserts that the laws of physics must be the same in all inertial systems. I maintain that it is this very fact of the existence of such a fundamental principle on which the theory is built which is the reason for the observation that we do not see a multitude of interpretations of the theory of relativity. We accept, for instance, that the equations of the theory inevitably imply that clocks really run at different speed as seen in reference frames which are moving relative to each other, and that this is indeed a statement about the relative course of time in these reference frames.of relativity. It so happened that almost all relativistic equations which appear in Einstein's publication of 1905 were known already before, mainly through Lorentz, Fitzgerald and Poincaré - simply as an attempt to interpret experimental data quantitatively. But only Einstein created the conceptual foundations, from which, together with the constancy of the velocity of light, the equations of the theory of relativity arise. He did this by introducing the principle of relativity, which asserts that the laws of physics must be the same in all inertial systems. I maintain that it is this very fact of the existence of such a fundamental principle on which the theory is built which is the reason for the observation that we do not see a multitude of interpretations of the theory of relativity. We accept, for instance, that the equations of the theory inevitably imply that clocks really run at different speed as seen in reference frames which are moving relative to each other, and that this is indeed a statement about the relative course of time in these reference frames.

Looks like he wishes to create the conceptual foundations from which the equations of QM arise; and is intending to derive those equations from the new conceptual foundations.

So, paradigm change is the name of his game.

 

[Jonti]

Zeilinger:
"I have purposely not dealt with questions like: Is there a border between micro- and macro physics? Is a new form of logic necessary for quantum processes? Has one's awareness an active, dynamic influence on the wave function? Such or similar positions were proposed by several physicists, but in my opinion they would all fall victim to Occam's razor: Entia non sunt multiplicanda praeter necessitatem."

I thought this quote was very odd. Occam's razor proscribes against overly elaborate answers, not overly difficult questions. The fact that Zeilinger is not concerned with these sorts of questions seems to underscore that there is no new explanatory value in these theories.

Surely it would be a violation of Occam to invent a border between different parts of science? What difference in kind lies either side of the border?

 

[Knotted]

Surely it would be a violation of Occam to invent a border between different parts of science? What difference in kind lies either side of the border?

Well as I say, a question cannot violate Occam's razor. It is just a question afterall. However it is a perfectly natural to ask what it is about quantum phenonmenon that makes them quantum phenonmenon and not classical phenonmenon. Why don't you get quantum entanglement between two rocks for example? How about two particles of dust? How about two particles of dust made up of only a handful of atoms each? How about two atoms? How about two electrons?

If we compare this to Einstein's theories of reltivity we should note that they are not just theories about objects travelling at near light speeds. They apply to all objects regardless of speed. Furthermore at the time it would have been reasonable to ask in the light of the Michelson-Moreley experiment why the speed of light is always constant irrespective of the motion of the observer whereas this clearly does not apply to relatively slow moving particles (or waves). Einstein's paradigm shift answers this question because it is a scientific theory and not just an interpretation of physical theory.

You can't interpret tricky questions away. At best (or rather at worst!) you can claim that they are unanswerable which is what the Copenhagen interpretation specialises in.

Edit to add: Thinking about it, and to be fair to Zeilinger, I doubt he thinks that the question violates Occam's razor but rather that answering the question either way violates Occam's razor. So I suppose he would claim that any theory which attempts to explain these sorts of questions is necessarily more complex and inelegant than a theory that does not attempt this. This sounds like a challenge to me.

 

[Knotted]

Yes. I don't know how the formalism works but it seems to be an attempt to describe quantum information (qubits) in terms of classical information (bits).
[\QUOTE]

Having read this:
http://www.quantum.univie.ac.at/publications/pdffiles/2004-09.pdf

I can see that there is not a new formalism, the New Scientist was a bit misleading in this respect. Its rather that the formalism of any particular state of a quantum system is given a classical information theoretic interpretation. What they are trying to do is quite reasonable but I don't think its earth shattering.

I think there is a good reason why the traditional hamiltonian formalism cannot be replaced by a probablistic formalism and that's because two different state vectors can lead to the same probabilities after measurement. In other words an electron can have a spin up with a probability of 1/2 in a particular direction in an (infinite) number of ways and this subtlety cannot be captured by classical information theory.

Does this subtlety matter? I think so - please stop me here if you can see I'm going wrong. I think quantum mechanics needs the richness of its traditional formalism. When it comes down to it this is my beef with the Copenhagen interpretation: if the formalism of unitary evolution is necessary to describe quantum mechanics surely its only reasonable to ascribe some sort of reality to state vectors in the formalism.

 

[Jonti]

Responding to post #16, that's the direction of thought alright, imho.

But one can "interpret" tricky questions away. Or at least one needs to ask the right questions to make sense of things. So (perhaps!) postulating a quantum/classical interface and then asking how that interface "works" is the wrong question. Perhaps the right question is to ask how one can avoid the notion of an interface in the first place.

Is the retina of the eye is a quantum/classical interface? Although the faintest glimmer that we see may need a handful of rods to be stimulated, an individual rod can respond to a single photon. It is a quantum receptor. What problem are we trying to solve with some supposed interface between the classical and quantum scales, when everything we see is, quite literally, mediated by quantum receptors?

And yes, QM applies to all scales (varying with scale) just as Relativity applies to all speeds. Buckyballs exhibit Interference in the lab. I don't doubt that entanglement of units comprising many elementary systems can be demonstrated.

However it is a perfectly natural to ask what it is about quantum phenonmenon that makes them quantum phenonmenon and not classical phenonmenon

Yes.

Yes, it is. The answer seems to be "they are comprised of a relatively small number of elementary systems". There's a lot of information in a rock.

<gives brick another kick>

 

[Jonti]

... an electron can have a spin up with a probability of 1/2 in a particular direction in an (infinite) number of ways and this subtlety cannot be captured by classical information theory.

But we can say that electron spin is an elementary system; something that can yield only one bit of data. That captures the subtlety.

 

[Knotted]

But we can say that electron spin is an elementary system; something that can yield only one bit of data. That captures the subtlety.

I don't think so. Are we talking about before or after measurement? Afterwards then yes, but before...

Surely the under the Copenhagen interpretation this is another one of those answerable questions.

If on the other hand we accord some sort of reality to the quantum state then it has an unlimited number of bits of information.

I can go through the maths with you on this even if I'm not familiar enough with physics to give you a concrete example of what I'm talking about.

I'll get back to you on post number 18.

 

[Diem K]

So......the universe may be just a mega quantum computer after all. (trying to calculate the question to the answer "42"?????)

This information space they speak about uses imaginary numbers. I reckon that imaginary numbers actually represent something. The imaginary numbers are in fact the axis of dimensions in a spacetime outside of "Our Universe". Imaginary to us but probably just as real as ours when viewed from a imaginary perspective.

 

[Jonti]

... an electron can have a spin up with a probability of 1/2 in a particular direction in an (infinite) number of ways and this subtlety cannot be captured by classical information theory.

But we can say that electron spin is an elementary system; something that can yield only one bit of data. That captures the subtlety.

I don't think so. Are we talking about before or after measurement? Afterwards then yes, but before...

Afterwards, certainly.

Zeilinger's principle, right now, is a brilliant didactic device for taking the mystery and confusion out of the concepts of quantisation; uncertainty; and entanglement.

As for the "before", I think the idea is to look at the math of elementary systems and combinations of elementary systems to see if/how the equations of QM can be derived. It's not something I've looked into. I don't even know how he defines information, come to that. But I'm intrigued that it contains the concept of order within its definition ...

Thanks

 

[Knotted]

I can concretise the phenonmenon that Zeilinger's principle does not capture.

Consider a photon and send it through a block of perspex. This slows the prgress of the photon for a short period so that when we consider the wave function of the photon it is now out of step. This is called a phase shift and its something that's completely unremarkable for a wave.

However its very difficult to describe what this means for a particle. There is a mathematical description - but the physical interpretation of this description is aparently nonsensical (although not actually paradoxical). In short it involves complex (ie numbers with 'real' and 'imaginery' parts) weightings. So if we are talking about the spin of a photon it might be 'up' with such and such a complex weighting and down with such and such a complex weighting. The complex weightings can be turned into probabilities by finding the squared moduli. However, two different weightings can have the same squared modulus.

So what I am saying is that Zeilinger's principle does not allow a complete description of quantum phenonmenon. A photon's spin prior to measurement (that is before its wave function has collapsed) is not an elementary system in that its spin is not just up or down with certain probabilities but up or down with certain probabilities up to a phase shift. The phase of the photon can in theory store an infinite amount of information even if this information is not directly accessible to us.

I think Bohr's philosophical outlook on quantum mechanics can be summarised as being an allergic reaction to the apparently nonsensical mathematical description of quantum particles. He didn't like imaginery numbers describing physcial reality. He had a similar problem with special relativity by the way.

 

[Knotted]

Is the retina of the eye is a quantum/classical interface? Although the faintest glimmer that we see may need a handful of rods to be stimulated, an individual rod can respond to a single photon. It is a quantum receptor. What problem are we trying to solve with some supposed interface between the classical and quantum scales, when everything we see is, quite literally, mediated by quantum receptors?

The above is the many worlds interpretation of quantum mechanics as I understand it. When the single photon jumps to a measured state, then the measurement device (in this case the eye) also jumps and presumably the observer also jumps. As I said I don't think that this is the way that Zeilinger sees it. I think he proscribes against answering the question at all rather than answering the question in the negative.

Yes, it is. The answer seems to be "they are comprised of a relatively small number of elementary systems". There's a lot of information in a rock.

<gives brick another kick>

This is a perfectly good answer and as far as I know you are right but I'm not sure why it should be true. Wave-particle duality, entanglement and other strange quantum pheonmenon disapear after 'meaurement'. What exactly constitutes a measurement?

 

[Jonti]

What is quantum mechanics trying to tell us?

Whoa, bud!

That description of the animal eye is just a description of the animal eye, as biologists understand it. Its accuracy no more implies any particular interpretation of QM than does the success of the Theory of Evolution (remember that molecular incidents are at the quantum level).

I guess you are thinking something like "the photon detection in our retinas is only another sub-atomic process, which according to Schrodinger's equation should add to complexity of superposition, not state reduction". Well, OK. But why should one conclude from that there exists a multiplicity of words (for one observer) rather than a multiplicity of observers (for one world)?

Wave-particle duality, entanglement and other strange quantum pheonmenon disappear after 'meaurement'. What exactly constitutes a measurement?

A measurement establishes a relationship. According to Wittgenstein, we cannot think of any object apart from the possibility of its connection with other things. In Philosophical Investigations he took that thought from the Tractatus a little further -- if everything that we call “being” and “non-being” consists in the existence and non-existence of connections between elements, it makes no sense to speak of an element’s being (non-being). source

That is not to deny reality. That there is such a thing as reality is something I often mention! And the very simplest way of interrogating reality is to play "Twenty Questions" -- to pose questions to which the world may answer either Yes or No. Again, this is not to give up on the quest to find out what things are really like. Instead, one is accepting that QM only describes the information we have about reality, and does not say what it is. That's fair enough, for, of course, it is our interpretation of QM that will tell us what the world is really like. The equations work just fine in telling us what (relations) to expect.

The collapse of the wave function ("measurement") just represents a change in the description of a particular observer/apparatus. It does not represent a change in reality. The change in the observer/apparatus comes about because that system (after the measurement) has new information about the situation.

 

[118118]

You fools. The view from nowhere is not possible.

 

[laptop]

I guess you are thinking something like "the photon detection in our retinas is only another sub-atomic process, which according to Schrodinger's equation should add to complexity of superposition, not state reduction".

I'm reminded of the sci.physics poster whose signature file (tagline) read somethng like:

Quantum theory tells me I must treat the measuring instrument classically. Why? What will happen to me if I don't?

 

[Knotted]

Whoa, bud!

I guess you are thinking something like "the photon detection in our retinas is only another sub-atomic process, which according to Schrodinger's equation should add to complexity of superposition, not state reduction". Well, OK. But why should one conclude from that there exists a multiplicity of words (for one observer) rather than a multiplicity of observers (for one world)?

Well because it does not end there. The whole of the human nervous system including the brain is made up of sub-atomic particles and you could just as well argue that measurement involves the mind jumping to the same state as the particle rather than visa versa. Of course it doesn't stop there - the whole universe is made up of sub-atomic particles, so that when a measurement is taken then the whole universe jumps to a new state. I don't think that this interpretation would effect the Zeilinger/Bruckner informatatic description of the measurement. In fact its very close - its not the quantum system that has changed but rather the relation of the system to the measurement apparatus which is ultimately the whole universe.

A measurement establishes a relationship. According to Wittgenstein, we cannot think of any object apart from the possibility of its connection with other things. In Philosophical Investigations he took that thought from the Tractatus a little further -- if everything that we call “being” and “non-being” consists in the existence and non-existence of connections between elements, it makes no sense to speak of an element’s being (non-being). source

But surely it makes no sense to have a purely informatic (ie. an abstract mathematical) relation without a corresponding physical relation.

That is not to deny reality. That there is such a thing as reality is something I often mention! And the very simplest way of interrogating reality is to play "Twenty Questions" -- to pose questions to which the world may answer either Yes or No. Again, this is not to give up on the quest to find out what things are really like. Instead, one is accepting that QM only describes the information we have about reality, and does not say what it is. That's fair enough, for, of course, it is our interpretation of QM that will tell us what the world is really like. The equations work just fine in telling us what (relations) to expect.

Does quantum mechanics describe information purely about observables? You might be surprised to learn that it doesn't! Phase shifts are not observable, neither are they random nor are they quantised (at least in the working model). How do we know about them? Because they effect the evolution of the system. Even if you could make all the possible enquiries as to the state of a particle at a particular point in time in an experiment (and that's not too daft an idea as you can run an experiment many times), then you still do not have all the information that will describe the evolution of the system. However if you can make some assumptions about the evolution of the system up to that point then you can predict its evolution after that point in an absolutely deterministic way without even having to make measurements!

In short the wave description of quantum processes (Schrodinger equation) is a more powerful tool than any probabilistic or informatic description and its perverse to not ascribe it any reality.

The collapse of the wave function ("measurement") just represents a change in the description of a particular observer/apparatus. It does not represent a change in reality. The change in the observer/apparatus comes about because that system (after the measurement) has new information about the situation.

But how does the system gain information without some physical effect? I find it very worrying that a pure abstraction - which is what the probability and information theory are - can determine reality. Abstractions are things that just exist in our heads.

 

[Jonti]

But surely it makes no sense to have a purely informatic (ie. an abstract mathematical) relation without a corresponding physical relation.

And surely it makes no sense to have a purely informatic (ie. an abstract mathematical) wave motion without a corresponding physical medium? Like the ether, for example.

Abstractions are just useful things that exist in our heads.

 

[Jonti]

I'm reminded of the sci.physics poster whose signature file (tagline) read somethng like:

Quantum theory tells me I must treat the measuring instrument classically. Why? What will happen to me if I don't?

You could end up on the twelth moon of Vtondik, trying to sell hyper-poisonous Acturian megadonkey urine to journalists from the Gargantuan Galactic Hysteria. And all before the day's first cup of warm tea!