Is the wave function real or abstract statistics?

[matrixrising]

cthugha,

This is exactly what I have been saying. This is why I talked about a stream of photons and I talked about the Casino where each individual spin is real in an ensemble of spins that create a statistical picture.

How can you say the individual spins that create the statistical picture are not real? Don't they have to be?

How can you produce single photons possessing the same spatial wave functions if the wave functions of a single photon are not real?

 

[matrixrising]

bhobba,

Simple question.

How can you have probabilities without the underlying reality being "real?"

 

[bhobba]

How can you produce single photons possessing the same spatial wave functions if the wave functions of a single photon are not real?

How can you produce coins that have the same probabilities when thrown if probabilities aren't real?

Obviously objects having the same property has nothing to do if that property is real.

You just don't seem to get a definite property an object has may not be real.

Thanks
Bill

 

[matrixrising]

Thanks bohm2,

You said:

1) If all sheets of papers have the same weight, then the average weight is equal to weight of the single sheet, in which case you have also measured the true weight of the sheet.

2) If the sheets have only approximately equal weights, then you can say that you have at least approximately measured the weight of a single sheet.

3) But if the weights of different sheets are not even approximately equal, then you have not done anything - you still don't have a clue what is the weight of a single sheet.

In this case the sheets(photons) are equal and this is exactly what I've been saying. From Lundeen Lab:

How the experiment works:Apparatus for measuring the wavefunction

1. Produce a collection of photons possessing identical spatial wavefunctions by passing photons through an optical fiber.

So according to this criteria, Lundeen is a huge success.

 

[bhobba]

How can you have probabilities without the underlying reality being "real?"

The same way coin faces are real and you can assign probabilities to them - the probability is a definite property and its not real - at least most wouldn't think it is.

We can assign a state to a quantum system. What a quantum system is, is a difficult issue - and even if its real - but that has nothing to do with this issue. Well actually it does - if a system isn't real the state is unlikely to be - but I am not even going there

If you want to chat about that one start a new thread - but the mods may shut it down because its probably well into philosophy territory rather than physics.

Thanks
Bill

 

[bhobba]

So according to this criteria, Lundeen is a huge success.

But not in the way you think it is.

It does not prove the state is real.

Thanks
Bill

 

[matrixrising]

bhobba, you said:

How can you produce coins that have the same probabilities when thrown if probabilities aren't real?

These probabilities can't exist if the underlying reality of the coins isn't real. It's just like there couldn't be probabilities of a quantum system if the wave function doesn't describe the underlying "reality" of the quantum system.

Again, probabilities must always be coupled with an underlying reality.

For instance, I couldn't give you the probability of finding Hobbits on planet Lexar because there's no underlying reality. But I can give you the probability of finding the electron in 2 different states because both states must be real.

I couldn't give you the probability that I'm a 19 year old basketball star because I'm 35 years old. There's no underlying reality so there's no probability of the event occurring.

Do you have an example of probability that's not associated with an underlying reality?

 

[Cthugha]

This is exactly what I have been saying. This is why I talked about a stream of photons and I talked about the Casino where each individual spin is real in an ensemble of spins that create a statistical picture.

How can you say the individual spins that create the statistical picture are not real? Don't they have to be?

You are mixing things up. This is absolutely unrelated to what people talk about when discussing whether the wave function is real or not.

Let me give you one (admittedly exaggerated and hilarious) example:

Morpho is kind of a superhero with the amazing ability to teleport somewhere spontaneously if some part of him is already there. This ability is triggered by rain falling on him and he cannot control it. He would like to go to the Bahamas for vacation every year for 10 years in a row, but getting there is not cheap, so he only goes there 30% of the time. Now, there are two possibilities:

1) Morpho actually goes to the Bahamas in 3 out of the 10 years and stays at home during the other 7 years.

2) Every year, Morpho cuts off one of his arms and legs (no problem, he is a superhero - he has healing powers) and sends it to the Bahamas. Once his arm and leg arrived there, he waits for the rain. Unfortunately, there is not that much rain on the Bahamas and in 7 out of 10 years it rains at his home first and he teleports home as a whole. In the other 3 years he teleports to the Bahamas.

Morpho's holiday wave function is now given by 3/10 Morpho at the Bahamas + 7/10 Morpho at home (please ignore normalization issues). Now the two possibilities above give examples of a non-realistic vs. a realistic interpretation of the wave function? The question to ask in order to find out whether the wave function is considered realistic, is whether the wave function LITERALLY decribes Morpho's state while each single plane is flying to the Bahamas.

In possibility one, this is not the case. Morpho is always really either fully at home or fully in the plane to the Bahamas. The wave function is not realistic because it does not describe the real state of Morpho in each run as Morpho is not 7/10 at home, but either fully at home or fully in the plane. The two states are real. The wave function is not.

In possibility two, the wave function is realistic. In every single year 3/10 of Morpho (his arm and his leg) are making the trip to the Bahamas. The wave function literally describes what is going on and is thus real. This is NOT about the underlying states at all.

How can you produce single photons possessing the same spatial wave functions if the wave functions of a single photon are not real?

Like in case 1 above. Single photon wave functions are always defined for an ensemble of identically prepared photons. If photons have the same wave function, this means the measurements are governed by the same probability distribution.

 

[bohm2]

A really cool site of how those researchers of the study in the 'direct' measurement of wavefunction did the measurements can be found below. The slides and video section is particularly useful:

Direct Measurement of the Wavefunction
http://www.photonicquantum.info/Research.html

 

[bhobba]

These probabilities can't exist if the underlying reality of the coins isn't real.

But that's not the issue you are arguing about.

You are claiming the STATE must be real.

I am claiming, like probabilities describing the sides of a coin, and a coin is a very real thing, the STATE, not the system, but the STATE, doesn't have to be real.

The issue of if a quantum system is actually real like a coin is not the issue here. For the sake of argument I am assuming it is in some sense real. However if it isn't, and many don't think it is, then it's very hard to think of the state as real - but I am not arguing like that.

Added Later
I am well aware of the issues of the PBR theorem and the view the underlying quantum system is in some sense real - but that is not the point I am making here.

Now I have mentioned it the OP may latch onto it, but if he does then I would ask him to please actually understand it:
http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/

Thanks
Bill

 

[Demystifier]

In this case the sheets(photons) are equal and this is exactly what I've been saying.

I think you have a problem to distinguish two different meanings of the word "photon". One meaning is a click in a detector (or perhaps a point-particle in the Bohmian interpretation) which of course is real. Another meaning is the wave function, which may or may not be real.

According to some interpretations, these two concepts of the photon are one and the same. For example, this is so in a von Neumann variant of Copenhagen interpretation, according to which the real wave function really collapses when a measurement is performed. It seems that you take such an interpretation for granted and do not consider a possibility for an alternative.

But according to other interpretations, such as Ballentine's or Bohm's ones, the word "photon" means only the former and not the latter. In such interpretations, wave function is not real.

So, when one prepares photons "in the same state", that means they have the same wave function. But it does not necessarily mean that the photons themselves are identical, because there are interpretations in which this may not be so.

Or to comment the quote above, the sheet is an analogue of the photon in the first sense, but not necessarily an analogue of the photon in the second sense.

 

[audioloop]

Simple question.

How can you have probabilities without the underlying reality being "real?"

or probabilities in absence of anything..

 

[bohm2]

I think you have a problem to distinguish two different meanings of the word "photon". One meaning is a click in a detector (or perhaps a point-particle in the Bohmian interpretation) which of course is real. Another meaning is the wave function, which may or may not be real.

Correct me if I'm wrong, but even within the Bohmian/deBB camp there is quite a big difference with respect to the ontology of the wave function. As I understand it, the Goldstein/Durr/Zanghi/Maudlin group treat the wave function differently (less real or non-committal, kind of like Bohmian Copenhagenists) than say Valentini and company (who perceive the wave function as more real). I took it that this is the reason why Valentini was so ecstatic about PBR and the Couder et al. oil drop experiments while not much about it was mentioned from the other camp? For instance see:

The nature of the wave function in de Broglie's pilot-wave theory
http://streamer.perimeterinstitute.ca/Flash/3f521d41-f0a9-4e47-a8c7-e1fd3a4c63c8/viewer.html

 

[Jilang]

Do you have an example of probability that's not associated with an underlying reality?

Er yes. The probability of a spinning coin being found to be heads or tails before you bring your hand down on it.

 

[matrixrising]

bhobba,

Yes, I'm claiming that the state must be real or there's no probability of the state occurring if it isn't coupled with an underlying reality.

The way I see it, QM isn't about whether the state is real. I think it has to be. Where probability comes into play is which state will be measured.

It's like a race with for runners. I could give you probabilities on who will come in 1st, 2nd, 3rd and 4th. What I can't do is give you probabilities of who will come in 10th because that's not an underlying reality and there's no probability of the event occurring.

So the probable states of the wave function have to be real states because if their not real states there's no probability of them becoming measured states. Like I said, there's no probability that you will measure the state where I'm a 19 year old basketball star because I'm 35 years old. Probability has to be coupled with an underlying reality.

I think the problem is when you try to apply the quantum wave function to our classical universe. You get things like Schrodinger's cat. I think decoherence answers some of these questions as the real quantum states decohere into mixed states. When this occurs the classical universe emerges but the real quantum properties don't just vanish, we just can't measure them in the classical world we experience.

This is why the emerging field of Quantum Biology is so exciting. If classical systems can use quantum properties for things like migration of birds, photosynthesis or with DNA, then why not with consciousness? Is consciousness connected to decoherence via quantum gravity a la Roger Penrose? These are exciting times.

I think in experiment after experiment has shown these quantum properties can be experimentally measured because the pure quantum states are real states that become mixed states via decoherence. Probability comes into play because the observer doesn't know which state will be measured.

IMHO, there's a universal wave function that can't be measured. This is why there's inherent randomness in nature. The pure "real" states of this universal wave function become mixed states and classical universes emerge.

At the end of the day, I think the wave function has to describe underlying states that are objective realities that exhibit quantum properties that we can measure.

 

[matrixrising]

Jilang,

The underlying reality is the states of the spinning coin (heads or tails). You couldn't have probabilities of where the coin would land if heads or tails weren't objective, real states. The states of the quantum system have to be objectively real if there's a probability that the states can be measured. How can you measure a state that doesn't exist?

The ensemble interpretation and most Copenhagen interpretations say you can't know the state of the system prior to measurement so just shut up and calculate. I believe they say this is because if you accept that the states are real states, then you have to accept the weirdness as being real also. So the objection of the states being real isn't scientific but semantic. It's based on the rejection that quantum weirdness is objectively real. So far, most experiments have suggested otherwise and there's no hidden theory that will turn Heisenberg into Newton so to speak.

 

[atyy]

Here is a paper that claims to show that the wave function can be interpreted as representing a state of knowledge - ie. the underlying true state may correspond to more than one wave function.

http://arxiv.org/abs/1303.2834
Psi-Epistemic Theories: The Role of Symmetry
Scott Aaronson, Adam Bouland, Lynn Chua, George Lowther

 

[Jilang]

Jilang,

The underlying reality is the states of the spinning coin (heads or tails). You couldn't have probabilities of where the coin would land if heads or tails weren't objective, real states. The states of the quantum system have to be objectively real if there's a probability that the states can be measured. How can you measure a state that doesn't exist?

The ensemble interpretation and most Copenhagen interpretations say you can't know the state of the system prior to measurement so just shut up and calculate. I believe they say this is because if you accept that the states are real states, then you have to accept the weirdness as being real also. So the objection of the states being real isn't scientific but semantic. It's based on the rejection that quantum weirdness is objectively real. So far, most experiments have suggested otherwise and there's no hidden theory that will turn Heisenberg into Newton so to speak.

Sure you can. Heads or tails are real states but until you bring your hand down you cannot say which one it in. Until that point it is best described by a superposition of the two states. There are theories that can reconcile the weirdness with what we understand so far about the universe. See previous posts. If you can believe in zero point energy, then the motion of particles can cause disturbances in this that can describe interference effects etc in quite a classical way. If you don't believe in it, then you are going to struggle as I did for quite a long time.

 

[matrixrising]

Demystifier,

You make some good points and this is why I think Lundeen was a huge success. It showed a one to one correspondence between the spatial wave function of a single photon and an ensemble of photons with identical spatial wave functions. So the state of a single photon was reconstructed even as the ensemble grew. Here's more about weak measurements from Wiki:

The weak value of the observable becomes large when the post-selected state, |\phi_2\rangle, approaches being orthogonal to the pre-selected state, |\phi_1\rangle.[1][4][5] In this way, by properly choosing the two states, the weak value of the operator can be made arbitrarily large, and otherwise small effects can be amplified.[6][7]

Related to this, the research group of Aephraim Steinberg at the University of Toronto confirmed Hardy's paradox experimentally using joint weak measurement’ of the locations of entangled pairs of photons.[8][9] Independently, a team of physicists from Japan reported in December, 2008, and published in March, 2009, that they were able to use joint weak measurement to observe a photonic version of Hardy's paradox. In this version, two photons were used instead of a positron and an electron and relied not upon non-annihilation but on polarization degrees of freedom values measured.[10]

Building on weak measurements, Howard M. Wiseman proposed a weak value measurement of the velocity of a quantum particle at a precise position, which he termed its "naïvely observable velocity". In 2010, a first experimental observation of trajectories of a photon in a double-slit interferometer was reported, which displayed the qualitative features predicted in 2001 by Partha Ghose[11] for photons in the de Broglie-Bohm interpretation.[12][13]

In 2011, weak measurements of many photons prepared in the same pure state, followed by strong measurements of a complementary variable, were used to reconstruct the state in which the photons were prepared.[14]

I think that last part is the ball game and like John Gribbin said, the last nail in the coffin of ensemble interpretations. He said:

However, hopes for turning quantum mechanics back into a classical theory were dashed. Gribbin continues:

"There are many difficulties with the idea, but the killer blow was struck when individual quantum entities such as photons were observed behaving in experiments in line with the quantum wave function description. The Ensemble interpretation is now only of historical interest."[9]

I think it's even worse with the recent Lundeen result. The identical spatial wave functions of individual photons were reconstructed over an ensemble of photons. This is a one to one correspondence of the spatial wave function of an individual photon and an ensemble of photons.

 

[matrixrising]

Jilang, you said:

Heads or tails are real states but until you bring your hand down you cannot say which one it in.

You're just describing the uncertainty of the observer as to which state will be measured. The states have to be objectively real in order for them to be probable states. The only reason you have a probability of measuring heads or tails is because the states heads and tails are an underlying reality.

How can the observer measure a probable state that's not an underlying reality? The states of the quantum system have to objectively exist in order for them to be probable states than can be measured by the observer.

 

[Jilang]

Jilang, you said:

Heads or tails are real states but until you bring your hand down you cannot say which one it in.

You're just describing the uncertainty of the observer as to which state will be measured. The states have to be objectively real in order for them to be probable states. The only reason you have a probability of measuring heads or tails is because the states heads and tails are an underlying reality.

How can the observer measure a probable state that's not an underlying reality? The states of the quantum system have to objectively exist in order for them to be probable states than can be measured by the observer.

Yes, you are correct the state heads and the state tails are an underlying reality, but the state half heads and half tails isn't. Quantum states are generally of the second kind until they are measured.

 

[matrixrising]

Jilang,

Why isn't that state half heads or half tails an underlying reality for the quantum system? This is the fallacy of Schrodinger's cat. People say it can't be an underlying reality for a quantum system as described by the wave function because it doesn't make classical sense. Why should it? Experiment after experiment has shown a quantum system just doesn't make classical sense unless you say the classical world emerged from these states of the quantum system. This way, there's no need to conform the underlying reality of the quantum system with your classical experience.

 

[atyy]

@matrixrising: yes it is possible that the wave function is the full and true state of single systems. However, take a look at the paper I linked to in post #52, where one could construct theories that reproduce quantum mechanics in which not only is an underlying true state can correspond to more than one wave function - ie. the wave function is at least in part a state of ignorance of the true underlying state.

 

[matrixrising]

atyy,

Thanks, I missed that and I will look at the paper.

 

[bohm2]

You're just describing the uncertainty of the observer as to which state will be measured. The states have to be objectively real in order for them to be probable states. The only reason you have a probability of measuring heads or tails is because the states heads and tails are an underlying reality. How can the observer measure a probable state that's not an underlying reality? The states of the quantum system have to objectively exist in order for them to be probable states than can be measured by the observer.

Maybe I'm misunderstanding but isn't this just the whole question about non-locality versus realism issue? Norsen in a previous post in this forum provided a local and non-realist (in some sense) model:

Here's a model that non-realistic but perfectly Bell local: each particle has no definite, pre-existing, pre-scripted value for how the measurements will come out. Think of each particle as carrying a coin, which, upon encountering an SG device, it flips -- heads it goes "up", tails it goes "down". That is certainly not "realistic" (in the sense that people are using that term here) since there is no fact of the matter, prior to the measurement, about how a given particle will respond to the measurement; the outcome is "created on the fly", so to speak. And it's also perfectly local in the sense that what particle 1 ends up doing is in no way influenced by anything going on near particle 2, or vice versa. Of course, the model doesn't make the QM/empirical predictions. But it's non-realist and local. And hence a counter-example to any claim that being Bell local requires/implies being "realist".

This is actually the type of model that some like Khrenikov advocate (from my understanding) but he also says that underneath, there's a subquantum reality and his does make different predictions. Actually he argues that this was also Einstein's view. Consider:

...The main distinguishing feature of the present Vaxjo interpretation is the combination of realism on the subquantum level with nonobjectivity of quantum observables (i.e., impossibility to assign their values before measurements). Hence, realism is destroyed by detectors transforming continuous subquantum reality into discrete events, clicks of detectors. The Vaxjo interpretation-2012 is fundamentally contextual in the sense that the value of an observable depends on measurement context. This is contextuality in Bohr’s sense. It is more general than Bell’s contextuality based on joint measurements of compatible observables.

https://www.physicsforums.com/showthread.php?t=721995

But I'm not mathematically competent enough to understand if his argument against Bell's assumptions for Bell inequality are valid. I was hoping someone would shed some light? Then, again I might be messing this up.

 

[bhobba]

Yes, I'm claiming that the state must be real or there's no probability of the state occurring if it isn't coupled with an underlying reality.

Why isn't that state half heads or half tails an underlying reality for the quantum system?

You do understand what probabilities are don't you? They are not real. They are, depending on your view, either something very abstract defined by the Kolmogorov axioms, or simply a confidence level you have in something being true as defined by the so called Cox axioms ie an extension of logic.

Neither is real in any sense most would call real - although you would probably find philosophers that argue the point. But physics is not philosophy and the most reasonable view is the usual one.

Many think the state is like that - but for some reason you simply do not get it.

Thanks
Bill

 

[bhobba]

You're just describing the uncertainty of the observer as to which state will be measured.

You are confused. The state is the uncertainty. The state tells us the expected outcome of an observation - it does not tell what outcome will be measured. This is the exact analogue of probabilities, and the spinning coin. While it is spinning we have zero idea what side it will land on, all we have is a certain confidence level in the likelihood of exactly what side it will land on. That is the state - ie it tells us this likelihood.

The measurements are real, the state tells us their expected outcomes. The state isn't real - or to be exact doesn't have to be.

Thanks
Bill

 

[bhobba]

People say it can't be an underlying reality for a quantum system as described by the wave function because it doesn't make classical sense.

I don't think anyone says the state can't be real and depend on an underlying reality - interpretations like DBB more or less say that by introducing things like a pilot wave.

That's not the issue here - the issue is MUST it be like that.

Thanks
Bill

 

[Cthugha]

I think that last part is the ball game and like John Gribbin said, the last nail in the coffin of ensemble interpretations. He said:
[...]

We had that already and I told you already that you are quoting things out of context. Again, if you actually bother to look at what is meant by ensemble interpretation in this context, reference 9 from wikipedia says:
"An interpretation of quantum mechanics originally developed by Albert Einstein in the hope of removing some (or all!) of the mystery from quantum theory. The basic idea is that each quantum entity (such as an electron or a photon) has precise quantum properties (such as position and miomentum), and the quantum wave function is related to the probability of getting a particular experimental result when one member (or many members) of the ensemble is somehow selected by experiment."

This is an old classical idea and NOT what is today known as Ballentine's ensemble interpretation. The ensemble interpretation does not assume precise underlying properties. Please stop repeating things you know are wrong and misinforming people.

I think it's even worse with the recent Lundeen result. The identical spatial wave functions of individual photons were reconstructed over an ensemble of photons. This is a one to one correspondence of the spatial wave function of an individual photon and an ensemble of photons.

What part of "Lundeen has not measured the wavefunction of an individual particle" is so hard to understand? I have given you an excerpt of a peer reviewed article from Steinberg's group beforehand clearly stating that discussing such properties of individual particles is meaningless.

Do you get the difference between an individual photon and a single photon state?

 

[matrixrising]

bhobba, You said:

You are confused. The state is the uncertainty. The state tells us the expected outcome of an observation - it does not tell what outcome will be measured. This is the exact analogue of probabilities, and the spinning coin. While it is spinning we have zero idea what side it will land on, all we have is a certain confidence level in the likelihood of exactly what side it will land on. That is the state - ie it tells us this likelihood.

Again, this can't be the case. You can't separate probable states from the underlying reality. The probable state gives you an expected outcome of an observation THAT'S AN UNDERLYING REALITY.

Go back to my example of the 4 runners in the race. I can give you an expected outcome of who we might observe coming in 1st, 2nd, 3rd and 4th. I can't give you an expectant value of something that's not an underlying reality. I can't give you an expectant value of who will come in 10th place. This is because 10th place isn't an underlying reality of a 4 man race.

If you have some evidence that you can divorce probable states from an underlying reality, let's see it.

In the case with the coin. You do have an idea of what state it will land on while it's spinning. It can only land on the underlying reality of heads or tails. Probabilities tell us about an underlying reality that can occur.

If I'm on the mound pitching to a batter, my probable states are limited to my underlying reality. So I can strike out the batter, walk him, he can hit a home run or another probable state will occur that's an expectant value of baseball. What I can't do is give you an expectant value of something that's not an underlying reality. I can't give you the probability that I will throw a touchdown to a WR while I'm pitching in the World Series. One, I'm not a professional baseball player and two the probabilities are restricted to the underlying reality of a baseball game.

So the state must be real before there can be a probable state.

 

[Cthugha]

Again, this can't be the case. You can't separate probable states from the underlying reality. The probable state gives you an expected outcome of an observation THAT'S AN UNDERLYING REALITY.

Please stop making up terminology which does not exist. Realism is well defined and "underlying reality" is not an existing term in that respect. States with probability 0 are trivially excluded. This is not what realism is about. It is not about underlying reality, it is about ACTUALLY being realized every single time.

In the case with the coin. You do have an idea of what state it will land on while it's spinning. It can only land on the underlying reality of heads or tails. Probabilities tell us about an underlying reality that can occur.

No! If it is real it "can" not only occur, it MUST occur.

If I'm on the mound pitching to a batter, my probable states are limited to my underlying reality. So I can strike out the batter, walk him, he can hit a home run or another probable state will occur that's an expectant value of baseball.

If you talk about an underlying reality, this automatically means that you consider the wave function as NOT realistic. In a non-realisitc setting you can strike out the batter, walk him or he can hit a home run. In a realistic setting you DO strike out the batter, walk him and he scores a home run simultaneously every single time. If you consider it as realistic, the wave function is literally all there is. There is nothing deeper, nothing underlying. Nobody denies that these underlying states are possible or realistic, but this is not what realism is about. It is not at all about the nature of the states. Realism is well defined and all about taking the wave function absolutely literally. So please stop twisting the meaning of existing terminology. This is not how these forums work.

 

[bhobba]

Again, this can't be the case. You can't separate probable states from the underlying reality. The probable state gives you an expected outcome of an observation THAT'S AN UNDERLYING REALITY.

You are being silly, very confused, or something - I really don't know what.

Again - the outcome of observations are very real - and when measured to have that value they have it - no question - that is not at issue - but we can only predict probabilities like with the spinning coin.

However if you are thinking they have those properties prior to observation and are real in that sense, then you run into the Kochen-Specker theorem:
http://en.wikipedia.org/wiki/Kochen–Specker_theorem
'The Kochen–Specker proof demonstrates the impossibility of a version of Einstein's assumption, made in the famous Einstein–Podolsky–Rosen paper, that quantum mechanical observables represent 'elements of physical reality'

Actually, even though it's usually not presented this way, it a simple corollary of the much more powerful Gleason's theorem I mentioned early on in the thread - but that's just by the by.

Added Later:
In relation to Cthugha comments what is real is what has probability 1 ie a dead cert, it must be, it has it for sure. The Kochen-Specker theorem proves, and its a proof so there is nothing interpretive about it, that you can't assign probability 1 to everything you can observe. Quantum systems can not have definite values independant of observing them - ie they are not real in the usual classical sense. The only out is if they get those values from measurement context - which is itself pretty weird.

Thanks
Bill

 

[bhobba]

If you have some evidence that you can divorce probable states from an underlying reality, let's see it.

Probable states? There is no such thing. The state is very definite - its not probable. But like probabilities it allows us to predict long term averages.

The state is what allows us to determine those probabilities. It's use is in the Born rule:
http://en.wikipedia.org/wiki/Born_rule
'The Born rule (also called the Born law, Born's rule, or Born's law) is a law of quantum mechanics which gives the probability that a measurement on a quantum system will yield a given result. It is named after its originator, the physicist Max Born. The Born rule is one of the key principles of quantum mechanics. There have been many attempts to derive the Born rule from the other assumptions of quantum mechanics, with inconclusive results; the Many Worlds Interpretation for example cannot derive the Born rule. However, within the Quantum Bayesianism interpretation of quantum theory, it has been shown to be an extension of the standard Law of Total Probability, which takes into account the Hilbert space dimension of the physical system involved.'

Aside from the Born rule a state tells us nothing at all. States are not probable - they are used to predict probabilities, but are themselves not probable.

You seem very confused about very basic terminology.

Thanks
Bill

 

[bhobba]

No! If it is real it "can" not only occur, it MUST occur.

Maybe my link to the Kochen-Specker theorem will help.

He may not realize you can't assign definite values to all observables - ie probability 1 - in the quantum formalism - at least some must be unknowable.

Thanks
Bill

 

[matrixrising]

cthugha,

You said:

What part of "Lundeen has not measured the wavefunction of an individual particle" is so hard to understand? I have given you an excerpt of a peer reviewed article from Steinberg's group beforehand clearly stating that discussing such properties of individual particles is meaningless.

This is just false.

When you look at Lundeen, he showed a one to one correspondence with the spatial wave function of a SINGLE PHOTONS with the spatial wave function of an ensemble of photons. The spatial wave function of a single photon was reconstructed over an ensemble of photons. It just doesn't get much clearer than that.

Like I said, Ballentine shows zero evidence that the wave function isn't real. All I see is a bunch of conjecture that's born out of the desire to remove the mysteries of QM whatever that means. It's just shut up and calculate. Here's David Merman:

"For the notion that probabilistic theories must be about ensembles implicitly assumes that probability is about ignorance. (The “hidden variables” are whatever it is that we are ignorant of.) But in a non-determinstic world probability has nothing to do with incomplete knowledge, and ought not to require an ensemble of systems for its interpretation".

A minimalist interpretation of QM is another form of shut up and calculate which is lacking. Where's the evidence that the quantum system isn't in multiple "real" states prior to measurement? This is what gives rise to the quantum properties that we see in experiment after experiment.

In fact, how can we do calculations on probable states if these probable states are not real when it comes to quantum computing?

More on Quantum Computing and Schrodinger's cat:

The Ensemble Interpretation states that superpositions are nothing but subensembles of a larger statistical ensemble. That being the case, the state vector would not apply to individual cat experiments, but only to the statistics of many similar prepared cat experiments. Proponents of this interpretation state that this makes the Schrödinger's cat paradox a trivial non issue. However, the application of state vectors to individual systems, rather than ensembles, has explanatory benefits, in areas like single-particle twin-slit experiments and quantum computing. As an avowedly minimalist approach, the Ensemble Interpretation does not offer any specific alternative explanation for these phenomena.

The single particle has to be in two real states in order for a calculation to occur. The single particle can be in two real states or a qubit prior to measurement.

This is from a paper titled A single-atom electron spin qubit in silicon.

Here we demonstrate the coherent manipulation of an individual electron spin qubit bound to a phosphorus donor atom in natural silicon, measured electrically via single-shot read-out7, 8, 9. We use electron spin resonance to drive Rabi oscillations, and a Hahn echo pulse sequence reveals a spin coherence time exceeding 200 µs. This time should be even longer in isotopically enriched 28Si samples10, 11. Combined with a device architecture12 that is compatible with modern integrated circuit technology, the electron spin of a single phosphorus atom in silicon should be an excellent platform on which to build a scalable quantum computer.

http://www.nature.com/nature/journal/v489/n7417/full/nature11449.html

When it comes to underlying states.

Of course all of these states are real and that's the point. All of these states are coherent and real prior to measurement and this is why we can show single particles in a state of superposition. So the underlying reality of the system(particle) is real. This underlying reality is the wave function in a pure coherent state where pure states simultaneously exist prior to decoherence.

Ballentine's blunder on the Quantum Zeno Effect.

Leslie Ballantine promoted the Ensemble Interpretation in his book "Quantum Mechanics, A Modern Development". In it [6], he described what he called the "Watched Pot Experiment". His argument was that, under certain circmstances, a repeatedly measured system, such as an unstable nucleus, would be prevented from decaying by the act of measurement itself. He initially presented this as a kind of reductio ad absurdum of wave function collapse.

Of course he was wrong when he said:

"Like the old saying "A watched pot never boils", we have been led to the conclusion that a continuously observed system never changes its state! This conclusion is, of course false.

Wrong.

One last thing. there was a poll taken by Anton Zeilinger at the Quantum Physics and Nature of Reality conference in Austria in 2011. Here's what they thought about ensemble interpretations.

Right interpretation of state vectors:

27%: epistemic/informational
24%: ontic
33%: a mix of epistemic and ontic
3%: purely statistical as in ensemble interpretation
12%: other

As you see, the ensemble interpretation got 3%.

I chose not to label the "ensemble interpretation" as correct because the ensemble interpretation makes the claim that only the statistics of the huge repetition of the very same experiment may be predicted by quantum mechanics. This is a very "restricted" or "modest" claim about the powers of quantum mechanics and this modesty is actually wrong. Even if I make 1 million completely different experiments, quantum physics may predict things with a great accuracy.

Imagine that you have 1 million different unstable nuclei (OK, I know that there are not this many isotopes: think about molecules if it's a problem for you) with the lifetime of 10 seconds (for each of them). You observe them for 1 second. Quantum mechanics predicts that 905,000 plus minus 1,000 or so nuclei will remain undecayed (it's not exactly 900,000 because the decrease is exponential, not linear). The relatively small error margin is possible despite the fact that no pair of the nuclei consisted of the same species!

So it's just wrong to say that you need to repeat exactly the same experiment many times. If you want to construct a "nearly certain" proposition – e.g. the proposition that the number of undecayed nuclei in the experiment above is between 900,000 and 910,000 – you may combine the probabilistically known propositions in many creative ways. That's why one shouldn't reduce the probabilistic knowledge just to some particular non-probabilistic one. You could think it's a "safe thing to do". However, you implicitly make statements that quantum mechanics can't achieve certain things – even though it can.

Here's more about the conference:

http://www.technologyreview.com/view/509691/poll-reveals-quantum-physicists-disagreement-about-the-nature-of-reality/

So again, the ensemble interpretation flies in the face of experiment after experiment. It's a way of saying Quantum weirdness can't be objectively real but the truth is, it's an underlying reality for the quantum system not the classical experience.