Where is the quantum system prior to measurement?

[hutchphd]

If by potentialities you mean there is the potential to measure it anywhere in the universe but in a single, localized position then that is not the same as saying the system is everywhere in the universe.

I guess we'll take your word for it. That is a polite way of bowing out of this particular monolog. But I really do appreciate you not using a bunch of jargon in your arguments.

 

[StevieTNZ]

If it is, then we require physical collapse.

There is no collapse in QM formalism.

 

[StevieTNZ]

If by potentialities you mean there is the potential to measure it anywhere in the universe but in a single, localized position then that is not the same as saying the system is everywhere in the universe.

Definitely not what I meant.

 

[physika]

Does something “have a location” when it’s not “measured”?

..and the inverse, how does know, that don't have it a location/ position?

 

[PeterDonis]

we appear to be talking at cross purposes here because I am specifically talking about the statistical interpretation.

No, you're not. You're talking about your concept of "location". But as far as the statistical interpretation is concerned, your concept of "location" doesn't apply to it either.

You have suggested previously that 'location' is ill-defined

I'm basing that on what is implicit in how you have been using the term "location". If you want to offer an explicit, rigorous definition of "location" instead of making me have to infer what you mean by it, by all means do so.

They can of course be asked.

Not in the cases I have described. In order for a question to even be asked in the first place, the concepts it is making use of have to make sense in the domain of discussion. Yours don't.

At this point I don't think I have anything further that is useful to contribute to this discussion.

 

[Lynch101]

I guess we'll take your word for it. That is a polite way of bowing out of this particular monolog. But I really do appreciate you not using a bunch of jargon in your arguments.

Yes, such impenetrable jargon as 'location', 'position', 'within', and 'finite region of space'.

But don't take my word for it, apply the simplest of basic reasoning.

Saying: we have the potential (there is a non-zero probability) to measure the system anywhere in the universe, is not the same as saying: the system is everywhere in the universe.

 

[Lynch101]

There is no collapse in QM formalism.

If the physical system is located everywhere in the physical universe, then collapse is required to explain our observations. This is entirely contingent on the proposition, 'the physical system is located everywhere in the physical universe'.

 

[Lynch101]

No, you're not. You're talking about your concept of "location". But as far as the statistical interpretation is concerned, your concept of "location" doesn't apply to it either.

I'm basing that on what is implicit in how you have been using the term "location". If you want to offer an explicit, rigorous definition of "location" instead of making me have to infer what you mean by it, by all means do so.Not in the cases I have described. In order for a question to even be asked in the first place, the concepts it is making use of have to make sense in the domain of discussion. Yours don't.

At this point I don't think I have anything further that is useful to contribute to this discussion.

Perhaps I am placing undue burden on others to infer what is meant. I have been working on the assumption that everyone is familiar with the idea of a 'finite region of space', and the notion of being 'within' that 'finite region of space'.

If at any point I am assuming too much, let me know and I can define what is meant more rigorously.

I'm going to assume that you are familiar with the concept of '3 dimensional space' and how to model/graph that using X, Y, and Z axes. I'm also assuming that , at some point during the course of your life you have made one, if not several, observations of boxes, be they cardboard or otherwise.

Now, we can model the 3D space of the box in the broader 3D space in which we find it. I'm assuming you know how to draw a 3D box on a graph using X, Y, and Z axes.

When we have the box drawn we can shade it in, so that it is a different colour from the rest of the 3D space on the graph. Let's say we shade the box blue and leave the rest of the space white.

Now, what is meant by 'located within a finite region of space' with regard to the box is, simply, somewhere on the part that is shaded blue. While 'not located within that finite region of space' would be somewhere on the part that is shaded white.

Is there anything there that is not clear?

 

[Lynch101]

Definitely not what I meant.

What did you mean by it then?

There are different ways to interpret what you said. I outlined one possible interpretation.

 

[physika]

There is no collapse in QM formalism.

However, exists collapse models and are testable.

 

[votingmachine]

The argument from Nowhere
5) If the system is not located anywhere in the universe then it is not in/part of the universe.
6) If the system is not in/part of the universe then it cannot interact with measurement devices which are in/
part of the universe.

A system that is not within a plane can interact with the plane. I'm not sure that #6 is a meaningful statement.

It either is a tautalogy, which then contradicts #5, since there is nothing that is not in/part of the universe, or it makes an unsupported statement that things not in/part of the universe cannot interact with the universe. I see no reason why a thing NOT IN the universe is forbidden to interact with a measuring device IN the universe

 

[Morbert]

I'm going to indulge myself and give the consistent histories answer.

We have a quantum system $s$ and measurement apparatus $M$ prepared in some initial state $\rho=\rho_s\otimes\rho_M$. The apparatus measures some observable $O$ at time $t_1$, with possible results $\{\epsilon_i\}$. We want to ask where the system is immediately prior to measurement, at time $t_1-\delta t$. We can model the location of the system with the observable $X$ and a suitably coarse-grained decomposition corresponding to possible position volumes $\{x_j\}$, such that $X$ and $O$ commute. We construct a state space $\mathcal{H}_{t_1-\delta t} \otimes \mathcal{H}_{t_1}$ as well as a suitable set of consistent histories $\mathcal{F}$. This set let's us extract quantities like $p(x_j|\epsilon_i)$. E.g. If our measurement result is $\epsilon_i$ then we can say that right before our measurement the system was located in the volume $x_j$ with probability $p(x_j|\epsilon_i)$.

 

[StevieTNZ]

If the physical system is located everywhere in the physical universe, then collapse is required to explain our observations. This is entirely contingent on the proposition, 'the physical system is located everywhere in the physical universe'.

Again, not necessarily. QM formalism doesn't have a non-linear attribute to the Schrödinger equation.

 

[StevieTNZ]

If the physical system is located everywhere in the physical universe, then collapse is required to explain our observations. This is entirely contingent on the proposition, 'the physical system is located everywhere in the physical universe'.

That's a very materialism kind of view. I subscribe to idealism.

 

[StevieTNZ]

What did you mean by it then?

There are different ways to interpret what you said. I outlined one possible interpretation.

Your supposed interpretation doesn't even read coherently, so I'm not sure what your view about my view is.

 

[jbergman]

This all strikes me as a somewhat bizarre discussion, Lynch101, and I agree with some of what you say. I have problems with the statistical interpretation and many others do too, as evidenced by the different interpretations.

That said, I don't understand the point of your questions. Are you trying to convince others of something? If so maybe a more direct route of laying out which interpretation you prefer might be more effective.

 

[Lynch101]

I'm going to indulge myself and give the consistent histories answer.

we can say that right before our measurement the probability of measuring the system in the volume $x_j$ is $p(x_j|\epsilon_i)$.

Is my amendment here correct?

 

[Lynch101]

Your supposed interpretation doesn't even read coherently, so I'm not sure what your view about my view is.

You said:

I would answer that with 'not necessarily'. Remember we are dealing with potentialities when we talk about the system being everywhere in the universe. Don't think of the system being in a classical state.

The system is either every everywhere in the universe or it is not. This is different from saying there is the potential to measure it everywhere (or anywhere) in the universe

That's a very materialism kind of view. I subscribe to idealism.

How does the 3 dimensional universe differ according to idealism, other than metaphysically?

 

[Lynch101]

This all strikes me as a somewhat bizarre discussion, Lynch101, and I agree with some of what you say. I have problems with the statistical interpretation and many others do too, as evidenced by the different interpretations.

That said, I don't understand the point of your questions. Are you trying to convince others of something? If so maybe a more direct route of laying out which interpretation you prefer might be more effective.

I don't necessarily have a preferred interpretation. I'm just trying to explore what QM tells us about the universe. I'm laying out my understanding as it currently is, with regard to the completeness* of the statistical interpretation. I am open to having that changed by way of reasoned discussion, or the unlikely alternative.

*By completeness I mean a complete description of the universe ala EPR's 'complete description of physical reality'.

 

[hutchphd]

The system is either every everywhere in the universe or it is not. This is different from saying there is the potential to measure it everywhere (or anywhere) in the universe

The cat is either alive or not. Same old stuff.
These are not new ideas, and restating them in different circumstances simply obfuscates

 

[Lynch101]

The cat is either alive or not. Same old stuff.
These are not new ideas, and restating them in different circumstances simply obfuscates

We might be talking at cross purposes here bcos we're in agreement on one point. The cat is either alive or dead. It is either alive or dead prior to opening the box.

An interpretation which only says, prior to opening the box, there is a 0.5 probability the cat is alive and a 0.5 probability the cat is dead, gives an incomplete description precisely because the cat is either definitely alive or definitely dead.

 

[Morbert]

Is my amendment here correct?

The amendment is fine, but not necessary. Consistent histories let's us make claims about the past not predicated on some counterfactual case where an additional measurement was performed at some point in the past. If we open the box and find a live cat, we can infer that the cat was alive and in the box before we opened it.

 

[EPR]

4 pages of idle discussion of layperson classical ideas and reasoning on quantum theory. If quantum systems behaved classically, there would be no separate theory.
I, and many others here, disagree that quantum theory is not a complete description of reality.
The quantum system is an integral part of the relative quantum field. Before measuring, there is only the field. The basic ingredient of the universe are not solid balls that you can assign a location to, but fields. Before you ask - fields are everywhere, because they are everything. They are the cat.

 

[Lynch101]

The amendment is fine, but not necessary. Consistent histories let's us make claims about the past not predicated on some counterfactual case where an additional measurement was performed at some point in the past. If we open the box and find a live cat, we can infer that the cat was alive and in the box before we opened it.

Can the same be said for the position of the system? You're statement said that it was located in the given volume with a probability $p(x_j|\epsilon_i)$. Does that probability equate to 1 after we make the measurement? i.e. does it say that the system always had a definite position? I'm guessing that the answer is no.

For any given region of space, the probability that the system is positioned in that region is either 1 or 0. That is, the set of values that comprise its position (it doesn't necessarily need to be one single value) includes that value with a probability of 1 or 0. The system is either in that position or it isn't, but it doesn't necessarily have to be in that position only.

This is a separate proposition to saying there is a probability $p(x_j|\X)$ that when measured it will be return a single value X.

 

[votingmachine]

*By completeness I mean a complete description of the universe ala EPR's 'complete description of physical reality'.

EPR was a clever proposal for an experimental setup to measure things beyond the allowances of Heisenberg's uncertainty. A way to demonstrate that uncertainty is JUST a necessary measurement error.

The experimental setup does not show that. It leads to the puzzling results that show (conclusively) that a complete description does not exist.

I too am puzzled by your arguments. It seems that you use want to use the knowledge gained as the result of a measurement as an argument that the universe knew, but we did not. The introduction of subsets seems puzzling and unnecessary.

I learned uncertainty as a measurement error (1970's). If you measure a baseball's position and momentum with a radar gun, the radar bouncing off the ball matters to the balls position and momentum. If the ball was thrown at night and we only had radar, we would necessarily have uncertainty imposed by the measurement process. But for macroscopic things, we generally have experimental errors much larger than the limits of uncertainty. With better equipment, we can get closer to the correct value. We add significant figures, and it is tempting to think we could arrive at a terminal decimal, beyond which it is all zeroes.

The complete descriptive set of information for that baseball does not exist. You can arbitrarily talk about the baseball being in subsets of the universe, but the complete descriptive set still does not exist. The part limited by uncertainty simply does not exist.

Maybe you have some other point by dicing up the universe, which I am not following.

 

[Lynch101]

4 pages of idle discussion of layperson classical ideas and reasoning on quantum theory. If quantum systems behaved classically, there would be no separate theory.
I, and many others here, disagree that quantum theory is not a complete description of reality.
The quantum system is an integral part of the relative quantum field. Before measuring, there is only the field. The basic ingredient of the universe are not solid balls that you can assign a location to, but fields. Before you ask - fields are everywhere, because they are everything. They are the cat.

You seem to be using the terminology a little loosely here. You say that the quantum system is an integral part of the relative quantum field [singular] and that, before measuring, there is only the field [singular]. Then you change to the plural when you say fields [plural] are everywhere.

We're talking about the quantum system prepared in the experiment. Is this part of the quantum system everywhere? If it were, then we should be able to measure it everywhere, with a probability of 1. If it isn't everywhere, but it is extended then we should be able to measure it everywhere it is, with a probability of 1. We don't however. This is part of what needs explaining.

There is no appeal to 'classical solid balls' here, since classical solid balls are not usually everywhere.

 

[Morbert]

Can the same be said for the position of the system? You're statement said that it was located in the given volume with a probability $p(x_j|\epsilon_i)$. Does that probability equate to 1 after we make the measurement? i.e. does it say that the system always had a definite position? I'm guessing that the answer is no.

So long as we partition the volumes accordingly, such that the observables $X$ and $O$ commute, we can say the system (or the centre of mass of the system or whatever) was definitely located in one of the volumes $\{x_j\}$. Though this is not the same as $p(x_j|\epsilon_i) = 1$. Instead it's $\sum_j p(x_j|\epsilon_i) = 1$

The commutation is important though. We cannot e.g. arbitrarily refine the possibilities $\{x_j\}$ into smaller and smaller volumes.

 

[EPR]

You seem to be using the terminology a little loosely here. You say that the quantum system is an integral part of the relative quantum field [singular] and that, before measuring, there is only the field [singular]. Then you change to the plural when you say fields [plural] are everywhere.

We're talking about the quantum system prepared in the experiment. Is this part of the quantum system everywhere? If it were, then we should be able to measure it everywhere, with a probability of 1. If it isn't everywhere, but it is extended then we should be able to measure it everywhere it is, with a probability of 1. We don't however. This is part of what needs explaining.

There is no appeal to 'classical solid balls' here, since classical solid balls are not usually everywhere.

Yes, the quantum field is everywhere. This is the only thing that is everywhere. Not "the quantum system" but the relative quantum field. You don't seem to grasp this and won't spend time as others did countering stubborn pedestrian reasoning.

 

[Lynch101]

So long as we partition the volumes accordingly, such that the observables $X$ and $O$ commute, we can say the system (or the centre of mass of the system or whatever) was definitely located in one of the volumes ##\

Am I interpreting this correctly when I liken it to saying, we can definitely say a dice is in one of its 6 positions?

Edit: not trying to be facetious

 

[EPR]

You are asking a nonsensical question in this thread which kind of gives away your incomplete knowledge of QT, rather than the incompleteness of QM. This naive question was asked in 1935 - but the theory has moved on and advanced immensely since then. It was relevant in the beginning when evidence of the correctness of QT wasn't as overwhelming as it is today and physicists were naturally still thinking in classical terms(like you). Not anymore. This question makes no sense in 2021.