Graduate Is the wavefunction subjective? How?

[zonde]

This is a chicken and egg situation but circular is i think a bad an inappropriate descriptor as it sounds like a deadlock which it ia not.

Let's not say that "it does not work" because it sounds like it does not work while I think that it works? - is this what you are saying?

Do you have some valid starting point for your reasoning? What is instead of what is not? And is it consistent with scientific approach? It does not seem so to me.

You have to understand that science does not cover all the thinkable explanations of the world. It covers only limited class of explanations. And it does not seem that your reasoning is anywhere near that "limited class of explanations".

 

[atyy]

People agreeing on objective facts is basic requirement for doing science. You can not relax this stance and still pretend that your philosophy has something to do with science.

"People" is subjective. What is a person?

 

[zonde]

"People" is subjective.

In what sense "people" is subjective?

What is a person?

For example me and you. A person who does the science is a primitive term in context of philosophy of science so it does not require definition.

 

[DarMM]

Basically I think one can argue that given a particular cut/physical situation/observed outcomes that there is a best wavefunction. The same kind of thing Jeffreys and Jaynes had for Classical Probability.

However because there is a Quantum de Finetti theorem you are also fine taking it subjectively like Savage, Ramsey and de Finetti did for Classical Probability.

So you just fall back to the interpretation of Probability theory in general.

 

[A. Neumaier]

Basically I think one can argue that given a particular cut/physical situation/observed outcomes that there is a best wavefunction.

This is not sufficient: Taking the cut to include a lot (system, detector, much environment), the corresponding best wave function should determine all probabilities about (system, detector, much environment), and hence should determine all conditional probabilities when taking the cut more narrowly, e.g., only (system, detector). But this conditional probability is not given by a wave function.

 

[DarMM]

This is not sufficient: Taking the cut to include a lot (system, detector, much environment), the corresponding best wave function should determine all probabilities about (system, detector, much environment), and hence should determine all conditional probabilities when taking the cut more narrowly, e.g., only (system, detector). But this conditional probability is not given by a wave function.

Could you describe what you mean in a bit more detail?

 

[julcab12]

"The wave function cannot be measured (its tiny changes cannot be distinguished by any apparatus that studies the physical system once) which is a good reason to say that "it probably doesn't objectively exist"

Basically, In this sense the complex conjugate square of the wave function that gives the probability for an event to happen, is objective. It is a real number and accumulating measurements with the same conditions always gives the same probability distribution, even though there are levels upon levels of modeling. The wavefunction is the mathematical modeling of what happens when "particle scatters" . It is not the wavefunction that interacts, it is the particle(blurry bunch) which interacts with the boundary conditions of a experiment that can be fitted with a wavefunction which complex conjugate squared gives the probability distribution for the experiment.

 

[atyy]

In what sense "people" is subjective?

For example me and you. A person who does the science is a primitive term in context of philosophy of science so it does not require definition.

"People" is subjective like "measurement apparatus".

 

[Fra]

Let's not say that "it does not work" because it sounds like it does not work while I think that it works? - is this what you are saying?

No, I was basically saying that I read your understanding of "objectivity" as what from my perspective is a deceptive illusion.

But I was trying to put it in more polite manner for the sake of discussion by saying that you make and observation that I partially agree with (that we have a self-referencing situation), but when you say its circular that implies to me you are missing the point.

Do you have some valid starting point for your reasoning? What is instead of what is not? And is it consistent with scientific approach? It does not seem so to me.

You have to understand that science does not cover all the thinkable explanations of the world. It covers only limited class of explanations. And it does not seem that your reasoning is anywhere near that "limited class of explanations".

To connect this to the scientific method, what I am talking about here belongs to the hypothesis generation part. This is the part that Popper tried to sweep under the rug byt instead focus on the deductive falsification events.

But if you have given unification approaches and thoughts you should know that one problem is that faces initial value problems, problems with naturalness etc, simple BECAUSE the state spaces are so large. As smolin etried to explain to death in books, this is a failure of what he calls the Newtonian paradigm. It is actually also related to the "unreasonable effectiveness of mathematics", which when you understand the reason for it is in fact very reasonable. Its effective because it applies to subsystems.

As I said, no one has yet published a theory of framework for this, that to my knowledge is a solution. But let's not avoid facing the problem just because we have no solution.

My staring point means to reconstruct a measure framework, from the perspective of a ficitve information processing agent. This has the advantage that as you scale down the complexity, the state space is NOT infiinte, it rather gets trivially small. The challenge is then to see how relation emerge as these interact and gain complexity. This process of scaling complexity corresponds exactly to the big band and TOE unification level: information processing agents are like spieces that POPULATE the universe, and they are further assocaite to elementary particles, and their RELATIONS encode also spacetime. The Science here is that this is a hypothesis, if this works and reproduces known physics or reducing the number of free parameter,, and thus increases the explanatory power, then it will also yield more predictions that can be tested.

But you can not apply Poppian falsification logic to the process of hypothesis generation! This is not how creative or evoltionary processes work. Most scientis keeps these dirty thoughts to themselves, and only present the "result".

/Fredrik

 

[Stephen Tashi]

Saying that probabilities are relative frequencies doesn't really make sense.

And defining a probability as the relative frequency of an event in a specific population doesn't produce a model of the probability of that event occurring in a "random" trial unless we assume there is a mechanism for independently selecting a member of that population that gives each member of the population the same probability of being selected. So the frequency definition of probability requires a non-frequency concept of probability in order to handle the usual applications of probability.

 

[Stephen Tashi]

. For a specific male, we can come up with different probabilities depending on how much information we have about him. So it's subjective.

Is the fact that people with different information assign different probabilities any more subjective than the situation where two problems in a textbook have different given information and different answers?

Person A with information Y, can claim his assignment of a probability P1 to an event is correct if he does experiments which set conditions as Y and produce results consistent with the value P1. Person B with information "Y and Z" can claim his assignment of a probability P2 to the event is correct if he does experiments which set conditions as "Y and Z" and produce results consistent with P2.

The "subjective" aspect seems to come from the viewpoint of an observer who knows the actual conditions are "Y and Z", and hence regards person A as honest but wrong. Likewise, an observer might know the actual length of the hypoteneuse of a particlular triangle is 10 meters and thus consider people who are working a homework problem where the hypotenuse of a triangle is given to be 8 meters to be honest, but wrong.

 

[A. Neumaier]

stating that the wavefunction is subjective. This means that it is perfectly valid that two different observers use two different wavefunctions to describe the same system. I do not understand how it makes any sense.

Consider the example of the probability for a UK male of 25 years of age to die within the next year. Clearly, this probability is well defined and exists regardless of whether person A and person B agree about it.

This is a misleading analogy.

The right analogy is to consider the example of the probability for John Jones (who happens to be an UK male of 25 years of age, but has many other properties) to die within the next year. This probability depends on which ensemble of people you regard John Jones to belong to. One of these ensembles is the set of UK male of 25 years of age, but another one is the subset of heavy smokers (or nonsmokers, depending on John Jones's habits). Thus different probabilities describe the same person.

Similarly in quantum physics: Once you specify the intended ensemble unambiguously, the state is fully determined by it.

 

[A. Neumaier]

Basically I think one can argue that given a particular cut/physical situation/observed outcomes that there is a best wavefunction.

This is not sufficient: Taking the cut to include a lot (system, detector, much environment), the corresponding best wave function should determine all probabilities about (system, detector, much environment), and hence should determine all conditional probabilities when taking the cut more narrowly, e.g., only (system, detector). But this conditional probability is not given by a wave function.

Could you describe what you mean in a bit more detail?

Given a large system in a pure state with wave function $\psi$, conditional expectations for subsystems are typically not described by wave functions but by density operators.

 

[DarMM]

Woops I should have said "a best state"

 

[A. Neumaier]

Two different predictions about the same event cannot both be correct

Predicting that it will rain tomorrow with probability 40%, and predicting that it will rain tomorrow with probability 60% are both correct, no matter whether it rains tomorrow.

 

[fluidistic]

Predicting that it will rain tomorrow with probability 40%, and predicting that it will rain tomorrow with probability 60% are both correct, no matter whether it rains tomorrow.

One is tempted to fully agree with you if the probability is associated to the knowledge or method of the person who tries to assess the probability.

On the other hand one is tempted to say that the maximum knowledge would lead to a single "correct" probability. For example if we assume that ergodicity holds (I'm probably not using the right word here). Let's say that we have infinitely many times the same system and check whether tomorrow it will rain and make the statistics. We would know with absolute certainty the probability that it will rain tomorrow, i.e. we would get a percentage. It would probably be different from 40% and 60%. People seem to believe that this percentage is the ultimate one, I think. But now it's clear to me that none is the ultimate one, at least when the percentage reflects the knowledge of the observer.

 

[A. Neumaier]

Let's say that we have infinitely many times the same system and check whether tomorrow it will rain and make the statistics. We would know with absolute certainty the probability that it will rain tomorrow, i.e. we would get a percentage.

1. You'll be dead before you have infinitely many independent tomorrows.
2. To give your statistics an objective ergodic meaning you need to include all sufficiently late tomorrows, and presumably there will not be any rain in the very far future of the Earth (if it continues at all to exist indefinitely). Thus it says nothing of interest for us.
3. What you get is only the probability that it will rain on an anonymous tomorrow. The probability whether it rains tomorrow, May 29, 2019, at the Stephansplatz in Vienna will still be definitely 0 (by today's forecast unlikely) or 1 (by today's forecast most likely), though we cannot yet tell for sure which one.

 

[DarMM]

A nice example of subjectivism in the quantum state @fluidistic is the case of two experimenters performing tomography measurements on two qubits.

Say one has the initial prior for the state of:
$$\rho_{+} = \frac{1}{2}\left(|00\rangle\langle 00| + |++\rangle\langle ++|\right)$$

And the other uses:
$$\rho_{-} = \frac{1}{2}\left(|00\rangle\langle 00| + |--\rangle\langle --|\right)$$

with $|\pm\rangle = \frac{1}{\sqrt{2}}\left(|0\rangle \pm |1\rangle\right)$

These are analogous to two overlapping priors in Classical Statistics.

They then perform a measurement on the first qubit in the $\{|0\rangle,|1\rangle\}$ basis and they obtain $1$. The first experimenter will then update the state of the second qubit to $|+\rangle$ where as the second experimenter will update it to $|-\rangle$.

These are actually orthogonal states. The analogue in Classical Statistics is updating to two posteriors with no overlap.

 

[Fra]

Predicting that it will rain tomorrow with probability 40%, and predicting that it will rain tomorrow with probability 60% are both correct, no matter whether it rains tomorrow.

And this makes a difference in one specific scenario: When you try to predict the action of the observer; from the perspective of another observer. This is IMO the trick and insight. The rationality assumption simply means that an external observers best guess, is that each OTHER observer acts randomly as per its subjective p-distributions.

If you repeat this logic, down to micro-observers (ie subatomic structures - not humans) this logic implies that interactions in-between observsers, are encoded by their relative information and subjective p-distributions about each other. From a very far distant dominant observers (laboratory frame) these inside observers, then should form like an equivalence class of "inside-observers" that could also be called gauges. As the choice if inside observers is arbitrary. But one can never reduce away the distant observer. This becomes a problem in cosmological models, when there is no "lab frame" that is dominant.

So in my view, understanding unification of forces, is another side of the same problem, to understand the interaction between observers encoding incomplete truncated p-measures about each others. The latter way of thinking however offers an interesting route to deeper insight.

Similar logical literally explains conflicts in social interactions - the explanation and cause, is simply the different information perspectives. This drives the conflicts. One usually says such problems are solved by mutual understanding in human world, but in physics the "inside observers" are physically constrained and its physically impossible for all obersvers to be in possession of the same information, so some fundamental interactions must be unavoidable.

/Fredrik

 

[A. Neumaier]

The rationality assumption simply means that an external observers best guess, is that each OTHER observer acts randomly as per its subjective p-distributions.

But this is an irrational assumption. Rationally, how other observers act must be determined by sufficient observation (or judgment must be deferred until such observation is available), and not by postulating some a priori subjective distribution for it.

 

[Fra]

But this is an irrational assumption. Rationally, how other observers act must be determined by sufficient observation (or judgment must be deferred until such observation is available), and not by postulating some a priori subjective distribution for it.

Admittedly this is a conjecture; its success depends on wether this conjectures helps solve the puzzle. But as I see it, this conjecture is "natural". It appears to ne to be the least speculative conjecture, and "deferring judgement" works in some human situation, but in a physical interaction this is not an option. Under timepress; assuming we think of interaction between observers as a realtime decision process, sometimes a suboptimal fast choice, rather than a more accurate but more slow considerations is what keeps you alive.

/Fredrik

 

[A. Neumaier]

Under timepress; assuming we think of interaction between observers as a realtime decision process, sometimes a suboptimal fast choice, rather than a more accurate but more slow considerations is what keeps you alive.

Yes, but science is not under time pressure. (Or rather, science done under time pressure is only very rarely good.)

There is no rational substitute for the complete lack of information except information.

 

[Fra]

Yes, but science is not under time pressure.

I think you missed my point. The process under time pressure is not human science, but real world physical interactions.

There is no rational substitute for the complete lack of information except information.

Its my firm understanding that the incompletness and uncertainty of information, and the constrained capacity to process information thrown at an observer, and its associated process is they key to understand unification of forces.

I think that the limitations of this process, is fundamental, and thus nature is faced with a situation of having to make decisions/actions based upon incomplete and incompletely processed information under time pressure.

/Fredrik

 

[PeterDonis]

Admittedly this is a conjecture

Conjectures and personal speculations are out of bounds for PF discussion.

 

[PeterDonis]

unification of forces

...is not the subject of this thread.

 

[A. Neumaier]

The process under time pressure is not human science, but real world physical interactions. [...] nature is faced with a situation of having to make decisions/actions based upon incomplete and incompletely processed information under time pressure.

Ah, you make not observers but Nature the epistemic subject whose knowledge is encoded in the wave function? But Nature never bets, as far as I can tell. How can it have a subjective but rational notion of knowledge?

Do you really think that a measurement device constantly gathers information under time pressure in order to know which result it should produce? Two photodetectors far apart don't have the complexity to gather, store, and process enough information about the nonlocal state of a possibly impinging photon pair to figure out the joint probability with which they should fire...

 

[Fra]

Conjectures and personal speculations are out of bounds for PF discussion.

My apologies.

Some of these discussions - both in btsm and sometimes the "interpretational QM" topics in this subformus are in my opinion typically always in a grey area. Interpretations, philosophical stances and personal conjectures sometimes float together.

/Fredrik

 

[Fra]

Do youreally think that a measurement device constantly gathers information under time pressure in order to know which result it should produce? Two photodetectors far apart don't have the complexity to gather, store, and process enough information about the nonlocal state of a possibly impinging photon pair to figure out the joint probability with which they should fire...

I will pass discussing this in detail as its not the main topic, but a closing comment is that yes I see a measurement device (or any interacting part) as a kind of "information processing" object. I put it in quotes because I view the computation as observer dependent spontanous processes.

/Fredrik

 

[Jehannum]

Predicting that it will rain tomorrow with probability 40%, and predicting that it will rain tomorrow with probability 60% are both correct, no matter whether it rains tomorrow.

Your example is merely a good demonstration that probability doesn't mean much with regard to single events (despite what Mr Spock says).

 

[A. Neumaier]

Your example is merely a good demonstration that probability doesn't mean much with regard to single events (despite what Mr Spock says).

It is a demonstration that it means nothing, from a scientific perspective.

In the form of subjective probability, it may be a useful guide for practical decision in the light of uncertainty. But to confuse subjective probability with science is in my view a big mistake.