Realism Definition and 66 Threads

I don't understand this accusation. Given a single system prepared in some state ##\psi = \sum c_i|i\rangle##, the probability ##\mathrm{tr} |\psi\rangle\langle\psi|i\rangle\langle i|##, according to Griffiths, is the probability that the system has the property ##i##. This is in contrast to...

I actually found this page while looking for a random bit of physics clarification for my dystopian story. I'm glad to be here, and extremely grateful for everyone who is clearly smarter than me and is willing to share their time to answer our shower questions!

In the thread general-argument-that-entanglement-can-only-be-created-locally @Cthugha explains why the monogamy argument used by @DrChinese in his entanglement swapping experiment explanation is bunk. Given that the monogamy argument is bunk, if the raw measurement values of photons of 1 and 4...

This is my first time posting, so please excuse any mistakes. I am grasping at straws here. I am working on a Hard-Sci Fi novel, plot, arcs, characters etc. are all worked out and i decided to take the deep dive in terms of Realism. For instance, there are no Fusion reactors. All that is...

In interpretations of quantum mechanics there are two types of physicists: those who care about ontology and those who don't. The ontologists, or realists, want to know what is the world made of. The non-realists, on the other hand, think that this question is not relevant to physics. Usually...

For this discussion I would like to continue referring to the entangled pairs 1,2 and 3,4 as we have in previous discussions. For background on this discussion refer to post-selection: pre-existing correlations or action at a distance where @DrChinese describes the entanglement swapping...

I read in an article that "Quantum physics is a highly mathematical theory that describes the nature of reality at the atomic and subatomic level". I also read another article that says quantum physics does not tell anything about reality. Can you give me some context about it in a way that is...

I would like to pose a question (previously posed to DrChinese in a personal message) regarding Bell Locality. From PeterDonis in another thread: Bell assumes that local realism requires the factorizability of the joint probability function. Most of the efforts to justify this assumption have...

It seems that with every discussion I engage in, new thoughts and questions about QM keep popping up. I'm sure this is pretty standard but I hope that my questions haven't crossed the line into being excessive. I know that in the EPR paper the authors set out a criterion that, if fulfilled...

Hi, Translated from German magazine "Spektrum der Wissenschaft", September 2009, p. 33 (original see below): That doesn't sound right. EPR even have "physical reality" in the title, though they might not mean with it the exact same thing as Bell. Why would we need Bell's argument if EPR...

Summary: Bell's theorem is often interpreted as a claim that either locality or realism is wrong. A recent theorem claims that realism is a consequence of the assumption of locality, so that locality must be wrong in any case. Recently, Bricmont, Goldstein and Hemmick wrote two (quite similar)...

In a paper much discussed on this forum (https://www.physicsforums.com/threads/does-the-bell-theorem-assume-reality.964219/),Roderich Tumulka, "The Assumptions of Bell’s Proof" (http://de.arxiv.org/abs/1501.04168) argues that locality entails two specific types of realism, which he calls R1 and...

Hi all, Not a question about completing homework here, but I'm a teacher looking to create a realistic engineering question for an assignment. I have an engineering scenario I've set for the assignment which is a junior engineer working for a marine engineering company so all of the questions...

This is a soft question, but I am reading Hawking's "The Grand Design" and he mentions that "Although it is not uncommon for people to say that Copernicus proved Ptolemy wrong, that is not true ... One can use either picture as a model of the universe." He goes on to say that we hold the...

Not sure if this reference has been posted yet, but I just saw it come through and thought I'd share. This is the "Big Bell Test Collaboration" using measurement choices provided by persons (as opposed to computer generated "random" choices). (The authors are a virtual who's who in the world...

What is wrong with the idea that the spooky correlation in the EPR experiment is simply the result of the initial difference in rotation between the two polarizers in this experiment? So if you rotate one of the polarizers relative to the other polarizer, that initial act of rotation is what...

What is the difference between counterfactual definiteness on one side and realism on the other? And what are their definitions? (references will be welcome if given).

Please consider the following premises and correct me if I'm wrong in anyone: Based on the results of the experimental investigation of Bell's theorem and violation of the Bell's inequality, locality in tandem with reality is not applicable to quantum systems (no theory of local realistic...

So I was doing some calculations last night on railguns for fun, and I got some very surprising results which seams like they must be wrong. The calculations are simple and I must have overlooked something. So we all know that F = B * I * L when all are orthogonal, a capacitor discharge is I =...

Hello! Recently I found this article: http://quantum-journal.org/papers/q-2017-07-14-13/pdf/ Being familiar with some basis of quantum formalism, I, nevertheless, experienced several difficulties with understanding of the theorem described in this paper. I would really appreciate if someone...

Why or why not?

Through Bell's inequality, we can see that any hidden variable theory of QM will have to satisfy the inequality, but as it doesn't, wave function must be the whole story and so we have to do away with realism. So when a measurement is done on one detector in the EPR experiment, the wave function...

Hi. Bell formulated local realism as follows: The probability of a coincidence between separated measurements of particles with correlated (e.g. identical or opposite) orientation properties can be written as $$P(a,b)=\int{d\lambda\cdot \rho(\lambda)\cdot p_A(a,\lambda)\cdot...

Hi. A while ago, I apparently had a wrong idea about the meaning of realism. I stood corrected: I'm still struggling with those subtleties. Would following formulation be more appropriate: "Realism means, that every observable ##x## is attributed a probability distribution ##p_P(x)## that...

A few weeks ago I created a discussion titled "How does Bell's inequalities rule out realism." Essentially my question was pertaining to how does removing realism retain locality and not violet Bell's inequality. Someone answered with the this, I'm not really happy with this explanation, but...

I understand Bell's inequality, and I can see how removing locality can produce the observed statistical correlations. However something that I often read is that eradicating realism can also generate the correlation observed in entanglement. I don't see how a particle not having definite...

Hi. In most articles on Bell's inequalities, both the reality and locality assumptions are thrown at the reader from the beginning. DrChinese however starts with only the reality assumption and shows that it doesn't comply with QM IF it were possible to measure two non-commuting observables...

Hi. I have a strange relation to Bell's inequalities, I understand (so I hope) all the maths but have lots of trouble with the implications of their violation. Currently: Say we assume QM to be realistic, it can't be local. There needs to be some sort of instantaneous signalling. Realism means...

Hi. I'm still confused about those three concepts. They sound pretty much the same to me, but this does not comply with Wikipedia's table of comparison of QM interpretations, where pretty much all combinations seem to be present. Actually, is the "Wavefunction real?" column even about...

I have a question with regards to quantum entanglement, and how it relates to the concepts of realism and locality. I am just an interested amateur who has self-studied QM in my free time, so perhaps I should first run my understanding by you first, to make sure it is accurate : the basic idea...

Usually its said that the violation of Bell's inequality means that any theory that contains the assumptions of locality and realism doesn't agree with QM and observations. But sometimes I hear people talk about counter-factual definiteness instead of realism(or maybe the presence of both!) as...

Hi. Bell's formulation of local realism is $$P(a,b)=\int\ d\lambda\cdot\rho(\lambda)p_A(a,\lambda)p_B(b,\lambda)\enspace.$$ Let's for simplicity assume there's only a finite number of states, so this becomes $$P(a,b)=\sum_{i} p_i\cdot\ p_A(a,i)p_B(b,i)\enspace.$$ I'm trying to translate this...

Do you find modern digital special effects convincing and realistic? Will they look outdated 20 years from now? Perhaps I see some digital special effects and don't realize they are digital. However, big digital landscapes and architecture (e.g. "Bladerunner" or the "Indiana Jones..." series...

Given the locality assumption : p(ab|xy,λ) = p(a|x,λ) p(b|y,λ) with λ defining a single valued realism: a,b,a'b' each equal ± 1 the inequality S = (ab) + (ab') + (a'b) - (a'b') ≤ 2 is derived. Previously Bell pointed out that classical indeterminism wouldn't be enough for any hidden...

Is reality mind-dependent ? I saw a lot of videos on internet arguing that the 'holographic theory' proves that our world is an illusion created by our brains.. and every person has their own individual world in his brain...just like a movie, they use QM as a proof, and Tom Campbell as a...

I think it's the idea that things exist even before we measure them, correct?

Bell, QM Ideas - Science 177 1972 :" Strictly, however. a hidden variable theory could be non-deterministic; the hidden variable could evolve randomly (possibly even discontinuously) so that their values at one instant do not specify their values at the next instant" From the locality...

I fell upon another discord between realism and quantum mechanics while studying Bell's theorem : If we consider measurement of 2 spin 1/2 particles, with operators A, A', B and B' which are set respectively at 0, 45, 90 and 135 degrees (like in Bell experiment), we have...

I thought this would be a cool kind of topic to put up for discussion. 1)How realistic would a moon base be for mining and production of metals. 2)How realistic would the moon be for a Rocket launch area don't know how to word that. Anyways since the moon has practically no gravity we could...

As the only thread I've ever started before (https://www.physicsforums.com/showthread.php?t=369328 ) attracted a lot of interest, became one of the most viewed threads in the forum, and was closed :-), I'd like to make a short update here. I have published a new article on the topic: "No...

Morrobay suggested we split off this discussion from another thread. I will post my summary of the EPR definition a bit later today.

Hello, I have to present Critical Realsim theory to class. I have been coming across words like Ontology and Epistemology. I made effort to see what those terms are and their relation to critical realism but I couldn't understand it. It talks philosophy. Can some help me to understand in simple...

I came across an article from 2007 talking about some experiemtns that are an extension of the experiments which originally tested for Bell's Inequality. These tests were supposedly designed to relax the locality requirements and test soley for realism. I'll quote a few pertinent sections...

What is the opposite of "realism" in quantum mechanics? I have been spending an awful lot of time reading about the philosophy of science where the opposite of "realism", insofar as "realism" constitutes a category coherent enough to be meaningfully negated, is "anti-realism". Is this true as...

The Goldwater scholarship application is approaching, and I think it's an excellent opportunity. However, I have a GPA less than the average of 3.95 (but above 3.8), have published no papers (but have been researching since late July), and all around am not a highly motivated individual. I'm...

Bell's theorem is generally thought to show that the world cannot be both local and real. http://en.wikipedia.org/wiki/Bell%27s_theorem In simplistic terms, Bell derives an inequality which allegedly must be satisfied if the world is both local and real. In practice, it is found in...

Homework Statement when a cable with non-zero mass is connected to a pole at both ends, the shape it assumes is called a catenary. it can be shown that for an electrical wire whose linear mass density is .9 kg/m strung between poles 30m apart(and making a 22 degree angle at each end) the...

Check this out: Violation of a temporal Bell inequality for single spins in solid by over 50 standard deviations, G. Waldherr, P. Neumann, S. F. Huelga, F. Jelezko, and J. Wrachtrup (2011) "Quantum non-locality has been experimentally investigated by testing different forms of Bell's...

The "no miracles" argument against scientific realism Let's assume that our best scientific theories tell us something true about the way the world *really* is, in an ontological sense. And further, for simplicity, let's assume a deterministic interpretation of those theories. In this view...

This is kind of an offshoot from: https://www.physicsforums.com/showthread.php?t=369328 Assume for a second that the controversial experiments are valid and Bell's theorem is true of the universe. I have often seen the philosophical analysis that if Bell's Theorem is true then either local...