What is Locality: Definition and 82 Discussions

In computer science, locality of reference, also known as the principle of locality, is the tendency of a processor to access the same set of memory locations repetitively over a short period of time. There are two basic types of reference locality – temporal and spatial locality. Temporal locality refers to the reuse of specific data and/or resources within a relatively small time duration. Spatial locality (also termed data locality) refers to the use of data elements within relatively close storage locations. Sequential locality, a special case of spatial locality, occurs when data elements are arranged and accessed linearly, such as traversing the elements in a one-dimensional array.
Locality is a type of predictable behavior that occurs in computer systems. Systems that exhibit strong locality of reference are great candidates for performance optimization through the use of techniques such as the caching, prefetching for memory and advanced branch predictors at the pipelining stage of a processor core.

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  1. vanhees71

    I The notion of locality in (Quantum) Physics should be clearly defined

    Unfortunately one of the threads about entanglement and Bell tests has again been closed prematurely. It has not been clarified what "locality" means. In the physics community, not involved in philosophical arguments about foundations of QT, it's clearly defined as the property of a...
  2. G

    I General argument that entanglement can only be created locally

    Hi. As far as I know, entanglement can initially only be created locally, for example by creating two photons at one place in a crystal, or by local forces. Sure, there's entanglement swapping, but the initial entanglement was still created locally. But I only know examples. Is there a general...
  3. M

    I Do Bell Experiments Show Local Overlap of Wave Functions Before Measurement?

    Consider experiments that demonstrate violations of Bell inequalities. I'm wondering about the spatial extent of the wave function of the particles BEFORE measurement. I assume the spatial extent is "very large," and my main question is whether they overlap. If the wave functions do overlap...
  4. A. Neumaier

    A An interesting paper about measurement and locality in QFT

    Bostelmann, H., Fewster, C. J., & Ruep, M. H. (2021). Impossible measurements require impossible apparatus. Physical Review D, 103(2), 025017.
  5. G Delta

    I Quantum Realism and Bell Locality

    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...
  6. G

    I Does EPR definitely rule out locality?

    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...
  7. Lynch101

    B QFT & QM Questions (about time, locality, gravity, etc.)

    Apologies if there are already an abundance of threads on related questions. I have tried searching for threads on here and have read quite a few, as well as reading other sources. I've kind of reached a point where I need help to parse some of the information that I have been reading and to get...
  8. Demystifier

    A Realism from Locality? Bell's Theorem & Nonlocality in QM

    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)...
  9. Dfpolis

    A Is the Counterfactual Argument for Locality and Realism Flawed?

    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...
  10. T

    I Locality and Wave Function Collapse Implications

    OK, so I'm trying to work out a few ideas regarding locality. I've studied at the undergrad level in the past (including quantum), but with professors that slaved away at proving math constructs and never bothered to indulge in clarifying the context of any concepts, so I'm pretty weak here...
  11. A

    I Math: classical to quantum locality

    Does anybody know if there is work being done on quantum locality vs nonlocality. Specifically, approaching the Planck scales there is no nonlocality. That is all points in space and time are local. This would also provide an explanation for Einstein Minkowsky's space time. Any material /...
  12. M

    I Is Nature Non-Deterministic Due to Nonlocality in Quantum Mechanics?

    From what I understand, the most reasonable explanation of the violation of the Bell inequalities is that nature is non local. If we accept this, is there a reasonable argument that nature is not deterministic? I.e. could it be that the probabilistic predictions from QM are just averaging --...
  13. R

    I Exploring the Mysteries of Entanglement and Non-Locality in Quantum Mechanics

    I’m reading in the lay literature that experiments on Bells inequality have shown that 2 entangled particles pass information simultaneously and therefore break the special relativity rule of c and therefore indicate a break from the concept of locality. I’m sure I didn’t phrase that sentence...
  14. entropy1

    B Exploring the Possibility of Retrocausality and Acausality in Quantum Mechanics

    Does the definition of locality in the QM sense include the prohibition of retrocausality?
  15. K

    I Expressing Locality in Vector Space for GR

    How do we express the locality of a vector space in general relativity? I mean, it's not clear what the boundaries of a given vector space are. To put in another way, we could, in principle, blindly consider that we have the entire of ##\mathbb{R}^4## at our disposal to describe, say, the...
  16. J

    A How are renormalizability and locality connected?

    In his paper Quantum Field Theory: renormalization and the renormalization group Zinn-Justin states: Low energy physics does not depend on all the details of the microscopic model because some RG has an IR fixed point or at least a low dimension fixed surface. Of course at this stage the next...
  17. morrobay

    B Bell Non Locality, Quantum Non Locality, Weak Locality, CDP

    When there are EPR/Bell test inequality violations and no signal faster than light, the terms: Bell Non Locality, Quantum Non Locality, Weak Locality and the Cluster Decomposition Principle: Initial state of space like systems can be factorized. Subsystems remain space like separated. Then final...
  18. Sunny Singh

    I Does realism imply locality or vice versa?

    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...
  19. G

    Mathematical formulation of local non-realism

    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...
  20. G

    I Difference between "realistic" and "predetermined"

    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...
  21. G

    I Impossible to exclude hidden variables without entanglement?

    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...
  22. LoveQM

    I How did Einstein see that Entanglement lead to Connectedness

    I am studying the history of Quantum Mechanics and was reading about particle entanglement. What I would like to know is how did Einstein see that particle Entanglement meant that particles would be affected by spooky action at a distance. I guess that spooky action at a distance may also be...
  23. hideelo

    I Entaglement, locality, and information

    As far as I understand, given that there is such a thing called entanglement, we know that there are non-local interactions. The line that this is usually followed with is "since no information traveled faster than light , locality isn't violated". I have a few interrelated questions about...
  24. F

    I Why do we require locality in quantum field theory?

    In quantum field theory (QFT) from what I've read locality is the condition that the Lagrangian density ##\mathscr{L}## is a functional of a field (or fields) and a finite number of its (their) spatial and temporal derivatives evaluated at a single spacetime point ##x^{\mu}=(t,\mathbf{x})##...
  25. thenewmans

    QM interpretation with something moving backward in time?

    It’s easy enough to find the interpretations that break counterfactual definiteness in order to maintain locality. But I’m not sure how to find the ones with something (perhaps information) moving backwards through time. The reason I ask is I’ve always had trouble with the idea that a...
  26. Markus Hanke

    Realism vs Locality in Quantum Entanglement

    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...
  27. J

    B Bell's Theorem basic question on contextuality & locality

    I'm familiar with Bell's Theorem.. have studied it over the years. I'd just like to confirm if my belief is correct. In short. It shows either particles don't exist before measurement or there are hidden variables.. you know all those non-counterfactual and locality arguments.. Specker theorem...
  28. D

    Interactions between field operators & locality in QFT

    Why is it required that interactions between fields must occur at single spacetime points in order for them to be local? For example, why must an interaction Lagrangian be of the form \mathcal{L}_{int}\sim (\phi(x))^{2} why can't one have a case where \mathcal{L}_{int}\sim\phi(x)\phi(y) where...
  29. NaOH

    Phonons & Collective Oscillations: Locality Experiments

    I am struggling with the concept of phonons and if they should be considered (experimentally) to be treated as collective oscillations of a certain region instead of the whole crystal. I know the title comes off as a little strange -- since phonons are not localised to anyone atom, but consider...
  30. D

    What is the difference between locality and causality?

    This has been causing some confusion to me as the two concepts seem very similar, if not the same (especially when taking special relativity into account). As far as I understand, even in classical physics (i.e. even before considering QFT and the like), one requires that interactions are...
  31. D

    Locality, unitarity & vacuum energy

    I've read in a set of lecture notes that the requirement of locality and unitarity in QFT imply that the vacuum must have a non-zero energy associated with it (http://arxiv.org/pdf/1502.05296v1.pdf , top of page 3 under heading "What is the problem?"). My question is, why does the locality and...
  32. D

    What is the definition of Locality (in QFT)

    I am slightly unsure as to whether I have understood the notion of locality correctly. As far as I understand it locality is the statement that if two events occur simultaneously (i.e. at the same time) then no information can be shared between them (they are causally disconnected). Thus a...
  33. D

    Simultaneous events, space-like separation & QFT

    First of all, sorry if this is in the wrong forum, wasn't quite sure which one to post it in given the question. My question is, given two space-time points ##x^{\mu}## and ##y^{\mu}##, if the events that occur at these points are simultaneous, i.e. ##x^{0}=y^{0}##, are the two events...
  34. G

    What's the problem with (non-causal) nonlocality?

    Hi, In all the discussions about EPR, Bell's inequality and interpretations of QM locality seems to be a property that nobody likes to drop light-heartedly. This is somehow understandable since SR is an extremely successful theory. But SR only says that we cannot transmit information faster...
  35. M

    Unitarity and locality on patgh integrals

    my question is this: you know than in feynman path integra, you integrate eiS/hbar along all the fields. you also know that S is real and that it is the integral of local functions (fields and derivatives of fields). you also know that path integral generates an unitary and local...
  36. K

    About locality in classical physics

    In wikipedia it says that "Coulomb's law of electric forces was initially also formulated as instantaneous action at a distance, but was later superseded by Maxwell's Equations of electromagnetism which obey locality." I don't really understand in which sense Maxwell's equations solve the...
  37. G

    Why all the clinging to locality?

    Hi, Bell demonstrated that there cannot be a local realistic theory that reproduces the expectation values of QM. I can see that a non-realistic theory is unsatisfactory, we would have to abandon the nice determinism we got so accustomed to in classical physics, from Newton to Maxwell to...
  38. DrChinese

    Three-Particle Quantum Nonlocality under Strict Locality Conditions

    Just posted to the archives is a great new paper from a top experimental team. These are some of the same individuals that performed the now standard citation regarding a Bell test under strict locality conditions. They have now extended their concept to GHZ states, and also close the...
  39. E

    Non locality of quantum mechanics

    Can we have a local hidden variable theory explanation for Bells theorem? The outcomes of the mesurement (measuring the electron spin of an entangled electron pair as Red or Green) can be random initially without any correlation at all. But by the time we compare the results of the two...
  40. Q

    Any loophole tactics to cheat locality with entanglement?

    I understand that relativity at least philosophically excludes the ability to use entanglement to instantaneously send information, but as I understand it, it seems only philosophically, and the hard problem is that you break the entanglement by measurement. (Before I go on, I'm sure that ^^...
  41. S

    General covariance vs. locality

    hi i read an article by S.carlip about quantum gravity, arXiv:gr-qc/0108040v1 , in this article carlip stated: why we need quantum gravity what's problems of quantum gravity and two ways of quantization of GR. I couldn't realize some clues in section of "the problems of quantum gravity"...
  42. andrewkirk

    Is there any hope at all for Locality?

    As I understand it, EPR proposed their entanglement thought experiment as a means of demonstrating that Quantum Mechanics was incomplete, and hence that the Copenhagen interpretation (which says that the wave function is a complete description of the state of a system) was wrong. They postulated...
  43. E

    Physical observables, locality, and a preferred basis

    Quantum mechanics says that physical observables are self-adjoint operators. Is this correspondence a bijection, ie can we realize any such operator as a physical observable? There are obvious practical concerns with physically realizing certain contrived operators. But are there any...
  44. thenewmans

    What interpretations break causality instead of locality?

    By Bell’s theorem, an interpretation of QM must break either locality or causality. Linked below is the only interpretation I know of that chooses to maintain locality. (I don't know many.) Do you know of any others? CAUSALLY SYMMETRIC BOHM MODEL...
  45. E

    Wheeler Feynman absorber theory and non locality

    As per the Wheeler Feynman absorber theory, there cannot be electromagnetic radiation without an emitter and absorber. If we had only a single electron in the universe then disturbing it (accelerating it) would not produce any radiation since there was nothing to absorb it. Hence it would...
  46. A

    How do the concepts of 'constant c' and 'locality' work in GR?

    Drawing on a number of threads in this forum, and my very limited understanding of relativity, I am intrigued by the following thoughts: If I have understood correctly, in GR, c is supposed to be only a 'local global constant', and not exactly a Universal constant. Meaning that, two distant...
  47. T

    Exploring the EPR Paradox: QM and Locality

    Sorry, I have 2 doubts about the EPR paradox. 1) Just check out if I am ok: What EPR proposed was that QM suggest that if two entagled particles, for example photons, prepaired in some special way, get away from each other then: a) if we measure their x-spin then one particle will get the...
  48. M

    Deutsch and Hayden on locality

    I couldn't find out if the following article had been discussed (it is probably well known), but there were many threads on locality/non-locality, so it might be of interest. On first reading I like it quite a lot, made some things clearer for me, but it will need some thinking and probably a...
  49. M

    Bell's Inequality: Must we ditch locality, realism or something else?

    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...
  50. haushofer

    Locality in QM and commutators

    Hi, I have a conceptual question concerning causality and locality in QM. Causality plays a role in second quantization when doing QFT, which one calls "micro-causality"; the commutators between fields disappear when the interval between them is spacelike. However, how does this fit in...
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