What is Causality: Definition and 186 Discussions

Causality (also referred to as causation, or cause and effect) is influence by which one event, process, state or object (a cause) contributes to the production of another event, process, state or object (an effect) where the cause is partly responsible for the effect, and the effect is partly dependent on the cause. In general, a process has many causes,
which are also said to be causal factors for it, and all lie in its past. An effect can in turn be a cause of, or causal factor for, many other effects, which all lie in its future. Some writers have held that causality is metaphysically prior to notions of time and space.Causality is an abstraction that indicates how the world progresses, so basic a concept that it is more apt as an explanation of other concepts of progression than as something to be explained by others more basic. The concept is like those of agency and efficacy. For this reason, a leap of intuition may be needed to grasp it. Accordingly, causality is implicit in the logic and structure of ordinary language.In English studies of Aristotelian philosophy, the word "cause" is used as a specialized technical term, the translation of Aristotle's term αἰτία, by which Aristotle meant "explanation" or "answer to a 'why' question". Aristotle categorized the four types of answers as material, formal, efficient, and final "causes". In this case, the "cause" is the explanans for the explanandum, and failure to recognize that different kinds of "cause" are being considered can lead to futile debate. Of Aristotle's four explanatory modes, the one nearest to the concerns of the present article is the "efficient" one.
David Hume, as part of his opposition to rationalism, argued that pure reason alone cannot prove the reality of efficient causality; instead, he appealed to custom and mental habit, observing that all human knowledge derives solely from experience.
The topic of causality remains a staple in contemporary philosophy.

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  1. phinds

    I Correlation vs causality implied by a graph

    The graph below shows a very clear, but not perfect, correlation between the red line and the blue line. That fact says nothing whatsoever about causality. BUT ... if you add in the additional fact that there is absolutely zero chance that the blue events cause the red events and a quite...
  2. S

    I One difference between GR and quantum mechanics

    I wanted to ask about a potential difference between general relativity and quantum mechanics phenomena - that we are observing them at different moments in time. Because causality has a speed limit (##c##), every point in space where you observe it from will be the closest to the present...
  3. P

    I A new interpretation of Quantum Mechanics

    These papers claim to present a realistic stochastic interpretation of quantum mechanics that obeys a stochastic form of local causality. (A lecture I recently attended mentioned these papers). It also claims the Born rule as a natural consequence rather than an assumption. This appears to me to...
  4. M

    Is there any way to send instantaneous signals w/o breaking causality?

    In Star Wars, they move FTL by accessing hyperspace which is a short-cut of sorts or like a wormhole that allows them to travel very fast without breaking causality as they are technically not in this dimension. FTL signals are also sent through this same dimension (called hyperwave...
  5. P

    B Cherenkov Radiation -- How does this not break causality?

    Hi, I want to try to solve this puzzle in my head. They say that faster than c travel would break causality. And yet particles can travel through a medium faster than light can in that medium. But surely if that can happen then a particle can arrive at a place faster than information about the...
  6. D

    Does causality exist in a block universe?

    I have read that if causality exists, then the cause must exist in the past light cone because causes can't go faster than light. However, as an implication of special relativity, space and time are interdependent, leading to a four-dimensional continuum. Since reality is a block universe (block...
  7. M

    I Faster-than-Light Causality-Flip: Thought Experiment Reference?

    A few years ago I was studying special relativity and came across a thought experiment that explored a faster-than-light causality-flip. It consisted of an observer on the track-side firing a bullet at a speeding train, with the bullet entering the back of a carriage and exiting the front. There...
  8. entropy1

    I Logical implication vs physical causality

    There is something I don't understand that I want to ask quantum physics experts here: Suppose the happening of event X results logically speaking in the happening of event A. So we could for instance have the following logical implication ##X.happens \rightarrow A.happens##. If this is...
  9. A

    Hilbert Transform, Causality, PI Controller

    I was told that PI controller is a causal filter, and has frequency response represented by H(w) = Ki/(iw)+ Kp. I was also told that causal filter should satisfy this relationship H(w) = G(w) -i G_hat(w) where G_hat(w) is the Hilbert transform of G(w). Does this mean that we cannot freely...
  10. S

    I Does entanglement interfere with causality?

    Suppose someone entangled 2 particles many years ago and kept particle E here on Earth and sent particle S a light year away from Earth. So the observation of particle E on Earth would fix the state of particle S a light year away. But they did it in such a way that observing particle E would...
  11. nomadreid

    I Are commuting observables necessary but not sufficient for causality?

    A couple of the sites that say that the vanishing commutator defines causality: https://www.physics.umass.edu/events/2020-02-07-causal-uncertainty-quantum-gravity https://phys.org/news/2019-11-aspects-causality-quantum-field-theory.html Is "define" too strong? Or, to put it another way: cannot...
  12. T

    Systems Non-Proper Transfer Fns: Causality?

    Prove that if a system's transfer function is not proper (order of numerator greater than order of denominator) then the system is not causal.
  13. entropy1

    I Decoherence and direction of causality

    If I use the expression ##(|A\rangle+|B\rangle)|M\rangle \rightarrow |A\rangle|M_A\rangle+|B\rangle|M_B\rangle## for decoherence, does that mean that we can infer that, IF the measured value is ##A## that THEN we will measure ##M_A##, OR that IF we measure ##M_A## THEN the measured value must...
  14. I

    I What does Causality really mean?

    In the wikipedia article of the observable universe I have read the following: "Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct...
  15. dontknow

    I Causality for internel vertex in Feynaman diagrams

    Eq 4.44 in Peskin and Schroeder. My question is: Does causality imply that time coordinates of z (internal vertex over which we doing the integration) should lie between the time coordinates of field phi(x) and phi(y)?
  16. entropy1

    I Determinism and causality in QM - a case

    I hope my thread won't be closed (too soon) and some forummers can shed their light over my question. Let's suppose a deterministic universe. I assume all events have a cause, that everything is cause and effect. Then, given that the state of the universe at some instant is X, and this leads to...
  17. entropy1

    I Does determinism exclude retrocausality?

    Suppose the system under examination is fully deterministic. Does that imply that effects follow causes and not precede them? For instance, if in this system Alice would respond to event X with A, but, if instead of X event Y would have happened, with B, does that mean she has no choice between...
  18. entropy1

    B Can there be causality when there is spacelike separation?

    If two events A and B are spacelike separated, is it then true that there can be no causal relationship between the two?
  19. Ackbach

    Prob/Stats The Causal Revolution and Why You Should Study It

    In the mid-1990's, an electrical engineer/computer scientist by the name of Judea Pearl started to change the world by greatly improving our understanding of causality. He brought together many strands of thought that had gone before him, then synthesized them into an integrated whole, with many...
  20. bhobba

    I Local Causality and Bell's Second Theorem

    Hi All I am a bit exasperated right now. On another forum a person claimed Bell's second theorem proved QM was not local. I carefully explained what local causality was, and what the theorem states: There exist quantum phenomena for which there is no theory satisfying local causality. It...
  21. Jamister

    A How Does Quantum Field Theory Preserve Causality?

    causality is a property that follows from QFT (or maybe even from the Dirac equation?) the simplest example is a scalar field with Lagranagian ##\mathcal {L}=\frac 1 2 \partial^\mu \phi \partial_\mu \phi - \frac 1 2 m^2 \phi^2## The fact causality is preserved follows by that [ϕ(x),ϕ(y)]=0...
  22. A. Neumaier

    A Born's rule for the QED electron violates causality

    Summary: Born's rule for the QED electron violates causality. [Since the thread where some of this material was presented was closed for further discussion, I summarize here the main content relevant for the above topic.] The free QED electron can be described in terms of a non-local...
  23. A

    I Born's rule, causality, and the Dirac equation

    [Moderator's note: Spin off from a previous thread due to topic change.] Actually, the form of the Hamiltonian does matter. Hegerfeldt admits that his results are not correct for the Dirac Hamiltonian unless one considers only positive energy solutions. And why should we do that? It is clear...
  24. ubergewehr273

    I Causality of magnetoresistance

    I am currently doing a research project on the topic "Anisotropic magnetoresistance" for which I have referrred various textbooks. All the textbooks state that for this phenomenon to be observed, it is necessary for the object to have more than one carrier type. This has been explained...
  25. fando1234

    I What does Fermat's principle of least time mean for causality

    I have been reading some fairly mind bending stuff about the principle or least time (and those of least action) raising questions about causality and free will. Can anyone explain this to me? Is this total 'woo woo' psuedo science, or are these philosophical questions widely accepted? Thanks...
  26. A

    A QFT Causality: Real Scalar Field & Probability

    Hello everyone! I have a question regarding the causality in QFT. If I take into consideration a real scalar field and I calculate: $$[\phi(x),\phi(y)] = 0 \space \space \space \space \space \text{if (x-y)}^2 < 0$$ Thanks to this relation we state that causality in QFT is preserved: a...
  27. R

    A Causal Nonseparability: Quantum Mechanics & Causal Principles

    Are timelike entanglement and experiments demonstrating causal non-separability by quantum superposition of causal orders an indication that causal principles may not be applicable to quantum mechanics?
  28. A

    Should the non-relativistic Navier Stokes Equations be modified?

    Choking mass flow seems to reflect the fact that fluid momentum density has a maximum value (in stationary conditions) equal to ##\rho_* c_*## where ##\rho_*## is the critical mass density and ##c_*## is the critical velocity, which is closely related to the speed of sound (see...
  29. ErikZorkin

    I Is Chronology Protection Still Relevant in Modern Physics?

    What is currently the common opinion on Chronology Protection manifested by Hawking almost 30 years ago? There does not seem to be any fully accepted no-go result for Thornian time machines. Energy conditions can be violated in QFT, semi-classical results suffer from counter-examples, Novikov's...
  30. J

    I Causality and quantum physics

    Let me present what I think is the understanding of a particular situation in quantum mechanics, and ask people to tell me whether I am right or wrong. To say that everything happens randomly in QM would be misleading at best. We get at least statistical prediction. But discussions such as the...
  31. J

    B Beginner Question: Causality & Relativity in Quantum Mechanics

    Hi everyone! Sorry for the bad English and the silly question! My mind isn't very Sharp, so I just want to make sure I understood it right... I've read the faq and I found this info amazing! If I understood correctly hahahaha! So, there's two main interpretations of the findings of...
  32. J

    I Can something be caused and be ontologically random?

    Or does ontological probability exist? I was reading an article that came up in my google searches ( https://breakingthefreewillillusion.com/ontic-probability-doesnt-exist/ ) ignore the free will philosophy stuff. But the author makes the claim that ontological probability simply does not...
  33. Derek P

    I What were Newton's thoughts on non-locality?

    [Moderator's note: spun off from another thread.] And yet modern physicists accept non-locality which is far worse :) Do you know where Newton expressed his misgivings? It would be interesting to know exactly what he thought.
  34. X

    A Comoving distance, causality volume and entropy

    Hello everyone ! I try to find the expression of the time derivative of the entropy for the CMB (photon gas) but I am stuck with the calculations. We are in the matter-domination area and at the present time (Ro=1). No radiation and no vacuum, only the curvature. The different equations are...
  35. mohamed amine

    B Understanding Causality in Quantum Mechanics

    can we find causality in quantum mechanic like the classical physics ?
  36. S

    A Causal Structure of Metric Prop.: Matrix Size Differs

    Proposition: Consider an ##n + 1##-dimensional metric with the following product structure: $$ g=\underbrace{g_{rr}(t,r)\mathrm{d}r^2+2g_{rt}(t,r)\mathrm{d}t\mathrm{d}r+g_{tt}(t,r)\mathrm{d}t^2}_{:=^2g}+\underbrace{h_{AB}(t,r,x^A)\mathrm{d}x^A\mathrm{d}x^B}_{:=h} $$ where ##h## is a Riemannian...
  37. TheQuestionGuy14

    B Time Travel & Causality in General Relativity

    According to General Relativity, everything must be causal, something from the future cannot effect the past, and spacetime geometry is this way. By this logic, does this mean that if we were to ever time travel, via any means, arriving in the past is a violation of causality, as you are...
  38. JTC

    A Causality in differential equations

    Hello, I am studying control theory. And I have encountered something I have never considered or thought about. Consider a system with y as the output differential equation and u as the input. any(n) + ... + a1y(1) + a0y = bmu(m) + ... + b1u(1) + b0u Here, the subscripts indicate...
  39. K

    B Preserving causality in the EPR experiment

    I have previously posted Preserving local realism in the EPR experiment . I have since given up on simulating local realism since I now understand it is impossible. However I have not given up on causality. Attached is code that simulates the EPR experiment and gives the same result as what...
  40. K

    I Why Is a Violation of Causality a Problem?

    I've never understood the problem with a violation of causality. Obviously we are talking about in the context of FTL travel, probably one of the most asked about topics there is. Everyone wants it to be a thing. While I see the benefits of it, I don't care about if it could be possible or not...
  41. J

    B Kim et al, 1999 experiment and causality

    Hi everyone! Sorry for my bad English! I read old posts in this forum, googled it and still can't figure out one thing: What other explanation could there be, other than a random event in the future determined if the photon behaved as a particle or wave in the first detector? Thanks a lot! I...
  42. P

    I Some questions about time and causality in the MWI

    Forgive my novice question; but, how does one explain the fact that decoherence doesn't contradict the evolution of the wavefunction in every world? Meaning, how is causality preserved in each world and what concept of time is professed wrt. to each world in the MWI? In other words, it seems...
  43. J

    B Causality and the Lorentz transformation

    Hi everyone! Sorry for my bad English! Please, suppose you have a subject A that opens his arms like a "T", in each hand he holds a laser and shoots the light at the same time. There are 2 targets at the same distance and, to A, the light hits both targets simultaneously. I Know that in some...
  44. A

    B Is Time Travel Possible? Exploring the Speed of Light and the Nature of Time

    I just wanted to share this idea with other people who may be interested: I watched a PBS Space Time episode about the speed of light more accurately described as the speed of causality. And I Submit! That "time" is simply a interaction between atoms. And though an interaction can be...
  45. binbagsss

    Quantum Theory, propagator and causality, commutator

    Homework Statement Question: To find/ explain why there exists a continuous lorentz transformation that flips the sign for space-like separation but not time-like. Homework Equations Signature ## (-,+,+...) ## Definition of lorentz transformation: ##x^u=\lambda^u_v x^v ##...
  46. F

    I Does a field operator always commute with itself?

    In quantum field theory (QFT), the requirement that physics is always causal is implemented by the microcausality condition on commutators of observables ##\mathcal{O}(x)## and ##\mathcal{O}'(y)##, $$\left[\mathcal{O}(x),\mathcal{O}'(y)\right]=0$$ for spacelike separations. Intuitively, I've...
  47. M

    B Speed of light or speed of causality?

    [Moderator's note: this was originally the second part of a post in another thread; it has been moved to this separate thread.] PLEASE BE ADVISED: I'm a complete ignorant with regards to the details of what I'm about to say and I've never looked at the mathematics of the subject, let alone...
  48. MattRob

    I EFE: Stress-Energy & Spacetime Curvature

    So, rather than causality and time travel paradoxes and the like that are usually discussed about relativity, I'm curious about something else. On one side of the Einstein Field Equations is the Stress-Energy Tensor, along with some constant coefficients (G, c^-4, etc), which essentially...
  49. S

    I Causality preserved in Klein-Gordon equation

    Hello! I am reading Peskin's book on QFT and in chapter one he shows that ##[\phi(x), \phi(y)] = D(x-y) - D(y-x)##, with ##D(x-y)## being the propagator from ##x## to ##y##. He says that if ##(x-y)^2<0## we can do a Lorentz transformation such that ##(x-y) \to -(x-y)## and hence the commutator...
  50. S

    B Trying to understand how FTL would violate causality....

    So I'm not a professional scientist, but rather an avid physics fan. This is one question that no matter how much I research I can't find a clear answer... So for the sake of argument, let's assume that you could actually build something like the Alcubierre Drive and go FTL (I know a lot of...