Causality Definition and 188 Threads

Consider a partial differential equation describing the evolution of some function of a system which varies with time and space. A set of initial conditions and boundary are absolutely necessary for solving the equation. However, there are some numerical iterative methods for solving...

not to be impolite, but i truly view randomness in reality as something you can trick your kids into accepting along with santa, the tooth fairy etc. when compared to causality the idea of true randomness existing in reality seems incredibly weak to me. is there any logical way to...

not to be impolite, but i truly view randomness in reality as something you can trick your kids into accepting along with santa, the tooth fairy etc. when compared to causality the idea of true randomness existing in reality seems incredibly weak to me. is there any simple logic which can...

Hi, I am confused about my solutions to the following governing equation: u_{tt}-c^2u_{xx}=F_{xx} For F=A(x)sech^2\left(\frac{x-c_gt}{B}\right) Where c,c_g,B \in \mathbb{R} and A(x) is a linear function. Also, we have c_g<c. Substituting physical values for the parameters, I...

It is well-known that associated with the Kerr solution which represents a rotating black hole, there can be a region of space-time where there are loops in space time (non simply connected paths which are navigable in principle). If this is so, it breaks causality and permits time travel in...

I am having trouble understanding how special relativity reconciles the concept of causality. In one frame of reference event A may be followed by event B, but in another frame of reference event B may occur before event A. In the first frame of reference an observer may claim that event A...

In Peskin and Schroeder, we calculate that the propagator D(x-y)=\langle 0|\phi(x)\phi(y)|0\rangle to be non zero even if x and y are space-like separated (although it's exponentially decaying). This suggests (given our interpretation of this quantity) that a particle CAN propagate between these...

In SR. Anything FTL or superluminal can affect causality because there would be some frame where things move backward in time. Since SR is equivalent to Lorentz Ether Theory. And LET is about additional dynamics that occurs in the backdrop of Newtonian absolute space and time. Then how can you...

What is causality? Can anyone give an explanation of causality?? Or maybe an article where causality is explained?.

I was thinking about rapid changes in magnetic fields and the mechanics of cause and effect: Suppose you have a: Primary coil with switch and a battery and a separate Secondary coil perhaps hooked up to a oscilloscope. In the first femtosecond in which you flick the switch and dc...

Hi All, So I'm at the point where my brain is numb. I've been struggling for the past few hours trying to understand causality. Specifically, I have an input-output relationship y(t) = x(|t|). Determining if this is causal has been very difficult. Causal means that the output at any given...

Is it possible to communicate through an Einstein-Rosen bridge without violating causality? I suspect that it is possible as long as time dilation occurs during the process of moving one end of the bridge at relativistic speeds as in the following scenario: Imagine an Einstein-Rosen bridge that...

I've been reading an <URL=http://www.nybooks.com/articles/archives/2011/oct/27/symmetry-key-natures-secrets/> article </URL> by Steven Weinberg on symmetry, written for laymen, in the New York Review of Books. Weinberg describes as simply as he can how symmetry lies at the heart of the Standard...

A question I have puzzled over for a year now is how we define time. We chose light as the fastest thing we know (currently) as our mathematical limit, as only massless particles can only reach c our calulations of Gr and Sr are based on this. Unitl I started hearing terms of backwards in time...

Hi If two events are separated by a time-like interval, then all inertial reference frames will agree on the order of the two events. For example, if event A occurred before event B in one inertial reference frame, then event A occurred before event B in all inertial reference frames. The...

Exceeding the speed of light would necessarily violate causality to some reference frames. I think the derivation is related to group velocity. How does it show that if c is exceeded, cause and results could be reversed to some reference frames? And why it is so significant?

IF tachyons existed,would they violate causality?

Can someone please elaborate these lines: "Causality applies only to a system which is left undisturbed. If a system is small, we cannot observe it without producing a serious disturbance and hence we cannot expect to find any causal connexion between the results of our observations. "...

Please teach me this: What does causality principle mean when space time dissapear(e.g being inner black hole or before Big Bang).Does it meaningless to say about causality when having not the time. Thank you very much in advance.

Does FTL transmission of information (via 1 entanglement or 2 any means) violate causality? FTL = faster than light1. I argue that FTL (of information) does NOT violate causality or relativity. 2. Also FTL (of massless information) is possible via quantum entanglement. All you need is a DCQE...

Can something travel backwards in time i.e back to the future sort of thing and not violate causality? Or is the very presence of something traveling to the past a violation of causality?

Entangled particles seem to have 'causal impact' on each other 'instantly' violating the allowed speed-limit of causal influence i.e. 'c'. When one of the entangled particles is measured it has an impact on the other instantly. These two events (i.e. 1. the measurement of the first particle and...

Homework Statement Determine if y(n)=a^(|n|) is causal Homework Equations A system is causal if the output taken at anytime depends only on present and past inputs. The Attempt at a Solution I think the system is causal because the exponent, |n|, would represent a present value...

Homework Statement For each of the following systems, determine whether or not the system is linear, time-invariant, and causal. a) y[n] = x[n]cos(0.2*PI*n) b) y[n] = x[n] - x[n-1] c) y[n] = |x[n]| d) y[n] = Ax[n] + B, where A & B are constants. Homework Equations The Attempt...

Hi, I'm new, both here and to the quantum world. I understand that an entangled pair cannot violate causality, because by analyzing half of that pair, one cannot determine whether the particles are in a superposition of states or not. Since there is no way to determine if a given entangled...

Hi, I'm new so I hope I post at the right place ( I think I posted wrongly once already). (http://discovermagazine.com/2010/apr/01-back-from-the-future/article_view?b_start:int=1&-C=) I was just reading about this article on Discover Magazine which suggests that experiments show that events...

Homework Statement Show that Fourier transform does not violate causality. In other words, let \hat{E}(\omega) be Fourier transform of function {E}(t). Show that E(t_1), as evaluated from inverse Fourier transform formula using \hat{E}(\omega), does not depend on E(t_2) for t_2>t_1...

Hi all, The following is probably a very stupid question, but could anybody please tell me what they think? It has been bugging me for quite a while. I'm a bit confused about the probabilistic interpretation of Quantum Mechanics. I can't see how it necessarily follows from the experiments...

causality in GR (was "Is event sequencing relative?") The recent thread on causality, titled "Is event sequencing relative?," has gone in two directions, one discussing frame-dependence of time-ordering in SR, and the other discussing causality in GR. The SR posts were much more voluminous than...

I apologize if this has been asked before. I searched numerous times and couldn't find any discussion on this specific topic. Every description I've read of the impossibility of FTL signaling uses some variation of this diagram: http://www.theculture.org/rich/sharpblue/archives/000089.html...

This is an attempt at a “heuristic point of view” for quantum physics that treats it as an evolutionary process. I hope it’s clear that I’m not proposing any new theory, but only trying to bring out some implications that are as well-established as anything can be, in this murky field. Please...

So much hay is made out of the fact that quantum theory—and its associated experiments—violates the principle of local causality, as canonically developed by the classical (Newtonian) and relativistic (Einsteinian) models. But no one ever really asks about what these models are 'truly' saying...

I understand that certain vectors in space-time (spacelike vectors) present a non-causal situation where E2 which takes place at a time after E1 in the rest frame cannot physically be a consequence in a different frame at sufficient speed. but there is also the relationship that arises from the...

I've been doing a lot of reading on Psi-phenomena experiments as of late, and it appears as though an overwhelming number of experiments are producing statistically compelling positive results (although, these are small results that are produced over long period of time). I find this amazing as...

According to Heisenberg uncertainty principle, certain events such as double slit and decay of an atom has no causal history, hence a violation of causality, uncaused events. But relativity states faster than light travel violates causality. Since quantum mechanics does not respect...

I don't know if this belongs in Philosophy or Skepticism/Debunking... I seen the section of the paper with the daily horoscopes and got to wondering: How would physics change if one of these Miss Cleo or Edgar Cayce type people were real (capable of consistently and accurately stating what...

I do not know the details, but I have read that some theories allow backwards time travel using wormholes. Backwards time travel seems so impossible because of things like Grandfather's paradox and such. I had an idea and was wondering if anyone who knew more than me about the subject could...

It seems to me a lot of what quantum mechanics is essentially saying is that "causality of any given event is equal and opposite to the causing event" - leading to entanglement. This is in some way analogous to the Newton's laws of "action and reaction are equal and opposite". What I...

From my amateur readings in relativity, one of the arguments against tachyons is that causality would be violated locally. But how? Let's say we have observer A and B with synchronized clocks that are separated by a reasonable distance d known to them. A sends B a photon at A's clock t0...

Hi All, I am currently reading stuff about the propagator and causality in QFT at the moment and I don't really understand it. Could anyone explain this to me? I understand that a propagator is a function which describes how particles and anti-particles travel from one place to another, but...

Hi All I just don't get what "causality" means in relativity. Regular meaning: Cause before effect, sure, but what does it mean in relativity? Why should all observers have to agree about the order of events? Or have I missed something in the definition of relativity? Why does it matter?

Hi, I need help in determining if a system is causal or not. So what I knew is that for a system to be causal is that it has to depend on past and present inputs. However, I don't completely understand the meaning of that definition. So for example if I have a system y(n) = x(n3) how do we...

The Feynman propagator in QFT is not zero for space-like separation, but we say this does not mean that causality is violated, we should check the commutator of field operators instead, and the commutators vanish for space-like separation. My question is: why do we use commutators to check...

Everything I've read has said that causality in the universe isn't violated because entangled particles don't transmit information (because measured values are random compliments). All of this spoke about measurement. If entangled atoms are created (such as those 2006 on), can properties...

An important part of SR is explaining which events may cause other events (e.g., a signal cannot get from A to B when they are space-like separated). Moreover, I vaguely remember that at least some minor arguments in relativity actually rely on the assumption that causality must not be...

Hello all. I am merely an inquirer into physics; not even an amateur. The question that has puzzled me with regard to quantum theory/physics/mechanics, is the status of causality. What is the status of causality in quantum theory? I would be grateful if anyone could explain this to...

Hello, I read somewhere that the second derivatives of coordinates in Lagrangian would violate causality. Why is this so? Does that mean that the whole concept of jerky mechanics violates causality? Thanks

I came up with a sort of thought experiment to help me ask this question. It goes as such: Jack, Jill, and Joe sit near two buttons (Button A, and Button B). Joe sits directly in the middle of the two buttons, and is to push the buttons at the appropriate time. Jack and Jill sit on the left...

I have been walking around with the notion that "quantum entanglement implies a sort causal relationship due to the states having a shared history". I am now not so sure that this is correct. When I talk about entanglement, I use the argument that the preparation of the entangled state...

There's a common heart defect called a PFO, Patent Foreman Ovale. http://www.google.com/search?hl=en&q=pfo+stroke+risk&btnG=Google+Search&aq=f&oq=pfo+stroke+risk It's thought to cause stroke and migraines in some people. 25% of the general population has a PFO, and 40% of people who have a...