Causality Definition and 185 Threads

I was trying to think in general means to localy preserve causality. By "means", it means to include (or not) varying speed of light and faster than light sign propagation. By varying speed of light, it means that light speed can localy depend on the most generical parameters you can get. Don't...

Hi all, this is part of my assignment where I have to write an essay of a range of 6000-8000 words. Here goes : Consider the concept of causality. Could a killer use the principle of special relativity to argue that, in a certain reference frame, his/her victim died before the killer fired...

This is a question i asked my tutor via email... kind of in a hurry to get it answered so i can fully understand causality for an assignment due on monday.i'm having trouble understanding the causality of the attached tutorial question... if there is an input 'x(t)', for any 't<0' is this input...

Logic and causality? Hi, what implications does quantum physics have on the realm of causality? For instance, due to the wave-particle duality, is it reasonable to say that the universe can be explained through causality? How does this change the concept of 'logic'? Intuitively, we believe...

I didn't know where to ask this question, so excuse me if I posted it in the wrong place. Recently I've been listening to a video in which a physicist asked a question to the public (in a high school I believe). I've had my own idea about the answer of the question, but the physicist (Étienne...

Can anybody prove or give a bit detail about the causality condition i.e h(t) = 0, t<0 for continuous-time LTI system. And based on this how a continuous time LTI system is causal if, x(t) = 0, t<0.

This is my first post, so if I am in any way out of line for the the norm on this site please forgive and instruct me. That said, I found this site while trying to comprehend a physics issue I just cannot seem to get my head around. That would be the claim that faster than light travel woudl...

Hello I was just wondering how, if a wormhole were possible such that one could travel from point A to point B instantly, how this would violate causality. I have heard that it would, but I don't see how that would work.

Homework Statement Is the following input/output (x is input, y is output) system linear, time invariant, causal, and memoryless? Answer yes or no for each one.Homework Equations y(t)=2x(t)+3The Attempt at a Solution My instinct tells me it's linear, but for some reason I have trouble showing...

[SOLVED] Klein-Gordon Causality calculation Homework Statement In Peskin and Schroeder on page 27 it is stated that when we compute the Klien-Gordon propagator in terms of creation and annihilation operators the only term that survived the expansion is...

Supposedly nothing can travel faster than the speed of light because this would violate causality and produce paradoxes. Someone on Planet Alpha will travel to Planet Beta at ten times the speed of light, so that to someone watching from planet Gamma it will LOOK like the person was on Beta...

I figured out this one, just thought it was quite nice... We start with the only requirement that the Green's function of the propagator is causal in the sense that it propagates stricktly forward in time, so that the Green's function is zero at t<0. Using the Heaviside step function we can...

I was told in class that both the Dirac equation and the Klein-Gordon equation violate causality, even though they're relativistic invariants, and that this wasn't surprising because the 2 postulates of special relativity don't imply causality. Is this true?

I have a question, but I am not sure how to express it. I have been thinking about the idea of the universe as a four-dimensional object, with time as just another dimension. I have also been thinking about David Deutsch's idea of the universe as a sequence of quantized slices or slides...

From the wikipedia entry: "Suppose a particle (such as a photon) emitted from a source could interact with one of two detectors. According to TIQM, the source emits a usual (retarded) wave forward in time, the "offer wave", and when this wave reaches the detectors, each one replies with an...

Anyone read about this? http://cosmiclog.msnbc.msn.com/archive/2007/07/17/274531.aspx I'm not sure I agree with that part. I'd say that the effect in signal B would at best show up simultaneously as Cramer tampers with signal A. Creating that longer circuitous route for signal A could...

What happens with causality at the Planck scale? Can effects "precede" causes? I would like to know what happens with causality at the Planck scale, explained in "educated layman" terms, if that's possible... :) Might effects "precede" causes in time? Do we have to redefine causality at the...

After reading several papers and seeing gore's movie on GW I'm still searching for solid scientific causal evidence (versus correlations or circumstancial) that anthropogenic greenhouse gases are the cause of global warming in the post-industrial age. I accept we are in a warm epoch...

I was having an argument with some of my friends last night and I needed to explain why faster than light travel or infomation traveling faster than c violates causality. Unfortunately I studied this a long time ago and don't quite remember. Could anyone give me a brief explanation why? I...

I was thinking that there are all these laws of nature that describe physical systems, and our senses receive input from these systems. However, once the input has been delivered, it dissappears into the black hole of our consciousness, where it is manipulated by some unknown principle. Once...

I know that I have been asking that question before and that people are probably tired of it :redface:. I have done multiloop QFT calculations but when I get back to the fundamentals, something is really bugging me. There are several issues but let m start with a question that would...

I have these ideas about these things and I would like your opinion. You may not agree, but it is what I think. First, I would like to say that Fate/Destiny and Causality are linked. To me, fate predestines things and people, which is why people or outside infulences of a person control...

Choosing the Lorenz gauge implies that sources of the EM potentials at a given point are the charge density (for scalar potential) and current density (for vector potential) that cross a collecting sphere converging at the speed of light toward that point. It is often said that the retarded...

I'm having trouble working this problem. I don't know where to begin. Here's the problem: Let P and Q be any events, P causing Q via propagation of some signal. Let the speed of the signal, call it U, be greater than the speed of light c. In S, the time seperationg is given by delta_t and...

Causal Dynamic Triangulation starts out with the premise that causality is preserved, even elemental to the theory, but I have not yet understood what makes CDT causal, aside from the title. Where do I look for the cause and effect sequence in CDT? Thanks, nc

I have a question about quantum entanglement experiments, such as the two-photon "delayed choice" experiment performed by Aspect et al. http://prola.aps.org/abstract/PRL/v49/i25/p1804_1 . Can anyone estimate how much time elapses between the arrival of a single photon at the detector, and the...

On another message board, I have proposed a definition of causality. No one there has been able to give me significant feedback on it. I think that it is appropriate to the QM thread because the parts that are applicable to general physics are pretty much beyond dispute; it is the parts that...

As far as I understand, FTL communication (or instantaneous communication) is impossible because one cannot define what "instantaneous" means, so you run into problems. What if there were some kind of sub-/hyperspace with an absolutlely defined time and instantaneous messaging? Do the paradoxes...

the causality problem and tunneling?

Hi everyone, I'm new here and i have to say this place is awesome! I will definatly be poking around here :biggrin: something that has bugged me ever since i thought about it. Does quantum entanglment (when used to send a signal) violate causality?

do tachyons exist or not?if so causality will be failed! is there any particle that can travel faster than photon and still preserve the einstein's postulates? if they exist how can we explain the space like separated events that voilate the causality.

why does Bell's experiment damage causality or cause such problems regarding faster than light information via the instantaneous and corollary collapse of the wave function? photons do not experience time, to them the spin measurement and the emission occur simultaneously...

This is a pretty basic concept of relativity that used to make sense to me but I have since become a little unclear on the issue. The question is how can one violate the principle of causality simply by broadcasting information that travels faster-than-light?

Causality Causality, the law of cause and effect, is the most general law used to describe the (physical) reality. The common conviction was that causality holds everywhere, at all time and in all cases. Since modern physcics and quantum mecahnics, this concept of reality has been altered...

This issue was brought up in the thread, "I think therefore I am", by Manuel_Silvio; and I wanted to get some answers to the question: Is Causality necessarily true? Here is an example that Manuel used, and I think it sheds some serious light on the matter: Suppose I flip a coin, and get...