Questions tagged [causality]

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How does the loss of causality violate the postulates of special relativity?

Apart from the logical absurdities of losing causality between 2 causally disconnected events. I am not able to pinpoint how this violates the 2 postulates of special relativity. In other words, I ...
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Interpretation of Feynman propagator for massive scalar field in position space

I've always treated propagator in the momentum representation so when it diverges, we are on-shell. But what is the interpretation of light-cone divergences in position space? If it is something we ...
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Application of the principle of causality to classical electrodynamics

I am reading Griffiths' Introduction to Electrodynamics in which he shows that the retarded and advanced potentials, e.g. the retarded scalar potential $$ V(\mathbf{r},t) = \frac{1}{4\pi\epsilon_0} \...
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What is causality? [closed]

I was looking a few videos on youtube and I came across a video named the speed of light is nothing related to light. In the video, it was said that speed of light is actually speed of causality so ...
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Are causal sets based on set-theory?

There is a theoretical approach with the aim of formulating a quantum gravity theory which uses causal sets. Are these sets based on mathematical set theory? Are causal sets part or belong to the ...
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1answer
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Determining global hyperbolicity

Given a spacetime metric, how can one show that the spacetime is globally hyperbolic? I know that a globally hyperbolic metric has a Cauchy surface, but how can we determine the existence of a Cauchy ...
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1answer
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Changing the signature of the metric and consecuences in the causal structure of the spacetime

I was reading about the implications in the causal structure due to a change in the signature of the metric. I know that if you choose a spacetime $(M,g_{ab})$. With $g_{ab}$ a Lorentzian metric, of ...
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Gravity at light speed

my question in regards to light. Since gravity warps space time, and we have discovered gravitational waves. Would the light at the front of the wave, be traveling faster than lightspeed? Essentially ...
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4answers
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Does circular motion cause centripetal force OR does centripetal force cause circular motion?

Does circular motion cause centripetal force, or does centripetal force cause circular motion, or are they both occurring hand in hand together instantaneously? One more question: If I project a body ...
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1answer
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Constraints of Contact Forces

Are contact forces limited to the speed of light like non-contact forces like gravity? If I took an infinitely long newton's cradle and placed in a vacuum with zero energy loss, would the time between ...
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Spacelike, timelike, lightlike vectors and the light-cone structure

Consider a semi-Riemannian manifold which of these statements is false: All vectors on the light-cone are light-like, all vectors in the interior of the light-cone are time-like and all vectors in ...
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2answers
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If the limiting speed of a signal in classical physics were $c$ rather than infinity, would simultaneity be an absolute concept or a relative one? [closed]

If the limiting speed of a signal in classical physics were $c$ rather than infinity, would simultaneity be an absolute concept or a relative one?
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How fast is electrostatic force? [closed]

Suppose we have a charge $Q$ in deep space (isolated), now suppose another charge $q$ appears instantly (no matter how). Obviously it will feel electrostatic force but the question is how quickly (...
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Light-like normal vectors

Can someone please show me how to mathematically establish that the normal vector to the event horizon of a Kerr Black Hole is light-like?
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FTL communication and paradoxes with local causality

I have Yet Another Question about FTL communication, causality and sending a message into your past. I've read this article and this excellent answer and I understand why it's possible to find a ...
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Divergence of a vector which has explicit and implicit position dependence

I am doing EMT and I am trying to calculate the divergence of this current density given as, $$\vec{J}(\vec{r}', t_r) = \vec{J}(\vec{r}', t - \frac{|\vec{r}-\vec{r}'|}{c})$$ for $\vec{r} = (x,y,z)$ ...
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Causality and anti-particles

How can I quantitatively and qualitatively understand the fact that there is a relevance between the existence of anti-particles and causality?
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1answer
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What Ron Mallett doing for time machine here? [duplicate]

Here Ron Mallett pouring liquid chemical on array of lasers for progress of time machine. I didn't understand it. Source What exactly Ron Mallett doing for time machine here?
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1answer
75 views

Resolving the measurement problem with mathematical theorems? [closed]

The key debate, around the measurement problem is whether collapse should be interpreted as a physical process(Bohmian Mechanics) or as an immaterial process(e.g. Copenhagen Interpretation, ...
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Does effect of force travel faster than light? [duplicate]

Suppose force (sufficient to move a block & imagine it(the block of course) to be extremely long and rigid ) is applied at one end of the block and the Block starts moving. Now force must be ...
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How to realize explicitly an $SO^+(1,3)$ Lorentz transformation of $(x-y)$ to $(y-x)$ for space-like separation?

Consider two spacetime points $x, y$ which are space-like separated. How can one realize explicitly a proper, orthochronous Lorentz transformation between two frames such that $x-y$ becomes $y-x$? ...
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10answers
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How fast does gravity propagate?

A thought experiment: Imagine the Sun is suddenly removed. We wouldn't notice a difference for 8 minutes, because that's how long light takes to get from the Sun's surface to Earth. However, what ...
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What is the null vector for a metric?

I am studying the Robertson Walker metric. I now understand what the geodesic looks like but what is a null vector of the geodesic? Is it just the tangent vector to the geodesic curve?
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Reversibility = non-causality. Can this be right?

I read yesterday the Norton Dome's paper, which shows that some Newtonian systems can be non-causal, based on specific solutions of Newton's laws. The author justifies the solutions in very nice, ...
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1answer
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Is temporal causality broken by quantum entanglement?

When one particle of an entangled pair is measured, it forces the state of the other particle. This effect propagates faster than we can measure, certainly faster than light and possibly ...
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1answer
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What happens when you remove the mass inside a black hole?

Imagine you could delete the sun from its existence at an instance. Information cannot travel faster than the speed of light so the earth will keep orbiting the sun for about 8 minutes without knowing ...
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Simultaneity and Tachyons

I open this question because the discussion on @Demigan's question did not come to a satisfactory conclusion. One of the best discussions on tachyon relativity that I’ve seen is by David Bohm in his ...
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3answers
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Difference between action-at-a-distance and a field according to Maxwell?

My question is more on a historical note that involves Maxwell’s equations. Besides the information that I have obtained from textbooks, I am mainly getting it from History of Maxwell's Equations and ...
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Infinite Speed of Light

I recently watched a video that stated that Newtonian Mechanics assumed an infinite speed of light. That same video, "PBS Space Time: The Speed of Light is Not About Light", stated that if the speed ...
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Would Doubly Special Relativity or Mach's Principle allow faster-than-light travel to occur without violating causality?

Doubly Special Relativity posits that the Planck length is the same in all reference frames. Mach's Principle posits inertia is produced by the combined mass of the universe. From my limited ...
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2answers
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Lorentz vectors orthogonality

I am reading through the book "Electrodynamics and Classical Theory of Fields and Particles" by A.O. Barut, and I'm still currently in the first chapter of the book in which he is discussing Lorentz ...
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1answer
120 views

Reverse entropy, reverse causality and physical laws

I do not have any scientific education and I am far away from understanding relativity, quantum mechanics and such. I am just wondering about entropy, causality and if we could reverse these in a ...
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1answer
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If there is a point in a past set, does its chronological future interset a future set?

This post concerns the causality of spacetime $\mathcal M$. A future set $F$ is defined to be the chronological future of some set $S\in \mathcal M$, ie., $F=I^+[S]$. Similiarly, a past set $P=I^-[S'...
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1answer
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What is the mathematical meaning of locality?

I have read on the Principle of locality Wikipedia page that: "The special theory of relativity limits the speed at which all such influences can travel to the speed of light, c. Therefore, the ...
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Given a metric what is the condition that 2 points are causally linked?

In Minkowski space-time two points $x$ and $y$ are causally linked if they are within each other's lightcones. $|x-y|^2<0$. Given a general metric $g^{\mu\nu}(x)$ with no time-loops or exotic ...
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What is an equation which tells you if two points are time-like separated in curved spacetime?

I was thinking about how to tell if two points in a general spacetime are time-like separated. I think the only way of doing this is checking every path from $x$ to $y$ and seeing if one of the paths ...
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Does the light-cone at every point plus a scale uniquely define a spacetime metric?

In general relativity, knowing the local light-cone shape at each point (i.e. the tilt, and angles of the light cone) doesn't seem enough to get the metric. Do we also need a scale as well at each ...
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What are some scenarios where FTL information transfer would violate causality?

I've always heard people saying, "Faster than light information transfer can't happen because it would violate causality! Effects can precede their causes!" However, I'm trying to think of a ...
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4answers
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Why is the speed of causality equal to the speed of light?

I heard that the most fundament concept is Causality, and also that it is turn out that speed of light has nothing special in it so that It is ultimate speed limit but because it is happen to be ...
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Particle picture in position space in quantum field theory

When I operate $a^{\dagger}_k$ on vacuum, $|0\rangle$, I get a particle created in momentum space with a 4-momentum equal to $(\omega_k, \vec{k})$ where $\omega_k=\sqrt{m^2+\vec{k}^2}$ here I'm only ...
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Do the forces between Earth and Sun point in the directions that the Earth and the Sun were 8 minutes ago?

No information can travel faster than light, so does the force between Earth and Sun point in the direction that the Earth was 8 minutes ago or in the direction that the Earth is now?
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The dynamics of a cornering wheel

Can a rolling wheel create a side force without first rotating on a vertical axis? There is something wrong with the way we describe how a cornering vehicle wheel creates a cornering force. I think ...
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Simulation of Feynman path integral in literature

Can someone provide me a numerical simulation of Feynman path integral? Where the contribution of each path is added individually so that I can understand how much do the paths outside the light cone ...
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Causality, branch cut choice and analytic continuation of Euclidean 2-pt. correlator in 2D CFT

In 2D CFT, the Euclidean two point correlator of a primary operator $\mathcal{O}$ with conformal weights $h$, $\bar{h}$ is given by $$ \begin{align} \langle\mathcal{O}(z,\bar{z})\mathcal{O}(0,0)\...
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If the method of FTL cannot be observed, does it still break causality [duplicate]

So, say we discover a method of FTL. However, anyone or anything that makes use of this FTL is unable to be observed by the outside world. For example. In the year 3000 a ship leaves Earth headed 6 ...
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Irreversible processes in special relativity

According to special relativity (as I understand it) simultaneity is no longer a universal concept in special relativity. Consider two events A and B which are simultaneous in reference frame 1; in ...
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In QFT, why does a vanishing commutator ensure causality?

In relativistic quantum field theories (QFT), $$[\phi(x),\phi^\dagger(y)] = 0 \;\;\mathrm{if}\;\; (x-y)^2<0\,.$$ On the other hand, even for space-like separation $$\phi(x)\phi^\dagger(y)\ne0\,.$...
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Time Ordering and Causality in General Relativity

The time-ordering of two space-like separated events is undefined in special relativity. Is there an analogous concept in GR?
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What is the chain of cause(s) and effect(s) which does a butterfly's wing-flapping cause a hurricane 1000's of kilometers further away?

I once asked if the butterfly effect in the weather system is a real effect: a butterfly flaps her wings, which can cause a hurricane thousands of kilometers further. But how will this happen? To be ...

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