Questions tagged [causality]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
-1
votes
2answers
90 views

Can you fall into a black hole, and then back out again?

There is a innumerable number of questions on this site about black hole event horizons, the possibility of falling in and back out again, but none of them answer my question specifically. I have read ...
0
votes
1answer
46 views

What is a naked singularity?

What is a naked singularity? Would a naked singularity be one that that the event horizon is so small that it is the same size as the singularity? what could make one that small?
-1
votes
2answers
159 views

Can gravity act through time? [closed]

I know, that gravity acts through time and space, as it propagates at the speed of light, through space. I mean to discuss whether gravity has an effect in spacetime, along the time axis. I'm not ...
1
vote
1answer
87 views

What's wrong with this “proof” that QFT violates causality?

In An Introduction to Quantum Field Theory, by Peskin and Schroeder, when discussing the quantized real Klein-Gordon field ($\phi=\phi^\dagger$), they show the commutator $[\phi(x),\phi(y)]$ vanishes ...
0
votes
1answer
35 views

(Anti)commutators at different times

Why does the commutator of two operators evaluated at different times vanish? Take for instance a fermonic field $\psi_\sigma (\vec{x},t)$, which satisfies the well known anti-commutation relations ...
1
vote
0answers
33 views

What conclusions can we draw from Thomas Breuer self-reference theorem?

This question is based on the another question of mine. Can we conclude one of the following statements from the results of Breuer? (1) The universe constantly receives information (influence) from ...
0
votes
0answers
33 views

Does the notion of blurriness of lightcone appear in any theory of quantum gravity?

In the above diagram, black lines are $x=\pm t$ and the highlighted space is what I meant by the blurriness of the lightcone. Personally I have 2 arguments and both seems to suggest there shouldn't be ...
0
votes
1answer
56 views

If an object is pulled at one end, how fast would an impulse travel to the other end in a realistic scenario?

In SR, there are a couple of paradoxes such as the bug-rivet paradox that require us to take into account a finite speed of impulse. Suppose I have a rod at rest, and I yank one end to some speed. I ...
0
votes
1answer
32 views

Alternative to the “eraser” in the Quantum Eraser experiment?

I haven't seen any literature on the difference between erasing the photon's which-slit information vs just hiding it forever. Erasing quantum-information is effectively just a perpetual quarantine ...
2
votes
1answer
63 views

Are following statements valid for quantum gravity?

In the concluding section of this post user Chiral Anomaly states following: On the other hand, since any stable marriage of quantum theory and gravity (in the sense of general relativity, not just ...
1
vote
2answers
121 views

Force creates the motion or Motion creates the force?

Motion Creates Force ?: When you move your hand (to push a box for example), it creates a force. When electron moves through a wire it creates electrical force. Or Force Creates Motion ?: Gravity ...
3
votes
0answers
36 views

How can we prove that a non-linear equation of motion for a classical scalar field satisfies causality?

Let $\phi$ be a classical scalar field in $1+D$-dimensional spacetime with coordinates $(t,\vec x)$, and consder the equation of motion $$ \newcommand{\pl}{\partial} (\pl_t^2-\nabla^2)\phi+m^2\phi+ g\...
6
votes
3answers
245 views

Why doesn't finite field propagation speed contradict Gauss's law? [duplicate]

[Edit] Not sure why this was closed. The answers there do not answer my question, and are not even correct... Imagine a charge sitting in space. It causes an electric field everywhere, with magnitude ...
0
votes
1answer
59 views

Variation of the pole-barn or train-tunnel paradox ( does it break causality )

I know that in the standard train tunnel paradox, the train shrinks in the tunnel frame and the tunnel shrinks in the train frame. Paradox is resolved by the fact that even though both doors of ...
-3
votes
4answers
143 views

Why nobody is revising Newton law of universal gravitation to show that the force don't instantly act on the object? [closed]

I think Sir Newton was aware of the serious flaw when he formulated the law of gravity. We all know time is an important component in doing science, but I don't remember that anyone tried to revise ...
4
votes
3answers
114 views

What would prevent object from experiencing an infinitely powerful jerk in an instant?

Unlike speed which is capped for anything with rest mass at speed of light in a vacuum, what would prevent an object to undergo infinite acceleration in an instant? I assume in theory if we can apply ...
0
votes
2answers
74 views

Is causality violated in QFT?

I'm studying QFT, and Peskin is his book takes a couple of paragraphs to talk about causality in QFT, using the Klein-Gordon field as an example. The book says on p. 28: To really discuss causality, ...
1
vote
1answer
19 views

Difference between chronological future and domain of dependence

Given the following standard definitions of the two concepts, I fail to see how the chronological future differs from the future domain of dependence? Chronological future: The chronological future of ...
3
votes
2answers
137 views

Quantum: Is it possible to determine the past knowing the present?

Due to quantum randomicity, it's impossible to determine the future knowing the present. But is it possible to determine the past knowing the present? As far as I understand, it is impossible because ...
-1
votes
2answers
64 views

Is the probabilistic nature of QM simply just randomness (does it exclude causality)? [closed]

I have read this question: What is the reason that Quantum Mechanics is random? where Puk says in a comment: I see. I would call both "random", with the degree of "randomness" ...
1
vote
0answers
31 views

What happens when you get rid of a singularity? [closed]

There's a pretty common physics chestnut about what would happen if the sun just up and disappeared. "How long would it take for us to notice?" The answer is of course roughly eight minutes--...
0
votes
0answers
19 views

Does quantum mechanics invalidate causality and determinism? [duplicate]

The conductors of this experiment claim that causality is broken or at least made fuzzy by quantum mechanics. Is this really the case?
-1
votes
2answers
67 views

Exceeding the speed of light by means of a shadow, will we ever be able to transmit information faster than light? [closed]

I bumped into this: Can a shadow move faster than the speed of light? while trying to see if I could find out anything about what I'd been thinking for 2 years now. Bear with me here, cause I'm only ...
6
votes
1answer
173 views

Why can't light travel past the event horizon?

Since the event horizon is defined as the boundary within which the escape velocity is greater than the speed of light, and escape velocity is the speed required for that object to reach infinity away ...
2
votes
2answers
76 views

Causality: Two definitions

The general definition of causality is that the principle of the 'effect never occuring before the cause', as in Wikipedia. The book 'Picturing Quantum Processes' (pg: 262) defines causality as states ...
2
votes
0answers
39 views

Causal past of future null-like infinity for a black hole

I can't understand following statement from Carroll book [Future] event horizon can be equivalently defined as the boundary of $J^-(\mathcal{I}^+)$, causal past of future null infinity. I made use ...
0
votes
1answer
76 views

Can quantum particles really communicate in the past?

The quantum entanglement and delayed choice quantum eraser variation to the double slit experiment has given very strange results. So if a particle is detected then the pattern is changed. Does the ...
3
votes
1answer
55 views

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 ...
4
votes
2answers
246 views

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 ...
0
votes
1answer
38 views

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 ...
2
votes
1answer
71 views

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 ...
5
votes
1answer
96 views

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 ...
1
vote
1answer
38 views

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 ...
2
votes
0answers
108 views

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 ...
0
votes
3answers
48 views

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 (...
0
votes
0answers
32 views

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 ...
1
vote
0answers
45 views

Causuality-effect relation and time order

We know that from view of special relative theory, there is no Lorentz transformations that converts or reverses the time order in causuality-effect relation. Now my question is: if there is no ...
1
vote
0answers
19 views

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 $\vec{r} = (x,y,z)$ ...
-3
votes
1answer
72 views

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?
1
vote
1answer
81 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, ...
0
votes
0answers
48 views

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 ...
3
votes
0answers
70 views

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 $y-x$? ...
2
votes
1answer
66 views

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 ...
1
vote
1answer
65 views

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 ...
0
votes
0answers
48 views

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 ...
1
vote
0answers
53 views

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 ...
2
votes
2answers
61 views

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 ...
2
votes
1answer
79 views

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 ...
1
vote
0answers
42 views

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 ...
0
votes
2answers
85 views

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 ...

1
2 3 4 5
14