Questions tagged [causality]

The influence one event, process, or state, has on another event, process, or state, whereby the latter is at least partly dependent on the former.

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In a black hole, why the speed of a photon matter to it to escape the black hole?

I read that a black hole doesn't attract light but bend it. By that, I understood that the photon is going forward but the space-time is so bent on itself that the photon goes forward infinitely into ...
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How is the singularity of Schwarzschild space-like if a one can take a time like path to it?

It is known that when one crosses the event horizon of a Schwarzschild black hole, one cannot return and is destined to hit the $r=0$ horizon. My understanding is that this can be seen from the ...
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Normal to the hypersurface

I have a given metric and I want to choose a spacelike hypersurface and find the normal to that hypersurface. I know that if the hypersurface is spacelike, then the normal is timelike. The given ...
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Can a causal relationship ever be established with absolute certainty (in principle)? [closed]

Is it possible in principle to ever establish or prove a causal relationship exists between two variables or events?
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Could the speed of causality be (significantly) faster than $c$?

The other day my son (13) asked me whether it was possible that light went very slightly slower than our best measured $c$, and at the same time had a very tiny mass, but we aren't able to measure ...
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Is anything in the universe instantaneous? [closed]

By my logic, there should be some time lag between the action and the reaction, however small the lag.So can we say that an effect to a reaction happens instantaneously in our universe?
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Invariant of time-order in lightlike interval

I'm trying to prove that the time order is invariant in a lightlike interval, I have this $$P_1=(X_1^0, X_1^1,0,0)$$ $$P_2=(X_2^0, X_2^1,0,0)$$ Two lightlike events in a inertial frame where $t_2>...
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What are Time Capsules in Julian Barbour's theory of a Timeless Universe?

Barbour (The End of Time, The Janus Point) describes Time Capsules as Nows (instants of the universe) with awareness of other instants. That we experience time because we 'live in a Time Capsule'. I ...
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Self-coupling of gravity and gravitation escaping a black hole - contradiction?

The field equations are non-linear, that can be interpreted as gravity is coupling with itself, see for example here: Non-linearity and self-coupling of gravity I'm trying to understand what that ...
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Reconciling special relativity and quantum mechanics

I have been referring to QFT for the gifted amateur, p. 75. To evaluate whether a particle can exist beyond its forward light cone, we check if it has a non-zero amplitude. The amplitude being ...
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Is the set of reachable arrangements of an indeterministic universe (of a given material substrate) sensitive to its initial arrangement?

Suppose two equally massive universes have an identical material substrate of the same fundamental particles. Suppose then that these two universes initially have different arrangements of these same ...
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Is the set of reachable states of an indeterministic universe sensitive to its initial conditions?

Suppose two universes with the same amount of mass-energy and evolving according to the same natural laws, but having different initial conditions. Is the set of states that are reachable by the ...
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Why does an Alcubierre drive, travelling FTL, violate causality, if the universe expanding FTL doesn't?

An Alcubierre drive seems to be plausible as a means to travel faster than light, because it doesn't move the object itself, but the space around it. it's said that matter and information can't move ...
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Could I, within my lifetime, reach any star I wanted if I went fast enough?

Disclamer: I'm not talking about FTL travel here. I'm also not talking about any weird space warping mechanics like wormholes and such. I've always thought that if a star was 4 light years away, then ...
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What is a causal structure?

The notion of "causal structure" brings up many different notions in general relativity. It is associated with the fiber bundle $\pi : \mathcal{C} \to M$ set of every light cone at every ...
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Can quantum field excitations propagate faster than light?

(Let's assume we are in the Klein-Gordon free field theory) If we had e.g. a localised field configuration (i.e. field state which is a field configuration eigenstate) at $t=0$. (By localised field ...
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Lamb shift at the level of four-potential seems to violate causality

In QED, it is well known that in a suitable renormalization scheme, and in a static case, the potential energy taking into account the Lamb shift of the electron around the nucleus of charge $Ze$ in a ...
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Signature of the Minkowski metric tensor

In special relativity, events happen in the Minkowski spacetime, with signature $(3,1)$ or $(1,3)$. I was wondering about the need of different sign for temporal and spatial coordinates. Looking ...
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Can we cut/sew path integrals along surfaces which aren't everywhere spacelike?

Usually when we work with the path integral, we specify boundary data on spacelike hypersurfaces. But, at least formally, we can also write down path integrals where the boundary has timelike parts. ...
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Neutrinos and black holes

As a new user I could not comment on Do neutrinos of any flavor get trapped in black holes? My question is that the Ice Cube facility has mapped Neutrinos coming from black holes, as stated in ...
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Impossibility of closed timelike curves

Hawking's Chronology Protection Conjecture says that the laws of nature must always conspire to prevent a CTC from forming. Why can't we conclude that this is proven? An inconsistent CTC is s ...
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Does "Superluminal travel of non-information" means we already "achieved" superluminal speeds?

From what I understood of Vsauce video talking about "Superluminal travel of non-information," the absence of information seems to travel faster than the speed of light, since we perceive ...
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Penrose diagrams for non-spherically symmetric spacetimes

As far as I have seen, Penrose diagrams are composed for spacetimes where there is spherical symmetry. The angular degrees of freedom are suppressed so as to understand the causal properties of ...
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Feynman propagator for spacelike points

When I calculate the feynman propagator for spacelike points for free scalar quantum field it is not zero. How do I interpret this result. Since it seems to me that it violates causality.
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If a star passes near another star will that star feel gravitational influence immediately or with a delay? [duplicate]

If a star passes near another star will that star feel gravitational influence immediately or with a delay? Assuming that the distance is a large number and the stars are very massive?
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Quantum Field Theory on non-globally hyperbolic spacetimes?

In all the references I have found on QFT in curved spacetime, they treat only globally hyperbolic Lorentzian spacetimes, not Lorentzian spacetimes in general. Are there any references which discuss ...
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Why doesn't this thought experiment with a localized source and an absorbing detector violate causality in quantum field theory?

Essentially all standard relativistic quantum field theory textbooks give the same argument for why the theory obeys causality. First, one computes the quantity $\langle 0 | \phi(\mathbf{x}) \phi(\...
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Any problem creating a global time function given known spacetime topology?

Gödel says the absence of a global time function seems to imply an absurdity. For it enables one e.g., to travel into the near past of those places where he has himself lived. But is it not true ...
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Why doesn't QM violate causality? Has the definition of causality been stretched too far? [duplicate]

For example, if someone does the double slit experiment, their device will pick up a localized measurement. If they were to ask why the particle was measured at that specific location, there would be ...
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If gravity can catch up a light photon (speed=$c$) and change its wavelength is it faster than light?

Why can gravity catch up a light photon (speed=$c$) and change its wavelength? How can that be logic although nature shows somehow it is... Maybe gravity has different speed than gravitational waves ...
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What is the form of the conformal covariance equation in a 2D Lorentzian CFT?

The naive expectation is that a $2D$ Lorentzian correlator should obey a covariance equation of the form $$A_n(z_{i})=\Bigg(\prod_i (c z_i+d)^{h_i}(\bar{c}\bar{z}_i+\bar{d})^{\bar{h}_i}\Bigg)A_n\Big(\...
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How does a scalar potential $V$ that follows $\rho$ momentarily lead to infinite propagation velocity?

$$\nabla^2V(\mathbf r,t)=-\frac{\rho(\mathbf r,t)}{\epsilon_0}\implies V(\mathbf r,t)=\frac1{4\pi\epsilon_0}\int\frac{\rho(\mathbf r',t)}R\mathrm d\tau'$$ I am trying to understand how this equation $...
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Are there any yet unresolved SR paradoxes?

I'm asking apart of the famous twins-paradox of special relativity theory and the ladder-paradox which have been resolved in the literature if there are still some paradoxes or variations of old ones ...
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15 votes
4 answers
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Contradictions caused by moving faster than light

There was a Joe Rogan episode with Brian Greene where Joe thinks aliens are watching us because the universe is infinite and there are an infinite number of them. So some of them must be watching. ...
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What is the fundamental observable in casual set theory?

In ordinary quantum theory or string theory, the fundamental observables are correlation functions or scattering amplitude that can be measured by particle physics experiments . In loop quantum ...
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2 votes
1 answer
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Causality for Many-Worlds interpretation

My (superficial) understanding of the Many-Worlds interpretation of QM is that it accounts somewhat for the fundamentally probabilistic nature of QM... but to my mind it doesn't seem to capture non-...
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Can I conclude that acceleration happens a bit later after force is felt?

We define forces like electric force, magnetic force and gravitational force etc, to be caused by field lines such as electric field, magnetic field and gravitation field respectively. Since these ...
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Physical properties of an event horizon

This question may seem a little naïve, but I need help with the basics of black hole physics. I'm having difficulty understanding the topology of the event horizon. Apologies for any errors in ...
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Entaglement and causality violation. Devices that detect pure states

I have not seen a similar question to mine on the site. Please forgive me if there is any. When I studied quantum mechanics and the entanglement phenomenon, I was told that, although when one wave ...
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Faster than light travel that does not break causality

I understand that any faster than light travel can be seen as time travel, or breaking causality, in some other reference frame. My question is, will this always be the case for every instance of ...
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8 votes
3 answers
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Is there any *global* timelike Killing vector in Schwarzschild geometry?

I have been dealing with the following issue related to the Schwarzschild geometry recently. When expressed as: $$ ds^{2}=-\left(1-\frac{2GM}{r}\right)dt^{2}+\frac{1}{1-\frac{2GM}{r}}dr^{2}+d\Omega_{2}...
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Doesn't Veritasium's Recent Video About Circuits Violate The Speed Of Light?

A recent Veritasium video discusses the following circuit: ...
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When the Earth suddenly stops pulling [closed]

Let's say the Earth stops attracting objects to itself all of a sudden. So, I was wondering what would happen to a person standing on the surface of the Earth? (Neglect the effect of the rotation of ...
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Information travel in the universe

I was wondering how information travels in the universe? I know that information cannot travel faster than the velocity of light, but how exactly does this transfer happen? Like is there any physical ...
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3 votes
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Does dark energy violate causality?

Assume a perfect fluid with $p = w \rho$, approximately flat space-time and the existence of a hidrostatic equilibrium solution $\rho_0$ for $\rho$. With the definition of the speed of sound $c_s^2 = \...
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Is the collapse of the wavefunction a contradiction of special relativity?

During the collapse of the wavefunction, the electron density spread over million of miles gets concentrated in very small region in literally no time. This means that electron density travels at ...
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What is the cause and what is the effect in the Bernoulli effect?

There is widespread confusion (among learners) about the Bernoulli effect, and I think a large part of this confusion is owing to muddling up cause and effect. So I am providing this question and ...
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2 votes
1 answer
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Why do some diagrams of the particle horizon, observable universe etc show the past light cone as hitting ~20glyr out from us at time zero?

This question is mainly in reference to this question: Is the observable universe equivalent to 'our' light cone?, and the answer, which is great. But what I can't wrap my head around is why ...
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2 votes
2 answers
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Proof for impossibility of FTL Signals

Is there is formal proof for the fact that signals must always travel at a speed less than the speed of light in a vacuum? I understand that special relativity dictates that for massive particles to ...
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2 votes
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Global conservation + Lorentz invariance = local conservation?

On the page 83 of "Quantum Field Theory Lectures of Sidney Coleman", Coleman showed an interesting example: It seems that global conservation law and local conservation law can be related. ...
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