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Questions tagged [faster-than-light]

"Faster-than-light", also known as superluminal velocities, refers to any sort of travel at a speed greater than the speed of light. Prohibited in mainstream physics due to the Special theory of relativity.

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In SR, why do we claim length contraction rather than faster than $c$ travel in the rocket frame? [closed]

In special relativity, a rocket traveling at .5c will take .86 years (in the astronauts frame) to travel 1 light year (in a stationary observer frame). There are two possible ways to look at this ...
foolishmuse's user avatar
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Please help me with this paradox [closed]

Physicists believe that some galaxies are moving away from us at faster than the speed of light. A galaxy that is moving away from us at faster than the speed of light would be moving backwards in ...
Cecilia's user avatar
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Whats wrong with concept of "faster than light" information transfer device? (not about technical implementation, just about theory) [closed]

Yesterday, while lying in bed, an idea came to me, and I don’t understand why it won’t work? Setup: 1.1) Two infinite stores of entangled pairs of photons, each connected to a double-slit device. 1.2)...
Nikolay Prays's user avatar
3 votes
2 answers
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Could a delayed choice Aharonov-Bohm experiment be used for FTL information transfer?

Tim Maudlin about a delayed choice Aharonov-Bohm experiment, the section between 1:35:00 and 1:38:30 In the interview above Tim Maudlin mentions some sort of delayed choice Aharonov-Bohm experiment. ...
Cristian Dumitrescu's user avatar
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2 answers
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If the speed of causality changes, could you go FTL?

In the middle of some research, I reached a sort of confusion that I’d like to sort out. In flat space FTL is impossible, because in a Minkowski metric, $$\mathrm{d}s^2=c^2 \mathrm{d}t^2-\mathrm{d}x^2-...
controlgroup's user avatar
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Transmitting Data faster than the speed of light using entangled particles [duplicate]

If we have a pair of super-asymmetrical entangled particles, and move them a light year away so that they retain their quantum entanglement, and we set a clockwise spin (or vertical polarization) as 0 ...
SWIRF's user avatar
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Does the fact that we are able to see CMBR implies that universe expanded faster than light?

Supposedly, the universe underwent rapid expansion immediately after the big bang, surpassing the speed of light. If we can detect remnants from that era, does this suggest they moved faster than ...
Mr. Spock's user avatar
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How to make meaningful experiments and the methods of doing so [closed]

I have thought of an experiment to test for statistical significance in a quantum entangled system. The proposed experiment is as follows: Suppose there are 3 entities all in a straight line from each ...
Dakota Wharton's user avatar
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Faster than the Speed of Light with No Cerenkov Radiation

A charged particle in vacuum and stable motion would induce a time-variant but non-radiating electromagnetic field, whose pattern moves at exactly the particle's speed, but in a medium with lower ...
Meatball Princess's user avatar
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How is Alcubierre's warp drive propeled forward?

What is the exact mechanism of the warp drive that propels it forward? I know that it creates negative pressure behind it and a positive pressure in front of it but how does this actually propels it ...
Euler-Masceroni's user avatar
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Could reducing entanglement by unitary operations allow for FTL-communication? (and why not?)

About the closure: This Question is about why manipulating 1 particle of an entangled pair unitarily can’t cause measurable consequences on the other and how this manifests in the concretely described ...
Zaph's user avatar
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Does relative motion allow for speeds $>c$?

If motion is relative, (so if X was stationary and Y was moving at v m/s, we could think of this as Y being stationary and X moving at -v m/s), could we not create a scenario in which a stationary ...
bbqribs2000's user avatar
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Can a non-local theory be consistent with special relativity?

If there was a non-local theory that explained quantum entanglement correlations, does it follow that it would violate special relativity?
Hume's user avatar
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Can the velocity of an image produced by a plane mirror be greater than that of light?

We are currently studying ray optics in school and it made me wonder if the velocity of an image produced by a plane mirror can theoretically be greater than that of light. Using the relation $v_i = 2 ...
Milkprisonersvostok1's user avatar
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Does the no signalling theorem in quantum mechanics beg the question?

I had always thought similarly and then came across a paper here that argues this. The abstract is as follows: Many authors state that quantum nonlocality could not involve any controllable ...
inquisitive 's user avatar
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Do superluminal shadows drop the local temperature on distant objects?

There are lots of examples online of the scenario of someone with sufficient machinery casting a shadow of their thumb on the moon. It's argued the shadow travels faster than light, instantaneously ...
Svenn's user avatar
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How do non-local correlations occur in QM without a cause? [closed]

The Copenhagen interpretation of QM ultimately amounts to asserting that non-local correlations occur without a cause since that cause would involve propagation of information faster than the speed ...
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What are the implications of the EPR bridge information metric being invariant under all conditions, including distance in this universe?

What if the reason why instantaneous state information is able be transmitted between entangled particles through an EPR bridge is that the metric that this is conveyed in is invariant under all ...
Odysseus Ithaca's user avatar
5 votes
1 answer
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Would the effective speed of an Alcubierre drive be limited by the propagation speed of gravity?

The idea of a warp drive is to "expand space behind the ship and contract it in front"- in this way reaching a target destination faster than one could conventionally. However, the actual ...
elfeiin's user avatar
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Two-way tachyonic anti-telephone

Consider the two-way tachyonic antitelephone where the speed at which message is transmitted is $a$. A person $A$ sends a message to $B$ which is moving away with a speed of $v$ with respect to $A$. ...
Dr. user44690's user avatar
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3 answers
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One-way Tachyonic anti-telephone

When you have length contraction in special relativity $$L' = L/\gamma$$ the interpretation is that $L'$ is the length of an object with rest-length $L$ moving with respect to an observer at rest. ...
Dr. user44690's user avatar
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2 answers
102 views

Can we use the fabric of spacetime to go faster than the speed of light?

If the fabric of spacetime isn't bound by the limit of the speed of light (the universe is expanding faster than the speed of light), could humans somehow wrap a spaceship in a bubble of the fabric of ...
Kellan Heerdegen's user avatar
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1 answer
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How can resolution of particle entanglement be detected, and why can't it be faster than light communication?

Sorry for the length, but this is driving me crazy. And yes, there are other questions on this issue and I have reviewed them, but I cannot see the answer stated simply. What is different about my ...
RalphBerger's user avatar
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Speed in a medium

Let's say, that there is medium, where the speed of light is $10^8 \, \rm m/s$. So in that medium if there exists a particle that is moving through without any hindrance what would be the speed limit ...
Le nerd's user avatar
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Faster than light is possible? [duplicate]

I know that some particles can go near or more than half the speed of light. So, say we shoot two particles in opposite directions at more than half the speed of light. Say one is moving at 50% the ...
user392759's user avatar
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2 answers
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How does the "York time" measure the expansion of space; why is it equal to the divergence of the comoving observer's four velocity for warp drive?

The mysterious York time, θ is important in warp drive topic. It is plotted on the famous diagrams and is considered the measure of the mechanism that "drives" the warp drive bubble at ...
Attila Janos Kovacs's user avatar
-1 votes
4 answers
119 views

Quantum entanglement and speed of transmitting information [closed]

Imagine Alice and Bob have two pairs of entangled particles, pair A, and pair B. Imagine they have agreed beforehand that pair A measurement preceding pair B measurement constitutes a bit with value 1 ...
Abhishek Nair's user avatar
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About information transmission speed [duplicate]

Einstein says information cannot be transmitted faster than light. Say I set an alarm that ring at 9:00 am. I go to school, and wait until 9:00 am. Then I tell my friends that my alarm rang. If the ...
tneserp's user avatar
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Can entanglement witnesses on GHZ states with $n > 2$ violate the non-communication theorem?

In experiments involving entangled photons, measuring entanglement in systems with more than two particles ($n > 2$) often employs one photon as a herald to distinguish signal photons from noise. ...
Scott Stults's user avatar
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Spacetime that allows matter to rotate faster-than-light

Is there a solution to Einstein's equations which allows: the object to be rotating at sub-light speed when viewed from within itself. for a distant observer the object to rotate at superluminal ...
Ember Edison's user avatar
1 vote
1 answer
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Why the phase velocity of X-rays inside glass is faster than $c$?

For hard X-rays the refraction index of glass becomes slightly $n<1$ which means that the phase velocity (not group velocity) of X-rays inside glass is larger than $c$ the group velocity speed ...
Markoul11's user avatar
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8 votes
1 answer
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Could information be transferred through a wormhole?

There was a paper published recently about the possibility of sending messages through a wormhole,see reference here. It has also been speculated that any entangled pair of particles—even particles ...
Cristian Dumitrescu's user avatar
-2 votes
1 answer
86 views

Will this hypothetical circular singularity FTL travel warp drive work? [closed]

Not a physicist, but just wanted to know if this would work in theory: Since nothing can practically travel faster than the speed of light (for now until proven otherwise), the only way for ...
notorious-raccoon's user avatar
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0 answers
17 views

Is it possible to have a medium rarer than vacuum? [duplicate]

I was wondering whether it is possible to have a medium rarer than vacuum. If that is possible then we can increase the speed of light beyond $c$. Might sound like a weird question.
KIngK's user avatar
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1 answer
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Lorentz transform causes Faster than light motion for Spacelike-separated object?

Consider a 5-meter rod which exists on the x-axis of a frame of reference: Now consider an observer moving at a velocity $0.1c$ relative to this reference frame, from right to left. Their frame of ...
Anuj Manoj Shah's user avatar
-4 votes
1 answer
76 views

What would happen if two super-massive black holes collide faster than the speed of light? [closed]

I know objects can't move through space faster than light. But there's no law against the expansion of the universe increasing the distance between two objects faster than the speed of light. But this ...
jo-erlend's user avatar
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1 answer
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Is it possible to know if an entangled particle's state is a superposition or collapsed? [duplicate]

I understand it's not possible to transmit information using entangled particles due to the randomness of the measure results. But what if the act of measuring itself IS the information? Let's say ...
Zbelko's user avatar
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-4 votes
1 answer
85 views

FTL Communication using Quantum Entanglement (A new Approach) [closed]

Ok i have a proposition: Imagine there are two people 1 on earth and other in space. They syncronised their clocks before they left earth and agreed that they will factor in time dilation and ...
ayoosh iyer's user avatar
1 vote
1 answer
53 views

Speed of light getting lower in densed medium [duplicate]

In densed medium speed of the light gets lower so in this kind of situation is there anything which can travel quicker than light?
Shayaan's user avatar
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0 answers
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Communication via entanglement [duplicate]

For years now i have in my haed a thought experiment for information exchange via quantum entanglement. And i am aware that something must be wrong with it but i can't figure out what it is. The ...
GMatthes's user avatar
-2 votes
1 answer
81 views

FTL communication setup. Why wouldn't this work?

The setup is similar to quantum eraser experiments (see below). The laser pulses at regular intervals to send bunches of photons. They get split in half as entangled particles. One beam is sent 1 ...
nocies's user avatar
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-1 votes
1 answer
83 views

Instantaneous transmission of data across arbitrary distances via quantum entanglement [duplicate]

As a forward, I'm no a physicist or a student of it. In fact I'm pretty ordinary. So if I mischarecterize some concepts, bear with me. So I was reading up on some of the new technologies and then I ...
Maninderjit Buttar's user avatar
0 votes
1 answer
107 views

Faster than light communication by entangled photons [duplicate]

Faster than light communication is not possible. If I measure the polarization of an entangled photon and it turns out to be right circularly polarized. In that instant, dont I know that someone ...
Richard Coppack's user avatar
2 votes
2 answers
96 views

Speed of wave more than $c$

We are always told that information cannot travel faster than light (speed $c$). So, my question is, if we talk about a wave lets say a transverse wave. We can define a wave as the systematic ...
krishna gupta's user avatar
0 votes
4 answers
155 views

We can't go faster than the speed of light. Can we accelerate light, then? [closed]

If there's a way to artificially accelerate light, or when it's naturally faster such as around a blackhole, then in that case, would it be possible to go past the 299792458 m / s limit?
No Name's user avatar
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-2 votes
3 answers
103 views

Can gravity make something faster than light? [duplicate]

Scenario, Let's say we have complete vacuum and nothing in the universe. If we place 2 bodies at infinite separation and have HUGE masses ($m1, m2 \sim 10^{1000}$ kg or something): They will attract. ...
0xdead's user avatar
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1 vote
1 answer
147 views

How does a refractive index of less than one not violate relativity?

If I am not mistaken, this video says that X-rays travel faster in glass than in a vacuum. Special Relativity says that information can not travel faster than the speed of light in a vacuum, so what ...
ACertainArchangel's user avatar
-2 votes
2 answers
218 views

Are there cases in quantum field theory's formalism were virtual particles are allowed to exceed the $c$ speed limit?

Virtual particles even today contrary to the overwhelming evidence in my opinion that they have a real effect on normal particles (i.e. Casimir effect, $g-2$ muon Fermilab experiment) are considered ...
Markoul11's user avatar
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Can a big enough Giant travel many lightyears in just a few seconds? [closed]

We, as humans, given our height and size, view the world from the same general perspective. An ant, on the other hand, will understand the same world in a completely different way, given how limited ...
No Name's user avatar
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0 votes
1 answer
79 views

FTL Length contraction? [closed]

I found this interesting question in a textbook about special relativity: A length-contracted object has length $L=\frac{L_0}{\gamma}$. Joe differentiates this with respect to time and finds $$\frac{\...
Thibaut Klinger's user avatar

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