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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Exceeding the speed of light by the acceleration of electron [closed]

What I found is that the acceleration of electrons by the proton when it is separated by a distance of $r=10^{-10}$ m is $a=2.5\cdot 10^{22}$ m/s$^2$, then why does the electron not exceed the speed ...
Arnav '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
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How many orders of magnitude faster was the speed of cosmic inflation compared to the speed of light $c$?

Inflation guy Andrei Linde says it like this: … "In that microscopic time interval ($10^{-35}$ sec), the size of the cosmos grew dramatically, going from a diameter of $10^{-33}$ centimeters — ...
Markoul11's user avatar
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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 ...
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3 answers
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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
3 votes
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. ...
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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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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 ...
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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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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
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4 answers
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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 ...
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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
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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 ...
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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
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1 answer
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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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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.
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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
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1 answer
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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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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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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
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1 answer
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Explain Time dilation for me with many easy to comprehend examples and reasons [closed]

I can’t wrap my head around this. So didn’t Einstein came to believe time stops because he imagined watching a clock tower as he raced away in a near light speed train? He would then notice that the ...
user3283015's user avatar
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1 answer
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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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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
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1 answer
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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 answer
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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
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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
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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
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4 answers
152 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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3 answers
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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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Can an inertial frame observe another frame moving faster than $c$? [duplicate]

Why is it impossible to observe someone moving faster than the speed of light? Suppose there is a frame A. frame A can observe something moving at the the speed $c/2$ right? So suppose there’s two ...
Junaid's user avatar
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1 vote
1 answer
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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
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2 answers
210 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
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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
1 vote
1 answer
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What is innermost unstable circular orbit (IUCO)?

In the paper Tachyon motion in a black hole gravitational field by V. M. Lipunov he writes: (…) Circular orbits for tachyons begin at the distance of $ 3/2~r_g $, i.e., at the distance of the ...
JanG's user avatar
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1 vote
1 answer
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Different Escape Velocities of Black Holes?

I am no physics major nor math major to this but merely an amateur cosmology enthusiast, so in my previous inquiries I wasn't able to find anything on the premise that if all black holes obviously ...
Deadweed1's user avatar
3 votes
1 answer
128 views

Confusion regarding recessional velocity and Lorentz transformation

Consider that you are receding at a velocity faster than the cosmic speed limit (say, $2c$ with respect to $A$) due to the expansion of our universe. According to me, $A$ is moving at $2c$ and thus ...
user avatar
6 votes
1 answer
321 views

Are there any Alcubierre Style metrics for sub-luminal speed warp drives?

In most literature I have found, research into the Alcubierre Metric, and Warp Drives seems to be highly focused on the plausibility of superluminal travel. Today I was thinking to myself that maybe ...
RudyJD's user avatar
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5 votes
1 answer
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Stuck on thought experiment about light [duplicate]

Say we have a very long fluid pipe with the width of a few astronomical units, and that this pipe is perfectly resistant to sustain the stress of a perfectly incompressible fluid going through it ...
Ícaro Lorran's user avatar
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0 answers
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What force could theoretically redirect the Higgs field? [duplicate]

I’d just like to point out I am by no means a physics expert, or indeed a particularly knowledgable nerd on this subject. I am a minor and a wannabe sci-fi writer who is trying to come up with an idea ...
user98816's user avatar
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Refraction of a Ray of Light [duplicate]

Why can no medium have a refractive index less than 1? Explain with Snell's Laws of Refraction of Light.
Samik Hazra's user avatar
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0 answers
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If a photon travelled in the opposite direction of another photon [duplicate]

If a photon travels in the opposite direction as another photon, then what is the speed of the second photon relative to the first. Is it 2 times the speed of light? Also what if two photons travelled ...
Anish Kommireddy's user avatar
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1 answer
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Please give me a single sentence explaining why faster-than-light morse code through entanglement isn't possible? [closed]

Problem with past explanations is they emphasize the need for random choice of measurement angle, but my understanding is that was only necessary in experiments seeking to remove any possible loop-...
John Strider's user avatar
1 vote
1 answer
703 views

Why Going Faster-Than-Light (FTL) Leads to Time Paradoxes? [duplicate]

In this video: https://www.youtube.com/watch?v=an0M-wcHw5A&lc=UgxqC71gefTRIuVubGt4AaABAg.9jI6ltMIeu59jx2P8cpn_z In the video the following events happen: A supernova goes off. Earth sees the ...
Rick's user avatar
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4 votes
2 answers
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How to show that a if $v > c$ there is a frame which breaks causality in special relativity?

I'm reading about special relativity and looking at the Lorentz transformations. I'm reading that: If $v > c$, we can find a frame in which $t_2' < t_1'$, i.e. a signal arrived before being ...
user1551817's user avatar
1 vote
2 answers
406 views

Isn't the universe older than 13.8 billion years? [duplicate]

To preface this, I'm not an expert, I'm just an avid astronomer with little mathematical knowledge. I was watching a video that was explaining the cosmic scale and how the observable universe is only ...
JamesM's user avatar
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