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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What from our current understanding in physics prohibits vacuum space to be possible a superluminous medium? [closed]

Thus, an exotic form of energy-matter at a higher energy state than our normal matter and luminous $c$ bounded energy of our spacetime. A different space-time domain out of phase from our spacetime ...
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Problems with negative pressure, imaginary speed or super-luminous speed?

Currently, dark energy is described as a being that exerts a negative pressure while having a positive energy density. However, there is a serious problem when considering a physical existence with ...
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Tachyon velocity in relation to light speed [duplicate]

tachyonic particle are merely hypothetical particle that always travels faster than light., But if real, how fast would they be?
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What would happen if the two mouths of a wormhole are receding away from each other faster than light?

If wormholes could form naturally, and point A and point B were in galaxies receding from each other faster than light, what would happen to something going from one end to the other? Physicist Kip ...
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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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FTL travel without time travel (again)

In discussions about FTL communication and time travel, there is a simple thought experiment: the relativistic duel which is used to demonstrate that FTL travel implies time travel (I know it has a ...
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Can we make electron drift velocity faster than light by reducing area of resistor?

We know that $I= nqAV_d$. Can we send high current ($I$) through a "fat wire" (more $A$) then reduce $A$ at the resistor so much that $V_d$ becomes faster than light in order to maintain $I$?...
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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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Technical meaning of "no faster-than-light communication"?

I often read sentences like "relativity forbid faster-than-light communication" or "quantum entanglement cannot be used to convey information faster than light", but it seems to me ...
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Can Higgs particles move faster than the speed of light in the high energy (temperature) regime? [duplicate]

In the standard model, Higgs particles have negative mass squared term in the SM lagrangian and hence, the Higgs is tachyonic in nature. This isn't a problem since -at low energy (temperature)- the ...
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Why do they say there is no signal in the Cramer-Herbert nonlocal quantum communication scheme?

I refer to the paper "An Inquiry into the Possibility of Nonlocal Quantum Communications " , by John Cramer and Nick Herbert. Section 6, a wedge - modified path entangled EPR experiment ...
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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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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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Why isn't this a way to transfer information faster than light using quantum entanglement?

Suppose Alice and Bob have entangled particles A and B that are very far apart. Alice uses Particle A to send information through its spin along the x axis, and Bob uses Particle B to receive this ...
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If I had a car which could go with a speed of light, could I drive it at night? [duplicate]

Just theoretically, when I turn on the lights in my super fast speed of light car, would I see the road if the light can't go faster than my car?
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Can we observe the universe expanding faster than light?

I am looking at the sky, and I see two objects moving away from each other with speed greater than the speed of light. Light from one object is not fast enough to reach the other. So I decided to help ...
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If ER = EPR conjecture is true would it allow faster than light (FTL) communication?

If entanglement is really carried through by wormholes can't we for instance use that wormhole to send information through it? If we understand that maybe we can scale up the wormhole to allow people ...
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Why is it assumed that special relativity does not apply to a universe expanding faster than light?

An argument I hear repeatedly is the light-speed limit only applies where spacetime is flat, so faster-than-light speed is possible where spacetime is curved. Thus special relativity does not apply ...
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Is there empirical evidence supporting a universe expanding faster than light?

We receive no light from galaxies beyond the cosmological horizon, but if they were moving away only at light speed, it seems to me their light wouldn't reach us. Is there any observations or ...
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Why is FTL travel impossible if the universe expands FTL?

If the universe is expanding spacetime faster than light (FTL), is FTL travel no longer completely impossible? Do not care about energy requirements or needing new tech, just if it is NOT physically ...
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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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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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Faster-than-light gravitational waves and faster-than-light expansion in the inflation

I have no introduction to the inflationary epoch. I know, however, that during this time space-time expanded with a speed faster than the speed of light. If gravitational waves are perturbations of ...
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Could Gott's Cosmic String Time Machine hypothetically be used as a poor man's Alcubierre drive?

I have read much speculation about Gott's theoretical use of cosmic strings for time travel, but if the colliding cosmic strings accelerated the spacecraft faster than light, as Gott theorizes, could ...
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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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Questions on observations of faster than light recession of galaxies [duplicate]

I've been reading several threads here and online articles trying to absorb the current understanding of observations of far galaxies receding faster than the speed of light, it is said because the ...
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But why can't i travel faster than the speed of light? [duplicate]

I'm laying in my bed right now. Am I traveling 0mph? Am I traveling 850-ish mph (south texas) as the earth rotates? Am I traveling 67,000mph as my planet orbits the sun? Am I traveling 560,000mph as ...
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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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The wave function collapse and uncertainty principle [duplicate]

If we measure the position of a quantum mechanical particle, then, according to the postulates, the particle's wave function collapses into a delta function and the measured result is one of the ...
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Big Bang and relativity [duplicate]

Wasn't the big bang's explosion itself faster than speed of light? how does this not violate relativity, I had read an explanation earlier but it wasn't sufficient, can someone explain to me how the ...
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Can an object theoretically reach, or exceed the speed of light? [duplicate]

I'm sorry if this is a naïve question, but it's been bugging me for a bit. If a spacecraft were traveling in a perfect space with unlimited fuel, could it not, assuming it is not influenced by other ...
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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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If spacetime can expand faster than the speed of light, then can a black hole do that too?

I have read this question: Yes, the expansion of space itself is allowed to exceed the speed-of-light limit because the speed-of-light limit only applies to regions where special relativity – a ...
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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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Cherenkov Radiation: Does it need to be faster than light in the certain medium?

I understand that when a charged particle moves through a medium and excites the atoms nearby, it produces a blue light when the atoms 'de-excite" However, I don't understand why it has to be ...
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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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Imaginary Lorentz factor in special relativity [duplicate]

This thing is making me confuse, what is mean by imaginary Lorentz factor in Physics? What is the physical meaning of imaginary?
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These guys occur but why? [closed]

We all know that if we consider the assumption of Einstein that is no material object can travel faster than light to be true then two effects that are Length Contraction And Time Dilation seem to be ...
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Is pulling a string instantaneous at both ends? Why is it or isn't it? [duplicate]

This is a question that has bothered me for quite some time but I don't have a clue where to start in researching it. Let's say we have a string which is arbitrarily long, light enough to not take ...
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How does change in Temperature affect Refractive Index/Optical Density of a medium?

In my school book its stated that: With increase in temperature, the speed of light in a medium increases, so the refractive index of medium decreases. I read in another answer that: Refractive ...
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Some help in understanding energy conservation relating to special relativity

Consider the decay of particle $A$ into particles $B$ and $T$ where $T$ is the tachyon particle. The conservation of energy equation can thus be expressed as $$m_A=\sqrt{p^2+m^2_B}-\sqrt{p^2-m^2_T}\,.$...
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Why would an FTL-drive imply time travel? (other answers and questions unsatisfactory)

I've been spending quite some time trying to understand why an FTL-drive would also imply time-travel, but every answer I can find seems to mainly be about semantics and perception. I will break it ...
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Velocity addition for tachyons

How does the velocity of a tachyon transform under a Lorentz boost? Suppose we only consider motion along the $x$ direction for simplicity. If the velocity of the tachyon is $u$ in the lab frame, what ...
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Relativistic particles and quantum fields and time like cone

Considering that a "classical" relativistic particle remains inside the time-like cone, does it guarantee that a quantum field must also do that for each of its path history? or it has to be ...
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If a muon travelling fast can “extend” its lifespan due to relativistic effects, would the muon see itself travelling faster than light?

In other words, if I put a bomb set for 2.2 microseconds and send it out at .99c, would it travel further than (.99c x 2.2 microseconds)? And if it does, like muons do, wouldn’t the bomb be able to ...
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How can spacetime be expanding faster than the speed of light? [duplicate]

How can spacetime be expanding faster than the speed of light when the speed of light is the speed limit of the universe?
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Can a particle with non-zero rest mass "tunnel" into the tachyon world without having to cross the $m=\infty$ barrier?

In the above diagram, I've indicated the variation of mass of a particle with its velocity using the solid curve for $v < c$ and using the long dashed lines (which lie in the complex plane) for $v &...
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How warp drive could be faster than light? [closed]

If the speed of gravity is as fast as the speed of light then there is no way a warp drive could curve the fabric of spacetime faster than the speed of light. Then how does a warp drive actually make ...
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Tachyons as vector representations on the surfaces transitivity of Lorentz group?

In Wikipedia's surfaces of transitivity (of Lorentz group $G$, it says "Standard vectors on the one-sheeted hyperbolas would correspond to tachyons. Particles on the light cone are photons, and ...
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Can we observe an event that occurs more than 13.7 billion light years away? [duplicate]

In Kurzgesagt's latest video about the largest black holes, the narrator says that two black holes have been observed orbiting each other at a distance of 17 billion light years from Earth. So light ...
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