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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Is the kind of physics proposed for "warp drive" related to the way that space really is expanding?

As I understand, some parts of Universe really are moving faster than light -- is this expansion something we think we can create artificially? And if we can do this artificially, could it be done a ...
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Why do we need inflation?

wiki (https://en.wikipedia.org/wiki/Inflation_(cosmology)) says that immediately after BB there was expansion at speed greater than $c$, what makes this necessary, what would happen if expansion took ...
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Faster than light information

I've seen there are a few answers on here previously about faster than light information travel, and my understanding is that it is impossible. However, I've just read an article https://www....
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Does the collapse of an entangled photon triplet allow FTL communication? [duplicate]

I have read the assertion on other posts that if the entanglement of one photon of an entangled triplet is broken then the whole system collapses and the remaining two are no longer entangled, has ...
2 votes
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Special Relativity and Light [duplicate]

I just started learning about relativity in my physics class and would like some help understanding the concepts. My question is imagine two objects start emitting light and are 1 lightyear away from ...
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FTL signaling by direction? [duplicate]

If the axis of a spin is determined by the first measurement, would using that to tell humans on Earth whether a planet light-years away is habitable be FTL communication? Depending on measurement ...
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1 answer
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Will light be travelling faster than the speed of light? [duplicate]

If a photon is emitted from a light source travelling with some velocity, then surely the photon emitted in the direction of travel would have a velocity equal to the speed of light plus the velocity ...
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The phase velocity of a massive field is greater than $c$ [duplicate]

Assuming $c=1$, $v=\frac{\omega}{k}=\frac{\sqrt{k^2+m^2}}{k}>1$, for $m \neq 0$. Why is it not an issue that this $v$ is greater than the speed of light?
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Can an object move faster than light in an accelerated frame of reference?

In an accelerated frame attached to an accelerating rocket the Lorentz contraction of the rest frame is steadily increasing, which means that distant galaxies are getting closer and closer. Does this ...
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Quantum entanglement information through time of collapse

(I've tried my best to find an existing question that asks this question exactly) From what I understand, given two entangled particles, one held by Alice and one by Bob, when a measurement is done by ...
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3 answers
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What would "break" in reality if I had a perpetual motion device?

Let's say aliens came and gave me a small box that outputs more energy than is input. As one example, the box can take current and voltage $I$ and $V$ as input, and output $I$ and $2\cdot V$. Or I can ...
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Example of information travelling faster than the speed of light?

In the following situation, information seems to travel faster than the speed of light. Is there a mistake in my reasoning? Suppose we have an electric circuit. For times $t<0$, there is no current ...
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Why can't any object gain the speed of light? [duplicate]

Suppose a object A is moving towards left with 200,000 km/s and objects B moving with 200,000km/s towards right. According to this above Statement, this could be happened because Speed of objects is ...
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Isn't There A Much Simpler Way To Explain Why Quantum Entaglement At Distance Isn't Utile - That Spins Already Exist & React To Detection Predictably? [closed]

Tell me if this concept works for explaining in a much simpler way, why purposeful entanglement outcomes like FTL communication cannot work - and without relying on complex analyses of 'spooky action',...
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If galaxies beyond the cosmological event horizon move faster than light is then that motion a combination of their KE and space expansion?

If galaxies beyond the cosmological event horizon move faster than light is then that motion a combination of their KE and space expansion? Their KE alone isn't enough for them to move faster than ...
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Does a smooth world sheet imply strings moving faster than light?

In string theory, one wants to study the interaction of strings throughout time. The interacting strings sweep out a surface in Minkowski space. To write down an action for the string, we need to ...
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Why would FTL travel break causality, as oppose to the relative time reconciling as in the Twin Paradox? [duplicate]

I have heard that if faster than light travel were ever made possible, such as by an Alcubierre drive, the user would be taken backwards in time, violating causality. This is odd to me, as it already ...
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Can one record a speed faster than $c$?

A ship goes to the moon at 0,5 c, the captain will record on his clock about 2 seconds and a half, right? Now he increases the speed to 0,999 c (or more), thanks to relativity he should record on his ...
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Does anything "break" in physics if you allow for instant (faster-than-light) communication?

Assume that two entities, Alice and Bob, can communicate thoughts literally instantly. If Bob thinks "Alice, I want you to jump", then Alice (many, many light-years away) will know that ...
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Alpha particle moving faster than the speed of light

In this problem I was solving a beam of uniform cross section carrying a current of $0.25\ \mu A$ by alpha particles. The mass of an alpha particle is $m_\alpha=4m_p$, where $m_p$ is the mass of a ...
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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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3 answers
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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 ...
0 votes
3 answers
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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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