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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Geocentric frame of reference and superluminal speeds

I have a couple of questions on frames of reference. From my understanding, we can do math in an accelerating frame of reference as long as "fictitious" force terms are correctly added. From this ...
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Time travel is possible? [on hold]

Is the time travel theory of Einstein practical?If yes,then how can we travel faster than light ?
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Can gravity accelerate an object past the speed of light?

Imagine we have something very heavy (i.e supermassive black hole) and some object that we can throw with 0.999999 speed of light (i.e proton). We are throwing our particle in the direction of hole. ...
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Why can't gravity force an object past the speed of light? [duplicate]

I hope this question is not a duplicate (it doesn't seem to be) and that it is appropriate for this site. If we had a universe with only two bodies. One is ultra massive, and the other is very small. ...
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Instantaneous quantum features

Two of the most striking quantum oddities are entanglement and the wave-function collapse or state vector reduction. Firstly, quantum entanglement is the quantum phenomena involving states of ...
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Why does FTL not leave behind a motion blur? [closed]

I once thought anything traveling faster than light would leave behind a motion blur that on one end recedes at the speed of light and at the other increases at the velocity of the object. If an ...
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“High-Frequency Gravitational Wave Generator” patent from U.S. Navy, among other things [closed]

A scientist going by the name Salvatore Cezar Pais, employed by the U.S. navy, was recently granted the following eyebrow-raising patents: -High frequency gravitational wave generator (10322827) -...
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Relative speed when getting close to the speed of light

I was thinking about the relative speed of an observation reference frame and an object which has been accelerated to a speed close to the speed of light. I'm by no mean an expert and the last physics ...
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A telegram from Mars

Say, people fly to Mars, get in trouble, and want to send us a SOS signal. The average distance is 225 Gm, so they must wait 25 minutes to hear our response at the speed of light. This may just be too ...
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If tachyons existed, would we modify the theory of relativity?

In relativity tachyons cannot exist and they are theoretically viewed as objects with imaginary mass according to relativity, but since tachyons violate relativity, why do we use this theory to ...
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How can I show that the speed of light in vacuum is the same in all reference frames?

I have regularly heard that the Michelson-Morley experiment demonstrates that the speed of light is constant in all reference frames. By doing some research I have found that it actually demonstrated ...
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Is it possible that the universe is not expanding faster than the speed of light? [closed]

What if the speed of light increases proportionately to the expansion of space? Is it possible that light traveling in the medium of space gets to travel faster if the medium is expanding? An analogy ...
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The choice of measurement basis on one half of an entangled state affects the other half. Can this be used to communicate faster than light?

It is often stated, particularly in popular physics articles and videos, that if one measures a particle A that is entangled with some other particle B, then this measurement will immediately affect ...
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To an observer in a black hole, would light be stationary? Would it be as if the black hole is accelerating faster than the speed of light?

Taking into account that we know that gravity and acceleration are fundamentally indistinguishable from each other, Would an observer in a black hole believe that he's accelerating upwards faster than ...
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-Thought Experiment- At superluminal speeds, to what degree would vision be impaired? [closed]

I was thinking about superluminal travel when thinking about advanced civilisations in the future. I was also thinking about the Doppler effect; so I decided to think about how light may be affected ...
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Would possibility of instant communication break physics? [duplicate]

I recently read a sci-fi book, where some (very few) people can communicate telepathically, which happens to be instantaneous. So, every spaceship has a crew member who telepathically communicates ...
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How do we know quantum entanglement works no matter the distance?

It is said quantum entanglement works regardless of distance. 2 particles can be entangled and information is shared instantaneously, even if they are lightyears away from each other. But how do we ...
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Does light travel faster in between Casimir plates?

Speed of light is in general $c/n$ where $n$ is a refractive index. But for example introducing two parallel plates with very small spatial separation will perturb the energy density of vacuum ...
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Test the non-signaling principle

Has the non-signaling principle in quantum mechanics been tested experimentally?
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Quantum Entanglement and Faster than light Communication

Suppose, Alice has a Billion of photons in random states, while Bob has their entangled pairs. Suppose, Alice can measure the spin of the photons in X axis, while Bob can measure their spin in an axis ...
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Can something travel faster than the speed of light? [duplicate]

I understand this is a very complicated question to answer as no one really knows. However if gravity exerts an infinite force in the singularity of a black hole, then can't it travel faster than the ...
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Do photon inside event horizon exceeds speed of light?

Event horizon is a region of space whereby nothing with information can escape, so I imagine that a photon falls into this region of space does it accelerates toward the singularity if it exists? Do ...
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Will free-fall object into black hole exceed speed of light $c$ before hitting black hole surface?

In Newtonian mechanics, if we throw an object in against direction of gravity with speed $v$ and it achieve max height of $h$. Now if we allow object to fall from that height $h$, it will eventually ...
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Would close to light speed travel be possible if all atoms in the system were instantly given “forward motion”?

I have heard people say that based on our current understanding and ideas for possible/current technology no person would ever be able to even travel at a solid (70-80%) the speed of light because ...
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Is it possible for information to be transmitted faster than light by using a rigid pole?

Is it possible for information (like 1 and 0s) to be transmitted faster than light? For instance, take a rigid pole of several AU in length. Now say you have a person on each end, and one of them ...
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Can entanglement be explained as a consequence of conservation laws?

This article at NewScientist magazine (subscription required) describes entangling photons by passing them through a half silvered mirror. http://www.newscientist.com/article/mg21929282.100-quantum-...
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Illusion that $v > c$?

I am currently studying length contraction in special relativity (and having the hardest time getting the harder exercises in my book right) and there is the following exercise in my book is driving ...
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Speed of at expansion at the start of the big bang [duplicate]

If I understand the basics of the big bang correctly it starts with a very small dense point. At the moment of the big bang, less then microseconds after, the universe is already the size of our solar ...
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Would an observer going faster than the speed of light in a vacuum be able to observe photons that they emit? [closed]

If I could exceed the speed of light in a vacuum, would I be able to see photons that I previously emitted? Would this be theoretically possible?
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Can Quantum Entangled particles convey information faster than speed of light? [duplicate]

Can Quantum Entangled particles convey information faster than speed of light. If they don't what was wrong with John Bells experiment?
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Why do physicists say information can't travel faster than light speed?

I often hear in physics videos light speed is the ultimate speedlimit two parts of the universe can communicate at, or even that speed of light is actual speed of causality. Where does that notion ...
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Speed of Light & Distance [duplicate]

If I have a transmitter that signals a relay which turns off a light off which is 300 000 km away – it has travelled at the speed of light. If I connected a rope (which does not stretch) which is ...
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Thought experiment about no-cloning theorem and FTL information

The quantum no-cloning theorem states that one cannot "build" a perfect cloning device for arbitrary quantum systems. There also exists a famous thought experiment where Alice transmits information ...
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Aging while traveling faster than speed of light? [closed]

theoretically, if organic matter was able to travel faster than the speed of light, without becoming "pure energy", and since theoretically traveling faster then the speed of light would travel ...
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How far away must a galaxy be for its light never to reach us due to the expansion of the universe?

My understanding is that at the present rate of expansion of the universe some galaxies are growing more distant from us at such a rate that light from them will never reach us. My question is how far ...
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Does special relativity predict superluminal speeds?

Assume that we have a long Born-rigid rod with a length $L_0$ in which the speed of light is the ultimate speed for sending information. If there is a tiny missile at the right end of the missile that ...
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Feynman diagrams

Feynman diagrams are drawn on Space-time graphs. So is it possible for any particle path in that diagram to have a slope smaller than 45° or greater than 135°, i.e. can they travel faster than light? ...
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Why didn't Lorentz conclude that no object can go faster than light?

Based on Lorentz factor $\gamma = \frac{1}{\sqrt {1-\frac{v^2}{c^2}}}$ it is easy to see $v < c$ since otherwise $\gamma$ would be either undefined or a complex number, which is non-physical. Also, ...
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How Can the Universe Be Bigger Than It is Old? [duplicate]

My question is this: If we can look back to roughly 500m years after the big bang and have estimated the age of the universe at 13.7B years, why is the galaxy we are looking at not a part of the non-...
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Traveling to another galaxy impossible for ever?

If galaxies are moving apart from each other faster than the speed of light, does that mean that it's impossible to travel to another galaxy, regardless of what technology get discovered? Because you ...
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What is Cherenkov radiation? [duplicate]

What is Cherenkov radiation? I came across this concept when I was learning SR. Why can't particles moving at speed of excess of speed of light in the medium. Why it does not violate the limitation ...
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Can light in a medium travel faster than speed of light $c$ in vacuum?

Refractive index of medium $m$, $n_m$, is given by $$n_m = \sqrt{\mu_r\epsilon_r}$$where $\mu_r$ and $\epsilon_r$ are permittivity and permeability of the medium respectively. And, velocity of light ...
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So is quantum entanglement actually FTL “communication” or is it mundane pre-determination?

I have to say right off the bat, I'm a little frustrated that there seem to be very contradictory answers about this, at least to a layman like me. If two particles are entangled and you separate them ...
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Does gravity sometimes get transmitted faster than the speed of light?

Consider Earth moving around the Sun. Is the force of gravity exerted by Earth onto the Sun directed towards the point where Earth is "right now", or towards the point where Earth was 8 minutes ago (...
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Significance of the LIGO experiment with respect to length contraction

it might be best to first detail my (admittedly limited) understanding of the LIGO experiment. a beam of light is split along two 4Km evacuated pipes then reflected back where their interference ...
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Could dark matter/dark energy turn out to be tachyonic?

Today, I was watching the Inexplicable Universe with Neil deGrasse Tyson. He spoke about Dark Matter, Dark Energy, and then he spoke about Tachyons. Naively, I thought what if the reason we can't ...
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Rocket faster than light?

In this article, wikipedia describes a constantly accelerated rocket, assuming special relativity : $$ x(\tau) \;=\; \frac{c^2}{a} \left(\cosh \frac{a \ \tau}{c} -1 \right) $$ The proper time $\tau$ ...
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Turning on headlights near light speed [duplicate]

If i turn headlights on in a car at v = 0.99*c, will the headlight speed be 0.01*c? I know speed of light is always the same but it really confuses me? My question is, does space contract so much at ...
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speed of freezing vs. moving [closed]

An idea came to my mind and like to discuss it. We know that out there in the space the absolute zero (aka. -273 C) is almost reached where all the particles and atoms would freeze up and stop giving ...
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Observing supraluminally receding galaxies – is the “swimmer against variable current” analogy valid? [closed]

Davis and Lineweaver in Superluminal Recession Velocities state that “galaxies with distances greater than $D=c/H$ are receding from us with velocities greater than the speed of light and superluminal ...