"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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My theory to travel near the speed of light. Why will this theory not work?

Why can't a spacecraft travel near the speed of light? Here's my theory. We assemble the spacecraft in the Earth's orbit just like the International Space Station, each time, equipping it with lots ...
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Could my idea of Faster-Than-Light communication using quantum entangled particles be feasible? [duplicate]

I am most likely completely off but I have an idea on how we might be able to exchange information using spins only (provided that we prepare for the exchange of information): We communicate using ...
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26 views

Why can't we use a simple stick to communicate faster than light? [duplicate]

Assuming I and a partner are each holding an end of a very light lightyear long stick, could I transmit morse code faster than light to my partner by tapping or wiggling that stick? Wouldn't he feel ...
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Group and phase velocity - why can the latter be faster than light? [duplicate]

The phase velocity can be faster than light. Some argue that the phase velocity doesn't convey information, but this doesn't convince me. We can emit a wave of a single one frequency. Then it will ...
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33 views

Do wormholes only allow FTL travel in “folded” spacetime?

Faster than light wormhole travel depicted in science fiction and in popular science articles seems to assume that rather than being flat (with dimples centered around large masses), spacetime is ...
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Telescopes and faster than light travel [closed]

If sometime in the future we master faster than light travel, could we solve past crimes by warping to a place in space where the light from Earth is just arriving from that time period and using a ...
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2answers
134 views

Is it possible to go faster than the speed of light in vacuum?

If it is possible for particles to go faster than the speed of light in certain events, would it be possible to create a situation in which the barrier of the speed of light can be crossed?
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29 views

Getting an object to travel at or near light speed by adding velocities [duplicate]

Firstly I'll just give a brief example of where my query came from. I was watching the episode of Futurama where Bender meets God after being fired from the planet express ships torpedo tube. The crew ...
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70 views

Can you break causality if you are able to instantaneously perceive a distant system? [closed]

It is known that relativity plus FTL communication implies violation of causality, but now I propose the following thought experiment: Suppose that you have a magical spyglass that can be used to ...
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75 views

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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100 views

Can we accelerate photons to travel at speed of $1.5c$? Or any $xc$ when $x > 1$? [closed]

Can we move photons to travel at speed greater than speed of light in vacuum? If no then why? For example: I want to send some photons at 1.5c. Is that possible? How a photon of light can go from 0 ...
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56 views

Tachyons and Lorentz velocity transformation

In general, is it possible to apply the Lorentz velocity transformation to a tachyon? I have tried to do so but the results seemed very illogical. Here's my attempt: suppose an evil spaceship named ...
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How come an electron's wave function being nonzero at far distances doesn't mean it can travel faster than light? [duplicate]

I think the wave function of a free electron is nonzero almost everywhere. In particular there are regions of space arbitrarily far away where the electron has positive probability of being found. If ...
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79 views

Black hole's effect on itself with faster than the speed of light [closed]

If something were pulled into a black hole, my understanding is that you would approach the speed of light. Upon hitting the event horizon, you would be moving the speed of light. After that, you ...
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Confusion in phase and group velocity

This question is based on this question asked in physics SE. In this question, they say that phase velocity greater than velocity of light. Ok, greater than velocity of light for phase velocity is ...
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141 views

Can space move? [closed]

I have some questions; I hope you don't mind: $\bullet$ If the space between two distance galaxies is increasing, then is the volumes of space in which the galaxies find themselves also moving apart? ...
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5answers
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Could gravity accelerate light? [duplicate]

Gravity causes anything with energy to accelerate toward the source. Black holes, for example, have such strong gravity that they pull in light and don't let any escape. But can acceleration still ...
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96 views

Take advantage of time dilation or create a warp drive? [closed]

It is my understanding that time dilation slows down perceived time relative to the outside of a given vessel as it approaches the speed of light. Does that not mean that the inhabitants of said ...
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2answers
105 views

Backwards in time?

A “Universe Today” article titled “Galaxies Are Moving Away From Us Faster than the Speed of Light” prompted the following question, which the author of the article was unable to answer: “Would such ...
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Can the force of Gravity be used to travel faster than light? [closed]

This question is just an idle curiosity of mine, but after reading the Honor Harrington novels, I was intrigued by the concept of using gravity to surpass light speed. Any thoughts?
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Can we prove absolutely that FTL = causality violation

I've been wondering about this for a long time. Given that special relativity is normally true, can we still prove that causality violation must occur if FTL is found? All proofs I can find, depend on ...
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2answers
135 views

Does the uncertainty principle imply the existence of particles that exceed the speed of light?

The uncertainty principle allows for the creation of virtual particles (with non-zero mass) that exist for very short durations. This allows empty space to have particle pairs that pop into existence ...
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1answer
63 views

Speed of light, velocity limits and superluminal travel [closed]

I know that a massive object cannot reach the speed of light as it would require an infinite amount of energy to do so (though my knowledge of the reasons of this phenomenon is very limited). ...
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84 views

Is velocity of de broglie wave faster than light? [duplicate]

In one of the properties of matter waves is that it can travel faster than light. In my test I was asked to prove this. There are derivations of both can travel faster then $c$ cannot faster than ...
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Speed of light in zero-index material or similar

I've always thought that the maximum speed of light is achieved in vacuum. Now in some "popsci" news there are references as if there are mediums where light can go faster. Are these zero-index ...
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4answers
195 views

Why can't anything travel faster than light?

It is a well known fact, that nothing can travel faster than light. I have discussed that fun fact numerous times with my 8 year old son. One day he asked "why?", and I realized that I didn't know the ...
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Tomorrowland movie and tachyons? [duplicate]

Would be possible if tachyonic existed to send info to the past or see the future? since the tachyons according to special relativity could travel to the past? i have searched in wikipedia and the ...
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84 views

How can light cross $c$ in the given hypothetical experiment? Where I am wrong? [closed]

There is a concave mirror, which has somehow maintained the speed $\frac{c}{2}$ toward west ( for instance) , and there is a light wave or you can say a ray of light is moving in N-E direction. So we ...
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1answer
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Quantum entanglement and information transfer

I know it was stated many times that information transfer using entanglement is not possible and I am most probably wrong but I would be glad if you can at least point me to where I am mistaken. If ...
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Physics behind this neutrino-related joke

In the comment section of a newspaper article reporting on the 2015 Nobel Prize for Physics, which was awarded for work on neutrino oscillation, I found the following joke: "I'm sorry, we do not ...
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Does my interstellar pole thought experiment violate casualty? [duplicate]

I have heard that it is impossible to send a signal faster than light. However, what if I had a long (4.5 light years) pole and placed one end on Earth and the another end around Proxima Centauri. If ...
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2answers
94 views

Can less gravity speed up time? [closed]

We know more gravity slows down time per Einsteins Theory of Relativity. However will a significantly less gravitational pull speed up time? Or is "our time" aka earth standard of time the fastest ...
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3answers
79 views

Equal and opposite reaction at light speed

My knowledge of physics is very limited. And this question is only really to help me put to rest a question i have had for some time. I would like the answer to be a simple one as i am not really in ...
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How Energy can be real if C² isn't real? (E=MC²) [closed]

So, Nothing can go faster than speed of light. How come the Energy be real if C² isn't real? Is it even allowed to square C? How can we use C² as a constant as it has not representations in ...
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Would a tachyon be able to escape a black hole?

Or at least escape from a portion of the hole inside the photon horizon?
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What do you see if you directly observe your destination while in warp? [closed]

Say you are traveling in a warp bubble towards Earth from 10,000 lightyears away with an ETA of 24 hours. On the front of your ship, you mount a high powered telescope pointed directly at Earth (your ...
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Speed of entangled particle changes [duplicate]

If two particles are entangled at a distance of light years, does changing one affect the other instantaneously, or does it take years to occur? What gives us the answer to this question?
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Can light travel with a speed less than its speed at same time?

I know that the velocity of light with respect to anything is constant ($c$) . What, then, is velocity of light with respect to light?
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Alongside a light ray (in another medium)

It is a said fact that the speed of light is insurmountable. But can the validity of this fact be questioned in another medium? If I pass a beam of light in, say water (here the light speed is ...
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61 views

Observable Universe from two different perspectives

My layman understanding is that the universe is much bigger than that we can observe however due to the cosmological constant the observable universe is the matter etc. that is not moving away from us ...
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“FTL” Communication with Quantum Entanglement? [duplicate]

Can quantum entanglement make sending a message, whether audio, video, or even Morse code, instantaneous between two points (faster than it could travel normally at the speed of light)? Let me first ...
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4answers
174 views

Can FTL-Communication between two points in the same frame of reference break causality?

Hi I want to get to the bottom of some thaughts I have and for that I need an answer to a - I have to admit - highly constructed example. Lets assume - against all possibility - we find a strange ...
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What is special about quantum entanglement? [duplicate]

Get two pieces of paper. In secret write the same number on both papers. Transfer one paper to the Moon. Look to the paper which is left at the Earth. Voila! We know what is on the Moon paper. The ...
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93 views

Do wormholes violate causality [duplicate]

Does opening and closign a wormhole to send a message within seconds across the galaxy violate causality? Wouldn't different observers disagree about the order of events and what effected what? Is ...
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76 views

Can someone explain why this QM FTL communication setup is wrong?

So I thought I understood the double-slit experiment and EPR paradox until this setup occured to me. It combines EPR entanglement with "which-way" double slit setups. I know it must be wrong, but I ...
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Black Hole horizons and the Equivalence Principle?

In the reference frame of a freefalling observer, does crossing the event horizon not cause a contradiction between two classical principles that supposedly apply at the event horizon: the equivalence ...
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Since space expands (and can theoretically contract) faster than light, does that mean that in a big crunch information could travel FTL?

Layperson here. In a theoretical big crunch with space contracting faster than the speed of light, would information be travelling faster than speed of light? Because the points A and B themselves ...
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What would happen in this “close to the speed of light” scenario?

Say you had a really long pole made of a super strong material, and at the you turned it through an angle of (for example) 45 degrees. Turning the pole through a small angle at the bottom would ...
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What is the difference between the expansion of space and the Alcubierre drive?

The Alcubierre drive violates causality. As far as I know the expansion of space does not. The usual explanation for why space is allowed to go FTL is that the matter doesn't move. The Alcubierre ...
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How does a shadow appear to break the speed of light? [duplicate]

Take the image below for example: For the shadow to travel from point A to B would be extremly fast on the surface on the moon but probably not breaking the speed of light. But if the moon were 20 ...