"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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Does EPR permit information to travel faster than light? [duplicate]

This question always throws me: Discuss if the EPR paradox violates special relativity? The information of the state of one particle is instantaneously transmitted to the other particle, but ...
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147 views

Navigating a Time Machine

Notes: The background for this question is working out details of a sci-fi story. Answers to the effect of "time travel isn't possible" or "FTL isn't possible" are therefore not helpful. I'm looking ...
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141 views

Is it possible to apply force to a light particle?

I know, the universal speed limit is the speed of light $c$. So, is it possible to apply more force to a light particle? What would happen to it if we could?
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153 views

Travelling at a relative speed greater than the speed of light [duplicate]

I've wondered about this since I was a kid. I've been told the speed of light is a constant ($c$), which would mean that light always travels at the same velocity. Now, here's what interests me: if ...
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4answers
2k views

Can internet speed be faster than speed of light?

We send email in order to transfer information and, over time, the technology used to send email improves to send email at faster rate. Since we use the Internet to send information from one place to ...
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1answer
74 views

Superluminal speed?

I came by the quotation below. I'm confused: does it mean that it's actually possible for light and even material objects to move faster than light? Gravitational fields are present the velocities ...
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2answers
239 views

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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2answers
1k views

Time Reversal in a Black Hole

I had a lively discussion with a person about black holes recently, and was making the point about gravitational acceleration in GR being paralleled by speed in SR. One thing that I know people talk ...
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17answers
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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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31 views

Is a Super-luminal Laser spot possible? [duplicate]

Note:This is not the same as Is the "How to break the speed of light" minute physics video wrong? because a larger distance is used in a different direction so that the time of flight of the ...
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57 views

Can we make a particle travel faster than $c$ in this way? [duplicate]

In my sixth grade science class our teacher asked us, for homework, if it was possible to have anything travel faster than light. Thinking about this, I came up with a rough idea of a way to make ...
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1answer
112 views

Would one-way FTL travel be safe from a causality standpoint?

Any demonstration I've seen of using FTL signals to violate causality seemed to involve an exchange of FTL signals. Would FTL travel be consistent with causality if it always involved motion in one ...
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1answer
47 views

Is there serious research on superluminal travel? [closed]

I was wondering if there are any serious attempts, or any ideas for loopholes in the current theories, that would enable us humans to travel with a speed greater than the speed of light?
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1answer
107 views

Can we travel faster than the speed of light? [duplicate]

So my question is completely a theoritical question. For example i have a stick made of the strongest material and lightest material and its lenght is as long as the solar system's diameter. The end ...
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1answer
64 views

Tachyons and the light barrier

I read somewhere that if something breaks the light barrier, i.e. a tachyon, that it will take infinite energy to make it go slower than the speed of light. So, does that mean that the object will ...
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4answers
169 views

Exceeding the speed of light using gravity? [duplicate]

From what I have learned, objects must accelerate as they approach a heavy mass. But I also know that they cannot travel faster than the speed of light. What if you had a proton travelling at ...
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3answers
252 views

How can light travel at a speed greater than the speed of light

I was reading John Rennie's answer here, Can light travel faster? I now know that the sentence ''the speed of light is always constant in vacuum'' is just an oversimplification, for example light ...
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38 views

What is the speed of gravity? [duplicate]

Hypothetically, let`s say that one day our Sun is suddenly removed from the galaxy. For us, on earth, would take up to 8.3 minutes to notice that the sun was removed, since the distance from the earth ...
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2answers
149 views

Special Relativity - Distance Not Increased?

I just watched the movie Interstellar and the question was asked of why/how high-speed travel would slow time within an area. Curious as I am, I watched several YouTube videos to quickly 'educate' ...
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249 views

Is dark matter moving faster than light? [closed]

My way of thinking is as follows: Consider a balloon. Let this be blown into a nearly elliptical sphere. Now, the temperature inside the balloon is increased by some means; this leads to the ...
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2answers
384 views

Energy transfer using quantum entanglement

Can we transfer energy from one place to another separated by arbitrarily large distances without any time lag? For instance, if Alice and Bob are two observers making measurements having a singlet ...
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2answers
71 views

Expanding universe and speed of light [duplicate]

Galaxies are moving away from us proportional to the distance between us and them , but nothing can travel faster than light, so even the farmost galaxies should be travelling away from us along with ...
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3answers
422 views

Acceleration due to Gravity: Free Fall [duplicate]

If we are in a free fall which implies we are accelerating at 9.8 m/sec every sec. And let's say that we are falling into a pit that has enormous depth. So isn't this be possible that we may ...
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Does entanglement not immediately contradict the theory of special relativity?

Does entanglement not immediately contradict the theory of special relativity? Why are people still so convinced nothing can travel faster than light when we are perfectly aware of something that ...
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1answer
200 views

Thought experiment on graviton breaking the speed of light [closed]

The effect of gravity travels at the speed of light. Suppose we can entangle a pair of gravitons (which are only theoretical, but who knows for sure?) and separate them over a vast distance. Hold on - ...
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If I move in a bus moving at the speed of light wouldn't I be disproving the laws of physics? [duplicate]

I'm just in 10 grade , so please bear with me. Just imagine If a bus was travelling at the speed of light , and I was was running inside it, wouldn't I be moving faster than light?
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Will an object always fall at an infinite speed in a black hole?

Most of you if not everybody will agree that the stronger the gravitational pull, the faster an object will fall. For example, on a planet with 50 times the gravity of Earth, any object will hit the ...
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2answers
118 views

Is FTL communication compatible with Lorentz ether theory?

I have come to understand, that faster-than-light communication is problematic with special relativity, because it leads to the possibility of sending signals into the past. I also read about the ...
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4answers
314 views

Could a photon travel faster than the speed of light in vacuum?

If the cosmic speed limit is the speed of light in vacuum, then what happens when a photon traveling through space meets gravity? Wouldn't gravity pull on the photon that's already traveling at max ...
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196 views

About the nonlocality of QM and faster-than-light/backward-in-time machines

The fact the quantum mechanics is nonlocal is known already for a long time, since the Bell works (1966 and later) and the Aspect's group experiments confirming the Bell-type CHSH inequality (1980 ...
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A theoretical speed of light question [duplicate]

This is a hard question to explain so bear with me. Let's say that Earth is moving at 1/3 the speed of light to the 'right' (obviously I realize there is no constant left or right). If I were to ...
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5answers
430 views

How can I explain this fallacy of conveying information faster than Light?

First statement of this question: In superluminal phase velocities, what is it that is traveling faster than light? says that information cannot be transmitted at a velocity greater than speed ...
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1answer
51 views

What is the factor that controls the speed of electrons accelerating in vacuum?Won't they accelerate infinitely? [duplicate]

We all know that speed of light can not be exceeded. So the question is if electric field accelerates electron in a vacuum tube with enormous length won't the electron accelerate till a point where it ...
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31 views

Faster than light travel at half speed [duplicate]

Peter and Susan are facing each other in outer space. Both of them ignite their their incredibly powerful jet pack thrusters and accelerated away from each other to just over half the speed of light. ...
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3answers
256 views

Why can a particle have a nonzero amplitude outside its forward light-cone?

I'm having trouble grasping an idea that I think that is a very basic part of  quantum field theory. Many introductory QFT resources I have consulted often pose the following question: What is ...
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2answers
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What do physicists mean by “information”?

On the question why certain velocities (i.e. phase velocity) can be greater than the speed of light, people will say something like: since no matter or "information" is transferred, therefore the ...
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65 views

Would an Alcubierre drive actually allow FTL travel? [duplicate]

If I do not phrase this question right, please forgive me in advance because I am a layman on the subject of physics, but a software engineer, nonetheless. I do understand many technical subjects. ...
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2answers
96 views

Did the Earth (amongst other things) travel faster than light?

It's often said that when you look far across space with a telescope you are looking back in time, as the light has only just reached our position in space. However, given that the Earth and many ...
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51 views

Does a force propagate instantaneously to move the other side of the box of length one light-year? [duplicate]

This is a question of curiosity, and not for any academic purposes. Suppose I push a box along a surface that allows it to slide. When I initially start pushing it on one side, how long does it take ...
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3answers
985 views

Sending information faster than light

If I could ever send my friend any information faster than light it would violate causality. If he just guesses the information and acts on it before he could ever recieve it, everything is fine. What ...
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5answers
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What does 99.9% speed of light mean when there is no absolute velocity?

So when people say: 'I am approaching the speed of light, and to get to 100% light I would need infinite energy' they are essentially saying that this situation is impossible? I read this in ...
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2answers
732 views

Does light have initial velocity? [duplicate]

You are standing still in a vacuum, and you throw a ball that moves 10 m/s away from you. Now you start moving in one direction at 5 m/s, and throw the ball in the other direction, away from the ...
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2answers
436 views

Why does moving near light speed keep you young? [duplicate]

As was shown in the movie Interstellar, when you go close to a black hole or move near the speed of light in space, then your clock runs slower than a clock on Earth. In the movie, Matthew ...
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5answers
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Thought experiment regarding an object approaching a mirror

Here's a thought experiment I came up with in class today when my mind drifted (I however highly doubt I'm the first to think about this since it is pretty rudimentary) : Let's say superman ...
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5answers
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Why does the speed of light totally prevent instantaneous information exchange?

Based on the classical light-cone approach it's easy to see you can't transmit information faster than $c$ but why does the speed of light (as far as I know) treat information transmission in this way ...
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2answers
204 views

Non-locality in non-relativistic Quantum Mechanic

I guess the following obvious question is answered by any flavor of relativistic Quantum Mechanics, but I just wanted to check whether I understand correctly: Is it correct that nonrelativistic QM ...
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0answers
107 views

What're some criticisms of the paper “Six observations consistent with the electron neutrino being a tachyon with mass: mνe² = −0.11±0.016 eV²”?

Today I read about this paper making the case that neutrinos have imaginary mass and travel faster than light. I want to get excited, but I have no way to know how likely it is that this paper will be ...
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4answers
366 views

Faster-than-$c$ photons

As far as I know, according to quantum field theory, there are some photons that go faster than c, which is the speed of light in vacuum. However, there seems to be a paper and a corresponding ...
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4answers
651 views

Exploring beyond event horizons

In the expanding universe the velocity of separation between galaxies depends upon how far they are. If they are much far away will they have relative velocity of separation greater than speed of ...
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Faster than light possibility? [duplicate]

According to general relativity, speed is relative, so for example if you are running at 20 km/h and a car passes you at 30 km/h, the runner is actually moving at 50 km/h relative to the car. Now ...