# Tagged Questions

"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 light accelerate as it nears a black hole? [duplicate]

As light is affected by gravity ( gravitational lending and black holes), it would seem that gravity causes acceleration. Acceleration has two parts: direction and magnitude. It is clearly evident ...
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### If a car is travelling faster than the speed of light, do the headlights still work? [closed]

If a car is travelling faster than the speed of light, do the headlights still work? If you can help because i really need to know i am going on a trip with my car tomorrow!
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### Front velocity and Superluminal group velocity

In some cases, according to Wikipedia, the envelope of a gaussian beam can go faster than speed of light hence leading to superluminal group velocity. However, the signal/energy still propagates at ...
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### Signal travels with speed greater than light breaks causality

Signal can't travel at speed greater than light speed in vacuum which is a assumption of special relativity. But if a signal travels at speed greater than $c$ then it will violate causality. I tried ...
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### What field property may allow faster than $c$ speed?

What field property may allow faster than $c$ speed? Is there theoretical field or what property it needs to have to allow wave speed larger than $c$? What is the speed of the gravitational wave? Is ...
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### Something almost faster than light traveling on something else almost faster than light [duplicate]

Possible Duplicate: Travelling faster than the speed of light Double light speed Lets say that an airplane can fly at 4/5 of the speed of light, and I can run at 2/5 of the speed of light, ...
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### Rate of expansion of universe during big bang [duplicate]

We say big bang was the explosion not in the space but of the space itself that took place in a fraction of seconds. Speaking practically, we say the universe has no edge and is infinite. If the ...
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### Is the GW150914 signal consistent with a superluminal gravity wave burst?

I've been following the news about the detection of gravity waves with interest and had a question for those with a physics background. I've gathered that the preferred explanation for GW150914 (Fig 1)...
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### Why relativity doesn't rule out Inflation theory? [duplicate]

Nothing can go faster than the speed of light, then how at the time of inflation space expanded faster than the speed of light? Clearly universe had already begun at the start (10−36 seconds) of ...
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### How is it that we can send signals faster than the speed of light?

I came across this while reading The Feynmann Lectures on Physics (Vol.1,Ch.7)- According to Newton, the gravitational effect is instantaneous, that is, if we were to move a mass, we would at once ...
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### Can space expand with unlimited speed?

According to this article on the European Space Agency web site just after the Big Bang and before inflation the currently observable universe was the size of a coin. One millionth of a second later ...
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### Is it accurate to say that nothing can travel faster than $c$ in a GR context, where more space can be created?

Years ago, my brother and I had an argument where I was trying to convince him that nothing could travel faster than the speed of light. I was pursuing this in the context of Special Relativity. My ...
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### Faster Than Light Communication Using Gravity?

Suppose two parties $A$ and $B$, some distance apart and at rest relative to each other both had control of one massive local object each. If party $A$ lifted their local object upward relative to $B$...
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### Speed bigger than light? [duplicate]

We know, according relativity theory, no information or matter can travel with velocity bigger than light. However, consider the following situation: a completely empty water hose is hypothetically ...
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### Do gravitational waves travel faster than light?

In Feb 12, 2016 edition of Times of India, an article read [with the discovery of gravitational waves, we will be able to] Track Supernovas hours before they're visible to any telescope because ...
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### Information can't travel faster than $c$

When we say that information cant travel faster than light, we mean that phase velocity can go beyond $c$ but the group velocity can't. Hence, we say that a plane wave carries no information. What I ...
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### Can absolute speed of object be measured? [closed]

Let's say there are two objects in space - Station and huge non-transparent sphere. Sphere starts to move from station 5000 km/h. Inside the sphere, beam of light is produced in direction the sphere ...
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### My theory to travel near the speed of light. Why will this theory not work? [closed]

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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### 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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### What will I see if I travelled to a distant planet in 100 times faster than speed of light and look back? [closed]

Consider this scenario. I enter a space ship at 10:00 AM, it starts to move at a speed 100 times faster than light, I travel for 55 mins. And then slow down to very much less than speed of light and ...
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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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### 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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### 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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### Does the special theory of relativity form the foundation of modern physics?

Does the Special Theory of Relativity "form" the foundation of Modern Physics? My question is in reference to Geoff Brumfiel's Scientific American article "Particles Found to Travel Faster than Speed ...
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### 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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### Does the induced Electric field develop instantly or lags by $\frac rc$?

Consider a loop of radius $r_0=3 \times 10^8$ cm. A thin bar magnet is passed through its center. This implies that the magnetic flux through the loop will change. Now according to Faraday's law a non ...
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### How does measurement affect multi-particle entangled particles?

It is my understanding that you can have two entangled particles, A and B, and measure their spins from two different angles, X and Y, such that: If you measure A using one angle (e.g. X), there's ...
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### 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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### Faster than light signals and the price to be paid if we accept them : a very simple protocol

Some physicists currently understand entanglement as transferring information instantaneously, yet not violating causality. Is this really a satisfactory explanation, or should be look for something ...
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### Neutrino unaffected by gravity

Are neutrinos affected by gravity? If not, could that be a plausible reason for a neutrino taking a shorter path than light, since light is affected by gravity?
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### 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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### 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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### 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 to ...
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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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### Double light speed

Let's say we have $2$ particles facing each other and traveling at speed of light Let's say I'm sitting on #$1$ particle so in my point of view #$2$ particle's speed is $c+c=2c$, double light speed? ...
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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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### Is quantum entanglement functionally equivalent to a measurement?

I saw the following talk the other day: http://www.youtube.com/watch?v=dEaecUuEqfc&feature=share In it, Dr. Ron Garret posits that entanglement isn't really that "special" of a property. He ...
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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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### Phase velocity greater then the speed of light?

It is my understanding the the phase velocity of a wave can be greater then the speed of light. So imagine we had a wave packet consisting of a single sinusoidal wave; $$y=\sin(\omega t-kx)$$ Then ...
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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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### Impulse travelling faster than light [duplicate]

There have been conducted many experiments in which light impulses traveled faster than light like the one in Princeton in 2000. This phenomenon has something to do with quantum entanglement. Does ...
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### 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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### 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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### 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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### 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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### 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). Couldn'...
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### 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 ...
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 \$...