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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Speed of light $> c$? [duplicate]

lets say we have two person A and B. Person A is holding a light source (lets call this light source 'S1') which is pointed towards north. Now person A starts moving at speed 0.86c WRT (with respect ...
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Is the photon an exception to Special Relativity?

This may have been asked before, but nonetheless I am unable to find it if so. We know Einstein's theory of relativity is confirmed experimentally, and so any postulations made in theory must be true. ...
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Can a shadow move faster than the speed of light? [duplicate]

I'm just a layman with no real science background (a) I'm not really sure what a shadow is. Some people are saying that it's the absence of something (a photon?) and therefore it is not subject to ...
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Help me understand this example about FTL = time travel [duplicate]

Searching for clear explanations of why FTL equals time travel I found this http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel Go at the bottom, when he draws the blue lines. He ...
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Why is the radius of the universe larger than? [duplicate]

It's always been in the back of my head that the Universe is 13.8~ billion years old and that the Observable Universe is 46~ billion light years in radius. How is this so? It would logically be only ...
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174 views

Spooky-action-at-distance, why it was claimed by Einstein?

If I understand "popular quantum mechanics" right, there is no faster-than-light communication via two entangled particles, because changing one of the particles (with the purpose to transfer a signal ...
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360 views

Can Quantum Teleportation be accomplished faster than the speed of light? [duplicate]

Let us say Alice wants to communicate state |T> (also a qubit) to Bob. Given, they have an EPR Pair shared amongst them. Alice interacts her qubit with |T> and then sends the measured state (classical ...
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3answers
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Why is this argument about light speed not true? [duplicate]

Long ago I was watching a scientific video about light speed. At one point, the person said to imagine the following scenario: You are on a train going from the Solar System to the Alpha Centauri ...
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721 views

What is the effect of gravitational field on an object moving at the speed of light? [closed]

If a body moving at the speed of light moves towards another stationary body having much greater mass then,this body makes the moving body to accelerate under its gravitational field in such a way ...
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Speed of light paradox?

So reading about how it's impossible to accelerate an object to the speed of light relative to another, I thought of this hypothetical situation: What if you had this row of rocks, floating in space ...
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From the speed of light being an invariant to being the maximum possible speed

As I understand it, the special theory of relativity is based on two principles - that there is no preferred inertial frame (which is common sensical once we realize that all motion is relative motion)...
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1answer
239 views

Superluminal clarification and FTL information transmission

Sixty Symbols recently released a video about superluminal motions (https://youtu.be/IsEDigUHsOQ). This sparked a question I hadn’t considered before – although, I’m fairly sure it must be rather ...
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Speed limitation [duplicate]

I was thinking about something and I wish to share this thought with you in order to understand better something that bothers me. Relativity theory says that the speed of light is the highest ...
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186 views

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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Finding the speed of laser spot

My friend and I were working on a problem which is to find the speed of the laser spot on the wall when you flick the laser pointer [ I know it can go faster than the speed of light as said in many ...
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A quantum entanglement experiment

Suppose we have an entangled electron-positron pair, such that total spin is zero. Separate them, and let Alice measure the spin (along $z$) of the electron, obtaining, say, $+\frac{1}{2}$. All the ...
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Can an object with mass travel at the speed of light?

according to the Einstein, no object mass with can reach the speed of light. but in the electron gun the speed of electron can be calculated from $$E_k = \frac{1}{2}mv^2 = eV$$ and because $m$ and $e$ ...
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294 views

Why do two objects traveling at the speed of light not collide at 2 times the speed of light?

I was watching a Brian Cox lecture, and he touched upon the notion that if two objects were moving towards eachother at the speed of light and collided, they would collide at no greater than the speed ...
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1answer
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Could we travel faster than the speed of light in a medium, but slower than the speed of light in vacuum?

It is well accepted that nothing with mass can travel at the speed of light in vacuum, $c$. Now let's say that a light wave is traveling through a medium that slows the wave's speed significantly (...
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4answers
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Acting on an object at a distance faster than light, or making small cogs immovable [duplicate]

Here's my question; If we have a line of connected cogs, arranged in such a way that for any one cog to move each other cog would necessarily have to move also, and that line of cogs were of an ...
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2answers
306 views

Is the speed of causality $c$ or $\frac{c}{\epsilon}$?

Is the speed of causality $c$ or $\frac{c}{\epsilon}$ where $c$ is the speed of light in vacuum and $\epsilon$ is the dielectric constant of the medium? I searched the net but could not find a good ...
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1answer
125 views

Faster than light communication

Assuming the right equipment why won't this scenario work? Two source devices capable of producing entangled photon pairs at set intervals and two detectors capable of descriminating the state of the ...
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Twin Paradox: Why does't the traveling twin measure faster-than-light photons on Earth?

Sorry if this question has been asked, but it was difficult to search through given the volume of Twin Paradox questions. Anyway. My question isn't with the twin paradox per se; it's with what the ...
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Faster than light movement and time travel simple explanation

I've read Stephen Hawking's Briefer History of Time and when it got to time travel back at faster than light speeds it felt natural to me. However a few months later when I talked to a friend I couldn'...
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If the universe is expanding faster than light speed does that mean that stars can intercept/overtake light photons that they have previously emitted?

If parts of the universe are accelerating faster than the speed of light does that mean that stars can catch up with and overtake the light photons that they have previously emitted traveling in the ...
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1answer
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The speed of light and electrons [duplicate]

In physics as we understand it today, can an electron be made to move faster than the speed of light in vacuum? Whether by natural causes, or man-made means?
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72 views

Can superfluids communicate faster than light?

According to this video: https://www.youtube.com/watch?v=ueVTzEB3tJ8 A superfluid "flows without friction" and "all of the atoms in a superfluid are in the same quantum state." What strikes me as odd ...
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4answers
778 views

Uncertainty principle and the speed of light

If an EM wave only gives us a probability of where a photon may be at a given moment, and the HUP tells us that we can't know the exact location of the photon. Then would it be correct to say that a ...
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1answer
67 views

Does a person feel a change in speed of data transfer when earth rotates?

This question has been bothering me for a while. The title wouldn't do justice with what i asked so let me put forth the scenario. Suppose a person lives on equator, he has a transmitter that he ...
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Scenario of Crossing the speed limit of our Universe [duplicate]

One of Important conclusions of Einstein's Theory of Relativity is that we cannot cross or break the speed limit set by the laws of physics that is the speed of causality consider this scenario: ...
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1answer
129 views

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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1answer
717 views

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

It is common knowledge that not even light can escape black holes, but since the black hole is emitting gravitons, and the gravitons travel in the direction away from the black hole, and it is ...
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3answers
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How matter waves travel faster than light?

I read this in my physics textbook. It says that matter waves travel faster than light. Why is it so? Also are matter waves G-Waves?
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587 views

What would be the implications of faster-than-light travel? [closed]

In $1994$, Miguel Alcubierre, a theoretical physicist and long-time Star Trek fan proposed a mathematically-sound method of manipulating spacetime to allow for faster-than-light travel, essentially ...
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4answers
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Can a rocket with no forces acting upon it except a single push force with constant acceleration keep accelerating forever?

I was wondering why a rocket with no opposing forces acting upon it couldn't keep accelerating given that it has the potential to release enough energy to maintain its acceleration at all costs. I ...
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1answer
85 views

Velocity of massless particles in $\mathrm{AdS}_4$ space-time

In spherical coordinates in a $(1+3)$-dimensional space-time one has the $\mathrm{AdS}_4$ metric $$ds^{2}=-\left(1+k^{2}r^{2}\right)dt^{2}+\left(1+k^{2}r^{2}\right)^{-1}dr^{2}+r^{2}d\Omega ^{2}.$$ ...
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Will observer measure a faster-than-light object in this example?

Have two ships $S$ and $T$. For simplification, lets make everything 1-dimension. In addition, instead of working with variables, I will work with numbers directly (easier). Shall we start? ...
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1answer
320 views

Can strings go faster than light?

I have been wondering if strings in string theory can go faster than light, as it is one dimensional when it does not vibrate? So do the same limits apply to it, I googled it but could not find a ...
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1answer
372 views

An infinitely long rod [duplicate]

Let's say I have an infinitely long rod which I use to pass information to my friend on the other end. If the rod moves towards my friend, it means I sent a 1 and if the rod moves away from my friend, ...
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1answer
649 views

can light go faster than light speed? [duplicate]

Foreword. Since light can't escape from a black hole, we can assume that light is influenced by gravity. So I can imagine that light that would otherwise escape from a black hole is in fact ...
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2answers
42 views

To go to a distance which is far with the speed of linght in time smaller than the distance light can not go [closed]

My question is this say that we have a particle and this particle will go to a place that is 200 light years away and we want to go there in 10 light years. Is this possible?
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2answers
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Alcubierre Drive: Visibility

Suppose if you were standing still relatively looking at an active Alcubierre Drive. I am aware of the fact that if you are inside an Alcubierre bubble you would not be able to see outside of it. I ...
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3answers
144 views

If an infinite universe containing only a single object, is the object at rest?

Imagine there exists only a single object (say a 1 metre sphere). There is nothing else in all directions. Is the object moving or at rest? Is it even possible to tell, given that there is no frame ...
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What is the evidence that distant galaxies are moving away from us with speeds greater than $c$, due to space expansion?

I came up with this query after @Rob Jeffries's answer to a previous question of mine. So, is there any evidence that distant galaxies are moving away from us with speeds greater than $c$, due to ...
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A rope tied to another galaxy

Suppose there is a strong stiff rope tied to a distant galaxy. The rope is so long that it passes by us here on Earth. If the galaxy is so far away that it moves away from us faster than the speed of ...
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0answers
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Hubble's Law paradigm [duplicate]

I have seen a video on Khan Academy about the Hubble's law. And my question is if the "Hubble's constant" increases by (70.6 km/sec)/parsec then could we reach such a velocity that it gets faster ...
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Is this equivalent to Einstein's postulates of Special Relativity?

Einstein's postulates of Special Relativity are: The laws of Physics look the same in all inertial reference frames; The speed of light is always observed with the same value $c$ in every reference ...
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4answers
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Expansion of space vs movement within space [duplicate]

I understand that some very distant objects (galaxies) are moving away from us at speeds exceeding the speed of light and that such expansion induced speed is not limited by the theory of relativity. ...
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1answer
61 views

Quantum Tunnelling and $c$

What prevents a particle travelling at a speed infinitesimally smaller than that of $c$ tunnelling a slightly further distance than it would have otherwise and thus have travelled faster than the ...
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2answers
214 views

Prepared states and quantum entanglement [duplicate]

Imagine two entangled quantum particles in the singlet state, one held by Alice and the other by Bob. Alice and Bob are both widely separated. Bob measures his spin in some axis and finds it to be ...