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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Time dilation due to space expansion

As we observe a remote galaxy, we see it with a redshift. The most distant galaxy discovered to date is GN-z11 visible with the redshift of $z=11.09$. For simplicity, let's assume no gravitational ...
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Quantum Entanglement - faster than light communication [duplicate]

very new here - first question in fact. So, don't be fooled by the title of my question. I understand that the Bell Paradox - and non-locality - prevents information being exchanged in a faster than ...
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How is faster than light travel analogous to time travel? [duplicate]

According to this video, faster than light travel is analogous to time travel. Does this mean that if I could instantly teleport 1 light year away, and then sent a laser pulse to my friend, my friend ...
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Performing Three Consecutive Measurements in Different Bases on Entangled Particles

Suppose Alice and Bob each have a spin-$\frac{1}{2}$ particle which are entangled in the spin-$0$ state $ \lvert 0, 0 \rangle = \frac{1}{\sqrt{2}} \lvert +z, -z \rangle + \frac{1}{\sqrt{2}} \lvert -...
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Faster than light: A thought experiment involving gravitational forces between two masses

Well, I'm in a way, not qualified to ask this question as I've just started physics and presently learning Newtonian mechanics. Still I'm asking this out of curiosity, but quite serious as I am ...
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Relativistic speed and quantum entanglement [duplicate]

Just a thought experiment. First we entangle two particles, and then send one of them on a space journey, make it travel really fast. First we synchronize the watches, of course. So, after some time ...
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Is it physically possible for gravity to accelerate an object with mass to the speed of light? [duplicate]

Is it physically possible for an object to achieve the speed of light if it is in a gravitational field strong enough and the mass does not collide before it attains a velocity of $c$? It is true that ...
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How can light speed be measured relatively? [duplicate]

Following scenario: Two rockets leave a planet, heading opposite direction. Assuming the rockets are capable of accelariting highly - when would there be a barrier? Einstein said, nothing can be ...
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Time dilation and length contraction for light and how this is interpreted where space is expanding faster than the speed of light

First off I am an engineer and not a scientist. Consequently my course work emphasized classical mechanics and I was never formally introduced to topics like relativity and quantum mechanics in ...
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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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Reason for Nothing Moving Faster than the Speed of Light

I’m currently in the process of learning about special relativity, of which one fundamental concept is that nothing can move faster than the speed of light. There appear to be numerous sources for ...
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Do the electrical and magnetic fields around a photon move faster than the speed of light?

I have seen similar questions to this, but I can't seem to get a firm answer. My understanding is that photons move in straight lines at the speed of light. These photons have perpendicular electrical ...
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Time dilation beyond cosmic horizon

The observable universe is limited by a cosmic horizon. Galaxies beyond the horizon move away from us faster than light, so we cannot see them. If we could see a planet close to our horizon, we would ...
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Superluminal speed at cosmic horizon [duplicate]

The observable universe is limited by a cosmic horizon. Galaxies beyond the horizon move away from us faster than light, so we cannot see them. Imagine a spaceship in the vicinity of our horizon. If ...
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Super Fast Message [duplicate]

It is known that a shadow can travel faster than the speed of light and break no known laws of physics, because it is not an actual thing. A shadow is just the blockage of light. However in the ...
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How can quantum entanglement not be non-local?

I know this kind of question has been brought up many times.I have read many posts here regarding this but I still have a problem with a certain aspect of it so please bear with me. Lets consider the ...
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Is my argument deducing from Maxwells equations the exclusion of faster than light travel flawed?

When Maxwell's equations are solved, one of the solutions is electromagnetic waves that should move at a certain speed ($c = \frac{1}{\sqrt{\mu_0 \epsilon_0}}$). Now, one could argue that since ...
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Photons are faster than the speed of light because they travel in transversal waves?

This is my first time posting here, I am a school student who is just curious. So today I was wondering about how light works and how it travels, and this thought came to my mind: Light is made of ...
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How do we know tachyons don't exist?

As I mentioned yesterday, Hollywood screenwriter working on a TV pilot about physics trying to get the details right. What empirical evidence is there that tachyons do not exist? I understand that ...
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Causality in quantum field theory with particles going faster than light

So I have read Feynman's QED, and it seemed to me from this that, if we are to build any sort of semi-intuitive picture of what particles might be doing, we have to account for particles going faster ...
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Why do the neutrinos (with mass) from a supernova arrive before the light (no mass)?

I've already read the below questions (and their answers) regarding neutrinos vs. electromagnetic waves propagating through space, but I'm still not clear on something. Neutrinos arrived before the ...
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Do neutrinos travel faster than light? [duplicate]

There are particles like tachyon which moves faster than light theoretically,does this holds good enough for neutrinos?
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What is the relationship between the absolute nature of the speed of light and the indeterminate nature of Heisenberg’s uncertainty principle? [duplicate]

What is the relationship between the absolute nature of the speed of light and the indeterminate nature of Heisenberg’s uncertainty principle? Or to phase it differently, can any of a particle’s many ...
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Why specifically does FTL violate causality? [duplicate]

Take this non-FTL scenario, involving a phone call and the postal service. I send a postcard to my friend in Paris, asking whether they would like to visit me. Since it will take some time to arrive,...
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Special Relativity

Does special relativity require faster than light information transfer to verify length contraction and time dilation? How does the "outside observer" measure these variables? I guess the outside ...
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Causality and speed of light

It is accepted that the speed of light is the speed of causality. If we exceed the speed of light, the order of cause and effect breaks down. This happens as we see our surroundings moving backward in ...
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Problem related to tachyon particles [duplicate]

Are Tachyons practically possible to exist? if they are how can we harness them? I have already tried finding answers but none are satisfactory. please help.
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How much time will it take to move an object whose length is equal to one light year?

Suppose there's a stick whose length is one light year and I push it from one side by one centimeter. How much time would it take for its other side to move by one centimeter and why?
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How fast is information transferred between the two entangled particles? [duplicate]

In the process of 'teleporting' a photon with a pair of entangled electrons, how is the information transferred between the two entangled particles? Could it be that the information is travelling at ...
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5answers
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Does light travel faster if fired in the direction of Earth's rotation as opposed to against it?

Recently I entertained a silly thought about if the earth's rotation can be "harnessed" to do work. So my question is: We know that earths rotation is eastward. If i set up 2 mirrors on 2 different ...
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Why a body can not be accelerated to speed of light in vacuum? [duplicate]

Well i know that it needs infinite energy..but the term infinite is itself not physical so i am not satisfied with this answer ...but what would happen if we provide a constant acceleration to an ...
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Is velocity a vector in relativity?

Adding two velocities which are comparable to the speed of light does not obey vector addition rules. eg: I am moving at a velocity $c/2$ wrt you along $x$ axis. I throw an object with $c/2$ ...
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Travelling at a speed faster than light [closed]

Imagine yourself to be bat. You cant see anything. You don't have eyes. All you can do is echolocate, using ultrasound. Now imagine something is moving away from you faster than the speed of sound. ...
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If you fall for a long enough period of time, would you eventually hit or break the speed of light? [duplicate]

If you theoretically fall through an infinite hole, and since the longer or higher you fall, the faster you would progressively go, would you eventually hit or even surpass the speed of light, and if ...
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How would items consumed by an Alcubierre Drive warp bubble pass?

Sorry in advance for my lack of physics knowledge, but I have a question as relates to the theory of Alcubierre drives and warp bubbles. If I understand this I might be able to "get it". Let's ...
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Entanglement question

If photons A and B are entangled and A shows, say, spin up, then B will show spin down. My question is, can a researcher change the spin of A, say by putting it through some kind of filter? If so, ...
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What Is The Reference Frame For The Velocity Of An Object In The Universe?

As I understand it, movement of two objects is relative to one another. Velocity is always in relation of one thing to another. A car travels at 100km/h (60mi/h) relative to the rotating Earth surface ...
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Do string-wave functions always spread superluminally?

When one calculate the amplitude for a particle to propagate between two points, the results seems to violate causality. One book that makes some comments about this is Peskin & Schroeder, chapter ...
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Where is the scientific evidence to support the assertion that nothing can travel faster than light in vacuum? [duplicate]

It is true that so far, nothing has ever been observed to travel faster than light in vacuum. However, just because nothing so far has yet to travel faster than light does not mean that nothing in the ...
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Is there non-locality in the AdS/CFT?

Many String theorists are trying to restore bulk locality in the AdS/CFT. So does that mean the CFT, the boundary, is non-local? Does matter travel faster than light on the CFT?
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Potential FTL Implications of quantum “weak measurement”?

Physics noob here. I can't find a good answer to this thought experiment that is consistent with general relativity and It's really bothering me. I'm probably missing something huge but just can't ...
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1answer
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Mutually inaccessible galaxies

It is said the farthest galaxy we can see in one direction is beyond the cosmic horizon of the farthest galaxy we can see in the opposite direction; they can't see each other. Doesn't this contradict ...
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Superluminal Thought Experiment [duplicate]

If I had a weightless, indestructible rod that was 1,145,915,590 meters long and I moved it 15° would the end of the rod go faster than the speed of light? (Assuming it's path is unobstructed.) ...
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Can we slow down light? And then travel faster than it? [duplicate]

Well, first of all, I am not a physics major, just a high school student. Watching a bit of cosmos and some physics at school got me thinking about this. Well, the earth exerts acceleration due to ...
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Do quantum particles communicate?

So, 2 days ago I learned that quantum entanglement is just about our perception. There is not an active link between particles and they are not communicating with each other. But then, while surfing ...
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Can a component of velocity be greater than the speed of light?

Suppose a particle is travelling with a velocity v. Can a component of this velocity(let's say the y-component) be greater than the speed of light c?
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Does the Milky way have relativistic mass against galaxies which are moving away from it at high speeds?

According to the article cited behind, and to a post in Astronomy SE , there are galaxies moving away from Milky Way faster than light, even at speeds of 2.3c . According to this article Can two ...
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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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308 views

What can you say about an event outside your Light-Cone? [closed]

I'm taking a Special Relativity course and lately I've been wondering about this thing for some time. Imagine I'm at the origin of my spacetime lattice (hope I can say this), and I've synchronized ...
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Why is light bent but not accelerated?

Light is bent near a mass (for example when passing close to the sun as demonstrated in the famous sun eclipse of 1919). I interpret this as an effect of gravity on the light. However, it seems (to ...