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.
943
questions
3
votes
1
answer
74
views
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 ...
- 268
3
votes
1
answer
666
views
Superluminal travel without time travel
Can superluminal travel or communication be possible without leading to the possibility of closed timelike curves (CTCs) and causality violations?
I have seen conflicting opinions regarding this ...
- 1,398
3
votes
1
answer
239
views
Many times speed of light [duplicate]
http://www.huffingtonpost.com/2014/03/24/theory-of-everything-big-bang-discovery_n_5019126.html
What does "many times speed of light" really mean in this context? For a layman it's easy to draw wrong ...
- 225
3
votes
4
answers
1k
views
Break speed of light with infinite mass
I've heard that a spacecraft could never exceed the speed of light because it's (relativistic) mass quickly approaches infinity and therefore there could never create a big enough rocket to propel it ...
- 942
3
votes
2
answers
3k
views
Can we determine whether or not a particle is entangled?
Suppose Shaniqua and Tyrone have four pairs, a, b, c, and d, of entangled particles. They take their particles and go very far apart. If Tyrone can determine whether or not a particle is still ...
- 141
3
votes
2
answers
137
views
How does the "York time" measure the expansion of space; why is it equal to the divergence of the comoving observer's four velocity for warp drive?
The mysterious York time, θ is important in warp drive topic. It is plotted on the famous diagrams and is considered the measure of the mechanism that "drives" the warp drive bubble at ...
3
votes
1
answer
184
views
Richard Feynman Nobel Lecture, typo error?
In the Richard P. Feynman Nobel Lecture, I think I saw a typo in his explanation of the retarded waves. I post it there because I did not saw anywhere on the web someone who noticed it. It is an old ...
- 83
3
votes
2
answers
368
views
Is this solution for interstellar travel viable?
I have in mind a way to enable FTL travel. Is this way viable?
In the paper:
"Weighing the vacuum with the Archimedes experiment"
we can see the dependency of the gravitational repulsion ...
- 113
3
votes
1
answer
108
views
Why can’t an elementary particle be forced to have a particular outcome in an entangled pair?
I read in a blog Quantum Entanglement: Slower Than Light that one can not force a particle from an EPR pair to have a not statistical outcome for the entanglement parameter. I can not understand why? ...
- 641
3
votes
1
answer
73
views
An electron in time
I've read many times now that when one measures the spin of an entangled electron (for example) the state of its partner is known instantaneously and this is true across any theoretical distance.
...
- 89
3
votes
1
answer
745
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 ...
3
votes
1
answer
457
views
Is the GW150914 signal consistent with a superluminal gravitational wave burst?
I've been following the news about the detection of gravitational waves with interest and had a question for those with a physics background. I've gathered that the preferred explanation for GW150914 (...
- 870
3
votes
2
answers
382
views
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 ...
user32348
3
votes
2
answers
634
views
How does gravitation propagate along curved spacetime?
In this wikipedia article it is described how a beam of light, with its locally constant speed, can travel "faster than light". That is to say it travels a distance, which, from a special ...
- 8,453
3
votes
1
answer
176
views
Collision of hypothetical Tachyon with normal particle?
If we are dealing in one dimension, what will happen if a hypothetical particle Tachyon (pure imaginary rest mass, $v>c$ and real momentum & total relativistic energy)? Will it interact with ...
3
votes
4
answers
1k
views
Is the maximum possible measurable velocity = 2c
What is the maximum velocity that can be measured between two objects? Is $2c$ the correct answer?
Two photons (A & B) are emitted simultaneously from my position; photon A going north and ...
- 39
3
votes
2
answers
2k
views
Klein-Gordon equation and wave velocity
It looks like solutions of the KG eqn travel faster than light, because if
$$\omega^2 - k^2 = m^2$$
then
$$\mid\ \omega\mid \ > \ \mid k\ \mid$$
and I thought the wave velocity was $\omega / k$.
...
- 261
3
votes
3
answers
925
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 ...
- 517
3
votes
1
answer
630
views
Exploiting the Heisenberg Uncertainty Principle as a means to communicate
It seems as though I've come across a rather unusual conclusion that could either simply be a misinterpretation or a contradictory discovery. I seem to have found a way to utilize the Heisenberg ...
- 3,831
3
votes
1
answer
991
views
Relative Speed vs speed of light [duplicate]
Possible Duplicate:
Travelling faster than the speed of light
Someting almost faster than light traveling on something else almost faster than light
I've got two questions which are related and ...
- 203
3
votes
1
answer
323
views
Can we observe the universe expanding faster than light?
I am looking at the sky, and I see two objects moving away from each other with speed greater than the speed of light.
Light from one object is not fast enough to reach the other. So I decided to help ...
- 2,117
3
votes
1
answer
602
views
Does phase velocity or group velocity change when light enters a new material? Contradictory sources
I'm so confused. I've read in this book (page 28) that group velocity of light can exceed $c$ in certain gases. However a lot of people online and in the forums say that phase velocity can exceed $c$.
...
- 133
3
votes
1
answer
147
views
A telegram from Mars
Say, people fly to Mars, get in trouble, and want to send us a SOS signal. The average distance is 225 Gm, so they must wait 25 minutes to hear our response at the speed of light. This may just be too ...
- 12.6k
3
votes
1
answer
151
views
Black Hole rotation and acceleration
I have been reading some about the black holes and the rotation about it, and have also heard about the fastest spinning black hole (NGC 1365), which as I understand, its rotation is 86% the speed of ...
- 97
3
votes
1
answer
141
views
Can scatter interference patterns from entangled pairs carry information?
I am having problems wrap around why you can't send information faster than light with a similar setup to the quantum eraser experiment. ( https://arxiv.org/abs/quant-ph/9903047v1 )
What I mean is, ...
- 175
3
votes
1
answer
491
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 ...
- 6,826
3
votes
1
answer
103
views
Spacetime that allows matter to rotate faster-than-light
Is there a solution to Einstein's equations which allows:
the object to be rotating at sub-light speed when viewed from within itself.
for a distant observer the object to rotate at superluminal ...
- 131
3
votes
0
answers
224
views
How warp drive could be faster than light? [closed]
If the speed of gravity is as fast as the speed of light then there is no way a warp drive could curve the fabric of spacetime faster than the speed of light. Then how does a warp drive actually make ...
- 141
3
votes
0
answers
93
views
Why can't quantum tunnelling carry energy or information faster than light?
A few experimenters have at one time or another claimed that quantum tunnelling allows the transfer of information or energy at superluminal speeds.
One was the idea that music was carried across a ...
- 7,372
3
votes
0
answers
80
views
Why does FTL not leave behind a motion blur? [closed]
I once thought anything traveling faster than light would leave behind a motion blur that on one end recedes at the speed of light and at the other increases at the velocity of the object. If an ...
- 131
3
votes
1
answer
95
views
Is it possible that the universe is not expanding faster than the speed of light? [closed]
What if the speed of light increases proportionately to the expansion of space? Is it possible that light traveling in the medium of space gets to travel faster if the medium is expanding? An analogy ...
- 31
3
votes
1
answer
106
views
Faster than light speed transfer of certain event
I am CS/Math person I am not quite sure what it means in physics
information cannot be transferred faster than light (FTL). I tried to understand the proof of no transfer theorem but I lacked the ...
- 31
3
votes
0
answers
57
views
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 ...
- 12.6k
3
votes
5
answers
575
views
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 ...
- 215
3
votes
2
answers
799
views
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 ...
- 153
3
votes
0
answers
474
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?
...
- 243
3
votes
1
answer
132
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 ...
- 258
3
votes
0
answers
158
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 ...
- 172
3
votes
1
answer
316
views
Relative speed when getting close to the speed of light
I was thinking about the relative speed of an observation reference frame and an object which has been accelerated to a speed close to the speed of light. I'm by no mean an expert and the last physics ...
- 31
3
votes
3
answers
686
views
Does light travel faster in between Casimir plates?
Speed of light is in general $c/n$ where $n$ is a refractive index. But for example introducing two parallel plates with very small spatial separation will perturb the energy density of vacuum ...
- 856
2
votes
3
answers
673
views
If it turns out that neutrinos do travel at faster than lightspeed, how will the success of special relativity be explained?
As per in the title. If it turns out that neutrinos do travel faster than the speed of light, how will the success of special relativity be explained? My apologies if this has been asked before; I've ...
2
votes
2
answers
317
views
A problem with $E = mc^2$
(Rest) mass of proton = (rest) mass of neutron (approximately) = $1.67 \times 10^{-27}$ kg.
let $m$ be the mass of nitrogen atom then $m = 2.32 \times 10^{-26}$ kg.
$c = 3 \times 10^8$ m/s (approx).
...
- 173
2
votes
2
answers
2k
views
Can gravity accelerate an object past the speed of light?
Imagine we have something very heavy (i.e supermassive black hole) and some object that we can throw with 0.999999 speed of light (i.e proton). We are throwing our particle in the direction of hole. ...
- 151
2
votes
2
answers
325
views
Proof for impossibility of FTL Signals
Is there is formal proof for the fact that signals must always travel at a speed less than the speed of light in a vacuum?
I understand that special relativity dictates that for massive particles to ...
- 171
2
votes
2
answers
329
views
Is pulling a string instantaneous at both ends? Why is it or isn't it? [duplicate]
This is a question that has bothered me for quite some time but I don't have a clue where to start in researching it.
Let's say we have a string which is arbitrarily long, light enough to not take ...
- 23
2
votes
1
answer
591
views
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 ...
- 183
2
votes
2
answers
1k
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 ...
- 131
2
votes
1
answer
277
views
Dark energy as negative matter for Alcubierre drive
Can dark energy be used for the Alcubierre drive as a substitute for negative mass? After all, to make the Alcubierre drive work, it is necessary to expand the universe behind it, and that is what ...
- 23
2
votes
2
answers
3k
views
Are virtual particles limited by the speed of light? [duplicate]
I have recently been reading about Quantum Electrodynamics which I found very interesting, but even more confusing.
I understand photons mediate the electromagnetic force and interactions between ...
2
votes
3
answers
2k
views
Does this count as moving faster than light?
I'm not familiar with any complicated physics equation, however I do understand some basics. Suppose there is two objects, both of them are moving away from each other in a 3-dimensional space, which ...
- 167