Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

1
vote
1answer
57 views

Faster than light in quantum gravity?

Imagine there's two objects a light second apart in a space with a certain metric. So no signal can reach the other under a second. But in quantum gravity where we sum over metrics, there may be a ...
-2
votes
0answers
46 views

Light's velocity is greater than velocity of light in vaccum [duplicate]

Suppose there's a light torch moving around its center with an angular velocity $\omega$. So the light which goes $r$ distance from the torch has a linear velocity $v=r\omega$. Now if $\omega =.5c $ ($...
-2
votes
0answers
43 views

Does a shadow truly have a speed? Is it an illusion? [duplicate]

If a shadow is no information, does that mean when you say a shadow is faster than the speed of light it is the equivalent of saying no information is faster than the speed of light? If a shadow is ...
1
vote
2answers
156 views

Why doesn't Faster Than Sound information transfer imply time travel or violate causality? [closed]

I am struggling to understand the answer to What are some scenarios where FTL information transfer would violate causality? In particular, I have not seen a satisfactory rebuttal to the comment from ...
0
votes
3answers
74 views

Does the Einsteins theory of a clock tower observed from a tram really explain time dilation?

We were shown a video in our class about time dilation which explained a Einstein's theory - the one where he was travelling in a tram and realized that if he travels at light speed, time will flow ...
3
votes
2answers
69 views

What happens if an object that is rotating very fast also travels very fast?

For example, if you throw a frisbee and it travels away from you while spinning clockwise. At any single point in time, the left side of the frisbee will be traveling away from you faster than the ...
0
votes
0answers
30 views

How is time dilation associated with a ship with an Alcubierre drive?

Would a round trip cause the astronaut to age less or more or the same as an Earthbound twin? Normally, time dilation works as length contraction (an astronaut would see length contract as 1/gamma, ...
-2
votes
2answers
58 views

What is a light cone? [closed]

What is a light cone? Why we can't escape the light cone? Why the speed of light being the limit for us to escape the cone the future and the past events of the light cone is that governs the future? ...
0
votes
3answers
55 views

Travelling at lights speed of light as universe expanding

I have read that the object, the light of which is reached us in 13.8 billion years is actually about 46 billion light years away from us now, due to the expanding Universe. Lets assume that we ...
1
vote
0answers
45 views

Why is the observable universe 90 billion light years in diametre? [duplicate]

The question is fairly simple, we know that the universe has been expanding for 13.8 billion years, so how did they determine the size of the universe that we can observe, and why can we not peek ...
1
vote
3answers
79 views

Speed of Light As a Maximum Speed Limit [duplicate]

I know the speed of light problem has been beaten do death by hundreds of questions and answers, but I wanted to explore a new possibility and perhaps show an indication that light-speed as a constant ...
1
vote
2answers
97 views

How can the Alcubierre drive itself move faster than light?

Assume that we have constructed an Alcubierre drive (we somehow managed to overcome all the difficulties). Now we want to want to move an object from galaxy A to galaxy B. We place it in the ...
1
vote
0answers
42 views

Can it be that apparent faster than light speed of shadow/laser dot is not actually faster than speed of light? [duplicate]

Many state that in fact laser dot or shadow can move faster than light but I beg to differ. My question, rather statement would be that nothing, not even apparent illusion of shadow or laser dot is ...
-1
votes
0answers
28 views

How are electromagnetic waves ejected along the axis of a black hole? [duplicate]

In the model of a black hole as shown. But I had a doubt that a stream of electromagnetic waves is ejected along the axis of black holes. How? But even light can't escape from it.
0
votes
1answer
46 views

Interpreting doubling of metric

Say you had coordinates $(x,y,z,t)$ and a beam of light traveling at speed=1. Now you make a change of coordinates $x'=\frac{1}{2}x, y'=\frac{1}{2}y, z'=\frac{1}{2}z, t'=t$ So now you have a metric ...
0
votes
0answers
28 views

How can the universe expand faster than the speed of light? [duplicate]

In Neil deGrasse Tyson's Astrophysics for People in a Hurry, he writes: By now, one second of time has passed. * The universe has grown to a few light-years across... If nothing can move ...
-4
votes
1answer
67 views

How is traveling back in time different from traveling at a negative velocity? [closed]

A simplified explanation of why you can't travel through space faster than the speed of light is that you are already traveling at the speed of light, through spacetime. If you are stationary in ...
-1
votes
1answer
34 views

Seeing the Big Bang [duplicate]

The Big Bang happened almost 14 Billion years ago. Theoretically speaking , if we could teleport (Instant teleportation) to somewhere that’s 20 Billion light years away from the Earth , if we looked ...
-1
votes
1answer
45 views

Why do the velocity components of molecules lose their independence when their velocity is more than speed of light?

In maxwell velocity distribution, maxwell assumed that the velocities of molecules are smaller than light, if the velocities are greater than light, then all the three components will no longer ...
-3
votes
3answers
164 views

What's the fuss over quantum entanglement about? Is it because people have misunderstood? [closed]

The first video I've seen about quantum entanglement claimed that changing A's spin will immediately take effect on B's spin as well. The more I read into this topic the less it seems that this is ...
2
votes
3answers
117 views

Faster-than-light communication using Taylor's theorem? [closed]

I was thinking about Taylor's theorem and how if a function $f(x)$ is analytic at a point $a$ and one can measure all the derivatives at $a$, $f^{(n)}(a)$ then one knows the complete behaviour of the ...
0
votes
3answers
118 views

Questions on Bell's theorem and Disproving the hidden variable theory

I'm not a physicist (computer science background), but always was fascinated with the concept of entanglement. As many, the first intuition I had was - well, the two particles share some knowledge ...
0
votes
1answer
117 views

Check where am I wrong. Here is how information can be sent faster than light [duplicate]

If I have a very long rigid rod which is of rectangular cross section and small mass. Let it's length be 1 light year and total mass be 1 kg now at one end if I rotate that rod, since the rod is rigid ...
-3
votes
4answers
122 views

Is the common interpretation of quantum entanglement just a perversion? [duplicate]

The idea of spooky action at a distance seems to imply that the information was always present at each end, but the common interpretation is that information can be transmitted instantaneously. Is ...
1
vote
0answers
34 views

How can black holes have charge and gravitate? [duplicate]

I seem to misunderstand the whole concept of calibration bosons. Let`s imagine a charged black hole. It does not let out anything that travels at any speed less than or equal to the speed of light, ...
0
votes
1answer
37 views

Can I change the speed of light in vacuum? [duplicate]

General theory of relativity proved that gravity does attract light ( photons ), what if I project a beam of light radially towards a black holes will it increases it's speed or not?
0
votes
0answers
36 views

Why can not we go faster than light? [duplicate]

The special theory of relativity implies that only particles with zero rest mass may travel at the speed of light but what's the actual reason. It days that if it happened we can perform time travel, ...
-4
votes
1answer
105 views

Can someone explain in a simple manner that How can we use Quantum entanglement to transfer data instantly when we seperate photons? [duplicate]

So I'm an IT engineer and i just watched a video about Quantum entanglement, that somehow when we split the entangled photons, any change happening to one of them will be reflected to the other one ...
2
votes
0answers
66 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 ...
1
vote
1answer
42 views

Entangled qubits measurement

I have two entangled qubits. I measure one of the qubits and get a 1. Am I correct in saying that the second qubit instantaneously collapsed to a correlated state, even before I measured it? Or does ...
0
votes
1answer
39 views

Is there a way to determine if one qubit of an EPR pair has collapsed after the other was measured?

My friend on the other side of the universe and I share the respective qubits of 2 EPR pairs. My friend measures one of the qubits, so one of my qubits will collapse. Must I measure this collapsed ...
0
votes
1answer
49 views

Why does quantum entanglement break?

Why does quantum entanglement break when the corresponding particles are intefered with? Is there possibly any way to actualy use it, such as in interstellar communication?
0
votes
1answer
53 views

How does going faster than light cause going backward in time? [duplicate]

I have read in many places that some virtual particles can "travel faster than light (1)" and thereby "go backwards in time (2)". My question is about the connection between these two. I have always ...
4
votes
3answers
188 views

Why can't a ladder sliding down a wall go faster than light?

I know the title sounds ridiculous, but when I took calculus in college we had a problem like this. The result seemed unreal to me, but I can't figure out the reason why it doesn't work. This was the ...
1
vote
0answers
55 views

How come no information can travel faster than light when we can measure a black hole's mass? [duplicate]

So I learned about the Schwartzchild radius, which is the radius of an object's event horizon. But how we define an event horizon is that it's a region of space where the gravitational acceleration ...
0
votes
0answers
31 views

Effects of negative energy density on properties of black hole horizon (and nearby spacetime)

Some background: Hawking's radiation (https://en.wikipedia.org/wiki/Hawking_radiation) is counter-intuitive in at least two sense. First is that it leads to a complete evaporation of the black hole in ...
1
vote
2answers
63 views

Do Electrons revolve with super-light speed? [closed]

Faster the particle, smaller wavelength. In the electron microscope, we use electrons because of its smaller wavelength? Does it mean electrons travel faster than light? Or simply measuring its ...
1
vote
3answers
192 views

What is the limiting factor of the speed of light?

Have been really struggling for some considerable time to understand the universal limitation of speed i.e. it is not possible to travel faster than the speed of light. In particular - what is the ...
0
votes
3answers
91 views

Quantum entanglement, how do we know there was no spin? [duplicate]

Im not a scientist, so go easy on the explanation! As I understand it we can create two entangled particles. The entangled particles have a spin property which is opposing. When we measure one of the ...
-1
votes
1answer
73 views

If instead of $c$ we reformulate the Lorentz transformations to have $c \rightarrow c+1$, would any law of physics be broken? [closed]

What I mean is that suppose we can go to a speed greater than the speed of light, i. e., $c+1$, with the speed of light still being $c$. That said, in my new transformations, two events couldn't ...
0
votes
0answers
12 views

Speed of the Accelerating Expansion of the Universe [duplicate]

So I heard that the universe is exponentially expanding faster than light, but I heard it just expands 72 km/s per megaparsec, I am not sure what is what, if someone can give me a logical or ...
0
votes
1answer
42 views

Speed of Light and Relative Velocity [duplicate]

Yesterday I was going through the idea of Relative Velocity in which, when the bodies are moving in opposite directions, their velocities add up. So, if one of the bodies in consideration is light, ...
4
votes
2answers
119 views

If quantum cloning was possible would entanglement enable faster than light communication?

Assume quantum mechanics allowed you to clone particles. How could you use quantum entanglement to communicate faster than the speed of light? In the 1980s a scientist proposed using quantum cloning ...
0
votes
1answer
74 views

Would communication of information from the future require a block time structure? [closed]

If faster-than-light travel (through wormhole tunneling or some other exotic means) was discovered in future, such that it allows information to be communicated from the future to the present, what ...
0
votes
1answer
52 views

Space expansion and speed of light

I recently saw a video on gravitational waves that says that expansion of space can only be measured due to changes in speed of light as everything else that could have been used to measure the ...
8
votes
2answers
5k views

Can the increase in thickness of a piece of paper which can be folded infinitely surpass the speed of light? [closed]

Supposing I have a piece of paper that can be folded infinitely. In the first $5 \, \mathrm{s}$, I fold it to twice its thickness. In the next $5 \, \mathrm{s}$, I fold it to 4 times. If I fold it to ...
-3
votes
1answer
120 views

Theory on how to break the speed of light [closed]

I am 14 years old and I think I have a good grasp on physics but I have a question. Imagine you were to shrink everything in the universe (except for yourself) down to the size of an atom and it was ...
0
votes
2answers
43 views

Does the location of the cosmic horizon depend on the local speed?

In the current cosmological model the observable universe is limited by a cosmic horizon. We can't see galaxies beyond the horizon. Imagine a spaceship in the vicinity of our horizon. If the ship is ...
3
votes
1answer
56 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 ...
2
votes
2answers
134 views

Does our Galaxy move at the speed of light? [closed]

I am not a physicist, but I have a few questions that bother me for a while: As we do not know if the Universe is infinite or not I assume we do not know our whereabouts in it; We know,though, there ...