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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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, ...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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176 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?
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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Speed of light limitations [duplicate]

In any circular cyclotron, how can the proton projectiles approach each other at more than 50% of the speed of light without exceeding the speed of light relative to each other?
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Do gluons move faster than light?

Gluons are massless so move at the speed of light. Gluons also are supposed to exchange gluons themselves. Wouldn't this require the gluons which are exchanged between gluons to move even faster than ...
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Could we construct an experiment to measure the speed of light greater than c?

As I understood we were not able but then i read John Rennie's question and answer here: Does light really travel more slowly near a massive body? And got me a little bit curious. He says: We ...
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Would particles in this container go over light speed? [duplicate]

Imagine a container which contains a speaker and gas at normal pressure inside. Now imagine it moving at almost light speed (maybe c-100m/s) if the speaker makes a sound, causing particles to move at ...
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1answer
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Pulling a Metal Bar in Space [duplicate]

Let's say I have a metal bar (which does not expand or contract at all) that's 1 light-second long which is connected to a block at the end. I am in space holding the other end of the bar. If I pull ...
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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, ...
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Is it a coincidence that non-relativistic quantum mechanics prevents superluminal communication?

So non-relativistic quantum mechanics prevents superluminal communication. Given a bipartite state $\rho_{AB}$, the reduced density operators for systems $A$ and $B$ are given by the partial traces $$...
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Can relative velocity of a particle exceed the speed of light? [duplicate]

Consider two particles (having same mass) moving with constant velocity very close to speed of light, say $0.99c$ in opposite directions. Will the magnitude of their relative velocities exceed the ...
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A question regarding information [duplicate]

Consider a continuous system of cogs which extend from the sun to the earth. Light takes eight minutes to reach the earth. However, if one was to rotate the initial cog(near the sun) then the all the ...
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Relativity and the addition of speed [closed]

Two rockets, that can each travel slightly faster than half of the speed of light, are launched from opposite sides of the planet. Why isn't rocket A traveling faster than the speed of light relative ...
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4answers
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Observing an event in the past?

I'm writing a Sci Fi novel and I'm trying to come up with a (fairly) realistic or at least vaguely plausible mechanism for this person's ability to exist and function. Hypothetically, would it be ...
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Speed of Light & Distance [duplicate]

If I have a transmitter that signals a relay which turns off a light off which is 300 000 km away – it has travelled at the speed of light. If I connected a rope (which does not stretch) which is ...
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Faster than the speed of light [closed]

Could I ask a question about light? Let's say light travels at a $45^{\circ}$ angle, so the vector velocity would be (c, c) i.e. travels c on the x axis and c on the y axis. Then wouldn't the ...
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Could this be faster than the speed of light? [duplicate]

Let's say that I have some type of long bar. It is perfectly incompressible. On one side I have a sensor that detects any force. On the other end, I hit the bar with a hammer. From the moment my ...
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1answer
149 views

If tachyons existed, would we modify the theory of relativity?

In relativity tachyons cannot exist and they are theoretically viewed as objects with imaginary mass according to relativity, but since tachyons violate relativity, why do we use this theory to ...
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136 views

Special Relativity-Simultaneity

If two events are simultaneous in one reference frame, are they simultaneous in all reference frames? Please provide thorough qualitative explanation If blue light is going at speed $c$, with red ...
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Light and force

We know that photons also have momentum though they do not have mass given by the equation : $E=pc$ Then why can't we apply force to light? I mean we can apply fore and increase its momentum and ...
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Matter beyond the event horizon should time travel? [duplicate]

when anything passes the event horizon of a blackhole, it must be moving faster than light as even light cannot escape. So then, shoundnt it time travel?
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Distance change per time and velocity not the same is Special relativity? [duplicate]

Many formulas in Special relativity have v - velocity. And theory says there is no absolute velocity only relative and it cannot be greater than speed of light. Consider this thought experiment: ...
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491 views

Quantum entanglement used for FTL communication? [duplicate]

I'm aware of many ideas people have come up with for this question. I understand why they don't work. However I was thinking about another method involving an array of multiple entangled particles. ...
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140 views

What prevents two objects from falling toward each other faster than the speed of light?

I was thinking about what happens when two objects fall toward each other in space. The farther apart they are when they begin falling, the faster they will be traveling when they hit each other due ...
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Can someone explain this causality argument about the speed of light from Special Relativity?

I was watching this Yale lecture by R. Shankar. From 8:29 to 15:05, he gives an argument for why theory of relativity "demands" that it should be impossible for events to influence other events ...
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What would prevent two black holes from hitting speed of light in the flowing scenario?

If two super massive black hole are 10 l.y away and completely still relative to one another... They will start moving towards each other due gravity but they will never reach each other due universal ...
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Faster than light in a medium [duplicate]

It is a remarkable well-stablished fact that the light velocity in vacuum, $c \simeq 3.10^8 m/s$ is the upper limit for the velocity of ordinary matter, never to be achieved. It is also well-...
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How viable is using Quantum Entanglement for long distance communication? [duplicate]

In fiction, (notably Ernest Cline's novel Armada and Charles Stross's books Singularity Sky and Iron Sunrise) Quantum Entanglement is used for long distance communication. In reality, given our ...
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If mass is invariant then why cant we travel faster than light? [duplicate]

I recently learned that relativistic mass isn't actually real or popular and that mass is actually invariant and not dependent on velocity. My entire sense of why we couldn't travel faster than light ...