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 to show that a if $v > c$ there is a frame which breaks causality in special relativity?
I'm reading about special relativity and looking at the Lorentz transformations.
I'm reading that:
If $v > c$, we can find a frame in which $t_2' < t_1'$, i.e. a signal arrived before being ...
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Isn't the universe older than 13.8 billion years? [duplicate]
To preface this, I'm not an expert, I'm just an avid astronomer with little mathematical knowledge.
I was watching a video that was explaining the cosmic scale and how the observable universe is only ...
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Simultaneous measurements of two entangled particles [duplicate]
Experimental evidence reject the local hidden variable theory, so let's say quantum mechanics is right and the wave function does instantaneously collapse upon measurement.
Suppose we have two ...
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Can an object appear to be moving faster than light due to time dilation?
If I were to travel tword earth from a distant star at .9 C, I would see that earth would be experiencing more time than I would, but does this mean that I would see earth approaching at more than the ...
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Nonlocality of a bug on movie screen
I am currently learning quantum mechanics using Griffiths. In the appendix, he goes to talk about EPR and Bell's inequality, and that experimental verification of Bell's inequality rejects the "...
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What is the state of an entangled photon after its twin is absorbed?
Let's two photons are entangled in polarization after a laser beam passes through a Betha Barium Borate crystal. They take different paths and one of them (1) is absorbed in a black sheet. What is the ...
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Quantum Entaglement and EPR [closed]
I was studying the EPR Paradox and Bell's theorem . My question is how does this information travel between two entangled particles, has there been any research into this?
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Is it possible to test if the entangled twin of a particle has already been measured or not? [duplicate]
Suppose a pair of entangled particles having opposite up/down spins are produced on Earth.
These two particles are then separated, one remaining on Earth, and the entangled pair being brought by ...
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Does it matter when we measure the spin of the other entangled particle?
Let's say, we have 2 entangled particles: A and B which are a light-year away from each other.
We know if we measure the spin of particle A, we can be certain the spin of particle B will be in the ...
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Why do we assume that we can change the past by sending signals backwards in time? [closed]
This might be a stupid question, but hang in with me-
From what I've seen, the biggest argument against superluminal signaling is that you would be able to send a message backwards in time that could ...
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Where can I learn more about superluminal signaling in curved spacetimes?
Typically, when discussing superluminal signaling in flat spacetime (specifically, how particles travelling faster than the speed of light can travel backwards in time in the frame of reference of a ...
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A simple counter-example to the no-communication theorem? [duplicate]
Let's say Alice and Bob would like to communicate through entangled qubits. They have a machine that generates qubits in the state
$$
| \psi \rangle = \alpha | 0 0 \rangle + \beta | 1 1 \rangle .
$$
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When does the distribution change in interference/which way measurements compared to the time of the type change of the measurement?
Does anyone know of any experiments that have looked at the temporal relationships of this?
Measurements that show the dual nature of the particle/wave are well known. The fundamental feature of which ...
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Space falling faster than light after it falls inside the event horizon of a black hole?
Typing my question directly so people know what I am asking, afterwards providing background and context.
Q: What does it mean when space is falling, faster than light?
(I am specifically wondering ...
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Why does the Alcubierre drive need a negative energy ring specifically?
Now, maybe this is a result of my poor understanding of spacetime, but a theoretical warp bubble contracts space in front, and expands it in the back. Positive energy always contracts, so I get the ...
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