# Tag Info

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The equivalence principle only holds for extremely small regions of spacetime. Which means they hold for short time intervals as well as small spatial regions. Consider an event near the event horizon. If the event is outside the horizon there might be a frame moving away from it that cover a very small region that is also completely outside the horizon and ...

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An object inside a black hole horizon cannot send signals outside of the horizon, but something falling into the black hole can fall through the signal. Take the example of the camera attached to the astronaut's foot. When the astronaut is halfway through the horizon, the camera is about a meter inside the horizon and the transmitter is about a meter ...

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First of all I would like to thank you for letting me participate of this discussion. I've been trying to get an answer for this question myself for at least six years now. Ever since I've realized that the experiment hasn't been done. Then one day in the same year (2009) I found a video on YouTube made by a German Blacksmith named Martin Grusenick. We've ...

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You have a good intuition on the possible answer because it does involve oscillations, but you need to visualize the string differently. The origin of the conundrum is not quantum, but relativistic. Here's why: Consider an inertial frame O and set up a string spanning the entire $x$ axis, stretching from $x \rightarrow -\infty$ to $x \rightarrow \infty$. ...

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You are not travelling faster than light in the sense that if you send some light to your destination it gets there before you do. It can be faster than light in the sense that if space is isotropically and homogeneously distributed with energy and such then there is an obvious global frame and distance in the global frame between two points can decrease ...

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In the context of this question please assume that the material is super-super strong and somehow a future human race has found a way to build a 24 billion meter long pole, and that there's a planet somewhere where there are no other nearby objects with lots of gravity to pull the pole around in outer space. If these are entirely unrealistic assumptions ...

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If you don't want to violate causality then you can only have a few types of faster than light travel. One is to not allow it to slow down. Another is to only allow it to go in one direction and hope the universe is infinite. Otherwise it is rather trivial to use regular slower than light motion between some FTL trips to generate a time machine. As for ...

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The diagram of the experiment has a large box bearing the legend "coincidence counter". The experiment is measuring fringes in the probability of a match in the photons' location. The probability for each individual photon to arrive at a specific place is not changed by different measurements. The probability of a match in location when the results are ...

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The entanglement is always based on pair production of the involved particles. And all thoughts about faster-then-light evaporates to dust, if one understand that the entangled parameters are given at the moment of the pair production. At the moment, we measure the entangled parameter from one of the particles our unknowledge about the parameter collapses. ...

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I'm still not certain I understand things correctly, but I'll answer my own question with my current understanding. There are different types of multi-particle quantum entangled states; GHZ is one of them. The proposed scenario with GHZ would NOT work. It mistakenly assumed that after one particle is measured, the other two would measure the opposite ...

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I am not sure I agree with the statement that this is not possible. Here is my scenario. We have two space explorers who both set off from Earth at the same time. Their destination is in opposite directions. The travel at the same speed. When they set-off from earth, at that time, a beam of entangled electrons are generated. One particle is transmitted ...

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First off, I want to point out that the word communication is a bit misleading. You cannot communicate information through quantum entanglement (No-communication theorem) If you try to measure the properties (spin) of, say, an electron $$|\psi_{electron}\rangle = \alpha |\uparrow\rangle + \beta |\downarrow \rangle,$$ you have the probability of measuring ...

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No. Wormholes do not play a role in entanglement. In fact, entangled particles don't 'communicate' in the usual sense; instead, they show nonlocal correlations which can sometimes exceed what you'd expect from, say, a pair of boxes containing socks of different colours. What Einstein got wrong wasn't the 'spooky', it was the 'action' - neither particle acts ...

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All conservative phenomena (not laws), do indeed, take a finite time to propagate, therefore "information" can't travel faster than light. Also, just because phenomena take time to propagate, does not mean that the phenomena are not being conserved at any given instant of time. In fact, there is no moment, when the phenomena are not conserved!

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Others have explained that they don't propagate. That's a real puzzler though, and the real question is how does the stuff (energy, charge, whatever) always add up when a transfer takes finite time? The answer to figuring that out was a profound pillar of modern physics: the field contains momentum (etc.). So while an electron is handshaking with another ...

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Possibly in the slightly negative energy region of a Casimir mirror pair However, the effect is really small

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There may be scope in this question to mention the faster than light (FTL) capabilities of Tachyons (should they exist). If (in the language of Speacial Relativity) we apply the first postulate of SR to tachyons and there is an instantaneous transmission of information in one inertial frame then it would be true to say this occurs in all inertial frames. I ...

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Let's look at an example, electromagnetism. The electromagnetic field (the combination of electric and magnetic fields) has momentum. Charges have momentum. The charge feels a force right where it is, a force based on the fields right where it is. This changes the momentum of the particle. The field loses an equal and opposite amount of momentum and also ...

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See https://en.wikipedia.org/wiki/Continuity_equation - I was just writing some text there that I think helps explain. Continuity equations are a stronger, local form of conservation laws. For example, the law of conservation of energy states that energy can neither be created nor destroyed—i.e., the total amount of energy is fixed. But this ...

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Conservation laws do not propagate instantaneously (or really at all), it really means that some property of the system does not change over time. In the case of momentum conservation, the information about the collision propagates (at most) at the speed of sound in the medium. This is why you see the cars continuing along their path during a collision: ...

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Conservation laws don't "propagate". They are inevitable consequences of symmetries of the dynamics by Noether's theorem, and the dynamics propagate with whatever finite speed they do.

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Exactly what here is referred to be "faster than light?"  By fast than light it means that if you put a light beam to your left and to your right and you ball take off like racers running towards a take across a finish line that you get to the finish line first. And how does this work? Are you clumping together a punch of exotic matter at the ...

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I think the comment was talking about a race type situation. For instance if you had a 50m dash with a bunch of runner lined up horizontally and running towards a horizontal finish line with some tape across the finish line they could race and see who hits the tape first. It is exactly (and only that sense) that the warp drive arrives first. Let's say ...

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