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I often hear in physics videos light speed is the ultimate speedlimit two parts of the universe can communicate at, or even that speed of light is actual speed of causality.

Where does that notion come from and where do physicists get the confidence to say that when they don't have a complete theory of all forces . Signals can in theory be sent through wormholes or warp drives faster than light would carry the , I'm not saying warp drives exist I am saying they exist in theory, thus it is one exaplee how there can be faster than light communication, so what exactly does in physics forbid faster than light communication? What evidence is there( theoretical or physical of impossibility of the above)

My point is how does all thus relate to general questions of quantum mechanics and censorship conjectures. People are always quick to point out intengelment doesnt deliver info since info can't be delivered faster than light but this is just a presumption not a fact right?

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    $\begingroup$ @Matko, What theory permits a "warp drive" to exist? $\endgroup$ – Solomon Slow May 6 '19 at 14:49
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    $\begingroup$ @Will Presumably they are taking about something like an Alcubierre drive, which from my understanding would be similar to a worm hole in the sense that neither is really talking about FTL travel according to relativity, but to some observers it would appear that way. $\endgroup$ – JMac May 6 '19 at 14:55
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    $\begingroup$ Some inappropriate comments, and replies to them, have been removed. Be kind to each other, please. $\endgroup$ – rob May 6 '19 at 18:26
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Our theories of relativity state that it cannot go faster. However, you bring up a particular corner case that is worth noting. The theories state that nothing can go from one point to another faster than the fastest light can travel between them in a medium. Note I added a few extra words to the typical phrasing. It is not hard at all to move faster than light if you have the light take an especially slow path, such as bouncing it between a bunch of mirrors so it has to travel thousands of times the distance, or by passing it through a medium which slows light down.

In your wormhole case, you have created a path through spacetime between the two points. However fast you can transmit information through the wormhole, light can travel through that same wormhole at least as fast. This light will arrive at the second point much sooner than light which goes "the long way around." It's not the long way around path that matters for the information theoretic limits, it's the shortest path.

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  • $\begingroup$ My point is how does all thus relate to general questions of quantum mechanics and censorship conjectures. People are always quick to point out intengelment doesnt deliver info since info can't be delivered faster than light but this is just a presumption not a fact right? $\endgroup$ – Matko May 6 '19 at 19:25
  • $\begingroup$ I specifically stated light speed meaning c..not c/e $\endgroup$ – Matko May 6 '19 at 19:27
  • $\begingroup$ @Matko The case with entanglement is easier. Entanglement cannot deliver information faster than light because the math shows it cannot. That's an easy one because it specifies the mechanism, so its no longer proving a negative. Proving that no methods exist to go faster than light ends up requiring one to prove a negative. However, we have yet to see any indication that faster-than-light communications are possible, so that strongly suggests that, should it exist, that will require a major rewrite of physics as we know it. $\endgroup$ – Cort Ammon May 6 '19 at 20:57
  • $\begingroup$ But my point is FTL communication is not inconsistent with physics right? $\endgroup$ – Matko May 7 '19 at 8:14
  • $\begingroup$ I wanted proof by contradiction $\endgroup$ – Matko May 7 '19 at 8:15
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The notion comes from special relativity and the geometry of Minkowski space. To travel from point A to point B faster than light is prohibited because, essentially, there is no path available to make that journey. For example, suppose that we measure the distance between two points on a flat table to be 30 cm. Along what path will the distance between them be shorter than 30 cm? Such a path does not exist.

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  • $\begingroup$ Ok but just to clarify the notion is wrong or at least unproven right? $\endgroup$ – Matko May 6 '19 at 14:45
  • $\begingroup$ It is proven within the context of special relativity. Given the assumptions, the conclusion follows deductively. Whether it is true in reality cannot be proven in the same way. On the other hand, it can be easily disproven by demonstrating a counterexample. $\endgroup$ – Rodney Dunning May 6 '19 at 14:51
  • $\begingroup$ I am expecting a quantum mechanical answer because in classical physics ( relativity including) there is nothing about not being able to send info faster than light except in spacial cases like near minkowski spacetime.. $\endgroup$ – Matko May 6 '19 at 14:58
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    $\begingroup$ @Matko What he's saying is that the assertion "no information can travel faster than the speed of light" can be disproven via counterexample by demonstrating an experiment which shows a situation where the information travels faster than light. $\endgroup$ – Cort Ammon May 6 '19 at 14:59

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