Editing Faster-than-light communication (section)

==Proposed mechanisms==
[[File:Faster than light implies time travel diagram.svg|thumb|Spacetime diagram showing that moving faster than light implies time travel in the context of special relativity. A spaceship departs from Earth from A to C slower than light. At B, Earth emits a tachyon, particle that travels faster than light but forward in time in Earth's reference frame. It reaches the spaceship at C. The spaceship then sends another tachyon back to Earth from C to D. This tachyon also travels forward in time in the spaceship's reference frame. This effectively allows Earth to send a signal from B to D, back in time.]]

===Tachyons===
[[Tachyon|Tachyonic particles]] are hypothetical particles that travel faster than light, which could conceivably allow for superluminal communication. Because such a particle would violate the known laws of physics, many scientists reject the idea that they exist.<ref name=Tipler/> By contrast, [[tachyonic field]]s{{snd}}quantum fields with imaginary mass{{snd}}do exist and exhibit superluminal [[group velocity]] under some circumstances. However, such fields have luminal [[signal velocity]] and do not allow superluminal communication.<ref name=Randall/>

===Quantum nonlocality===
[[Quantum mechanics]] is non-local in the sense that distant systems can be [[quantum entanglement|entangled]]. Entangled states lead to correlations in the results of otherwise random measurements, even when the measurements are made nearly simultaneously and at far distant points. The impossibility of superluminal communication led Einstein, Podolsky, and Rosen to propose that quantum mechanics must be incomplete (see [[EPR paradox]]).

However, it is now well understood that quantum entanglement does not allow any influence or information to propagate superluminally.

Practically, any attempt to force one member of an entangled pair of particles into a particular quantum state, breaks the entanglement between the two particles. That is to say, the other member of the entangled pair is completely unaffected{{Dubious|Incorrect description using "completely unaffected" and "random"|date=October 2024}} by this "forcing" action, and its quantum state remains random;{{Dubious|Incorrect description using "completely unaffected" and "random"|date=October 2024}} a preferred outcome cannot be encoded into a quantum measurement.<ref>{{Cite web |last=Siegel |first=Ethan |title=No, We Still Can't Use Quantum Entanglement To Communicate Faster Than Light |url=https://www.forbes.com/sites/startswithabang/2020/01/02/no-we-still-cant-use-quantum-entanglement-to-communicate-faster-than-light/ |access-date=2024-05-28 |website=Forbes |language=en}}</ref>

Technically, the [[Wightman axioms#W3 .28local commutativity or microscopic causality.29|microscopic causality postulate]] of [[axiomatic quantum field theory]] implies the impossibility of superluminal communication using any phenomena whose behavior can be described by orthodox quantum field theory.<ref name="Eberhard" /> A special case of this is the [[no-communication theorem]], which prevents communication using the [[quantum entanglement]] of a composite system shared between two spacelike-separated observers.

===Wormholes===
If [[wormhole]]s are possible, then ordinary subluminal methods of communication could be sent through them to achieve effectively superluminal transmission speeds across non-local regions of spacetime.<ref>{{Cite web |last=Morris |first=Brandon Q. |date=2021-03-16 |title=Tiny Wormholes May Be Usable for Interstellar Communication |url=https://thedebrief.org/tiny-wormholes-may-be-usable-for-interstellar-communication/ |access-date=2023-01-06 |website=The Debrief |language=en-US}}</ref> Considering the immense energy or [[exotic matter]] with [[negative mass]]/[[negative energy]] that current theories suggest would be required to open a wormhole large enough to pass [[spacecraft]] through, it may be that only atomic-scale wormholes would be practical to build, limiting their use solely to information transmission. Some hypotheses of wormhole formation would prevent them from ever becoming "timeholes", allowing superluminal communication without the additional complication of allowing communication with the past.<ref name="urlSkinny wormholes could send messages through time | New Scientist">{{cite web |url=https://www.newscientist.com/article/dn25596-skinny-wormholes-could-send-messages-through-time/ |title=Skinny wormholes could send messages through time &#124; New Scientist }}</ref>