Superluminal communication

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Superluminal communication is the hypothetical process by which one might send information at faster-than-light (FTL) speeds. The scientific consensus is that faster-than-light communication is not possible and to date superluminal communication has not been achieved in any experiment.

Some theories and experiments include:

According to the currently accepted theory, three of those four phenomena do not produce superluminal communication, even though they may give that appearance under some conditions. The third, tachyons, arguably do not exist as their existence is hypothetical; even if their existence were to be proven, attempts to quantize them appear to indicate that they may not be used for superluminal communication, because experiments to produce or absorb tachyons cannot be fully controlled.[1]

If wormholes are possible, then ordinary subluminal methods of communication could be sent through them to achieve superluminal transmission speeds. Considering the immense 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 theories of wormhole formation would prevent them from ever becoming "timeholes", allowing superluminal communication without the additional complication of allowing communication with the past.[citation needed]

The microscopic causality postulate of axiomatic quantum field theory implies the impossibility of superluminal communication using phenomena whose behavior can be described by orthodox quantum field theory.[2] 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.

Some authors have pointed out that using the no-communication theorem to deduce the impossibility of superluminal communication is circular, since the no-communication theorem assumes to start with that the system is a composite system.[3] However, these authors do not address the proofs of the impossibility of superluminal communication which depend on the microcausality postulate rather than on the no-communication theorem.

Birgit Dopfer's experiment[edit]

Although such communication is prohibited in the thought experiment described above, some argue that superluminal communication could be achieved via quantum entanglement using other methods that don't rely on cloning a quantum system. One suggested method would use an ensemble of entangled particles to transmit information,[4] similar to a type of quantum eraser experiments.[5][6][7]

Birgit Dopfer, a student of Anton Zeilinger's, has performed an experiment which seems to make possible superluminal communication through an unexpected collective behaviour of two beams of entangled photons, one of which passes through a double-slit, utilising the creation of a distance interference pattern as bit 0 and the lack of a distance interference pattern as bit 1 (or vice versa), without any other classical channel.[6][8] Since it is a collective and probabilistic phenomenon, no quantum information about the single particles is cloned and, accordingly, the no cloning theorem remains inviolate.[9][10][11] Physicist John G. Cramer at the University of Washington is attempting to replicate Dopfer's experiment and demonstrate whether or not it can produce superluminal communication.[12][13][14][15]

See also[edit]

References[edit]

  1. ^ Feinberg, Gerald (1967). "Possibility of Faster-Than-Light Particles". Physical Review 159 (5): 1089–1105. Bibcode:1967PhRv..159.1089F. doi:10.1103/PhysRev.159.1089. 
  2. ^ Eberhard, Phillippe H.; Ross, Ronald R. (1989), "Quantum field theory cannot provide faster than light communication", Foundations of Physics Letters 2 (2) 
  3. ^ Peacock, K.A.; Hepburn, B. (1999). "Begging the Signaling Question: Quantum Signaling and the Dynamics of Multiparticle Systems". Proceedings of the Meeting of the Society of Exact Philosophy. 
  4. ^ Millis, M.G.; Davis, E.W., eds. (2009). Frontiers of Propulsion Science. Progress in astronautics and aeronautics. American Institute of Aeronautics and Astronautics. pp. 509–530. 
  5. ^ Strekalov, D.; Sergienko, A.; Klyshko, D.; Shih, Y. (1 May 1995). "Observation of Two-Photon "Ghost" Interference and Diffraction". Physical Review Letters 74 (18): 3600–3603. Bibcode:1995PhRvL..74.3600S. doi:10.1103/PhysRevLett.74.3600. PMID 10058246. 
  6. ^ a b Dopfer, Birgit (1998). Zwei Experimente zur Interferenz von Zwei-Photonen Zusẗanden (PhD Thesis). Univ. Innsbruck. 
  7. ^ Zeilinger, Anton (1999). "Experiment and the foundations of quantum physics". Reviews of Modern Physics 71 (2): 288–297. Bibcode:1999RvMPS..71..288Z. doi:10.1103/RevModPhys.71.S288. 
  8. ^ The reason why her results are still controversial is the fact that she actually used a classical channel in order to reduce the background noise. It is currently not possible to certainty determine whether the classical channel in such a setup is necessary just to remedy the current lack of technology, or there is something deeper that makes it unavoidable.
  9. ^ Jensen, Raymond (2006). Is faster-than-light communication possible using entangled photonsand a double slit?. 
  10. ^ Paulson, Tom (14 November 2006). "Going for a blast into the real past". Seattle Post-Intelligencer. Retrieved 11 July 2011. 
  11. ^ Barry, Patrick (30 September 2006). "What's done is done… or is it?". New Scientist 191 (2571): 36–39.  (subscription required)
  12. ^ Cramer, John G. (3 April 2010). "Quantum Entanglement, Nonlocality, and Back-In-Time Messages". Norwescon 33. 
  13. ^ Friedlander, Paul. "Experiment". paulfriedlander.com. 
  14. ^ Paulson, Tom (14 November 2006). "Going for a blast into the real past". Seattle Post-Intelligencer. Retrieved 11 July 2011. 
  15. ^ Barry, Patrick (30 September 2006). "What's done is done… or is it?". New Scientist 191 (2571): 36–39.  (subscription required)