Superluminal communication

Main article: Faster-than-light

Superluminal communication is the hypothetical process by which one might send information at faster-than-light (FTL) speeds. The current 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 fourth, 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.

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 argued that using the no-communication theorem to deduce the impossibility of superluminal communication is circular, since the no-communication theorem assumes that the system is composite.[3]

However, 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 experiment where the observation of an interference pattern on half of an ensemble of entangled pairs is determined by the type of measurement performed on the other half.[5][6][7] In these cases, though, the interference pattern only emerges with coincident measurements which requires a classical, subluminal communication channel between the two detectors. Physicist John G. Cramer at the University of Washington is attempting to perform one type of these experiment and demonstrate whether or not it can produce superluminal communication.[8][9][10]

See also

References

  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. ↑ Orthodox quantum theory does not permit superluminal entanglement communication. This is proved from the linearity and unitarity of the theory's premises. In May 1978 Jack Sarfatti filed for a patent for a "faster-than-light quantum communication system," which would be able, he said, to transmit a human voice instantly across vast distances without any possibility of eavesdropping.[47] That there could be no eavesdropping is now a feature of quantum cryptography, which did not exist in 1978. However, like Nick Herbert's FLASH (discussed by Kaiser) that led to the no-cloning theorem. Sarfatti's design also did not work because it depended on orthodox quantum theory whose linearity and Born probability rule assumptions forbid such communication between different subsystems of an entangled system. Sarfatti's research in this field has continued and is summarized here by John Walker: https://ricochet.com/saturday-night-science-flying-saucers-explained/ Sarfatti has introduced a new concept "back activity" nonlinear non-unitary "post-quantum physics," which is to quantum theory as general relativity is to special relativity. Using the work of David Bohm on pilot wave theory (1952 as extended by Yakir Aharonov and most recently by R. I. Sutherland, Sarfatti no longer uses the word "superluminal" which contradicts at least the spirit of Einstein's relativity if not the letter. It has been shown by Huw Price et-al http://prce.hu/centre_for_time/jtf/retro.html that retrocausal future causes of present effects explains what appears to be superluminal entanglement completely consistent with relativity. The post-quantum back-reaction of Bohm's "hidden variable" (aka "be able" J.S. Bell) on its pilot wave enables effective communication between parts of an entangled whole in violation of the no-signaling theorems of orthodox quantum theory. Post-quantum theory has been shown by Antony Valentini to permit hyper-computation in which P = NP http://arxiv.org/abs/quant-ph/0203049 Strekalov, D.; Sergienko, A.; Klyshko, D.; Shih, Y. (1 May 1995). "Observation of Two-Photon "Ghost" Interference and Diffraction" (PDF). Physical Review Letters 74 (18): 3600–3603. Bibcode:1995PhRvL..74.3600S. doi:10.1103/PhysRevLett.74.3600. PMID 10058246.
  6. ↑ Dopfer, Birgit (1998). Zwei Experimente zur Interferenz von Zwei-Photonen Zusẗanden (PhD Thesis) (PDF). Univ. Innsbruck.
  7. ↑ Zeilinger, Anton (1999). "Experiment and the foundations of quantum physics" (PDF). Reviews of Modern Physics 71 (2): 288–297. Bibcode:1999RvMPS..71..288Z. doi:10.1103/RevModPhys.71.S288.
  8. ↑ Cramer, John G. (3 April 2010). "Quantum Entanglement, Nonlocality, and Back-In-Time Messages". Norwescon 33.
  9. ↑ Paulson, Tom (14 November 2006). "Going for a blast into the real past". Seattle Post-Intelligencer. Retrieved 11 July 2011.
  10. ↑ Barry, Patrick (30 September 2006). "What's done is done… or is it?". New Scientist 191 (2571): 36–39. doi:10.1016/s0262-4079(06)60613-1. (subscription required)
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