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Quantum Ansible
 Image from Steve Bowers | |
| A supposed 'Quantum Ansible' link between 38 Arietis and the Pleiades Cluster, which would allow instantaneous communications. This method of communication remains a myth or rumour, and is probably impossible due to problems with reverse time travel (which seems to be forbidden in this universe, since it would lead to causality violations). | |
Quantum entanglement is a phenomenon in which two or more particles become interlinked such that measuring the quantum state of one particle affects the outcome of a measurement taken of a second particle. Perhaps the simplest example of this can be seen in a photon passing through a polarization filter: the photon is split into two lower-energy photons by the filter, each of which exists in a superposition of two possible polarization states (vertical or horizontal), and which also must exhibit opposing polarizations in order for the total angular momentum of the system to be conserved (i.e. if one photon is vertically polarized, the other must necessarily be horizontally polarized). If the polarization state of one photon is measured, thereby collapsing the wavefunction of the photon into one of the two possible options, then the polarization state of the second photon will invariably be found to be the opposite of the first. This rule holds true even if the photons are many light-years apart when they are measured, and the timing of the measurements is such that there is not enough time for light (and thus information) to have traveled between the locations where the measurements were taken.
This remarkable property of quantum systems has long captured the imagination of modosophont fabulists and engineers alike, for whom the seemingly instantaneous communication between entangled particles evokes the notion of sending messages across interstellar distances faster than the speed of light would otherwise permit. However, it has been known even since the early history of quantum mechanics during the Atomic and Information Ages on Old Earth that quantum entanglement cannot be used as a basis for faster-than-light communication: quantum wavefunctions collapse in a purely random and probabilistic manner, and thus it is impossible to use the outcomes of quantum measurements to encode meaningful information.
Despite this well-established and empirically verifiable fact, there have been countless instances across the history of Terragen civilization (and beyond, according to the recorded histories of various xenosophont cultures) where charlatans, scammers and con artists have claimed to have discovered a workaround enabling faster-than-light communication using quantum entanglement, or else claim to have stumbled upon or been gifted clarketech artifacts that can accomplish this feat. Commonly referred to as "quantum ansibles", these devices have invariably failed to hold up to professional scrutiny, with the "instantaneous" communications they seemingly allow almost always being revealed to be elaborate illusions facilitated by co-conspirators separated in time and space.
Many modosophonts believe that quantum ansible technology is employed by the archailects to communicate across interstellar distances; while much of the technology developed and used by higher transapients remains impenetrable to modosophont-accessible scientific methods, and the archailects themselves have on numerous occasions demonstrated preternatural foresight or seemingly inexplicable knowledge of far-distant events, all observations to date have remained consistent with these being a product of their prodigious simulation and prediction capabilities rather than actual causality-violating communication.
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Development Notes
Text by Andrew P.
expanded 3 July 2025 from an original by an M. Alan Kazlev, with additions by Anders Sandberg
Initially published on 19 December 2001.
expanded 3 July 2025 from an original by an M. Alan Kazlev, with additions by Anders Sandberg
Initially published on 19 December 2001.
Additional Information
A link to an essay by former contributor Richard Baker about faster-than-light communications, that shows that this would lead to causality violations.
http://www.theculture.org/rich/sharpblue/archives/000089.html (...faster than light travel or communication, special relativity and causality cannot coexist.)
http://www.theculture.org/rich/sharpblue/archives/000089.html (...faster than light travel or communication, special relativity and causality cannot coexist.)
