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It may not be a big market, but it’s presumably a lucrative one: To meet the needs of consumers who are in the business of transmitting classified national secrets, physicists are working on an absolutely secure communication system that uses the strange laws of quantum mechanics to encode information. The latest experiments in this field, called quantum cryptography, produced a system that researchers say would theoretically work to transmit information around the globe.

The system relies on a concept known as quantum entanglement to establish hack-proof communication. Entanglement allows two particles to be quantum-mechanically connected even when they are physically separated. Although the specific condition of either particle cannot be precisely known, taking measurements of one will instantly tell you something about the other. The trick can’t be used to actually send information, because each particle’s condition is random until it is measured. But entanglement can be used for encrypting data if a sender and a receiver make measurements on a number of entangled particles and then compare their results [Nature News].

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Of all the weirdness in the universe, the quantum mechanics phenomenon called “entanglement” may be the most mind-boggling. Physicists have long shaken their heads at the theory that two particles that become entangled will always and instantly mirror each other’s properties, no matter how far they are separated, which seems to go against all other physical understanding. In the everyday world, objects can organize themselves in just a few ways. For example, two people can coordinate their actions by talking directly with each other, or they can both receive instructions from a third source…. But quantum mechanics allows for a third way to coordinate information [Nature News].

Einstein rebelled against the notion of quantum entanglement, derisively calling it “spooky action at a distance”  [LiveScience]. Entanglement would look a lot less spooky if we could prove that an entangled object releases an unknown particle or some other signal at high speeds to influence its partner, giving the illusion of a simultaneous reaction [LiveScience]. But a new study shows that if some hidden signal is passing between the separated particles, it would have to travel at 10,000 times the speed of light. As this explanation seems impossible, the research team favors the alternate, weirder idea: that a measurement on one photon instantly influences the other [New Scientist].

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