Wednesday, October 23, 2013
Alice, Bob and Carol (story fragment)
Question 1: Alice and Bob want to exchange secret messages that Carol cannot crack. Explain how they can use quantum mechanics to communicate without Carol being able to eavesdrop.
Gwen stared hopelessly at the test paper in front of her. Had this been covered in class? She remembered nothing. Anyway, who cared about how, she thought. What mattered was why. Carol loves Bob, Gwen writes, and she thought that Bob loved her in return. But in truth Bob loves only Alice and so he wants to communicate secretly with her. Carol finds out, of course, because Alice carelessly gives herself away when she leaves her computer logged on, incriminating email in plain sight. Well, not far from plain sight, anyway, not so far that it takes Carol more than a few minutes of searching to find the messages Alice has exchanged with Bob.
Question 2: What is a black hole?
Bob's heart, writes Gwen. Bob's cheating, faithless heart is a black hole. Carol poured her feelings into it but nothing could escape it.
Question 3: Explain the concept of quantum entanglement.
Bob and Carol were entangled, writes Gwen. At least, Carol thought so. But Bob also became entangled with Alice. Quantum particles are monogamous, entangled strictly in pairs. In order to become entangled with a third particle, the first pair must break off their relationship. Apparently, not so with Bob, who cheerfully carried unknowing Carol along in his orbit while he circled Alice.