A Quantum Game

Bell came up with “nonlocal” games, which require players to be at a distance from each other with no way to communicate. Each player answers a question. The players win or lose based on the compatibility of their answers. One such game is the magic square game. There are two players, Alice and Bob, each with a 3-by-3 grid. A referee tells Alice to fill out one particular row in the grid — say the second row — by putting either a 1 or a 0 in each box, such that the sum of the number...

 Blockchains

Ownership on the Bitcoin blockchain is determined by a pair of cryptographic keys. The first, called the public key, resides in the blockchain for anyone to see. The second is called the private key, and its owner keeps it safe from view. The two keys have a special mathematical relationship that makes them useful for signing digital messages. Here’s how that happens: Helmut takes a message, combines it with his private key, does some calculations, and ends up with a long number. Anyone who...

 The Gevulot

‘It’s a nice thought.’ He offers her his hand. ‘I am Paul. I got a little lost: all those moving streets. I was hoping you could tell me the way out.’ A trickle of emotion bleeds through his rough visitor’s gevulot: a sense of unease, a weight, a guilt. Xuexue can imagine the old man of the sea sitting on his back. It feels very familiar. And suddenly it is more important to talk to the stranger than to smile at the robot. ‘Sure I can,’ she says. ‘But why don’t you stay ...