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Letter: Superluminal siblings

Published 19 September 2007

From Nick Webb

Robbie and Fred are twins who live together. Wearing identical suits, they leave their house at the same time heading in opposite directions. One twin carries a hidden green wallet; the other has a red one. The wallets are not visible.

Unfortunately, Robbie is mugged and the redness of his wallet is revealed. In quantum terms he is measured and forced to take a value.

An observer can now deduce that Fred’s wallet is green, and if put to the test this will prove to be the case no matter where or when Fred is interrogated.

There is no need for faster-than-light communication or spooky interaction at distance – just knowledge of the initial conditions. I can’t see anything wrong with this analogy. Am I missing something?

• No, it’s exactly right.

London, UK

Issue no. 2622 published 22 September 2007

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