For your eyes only

浪子

Weird quantum connections won't let you break Einstein's ultimate speed limit. But they will help you keep a secret

The EPR paradox would be truly alarming -- as opposed to just puzzling -- if you could dabble with the spooky communication between the two particles to transmit an instantaneous message. If you could somehow choose the outcome of a measurement at your end, you would simultaneously engineer the outcome at the other end because of the way the two particles are entangled. The spooky connection would then let you send a message immediately to someone light years away. That would spell big problems for relativity theory, which strictly forbids any meaningful signals from travelling faster than the speed of light.

But Einstein can rest easy. This stratagem won't won't work because the result of your measurement can only ever be a fifty-fifty shot. You have no control over what is measured at your end, let alone the other.

That's not quite the end of the story, though. It's true you can't use the spooky connection to beat the speed of light, but you can use it to send ultra-secure coded messages. Not only that, but quantum theory actually lets you know if a spy has tried to tamper with your message.

Mathematicians have devised a variety of codes that depend on the use of a "key"--a number known only to the person sending a message and the recipient. Here's how it works. The sender transforms a written message into a set of binary digits, then scrambles the digits by applying a mathematical transformation using the key. The recipient receives the scrambled signal, undoes the mathematical transformation using the key, and thereby reconstructs the original message. Simple.

hilary

<>it's sure a good article</P><>but it seems to be too specialized</P><>i mean physics</P><>you know, i'm rather poor at physics</P><>but what i wonder is</P><>why do you give it the name of "for my eyes only"?</P><>wait for your reply</P>