If you were a spy, how could you ensure that an encrypted message got safely to your allies? Send it using entangled particles! Here, watch how a technique called quantum cryptography could save a state secret from falling into enemy hands.

Major funding for "The Fabric of the Cosmos" is provided by the National Science Foundation.

Additional funding for this program is provided by the Arthur Vining Davis Foundations.

National corporate funding for NOVA is provided by The Boeing Company. Major funding for NOVA is provided by David H. Koch, the Corporation for Public Broadcasting, and PBS viewers.