Energy-free communications

According to the laws of physics, you have to expend energy to communicate. It turns out, though, that you don't have to send that energy to the other party. This is useful because communications that happen without sending energy to another party are theoretically impervious to eavesdroppers.

A study by a Texas A&M University researcher shows that two parties can communicate without putting energy into the communications channel by modulating and monitoring the channel's natural noise.

In ordinary communications, signals are transmitted using light or electricity. In contrast, the researchers' scheme uses ever present temperature fluctuations or zero-point energy. Zero-point energy consists of virtual particles like photons that pop in and out of existence in a vacuum. Because eavesdropping on such a signal either alters the characteristics of the noise in the channel or throws off the timing of signals, it is always possible to detect any eavesdroppers.

The method could eventually be used to provide potentially perfectly secure communications.

Stealth Communication: Zero-Power Classical Communication, Zero-Quantum Quantum Communication and Environmental-Noise Communication
abstract
http://arxiv.org/abs/physics/0508135

complete paper (PDF)
http://arxiv.org/pdf/physics/0508135