Uncertainty principle demonstrated at macroscopic scale

Science News : Werner Heisenberg’s uncertainty principle is a central tenet of quantum mechanics. It states that one can’t have precise knowledge of both the position and momentum of a particle: Any method of measuring one of the two values for a particle would change both. Now Thomas Purdy and his colleagues at JILA in Boulder, Colorado, have demonstrated that the principle also holds true at the macroscopic level. The researchers created a drum by stretching a flexible silicon nitride skin across a frame 0.5 mm to a side, placed the drum between a pair of mirrors, and cooled the system to 4 K. They then shot a laser through the drum so that the photons bounced back and forth between the mirrors. The photons transferred momentum to the drum before entering a detector that calculated the drum’s position. The picometer-sized vibrations that resulted in the drum were in strict agreement with Heisenberg. Similar setups, albeit on a larger scale, are being used in an attempt to detect gravitational waves. The work of Purdy’s group will be useful for calibrating those instruments.