Heisenberg's Laser

The Heisenberg Uncertainty Principle is a long-established key component of quantum physics. It states that the minimum uncertainties in measurement of complementary variables (for example, momentum and position) are inversely proportional to each other. The more precisely we know one, the greater the uncertainty in the other. This is expressed mathematically as Dp Dx ≥ h/2p where p is momentum, x is position (distance from some point) and h is Planck’s Constant, approximately 6.63 x 10-34 J s or 4.14 x 1014 eV s.

This activity is designed to enable students to empirically demonstrate the Uncertainty Principle by measuring the uncertainties in position and momentum of photons in a laser beam. We direct the laser through a small opening resulting in diffraction of the beam. The size of the opening reveals Dx while the width of the central maximum gives us Dp. Changing the size of the opening changes the width of the central maximum.