If Time Flowed Backwards, Who Would Ever Know

Norman F. Ramsey, Higgins Professor of Physics, has recently conducted research which gives strong support to theories that nature would look the same if time flowed backwards.

It is physically impossible for time to actually flow backwards; you can't relive Gettysburg. However, there is a lack of experimental evidence to prove that the actions of the fundamental particles of nature would be different if they ran backwards.

Ramsey, two Harvard grad students, and a physicist at Oak Ridge National Laboratory in Tennessee began investigating the charge properties of the neutron early last summer to check time reversal theories.

Under time reversal the neutron would reverse the direction of its spin. If the particle had an electric dipole moment--a plus and a minus charge arranged in dumbell fashion--the field created by this charge structure would change when its spin was reversed.

Thus, if the particle had a dipole, that alone would be enough evidence to show that time is non-invariant.

Ramsey and his colleagues began by putting very slow neutrons in a weak magnetic field, causing them to precess like tops. These spinning neutrons were directed through a strong electric field which would cause a dipole to change its precession frequency. However, the physicists recorded no change in the spinning of the neutron.

Previous work on the charge structure of the neutron had determined that if a dipole existed, the dipole moment divided by the charge on the proton of the particle must be less than 5 x 10 to the negative 20th centimeter. Ramsey's work through January, 1968, has lowered this limit by a factor of 1000, and still no evidence for the existence of the dipole has been found.

Ramsey plans to continue the experiment with certain refinements in order to lower the limit approximately ten times, or to discover the size of the dipole.