Magnetic monopole search, past and present

The feature article by Arttu Rajantie describes the various hypotheses concerning the existence of magnetic monopoles and attempts to discover them. However, it did not cover some of the earlier efforts―in particular, those by Henry Kolm and by Luis Alvarez. Both men thought that a search for magnetic monopoles in deep-sea sediments might be productive because in deeper parts of the oceans, the sedimentation rate is about 1 millimeter per millennium. With a constant supply of extraterrestrial material, the slow sedimentation rate would help in finding monopoles because they would be more concentrated than in other sediments.

I was involved in both of those attempts because of my interest in deep-sea sediments and their ability to record polarity changes in Earth’s magnetic field. ¹ Alvarez’s method at the University of California, Berkeley, was to take a sample of sediment and pass it through a circular solenoid; the current in the solenoid would have increased each time a monopole passed by. I do not believe Alvarez had any positive results.

Kolm was a staff member at the Francis Bitter National Magnet Laboratory at MIT, and his method was to move the sediment across a strong magnetic field, ² which would cause a monopole to be dragged out from within a magnetic particle, pulled through the magnetic field, and then trapped in an emulsion. He received barrels full of sediment off a vessel from the Scripps Institution of Oceanography working in the Pacific Ocean and one from the University of Miami working in the Atlantic, but he saw nothing in them that was very promising. He then designed a magnetic rake to be towed behind a vessel and dragged through the sediment. The idea was to gather magnetic particles that might have collected monopoles and to sample a much greater volume of sediment than could be provided with barrel dredges. I do not believe he obtained any positive results.