What’s rarely mentioned today about Aschoff and Wever’s famous bunker, built just a few years later, is that it contained not just one underground apartment, but two. The parallel units were almost identical, with matching beds, kitchens, and record players. But there was a very important difference: One of them was completely enclosed within a hefty capsule of cork, coiled wire, glass wool, and steel, through which no electromagnetic radiation could pass; anyone living inside was completely cut off from the Earth’s magnetic field. The aim was to show that the shielding made no difference to the volunteers’ biological clocks, and prove, once and for all, that Brown was wrong.
Between 1964 and 1970, more than 80 volunteers stayed in the two units. As Aschoff predicted, their circadian rhythms did continue. But there was a problem; the results in the two groups were not the same. In the unshielded bunker, isolated from clocks and sunlight but still exposed to magnetic fields, people’s sleep and waking patterns departed from the solar day, reaching an average period of 24.8 hours.
But when magnetic fields were also blocked, the volunteers’ circadian cycles deteriorated further. Their day length slipped even longer. There was significantly more variation between individuals. And their different rhythms were much more likely to become uncoupled. As mentioned earlier, Aschoff championed desynchronization as one of his key discoveries. Yet over those six years, it only ever occurred in the shielded bunker, cut off from the Earth’s magnetic field. Wever found that if he exposed the volunteers to a similar artificial field, all of these effects were reversed.