The results were astonishing: a magnetic field tuned to 1.3 MHz (that is, oscillating at 1.3 million cycles per second), thousands of times weaker than even the earth’s field, could nevertheless disrupt the birds’ ability to orientate themselves. But increasing or decreasing the frequency of the field made it less effective. So the field appeared to be resonating with something vibrating at very high frequencies in the avian compass: clearly not a conventional magnetite-based compass, but something consistent with an entangled radical pair in a superposition of singlet and triplet states.
