RICHARD FEYNMAN called the fine structure constant, alpha, “one of the greatest damn mysteries of physics: a magic number”. One puzzle is whether this constant of nature has always had the same value. A signal from the early universe could answer that.
Alpha determines the strength of the electromagnetic force. Its value can be calculated by studying the so-called 21-cm line in the spectrum of neutral hydrogen atoms in the universe. The spectrum has a blip at a wavelength of 21 centimetres because the atoms absorb light at this wavelength in a manner that depends on alpha.
To find out…
