I read a book about the Danish physicist Niels Bohr and his (now) quantum theory, written in about 1913. There was a description of the hydrogen atom, the simplest of all atoms – just one particle in the nucleus, the positive proton, and one negative electron circulating around it. I was about 14 years old.

I had read about how light, emitted from atoms which are greatly excited, defines a set of coloured ‘lines’ called spectral lines. These lines each have a wavelength which can be carefully measured. A Swiss schoolteacher named Johann Jakob Balmer measured the wavelengths, and developed a formula that predicted the wavelength of the lines accurately. ‘It’s like fingerprints of nature’, the book said.

Bohr found that the hydrogen atom, with its single electron attracted to the positive nucleus, would – if the electron were given extra energy – bounce back and radiate a colour of light, according to a formula. This formula had in it the value of the charge of the electron, the mass of the electron, a key number called Planck’s constant, and some πs and 2s. When worked out, Bohr’s picture of the atom gave exactly the same wavelengths of light as Balmer’s measurement.

This was the most amazing thing I had ever seen. Niels Bohr’s opinion of how a hydrogen atom worked, and the measurement of light from an excited hydrogen atom, agreed perfectly. Incredible! I was hooked.

Leon Lederman is coauthor of The God Particle: If the Universe Is the Answer, What Is the Question? (buy this book from Amazon (UK) or Amazon (USA)), and Symmetry and the Beautiful Universe (buy this book from Amazon (UK) or Amazon (USA)). See his website.