ABSTRACT
I was at a conference in the Los Angeles Convention Centre in 2001. I had a spare morning or afternoon; I forget which. I decided I would visit the nearby Griffith Observatory Museum, which was a short taxi ride away. The exhibit at the time showed the hydrogen spectra of stars recorded by Edwin Hubble (1889–1953). These were compared with those on Earth, i.e. the laboratory spectra. According to the brightness of a particular type of star, which allowed its distance from Earth to be estimated, a method developed previously by Henrietta Leavitt (1868–1921), the spectra from different stars were placed one above the other according to their distance from Earth; those measured on Earth in the physics laboratory were also given as a reference. The spectral lines gradually showed a bigger and bigger shift in their position towards longer wavelengths. This is the so called ‘red shift’ effect. This means that the more distant the star is from Earth the greater its speed is in receding away from us. These are the observational, experimental, raw data that underpin our knowledge that not only is the universe expanding but also, if we were to count back in time, there must be a moment when all matter in the universe was concentrated at a single place. There must then have been an almighty explosion at the start which is referred to as the ‘Big Bang’. Incidentally, we are not at the centre of that Big Bang. We too are receding from our neighbours as they are receding from us.
