Unravelling the Big Bang with Planck

The Planck satellite is named after the German physicist Max Planck (1858-1947, pictured to the left). In attempting to explain the spectrum of ‘black body’ radiation (the radiation emitted from a perfect absorber) Planck introduced the concept of energy quanta. This was the first step towards quantum mechanics (which underpins so much of the fantastic technology that we take for granted every day). The satellite was named after Planck in 1996 by the then ESA Director of Science Roger Bonnet. (Previously the satellite went under the clumsy acronym COBRAS/SAMBA). Bonnet chose the name because the satellite is designed to study the black body radiation left over from the hot Big Bang. This is quite a good reason, but I think an even better argument for naming our satellite after Planck comes from his perceptive discovery of so-called ‘natural’ units. Here is what Planck says about these natural units:

"These necessarily retain their meaning for all times and for all civilisations, even extraterrestials and non-human ones"

Fundamental physics involves three constants of nature:

The first is Planck’s constant which tells us the scale of the quantum world. The second is the speed of light, encoding the Einstein’s relativity principle. The third is Newton’s constant, which quantifies the strength of the force of gravity. For a theoretical physicist each of these constants can be taken to be unity. Their values expressed in familiar units, metres, seconds and so on, are of no fundamental significance. Our standardised units are human constructions, chosen for our convenience. (This is why Planck refers to ‘extraterrestrials’ in the quotation cited above.) So, a metre is roughly the length of a long step, a second is about the time interval between heartbeats, and a kilogram is about the maximum amount of pasta that you can eat. Let’s see the values of Planck’s ‘natural’ units in terms of our more familiar units: