But the physicists, being physicists, had gone further than this and measured the amount of light radiated. Unlike the blacksmiths, they were also interested in the parts of the spectrum that were not visible to human eyes.
A small diversion: If we look at sunlight through a prism, we get a rainbow of colours, just like a real rainbow. Physicists call this rainbow a spectrum (see Figure ct2). A physicist 's spectrum includes invisible 'colours ' in the infra-red and ultraviolet as well as the visible colours. But physicists do not call them colours; to them they are frequencies. This comes from thinking of light as a wave, much like an ocean wave. As waves pass a point, we count the number of wave crests we see every second. This is the frequency of wave crests. The colours we can see each fall into a range of such frequencies, so a spectrum made of frequencies is also a spectrum of colours.
Another way to understand colour is through its wavelength, which is the distance between one wave crest and the next. This is related mathematically to frequency, as shown in figure ct2, so we can use either term. We 're going to go with frequency. If you’d be happier with the word ‘colour,’ then, wherever you read ‘frequency,’ just think ‘colour ' and you won 't lose …show more content…
Using empirical equations like this is a common trick in science; find a mathematical function that fits what you’ve observed, then use that as a clue to what’s happening behind your observations. Planck had taken this second step, and was looking for a theoretical derivation of what became Planck’s Law. This gave him a more fundamental understanding of the process of radiation.
It is ironic, then, that Planck needed to quantise light to get his derivation to work. He had used Boltzmann’s equation to better understand the process but this understanding was that light came in quanta. Planck very definitely did not believe that light actually came in quanta. He considered it just a mathematical trick to make his equation work. Having worked with classical physics all his life, he was used to looking on light as a wave and using wave-based equations to accurately predict its behaviour. His ‘imaginary’ discrete energy packets had no place in this structure.
Planck’s equation was not, at first, very popular. The rest of the physics community had the same problems with it as he did, the fact that he had to use a mathemagical trick to get the right curves for blackbody radiation. Light did not come in quanta, so there had to be a better equation waiting to be found.
Albert Einstein had other