2.1 What Albert Did
Setting the scene for special relativity
1905 was a big year for Uncle Albert and for physics. He published a paper on Brownian motion which helped finally convince everyone that atoms were real (there were still doubters at that time) and another on the photoelectric effect which began to persuade the world that light is quantised, so laying the foundations of the idea of wave-particle duality which would soon enable quantum theory to burst onto the scene. In the same year he also published what we now call his special theory of relativity which challenged everyone’s understanding of the nature of space and time.
The theories that have grown out of these beginnings - quantum physics and relativity - are very different in nature and, indeed, making them fit together properly has caused many a headache since. We, nevertheless, are going to engage with both of them. Our plan is to learn just enough about relativity to arrive at the relationship between the momentum of a photon and its wavelength, because that is going to be our route into quantum theory. Along the way, though, we’ll derive the most famous equation in the world, which will be a nice bonus. So let’s hold off on thinking about quanta for the moment, and focus on space, time and energy.