Chapters Four and Five - The Uncertainty Principle & Elementary Particles and the Forces of Nature

Chapter Four goes in depth about energy, and more specifically, light energy. The main idea of the chapter, however, is the uncertainty principle. The uncertainty principle was created by a German scientist in 1926 by the name of Werner Heisenberg. His principle stated that: In order to predict the future position and velocity of a particle, one must first be able to measure its present position and velocity correctly. Hawking states that the easiest way to do this is to shine light on the particle. By doing so, some of the waves of light will be scattered by the particle, showing where the particle is. However, the position of the particle will not be accurately determined with a long wavelength, therefore a beam of light with a short wavelength must be used. Because of Planck's quantum hypothesis, a small amount of light can not be used anyways. A full quantum of one of more must be used. The quantum will change the particle's velocity because of the energy packed into it, though. This means that it can't be accurately determined. Thus, the uncertainty principle is formed. 

Chapter Five discusses the forces of nature and the effects they have on elementary particles. The forces of nature consist of air, water, fire, and earth. Elementary particles were originally thought to be protons and neutrons, but this theory has been disproved. The true definition of an elementary particle varies depending on the element. Their size determines the smallest particle within the atom, deciphering what the elementary particle is. The forces of nature (being air, water, fire, and earth) have varying impacts on the elementary particles, depending on what they are. This chapter was slightly confusing for me because everything was so "up in the air". There weren't very many concrete and definite theories.