7. Quantum mechanics
            Particles and waves
            Uncertainty principle
            Scroedinger’s cat

 7. Quantum mechanics

            In the 1920’s Scroedinger expanded on the ideas of Planck and Einstein who proposed that energy of light photons were quantized and of Bohr who proposed that electrons were waves to create quantum machanics, in particular, wave mechanics.
            In wave mechanics, particles are emitted and absorbed as quanta, all or nothing, and yet travel as a wave. This is the famous wave-particle duality.
            Richard Feynman illustrates the wave particle duality using the two slit experiment in which a particle appears to pass through two slits at the same time. He says that all of quantum mechanics is illustrated by the two-slit experiment but that alas, no one understands the two-slit experiment. (Video of two slit experiment)
            Werner Heisenberg came up with a different formulation of quantum mechanics called matrix mechanics. He also came up the Heisenberg uncertainty principles the most famous of which states that you cannot simultaneously know the position and momentum of a particle precisely. A second uncertainty principle applies to energy and time.

            The uncertainty principle together with chaos theory, the idea that in a complex system the uncertainty in predicted position and momentum will grow exponentially over time, provides a scientific basis for free will.
           
            Quantum mechanics produces paradoxes such as Schroedinger’s cat. Particles in quantum mechanics can be in two states at the same time, but when you look at the particle you only find it in one state. Schroedinger invented the idea of a cat who was in two states at the same time, alive and dead, and yet the cat did not enter one of these states until someone looked at it. Recently scientists have created a small vibrating diving board, big enough to be seen by the human eye, which was in two states at the same time, and which when examined is found to be in one state or the other.

            The shortest wavelength associated with a article comes if the rest mass of the particle is converted into energy, that energy will have a wavelength called the Compton Wavelength. This means that every massive particle has  a wave nature.