Essays and Ideas

Hundreds of years before the double slit experiment, thinkers and scientists argued about the nature of light. In the 17th century, French scientist and astronomer Pierre Gassendi and Sir Isaac Newton argued that light propagates through space as a steady stream of particles. In the early 1760s Leonhard Euler maintained that light was a wave propagating through aether. Euler argued that if the sun were constantly emitting particles it would be rapidly decreasing in size. The theory behind Thomas Young's experiment is straightforward. Unlike particles, waves obey the mathematical principle of superposition and also unlike particles, waves have the potential to interfere with one another. Young passed monochromatic light through two slits in an otherwise opaque partition onto a dark screen. When light was allowed to pass through only one slit at a time the light was distributed on the screen evenly. When light was allowed to pass through both slits at the same time he observed an i...

Most of us are familiar with the three primary of phases matter: solid, liquid and gas. If you think about it, phase transitions are a mysterious and mystifying thing. Continuously raise the temperature of liquid water and you won't see anything change until a seemingly arbitrary threshold is surpassed (100 degrees Celsius) and then everything suddenly changes - the water boils! It seems there isn't a smooth transition between the liquid and gas phase of water because there aren't any intermediate steps between them. I can raise the temperature of ice by 50 degrees and nothing will happen to the ice, but raise the temperature one degree above 0 degrees Celsius and suddenly my ice is completely transformed into water with completely different properties! Phase transitions are an example of critical phenomena – below a certain threshold one set of properties are exhibited and above a certain threshold a completely different set of properties are exhibited without any groun...