An important physics principle, formed in the twentieth century
Picture a drawing with sunlight in it. If you were to draw it, how would you represent the rays of sunshine? Perhaps, you could draw a series of discrete lines from a smiling sun in the blue, or maybe you should instead draw ripple-like waves? Of course, when drawing, human creativity and feelings dictate what is drawn. However, the physics perspective of analyzing light rays was based on centuries of new discoveries about this topic, including data from various experimentations. This article will take us into the historical development of various theories pertaining to this principle!
What is wave-particle duality?
Historically, light has been thought of as particles. Common properties of light, like reflection and refraction, are explainable using the concept that light is composed of particles. Newton himself believed strongly in the particle nature of light. However, by the late eighteenth and early nineteenth century, the English physicist Thomas Young proved, through his famous double slit experiment, that light is better explained as a wave.
Thomas Young’s experiment demonstrated two properties of light that cannot be explained by the particle nature, which are diffraction and interference. Take a look at the diagram below:
As you can see, the light waves traveling through the two slits actually have an effect on each other, thus producing the pattern of bright-dark spots on the wall that the light is projected upon. Now, imagine if light were particles. Then, particles should not be able to cause areas of overlap like waves could. Now, onto the other property, which is diffraction; diffraction simply refers to the bending of light around a corner, or perhaps spreading out after passing by a little opening.
Young also noticed that light diffracted slightly through the two openings, thus further giving evidence that it is a wave! Take a look at this photo (the gray wave indicates the diffracted light):
The twentieth century
By the early twentieth century, however, physics and science were going through a period of rapid new discoveries; many previously-made theories had to be reconsidered. It was during this time period that physicists like Planck, Einstein, and Compton pushed for the particle nature of light once more. However, their theories were more specific than Newton’s centuries ago. Specifically, Einstein proposed that light contained discrete particles (or photons), each of which contained a discrete (specific, limited) amount of energy.
This assumption by Einstein actually formed the basis of quantum physics–that is, treating energy as discrete and existing as “bundles” of countable energy.
The wave-particle duality of electrons
However, the wave-particle duality is not only applicable to light, but also to what we think of as particles, like electrons. Electrons are considered to be particles within atoms that are negatively charged. In the early-twentieth century, another physicist, Louis de Broglie, proposed that electrons actually demonstrated wave-like properties as well, in the sense that they had wavelength and frequency. This is another interesting idea, stemming from the principle of wave-particle duality!
Being open-minded in interpreting physics
The principle of wave-particle duality is truly versatile! One can argue that certain particles have wave-like properties, but also that certain waves can also possess particle-like properties. This demonstrates the importance of interpreting many properties of our physical world with complexity and nuance. The wave-particle duality is truly a crucial physics principle.