On most days you wake up to the light of the sun in your room but have you ever wondered what it really is? Is light just a ray of particles streaming through space that happened to land on your eyes? Or is light much more complex than that? The latter is true and avoiding some very deep physics there are three main reasons. Light obeys the Uncertainty Principle, it is both a particle and wave, and the speed of light is always constant.

In 1803, a man named Thomas Young set out to prove that light was a wave instead of just a particle as accepted by the Royal Society at the time (Lees 77). Instead he experimentally proved light was a wave. To test if light was a wave, he set-up the double slit experiment (Lees 77). In this experiment he put two metal slits in a metal sheet and a light that would shine on the slits that would project the light onto a wall in a darkroom (Lees 78). What he discovered was there was an interference pattern meaning rather than two white bands on the wall there was a collection of bands on the wall. He deduced that the light went through the slits as a wave and interacted with itself just like when two ripples of water meet (Lees 77). Scientists would accept the wave theory but in 1927 Arthur H. Compton proved light was also a particle since when light strikes an electron the electron actually recoils as if struck by a particle. It was even found that the light had actually lost energy, momentum, to the electron (Nave Compton Scattering). This means light is both a wave and a particle. What's even more interesting is the French scientist Louis De Broglie in 1924 applied waves to matter and showed that all particles, and thus all things made of them, can behave as waves as long as they are in motion though this property diminishes extremely quickly with particles of more mass (Greiner 29 & Purdue Department of Chemistry). An example of non light particles behaving like waves and particles are electrons. Since electrons have an extremely small mass and move extremely fast they must be perceived of as waves especially when “orbiting the nucleus of an atom” or else descriptions of their behavior become very inaccurate (Purdue Department of Chemistry). There is another extremely important property of light.

The Uncertainty Principle is another key property of light. Previously light was determined to be a wave and particle though scientists tried to define the wave of light into a point. They used light with the same wavelength with hopes of them canceling each other out to create a point where the light is (Gribbin 103). They arose at the problem that adding more light waves to reduce uncertainty in the position of the light actually made its momentum, how much force an object has, more uncertain(Gribbin 104). This also works the other way with more momentum being added that causes more uncertainty in location of this point. The developer of this theory, Werner Heisenberg, stated “[T]he more precisely the position is determined, the less precisely the momentum is known” (Libretexts). Luckily, the amount of uncertainty can be calculated allowing for ranges of the waves momentum and position (Libretexts). The Uncertainty Principle also applies to all particles since all particles can act as a wave though once again this effect diminishes with larger particles (Purdue Department of Chemistry).

The last strange property of light is that its speed is always constant. Light always travels at light speed and in a true vacuum this is exactly 299,792,458 metres per second, scientists call this value C(Britannica). Albert Einstein developed in his special theory of relativity that the speed of light is always constant regardless of the observer (William “What if you traveled faster than light?”). This means if you are standing still or traveling at 100 miles per hour towards light it will always be traveling at C. The Speed of Light also serves as the speed limit of the Universe for all particles and information. Particles with mass need an infinite amount of energy to allow for light speed and light, and other particles without mass, travel at exactly C (William “What if you traveled faster than light?”).

In conclusion, light is more than what illuminates your house at night. It led to the discovery that all particles, including itself, can behave as a wave and as a particle. Werner Heisenberg developed the Uncertainty Principle that makes it so light ,and all particles, have a measurable amount of uncertainty about them. Finally, light moves at a constant speed and serves as the speed limit of the universe.

Work Cited
Lees, James. Physics in 50 Milestone Moments. NEW BURLINGTON BOOKS, 2017. Accessed 20 February 2018.

Greiner, Walter. Quantum Mechanics: an Introduction. Springer, 1989. Accessed 20 February 2018.

The Editors of Encyclopædia Britannica. “Speed of Light.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 5 Jan. 2018. Accessed 20 February 2018.

Gribbin, John. Get a Grip on Physics. Dover Publications, 2013. Accessed 20 February 2018.

Gibbs, Phillip. “Does Light Have Mass?” Does Light Have Mass?, 11 Nov. 1997. Accessed 20 February 2018.

“Louis-Victor De Broglie.” Louis, Purdue Department of Chemistry.

Libretexts. “Uncertainty Principle.” Chemistry LibreTexts, Libretexts, 13 June 2017.

Harris, William. “What If You Traveled Faster than the Speed of Light?” HowStuffWorks Science, HowStuffWorks, 21 July 2011.

“Chapter 2: Relativistic Mechanics Introduction.” Received by Students , Ps.uci.edu, University of California Irvine School of Physical Sciences, 16 Jan. 2013.

Nave, Carl R. “Compton Scattering.” HyperPhysics, Georgia State University Department of Physics and Astronomy.