# Three Essential Concepts of Modern Physics

Modern Physics is full of interesting and important ideas. These concepts are apparent in many aspects of our lives, such as the observed speed difference when two cars pass each other in opposite directions, black items (such as shirts) are warmer in light than white items, and burglary alarms. These effects are due to relativity, blackbody radiation, and the photoelectric effect, respectively.

The first would be Einstein’s Theory of Special Relativity. It consists of two main postulates: objects move relative to their reference frames and nothing can exceed the speed of light. The first postulate explains why counter-intuitive things happen outside of the moving reference frame. These odd events are time dilation and length contraction. Time dilation is where an object in a moving reference frame (such as a clock on a spaceship) appears to “run slow.” What is actually happening is the clock is running at the proper time in the spaceship’s reference frame while another observer in a different frame of reference (such as Earth) will see the clock have longer time intervals. In the case of length contraction, a moving object will appear to be longer or shorter when viewed from an outside reference frame. A good example of this would be two cars passing each other on the highway in lanes of opposite directions. A driver in one of the cars would see their car to be its actual or proper length, while the other driver, in their respective frame, would see the first’s car as being incredibly short. The second postulate places an upper limit on how fast objects can travel. If anything were to exceed the speed of light, then odd things such as distortion and suddenly traveling back in time would theoretically happen. (Tipler)

The second would be Blackbody Radiation. This idea is based on how ideal blackbodies would absorb any and all light that is shone on the surface and emits heat simultaneously. Essentially, “It is a hypothetical object which is a “perfect” absorber and a “perfect” emitter of radiation over all wavelengths.” (Swinburne University). It explains why wearing a black T-shirt in direct sunlight feels much warmer than wearing a white shirt, or why most old stoves are black.

The last essential idea would be the Photoelectric Effect. It was unexplainable by Classical Physics since that branch of physics only treats light as a wave. It was not until the field of Quantum Mechanics was created that the idea of light as a discrete particle  was formed. Two scientists named Franck and Hertz discovered that the photoelectric effect operated on this idea of light as a discrete particle. The photoelectric effect works by having electrons ejected from a plate of metal once an incident light is shone onto a metal plate. Once this light is strong or bright enough, the electrons are ejected from the plate. This is an all or nothing event, meaning that when the light is strong enough to eject the electrons, it ejects all of them. (Duffy). This process is used in everyday equipment such as smoke detectors, where smoke blocks that required incident light and causes an alarm to sound.

In conclusion, everyone experiences relativity, blackbody radiation, and the photoelectric effect in their day-to-day lives. It may not always be apparent, but they are working in the background.

Word count: 356

Written by Alexis K.,

Edited by Shane Warga

References:

Duffy, Andrew. “Class notes.” Boston University, n.d. Web. 31 Mar. 2017.

Tipler, Paul Allen, and Ralph A. Llewellyn. Modern physics. 6th ed. New York: W. H. Freeman and Company, 2012. 134-135. Print.

“Blackbody Radiation | COSMOS.” Centre for Astrophysics and Supercomputing. Swinburne University of Technology, n.d. Web. 31 Mar. 2017.