For 2 millennia of human history, classical physics has been studied on the macroscopic scale. By the early 20th century, modern physics was developed, giving us a better understanding of the world on the microscopic scale. Unprecedented ideas and findings led to further developments in modern physics. One of them was the debate between scientists whether light is a particle or a wave. Then, how about humans? Are they waves or particles?
*Waves are continuous and repeating patterns where energies are carried and spread.
Particles are extremely small parts of matter that constitute molecules, nucleus, and atoms.
Ultraviolet Catastrophe and Planck’s Law - Quantum
Blackbody is an idealized body that absorbs all radiation falling on it. Looking at its temperature, the intensity of energy coming from the black body could be predicted. Later, an equation for the intensity of energy, the Rayleigh-Jeans law, was proposed based on the idea that light is a wave. As frequency grew, the intensity of energy grew accordingly. However, the Rayleigh-Jeans law could make right predictions only before the frequency of light reached the ultraviolet range. In the experiments, it was shown that the blackbody gets to its peak intensity at a certain frequency and starts to drop in intensity. This incident is called the ultraviolet catastrophe. This problem was perfectly resolved by a new equation proposed by Max Planck. In Planck's law, there is a new concept called quanta, small packets of electromagnetic energy that cannot be further divided. The energy in each quantum equals frequency multiplied by Planck’s constant. Planck’s law was significant because physicists previously thought that energy was continuous, not in separate packets.
Photoelectric Effect - Photon
Albert Einstein came up with the idea that light energy travels in small packets, called photons, which make light behave like a particle in some circumstances. He proved this using the photoelectric effect. Photoelectric effect is a phenomenon in which electrons are ejected from the surface of metal, where light is shined on, and those ejected electrons are called photoelectrons. If light is a wave, the kinetic energy from photoelectrons should increase with the light amplitude and the electric current should increase with the light frequency. Nevertheless, the experiment showed that the kinetic energy from photoelectrons increases with the light frequency and the electric current increases with the light amplitude. This result was completely opposite from the classical description of light as a wave. From the Photoelectric Effect Testing, Einstein stated that light can behave like particles of electromagnetic energy. Planck’s law could also be used to calculate the energy of photons.
Double-Slit Experiment
In the double-slit experiment, there are two walls where the one in front has two slits. When light is shined at the front wall, it separates into two waves as it reaches the two slits. Bright stripes are formed on the next wall, and these are the result of two waves interfering with each other. This stripe pattern is called an interference pattern, which is common for waves. Then, how about electrons? When electrons are fired at the walls, the exact same phenomenon happens.
In this second experiment, a detector is placed near the slits. When electrons are fired, the particle pattern with two stripes that have almost the same shape as the rectangular slits can be seen on the wall. In other words, electrons behave like particles when their path gets observed by a detector. These two experiments tell us that electrons behave sometimes like particles and sometimes waves. As electrons and light, having characteristics of both particles and waves is called wave-particle duality.
Humans are both Waves and Particles
Everything in the universe, including humans, is both wave and particle at the same time. There is neither beginning nor end. Quantum mechanics is considered as the most successful theory ever and it has been teaching us how the world really works at the scale of atoms and subatomic particles. As the field of quantum mechanics gets further explored, we will definitely gain a better understanding of the universe.
Comments