At the base of modern physics is something called quantum theory. It explains the behavior of energy and matter on different atomic levels - atomic and subatomic. Quantum theory encompasses the working of the realms of physics commonly referred to as quantum physics and quantum mechanics and it offers up a rather interesting look into the foundations of modern physics.
The beginnings of quantum theory
Quantum theory was first presented to the general public in the year 1900, by a physicist named Max Planck. He presented the theory to the German Physical Society, specifically by presenting the results of an experiment he had done looking into the color of radiation from glowing bodies (not human bodies, physical bodies).
In the experiment, he found that if he assumed that energy existed in individual units similar to matter, that he would find the answer to the original question posed in his experiment. Thinking of energy in this way was new and allowed the energy to be easily quantified. These units of energy that he was able to quantify were named quanta by Planck in his writings about the experiment and subsequent mathematical equations.
The equation that formed the beginnings of quantum theory demonstrated that at certain temperature levels, the energy that was let off from a glowing body would exist in different areas of the spectrum of color, or wavelength. Planck initially imagined that his discovery of quanta would set in motion the creation of a new theory, but what actually ended up happening was that it completely rewrote humanity's understanding of the laws of nature.
In 1918, Planck won the Nobel Prize for his discovery and research on quanta. It is important to note though, that while Planck's research began the foundation of modern quantum theory, tens to hundreds of other scientists worked in the years prior to set Planck up to make this discovery just at the point that he did. Taking a closer look at the timeline, we can see how the theory progressed after the discovery.
The timeline of quantum theory development
1900: Planck makes the initial discovery, or rather assumption, that energy was made of units called quanta.
1905: Albert Einstein theorizes that energy and radiation could be quantified in the same way that Planck had theorized of quanta.
1924: Louis de Broglie first proposed that there was no difference between energy and particles in his theory of wave-particle duality, also demonstrated in the famous double-slit experiment.
1927: A scientist by the name of Werner Heisenberg theorized that the measurement of two complementary values at the same time, such as the position and momentum of a given subatomic particle, would be impossible. This stands starkly in contrast to traditional physics and became known as the uncertainty principle.
Now that we've taken a closer look at the timeline of quantum theory development, let's take a closer look at who exactly Max Planck was.
Who was Max Planck?
Born in April of 1858, Max Karl Ernst Ludwig Planck (quite the name) was a theoretical physicist who was the originator of quantum theory, which, as we've discussed, afforded him the Nobel Prize in Physics in 1918. During his lifetime he made major contributions to the field of theoretical physics but the quantum theory remains his largest accomplishment.
Quantum theory at the hands of Planck completely revolutionized our understanding and conceptualization of quantum particles and processes. It could be equated in gravity of the theory of Alber Einstein's theory of relativity that changed our understanding of space and time.
Both quantum theory and the theory of relativity exemplify the foundations of all of the 1900s physics, forcing researchers to rethink how they approach the world around them.
Planck passed away at the age of 89 years-old in 1947 in Germany.
Interpreting quantum theory
The main methods of interpreting quantum theory are known as the Copenhagen interpretation and the many-worlds theory. The Copenhagen theory proposes that a particle is whatever it is measured to be. In other words, if you measure a particle as a wave, it's a wave. However, it also states that you can't assume that it has any specific properties or that it exists until you measure it. It's an off-the-cuff way of insisting that physical reality doesn't actually exist until you observe it. This leads way to the idea of superposition, which means that any given particle or object can be in any number of potential places at once during the period that we don't know its position, or aren't observing it.
The famous thought experiment of Schrodinger's Cat is the perfect exemplification of this interpretation of the quantum theory.
The many-worlds theory or multiverse theory. This states that as soon as the potential for an object to exist occurs, the universe splits into a series of parallel universes where both states of that object exist. This theory is the basis of TV shows like Rick and Morty or other popular science fiction stories, but at the end of the day, it's a very real interpretation of the quantum theory.
Both Stephen Hawking and Richard Feynman expressed that they preferred the multiverse theory style of interpretation.
At the end of the day, quantum theory and Planck's research have drastically influenced the work of physicists and researchers over the last 100 years. The implications of quantum theory can be a little mind-boggling though, even causing Planck himself to balk at them during his time. The foundational principles of the theory, however, continue to be repeated and proven through subsequent experimentation. Physics in many ways still will be fleshed out in the next century, but its foundation of quantum theory laid by Max Planck is likely here to stay.