The Great Nobel Prize winning physicist Richard Feynman was once asked to convey, in a single sentence, the most important scientific knowledge that humans possessed.
His answer was short and simple: “Everything is made of atoms.”
Learn more about atoms and how we discovered they existed on this episode of Everything Everywhere Daily.
Most of what the ancients knew of the physical word was wrong. Just flat out wrong. Aristotle, for instance, thought that everything in the world was made of just four elements: earth, air, fire, and water.
According to him, everything consisted of some combination of these four elements.
Almost every ancient culture had some ideas of how the world works, which wouldn’t really stand up to modern science.
That being said, given the state of knowledge hundreds to thousands of years ago, you can’t really blame them. Most of their ideas about the world were based on philosophy more than science. They had ideas that made sense to them but weren’t based on experimentation or observation.
However, there were a few cases where they basically got it right, even though they didn’t really know it at the time.
This is the case with the theory of atoms.
What we call science used to be part of philosophy. The branch of philosophy which dealt with the natural world was known as natural philosophy.
One school of ancient natural philosophy was called atomism.
There are two ancient civilizations that each independently developed theories of atomism: Greece and India.
Around 600 BC, one of the Vedic schools of thought was known as Vaisheshika. It was developed by the Indian philosopher Kanada and postulated that the world could be reduced to indivisible bits known as param??u.
According to the Vaisheshika school, everything was made up of param??u, and everything in the world could be thought of as a combination of param??u and the interactions between them.
About 200 years later, the same idea was independently developed in Greece. A philosopher by the name of Democritus believed, like Kanada in India, that the world was made up of indivisible particles, which he called “atomos,” which means uncuttable.
According to Democritus, there were an infinite number of atoms of different sizes and shapes. They were always in motion, and the material’s nature reflected the atoms’ nature.
For example, water atoms would have been slippery. Iron atoms would be heavy with hooks that connected them together.
Sweet things were smooth and bitter things were jagged.
Also, according to Democritus, between the atoms, there was nothing. Just a void. Atoms couldn’t be created or destroyed.
Both Democritus and Kanada simply used deductive reasoning to come to these conclusions.
Aristotle didn’t believe in atomism. He thought that his four elements could continuously be divided forever. Moreover, he didn’t believe in a void, which was necessary if you believed in atoms.
Despite having written 80 different works, none of the writings of Democritus survived. Everything we know about him is what was written about him by others.
The works of Aristotle, however, did survive. His ideas eventually took hold and were revived during the Middle Ages.
However, there was a rediscovery of atomism in the 13th century, and there were scientists who believed in atomism, including Isaac Newton. At this point, while modern science was developing, believing in atoms was still pretty much a matter of philosophy.
Our modern-day understanding of atoms began to develop in the late 18th and early 19th centuries. There were discoveries being made on a regular basis about fundamental elements.
One of the first major steps toward figuring out atoms came from the French chemist Antoine Lavoisier, who postulated the Law of Conservation of Mass. He realized that in any chemical reaction, the total mass before and after the reaction was the same.
However, the big step in atomic theory came from the English chemist John Dalton.
Dalton developed what is known as the Law of Multiple Proportions, which stipulates that the masses in any compound were actually ratios of small whole numbers. He felt that each element, and there were new elements being discovered all the time, were their own unique atoms.
This theory made perfect sense. It explained chemical equations, and it explained the discovery of elements.
Throughout the 19th century, more evidence piled up consistent with the atomic theory of matter. Avogadro’s Law, the Ideal Gas Law, the discovery of Brownian Motion, and everything else discovered during this period gave continued support to the idea that everything is made of atoms.
This idea that atoms were the smallest unit of matter actually fell apart in 1897 with the discovery of the electron by British physicist JJ Thompson.
He found that there had to be a negatively charged particle that had a mass 1,800x less than hydrogen, which was the lightest known element.
Thompson figured that his new particle was smaller than an atom and was actually a constitution part of an atom.
With this new discovery, Thompson created a new theory of the atom which was dubbed the plum pudding theory. This theory held that there was a positively charged substance that the negatively charged electrons were embedded within, just like how raisins were embedded in plum pudding.
Thompson’s plum pudding model didn’t last and was disproven only a few years later.
The New Zealand physicist Ernst Rutherford put the plum pudding model to rest when he discovered that atoms had a very small, dense nucleus. Rutherford had already won the Nobel prize in 1908 for his work on radioactivity.
In a famous 1911 experiment known as the gold foil experiment, he actually set out to prove Thompson’s atomic model.
He fired alpha radiation particles at a thin piece of gold foil. He expected all the alpha particles to go right through. Instead, what happened is that some particles were reflected, often times in very odd angles, including straight back.
This result was unexpected and shouldn’t have happened if the plum pudding model was true.
Rutherford realized this could have happened only if two things were true. The first was an extremely dense, positively charged nucleus to the atom that reflected some of the alpha particles. The second was a whole bunch of nothing everywhere, allowing the particles to pass through.
Rutherford proposed a new model of the atom where there was a small, dense, positively charged nucleus, with small negatively charged electrons which orbited it like planets orbit the sun.
While this model did fit the data better than the plum pudding model, it raised just as many questions. What kept the electrons in orbit, and what did the nucleus consist of?
Just two years later, the Danish physicist Niels Bohr expanded on the model by explaining that electrons would have been parked at different levels depending on their energy.
That same year, 1913, another discovery needed to be explained. British radiochemist Frederick Soddy discovered that there were some atoms that had different weights. These became known as isotopes.
In 1919, Ernst Rutherford found that there were positively charged particles in the nucleus, which he dubbed a proton.
He assumed that there were neutral and positive particles in the nucleus. The existence of neutral particles, called neutrons, was confirmed by the English physicist James Chadwick in 1932.
With this new model, protons and neutrons were about the same weight, with protons having a positive charge and neutrons having zero charge.
With this, everything seemed pretty complete….except, of course, that it wasn’t. In fact, it was about to get even more complicated.
Researchers began to find a whole host of particles inside the nucleus, which were discovered by colliding atoms together in a particle accelerator.
I’m going to skip a lot of ground here, but there were a bunch of particles that were found that were even smaller than protons and neutrons. These particles, became known as elemental particles,
These included particles such as quarks, leptons, antiquarks, antileptons, bosons, photons, gluons, and neutrinos.
Amongst those I’ve listed, there are many different types and flavors.
The person who began to make sense of all this was the Caltech physicist Murray Gell-Mann.
He created a model that made sense of everything called the Standard Model. The standard model is probably worth its own episode at some point, but suffice it to say, it explained much of how atomic particles were put together.
Even the standard model, as much as it is explained, is still in need of updating as more and more discoveries are being made which don’t perfectly fit the model.
Our understanding of the atom still isn’t complete.
Understanding the workings of the atom has been one of the most important projects of humanity. How the atom works is the bedrock underlying every other science, including all chemistry and biology.
What started as philosophy in ancient India and Greece is still being developed today in the world’s largest particle accelerators 2,600 years from when it started.