Life on Earth started roughly 3.5 billion years ago. Since then, it has been evolving into more and more complex forms. Some 70-130,000 years ago, we Home Sapiens came into existence, and as our brains evolved, we began to think and wander about the universe. We were looking at objects around us and were asking what these objects are? How they formed? And so on. The most exciting part of our quest to understand the universe began when we started to explore the universe’s building blocks.
What exactly are the building blocks of the universe? Around 400 B.C.E., Democritus, a Greek philosopher, introduced the atom as the universe’s building blocks. According to his theory, the matter is composed of tiny indivisible particles, which he called atoms.
In 1803, an English school teacher, John Dalton, proposed a modern theory of the atom based on two assumptions. First, matter is made of atoms, which are indivisible particles. Second, all atoms of the same element have the same mass and properties. As the indivisible building blocks of the universe, the idea of atoms dominated the great thinkers’ minds till 1897, when J.J. Thomson discovered electrons. When J.J. Thomson experimented with a Cathode ray tube, he found that an atom is composed of negatively charged particles. He called them cathode rays, as they seemed to come from the cathode. Today, we know these particles as electrons. It was just the beginning of a new story in the history of humanity’s quest for understanding the universe.
In 1911, Earnest Rutherford bombarded alpha particles on a 0.00004cm think gold sheet. These alpha particles were emitted from a radioactive Radium. After passing through the gold sheet, these particles hit the zinc sulfate screen. By counting the number of sparks on the zinc sulfate screen, Rutherford concluded that almost all the atom’s matter was concentrated in the tiny volume situated in the atom’s center, and it is the nucleus of the atom. The nucleus contains most of the matter of an atom and is positively charged.
Later in 1932, Sir James Chadwick discovered neutrons. Now, the picture of the atom was clear. An atom is composed of a nucleus, which further consists of positively charged protons and electrically neutral neutrons, and negatively charged electrons, which revolves around the nucleus. In our schools, we have been taught that everything is made up of matter, and the matter is composed of atoms, which can be further subdivided into protons, neutrons, and electrons, and they are building blocks of the universe. But the story didn’t end here.
In 1964, two physicists, Murray Gell Mann and George Zweig, independently proposed the subatomic particles known as quarks to explain the behavior of particles discovered through high-energy atomic collisions. In 1968, scientists working in the Stanford Linear Accelerator Center found evidence for these particles’ existence. Now, we know that these protons and neutrons are made of quarks.
At this time, we know about six types of quarks: Up quarks, Down quarks, Top quarks, Bottom quarks, Charm quarks, and Strange quarks. When these different varieties of quarks combine, we get protons and neutrons. A proton is made of three quarks, two Up quarks, and one down quark.
On the other hand, a neutron is made of two Down and one Up quark. Quarks and leptons, i.e., electrons, are the building blocks of the universe.
Diagram of the Standard Model of particle physics. 12 fundamental particles that makeup matter and 4 fundamental force carriers. Vector.
The picture of the universe may seem clear now, as we have discovered the universe’s fundamental building blocks. These quarks and electrons are now considered indivisible particles. So, does the story ends here? Let’s go back to 1928. When Neil Bohr and other founders of Quantum mechanics were busy with the matter of matter, Paul Dirac was trying to unify Quantum mechanics, which deals with the subatomic world, with Einstein’s special theory of relativity, which deals with the objects moving at the speed of light.
After doing complex mathematical calculations, he developed an equation. This equation is now known as Dirac’s equation. This equation was able to explain things that are very small and are moving very fast. At first, Dirac didn’t appreciate it and thought of it as a mathematical error. But later, he realized that his equation is predicting something entirely new to science, and that is Anti-particles. Dirac equation predicted a particle whose mass and properties were the same as an electron but had a positive charge. Later, Dirac realized, and he proposed the existence of Anti-matter. The anti-matter particles are the same as matter particles but with opposite charge.
In 1932, Carl Anderson, a young professor at the California Institute of Technology studying cosmic showers in cloud chambers. The cloud chamber was used to detect particles, designed to visualize the passage of ionizing radiations. It consisted of a sealed environment containing supersaturated vapors of water or alcohol. The energetic charged particles interact with the cloud by knocking off an electron during collisions, which results in trails. Anderson also applied a magnetic field to the system, causing particles to curve according to their mass to charge ratio. Using this technique, he could study the different particles and behavior. It is hard for a normal eye to observe what is happening here, but what he observed was that all particles fell at distinct paths that can be assessed mathematically in their trajectory. However, in this picture, a strange particle managed to move opposite to the magnetic field, and he observed a path left by something positively charged with the same mass and speed as an electron. Yes, this was the first time an anti-particle for electron was discovered. They named it Positron. This discovery confirmed Paul Dirac’s assumption. In 1933, Paul Dirac was awarded the Nobel prize in physics for his achievement. Later, more discoveries were made, and now we know that for every matter particle, there exists an anti-particle for it.
Positron for electron, antiproton for proton, antineutron for neutron, and the list goes on. But this discovery again puzzled scientists. Let me ask the question again; what are the basic building blocks of the universe? Quarks and leptons? But they are matter particles. What about these anti-matter particles? Where did they come from? The answer may lie in the ultimate beginning, the Big Bang.
According to scientists, the universe started with the big bang roughly 14 billion years ago, and whatever exists today can be traced back to that event. The energy from the Big Bang should have produced equal amounts of matter and anti-matter particles. But when we look at the universe, from the tiniest specks of dots to the giant galaxies, we only see the normal matter. We can rarely find anti-matter particles in the universe. But why? Where is the remaining anti-matter? This is called the problem of anti-matter. Today, one of the significant challenges in the scientific world is to figure out what happened to the anti-matter. Why do we see an asymmetry between matter and anti-matter?
The exciting aspect of this whole scenario is that matter and anti-matter particles are produced in pairs. When they come in contact with each other, they annihilate and release energy. So, in the beginning, when the big bang produced these matter-antimatter particle pairs, these particles were also colliding and annihilating, filling the universe with pure energy.
So, if the matter and anti-matter particles were created and destroyed together, the universe must contain only the remaining energy. But this is not what we see today. As scientists have observed the universe, they have estimated that, luckily, in one billion collisions of matter and anti-matter particles, one matter particle survived. So, what we observe now, including the planets, stars, and galaxies, are the collisions’ leftovers. But it is still a mystery why one matter particle survived. But it is just one solution to the anti-matter problem.
Another explanation is that when the universe cooled down, the anti-matter could have separated and existed somewhere else, far away from our observable universe. There might exist anti-planets, anti-stars, anti-galaxies, and maybe even the entire anti-universe. A universe that is entirely composed of anti-matter. String theory also predicts the concept of parallel universes, with more dimensions than we know today.
String theory is another theory trying to unify all four forces in nature: gravity, strong force, weak force, and electromagnetic force. Don’t forget that PAUL DIRAC also attempted to unify the forces and came up with anti-matter.
Maybe we will discover much more in this field, and this will be an exciting journey.