Our curiosity to know about the composition of things around us, is not recent. As old as two and half thousand years ago, natural philosophers like Kanada and Democritus suggested that the Universe might consist of atoms. Their theories were mainly philosophical models and thought experiments, because of lack of advanced mathematics or experimental setup at that time. Despite the facts, it feels incredible that their thoughts somehow sparked the formal inquiry into matter and energy. We have kept asking ourselves the question of composition of matter in the Universe. Today we know much more about atoms, electrons, energy, and the their roles in the observable universe. Still the answer to that question is equally fascinating as it was in the antiquity. It takes us on a journey from the everyday objects (cats, cars and trees) to that unseen or un-seeable (if that’s a word) world scientists have been talking about for quite some time. So, where do we start? In his wildly famous science book Cosmos, Carl Sagan writes,
If you wish to make an apple pie from scratch, you must first invent the Universe.
— Carl Sagan
The universe is a strange place where the natural laws appear to be different depending on the size of the entities. Electrons with their bizarre uncertain probabilistic nature look very different than a normal tennis ball bouncing on the grass, although the latter one is made up of the prior one. Principally, you can zoom into the tennis ball and observe the weird phenomena of electrons. The laws are same (symmetrical) everywhere you go (see Gauge theory), it’s just the appearance of them changes.
Depending on the perspective, we are either trapped, or safely cushioned between the bizarre worlds — one with electrons, quarks, photons, and the other one with big stars, galaxies and super-massive blackholes.
It’s difficult, rather impossible for our minds which themselves are products of millions of years of evolution and cultural upbringings, to understand something that’s out of scale by such a large extent on both the ends. Understanding them takes special efforts on a personal level and a deep commitment to follow through several levels of abstraction. Language is often inadequate when we describe these concepts. After all, language as a tool to query and explain nature is only a recent invention of mankind!
Forces and the Model
It feels silly to distinguish between mathematics, physics, chemistry and geometry because they all fuse together when we start talking about what is elementary. The examples of this will follow, but really the knowledge we as humans possess today is a result of centuries of mathematics, abstraction and experimental verification. To study quantum mechanics, it would be worthwhile to quickly brush up on among other things, the force interactions and the standard model. All matter is thought to be created from interactions between the elementary particles and the forces of nature (not to be confused with earth, water, fire, air etc….!).
Forces
The forces observed in the universe are classified in four different types:
- Strong force — It is the force which binds the nucleus of an atom by keeping protons and neutrons together. It is the strongest (hence the name!) among the fundamental forces and operates in the range of femtometers (10-¹⁵ m). It is carried by gluons and mesons (2nd generation particles)
- Weak force — It is a force that is involved in the inter- nuclear phenomena like beta decay. It’s range (10-¹⁶ m or 10-¹⁷ m) and strength (less than million times compared to strong force) are pretty low, but important for things like fusion of Hydrogen atoms into Helium inside the stars or fission.
- Electromagnetic force — This is a force involving electricity and magnetism which gives rise to all chemistry and radiation (involving light) in the universe. Some of the known manifestations of this force are chemical bonds, electrons and atom interactions, molecules and alike.
- Gravity — This is what we all experience — interactions of a particularly ‘attractive’ kind! This is the glue that holds us to the earth, and stars within their galaxies. According to Einstein’s relativity, gravity is not a force but a curvature in space-time, and that view does not sit well with quantum mechanics. Gravity, among others is the only force which is not ‘quantized’ yet.
A little bit about Quantization
Quantization is an aspect of the force interactions mentioned above, where any given particle is thought to have very well defined energy levels. This means a particle can only be in certain energy levels, and not on a smooth continuous value scale. In this example of a bowling ball used to represent an electron, the electron can only jump between Level 1 and Level 2. It cannot be in between the levels.
We will look at this concept again in later articles, but something to remember for later — outside gravity, all particles are observed to obey this rule.
The Model
The Standard model is a framework that consists of elementary particles, force carriers and force field(s). If we look at the Standard Model, it is generally divided into:
- Fermions: Particles that essentially make up the matter and follow characteristics like half integer spins. They are further divided into 6 quarks and 6 leptons- electrons being part of leptons.
- Bosons: Force carrier particles follow different characteristics than Fermions, but help in facilitating the force interactions. There are 4 vector Bosons like photon (the light particle) and scalar Bosons like the famous Higgs Boson. Particle associated with gravity — the Graviton is only theoretically predicted addition to the Boson family.
In pop culture, we often use the phrase ‘to get to the bottom of something’ to mean — to investigate until the end. Elementary particles are the ultimate ‘to the bottom of everything’ in the universe. If you start investigating what makes the matter by slicing it down a step at a time (Carl Sagan’s example), you can’t go further than the elementary particles. Some of the well known of the group are Electrons and Neutrinos. There are many such particles which are just known to exist. Remember, language fails us here because languages have developed to describe phenomena at macro scale of plants and animals. The reasons for elementary particles to exist since the big bang are searched in Cosmology — study of origins of the universe. The elementary particles tend to interact with each other (with some exceptions) through force carriers in force fields and other non-elementary particles are created, which in turn create the matter we see around us everywhere.
The Standard model attempts to explain the existence of atomic nuclei, thermonuclear processes, radiation and chemistry (bonds, molecules), but It is far from the total picture of our understanding of the universe. There are some phenomena like dark energy/matter and matter-antimatter asymmetry that are unexplained by it. Gravity is another such elusive concept unexplained by Standard Model.
So, what’s next?
It is agreed that the standard model is imperfect and incomplete. Some have even said that the Standard Model is created after the fact and it is not a natural explanation of fundamental aspects of reality. Then there are some who claim ‘consciousness’ as the basic unit of the Universe. Very few of us would be qualified to talk about what is the most possible answer or more importantly, what to do with that answer.
Whether the True (with a capital T) nature of everything can be known or not, we are more interested in solving the daily problems of food, climate and health. This is where the computing aspect of quantum mechanics comes into picture.
During the introduction of the model, we saw the fermions and the bosons as the particle classes, with some spin values attached to them. Next, we are going to see how to exploit the same ‘Spin’ properties to get quantum states for computing.
Stay tuned!
