032 033 Unravelling the fabric of the cosmos: exploring the wonders of String Theory Theham Amarasinghe General relativity: Einstein’s crowning achievement published in 1915 unifying space, time, and gravity by showing that gravity isn’t actually a force, but merely the curvature of space-time. Quantum mechanics: a framework developed over a culmination of scientific effort spanning decades explaining the interaction between the smallest particles unifying three of the four fundamental forces. What do these theories have in common? It turns out that currently the answer to this question is not much, and that’s a major problem in physics. Currently there are four known fundamental forces: • Gravity – This force needs no introduction. It is the force that draws objects together according to its mass. • The electromagnetic force – This is the force that holds opposite electrical charges together. The force that keeps the negatively charged electron in orbit of the positively charged nucleus. • The strong nuclear force – This is the force that holds the subatomic particles that make up protons and neutrons together (quarks). • The weak nuclear force – This force is responsible for the interaction between subatomic particles. All known forces, including friction, tension, buoyancy, and others, can ultimately be understood as arising from the interactions of particles mediated by these four fundamental forces. The current goal in physics is a theory of unification of the forces in a single theory. By understanding the how interactions of these forces work, perhaps we may be able to understand the true nature of the universe. Now what exactly is quantum mechanics? As stated before, it is merely just a framework that models the behaviour of particles at the smallest of levels. These particles move in the universe and interact through the exchange of other particles. For example, the electromagnetic force is mediated through a particle known as the photon. All these different particles are accounted for in a theory named the standard model. This model contains two different categories of particles. Fermions, which largely makes up the matter that we see and interact with, and bosons, which mediate the forces between them. For example, the boson for the electromagnetic force is called a photon, also known as light. This image on the left is a visual representation of the standard model arranging the particles in a table form. The particles are grouped as either fermions or bosons. There are also further sub-groups that divide them. The image on the right is the most compact form of the standard model represented as an equation (this is also known as the Lagrangian). This equation is separated into 5 parts to explain certain parts of the model. For example, section 2, using almost half of the equation, explains interactions between bosons. So, this seems perfect right? We have all of physics wrapped up in one neat, elegant (albeit complex) equation. However, there is one major problem with this model. It doesn’t include gravity. As with the other forces, the curvature of space-time caused by gravity can be mediated by a force-carrier boson known as the graviton, but when this particle is integrated into the standard model, infinities appear which cannot be removed. This is a problem as infinities do not appear in nature. Hence, gravity cannot be described in the quantum scale. Furthermore, gravity is the weakest force by far. In fact, it is weaker than the weak force (the next weakest force) by a factor of 1029, thereby making it entirely negligible in quantum interactions. The standard model clearly doesn’t work when accounting for gravity, so how can this be solved? In the standard model, particles are envisioned as dimensionless points in the universe with innate quantum properties, including mass and charge. These are called point particles. The reason why we do this in the first place is because we don’t actually know what these subatomic particles look like, so we assume that they are points. This is because the way that we see things are governed by light. When light is reflected from surfaces, we absorb the light with our eyes and use the information gained from it to image our surroundings. However, at the quantum scale, light either doesn’t hit any particles at all, or when it does collide, it causes the particles to shift to a different position due to the extremely small scales. This means that we can never truly observe what a particle looks like. This concept is so important that it is named This image on the left is a visual representation of the standard model arranging the particles in a table form. The particles are grouped as either fermions or bosons. There are also further sub-groups that divide them. The image on the right is the most compact form of the standard model represented as an equation (this is also known a the Lagrangian). This equation is separated into 5 parts to explain certain parts of the model. For example, section 2, using almost half of the equation, explains interaction between bosons. So, his se ms perfect right? We av all of physics wrapped up n one neat, elegant (albeit omplex) equation. Howev , there is one major problem with this model. It doesn’t include gravity. As with the other f rces, the curvature of space-time caused b gravity can be mediated by a force-carrier boson known as the graviton, but when this particle is integrated into the standard model, infinities appear which cannot be removed. This is a problem as infinities do not appear in nature. Hence, gravity cannot be described in the quantum scale. Furthermore, gravity is the weakest force by far. In fact, it is weaker than the weak force (the next weakest force) by a factor of 1029 thereb making it entirely negligible in quantum interactions. The standard model clearly doesn’t work when accounting for gravity, so how can this b solved? In the standard model, particles are nvisioned as dimensionless points in the universe with innate quantum prop rties, including mass and charge. These are called po nt particles. The reason why we do this in the first place is because we don’t actually know wh t thes subatomic particles look like, so we assume that they are points. This is because the way that we se things are governed by light. W n light is r flected from surfaces, we absorb the light with our eyes and use the information gained from it to image our surroundings. However, at the quantum scale, light either doesn’t hit any particles at all, or when it does collide, it causes the particles to shift to diKerent position due to the extremely small scales. This means that we can never tru observe what a particle looks like. This concept is so important that it is named Heisenberg’s uncertainty principle where you can never precisely know the position an the momentum of a particle at the same time.
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