Author: haroonkhan
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First Generation Fermions
As it turns out, all of the most fundamental particles that eventually make up ordinary matter are fermions, with spin quantum number equal to 1⁄2. These include the familiar electron (e), along with two flavors of quarks that join to form protons and neutrons. These two kinds of quarks are called “up” and “down,” for no…
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Leptons and Quarks
We introduced the ancient Greek concept of atomos, a sort of tiny and indivisible particle from which the universe is made. Though this idea was seriously rekindled in the early nineteenth century, it didn’t take long to show that the particles then believed to be fundamental were actually made up of smaller things. But did this…
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Introduction
We extend our discussion of the fundamental interactions into a more detailed look at the relatively small number of fundamental particles we now know exist. We’ll see which particles participate in which of the fundamental interactions. We’ll find an interesting correspondence between electrons and quarks, and discover that they each come in three “generations.” We’ll…
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The Four Fundamental Interactions
Interaction Relative Strength Range Particles Influenced Strong 1 ~ 10-15 m Quarks Electromagnetic 10-2 Infinite Charged particles Weak 10-9 ~ 10-17 m Fermions Gravitational 10-38 Infinite Massive particles Surely, however, the odds are against us. A comparison of these interactions reveals differences (e.g., mass vs. color, infinite vs. subnuclei range) so profound that there can’t be much…
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A More Fundamental Interaction?
Physicists are reductionists who seek to explain how the universe works with as few fundamental laws as possible. While physicists are generally content that the universe can be boiled down to only four fundamental interactions, there is simultaneously a desire to see if it can’t be simplified even further. The goal to unify the four…
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The Weak Interaction
The fact that some nuclei are unstable. These are called radioactive nuclei, and their state and even identity can change spontaneously. These changes occur by the absorption and emission of energy in the form of alpha particles, electrons, positrons, and gamma rays. Radioactive nuclei that have too many neutrons compared to protons emit electrons in…
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The Strong Interaction
Ernest Rutherford’s nuclear model of the atom, consisting of a tiny massive nucleus surrounded by a cloud of electrons. With the discovery of the neutron in 1932 by James Chadwick it became clear that the nucleus is really formed of protons and neutrons. So a natural question would be, given the electromagnetic repulsion between the…
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The Electromagnetic Interaction
The physics of electromagnetic phenomena is governed by the electromagnetic interaction, which includes both electricity and magnetism. It is based on a quantity called charge, of which there are two varieties–positive or negative. Of course, not all particles are charged in the first place, and so-called “neutral” particles couldn’t care less about the electromagnetic interaction.…
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The Gravitational Interaction
Gravity was not only the first of the fundamental interactions we introduced in this book, it was also the first recognized by scientists. As far back, even, as Aristotle. We described gravity as an attractive force between all particles with mass, whether they are charged or not and whether they are big or small. Gravity…
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From Galaxies to Quarks
The universe is big. So big that we don’t really know precisely how big it is. The most recent estimates, based on scientific observations, give a radius of about 46 billion light years. (A light year is the distance that light, with all of its speediness, travels in a year.) While the universe contains mostly empty space,…