Category: The 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…

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…

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…

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…

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.…

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…

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,…

Nature presents us with the macroscopic world, everything we see about us on Earth, but also everything above us, in our solar system and beyond. Nature also presents us with microscopic entities such as atoms, which are made of nuclei and electrons. Nuclei are themselves composed of protons and neutrons. But is this the end…