In the first part of our new series, Govert Schillingexplains what particle physics is
Astronomy is the science of very large objects: planets, stars, galaxies and the Universe as a whole. In contrast, particle physics deals with the smallest things we know: the elementary building blocks of matter, particles smaller than an atom. With such a difference in scale, the two disciplines may seem to have little in common. However, they turn out to be inextricably linked. In this new six-part beginners’ course, we’ll explore the basics of what has become known as astroparticle physics.
To study the geology of the Moon, you don’t need to know about the behaviour of individual elementary particles. But astronomers wouldn’t understand the evolution of stars without knowledge of atomic processes like nuclear fusion. Supernova explosions would not happen were it not for the weird properties of neutrinos. Active galactic nuclei, powered by supermassive black holes, spew out the most energetic protons and electrons we have ever observed. And right after the Big Bang, our Universe was one big particle experiment.
Ancient Greek philosophers assumed that everything in nature consisted of just four basic elements: earth, water, air and fire. As long ago as the 5th century BC, Democritus of Abdera further suggested that all matter consists of fundamental building blocks, which he named atoms, from the Greek word for ‘indivisible’. But it wasn’t until the 19th century that we arrived at the modern view of atoms as the smallest representatives of the dozens of chemical elements in the periodic table.
Moreover, physicists discovered that atoms – despite their name – are not actually indivisible. Instead, they consist of even tinier particles.
Ups and downs
Today, we know that the material world is like a huge Lego edifice, built from just three different elementary particles: up quarks, down quarks and electrons. Since quarks are usually bound up in nuclear particles known as protons (two up quarks and one down quark) and neutrons (two downs and one up), it’s also fair to say that everything in the Universe consists of protons, neutrons and electrons. Atomic nuclei contain various numbers of protons and neutrons; the number of protons determines what chemical element we’re dealing with. Surrounding the nucleus is a cloud of electrons.
Electrons, protons and neutrons wer
