# Dirac Equation

Paul Dirac an English physicist who is known as the father of antimatter conducted research which marked the first time that something that was never before seen in nature was predicted, or postulated to exist based on theoretical rather than experimental evidence.  His discovery was guided by the human imagination, and arcane mathematics.  Dirac developed a theory that combined quantum mechanics, used to describe the subatomic world, with Einstein’s special relativity, which says nothing travels faster than light.  Through complex mathematical calculations, Dirac managed to integrate these disparate theories.  As a result, Dirac’s equation describes how particles like electrons behave when they travel close to the speed of light, and it also provides an explanation for the origin of Spin (angular momentum carried by particles) and it predicted the fine details of the Hydrogen Spectrum (spectral series wavelengths).  It was the first step towards what is called quantum field theory, which has given us the standard model of particle physics and the Higgs boson particle.

One crucial idea that has driven physics since Newton’s time is that of unifying scientific theories by attempting to explain seemingly different phenomena with a single overarching concept.  There are four fundamental forces in the universe being, gravity, electromagnetism, and the weak and strong nuclear forces.  Each of these is produced by fundamental particles that act as carriers of the force.  The most familiar of these is the photon, a particle of light, which is the mediator of electromagnetic forces.  This means that, for instance, a magnet attracts a nail because both objects exchange photons.  The graviton is the particle associated with gravity.  The strong force is carried by eight particles known as gluons.  Finally, the weak force is transmitted by three particles, the W+, the W , and the Z.

To better understand Dirac’s equation, we must understand what the world made of.  Ordinary matter is made of atoms, which are in turn made of just three basic components being, electrons whirling around a nucleus composed of neutrons and protons.  The electron is a truly fundamental particle (it is one of a family of particles known as leptons), but neutrons and protons are made of smaller particles, known as quarks.  Quarks are, as far as we know, truly elementary.  Our current knowledge about the subatomic composition of the universe is summarized in what is known as the Standard Model of particle physics.  It describes both the fundamental building blocks out of which the world is made, and the forces through which these blocks interact.  There are twelve basic building blocks.  Six of these are quarks, they go by the interesting names of up, down, charm, strange, bottom and top.  A proton, for instance, is made of two up quarks and one down quark.  The other six are leptons, these include the electron and its two heavier siblings, the muon and the tauon, as well as three neutrinos.

Dirac’s equation not only works for an electron with negative charge, but it also works for a particle that behaves like an electron with positive charge.  At first, Dirac did not appreciate the significance of this finding, and he just ignored it out of what he would later call ‘pure cowardice’.  Eventually he realized that his equation predicted something entirely new to science which is known as antiparticles.  He went on to assert that every particle has a mirror-image antiparticle with nearly identical properties, except for an opposite electric charge.  And just as protons, neutrons and electrons combine to form atoms and matter, antiprotons, antineutrons and anti-electrons (called positrons) combine to form anti-atoms and antimatter.  His findings led him to speculate that there may even be a mirror universe of antimatter.

If you think it is odd for a girl named Alice to fall through a rabbit hole into a fantasy world populated by peculiar, anthropomorphic creatures, well antimatter is just as peculiar, as in theory you may be able to step through a mirror to enter a different, yet somehow familiar world on the other side.  Physicists around the world are using high-tech machines to make particles of antimatter.  They think of antiparticles as mirror images of the particles that make up everything in our everyday world.  Just as you look like your image in a mirror, except that right and left are interchanged, a particle and its antiparticle are identical, except that they have opposite electrical charges.

## 7 thoughts on “Dirac Equation”

1. Well written, especially for the curious-minded who do not understand quantum physics – thank you !

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