by Sarah Marquart April 10, 2017 Physics
In Brief
  • The concept of antimatter has a surprisingly long pedigree—it was first hypothesized by Arthur Schuster in 1898.
  • Subsequently, Schuster's idea was developed and clarified by Paul Dirac, whose research first predicted something never before seen in nature.

World and Anti-World

Antimatter is not just the fictional fuel of the starship Enterprise and its journeys on Star Trek; quite the contrary. Antimatter is actually something that scientists are currently utilizing. In fact, antihydrogen was created in 1995 (though it didn’t last long).

To many people, antimatter probably sounds a lot stranger than it really is. In its most basic sense, antimatter is just matter with its electrical charge reversed. So, in this respect, antielectrons, called “positrons,” are like electrons but with a positive charge. Along the same lines, antiprotons are like protons but they have a negative charge.

However, although its definition sounds simple enough, antimatter behaves very strangely. At least, it does when it interacts with matter. Upon meeting, matter and antimatter annihilate one another in a flash of energy, leaving behind subatomic particles. This process results in an explosion that emits pure radiation traveling at the speed of light.

The Big Bang should have created antimatter and matter in equal amounts. If that had been so, everything would have been destroyed in, well, a bigger bang. But, as far as scientists know, there must have been one extra matter particle for every billion matter-antimatter pairs. Physicists are actually still trying to understand why the universe didn’t annihilate itself and why this asymmetry exists.

In fact, apart from dark matter and dark energy, some of the most captivating mysteries in modern day physics center around antimatter. So let’s delve into the history of this exotic stuff.

The Origins of Antimatter

Antimatter was first referenced in 1898 by Arthur Schuster, a British physicist. Schuster wrote two letters to Nature in which he hypothesized antiatoms, their presence in the Solar System, and how they would react when they came in contact with regular atoms.

“Large tracts of space might thus be filled, unknown to us, with a substance in which gravity is practically non-existent, until by some accidental cause, such as a meteorite flying through it, unstable equilibrium is established, the matter collecting on one side, the anti-matter on the other until two worlds are formed separating from each other, never to unite again.”

Schuster goes on to discuss how matter and antimatter can coexist in bodies of small mass. He suggested that they repel one another, almost like the opposite poles of magnets. This was just the beginning. Paul Dirac later took Schuster’s hypothesis and shaped it into what we recognize today.

Sir Arthur Schuster, looking suitably Edwardian, in a 1912 portrait by William Orpen. He was the first to propose the duality of
Sir Arthur Schuster, looking suitably Edwardian, in a 1912 portrait by William Orpen. He was the first to propose the duality of “matter and anti-matter.”

Dirac developed a theory, now known as the Dirac equation, that combined quantum mechanics (used to describe the subatomic world) with Einstein’s special relativity (which explains the world of the very large). It explained how electrons, traveling at near light-speed, behave.

Notably, his equation—which he referred to as “beautiful” (clearly modesty is not to be counted among Dirac’s qualities)—dealt with both electrons (regular electrons with a negative charge) and particles that behave like electrons but have a positive charge.

He realized, eventually, that his equation predicted antiparticles. Dirac hypothesized that for every particle imaginable, there exists an antiparticle that is nearly identical, but has an opposite electric charge. If you were to add together antiprotons, antineutrons, and anti-electrons, you would get anti-atoms and antimatter.

This insight alerted scientists to the possibility that there could be entire galaxies and universes made of antimatter.

Ultimately, Dirac’s research marked the first time that something never before seen in nature was “predicted.” His work even earned him the title, “the Father of Antimatter.” For his work, he was awarded the Nobel prize in physics at the age of 31.