“There’s the scarlet thread of murder running through the colourless skein of life, and our duty is to unravel it, and isolate it, and expose every inch of it.” So said detective Sherlock Holmes whose debut at the close of the nineteenth century in A Study In Scarlet coincided with a discovery that would become the black thread of physics, a mystery whose knots and tangles remain unexposed. That discovery, now known as matter’s twin, was antimatter.
Matter, quite simply, matters. Broken down to its smallest parts, it’s a bunch of miniscule particles. (What kind of particles? Elementary, my dear Watson.) Matter is the stuff that you, your house, 221B Baker Street, and the whole entire universe is made of. Except, there’s something more. The universe, we’ve now discovered, also contains a tricky substance called antimatter. Also made of individual particles, antimatter, though rare, can be produced by objects as varied as cosmic rays and decaying radioactive substances.
Sometimes referred to as matter’s equal but opposite, antimatter is the devious Moriarty to matter’s shrewd Holmes. Like these two intellectual rivals, anti-matter insists on being perfectly contrary to matter. Where a proton, for example, prides itself on its positive electrical charge, its antimatter mate, the antiproton, teasingly possesses a negative charge. And the negative electron finds its antimatter twin is the aptly named positron. Where matter says positive, antimatter cries negative and where matter demands negative, antimatter insists on positive.
Paul Dirac gets the credit for the deduction of antimatter. Dirac’s melding of special relativity with quantum physics left him some mathematical solutions that didn’t seem real. While some may have thrown these results away as red herrings, Dirac proposed it meant there were opposite particles (antimatter) for all the particles (matter) we understood. Dirac’s hunch was proved correct in 1932 by Carl Anderson, a Caltech physicist with his head in the clouds—literally. Working with a cloud chamber and a magnet, Anderson watched as cosmic rays passed through the chamber, their paths bent by the magnetic field. But to his surprise, this experiment revealed a rebellious little particle that behaved uncannily like an electron, except its opposite charge caused it to bend the other way. This was the positron—the twin of matter’s electron but for charge and spin.
While their parallelism seems beautiful in theory, if a particle and its antiparticle happen to meet, they blow up in a violent “annihilation,” exploding into pure energy. These bursts of energy leave behind confetti showers of gamma rays, what NASA looks for to determine where antimatter resides in space. Similarly, if you could hold an antimatter pencil, you wouldn’t know it from a pencil of matter except that near instantaneously you’d lose your matter-based hand.
Such annihilations may be the key to the mystery of antimatter’s near non-existence in our universe. Rewinding backwards, we realized in the birth of the cosmos, both entities were created from pure energy and upon annihilation with each other, were destined to return to energy. Yet, it’s surmised that for every billion antimatter particles created in the Big Bang, there were a billion and one matter particles. So, a residue of matter particles then remained after all the explosions and went on to create the universe we now live in. That could explain why only a tiny amount of antimatter in space has remained—so little, in fact, that no probe we have launched has ever made contact.
But we can make some here on Earth. Researchers at Brookhaven National Laboratory on Long Island in New York are doing that by brute force. By smashing together gold particles at nearly the speed of light, they exchange gold matter for energy. Like a last-minute eBay frenzy, this energy is then near-instantaneously swapped again for a smattering of other particles, some of which are antimatter. However, the true reward is when some of these antiparticles join to form new objects like antihelium, the antimatter twin of the gas we pump into birthday balloons. By creating antimatter, the modern-day gumshoes hope to fully confirm why it doesn’t exist more commonly in the universe.
But just because it’s a mystery doesn’t mean we haven’t found uses for antimatter. Much like NASA searches the galaxies for the signature of antimatter, a medical scanning technique called Positron Emission Tomography (PET) searches the human body. Instead of looking for gamma rays in the vast darkness of space, the scan injects positrons (harmless!) into our matter-based bodies and seeks the resulting gamma rays to detect potential problems like tumors. And Captain Kirk would have been resigned to boldly staying where many men had before (namely, Earth) had the Enterprise not been fueled by a concoction of antimatter.
So while matter matters, antimatter does too. Physicists suspect that uncovering the secret of why the cosmos’ ratio of matter to antimatter is unequal will help explain why we exist in the form we do. Until then, this Sherlockian game will remain afoot.