Matter's elusive dark twin: Most expensive substance in the universe

Indian Express

3 days ago

In 1930, theoretical physicist Paul Dirac was trying to reconcile quantum mechanics with Einstein's theory of relativity when his equations hinted at something strange: the existence of a 'mirror' particle identical to the electron, but with opposite charge. Its implications made him uneasy — that every particle has an antiparticle, and that perhaps the whole of nature is constructed in this way.
Dirac's calculation wasn't to be a mere mathematical quirk. Two years later, American particle physicist Carl Anderson found the positron, the electron's antimatter twin, in cosmic ray experiments. It was a moment of rare scientific poetry: a particle predicted by pure mathematics, then seen in nature.
Antimatter sounds like something from science fiction. And indeed, it has captured the imagination of writers from Star Trek (where it powers warp drives) to Angels and Demons (where it threatens to obliterate Vatican City). But antimatter is very real, though vanishingly rare in our universe. Whenever a particle meets its antiparticle, they annihilate in a flash of energy — converting all their mass, as per Einstein's , into pure light. That property makes antimatter the most energy-dense substance imaginable. A single gram could, in theory, produce as much energy as a nuclear bomb.
But if it's so powerful, why don't we use it? And why don't we see it everywhere?
Here lies one of the deepest mysteries in cosmology. The Big Bang, as we understand it, should have created equal amounts of matter and antimatter. But for reasons not yet fully known, the early universe tipped the scales ever so slightly toward matter — by just one part in a billion. That tiny excess is what makes up everything we see: stars, galaxies, people, planets. The rest annihilated with its antimatter counterpart in the early universe.
Physicists are still trying to understand why the universe has this imbalance. One possibility is that antimatter behaves slightly differently than matter — a tiny asymmetry in how particles decay, known as CP violation. Experiments at CERN and Fermilab are probing these effects, but so far, no definitive explanation has emerged.
The reality of antimatter: not just theory
Despite its elusiveness, antimatter isn't merely theoretical. We make it — routinely. In fact, hospitals around the world use positrons (antimatter electrons) every day in PET scans. The 'P' in PET stands for 'positron,' and the scan works by injecting a radioactive tracer that emits positrons. When these encounter electrons in the body, they annihilate and emit gamma rays, which are detected to create precise images of tissues.
Physicists at CERN's Antimatter Factory even trap anti-hydrogen atoms, composed of an antiproton and a positron, in magnetic fields for a few milliseconds at a time, to study their properties. The dream is to answer a simple but profound question: does antimatter fall down like regular matter, or does it somehow respond differently to gravity? Early experiments suggest it falls the same way, but the precision isn't yet conclusive.
Energy source or weapon?
Harnessing antimatter sounds like a sci-fi superpower, and indeed, the energy from matter-antimatter annihilation could, in theory, power spacecraft far more efficiently than any rocket we've built. But there's a catch: antimatter is mind-bogglingly expensive. Producing a single gram would cost about $60 trillion using today's particle accelerators. Worse, storing it safely is a nightmare. Let it touch anything, and boom, it annihilates.
That hasn't stopped the speculation. NASA has funded studies on antimatter propulsion, suggesting it could one day shorten interstellar travel. But for now, it remains out of reach, a gleaming prize at the edge of possibility.
Antimatter in space
Cosmic rays from deep space occasionally strike Earth's upper atmosphere, producing short-lived showers of antimatter particles. The International Space Station even carries an instrument called the Alpha Magnetic Spectrometer, scanning for signs of antimatter nuclei that could hint at entire regions of the universe made of antimatter — a speculative idea, but one not yet ruled out.
Neutron stars and black hole jets may also generate antimatter in tiny amounts, adding to the cosmic fireworks. But overall, the universe appears matter-dominated. Why nature chose this option, why there's something instead of nothing, remains among the deepest riddles in physics.
Final Reflections
In Star Trek, antimatter is a tame servant of human ambition. In reality, it's a fleeting, elusive shadow of the particles we know. Dirac's equations suggested a universe with perfect symmetry, but nature, like a mischievous artist, left a flaw in the mirror.
The story of antimatter reminds us that physics isn't just about numbers or formulas. It's about imagination, daring, and a relentless curiosity about the hidden sides of reality. Somewhere in the collision of matter and anti-matter lies a spark — of annihilation, yes, but also of wonder.
Shravan Hanasoge is an astrophysicist at the Tata Institute of Fundamental Research.