30 August,2026 07:29 AM IST | Mumbai | Nishant Sahdev
In 1966, three Soviet physicists turned this into a full theory: not just twin particles, but a whole second version of everything. Mirror atoms, mirror water, mirror rock, and even mirror sunlight. Pics/iStock
A few years ago, a story raced around the internet: NASA had found a parallel universe where time runs backwards. It was not true. A balloon over Antarctica had picked up some strange radio signals, and headline writers did the rest.
The real story is better. Serious physicists do think there may be a mirror world - not as a daydream, but as the answer to a riddle that has troubled them since 1957. And this year it stopped being an astronomer's argument. It became something the United Nations is worried about.
Hold up both hands, palms towards you. Same fingers, same thumbs - yet you cannot lay one exactly on top of the other. A left glove will never fit a right hand. Your hands are mirror images. Scientists call this handedness, and it is one of the deepest facts about the world.
Everyone once assumed nature had no preference between left and right. Here is the test. Film an experiment, and then hold the film up to a mirror. Whatever you see in the reflection should be something that could really happen. It may look unfamiliar; it should not look impossible.
In 1956, two young scientists, Tsung-Dao Lee and Chen Ning Yang, realised nobody had bothered to check. They asked a colleague, Chien-Shiung Wu, to run the test.
Wu used cobalt, a metal whose atoms slowly fall apart on their own, spitting out tiny particles. She cooled it colder than deep space, lined the atoms up, and watched which way those particles flew.
They flew out mostly one way. One direction was clearly favoured. So if you filmed Wu's experiment and held it up to a mirror, you would be watching something nature never does. The universe can tell left from right. Nobody has ever explained why.
Lee and Yang offered a beautiful escape. Maybe the universe has no preference after all - but only if you count everything, and we have not been. Maybe every particle we know has a twin built the other way round. Our half leans left, the other half leans right, and together they balance.
Ten years later, three Soviet physicists turned this into a full theory: not just twin particles, but a whole second version of everything. Mirror atoms, mirror water, mirror rock, and even mirror sunlight. And here is the part that stops you. This second world would not be far away. It would be right here - passing through this room, this newspaper, you.
Why would nobody notice? Because it would carry its own light, which our eyes cannot see, just as their eyes could not see ours. The two worlds would ignore each other entirely, with one exception: gravity. They would still pull on each other, the way the Moon pulls the sea.
That should sound familiar. For roughly ninety years, astronomers have had an embarrassing problem - galaxies spin far too fast. By rights they should fly apart, the way a merry-go-round spinning too quickly throws off anyone holding on. Something invisible is gripping them. Something heavy that gives off no light at all.
We named it dark matter, and we still have no idea what it is. A mirror world would be invisible for a very good reason. It is not a guess pulled from thin air; it falls out of the maths.
There is a bolder version. In 2018, three physicists suggested the Big Bang is not the beginning of everything but a mirror lying at the middle of it.
On our side, our universe, running forwards. On the other, a reflection running the other way. Neither came first.
Now the twist, and it has nothing to do with space.
You are handed too. The building blocks of every muscle, hair and drop of blood in your body are built left-handed. The sugars in your DNA are built right-handed. Every living thing shares this - every bird, every tree, every germ. Nobody knows why life picked one and stuck with it for four billion years.
In principle, you could build a bacterium the other way round. It would still eat, grow and multiply. It would simply be wearing its gloves on the wrong hands.
In December 2024, thirty-eight scientists - including two Nobel Prize winners, and several who had spent their careers trying to build exactly this - published a warning saying it must never be made.
Their reason is simple and frightening. Your immune system works rather like a guard who has memorised photographs of every known criminal. Over four billion years it has learned the shapes of left-handed life. A mirror germ would be a face it has never seen. The natural predators that keep germs in check would be equally blind, and so would many of our medicines.
Since then, ninety-six experts from over twenty countries have asked for a halt. UNESCO called for a worldwide ban. This March, a United Nations panel warned that pieces of such a creature are already being made in laboratories. And this year, the scientists who set the famous Doomsday Clock listed mirror life among the reasons they moved it closer to midnight than ever.
Most think a working mirror germ is ten to thirty years away. The scientists have asked to be stopped while stopping is still possible.
None of this is worth much unless it can be proved wrong. It can.
Telescopes could spot a mirror star, which would leak a faint, odd glow as it swallowed ordinary gas. Detectors buried deep in mines could catch the two worlds brushing against each other. And the mirror-Big-Bang idea predicts something specific about the very first instant, which telescopes in Chile and a Japanese satellite are now hunting for.
Notice the pattern. Every mirror question returns to the same thing: nature made a choice. The universe leans one way. Life leans one way.
Had the universe been perfectly balanced, the two halves would have wiped each other out at the start, leaving nothing but light and nobody to see it.
So the mirror world, if it exists, is not a place where a happier version of you is living a better life. It is the missing half of something broken - and quite possibly most of the matter in the sky.
Nishant Sahdev is a physicist at the University of North Carolina at Chapel Hill, US. He chases ideas that refuse to stay in laboratories, for your favourite Sunday mid-day.
