If someone turns on a light in Colaba, a bulb in Andheri flickers at the same instant – our chaotic city is a perfect Petri dish for quantum entanglement experiments
REPRESENTATION PIC
It’s a drizzly Sunday in Bandra. You’re at your usual café, watching the foam settle in your cappuccino. You stir it absent-mindedly and take a sip. And then, something strange happens: The foam rises again. The sugar you just added, dissolves into cubes. That warmth you felt? Gone. No, you’re not dreaming. You’ve just walked into a Quantum Café — a place where the rules of the universe don’t quite follow our everyday expectations.
In real life, time moves only one way. Ice melts, people age, spilled chai doesn’t leap back into the glass. This “arrow of time,” as physicists call it, is so intuitive that we never question it. But in the quantum world — the realm of atoms, electrons, and photons — this arrow gets a little wobbly. At that tiny scale, the laws of physics look the same whether time is moving forward or backward. In fact, if you were to film the motion of a single quantum particle and play it in reverse, there’s no way to tell the difference. It’s a principle called time-reversal symmetry. So why don’t we see this in real life? Why doesn’t your coffee unstir? The answer lies in entropy — a fancy word for disorder. Every time you stir sugar into tea or walk into a crowded Churchgate local, you’re moving from order to chaos. Entropy always increases with time. It’s the universe’s one-way street, and it’s why the mess in your room doesn’t clean itself. But under certain quantum conditions, time can appear to reverse — even if only briefly. And scientists are trying to understand how far we can stretch that boundary.
Let’s play with a thought experiment. What if Mumbai behaved like a quantum system? Imagine Andheri and Colaba are entangled. If someone turns on a light in Colaba, a bulb in Andheri flickers at the same instant. Not because of electricity, but because of quantum entanglement — a phenomenon where two particles (or people?) share such a deep connection that what happens to one affects the other, no matter how far apart they are. Einstein famously called this “spooky action at a distance”. But it’s very real. In fact, quantum entanglement has been observed between particles separated by kilometres. In China, it’s even been demonstrated between Earth and satellites orbiting 500 km above. The Indian government, too, is investing heavily in quantum communication systems — tech that could someday make our internet unhackable. Now imagine a local train operating on quantum principles. You’re both on it and not on it until your boss checks whether you’ve reached. That’s superposition, another key concept in quantum theory. It means a particle can be in multiple states at once — like a signal that’s both red and green. (Which is not too different from some Mumbai junctions.) In this city of contradictions, where a pothole and a Porsche can share the same square foot of road, quantum weirdness doesn’t seem all that far-fetched.
The Real-Life Quantum Café
The inspiration for this column came from a 2019 experiment at IBM, where scientists used a quantum computer to simulate the reversal of time. In simple terms, they took a quantum state, messed it up deliberately, and then reversed it back to its original condition — like unscrambling an egg, at least mathematically. It lasted just a fraction of a second. But it proved something profound: under the right circumstances, time can be nudged backward. This doesn’t mean we’ll be building time machines any time soon. But it challenges one of our most basic assumptions — that time always flows forward, no exceptions. In the quantum world, “always” is rarely absolute. And here’s where things get philosophical. Time, Consciousness, and Cappuccino: Some physicists believe the arrow of time is tied to observation. In other words, time behaves differently when we’re not looking. It’s only when a measurement is made — when a particle’s position or momentum is observed — that probabilities collapse into outcomes. Schrödinger’s cat is both alive and dead, until someone opens the box. Which raises the uncomfortable question: is time itself dependent on consciousness? If that’s true, then sitting in your café, sipping your drink, you’re not just passing time — you’re creating it. Every thought, every glance, every memory is part of the machinery that keeps time flowing forward in your corner of the universe. So maybe, just maybe, the universe outside is more fluid than we think. And the real reason your coffee doesn’t refill itself has less to do with physics and more to do with the fact that someone is watching.
All this may sound like sci-fi, but India is racing ahead in the quantum domain. With over '8,000 crore allocated under the National Quantum Mission, startups and research labs across the country — from Pune to Bengaluru — are building quantum computers, sensors, and encrypted networks. In a few years, your bank transactions might be protected by qubits. Your medical scans could be powered by quantum imaging. Even your Uber might be optimised using quantum algorithms. And who knows — maybe some day, a real café in Mumbai will serve as a demo site for quantum entanglement experiments. The menu will still have overpriced avocado toast, but your bill might arrive before you even order.
Physics doesn’t just live in labs or textbooks. It’s embedded in the way we make sense of our world, and sometimes, in the places we least expect — like a lazy Sunday cafe, where the milk is swirling and the mind is wandering. And in those moments, when the coffee cools and time slows just a bit, you might catch a glimpse of something bigger. Something quantum. Or maybe it already happened. And you’re just now remembering it.
Nishant Sahdev is a theoretical physicist at the University of North Carolina at Chapel Hill, United States. He believes that if any city could host a glitch in the space-time continuum, it’s Mumbai. X: @NishantSahdev
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