Can probability go beyond 100%? Indian scientists just did something unexpected
Imagine tossing a coin and being told there is a 120% chance it will land heads. It makes no sense. In the ordinary world, probability has a hard limit: it can never be greater than 100%, or 1.
But at the strange scale of quantum physics, scientists use another way of describing what can happen, and that number does not necessarily obey the same limit.
Physicists at India's Raman Research Institute (RRI) have now experimentally measured such a quantity and found it to be 1.17, crossing the upper limit that ordinary probability cannot exceed.
The result, published in the journal Quantum, is the first experimental measurement of a quantum measure greater than one. When you toss a coin, the probability of it landing as a head or tails is always 50-50. (Photo: Unsplash)
But scientists have not discovered a probability greater than 100%.
Instead, they have measured a quantity that captures something uniquely quantum: the interference between different possible paths taken by a particle.
In conventional physics, we often describe an event by asking what happens at a particular point in time. Quantum physics allows another way of looking at the problem, by considering all the possible paths a particle could take between its starting point and its final destination.
In the RRI experiment, researchers worked with photons, or particles of light. A photon travelling through their optical setup could take different routes before reaching a detector.
The researchers built an βevent-filterβ to select a particular collection of these possible routes.
They used a property of light called polarisation, the direction in which its waves oscillate, to distinguish between the different routes. They then erased that information, allowing the routes to interfere with each other.
This interference is crucial. Photo: India Today
Like water waves that can combine to form a larger wave, different quantum possibilities can reinforce one another. Quantum Measure Theory takes this interference into account when assigning a value to a collection of possible histories.
The researchers measured a quantum measure of approximately 1.17, very close to the predicted value of 1.18 after accounting for imperfections in the experiment.WHY CAN IT GO ABOVE 1?
The probability of detecting the photon still remains between zero and one. The number that exceeds one is the quantum measure, which incorporates the interference between different possible paths.
The experiment is significant because Quantum Measure Theory had largely remained a mathematical framework for thinking about quantum processes. The RRI experiment shows that this quantity can actually be measured in a laboratory.
The theory is also connected to attempts to understand some of the deepest questions in physics, including the search for quantum gravity, a theory that could reconcile quantum mechanics with gravity. Quantum mechanics is usually described in terms of the state of a system at a particular time and the outcomes obtained when we measure it. (Photo: Getty)
The researchers stress that the experiment does not prove quantum gravity or solve the quantum measurement problem.
Instead, it demonstrates that scientists can experimentally access a new class of information about quantum processes.
In the future, the event-filtering approach could potentially find applications in quantum measurement and quantum computing.
For now, the key takeaway is simpler: scientists have not broken the rules of probability. They have experimentally shown that the quantum world can be described by a measure that behaves differently from ordinary probability, and that strange quantity can now be measured.- EndsPublished By: Sibu Kumar TripathiPublished On: Sep 24, 2026 17:47 IST
