Take a weather forecast. It does not tell you whether rain will fall on your street at four o'clock. It gives you the chances. Quantum mechanics does the same for atoms. The forecast misleads on one point, and it is the important one. A forecast is uncertain because the forecaster lacks information, while the weather is doing something definite. In quantum mechanics there is no hidden answer. The result is undecided until it is measured.
Quantum mechanics is not a bet on the future. It has already been paid for. Transistors, lasers, medical scanners and the clocks that time-stamp financial trades all work because of it. Global chip sales reached 627.6 billion dollars in 2024, and every one of those chips rests on the behaviour of electrons in silicon.
What is new is the ability to handle atoms and particles of light one at a time. So when a project of that kind is called risky, be precise about the risk. The physics is settled. What is not settled is the engineering, the cost and the timing.
One misunderstanding does real damage. Quantum mechanics does not say that anything is possible. It is a strict set of rules that assigns exact odds, and many of those odds are zero. It forbids far more than it allows, which is why things can be built with it.
Quantum mechanics is the most carefully checked theory in science. The magnetic strength of the electron has been measured to about one part in a trillion, and it matches the prediction. No experiment has ever caught it out. A hundred years on, the theory works better than any story told about it.
Qubit · Superposition · Quantum entanglement · Quantum computer
It is the rulebook physics uses for atoms, electrons and light. It describes an object by a quantum state and gives the odds of each result an experiment can produce.
Quantum mechanics is the theory itself. Quantum physics is the wider field built on it. In everyday use the two words are interchangeable, and nothing important depends on the choice.
In a letter to Max Born in December 1926, he wrote that the theory delivers a great deal but that he was convinced God does not play dice. He doubted it until his death, and later experiments decided against him.
The smallest parts of the world, such as atoms and particles of light, do not follow the rules of everyday objects. Their energy comes in fixed steps, and science can only give the chances of what will happen.
It is confirmed to a precision no other theory reaches: the magnetic strength of the electron matches the prediction to about one part in a trillion. What is debated is what the theory means, not whether it works.
It already sits inside transistors, lasers, medical scanners and satellite navigation. A second generation of technology now handles single atoms and particles of light, which is what makes quantum computing and quantum sensing possible.
1. Planck, M., black-body radiation law, presented to the German Physical Society, 14 December 1900.
2. Fan, X., Myers, T. G., Sukra, B. A. D. & Gabrielse, G., Measurement of the Electron Magnetic Moment, Physical Review Letters 130, 071801, February 2023, doi 10.1103/PhysRevLett.130.071801.
3. Semiconductor Industry Association, global semiconductor sales 2024 (627.6 billion dollars), February 2025.
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