Since its formulation during the first part of the twentieth century, quantum mechanics has fascinated everybody who has tried to grasp it. Classical physics regarded the world to be deterministic; it claimed that if we just knew everything with enough precision, we should be able to predict what will happen tomorrow. Laws of nature, however, can be best explained by quantum mechanics, which is very different from classical physics: only the probability of a certain outcome of an experiment can be predicted. There is also a fundamental limit to how precisely certain pairs of physical quantities can be measured: when we improve the precision of measurement of one quantity, we lose it on another! Even more mind-boggling is the concept of entanglement. Two entangled particles can travel far from each other and still have a connection so that measurements on one of them immediately forces the other into a specific quantum state, regardless of the distance between them. Through the history of quantum mechanics, accomplished scholars and students alike have found this hard to accept, and argued that the theory must not be complete, that we are still waiting for its final version. Nevertheless, quantum mechanics has been proven to be a very successful theory. As far as we know, its predictions are all correct and technologies based on quantum mechanics are nowadays used everywhere: the smart electronic devices in our pockets, the energy efficient LED lamps, and the solar panels that harvest sunlight – deep inside they function because of the laws of nature explained by quantum mechanics.

It is often said that it is not possible to really understand quantum mechanics. This might be true, but with enough effort it is certainly possible to learn to master its machinery and use it to explain physical phenomena and develop new technology. Professor Pranawa Deshmukh writes in this book: “Quantum theory may shock and confuse us, but it is a successful theory of the physical world. It is cast in a mathematical framework which must be learned with patience and rigour.”

As a university teacher I know that the first course in quantum mechanics brings something special to many students. While classical physics seems to be completely settled and just for new generations to learn, quantum mechanics comes with surprises, riddles, and philosophical discussions.