Quantum mechanics is the most strange and successful branch of physics ever developed by humans. Its predictions have been confirmed with extraordinary accuracy in thousands of experiments, yet its philosophical implications still confuse physicists and philosophers. One of the most bizarre principles is quantum superposition.
In the classical world we know, objects are always in a specific state โ a coin is either heads or tails, not both at the same time. However, in the quantum world, particles such as electrons can exist in a superposition of states โ a mathematical combination of two or more different states at the same time. An electron can be in a superposition of 'spin up' and 'spin down' simultaneously.
The famous double-slit experiment visually demonstrates this. When electrons or photons are fired one at a time through two slits, an interference pattern forms on the wall behind โ meaning each particle effectively passes through both slits at the same time in a superposition state. However, when detectors are placed to see which slit the particle passes through, the interference pattern disappears and the particle behaves like a classical bullet.
The process in which superposition 'collapses' into a single state when measured is called 'wavefunction collapse' and is one of the most debated topics in modern physics. The classic Copenhagen interpretation states that particles do not have definite properties before being measured โ they only have probabilities. Today, quantum computers exploit this superposition to perform calculations that are impossible for classical computers.