Quantum mechanics is one of the most revolutionary theories in physics. Unlike classical physics, which describes predictable, deterministic behavior like a ball following a clear trajectory, quantum mechanics deals with probability and uncertainty at the atomic scale. At this microscopic level, particles don't follow definite paths but exist in probabilistic states, fundamentally changing our understanding of reality.
The double-slit experiment is one of the most famous demonstrations of wave-particle duality. When electrons are fired at a barrier with two slits, they create an interference pattern on the screen behind, just like waves would. This suggests that each electron somehow goes through both slits simultaneously and interferes with itself. However, when we try to observe which slit the electron goes through, the interference pattern disappears and the electrons behave like particles, going through one slit or the other.
Quantum superposition is perhaps the most counterintuitive aspect of quantum mechanics. It states that quantum systems can exist in multiple states simultaneously until they are measured. Schrödinger's famous thought experiment illustrates this with a cat that is both alive and dead at the same time. The cat's state is described by a wave function that is a combination of both possibilities. Only when we open the box and observe does the wave function collapse into one definite state - either alive or dead, each with equal probability.
The Heisenberg Uncertainty Principle is a fundamental limit in quantum mechanics that states we cannot simultaneously know both the exact position and momentum of a particle. The more precisely we measure one property, the less precisely we can know the other. This isn't due to imperfect instruments, but is a fundamental property of quantum systems. The principle is mathematically expressed as delta x times delta p is greater than or equal to h-bar over two, where h-bar is the reduced Planck constant.
Quantum mechanics revolutionized our understanding of atomic structure by showing that electrons exist in discrete energy levels rather than continuous orbits. These quantized energy levels explain why atoms are stable and why they emit light at specific wavelengths. When an electron transitions between energy levels, it emits or absorbs a photon with energy equal to the difference between the levels. The energy of each level is given by the formula E equals negative 13.6 electron volts divided by n squared, where n is the principal quantum number.