In quantum mechanics, a photon is the fundamental unit of energy that can be exchanged between particles. It is a quantum of light and other forms of electromagnetic radiation.

Entanglement is a key principle of quantum mechanics that challenges classical notions of causality. It refers to the phenomenon where two or more particles become correlated in such a way that the state of one particle cannot be described independently of the other, even when they are separated by a large distance.

According to the Copenhagen interpretation of quantum mechanics, the observer's physical interaction with the system, such as the act of measurement, causes the wave function to collapse, resulting in a specific outcome.

Superposition is a key principle of quantum mechanics that allows a particle to exist in multiple states or locations simultaneously. This concept challenges classical notions of determinism and causality.

The uncertainty principle in quantum mechanics states that certain pairs of physical properties, such as position and momentum, or energy and time, cannot be known with perfect accuracy simultaneously. This principle has profound implications for our understanding of causality and determinism.

The double-slit experiment is a classic experiment in quantum mechanics that demonstrates the wave-particle duality of electrons. In this experiment, electrons are fired through two closely spaced slits, and the resulting interference pattern on a screen behind the slits reveals the wave-like behavior of electrons.

Quantum entanglement is a key feature of quantum mechanics that allows two or more particles to become correlated in such a way that the state of one particle cannot be described independently of the other, even when they are separated by a large distance. This phenomenon has profound implications for our understanding of causality and locality.

Quantum tunneling is a phenomenon in quantum mechanics where a particle can tunnel through a potential barrier even if it does not have enough energy to overcome it classically. This phenomenon has important implications for various applications, such as the operation of transistors and the study of nuclear reactions.

The many-worlds interpretation of quantum mechanics is a controversial interpretation that proposes that there are multiple universes, each corresponding to a different possible outcome of a quantum measurement. According to this interpretation, all possible outcomes of a quantum measurement exist simultaneously in different universes.

Quantum decoherence is the process by which a quantum system loses its coherence and becomes entangled with its environment. This process is responsible for the transition from the quantum world to the classical world, as it causes the superposition of states to collapse and the wave function to become localized.

The pilot-wave theory of quantum mechanics is an alternative interpretation that proposes that there is a hidden variable that guides the behavior of particles. According to this theory, the wave function is a real physical field that guides the behavior of particles, rather than a mere mathematical description of probabilities.

Quantum teleportation is the phenomenon where the measurement of one quantum system instantaneously affects the state of another quantum system that is entangled with it, even if they are separated by a large distance. This phenomenon has important implications for the development of quantum communication and cryptography.

The transactional interpretation of quantum mechanics is an alternative interpretation that proposes that quantum events are explained in terms of advanced and retarded waves. According to this theory, the wave function is a real physical field that guides the behavior of particles, and the observer's consciousness does not play a role in determining the outcome of a quantum measurement.

Quantum superposition is the phenomenon where a quantum system can exist in a superposition of states, even if those states are macroscopically distinct. This phenomenon challenges classical notions of reality and determinism, and has important implications for the development of quantum computing.

The Copenhagen interpretation of quantum mechanics is a widely accepted interpretation that proposes that the wave function is a complete description of a quantum system, and that the act of measurement causes the wave function to collapse. According to this interpretation, the observer's consciousness does not play a role in determining the outcome of a quantum measurement.