Introduction to Physics: Core Concepts

• Physics is a natural science examining matter, its fundamental parts, motion, behavior through space and time, and related entities like energy and force.
• It stands as one of the most fundamental scientific disciplines.
• Physics aims to understand the behavior of the universe
• Physics employs the scientific method, formulating and testing hypotheses grounded in experimental observation.

Core Concepts in Physics

• Mechanics studies the motion of bodies acted upon by forces.
• Thermodynamics explores heat and its relation to other forms of energy.
• Electromagnetism explains phenomena involving electric charges and magnetic fields.
• Optics studies the behavior and properties of light.
• Quantum mechanics studies the behavior of matter and energy at atomic and subatomic levels.

Classical Physics

• Includes mechanics, thermodynamics, electromagnetism, and optics as developed pre-20th century.
• Assumes energy can take any continuous value.
• It relies on deterministic laws, where initial conditions enable precise prediction of future states.

Modern Physics

• Emerged in the 20th century via relativity and quantum mechanics.
• It is essential for understanding phenomena at extreme speeds (near light speed) or at very small scales (atomic/subatomic).

Quantum Physics

• A fundamental theory describing physical properties of nature at the scale of atoms and subatomic particles.
• Is also referred to as quantum mechanics or quantum theory.
• Provides a mathematical description of wave-particle duality.
• It deviates notably from classical physics, especially at atomic and subatomic levels.

Key Concepts in Quantum Physics

• Quantization: Certain physical properties, such as energy, can only take on discrete values.
• Energy levels of electrons in atoms are quantized, which leads to discrete emission and absorption spectra.
• Wave-particle duality: Particles exhibit wave-like properties, and waves exhibit particle-like properties.
• Electrons and photons behave as both particles and waves.
• Heisenberg's Uncertainty Principle: It is impossible to know both the position and momentum of a particle with perfect accuracy simultaneously.
• Accuracy in determining one property reduces accuracy in determining the other.
• Superposition: A quantum system can exist in multiple states simultaneously.
• A quantum system exists as a combination of multiple states until measured.
• Quantum entanglement: Two or more particles can become linked, sharing the same fate regardless of distance.
• The state of one particle instantaneously influences the state of the other, irrespective of distance.

Quantum Mechanics vs Classical Mechanics

• Quantum mechanics addresses discrete quantities, whereas classical mechanics often deals with continuous quantities.
• Quantum mechanics incorporates probabilistic outcomes, while classical mechanics assumes deterministic outcomes.
• Quantum effects are significant at the atomic and subatomic level, while classical mechanics accurately describes macroscopic phenomena.

Applications of Quantum Physics

• Lasers operate using the principles of quantum mechanics, particularly stimulated emission.
• Transistors in electronic devices rely on the quantum behavior of electrons in semiconductors.
• MRI uses quantum mechanics to visualize internal body structures.
• Quantum computing aims to use quantum phenomena like superposition and entanglement for computations impossible for classical computers.

Quantum Field Theory

• A theoretical framework combining quantum mechanics with special relativity.
• Treats particles as excited states of quantum fields.
• It underlies the Standard Model of particle physics.

Interpretations of Quantum Mechanics

• Copenhagen interpretation: Observation collapses the wave function into one definite state.
• Many-Worlds Interpretation: Every quantum measurement splits the universe into multiple universes, each corresponding to a possible outcome.
• Consistent Histories: Assigns probabilities to entire histories of a quantum system, providing a framework for discussing its evolution over time.