Modern Physics

Exploring relativity, quantum mechanics, and the fundamental nature of matter and energy

Subcategories

Nuclear Physics

Understanding atomic nuclei, nuclear reactions, and nuclear energy

Particle Physics

Understanding fundamental particles and the Standard Model

Quantum Mechanics

Understanding the quantum world, wave-particle duality, and quantum phenomena

Relativity

Understanding Einstein's theories of special and general relativity

Topics

Neutrinos are nearly massless, chargeless particles that interact only weakly with matter. They're produced in nuclear reactions, including fusion in stars and radioactive decay. Billions pass through your body every second, but they rarely interact, earning them the nickname 'ghost particles.'

What are quarks?

Quarks are fundamental particles that make up protons and neutrons. There are six types (flavors) of quarks: up, down, charm, strange, top, and bottom. Quarks combine in groups of two or three to form hadrons, and they're never found alone due to color confinement.

What are subatomic particles?

Subatomic particles are particles smaller than atoms, including protons, neutrons, and electrons that make up atoms, as well as many other particles discovered in particle physics. They include quarks (which make up protons and neutrons), leptons (like electrons), and force-carrying particles.

What is an atom?

An atom is the smallest unit of an element that retains the element's properties. Atoms consist of a nucleus (containing protons and neutrons) surrounded by electrons. The number of protons determines the element, while electrons determine chemical behavior.

What is antimatter?

Antimatter is matter made of antiparticles—particles with opposite charge to normal particles. Antielectrons (positrons) have positive charge, antiprotons have negative charge. When matter and antimatter meet, they annihilate, converting to energy.

What is dark matter?

Dark matter is invisible matter that doesn't emit, absorb, or reflect light, detectable only through its gravitational effects. It makes up about 27% of the universe's mass-energy, far exceeding visible matter. Dark matter's nature is unknown, but it's essential for explaining galaxy rotation, cosmic structure, and gravitational lensing.

What is nuclear fission?

Nuclear fission is the process where a heavy atomic nucleus splits into two or more lighter nuclei, releasing energy and often neutrons. Fission occurs when a nucleus absorbs a neutron and becomes unstable, splitting apart. Fission powers nuclear reactors and atomic bombs.

What is nuclear fusion?

Nuclear fusion is the process where two light atomic nuclei combine to form a heavier nucleus, releasing enormous energy. Fusion powers the Sun and stars, where hydrogen nuclei fuse to form helium. Fusion requires extremely high temperatures and pressures to overcome the repulsive force between positively charged nuclei.

What is the Higgs boson?

The Higgs boson is a fundamental particle discovered in 2012 that is associated with the Higgs field, which gives other particles mass. The Higgs field fills all space, and particles interact with it to acquire mass, explaining why some particles are heavy while others are light.

What is the standard model?

The Standard Model is the theory describing all known fundamental particles and three of the four fundamental forces (electromagnetic, weak, and strong). It organizes particles into quarks, leptons, and force carriers, and has been extremely successful in predicting and explaining particle behavior.

How do quantum computers work?

Quantum computers use quantum bits (qubits) that can exist in superposition (multiple states simultaneously) and entanglement (correlated states). This allows quantum computers to process many possibilities in parallel, potentially solving certain problems much faster than classical computers.

How does quantum mechanics work?

Quantum mechanics describes how particles behave at atomic and subatomic scales, where they exist in probability states rather than definite positions. Particles can be in multiple states simultaneously (superposition) until observed, and measurements affect what we observe.

How does quantum tunneling work?

Quantum tunneling occurs when particles pass through energy barriers they classically shouldn't be able to cross. Due to wave properties, particles have a probability of being found on the other side of barriers, even when their energy is less than the barrier height. This probability decreases exponentially with barrier width and height.

What is a quantum?

A quantum is the smallest discrete unit of a physical property. In quantum mechanics, many properties like energy, momentum, and angular momentum come in discrete packets (quanta) rather than continuous values. A photon is a quantum of light energy.

What is quantum entanglement?

Quantum entanglement is a phenomenon where two or more particles become correlated so that measuring one instantly affects the other, regardless of distance. Entangled particles share a quantum state and behave as a single system, even when separated.

What is quantum superposition?

Quantum superposition is the principle that quantum particles can exist in multiple states simultaneously until measured. A particle can be in a combination of different states (like spinning both up and down), with probabilities for each state. Measurement collapses the superposition to a single definite state.

What is Schrödinger's cat?

Schrödinger's cat is a thought experiment illustrating quantum superposition and the measurement problem. A cat in a box is simultaneously alive and dead until observed, representing how quantum particles exist in superposition until measured. It highlights the strange nature of quantum mechanics when applied to macroscopic objects.

What is the photoelectric effect?

The photoelectric effect occurs when light shining on a metal surface ejects electrons. Einstein explained it by proposing that light consists of particles (photons), with each photon's energy proportional to frequency. Only photons with sufficient energy can eject electrons, demonstrating light's particle nature.

What is the uncertainty principle?

The uncertainty principle states that we cannot simultaneously know precise values of certain pairs of properties, like position and momentum. The more precisely we know one, the less precisely we can know the other. This is a fundamental limit, not a measurement limitation.

What is wave-particle duality?

Wave-particle duality is the concept that particles like electrons and photons exhibit both wave-like and particle-like properties depending on how they're observed. They behave as particles in some experiments and as waves in others, showing that the classical distinction between waves and particles breaks down at the quantum level.

How does gravity bend space-time?

Gravity bends space-time because mass and energy curve the four-dimensional space-time fabric. According to general relativity, objects with mass create curvature, and other objects follow these curved paths, which we experience as gravitational attraction.

How does special relativity differ from general relativity?

Special relativity deals with objects moving at constant speeds in flat (non-curved) spacetime, describing time dilation and length contraction. General relativity extends this to include acceleration and gravity, describing gravity as the curvature of spacetime caused by mass and energy.

What are gravitational waves?

Gravitational waves are ripples in spacetime caused by accelerating masses, predicted by Einstein's general relativity. They travel at light speed, stretching and compressing space as they pass. Massive objects like merging black holes or neutron stars create detectable gravitational waves.

What is a black hole?

A black hole is a region of spacetime where gravity is so strong that nothing, not even light, can escape once it crosses the event horizon. Black holes form when massive stars collapse, creating extreme spacetime curvature described by Einstein's general relativity.

What is E=mc²?

E=mc² is Einstein's famous equation showing that energy (E) and mass (m) are equivalent, with c being the speed of light. It means mass can convert to energy and vice versa, explaining nuclear reactions and the energy in matter.

What is length contraction?

Length contraction (also called Lorentz contraction) is the phenomenon where objects appear shorter in the direction of motion when moving at speeds close to light speed. From a stationary observer's perspective, moving objects contract, with contraction increasing as speed approaches light speed.

What is relativity?

Relativity is Einstein's theory describing how space, time, and gravity work. Special relativity deals with objects moving at constant speeds, showing that time and space are relative. General relativity describes gravity as the curvature of space-time.

What is space-time?

Space-time is the four-dimensional combination of three spatial dimensions (length, width, height) and one time dimension. According to general relativity, mass and energy curve space-time, and this curvature is what we experience as gravity.

What is time dilation?

Time dilation is the effect where time passes slower for objects moving at high speeds relative to an observer. According to special relativity, moving clocks run slower than stationary ones, and this effect becomes significant near light speed.

Why can't anything travel faster than light?

Nothing can travel faster than light because reaching light speed would require infinite energy. As objects approach light speed, their mass increases and time dilates, requiring exponentially more energy. At light speed, these effects become infinite, making it physically impossible for anything with mass to reach or exceed this limit.