Undergraduate
  1. Classical mechanics  1.1. dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. projectile motion  1.1.4. Relative speed  1.1.5. Uniform circular motion  1.1.6. Non-uniform circular motion  1.1.7. Reference frames and transformations  1.2. Newton's Laws of Motion  1.2.1. First law of motion  1.2.2. Second law of motion  1.2.3. Third Law of Motion  1.2.4. Applications of Newton's Laws  1.2.5. Friction and its types  1.2.6. Free Body Diagram  1.2.7. Constraints and pseudo-forces  1.3. Work and Energy  1.3.1. work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy in classical mechanics  1.3.5. Conservative and non-conservative forces  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.4. Speed and collisions  1.4.1. Linear momentum  1.4.2. Conservation of momentum  1.4.3. Impulse and impact force  1.4.4. Elastic and inelastic collision  1.4.5. Center of mass and speed  1.4.6. Rocket Propulsion  1.5. Rotational motion  1.5.1. Torque and Angular Momentum  1.5.2. Moment of inertia  1.5.3. Rotational Kinematics  1.5.4. Rotational Energy  1.5.5. Rolling Motion  1.5.6. Precession and gyroscopic motion  1.6. Gravitational force  1.6.1. Newton's law of universal gravitation  1.6.2. Gravitational potential energy  1.6.3. Orbital mechanics  1.6.4. Kepler's laws of planetary motion  1.6.5. Gravitational field and potential  1.7. Fluid mechanics  1.7.1. Pressure and Pascal's Principle  1.7.2. Buoyancy and Archimedes' principle  1.7.3. Fluid Dynamics and Bernoulli's Principle  1.7.4. Viscosity and Poiseuille's law  1.7.5. Surface tension and capillarity  1.8. Oscillations and waves  1.8.1. Simple Harmonic Motion  1.8.2. Damped and driven oscillations  1.8.3. Coupled oscillations and common modes  1.8.4. Wave properties and types  1.8.5. Sound Waves and the Doppler Effect  1.8.6. Wave interference and superposition
  2. Electromagnetism  2.1. Electrostatics  2.1.1. Electric charge and properties  2.1.2. Coulomb's law  2.1.3. Electric field and electric potential  2.1.4. Gauss's Law  2.1.5. Capacitance and Dielectric  2.1.6. Electric dipole and potential energy  2.2. Electric circuits  2.2.1. Current and Resistance  2.2.2. Ohm's law  2.2.3. Kirchhoff's Laws  2.2.4. RC Circuit  2.2.5. AC Circuits and Reactance  2.2.6. Electric power and energy  2.3. Magnetism  2.3.1. Magnetic Fields and Forces  2.3.2. Ampere's Law  2.3.3. Magnetic dipole moment  2.3.4. Biot-Savart law  2.3.5. Magnetic Materials and Hysteresis  2.4. Electromagnetic induction  2.4.1. Faraday's Law  2.4.2. Lenz's law  2.4.3. Self and mutual induction  2.4.4. Transformers and Inductive Circuits  2.5. Maxwell's equations  2.5.1. Gauss's law for electricity  2.5.2. Gauss's law for magnetism  2.5.3. Faraday's law of induction  2.5.4. Ampere-Maxwell law  2.5.5. Electromagnetic waves
  3. Thermodynamics  3.1. Laws of Thermodynamics  3.1.1. Zeroth law of thermodynamics  3.1.2. First law of thermodynamics  3.1.3. Second Law  3.1.4. Third Law  3.2. Heat and work  3.2.1. Heat transfer (conduction, convection, radiation)  3.2.2. Thermal expansion  3.2.3. Heat engines and refrigerators  3.2.4. Carnot cycle and efficiency  3.3. Statistical mechanics  3.3.1. Maxwell–Boltzmann distribution  3.3.2. Entropy and Probability  3.3.3. Partition function  3.3.4. Fermi–Dirac and Bose–Einstein statistics
  4. Optics  4.1. Geometrical Optics  4.1.1. Reflection and Refraction  4.1.2. Mirrors and lenses  4.1.3. Optical Instruments  4.1.4. Fermat's principle  4.2. Wave optics  4.2.1. Interference in wave optics  4.2.2. Diffraction  4.2.3. Polarization  4.2.4. Coherence and holography
  5. Quantum mechanics  5.1. Wave–particle duality  5.1.1. Blackbody radiation in wave–particle duality in quantum mechanics  5.1.2. Photoelectric effect  5.1.3. Compton scattering  5.1.4. De Broglie wavelength  5.2. Schrödinger Equation  5.2.1. Time-independent Schrödinger equation  5.2.2. Particle in a box  5.2.3. Quantum Tunneling  5.2.4. Potential wells and obstacles  5.3. Quantum States  5.3.1. Wave function  5.3.2. Quantum operators  5.3.3. Heisenberg uncertainty principle  5.3.4. Angular momentum and spin
  6. Relativity  6.1. Special relativity  6.1.1. Lorentz transformations  6.1.2. Time expansion and length contraction  6.1.3. Relativistic energy and momentum  6.2. General relativity  6.2.1. Principle of Equivalence  6.2.2. Schwarzschild metric  6.2.3. Gravitational waves  6.2.4. Black holes and event horizons
  7. Solid state physics  7.1. Crystal structure  7.1.1. Bravais lattices  7.1.2. X-ray diffraction  7.1.3. Band theory  7.1.4. Phonons and lattice vibrations  7.2. Electrical and Magnetic Properties  7.2.1. Conductors, Semiconductors and Insulators  7.2.2. Superconductivity  7.2.3. Hall effect
  8. Nuclear and particle physics  8.1. Atomic Structure  8.1.1. Atomic Model  8.1.2. Nuclear binding energy  8.2. Radioactivity  8.2.1. Alpha, beta, gamma decay  8.2.2. Half life  8.2.3. Nuclear Fission and Fusion  8.3. Particle physics  8.3.1. Standard Model  8.3.2. Quarks and Leptons  8.3.3. antimatter  8.3.4. Fundamental interactions
  9. Astrophysics and cosmology  9.1. Stellar evolution  9.1.1. Star formation  9.1.2. Black holes and neutron stars  9.1.3. White dwarfs and supernovae  9.2. Cosmology  9.2.1. The Big Bang Theory  9.2.2. Dark matter and dark energy  9.2.3. Cosmic microwave background

Undergraduate → Astrophysics and cosmology → Cosmology ↓


Dark matter and dark energy


The universe we live in has many mysteries that scientists strive to solve. These mysteries include dark matter and dark energy. These two components are believed to make up about 95% of the universe, yet they remain elusive and largely theoretical. Understanding dark matter and dark energy is crucial to understanding the structure, evolution, and ultimate fate of the universe.

What is dark matter?

Dark matter is a form of matter that does not emit, absorb or reflect light, making it invisible and only detectable through its gravitational effects on visible matter, such as stars and galaxies. Although we cannot see dark matter, its presence is inferred from its gravitational effects.

Imagine you are looking at the night sky and you see stars and galaxies arranged in certain configurations. These configurations are so ordered that they cannot be explained by the gravitational pull of visible matter alone. Scientists believe that dark matter is responsible for this additional gravitational pull that governs the overall structure of the universe.

Historical background

The concept of dark matter dates back to the 1930s when Swiss astronomer Fritz Zwicky noticed that clusters of galaxies were moving much faster than predicted based on the visible mass of stars and gas. He theorized that there must be "missing mass" that we couldn't see.

Evidence of dark matter

Several observations support the existence of dark matter:

  1. Rotation curves of galaxies: The rotation speed of galaxies is inconsistent with the distribution of visible matter. The outer regions rotate at surprisingly high velocities, indicating the existence of additional mass. This mass is thought to be dark matter.
  2. Gravitational lensing: When light from distant galaxies passes near massive objects, the gravitational field causes the light to bend. Sometimes, the bending of light may not be due to visible mass alone, indicating the presence of dark matter.
  3. Cosmic Microwave Background (CMB): The radiation left over from the Big Bang, the CMB, exhibits temperature fluctuations that indicate the presence of dark matter in the early universe.

What is dark energy?

While dark matter is responsible for the structure of the universe, dark energy is associated with its expansion. Dark energy is a mysterious form of energy that accounts for about 70% of the universe and seems to be driving its accelerating expansion.

Imagine the universe as a balloon that is constantly inflating, causing galaxies to move away from each other. The force causing this inflation is thought to be dark energy.

Discovery of dark energy

In the late 1990s, scientists studying distant supernovae discovered that they appeared dimmer than expected, indicating that they were much farther away than initially thought. This observation showed that the universe is expanding at a faster rate, contrary to earlier expectations. This acceleration requires energy to drive it, now called dark energy.

Role in cosmology

Dark energy is very important in cosmology, the study of the origin and evolution of the universe. To understand its impact, consider the following:

  • Accelerating universe: Dark energy drives faster expansion, affecting the fate of the universe. If it continues to work as it does now, galaxies will move progressively farther apart, potentially leading to a "big pause" or "big rip."
  • Effects on large-scale structures: While dark matter tends to build up structures in the universe, dark energy tends to tear it apart, influencing the evolution of galaxies and galaxy clusters over time.
  • Cosmological constant: Albert Einstein introduced the cosmological constant into his equations for general relativity as a "fudge factor" to allow for a static universe. Since the discovery of an expanding universe, this constant has been reconsidered as a possible explanation for dark energy.

Nature of dark matter and dark energy

Determining the nature of dark matter and dark energy is one of the most important endeavors in contemporary physics. Although we have collected indirect evidence of their existence, their true nature still remains speculative. Various hypotheses and models attempt to describe these phenomena.

Hypotheses for dark matter

There are several possible candidates for what dark matter might be:

  1. Weakly interacting massive particles (WIMPs): These hypothetical particles interact with matter through the weak force and gravity, making them hard to detect.
  2. Axions: Another theoretical particle, axions, are light particles that, in addition to constituting dark matter, may help explain some phenomena in quantum physics.
  3. Primordial black holes: Small black holes that formed in the early universe may be part of dark matter.

Theoretical framework for dark energy

Dark energy theories are evolving but here are some popular possibilities:

  • Cosmological constant (Λ): Proposed by Albert Einstein, it suggests that dark energy is a constant energy density that fills space homogeneously.
  • Quintessence: A dynamic scalar field that evolves with time, as opposed to a static energy density.
  • Modified Gravitational Theory: Proposed changes to Einstein's theory of general relativity to eliminate the need for dark energy.

Visual examples and thought experiments

Dark matter and dark energy can be challenging to visualize due to their invisible nature. However, visual examples and thought experiments can help us better understand these concepts.

Visualizing dark matter

        <svg width="200" height="200" xmlns="http://www.w3.org/2000/svg">
            <circle cx="100" cy="100" r="80" stroke="black" stroke-width="2" fill="none"/>
            <circle cx="40" cy="100" r="10" stroke="black" stroke-width="2" fill="blue"/>
            <circle cx="160" cy="100" r="10" stroke="black" stroke-width="2" fill="red"/>
            <text x="65" y="95" fill="black">Visible Matter</text>
            <text x="160" y="95" fill="black">Dark Matter</text>
        </svg>

In this simple diagram, imagine a galaxy as a circle. The blue circles represent visible matter such as stars, while the red circle encloses the invisible but gravitationally influencing dark matter halo.

Thought experiment: cosmic expansion

Imagine a grid on the surface of the balloon. Draw points at the intersections. As the balloon inflates, watch how the points move apart. This shows how dark energy can move galaxies away from each other as the universe expands.

The importance of detecting dark matter and dark energy

Detecting and understanding dark matter and dark energy is important for several reasons:

  • Understanding cosmic evolution: These entities play a vital role in shaping the universe. Understanding them can help us predict future cosmic events and the ultimate fate of the universe.
  • Evolving theories of physics: Investigating the nature of dark matter and dark energy could lead to the development of new physics beyond the current standard model and general relativity.
  • Technological advancement: The discovery of these phenomena leads to advances in instrumentation and detection technologies, which are beneficial in a variety of scientific fields.

Current research and future prospects

Researchers use several methods and experiments to study dark matter and dark energy:

  1. Particle colliders: Devices such as the Large Hadron Collider attempt to produce dark matter particles during high-energy collisions.
  2. Direct detection experiments: Facilities such as the large underground xenon detector aim to capture the interaction of dark matter with ordinary matter.
  3. Space observatories: Missions such as the Euclid Telescope and the James Webb Space Telescope promise to provide deeper insights into dark matter and dark energy through observations of the expansion and structure of the universe.

The future of dark matter and dark energy research is promising, but it also has challenges. With advances in technology, breakthroughs are expected that will redefine our understanding of the universe.

Conclusion: Understanding the mysteries of the universe

The universe is a vast, complex fabric woven from visible and invisible threads. While we enjoy the glow of stars and galaxies, much of the universe remains hidden from our eyes, bound together by dark matter and driven apart by dark energy.

These concepts challenge our understanding and require innovative experiments, observations, and theoretical work. By unlocking these mysteries, we aim not only to explain the current structure and fate of the universe, but also to push the boundaries of what is possible in physics. Understanding dark matter and dark energy is not just about uncovering hidden forces – it is about seeing the universe and our place in it with new, enlightened eyes.


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Dark matter and dark energy

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