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 ↓


The Big Bang Theory


The Big Bang Theory is a central element in astrophysics and cosmology, which hypothesizes the origin and expansion of the universe. This theory states that the universe began about 13.8 billion years ago as a tiny, incredibly dense and hot point known as the singularity. This idea has shaped the way scientists understand the universe and is supported by various observational and theoretical inputs.

Early observations and development

In the early 20th century scientists began to understand that the universe was much larger and more dynamic than previously thought. A key figure in these discoveries was the American astronomer Edwin Hubble.

Hubble found that galaxies are moving away from us in all directions. This observation implies that galaxies are expanding, leading to the idea that the universe is expanding. This expansion can be visualized as the surface of an inflated balloon, with galaxies represented as points receding as the balloon inflates.

The concept of redshift

Hubble's observations were based on the redshift of the light coming from galaxies. The concept of redshift is important in cosmology and can be explained as follows:

The light coming from an object moving away is stretched, making it appear redder (hence 'redshift'). This is due to the Doppler effect, where the wavelength of light increases as the source moves away from the observer.

Let's illustrate the redshift phenomenon using a simple visualization. Imagine a wave emitted from a moving source:

The figure above shows a wave moving from left to right, which represents light waves coming from a moving source. As the wave moves away, its wavelength increases, which symbolizes the redshift effect.

Evidence in support of the Big Bang theory

Cosmic Microwave Background (CMB)

Another important evidence for the Big Bang theory is the cosmic microwave background (CMB) radiation, discovered by Arno Penzias and Robert Wilson in 1965. The CMB is the glowing afterglow of the Big Bang, which fills the universe almost uniformly.

The CMB is thought to be the heat left over from the initial explosion and provides a snapshot of the universe about 380,000 years after the Big Bang, when it had cooled enough that protons and electrons combined into hydrogen atoms. This event is known as "recombination", and from this point on, the universe became transparent to radiation.

Abundance of light elements

The Big Bang Theory also explains the observed abundance of lighter elements such as hydrogen, helium, and lithium. In the moments after the Big Bang, the universe was too hot for atomic nuclei to exist. As it expanded and cooled, conditions became perfect for nuclear reactions to occur, creating these lighter elements in a process known as Big Bang nucleosynthesis.

Theoretical foundations

General relativity

The theoretical foundations of the Big Bang Theory are strongly linked to Albert Einstein's theory of general relativity. Einstein's equations describe how matter and energy interact with the fabric of space-time. In essence, these equations state that the universe can either expand or contract, but cannot be static.

In a simplified form, the relation is expressed by Friedman's equations:

(dR/dt)^2/R^2 = (8πG/3)ρ - k/R^2 + Λ/3

where R(t) is the scale factor of the universe, G is the gravitational constant, ρ is the energy density, k is the spatial curvature of the universe, and Λ is the cosmological constant.

Inflation theory

Inflation theory is an extension of the Big Bang theory that helps solve many problems such as the horizon problem and the flatness problem. The theory states that the universe underwent a rapid exponential expansion during a tiny fraction of a second after the Big Bang.

The idea of inflation explains how regions of the universe can become so homogeneous and isotropic (i.e., look the same in all directions), even though they were initially causally unconnected.

Philosophical implications

The Big Bang Theory also has important philosophical implications. It raises questions about the origins of the universe and our place in it. Some consider whether the beginning of the universe implies the existence of a creator or what conditions existed before the Big Bang, although such questions often fall outside the scope of scientific inquiry.

Ongoing research and observations

Research on the Big Bang Theory and cosmology continues. Modern telescopes and observational techniques such as the Hubble Space Telescope provide a wealth of information about the early universe. Instruments such as the Planck satellite have helped map the CMB with unprecedented detail.

In addition, the discovery of dark matter and dark energy has raised new questions about the structure and fate of the universe. Dark energy, in particular, seems to be driving the universe's rapid expansion, thereby modifying the original Big Bang framework.

Conclusion

The Big Bang Theory remains the most compelling explanation for observable phenomena in cosmology. It explains the expansion of the universe, the distribution of galaxies, the abundance of light elements, and the cosmic microwave background radiation. As our understanding of physics grows, this foundational theory in cosmology continues to be refined and developed.


Undergraduate → 9.2.1


U
username
0%
completed in Undergraduate

← Prev (9.2)
Cosmology
Next (9.2.2) →
Dark matter and dark energy

Comments 



The Big Bang Theory

https://www.physicsflow.com/ug/9.2.1?pfal=en