13.2 Cosmic microwave background radiation

The cosmic microwave background (CMB) is the remnant radiation from the Big Bang, filling the universe with a nearly uniform glow of microwave radiation. It serves as a snapshot of the universe when it was just 380,000 years old, providing vital clues about its early conditions, structure, and expansion. The CMB plays a crucial role in understanding the universe's constituents, its expansion over time, and influences our comprehension of dark matter and dark energy.

Big Bang: The leading explanation for the origin of the universe, suggesting it began as a singularity around 13.8 billion years ago and has been expanding ever since.

Redshift: The phenomenon where light from an object moving away from an observer shifts to longer wavelengths, helping astronomers determine how fast galaxies are receding and thus supporting the expansion of the universe.

Anisotropy: The slight variations in temperature observed in the CMB that provide critical information about the density fluctuations that led to the formation of galaxies and large-scale structures.

The Big Bang Theory is the leading explanation for the origin of the universe, suggesting that it began as an infinitely small, hot, and dense point about 13.8 billion years ago and has been expanding ever since. This theory not only describes the birth of the universe but also connects to key concepts like cosmic expansion, the formation of galaxies, and the evolution of the cosmos over time, shaping our understanding of fundamental astrophysical principles and historical perspectives on astronomy.

Cosmic Inflation: A theory that suggests a rapid expansion of space in the early universe, occurring just after the Big Bang, which helps to explain the uniformity of the cosmic microwave background radiation.

Redshift: A phenomenon where light from distant galaxies shifts to longer wavelengths due to their movement away from us, providing evidence for the expanding universe predicted by the Big Bang Theory.

Nucleosynthesis: The process that occurred during the first few minutes after the Big Bang, where temperatures were high enough for protons and neutrons to combine and form the first atomic nuclei, laying the groundwork for future elements.

Temperature fluctuations refer to the small variations in temperature that can be observed in a specific region of the universe, particularly in the context of the cosmic microwave background radiation. These fluctuations are crucial as they provide insights into the density variations of matter in the early universe, influencing the formation of cosmic structures such as galaxies. Understanding these temperature changes helps scientists decipher the conditions that existed shortly after the Big Bang and how they led to the universe's large-scale structure today.

Cosmic Microwave Background (CMB): The residual thermal radiation from the Big Bang, which fills the universe and is a critical source of information about its early state.

Anisotropy: The variation in properties or characteristics (like temperature) in different directions, particularly in reference to the cosmic microwave background radiation.

Inflationary Universe: A theory that suggests a rapid expansion of space occurred just after the Big Bang, leading to a uniform temperature distribution with slight fluctuations that would become seeds for structure formation.

Structure formation refers to the process by which matter in the universe evolves from small density fluctuations in the early universe to the large-scale structures we observe today, such as galaxies, galaxy clusters, and superclusters. This process is heavily influenced by gravitational forces and the distribution of dark matter, shaping the cosmic web. Understanding structure formation is crucial to explaining how cosmic structures evolved and how they relate to phenomena like cosmic microwave background radiation, dark matter evidence, and potential dark matter candidates.

Cosmic Microwave Background Radiation: The afterglow radiation from the Big Bang, which provides a snapshot of the universe when it was just 380,000 years old, containing information about its early density fluctuations.

Dark Matter: A form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects on visible matter and radiation.

Halo Formation: The process by which dark matter halos grow over time through mergers and accretion of matter, playing a key role in structure formation by providing gravitational wells for baryonic matter to gather.

Isotropy refers to the property of being the same in all directions. In cosmology, it is crucial for understanding the uniformity of the universe at a large scale, particularly as observed in the cosmic microwave background radiation, which is remarkably uniform across the sky. This uniformity suggests that, on a cosmic scale, the universe has a consistent structure and distribution of matter.

Anisotropy: Anisotropy is the opposite of isotropy, where properties vary with direction. In cosmology, anisotropies in the cosmic microwave background can reveal important information about the early universe.

Cosmic Microwave Background (CMB): The CMB is the afterglow radiation from the Big Bang, permeating the universe and serving as a snapshot of the early universe's state, exhibiting isotropic properties.

Homogeneity: Homogeneity describes a uniform distribution of matter and energy in the universe, often used in conjunction with isotropy to describe the overall structure of space at large scales.

A blackbody spectrum is the characteristic distribution of electromagnetic radiation emitted by a perfect blackbody, an idealized physical body that absorbs all incident radiation, regardless of frequency or angle. This spectrum is solely determined by the temperature of the blackbody and follows Planck's law, which describes how energy is radiated at different wavelengths. Understanding the blackbody spectrum is essential for interpreting various astronomical phenomena, including the cosmic microwave background radiation.

Planck's Law: A fundamental principle that describes the spectral density of electromagnetic radiation emitted by a blackbody in thermal equilibrium at a given temperature.

Wien's Displacement Law: A law that states that the wavelength at which the emission of a blackbody spectrum is maximized is inversely proportional to its temperature.

Cosmic Microwave Background (CMB): The remnant thermal radiation from the Big Bang, which has cooled and redshifted to microwave wavelengths, exhibiting a nearly perfect blackbody spectrum.

Quantum fluctuations refer to temporary changes in the energy levels of a quantum system that occur due to the uncertainty principle, leading to spontaneous creation and annihilation of particle-antiparticle pairs. These fluctuations are fundamental to understanding the behavior of particles at the quantum level and play a crucial role in the early universe's evolution, particularly during the rapid expansion after the Big Bang and the formation of the cosmic microwave background radiation.

Uncertainty Principle: A fundamental concept in quantum mechanics stating that certain pairs of physical properties, like position and momentum, cannot be simultaneously known to arbitrary precision.

Inflationary Theory: A theory that suggests the universe underwent an exponential expansion during the first few moments after the Big Bang, driven by high energy density and quantum fluctuations.

Cosmic Microwave Background (CMB): The afterglow radiation from the Big Bang, which fills the universe and provides evidence for its early hot, dense state, influenced by quantum fluctuations.

Acoustic oscillations refer to the periodic sound waves produced in a medium, which can also describe the density fluctuations that occurred in the early universe, particularly in the primordial plasma before recombination. These oscillations played a crucial role in creating the temperature and density variations observed in the cosmic microwave background radiation, as they led to the formation of the structures we see in the universe today.

Cosmic Microwave Background Radiation: The afterglow radiation from the Big Bang, uniformly filling the universe, which provides crucial evidence for the hot Big Bang theory and contains information about the early universe.

Recombination: The process occurring roughly 380,000 years after the Big Bang, when electrons combined with protons to form neutral hydrogen atoms, allowing photons to travel freely and resulting in the release of cosmic microwave background radiation.

Baryon Acoustic Oscillations: Regular, periodic fluctuations in the density of baryonic matter (normal matter) in the universe that originated from acoustic oscillations in the early universe, influencing galaxy formation and distribution.

Angular scale is a measure of the apparent size of an object in the sky, expressed in angular units such as degrees, arcminutes, or arcseconds. It relates to how much of the sky an object occupies as seen from a specific point, allowing astronomers to understand and describe the size of celestial objects and the separation between them. Angular scale is especially important in observing distant astronomical phenomena like cosmic microwave background radiation, which spans large areas of the sky.

Cosmic Microwave Background Radiation (CMB): The remnant radiation from the Big Bang, filling the universe and providing a snapshot of the early universe, crucial for understanding cosmology.

Resolution: The ability of a telescope to distinguish between two close objects in the sky, which is often limited by angular scale.

Field of View: The extent of the observable universe that can be seen through a telescope or camera at a given moment, usually described in angular measurements.

Baryonic matter refers to the form of matter that makes up stars, planets, and living organisms, primarily composed of baryons such as protons and neutrons. This type of matter constitutes a small fraction of the total mass-energy content of the universe, as most of it is made up of dark matter and dark energy. Baryonic matter interacts with electromagnetic forces, allowing it to form atoms and, consequently, the visible structures we observe in the universe.

Dark Matter: A form of matter that does not emit or interact with electromagnetic radiation, making it invisible and detectable only through its gravitational effects on visible matter.

Nucleons: The collective term for protons and neutrons, which are the building blocks of atomic nuclei and are essential components of baryonic matter.

Cosmic Microwave Background Radiation: The afterglow radiation from the Big Bang, providing critical evidence for the early state of baryonic matter in the universe and its evolution over time.

Dark matter is a mysterious and invisible form of matter that does not emit, absorb, or reflect light, making it undetectable by traditional astronomical methods. Despite being unseen, it makes up about 27% of the universe's total mass-energy content and plays a crucial role in the structure and evolution of galaxies, influencing gravitational interactions in the cosmos.

Baryonic Matter: Baryonic matter is the ordinary matter made up of protons, neutrons, and electrons that forms stars, planets, and living organisms.

Gravitational Lensing: Gravitational lensing occurs when the gravity of a massive object, like a galaxy or cluster of galaxies, bends the path of light from objects behind it, providing indirect evidence of dark matter.

Cosmic Microwave Background Radiation: Cosmic microwave background radiation is the remnant radiation from the Big Bang that fills the universe and provides evidence for the early state of the cosmos, including insights into dark matter's influence on structure formation.

Dark energy is a mysterious force that is driving the accelerated expansion of the universe. It constitutes about 68% of the total energy density of the universe and affects how galaxies, galaxy clusters, and large-scale structures behave over cosmic timescales. This concept connects to many aspects of astrophysics, including the formation and evolution of the universe, the cosmic microwave background radiation, and our understanding of Hubble's law.

Cosmological Constant: A term introduced by Einstein in his equations of general relativity that represents a constant energy density filling space homogeneously, often associated with dark energy.

Lambda Cold Dark Matter (ΛCDM): The current standard model of cosmology that includes dark energy (Lambda) and cold dark matter as its primary components.

Quintessence: A dynamic form of dark energy that changes over time, unlike the cosmological constant which remains constant.

The power spectrum is a tool used in astrophysics to describe the distribution of power or intensity across different frequencies or scales. In the context of cosmic microwave background radiation, it reveals how fluctuations in temperature are distributed across various angular scales, providing insights into the early universe's structure and evolution.

Cosmic Microwave Background Radiation: The afterglow radiation from the Big Bang, filling the universe and providing a snapshot of the early universe approximately 380,000 years after its formation.

Angular Scale: A measure of the apparent size of an object in the sky, expressed in degrees, which helps describe how features in the cosmic microwave background appear on the sky.

Temperature Fluctuations: Variations in temperature detected in the cosmic microwave background radiation that correspond to density variations in the early universe.

Baryon density refers to the number of baryons, which include protons and neutrons, per unit volume in the universe. This measurement is crucial for understanding the amount of normal matter present, as baryons make up most of the visible matter in stars, galaxies, and interstellar gas. It is an important factor in cosmology, particularly in explaining the large-scale structure of the universe and how it evolved over time.

Critical density: The average density of matter needed for the universe to be flat, which plays a key role in determining the fate of the universe.

Dark matter: A type of matter that does not emit or interact with electromagnetic radiation, making it invisible, but it exerts gravitational forces and is believed to make up most of the mass in the universe.

Cosmic microwave background radiation: The afterglow radiation from the Big Bang, providing a snapshot of the universe when it was only 380,000 years old and offering insight into its early density and structure.

Acoustic peaks refer to the distinct oscillation patterns seen in the power spectrum of cosmic microwave background (CMB) radiation, which provide critical information about the early universe. These peaks arise from sound waves propagating through the hot plasma of the early universe before the formation of the cosmic microwave background, leading to variations in temperature and density that we can observe today. The positions and amplitudes of these peaks help cosmologists understand fundamental properties of the universe, including its geometry, composition, and expansion history.

Cosmic Microwave Background (CMB): The CMB is the afterglow radiation from the Big Bang, providing a snapshot of the universe when it became transparent to radiation, about 380,000 years after its formation.

Baryon Acoustic Oscillations (BAO): BAO are regular, periodic fluctuations in the density of visible baryonic matter (normal matter) of the universe, which are related to acoustic peaks and can be used as a cosmic ruler for measuring distances.

Dark Energy: Dark energy is a mysterious form of energy that makes up about 68% of the universe and is responsible for the accelerated expansion of the universe, influencing the distribution of acoustic peaks.

Dark matter density refers to the amount of dark matter present in a given volume of space. This invisible substance is thought to make up about 27% of the universe's total mass-energy content, influencing the gravitational effects that shape galaxies and larger structures. Understanding dark matter density is crucial for interpreting observations of cosmic microwave background radiation and for studying the expansion of the universe, as it plays a key role in the formation and evolution of cosmic structures.

Cosmic Microwave Background Radiation: The afterglow radiation from the Big Bang, filling the universe and providing crucial evidence for the Big Bang theory.

Hubble's Law: A fundamental observation in cosmology that states galaxies are moving away from us, with their velocity proportional to their distance, indicating an expanding universe.

Gravitational Lensing: The bending of light from distant objects due to the gravitational field of massive objects, which can reveal the presence and distribution of dark matter.

Inflationary models are theoretical frameworks that describe a rapid expansion of the universe in its earliest moments, right after the Big Bang. These models suggest that this exponential growth solved several major cosmological problems, including the uniformity of the cosmic microwave background radiation and the flatness of the universe. By proposing that the universe underwent a brief period of extreme inflation, these models provide insights into the large-scale structure and evolution of the cosmos.

Big Bang: The prevailing cosmological model explaining the origin of the universe, stating that it began from an extremely hot and dense state and has been expanding ever since.

Cosmic Microwave Background Radiation (CMB): The faint glow of radiation left over from the hot, dense state of the early universe, providing critical evidence for the Big Bang theory and supporting inflationary models.

Quantum Fluctuations: Small variations in energy density during the inflationary period, which led to the formation of structures like galaxies and clusters in the universe.