12.5 Dark Matter and Dark Energy

Dark matter is a type of matter that does not emit, absorb, or reflect any electromagnetic radiation, making it invisible and detectable only through its gravitational effects on visible matter. This mysterious substance constitutes about 27% of the universe's total mass-energy content and plays a crucial role in the formation and structure of galaxies and cosmic structures.

baryonic matter: Baryonic matter refers to the ordinary matter composed of protons, neutrons, and electrons that make up stars, planets, and living organisms.

cosmic microwave background (CMB): The cosmic microwave background is the afterglow radiation from the Big Bang, providing evidence for the early universe's conditions and influencing our understanding of dark matter.

gravitational lensing: Gravitational lensing is the bending of light from distant objects due to the gravitational field of massive objects, used as a method to infer the presence and distribution of dark matter.

Dark energy is a mysterious form of energy that makes up about 68% of the universe and is believed to be responsible for the accelerated expansion of the universe. It plays a crucial role in understanding how the cosmos behaves, particularly when considering observations related to the movement of galaxies and the cosmic microwave background radiation. By influencing the dynamics of cosmic expansion, dark energy ties into the framework of both the Big Bang Theory and our understanding of gravity on cosmic scales.

cosmological constant: A term originally introduced by Albert Einstein in his equations of general relativity, representing a constant energy density filling space homogeneously, often associated with dark energy.

redshift: The phenomenon where light from distant galaxies is shifted to longer wavelengths, indicating that those galaxies are moving away from us, which is evidence for the expansion of the universe.

accelerated expansion: The observation that the rate of expansion of the universe is increasing over time, attributed to the influence of dark energy.

Galactic rotation curves are graphical representations that show how the rotational speed of stars and gas in a galaxy varies with distance from its center. These curves are significant in understanding the distribution of mass within galaxies and highlight discrepancies between observed speeds and the predictions made by Newtonian dynamics, indicating the presence of dark matter.

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

Kepler's Laws: Three laws formulated by Johannes Kepler that describe the motion of planets around the sun, which can be applied to understand the dynamics of rotating galaxies.

Spiral Galaxies: A type of galaxy characterized by its spiral arms and a flat disk containing stars, gas, and dust, where rotation curves are often studied.

Gravitational lensing is the phenomenon where light from a distant object, like a galaxy or quasar, is bent around a massive object, such as a galaxy cluster or black hole, due to the object's gravitational field. This bending effect can create multiple images, magnify, or distort the appearance of the distant object, allowing astronomers to study the mass and structure of the intervening object and the universe itself. It provides valuable insights into the distribution of dark matter and the nature of cosmic structures.

Einstein's Theory of General Relativity: A fundamental theory of gravitation that describes how massive objects curve spacetime, affecting the path of light and leading to phenomena like gravitational lensing.

Dark Matter: An unseen form of matter that does not emit light or energy, detectable primarily through its gravitational effects on visible matter, such as in gravitational lensing.

Cosmic Microwave Background Radiation: The afterglow radiation from the Big Bang that fills the universe, providing information about the early universe and its structure, which can be studied using gravitational lensing.

The lambda-cdm model is a cosmological model that describes the universe's large-scale structure and evolution, incorporating dark energy (represented by the Greek letter lambda, \(\Lambda\)) and cold dark matter (cdm). This model suggests that the universe is flat, expanding at an accelerating rate due to dark energy, while dark matter plays a critical role in structure formation by influencing gravitational interactions.

Dark Energy: A mysterious form of energy that permeates space and accelerates the expansion of the universe.

Cold Dark Matter: A type of dark matter that moves slowly compared to the speed of light and is thought to clump together under the influence of gravity.

Cosmic Microwave Background: The faint radiation left over from the Big Bang, providing critical evidence for the lambda-cdm model and insights into the early universe.

The cosmic web is the large-scale structure of the universe, characterized by a vast network of galaxies, galaxy clusters, and dark matter filaments that interconnect in a complex, web-like pattern. This structure plays a crucial role in understanding the distribution of matter and the dynamics of cosmic evolution, as it is influenced by dark matter and dark energy throughout the universe's history.

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.

Galaxy Cluster: A large group of galaxies held together by gravity, often found at the intersections of the cosmic web's filaments.

Cosmic Microwave Background (CMB): The remnant radiation from the Big Bang, providing a snapshot of the universe when it was just 380,000 years old and offering insights into its early structure and expansion.

Large-scale structure refers to the vast formations of galaxies, galaxy clusters, and superclusters that make up the universe. These structures are not randomly distributed; instead, they exhibit a web-like pattern where galaxies are interconnected by filaments of dark matter and gas, with vast voids in between. Understanding these structures helps scientists learn about the distribution of dark matter and the overall evolution of the universe.

Cosmic Web: The large-scale structure of the universe consisting of galaxies and galaxy clusters interconnected by filaments of dark matter and gas.

Galaxy Cluster: A large group of galaxies held together by gravity, containing hundreds or thousands of galaxies along with hot gas and dark matter.

Dark Energy: A mysterious form of energy that is believed to be responsible for the accelerated expansion of the universe.

The big freeze is a theoretical scenario for the ultimate fate of the universe, where it continues to expand indefinitely until stars burn out, galaxies drift apart, and the universe becomes cold and dark. In this scenario, as cosmic expansion accelerates due to dark energy, the universe approaches a state of maximum entropy, leading to a lifeless, stagnant expanse with little to no activity.

Dark Energy: A mysterious force that drives the accelerated expansion of the universe, contributing to the big freeze scenario by causing galaxies to move away from each other at an increasing rate.

Heat Death: A state in which the universe has reached maximum entropy, where energy is uniformly distributed and no thermodynamic free energy exists to perform work, closely related to the big freeze outcome.

Cosmic Microwave Background Radiation (CMBR): The remnant radiation from the Big Bang that fills the universe and provides evidence for the expansion of space, playing a crucial role in understanding the universe's fate in scenarios like the big freeze.

The big rip is a hypothetical cosmological event in which the universe's accelerated expansion eventually tears apart all matter, from galaxies to individual atoms. This concept is closely tied to the effects of dark energy, which is believed to be driving the accelerated expansion of the universe, and raises questions about the ultimate fate of cosmic structures and the fundamental nature of spacetime.

Dark Energy: A mysterious form of energy that makes up about 68% of the universe, driving its accelerated expansion.

Cosmic Microwave Background Radiation: The remnant radiation from the Big Bang, providing evidence for the universe's hot, dense beginnings and its subsequent expansion.

Accelerated Expansion: The observation that the universe is expanding at an increasing rate, attributed to the influence of dark energy.

Cosmic microwave background radiation (CMB) is the afterglow of the Big Bang, representing a uniform field of microwave radiation that fills the universe and is a critical piece of evidence for the Big Bang theory. This radiation, which is remarkably uniform in all directions, provides insights into the early universe's conditions and supports the existence of dark matter and dark energy as it reveals the universe's large-scale structure and evolution.

Big Bang: The leading explanation for the origin of the universe, proposing that it began from a singularity approximately 13.8 billion years ago and has been expanding ever since.

Dark Matter: A form of matter that does not emit or interact with electromagnetic radiation, making it invisible; it is believed to make up about 27% of the universe's total mass-energy content.

Redshift: The phenomenon where light from distant galaxies is shifted towards longer wavelengths, indicating that those galaxies are moving away from us, providing evidence for the expansion of the universe.

Type Ia supernovae are explosive events that occur in binary star systems, typically involving a white dwarf that accumulates mass from its companion until it reaches a critical limit, resulting in a catastrophic explosion. These supernovae are important for understanding the universe because they have consistent peak brightness, making them valuable as 'standard candles' for measuring cosmic distances and studying the expansion of the universe.

White Dwarf: A white dwarf is the remnant core of a star that has exhausted its nuclear fuel, characterized by high density and low luminosity.

Critical Mass: The specific mass limit, known as the Chandrasekhar limit (approximately 1.4 solar masses), that a white dwarf must reach to initiate a type Ia supernova explosion.

Dark Energy: A mysterious form of energy that is thought to permeate all of space and accelerate the expansion of the universe, influencing our understanding of type Ia supernovae as distance indicators.

Baryon acoustic oscillations refer to the regular, periodic fluctuations in the density of visible baryonic matter (normal matter) in the universe caused by sound waves in the hot plasma of the early universe. These oscillations played a crucial role in the formation of the large-scale structure of the universe and are imprinted in the cosmic microwave background radiation as well as in the distribution of galaxies. Understanding these oscillations helps shed light on fundamental aspects of cosmology, including the nature of dark matter and dark energy.

Cosmic Microwave Background: The Cosmic Microwave Background is the remnant radiation from the Big Bang, providing a snapshot of the universe when it was about 380,000 years old, and carrying information about its early conditions.

Dark Matter: Dark Matter is 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.

Redshift: Redshift is the phenomenon where light from distant galaxies is shifted to longer wavelengths due to the expansion of the universe, allowing astronomers to measure the velocity and distance of these galaxies.

Weak lensing surveys refer to observational techniques used in astronomy to detect and study the effects of gravitational lensing on distant light sources caused by massive objects, like galaxies or clusters of galaxies. These surveys help map the distribution of dark matter by analyzing how light from background galaxies is distorted and stretched as it passes near massive foreground structures, providing insights into both dark matter and dark energy in the universe.

gravitational lensing: The bending of light from a distant object due to the gravitational field of a massive object located between the observer and the distant source.

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

cosmological surveys: Large-scale observations aimed at mapping the universe, measuring its structure, and understanding its evolution and composition, including the distribution of galaxies and dark energy.

The Integrated Sachs-Wolfe Effect refers to the phenomenon where the gravitational potential wells of large-scale structures in the universe affect the temperature of cosmic microwave background (CMB) radiation as it travels through them. This effect is crucial for understanding how dark energy influences the evolution of the universe and contributes to the overall energy density, impacting both dark matter and dark energy dynamics.

Cosmic Microwave Background (CMB): The CMB is the afterglow radiation from the Big Bang, providing a snapshot of the universe when it was just 380,000 years old.

Gravitational Potential Well: A region in space where gravitational forces cause a concentration of mass, affecting the motion of objects and light passing through it.

Dark Energy: A mysterious form of energy that makes up about 68% of the universe, driving its accelerated expansion.

Weakly interacting massive particles (WIMPs) are hypothetical particles that are considered one of the leading candidates for dark matter. They are characterized by their large mass and their ability to interact only through the weak nuclear force and gravity, making them incredibly difficult to detect. WIMPs play a crucial role in explaining the missing mass in the universe and how galaxies form and evolve.

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.

Supersymmetry: A theoretical framework in particle physics that suggests each particle has a corresponding superpartner with different properties, which could include WIMPs as candidates for dark matter.

Cosmic Microwave Background (CMB): The afterglow radiation from the Big Bang, providing evidence for the existence of dark matter by revealing the influence of mass on the evolution of the universe.

Axions are hypothetical elementary particles proposed as a solution to the strong CP problem in quantum chromodynamics, and they are also considered a candidate for dark matter. These particles are predicted to be extremely light and weakly interacting, making them difficult to detect directly. Their existence could help explain various phenomena in astrophysics and cosmology, especially in relation to the mysterious components of dark matter and dark energy in the universe.

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.

Strong CP Problem: The question of why quantum chromodynamics, the theory of the strong nuclear force, does not seem to violate the symmetry between particles and antiparticles.

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.

Sterile neutrinos are hypothetical particles that do not interact via the standard weak interactions like other known neutrinos, making them 'sterile' in a sense. They are proposed as a component of dark matter and could help explain certain anomalies in neutrino physics, including the behavior of oscillations observed in experiments.

Neutrino Oscillation: A phenomenon where a neutrino created as one type can transform into another type as it travels through space.

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.

WIMPs: Weakly Interacting Massive Particles, a class of potential dark matter candidates that interact via the weak nuclear force.

Primordial black holes are hypothetical black holes formed in the early universe due to density fluctuations shortly after the Big Bang. These black holes could vary in mass from very small to several solar masses and are considered as potential candidates for dark matter, connecting them to the mysteries of dark energy and the universe's structure.

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

Inflation: A rapid expansion of the universe that occurred in the first moments after the Big Bang, leading to uniformity and density fluctuations that could give rise to primordial black holes.

Event Horizon: The boundary surrounding a black hole beyond which nothing can escape, not even light, marking the point of no return for any matter or radiation.

Self-interacting dark matter is a theoretical form of dark matter that allows for interactions between its particles, which could lead to observable effects in cosmic structures. This concept proposes that dark matter is not only gravitationally interacting but can also scatter off itself, potentially altering the distribution and dynamics of galaxies and clusters. These interactions may help resolve certain discrepancies between observed galaxy behaviors and predictions made by standard dark matter models.

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.

Weakly Interacting Massive Particles (WIMPs): A leading candidate for dark matter, WIMPs are particles that interact via the weak nuclear force and gravity, making them difficult to detect.

Cosmic Structure Formation: The process by which matter in the universe organizes into galaxies and larger structures over time, influenced by the gravitational effects of both normal and dark matter.

Fuzzy dark matter is a theoretical form of dark matter that consists of ultra-light bosons, which are particles with integer spin that are less massive than typical dark matter candidates. This concept suggests that instead of being composed of point-like particles, dark matter may have wave-like properties, resulting in a smooth, fuzzy distribution. Fuzzy dark matter models aim to address some of the shortcomings of traditional dark matter theories, particularly in explaining the behavior of galaxies and cosmic structures.

Boson: A type of particle that follows Bose-Einstein statistics, which includes force-carrying particles like photons and gluons, as well as hypothetical particles like axions.

Cold Dark Matter: A model of dark matter consisting of slow-moving particles that clump together under the influence of gravity, forming structures like galaxies and galaxy clusters.

Wave-Particle Duality: A fundamental concept in quantum mechanics stating that particles exhibit both wave-like and particle-like properties, which is essential to understanding fuzzy dark matter.

The cosmological constant is a term introduced by Albert Einstein in his equations of general relativity, representing a constant energy density filling space homogeneously. This concept plays a significant role in modern cosmology, particularly in understanding the accelerated expansion of the universe and the nature of dark energy, which is believed to drive this phenomenon.

dark energy: A mysterious form of energy that makes up about 68% of the universe and is responsible for its accelerated expansion.

general relativity: Einstein's theory of gravitation that describes gravity as the curvature of spacetime caused by mass.

Lambda CDM model: The standard model of cosmology that incorporates the cosmological constant (denoted as Lambda) and Cold Dark Matter (CDM) to explain the large-scale structure and evolution of the universe.

Quintessence models are theoretical frameworks in cosmology that propose a dynamic form of dark energy, which changes over time and is responsible for the accelerated expansion of the universe. Unlike the cosmological constant, which is static, quintessence suggests that dark energy could vary in density and influence as the universe evolves. These models help to explain the mysterious behavior of cosmic acceleration and its implications for the fate of the universe.

Dark Energy: A form of energy that permeates space and accelerates the expansion of the universe, accounting for approximately 68% of its total energy content.

Cosmological Constant: A value introduced by Einstein in his equations of General Relativity to account for a static universe, later associated with dark energy.

Scalar Field: A field described by a single value at each point in space and time, often used in quintessence models to represent the dynamic nature of dark energy.

Phantom energy refers to a theoretical form of dark energy that has an equation of state with a parameter less than -1, leading to an accelerated expansion of the universe at an increasing rate. This concept is linked to the idea that such energy could contribute to the observed phenomena of cosmic acceleration, challenging our understanding of gravity and the fundamental nature of energy in the universe.

Dark Energy: A mysterious form of energy that makes up about 68% of the universe and is responsible for its accelerated expansion.

Cosmological Constant: A constant term introduced by Einstein in his equations of General Relativity, which is often associated with dark energy and describes a uniform energy density filling space homogeneously.

Equation of State: A relation between state variables, often used in cosmology to describe how different forms of energy influence the expansion of the universe.

Chameleon fields are hypothetical scalar fields that can vary their properties depending on the local environment, particularly in the context of gravity and dark energy. These fields are proposed to help explain the accelerated expansion of the universe by interacting differently with matter and energy at different scales. Their dynamic nature allows them to potentially mimic the effects of dark energy while being less detectable under certain conditions.

Scalar Field: A physical field that assigns a scalar value to every point in space, often used in theories to describe particles and forces.

Dark Energy: A mysterious form of energy that makes up about 68% of the universe and is responsible for its accelerated expansion.

Modified Gravity: Theories that propose changes to our understanding of gravity, which may provide alternative explanations for observations traditionally attributed to dark matter or dark energy.