29.3 The Beginning of the Universe
3 min read•june 12, 2024
The kickstarted our universe, sparking a rapid expansion that set the stage for everything we see today. In those first moments, the universe was a hot, dense soup of particles, with fundamental forces merging and separating as things cooled down.
As expansion continued, protons and neutrons joined up to form the first atomic nuclei. This process, called , created the lightest elements like hydrogen and helium. These building blocks would eventually come together to form the stars and galaxies we see today.
The Early Universe
First minutes of universe expansion
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- Universe began with Big Bang, rapid expansion from initial singularity of infinite density and temperature
- Marked beginning of time, space, matter, and energy ()
- First fraction of a second, four fundamental forces (gravity, electromagnetism, strong and weak nuclear forces) were unified
- As universe expanded and cooled, forces separated and became distinct
- Early universe extremely hot and dense, allowing creation of elementary particles
- Quarks and antiquarks formed and annihilated each other, creating (subatomic particle soup)
- formed, such as electrons and neutrinos (elementary particles)
- Within first few minutes, universe cooled enough for quarks to combine and form protons and neutrons ()
- Process called set stage for formation of first atomic nuclei (hydrogen, helium)
Formation of primordial elements
- As universe continued expanding and cooling, protons and neutrons combined to form first atomic nuclei
- Big Bang occurred within first 20 minutes after Big Bang
- First elements formed were lightest and simplest:
- Hydrogen (1 proton)
- (1 proton + 1 neutron)
- Helium-3 (2 protons + 1 neutron)
- Helium-4 (2 protons + 2 neutrons)
- Small amounts of -7 (3 protons + 4 neutrons)
- Relative abundances determined by conditions in early universe (temperature, density)
- No elements heavier than lithium-7 could form due to rapid expansion and cooling of universe
Evolution of universe composition
- As universe expanded, temperature and density decreased, allowing formation of more complex structures
- After Big Bang nucleosynthesis, universe consisted primarily of:
- Hydrogen and helium nuclei
- Free electrons
- Universe still too hot for electrons to bind with nuclei to form neutral atoms
- ~380,000 years after Big Bang, universe cooled sufficiently (to ~3000 K) for electrons to combine with nuclei, forming first neutral atoms
- Event known as or
- Universe became transparent to light, allowing photons to travel freely ()
- After recombination, universe entered , characterized by absence of visible light sources
- Matter began clumping together due to gravitational attraction, forming first large-scale structures ()
- As universe continued evolving, first stars and galaxies formed from large-scale structures, ushering in era of and
Cosmic Expansion and Early Universe Processes
- : Rapid exponential expansion of the universe in its earliest moments, explaining uniformity of cosmic microwave background
- : Process that produced excess of matter over in early universe
- Resulted in , allowing for the existence of matter in our universe
- : Describes relationship between galaxy's distance and its recessional velocity
- Observed through of light from distant galaxies, providing evidence for expanding universe
Key Terms to Review (32)
Alpher: Alpher was an American physicist who played a crucial role in the development of Big Bang nucleosynthesis. He is best known for predicting the abundance of light elements in the early universe.
Antimatter: Antimatter is a type of matter composed of antiparticles, which have the same mass as particles of ordinary matter but opposite charges. When antimatter and matter meet, they annihilate each other, releasing energy.
Baryogenesis: Baryogenesis is the process that describes the origin of the matter-antimatter asymmetry in the universe. It refers to the mechanisms that led to the predominance of matter over antimatter in the early universe, resulting in the universe we observe today, which is composed primarily of matter.
Bethe: Hans Bethe was a German-American physicist who made significant contributions to nuclear astrophysics, particularly in explaining how stars produce energy. He won the Nobel Prize in Physics in 1967 for his work on stellar nucleosynthesis.
Big Bang: The Big Bang is the prevailing cosmological model for the origin and evolution of the universe. It posits that the universe began as an extremely hot, dense state approximately 13.8 billion years ago, and has been expanding and cooling ever since. This theory provides a comprehensive explanation for the observed large-scale structure of the cosmos, the abundance of light elements, and the cosmic microwave background radiation.
Big Bang Nucleosynthesis: Big Bang nucleosynthesis refers to the production of the lightest atomic nuclei, such as hydrogen, helium, and lithium, in the early stages of the universe's evolution immediately following the Big Bang. This process is a crucial aspect of our understanding of the early universe and the formation of the elements that make up the cosmos.
Cosmic Dawn: Cosmic Dawn refers to the earliest stages of the universe, a period when the first stars and galaxies began to form after the cosmic dark ages. It marks the transition from a universe filled with neutral hydrogen to one with the first luminous structures that eventually led to the diverse cosmic structures we observe today.
Cosmic Microwave Background Radiation: The cosmic microwave background (CMB) radiation is the oldest light in the universe, originating from the time when the universe was only a few hundred thousand years old. It is a faint glow of microwave radiation that permeates the entire observable universe, providing crucial evidence for the Big Bang theory of cosmology.
Cosmic Web: The cosmic web is a large-scale structure of the universe, composed of galaxies, galaxy clusters, and filaments of matter that are separated by vast empty spaces called voids. It is a complex network that describes the distribution and organization of matter on the largest scales in the universe.
Dark Ages: The Dark Ages refer to a period in European history following the fall of the Western Roman Empire, characterized by a decline in social, political, economic, and cultural conditions. This term is particularly relevant in the context of understanding the beginning of the universe and the composition of the universe.
Decoupling: Decoupling refers to the process by which certain physical quantities or interactions become independent of each other in the early stages of the universe's evolution. This concept is particularly relevant in the context of the beginning of the universe and the fundamental nature of the cosmos.
Deuterium: Deuterium is an isotope of hydrogen with one proton and one neutron in its nucleus. It is also known as heavy hydrogen due to its greater mass compared to protium, the most common hydrogen isotope.
Deuterium: Deuterium, also known as heavy hydrogen, is a stable isotope of hydrogen with one proton and one neutron in the nucleus, compared to the more common hydrogen isotope which has only one proton. Deuterium plays a significant role in the context of mass, energy, and the theory of relativity, the spectra of stars and brown dwarfs, as well as the beginning of the universe.
Fusion: Fusion is the process where two light atomic nuclei combine to form a heavier nucleus, releasing an enormous amount of energy. This process powers stars, including our Sun, and is fundamental to understanding stellar evolution and the universe's energy dynamics.
Hubble's Law: Hubble's Law is a fundamental principle in cosmology that describes the relationship between the distance of a galaxy from the Milky Way and its recessional velocity. It states that the farther a galaxy is from our own, the faster it is moving away from us, indicating an expanding universe.
Inflation: Inflation is a sustained increase in the general price level of goods and services in an economy over time. It is a key concept in understanding the formation and evolution of galaxies, the age of the universe, the beginning of the universe, and the inflationary universe.
Inflationary universe: The inflationary universe is a theory that proposes a period of extremely rapid exponential expansion of the universe immediately following the Big Bang. It explains several key cosmological observations such as the uniformity of the cosmic microwave background radiation and the large-scale structure of the cosmos.
Lemaître: Lemaître was a Belgian priest, astronomer, and physicist who proposed the idea of an expanding universe. He is widely credited with formulating what would later become known as the Big Bang Theory.
Leptons: Leptons are a class of elementary particles that do not experience the strong nuclear force, but do experience the weak nuclear force and electromagnetism. They are fundamental constituents of matter and play a crucial role in the early stages of the universe's evolution.
Lithium: Lithium is a chemical element with the symbol Li and atomic number 3. It was one of the first elements synthesized in the Big Bang nucleosynthesis process.
Matter-Antimatter Asymmetry: Matter-antimatter asymmetry refers to the observed imbalance between the amount of matter and antimatter in the observable universe. This phenomenon is a fundamental puzzle in cosmology, as the Big Bang theory predicts that equal amounts of matter and antimatter should have been created during the early stages of the universe's expansion.
Neutrino: Neutrinos are nearly massless, chargeless subatomic particles that interact very weakly with matter. They are produced in large quantities during nuclear reactions, such as those occurring in the Sun and during supernova explosions.
Nucleons: Nucleons are the fundamental particles that make up the nucleus of an atom. They are either protons or neutrons, which together form the core of an atom and determine its chemical properties and behavior.
Nucleosynthesis: Nucleosynthesis is the process by which new atomic nuclei are created from existing protons and neutrons. This occurs primarily in the cores of stars through nuclear fusion reactions.
Nucleosynthesis: Nucleosynthesis is the process by which new atomic nuclei are created from pre-existing nucleons, primarily protons and neutrons. This process is responsible for the formation of all the chemical elements in the universe, from the lightest elements like hydrogen and helium to the heavier elements like carbon, oxygen, and iron.
Photon decoupling time: Photon decoupling time is the epoch in the early universe when photons stopped interacting frequently with matter and began to travel freely through space. This event led to the formation of the Cosmic Microwave Background radiation.
Quark-Gluon Plasma: Quark-gluon plasma is an extremely hot and dense state of matter that is believed to have existed in the early universe, shortly after the Big Bang. It is a state where the fundamental particles of matter, known as quarks and gluons, are not bound together in the usual way to form hadrons, such as protons and neutrons.
Recombination: Recombination is the process by which free electrons and protons in a plasma (ionized gas) combine to form neutral atoms, releasing energy in the form of photons. This process is a crucial aspect of the evolution of the early universe and the formation of spectral lines in various astrophysical contexts.
Redshift: Redshift is the phenomenon where the wavelength of light emitted from a distant object is shifted towards longer, or redder, wavelengths compared to the original wavelength. This shift in the observed wavelength is caused by the relative motion between the object and the observer, as well as the expansion of the universe.
Reionization: Reionization is a critical phase in the early history of the universe when the neutral hydrogen that permeated the cosmos after the Big Bang was re-ionized, transforming the universe from a neutral, opaque state to a transparent, ionized state. This process had far-reaching implications for the formation and evolution of the first stars, galaxies, and large-scale structures in the universe.
Spacetime: Spacetime is a four-dimensional continuum where the three dimensions of space and one dimension of time are intertwined. It forms the fabric of the universe, affected by mass and energy, especially in the presence of massive objects like black holes.
Spacetime: Spacetime is a fundamental concept in the theory of relativity that describes the four-dimensional continuum of space and time. It is a unification of the three-dimensional space we experience with the one-dimensional passage of time, forming a unified whole that underpins our understanding of the universe and the nature of gravity.