Chemistry

• Big Bang theory


  A cosmological model of the observable universe from the earliest known periods through its subsequent large-scale evolution
• The Big Bang theory describes how the universe expanded from an initial state of extremely high density and high temperature</b>
• The Big Bang theory offers a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure
• The Big Bang theory is compatible with Hubble's law - the observation that the farther away galaxies are, the faster they are moving away from Earth
• Extrapolating the cosmic expansion backwards in time using the known laws of physics, the theory describes a high density state preceded by a singularity in which space and time lose meaning
• There is no evidence of any phenomena prior to the singularity
• Detailed measurements of the expansion rate of the universe place the Big Bang at around 13 billion years ago, which is thus considered the age of the universe
• After its initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later atoms
• Giant clouds of these primordial elements - mostly 24% of the universe's ordinary matter is currently comprised of helium, about 74% hydrogen, and 2% of other elements (relative abundance) - later coalesced through gravity, forming early stars and galaxies, the descendants of which are visible today
• Besides these primordial building materials, astronomers observe the gravitational effects of an unknown dark matter surrounding galaxies
• Most of the gravitational potential in the universe seems to be in this form, and the Big Bang theory and various observations indicate that it is not conventional baryonic matter that forms atoms
• Measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating, an observation attributed to dark energy's existence
• Georges Lemaître first noted in 1927 that an expanding universe could be traced back in time to an originating single point, which he called the "primeval atom"
• For several decades, the scientific community was divided between supporters of the Big Bang and the rival steady-state model, but a wide range of empirical evidence has strongly favored the Big Bang, which is now universally accepted
• Edwin Hubble concluded from analysis of galactic redshifts in 1929 that galaxies are drifting apart; this is important observational evidence for an expanding universe
• In 1964, the CMB was discovered. This was a crucial evidence of the Big Bang Theory which predicted a uniform background radiation throughout the universe
• Timeline of the Big Bang

  1. Planck Epoch (or Planck Era), from zero to approximately 10-43 seconds

  2. Grand Unification Epoch, from 10 – 43 seconds to 10 – 36 seconds

  3. Inflationary Epoch, from 10– 36 seconds to 10– 32 seconds

  4. Electroweak Epoch, from 10– 36 seconds to 10– 12 seconds

  5. Quark Epoch, from 10– 12 seconds to 10– 6 seconds

  6. Hadron Epoch, from 10– 6 seconds to 1 second

  7. Solar System Formation, 8 - 9 billion years

  8. Today, 13 billion years
• The Big Bang theory and various observations indicate that dark matter is not conventional baryonic matter that forms atoms
• Our Sun is a late-generation star, incorporating the debris from many generations of earlier stars, and it and the Solar System around it form roughly 4 to 5 billion years ago (8 to 9 billion years after the Big Bang)
• Today


  13 billion years
• The expansion of the universe and recycling of star materials into new stars continues
• The singularity is not an established, well-defined part of the Big Bang model
• Cosmic expansion has not stopped at some point in time
• The relative abundance of hydrogen and helium in the universe today is part of the proof for the Big Bang Theory
• The Big Bang was not a big explosion that threw matter into many different directions
• Redshift


  Evidence 1 for Big Bang Theory
• Relative abundance


  Evidence 2 for Big Bang Theory
• Cosmic microwave background


  Evidence 3 for Big Bang Theory
• Timeline of Big Bang Theory

  1. Singularity

  2. Expansion

  3. Light element formation
• Hydrogen and helium atoms in stars began combining in nuclear fusion reactions once hydrogen-helium stars had formed from the action of gravity
• Fusion resulted in the formation of nuclei of new elements
• Stellar nucleosynthesis


  The process by which elements are formed within stars
• Main-branch proton-proton chain


  1. Deuterium formation

  2. 3He formation

  3. 4He formation
• The entire three-step proton-proton chain process releases about 26 MeV (megaelectronvolts) of energy
• A different process facilitates hydrogen fusion in main sequence stars with temperature greater than 15 million K
• Triple alpha process


  Carbon formation
• Heavier elements are formed during stellar nucleosynthesis through fusion reactions within stars
• The atomic number pattern of the elements in the alpha ladder shows an increase of 2 protons for each step
• The Big Bang Theory affects us by providing the origin of the universe and the elements that make up our world
• The era of nucleosynthesis is important because it is when the primordial hydrogen and helium were created, which are the key elements for life