Horizon: Black Holes (BBC) Big Bang nucleosynthesis. In physical cosmology, Big Bang nucleosynthesis (abbreviated BBN, also known as primordial nucleosynthesis) refers to the production of nuclei other than those of the lightest isotope of hydrogen during the early phases of the universe.
Primordial nucleosynthesis is believed by most cosmologists to have taken place from 10 seconds to 20 minutes after the Big Bang, and is calculated to be responsible for the formation of most of the universe's helium as isotope He-4, along with small amounts of deuterium (H-2 or D), the helium isotope He-3, and a very small amount of the lithium isotope Li-7. In addition to these stable nuclei, two unstable or radioactive isotopes were also produced: tritium or H-3; and beryllium-7 (Be-7); but these unstable isotopes later decayed into He-3 and Li-7, as above. Essentially all of the elements that are heavier than lithium were created much later, by stellar nucleosynthesis in evolving and exploding stars. Characteristics[edit] Chronology of the universe. Illustration of evolution of the universe from the Big Bang (left).
In this diagram, the universe is represented in two dimensions and the third (horizontal) dimension is time, increasing to the right. Summary[edit] The very earliest universe was so hot, or energetic, that initially no particles existed or could exist (except perhaps in the most fleeting sense), and the forces we see around us today were believed to be merged into one unified force. Space-time itself expanded during an inflationary epoch due to the immensity of the energies involved. Gradually the immense energies cooled – still to a temperature inconceivably hot compared to any we see around us now, but sufficiently to allow forces to gradually undergo symmetry breaking, a kind of repeated condensation from one status quo to another, leading finally to the separation of the strong force from the electroweak force and the first particles.
The Universe - Brian Cox Lecture. Origin of the Universe: The Big Bang.