![]() ![]() At around 100,000 years, after the neutral helium atoms form, helium hydride is the first molecule. At around 47,000 years, as the universe cools, its behavior begins to be dominated by matter rather than radiation. The recombination epoch begins at around 18,000 years, as electrons are combining with helium nuclei to form He + Composite subatomic particles emerge-including protons and neutrons-and from about 2 minutes, conditions are suitable for nucleosynthesis: around 25% of the protons and all the neutrons fuse into heavier elements, initially deuterium which itself quickly fuses into mainly helium-4.īy 20 minutes, the universe is no longer hot enough for nuclear fusion, but far too hot for neutral atoms to exist or photons to travel far. If primordial black holes exist, they are also formed at about one second of cosmic time. These particles include almost equal amounts of matter and antimatter, so most of it quickly annihilates, leaving a small excess of matter in the universe.Īt about one second, neutrinos decouple these neutrinos form the cosmic neutrino background (CνB). Initially, various kinds of subatomic particles are formed in stages. The earlier parts are beyond the grasp of practical experiments in particle physics but can be explored through the extrapolation of known physical laws to extreme high temperatures. Different stages of the very early universe are understood to different extents. Tiny ripples in the universe at this stage are believed to be the basis of large-scale structures that formed much later. ![]() It includes the Planck epoch, during which currently established laws of physics may not have applied the emergence in stages of the four known fundamental interactions or forces-first gravitation, and later the electromagnetic, weak and strong interactions and the accelerated expansion of the universe due to cosmic inflation. ![]() The first picosecond (10 −12) of cosmic time. It is generally considered meaningless or unclear whether time existed before this chronology: Outline Chronology in five stages Diagram of evolution of the (observable part) of the universe from the Big Bang (left), the CMB-reference afterglow, to the presentįor the purposes of this summary, it is convenient to divide the chronology of the universe since it originated, into five parts. ![]()
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