Universe! Early Universe

The Early Universe The early universe was Small, but expanding Hot, but cooling Dense, but expanding Chaotic High-energy photons (but losing energy) Quarks, but eventually atoms Violent collisions

The Early Universe Processes that explain the physical evolution of the early universe: Rapid Expansion Cooling As the temperature dropped, the energy shared between the colliding photons and material particles fell. Energy thresholds were passed, meaning certain interactions were no longer energetically possible. Density variations led to clumps, which in turn led to gravitational collapse and the formation of galaxies, stars and planets. The variations were a consequence of the initially chaotic conditions in the Big Bang.

Timeline The Planck Epoch time = 0 to 10-43 seconds temperature = ∞ to 1032 K Size = singularity to 10-35 (Planck length) The earliest point of time scientists can theoretically pinpoint is Planck time, or 10-43 seconds after the Big Bang. This moment, though definable, is poorly understood because of what happens to gravity at such high energies and small scales is very complicated to explore.

Timeline In the very early universe (Planck time to 4 s), one of the most important processes was pair production. The upper diagrams show how two gamma rays can unite to make an electron–positron pair, and vice versa. The lower picture is of such an event occurring at a high-energy particle accelerator.

Timeline The Inflationary Era time = 10-43 to 10-12 seconds temperature = 1032 K to 1015 K Size = 10-35 (Planck length) to 10-13 meters At the beginning (Planck time), the force of gravity separated from the other three forces, collectively known as the electronuclear force. At 10-36 s, separation of the strong force from the electronuclear force occurred, leaving three forces: gravity, strong, and electroweak forces. At ~10-12 s, the weak force condenses and separates from the electromagnetic force leaving us with the four separate forces we know today.

Timeline This period is also very important for the existence of matter in the universe. Individually, the strong and the electroweak forces behave exactly the same way toward matter and antimatter. The strong and the electroweak forces are mixed and act as a single force. Grand unification theories suggest that when this is the case, it may be possible to have particle reactions which create more matter than antimatter.

Timeline

Timeline The Era of Extinctions time = 10-6 to 1 sec temperature = 1013 K to 1012 K Electrons and positrons annihilate each other during this epoch. Quarks combine to form protons and neutrons. Quark/anti-quark pairs to combine into mesons. After this period quarks and anti-quarks can no longer exist as free particles. Neutrinos break free and exist on their own. Primordial background neutrinos? About 10–4 s after the Big Bang, the universe had cooled enough that photons could no longer produce the heavier elementary particles; the only ones still in equilibrium were electrons, positrons, muons, and neutrinos. This is called the lepton era.

Timeline The Era of Nucleosynthesis time = 1 second to 3 minutes temperature = 1010 K to 109 K (like inside a star) Formation of deuterium and helium, the first atomic nuclei. Why? Photons had insufficient energy to break atomic nuclei apart. Strong Nuclear Force! Nuclear fusion begins to occur as the universe is now cool enough for atomic nuclei to form and still hot enough for them to collide to form heavier elements.

Timeline No neutral atoms yet. All ions… a plasma! The universe was opaque. Free electrons in a plasma scatter photons very efficiently. At the end of this epoch, we expect the universe has about: 75% hydrogen 25% helium Trace deuterium, lithium, beryllium and boron Elements heavier than this do not have time to form before nuclear reactions stop.

Timeline The total energy of the universe consists of both radiation and matter. As the universe cooled, it went from being radiation-dominated to being matter-dominated. This happens at about 10,000 years.

Timeline The Decoupling Era (Part of Epoch of Nucleosynthesis) time = 379,000 years temperature = 3000 K and dropping At this temperature hydrogen nuclei capture electrons to form stable atoms. This event is known as recombination. The universe becomes transparent to light since photons no longer interact strongly with atoms. This means that what we normally think of as matter and energy become separate.

Timeline Photons now interacted with matter in a much more selective way: only those having energy exactly equal to energy level differences in the H or He atoms were absorbed. All other photons were ignored by matter. At this time the whole Universe was lit up like the inside of a neon sign (with no neon).

Timeline From this time forward matter and radiation were decoupled, that is, primordial photons were no longer energetically capable of influencing the future evolution of matter. The photons that once dominated the Universe just gradually cooled off. Eventually they couldn’t even excite H and He atoms to produce visible photons, so the Universe went dark.

Timeline In the very early universe, the pair production and recombination processes were in equilibrium. When the temperature had decreased to about 1 billion K, the photons no longer had enough energy for pair production, and were “frozen out.” We now see these photons as the cosmic background radiation.

Early Universe Timeline

Timeline WHAT HAS BEEN ACHIEVED? Lots of stuff was lost! Matter recovered from an inauspicious beginning (i.e., nearly self-destructed, bullied by photons) to evolve into the rich variety of structures observed on all scales in the Universe today. The composition of the early Universe was H (very simple stuff) and He (very useless stuff). No chemistry was possible! The Universe was boring! Not even a chunk of rock!

Universe Timeline