The Big Bang Theory, General Timeline The Planck Era. (Big Bang To 10^-35 Seconds) The time from the exact moment of the Big Bang until 10^-35 of a second later is referred to as the Planck Era. While we have no way of knowing what this era was like from the equations of physics (as they break down in this era), it is "assumed" to be somewhat as follows. The universe was a tiny hot gaseous soup (a plasma) consisting of packets of "primal" particles at extremely high energies. The universe was smaller than the size of a proton. During this phase physicists believe matter and energy were not separated as they are currently. The primal particles were packets of radiation unlike anything we know today. Also, the four primary forces of the universe as we know them today were believed to be one united force. The temperature of the universe was 1 x 10^32 degrees Celsius. This hot thick soup was intense and everywhere. It also began to instantaneously expand and cool extremely fast. Inflationary Model Added. (10^-35 to 10^-33 Of A Second) As shown in this chart developed by Alan Guth, the universe went through an expansionary phase that was faster than the speed of light (space-time is not limited by the speed of light, only objects "within" space-time are). In this brief interval of Inflation, the "observable" universe expanded by a factor of about 10^70 (1 followed by 70 zeros) from being unimaginably smaller than a subatomic particle to about the size of a grapefruit. That is the equivalent of going from about the size of a grape to the current size of the observable universe in the blink of an eye - awesome! Note that Inflationary theory does not say anything about the "whole" universe, only the observable universe. The Inflationary model does not make any statement about the whole universe which could in fact be infinite.
Reheating. (10^-33 to About 10^-10 Of A Second) Inflation was a period of super cooled expansion and the temperature dropped by a factor of 100,000 or so and continued to be cool during this phase. When Inflation ended the temperature returned to the pre-inflationary temperature, back up by a factor of 100,000. This period is called "reheating". The huge potential energy of the inflation field suddenly decayed and filled the universe with elementary particles and radiation similar to water vapor in the atmosphere condensing into water droplets forming a cloud. Because the fundamental principles of Inflation are not known, this process is not well understood. During Reheating, the elementary particles - photons, gluons, and quarks - were formed, but in a plasma state. Quarks and anti-quarks began to annihilate each other. However, for reasons not yet figured out, the mutual destruction of quarks and anti-quarks ended with a surplus of quarks. Because of this discrepancy stars, planets, and human beings exist today. Also, the four fundamental forces - gravity, the electromagnetic force, the strong nuclear force, and the weak nuclear force - formed and then separated during this time according to the Grand Unified Theory (GUT). The universe as we now know it had evolved. The laws of physics and the four forces of nature began to apply. Reheating ended at about 10^-10th of a second. Particle Era. (10^-10 to About 10 Seconds) As the universe continued to cool, the particle era consisted of the formation of two particle families - hadrons and leptons. Hadrons then formed two additional families - baryons and mesons. Hadrons are formed from quarks and baryons are "normal stable everyday matter" consisting of three quarks. Mesons are "short lived unstable particles" made of one quark and one anti-quark. All of the new mesons quickly annihilated each other leaving only protons and neutrons which would make up the nuclei of future atoms. The hadron epoch ended at about one second. The formation of hadrons was followed by the formation of leptons. Leptons consist of electrons, neutrinos, muons and taus. Muons and taus are very unstable and quickly decay. During this period most of the matter in the universe consisted of leptons and their anti-particles. The lepton era drew to a close when the majority of leptons and anti-leptons annihilated one another, leaving a comparatively small surplus of leptons to populate the future universe. The lepton epoch ended at about ten seconds.
Big Bang Nucleosynthesis (BBN) (10 Seconds to About 20 Minutes) After Inflation, the universe slowed down to the normal "Hubble Rate" and was filled with radiation and elementary particles, sometimes called "quark soup". As the universe continued to cool, new particles were formed out of pre-existing ones. This early formation phase is called the Big Bang Nucleosynthesis (BBN). With the temperature falling below 10 billion Kelvin, BBN took place from about ten seconds to about twenty minutes. The diagram at the left illustrates two of the common nuclear reactions which occurred during the BBN. It shows single proton ions and neutron ions combining to form deuterium nuclei, D, (containing one proton and one neutron) plus the emission of high energy photons, γ. Subsequently it shows two deuterium nuclei fusing to produce one nucleus of helium-3 (with two protons and one neutron) and one free neutron. Note that "atoms" were not yet forming, the above reaction shows just the "nuclei" of future atoms forming from ions. Experiments can be done in labs today demonstrating these early BBN nuclei reactions. The BBN theoretical calculations result in a nuclei abundance of about 75% hydrogen (1 proton nucleus), about 25% helium (2 protons and 2 neutrons in the nucleus), and about 0.01% of deuterium (1 proton and 1 neutron nucleus). Without this abundance of hydrogen nuclei, there would be no water and therefore no life as we now know it. That the observed hydrogen and helium abundances in early distant galaxies are very consistent with the above theoretical calculations is considered "strong evidence" for the Big Bang Theory. Big Bang Nucleosynthesis is one of the three pillars of support for the Big Bang Theory. Measurements from the WMAP satellite over nine years of collecting data (2001 to 2010) has recently confirmed the above ratios with much greater precision. One nice feature of the BBN is that the physical laws that govern the behavior of matter at these energy levels are very well understood. Hence the BBN lacks some of the speculative uncertainties that characterize earlier periods in the "theoretical" life of the universe. During all this time, electrons and photons interacted with each other so intensely (instantaneous collisions) that the universe was opaque, i.e. dark, no light (photons) could escape.
The Photon Era (20 Minutes to 380,000 Years) During this long period of gradual cooling, the universe is filled with plasma, a hot, opaque (in other words, NOT CLEAR) soup of atomic nuclei and electrons. This is not like the atoms of today! Think soup! After the first twenty minutes or so, the universe settled down to a much longer period of expansion and cooling in which change was less dramatic. High energy radiation (photons) dominated the cosmos. As the universe continued to cool, more and more matter was created. Expansion caused radiation to lose more energy than matter so that after a while, matter (nuclei) particles exceeded massless particles (photons). About 70,000 years after the Big Bang, radiation and matter were about equal in density, shortly thereafter matter began to dominate. Recombination (380,000 Years) For the next 310,000 years the universe continued to expand and cool, but was still fiery hot and dark. Any visible light was immediately scattered by collisions with the ubiquitous electrons and protons. It contained only the simplest elements, mostly hydrogen and helium ions. As the universe cooled further, the electrons (with a negative charge) begin to get captured by the ions (with a positive charge) forming atoms (electrically neutral). This process happened relatively fast and is known as "recombination". The first bits of structure began to form. These small clumps of matter grew in size as their gravity attracted other nearby matter. At about 380,000 years of cooling, light (photons) began to travel through the spaces between the atoms which now "bond" the electrons in their orbits. The universe had become transparent.
Dark Age (380,000 to 150 million years) The period after the formation of the first atoms and before the first stars is sometimes referred to as the Dark Age. Although photons exist, the universe at this time is literally dark, with no stars having formed to give off light. With only very diffuse matter remaining, activity in the universe has tailed off dramatically, with very low energy levels and very large time scales. Little of note happens during this period, and the universe is dominated by mysterious dark matter. Note: We aren t sure what dark matter is. We will discuss later in class! Remember: the universe is continuing to expand and to cool! Reionization (150 million to 1 billion years) The first quasars form from gravitational collapse. We will discuss quasars separately, because they are so interesting! But here is a quick definition: A quasar is the center of a galaxy, with very high luminosity. It is ultra bright. A quasar consists of a supermassive black hole surrounded by gas. As gas falls toward the black hole, energy is released in the form of electromagnetic radiation. In other words, super dense objects condense, and the intense radiation they emit re-ionizes the surrounding universe. Ionization means to knock the electrons off, essentially more plasma soup! From this point on, most of the universe goes from being neutral back to being composed of ionized plasma.
Star and Galaxy Formation (300-500 million years onwards) Gravity amplifies slight irregularities in the density of the primordial gas and pockets of gas become more and more dense, even as the universe continues to expand rapidly. These small, dense clouds of cosmic gas start to collapse under their own gravity, becoming hot enough to trigger nuclear fusion reactions between hydrogen atoms, creating the very first stars. The first stars are short-lived supermassive stars, a hundred or so times the mass of our Sun, known as Population III (or metal-free ) stars. Eventually Population II and then Population I stars also begin to form from the material from previous rounds of star-making. Larger stars burn out quickly and explode in massive supernova events, their ashes going to form subsequent generations of stars. Large volumes of matter collapse to form galaxies and gravitational attraction pulls galaxies towards each other to form groups, clusters and superclusters. Solar System Formation (8.5-9 billion years) 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 4.5 to 5 billion years ago (8.5 to 9 billion years after the Big Bang). Today (13.7 billion years) The expansion of the universe and recycling of star materials into new stars continues.
Cosmic Microwave Background (CMB). The first early radiation that could freely travel was the CMB, the remnants of which we can detect in the current universe 13.75 billion years later. 380,000 years is the earliest point in time we can ever look back and "see" because everything before that was part of the dark ages. Note the CMB picture above taken by the European Space Agency (ESA) Planck satellite. The Planck satellite launched in 2009 is the third satellite exclusively designed to map the early CMB. NASA has previously launched the COBE in 1989 and the WMAP in 2001. Currently, the earliest galaxy we can "see" is MACS0647-JD which is believed to have formed about 420 million years after the Big Bang. Where does this fit into your timeline?