Timeline of the Big Bang
From Academic Kids
According to the Big Bang theory, a sequence of events described below is believed to have taken place starting (13.7 ± 0.2) x 109 years ago, a time at which in general relativity there is a gravitational singularity.
General relativity cannot describe the Universe at this time, because the theory gives infinite values for the temperature and density of the universe. It is believed that general relativity is insufficient to make predictions about the very beginning of the universe and that such predictions require a theory of quantum gravity. Nevertheless, the time at which general relativity predicts a singularity makes a convenient starting point to begin the timeline, whether there was such a singularity or not.
Important for understanding this table is the concept of decoupling or freezeout. Imagine a block of ice and an aluminium Coca-Cola can. If you increase the temperature to an extremely high value, then both objects will vaporize, producing a mixture of water and aluminium vapor which can be considered a single entity. If the temperature decreases, then below a certain value the aluminium will condense and freeze and stop interacting with the water vapor. The temperature at which this occurs can be estimated.
Similarly, during the Big Bang, entities froze out and decoupled from the rest of the soup that made up the universe. The freezeout temperature can be estimated, and the temperature corresponds to the time after the Big Bang.
This timeline refers to the diameter of "the universe". This is not the total size of the universe, which may be infinite, but the historical radius of the spherical universe we can now in principle observe, about 13.7 billion light years. We cannot observe anything outside that sphere, as information from it would have taken longer to reach us than the life of the universe. As the universe expanded, what is now in that sphere occupied regions of different diameters at different historical times, and it is to those diameters that we refer.
Stephen Hawking has theorized that the events of the Big Bang (the expansion of a singularity into the current space time continuum) can be seen as a reversal of the events that occur in a black hole, where space-time condenses into a singularity.
Science tells us nothing about what happened from the time of the Big Bang until 10-43 seconds, a concept known as Planck time. After this, the time is grouped into epochs. At first, these are very short periods; of the seven epochs described below, the first five together last for three minutes.
- A length of 10-43 seconds is known as Planck time. At this point, the force of gravity separated from the other three forces, collectively known as the electronuclear force. A complete theory of quantum gravity such as superstring theory is needed to understand these very early events; however the present understanding of cosmology in string theory is very limited. The diameter of the currently observable universe is theorized as 10-35 m which is known as the Planck length.
- Separation of the strong force from the electronuclear force, leaving three forces: gravity, strong, and electroweak forces. The particles which are involved in the strong force are considerably more massive than the particles which are involved with the other forces and so are believed to "condense" out earlier.
Grand Unification Epoch
The Grand Unification Epoch covers the time from 10-35 to 10-12 seconds after the Big Bang. The temperature during this epoch is estimated to decrease from 1027 K to 1015 K.
- For the period of time between 10-35 seconds and 10-33 seconds, it is believed that the size of the universe expands to a size of approximately 10-32 m to 10-22 m. Postulating the existence of inflation solves a number of problems which are described in cosmic inflation.
- 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. Which means that there is no opportunity after this time for more matter to be created than 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.
- The temperature of the Universe is approximately 1025 kelvins. The Quark-Antiquark Freezeout begins and lasts until 10-5 seconds. At these temperatures, quarks are able to condense out but the temperatures are still too hot for protons and neutrons to exist.
- Birth of quarks, which appear in particle-antiparticle pairs. Quarks and anti-quarks annihilate each other to create photons, but quarks are created at a ratio of approximately 109 (1 billion) anti-quarks to 109+1 (1,000,000,001) quarks, resulting in one quark per billion matter-antimatter interactions. The mechanism causing this asymmetry, called baryogenesis is under active research and different theories are offered.
Free quarks multiply rapidly.
The Electroweak Epoch covers the time from 10-12 to 10-6 seconds after the Big Bang. The temperature during this epoch is estimated to decrease from 1015 K to 1013 K.
- The diameter of the observable universe increases to approximately 10-13 meters. The weak force, which involves massive particles, condenses and separates from the electromagnetic force, which involves a massless particle, leaving us with the four separate forces we know today.
The Hadron Epoch covers the time from 10-6 seconds to 1 second after the Big Bang. The temperature during this epoch is estimated to decrease from 1013 K to 1010 K.
- The temperature of the Universe is approximately 1013 K. Quarks combine to form protons and neutrons. The lowering temperature allows quark/anti-quark pairs to combine into mesons. After this period quarks and anti-quarks can no longer exist as free particles.
- Some scientists theorize that primordial black holes first appeared during this period.
- The temperature of the Universe is approximately 1010 kelvins. The existence of antimatter is cancelled out, as lepton/anti-lepton pairs are annihilated by existing photons. Neutrinos break free and exist on their own.
The Lepton Epoch covers the time from 1 second to 3 minutes after the Big Bang. The temperature during this epoch is estimated to decrease from 1010 K to 109 K.
1 second after the Big Bang
- Formation of hydrogen nuclei, the first atomic nuclei. 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.
Epoch of Nucleosynthesis
3 minutes after the Big Bang
- Three minutes after the Big Bang, the universe is too cool for nuclear activity to occur, and these reactions stop. At this point the universe consists of about 75% hydrogen, 25% helium and trace amounts of deuterium, lithium, beryllium, and boron. Elements heavier than this do not have time to form before nuclear reactions stop. By looking at conditions between 1 second and 3 minutes after the Big Bang, one can predict the elemental abundance of the Universe. These predictions are broadly in agreement with observations.
379,000 years after the Big Bang
- The temperature of the Universe is approximately 3000 kelvins. At this temperature hydrogen nuclei capture electrons to form stable atoms. This event known as recombination is particularly significant because free electrons are effective at scattering light, which is why fire is not transparent, while hydrogen atoms will allow light to pass through.
- This implies that this is the time at which space becomes transparent to light, since photons no longer interact strongly with atoms. This means that what we normally think of as matter and what we normally think of as energy become separate.
- The light from the moment at which the universe became transparent has been redshifted to radio waves and makes up the cosmic microwave background.
Epoch of Galaxies
A major event of this epoch is reionization.
We see astronomical objects as they were some time ago. The greater the time since the object was as we see it now, the greater the redshift in the electromagnetic radiation we get from it. In the following table, the variable z is a measure of redshift of objects in which, if we were to observe them, we might see the listed events taking place.
- z = 1500 - cosmic microwave background generated 379,000 years after Big Bang
- z = 15 - First reionization
- z = 6 - Oldest quasars
- z = 5 - Reionization ends
- z = 1 - Youngest quasars
For later events, see Timeline of the Universe.