Humans have always tried to answer the question; how did the
universe begin? And no one to date has definitive proof of what occurred at
t=0s. Our best explanation of this phenomenon is the Big Bang theory, where the
universe started from a singularity and expanded exponentially. This idea was
first thought of by physicist Georges Lemaître who proposed the entire universe
came from an infinitely hot and dense point (Home.cern,
2018). The evidence came later from Edwin Hubble who measured the
redshift of distant galaxies; He noticed that the further the galaxy the larger
amount of red shift was shown relative to the Earth. This formed the idea that
all galaxies are moving away from each other but at an accelerating rate. If
you were to think back and reverse this acceleration, then this must mean that
the whole universe came from a singular point. Further proof came from the
discovery of Cosmic Microwave Background Radiation (CMBR) by Arno Penzias and
Robert Wilson in 1975 (Wmap.gsfc.nasa.gov, 2018 a).
They discovered that there was a uniform cold radiation that appeared
throughout the universe. This revealed that the radiation must have been
produced when the universe was far smaller for it to appear so uniform. It was
produced just a few hundred thousand years after the big bang and has slowly
cooled as the universe expanded to become microwave radiation today.
Immediately after the big bang the universe was infinitely
small and dense; the energy was so high that we cannot know how the universe
behaved. From t=0s – t=10-43s is known as the Planck time and is the
area of time we know least about because we cannot recreate environments of
this high an energy (Physicsoftheuniverse.com, 2018 a).
It is thought that that the four fundamental forces (Strong, Weak,
Electromagnetic and Gravity) were all unified as an equal force. Gravity is
relatively a very weak force and is therefore difficult to unify with the other
3 forces. However, the larger the energy of 2 objects the larger the
gravitational force between them will be; this shows that in energies as high
as the early universe there is a possibility that gravity could be unified (Weinberg,
2015). If all the fundamental forces were to become unified, then this would
mean that there would only be one form of interaction between particles.
Therefore, there would only be one form of particles, interacting with one
another through one force (Trefil, 2013). This
would make the earliest age of the universe the simplest it could ever be.
The GUT (Grand Unified Theory) period from t=10-43s
– t=10-35s represented when the energy became low enough for gravity
to become a separate force (Physicsoftheuniverse.com,
2018 b). This resulted in just the unification of the Strong and
Electroweak (Electromagnetic and weak) forces and the first appearance of
elementary particles (Young et al., 2016 a).
There were only quarks, antiquarks and leptons (e.g. electrons) which all
interchanged continuously resulting in little differentiation between them. It
is thought that at the end of this epoch there were more quarks then antiquarks
to create the ratio we observe today; however there was only 1 more quark for
every 100 million anti-quarks (Silk, 2002).
From t=10-35s – t=10-32s occurred the
process known as inflation (Physicsoftheuniverse.com,
2018 c). This is due to the separation of the Strong force from the
Electroweak force; there is an energy shift between the unified and separation
of these forces (The Star Garden, 2018). This
outburst of energy caused the universe to expand at an incredible speed which
was faster than the speed of light. This initially seemed wrong as it did not
obey the laws of Physics which we are familiar with, that nothing can travel
faster than the speed of light. However, this law is for anything travelling
through space-time and not for space-time moving itself. Through inflation, the
universe expanded by a factor of 1027 becoming around 10cm in length
(Physicsoftheuniverse.com, 2018 d). Simultaneous
to this was the Electroweak epoch from t=10-37s – t=10-12s
which gave birth to new elementary particles. The W and Z bosons were formed as
well as the Higgs boson which formed from particle interactions.
From t=10-12s – t=10-7s was the age of
Quarks where the universe was composed of a Quark-Gluon plasma. The energy was
still very high, resulting in the quarks not having the ability to bond
together. Once the universe cooled enough at t=10-7s the quarks
could begin to bond starting the Hadron epoch. Quarks formed together to make
Hadrons (Protons and Neutrons) and anti-Hadrons. The Neutrons were formed from
collisions between Protons and Electrons, but energy and charge now had to be
conserved. This epoch ended 1 second into the life of the universe. Now with
the availability of hadrons and the temperature being large enough for nuclear
fusion, new heavier nuclei were formed. The nucleosynthesis epoch created a
composition of around 74% Hydrogen, 25% Helium and 1% heavier elements, this is
very similar to the ratio of elements which we see today (Young et al., 2016 b).
At 20 minutes the photon epoch had begun due to a large number
of annihilation reactions that took place between leptons and anti-leptons.
This resulted in a vast number of photons which created a plasma of atomic
nuclei and electrons which are not yet bound together. The temperature at this
time had now dropped to the point where nuclear fusion can no longer occur. After
240,000 years of the universe cooling over its expansion, the particles slowed
down enough allowing the electrons to bond to ionised nuclei creating the epoch
of recombination. With the universe now having neutral atoms rather than the
plasma previously, photons were being produced which weren’t scattered (Astronomy.swin.edu.au, 2018). These are the photons
which can be viewed today and therefore is the earliest era of the universe
which we can observe, an example of this is the CMBR.
The Dark Age began 300,000 years after the big bang and lasted
until the creation of the first star (Physicsoftheuniverse.com,
2018 e). There was still a small number of photons scattered around the
universe but very few in comparison to the universe today. There were different
densities of particles through the universe and due to the gravitational
attraction between these particles, the denser areas became denser causing them
to heat up under friction. After 150 million years the first Quasar forms
releasing large amounts of radiation to form an ionised plasma in the
surroundings again. As gravity continues to pull particles together there is
increased friction and pressure until nuclear fusion occurs again, forming the
first stars. The first few stars were super-giants and had a very short life
span, they exploded in supernovae to form new heavier elements. The remains of
old stars go on to fuel new stars in billions of years to come. As time goes on,
more stars and planets are formed to create solar system clusters at around 8.5
billion years after the big bang.
The future of our universe is very difficult to predict and
the main reason for this is the presence of dark matter. This is a mystery that
physicists are researching, it is another form of matter which does not emit
or reflect radiation and therefore we cannot be observed directly. Hence, we
cannot know precisely how much dark matter is in the universe and what the total
mass of the universe is. The basis on how the universe continues to expand
depends on its density; this is due to how strong the gravitational force will
act pulling all matter together. If the density is high, we will have a closed
universe which will cause the universe to eventually contract to a point (Map.gsfc.nasa.gov, 2018 b). If the density is just on
the critical density, then we will have a flat universe where the universe will
reach a finite size limit and then stay constant. Another possibility is the
universe is below the critical density and will therefore carry on expanding
forever at an accelerating rate. If the universe was to expand forever, this is
called the big chill due to the fact the universe will carry on cooling down
until it can no longer support life (Woollaston, 2018).
If the universe was to collapse in a big crunch, then there is a chance that this
could initiate another big bang which creates an eternal cycle.
The birth and end to the universe may still be
under a lot of speculation. However, it is still a large achievement that we
know almost precisely the life of the universe from a few hundred years all the
way until today. The life of the universe has taken place over billions of
years, with human civilisation being a small spec on that timeline with just a
few thousand years. The universe raises many questions and it’s humanity who
will forever push the boundaries for answers.