The Big Bang Theory in 10 mins - How our Universe came to be.
The Universe came into being 13.8 billion years ago.
It was compressed into an unimaginably small volume of space and began as an infinitely
hot dense fireball.
This state of affairs is described as a singularity.
It is hypothesised that at this time spacetime is extremely turbulent and warped,
giving it a foamy character.
The spacetime foam is also known as quantum foam.
Within this high density environment a quantum fluctuation can give rise to an entire Universe
such as ours.
During the Planck epoch all the forces are unified as one fundamental force; Supergravity.
When our Universe bursts into existence there is a sudden and rapid stretching of space everywhere.
As space stretches and cools it crosses a transition temperature where gravity separates
from the other forces.
Electromagnetism, the strong nuclear force and the weak nuclear force then act as one
single force; the grand unified force.
During this epoch the earliest elementary particles and antiparticles are created.
As space continues to stretch and cool, it crosses another transition temperature and
the strong force separates from the electroweak force.
This separation triggers a period of exponential, faster-than-the-speed-of-light stretching
of space known as inflation.
Einstein's theory of relativity says that nothing can move faster than the speed of
light in space but that does not preclude space itself from stretching faster than the
speed of light.
The stretching is caused by a repulsive form of gravity and the Universe doubles in size
at least 100 times, going from the from the size of a billionth of a proton to the size
of a grapefruit.
Inflation ends when the repulsive energy decays into ordinary matter and energy, at which
point ordinary Big Bang expansion takes over.
The elementary particles, created during the grand unification epoch exists as a hot dense
quark-gluon plasma that is distributed thinly across the Universe.
As the strong force separates from the electroweak force, particle interactions create a large
number of exotic and theoretical particles with unusual properties. An example of such
a particle is the Tachyon, a theoretical particle that travels faster than the speed of light.
The Higgs field is a quantum field that permeates all of space. Particle Interactions with the
Higgs field impart particles with their mass and the Higgs boson is the local excitation
of the Higgs field.
The Higgs field causes electroweak symmetry to break resulting in the electromagnetic
force and weak force manifesting themselves differently.
As the Universe cools to below 10 quadrillion degrees quarks, electrons and neutrinos along
with their antiparticles form in large numbers.
The four fundamental forces assume their present forms.
During this epoch a process known as baryogenesis creates an asymmetry in the creation of quarks
and antiquarks which results in slightly more quarks being produced. There is an extra quark
created for every billion quark antiquark pair.
When quarks and antiquarks make contact they annihilate each other to produce energy and
the surplus quarks will go on to form all the matter that we see in our Universe.
As the temperature of the Universe cools to
a trillion degrees the quarks combine to create protons and neutrons. Composite particles
made up of quarks such as protons and neutrons are known as hadrons.
In the extreme conditions of the hadron epoch electrons can fuse with protons to form neutrons
giving off neutrinos.
During this epoch some neutrons and neutrinos also recombine to form new proton electron pairs.
Random combining and and recombining is commonplace during this epoch.
At the end of the hadron epoch the majority
of hadrons and anti-hadrons annihilate each other. Leptons and anti-leptons now dominate.
Electrons come into contact with their anti particles, positrons to create energy in the
form of photons and photons collide with each other to form electrons and positrons.
10 seconds after the Big Bang the temperature of the universe falls to the point at which
new lepton/anti-lepton pairs are no longer created and most leptons and anti-leptons
are eliminated in annihilations, leaving a small excess of leptons.
The temperature of the Universe falls to a
billion degrees and for the first time atomic nuclei can begin to form. Protons and neutrons
combine through nuclear fusion to form the nuclei of the simple elements of hydrogen,
helium and lithium.
After about 20 minutes the temperature and density of the Universe has fallen to a point
where nuclear fusion is no longer possible.
The Universe is filled with a hot, opaque
soup of atomic nuclei and electrons.
The photons left over from the lepton/ anti-lepton annihilations from the lepton era are
scattered by these nuclei and electrons so visible light can not move freely.
As the Universe cools free roving electrons are captured by the atomic nuclei to form
electrically neutral atoms via a process known as recombination.
As a consequence the photons in the Universe are finally able to travel freely and this
event is known as decoupling. For the first time, the Universe has become transparent
to light, i.e. allows photons to travel freely through it.
By the end of this period the Universe is filled with a fog made up of 75% hydrogen
atoms, 25% helium atoms and just traces of lithium atoms.
The period between the formation of the first atoms and the first stars are referred to
as the dark ages even though photons were present at this time. The dark ages are so
called because no sources of illumination, i.e stars existed during this time.
In this period cold dark matter dominated the Universe.
Cold dark matter is a hypothetical form of matter that we currently don't know much
about. What we do know is that it's gravitational pull is required in addition to the gravitational
pull of ordinary matter for stars and galaxies to move in the Universe the way that they do.
It is estimated that in the Universe for every kilogram of ordinary matter there exists 5.5 Kg
of dark matter.
Over time gravity pulls matter together to
create the first quasars via gravitational collapse. The UV radiation emitted by these
quasars strip the hydrogen gas atoms of their electrons, creating an ionised plasma. This
process means the gaseous fog is lifted around the quasars and as a result transparent bubbles
form within the Universe.
Over time pockets of gas are pulled together by gravity to become more and more dense.
These clouds begin to collapse under the weight of their own gravity with temperatures soaring
to a point where nuclear fusion is triggered and the first stars are born.
The stars act as furnaces, forging heavier elements from the lighter elements they are
made of. The first stars are 100 times more massive than our sun, 20 time hotter, 10 times
more luminous and they shine ultraviolet blue. These first generation stars only live
for a few million years and once they burn through their fuel they die in a hypernovae
spewing out an enriched cloud of elements.
Then a process of stellar recycling occurs. Gravitational attraction pulls the debris
of the previous generation of stars together until a new star is created which then goes
on to create heavier and heavier elements. In this way every subsequent generation of
star creates a richer composition of heavier elements than the previous generation.
We are often said to be made of star stuff and it is because the elements that make us
have been forged within the guts of these stars.
Gravitational attraction creates not only stars but also the other structures we see
in the night sky; galaxies, groups of galaxies, clusters of galaxies and superclusters of galaxies.
Our Sun is a 1000th generation star and matter
coalesced around it to form the planets, asteroids, and comets of our solar system.
Stars continue to die and be created and the Universe continues to stretch.
In fact the Universe is stretching at an accelerating rate owing to a curious form of energy called
dark energy.
Like dark matter, dark energy is shrouded in mystery and many predict that the physics
of the future will be focussed on trying to learn more about the darkness in our Universe.
We have now come to the end of our journey, having worked our way through the entire evolution
of the Universe as described by the Big Bang theory.
Please note that the timings are approximations and some events mentioned in the different
epochs did overlap.
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