The Universe began not with a whimper but with a Bang! Everything in this Universe and
the Universe itself came into existence because of the commonly told Big Bang. It all started
when in 1922, a Russian Meteorologist, Alexander Friedmann proposed that the universe might
be expanding. In a very rare blunder, Albert Einstein, when came to know about this, rejected
his theory and with his erroneous calculations proved him wrong. Five years earlier, Einstein
had published the Static model of the universe and was very convinced that it was correct.
He claimed Friedmann’s theory to be violating the conservation of energy. After eight months,
however, Einstein admitted his mistake and published a retraction. The Equation of General
Relativity allows for the possibility of an Expanding Universe.
Today this Big Bang theory is an accepted idea of cosmology. The Expansion of the Universe
was first observed by Vesto Slipher in the Early 1920s and in 1929, Edwin Hubble who
had access to some world’s largest telescopes gave the Hubble Law. According to it, every
distant galaxy is moving away from each other with a velocity proportional to its distance.
The farther away a galaxy is, greater is the velocity with which it moves away. Then Arno
Penzias and Robert Wilson detected a background of microwave radiation known as the Cosmic
Microwave Background(CMB) radiations today, coming to Earth from all the directions. It
was an afterglow of the primordial, hot and dense Fireball. Today, with the data collected
from the Cosmic Background Explorer (COBE) satellite fits perfectly with the Big Bang
and that it accounted for the light nuclear isotopes like deuterium, hydrogen, helium-3
and others. The Big Bang theory is a success but in its traditional form as it was proposed
is incomplete. Though it’s called the Big Bang Theory, it does not tell us anything
about the Bang! It’s the theory of what happened after the Big Bang, describing how
the universe cooled and expanded, and how mater formed different Stars and Galaxies.
The theory does not tell us anything about the underlying physics of this explosion.
It not even mentions what caused the Bang, what Banged, why it Banged and what happened
before the Bang! The inflationary cosmos explains this and we will discuss the physics behind
it in this video. Could the Big Bang have been caused by the
gigantic bag of TNT, or a thermonuclear explosion? Or maybe a gigantic ball of matter collided
with a gigantic ball of anti-matter. In fact, none of these events are responsible for the
Big Bang and start of our Universe. The Big Bang had two very special and distinct features
that differentiated it from any typical explanation. First, On large scales Big Bang was far more
homogenous than any ordinary explosion. We must clarify you first while discussing homogeneity,
that the Universe is inhomogeneous in many ways. New York differs from California and
so are the Stars, galaxies and the clusters scattered through the space in a complex pattern.
Cosmologically, these are all small scale. On a large scale, like if we divide the Universe
into cubes of 300 million light years or more. We would find that each cube resembles the
others in all its properties like mass density, light output, etc. The biggest evidence of
it is the Cosmic Microwave Background(CMB) Radiations and data from the COBE satellite.
We would need a brief history about the Cosmic Microwave Background Radiation to explain
the uniformity of our Universe. The Early Universe was boiling and dense and it would
rip apart the electrons from the atoms which resulted in a plasma that filled the space.
This plasma was very opaque. So the protons making up the Cosmic Microwave Background
radiations, were absorbed and re-emitted constantly. After about 300,000 years the universe cooled
to form a transparent plasma of neutral atoms. Since then, the photons have travelled on
a straight path and provide us an image of a universe that was 300,000 years old.
Normally such uniformity is easy to explain, because anything comes to a uniform temperature
when left undisturbed for a long time. But in the Big Bang theory, the universe develops
quickly, leaving no time for the universe to evolve and uniformity to be established.
For the sake of discussion lets pretend that the universe contains blue creatures, each
having a furnace and refrigerator and have the task to create a uniform temperature.
These little creatures would then have to travel with nearly 100 times the speed of
light to make the temperature uniform. Since neither Antimatter nor sticks of dynamite
could travel faster than the speed of light, they cannot account for its uniform temperatures.
The classical form of Big Bang postulates that the primordial fireball filled the space
from the beginning. By assumption and not because of any physical process, it was assumed
that the temperature was same everywhere. We know this flaw as the ‘Horizon Problem’.
The second special feature of the Big Bang, which is very difficult to imagine arising
from a standard explosion, is a remarkable coincidence called the “flatness problem.”
This problem concerns the pinpoint precision with which we must specify the mass density
of the early Universe for the Big Bang theory to agree with reality.First, we need to review
a little vocabulary. If the mass density of the Universe exceeds a value called the critical
density, then gravity will be strong enough to reverse the expansion eventually, causing
the Universe to re-collapse into what is sometimes called the big crunch. If the mass density
is less than the critical value, the Universe will go on expanding forever. We know the
ratio of the actual mass density to cosmologists by the Greek letter omega ( ). General relativity
implies that the geometry of the Universe is Euclidean only if omega is one, so an
= 1 universe is called “flat”. Omega is very difficult to determine, but its present
value lies somewhere between 0.1 to 2. That seems like a broad range, but consideration
of the time development of the Universe leads to a spectacularly unique point of view.
= 1 is an unstable equilibrium point of cosmological evolution, so it resembles the
situation of a pencil balancing on its sharpened tip. The phrase equilibrium point implies
that if omega is ever exactly equal to one, it will remain exactly equal to one forever
- just as a pencil balanced precisely on end will, according to the laws of classical physics,
remain forever vertical. The word unstable means that any deviation from the equilibrium
point, in either direction, will rapidly grow. If the value of omega in the early Universe
was just a little above one, it would have rapidly risen toward infinity; if it was just
a smidgen below one, it would have rapidly fallen toward zero. For omega to be anywhere
near one today, it must have been extraordinarily close to one at early times. For example,
consider one second after the Big Bang, the time at which the processes related to Big
Bang nucleosynthesis were just beginning. For omega to be anywhere in the allowed range
today omega must have equaled one to an accuracy of 15 decimal places! This is mainly known
as the Flatness problem. These were some problem with the classic Big
Bang theory. [Pause] The property of Big Bang are very special and the laws of Physics provide
a mechanism for this sort of Bang. We know this mechanism as Cosmic Inflation. The Inflation
Hypothesis gives us a decent explanation of why is the Universe expanding from the Big
Bang, It puts the Bang in the Big Bang. After Inflation, the universe would have continued
to rise like the Hubble Expansion we see today. It answers four main questions- The problem
of smoothness, flatness, missing monopoles and expansion.
To solve the problems of smoothness, flatness, missing monopoles and expansion, the universe
needs to expand by a factor of 1025 in less than 10-30 sec. For this, the energy density
of the vacuum during inflation needed to be vastly stronger. Also, the universe stopped
inflating at some point to make way for regular Hubble Expansion. For this the vacuum energy
would have to drop from a very high value to zero. To understand this, we need some
Quantum physics and here Quantum Field Theory (QFT), which explains how a vacuum can have
energy. The universe id filled with these Quantum fields and it is has a field strength.
This field strength determines how much force a Quantum field exerts on other fields and
particles present. For example, a magnetic field, the stronger it is, the more it pulls
or pushes. A fundamental particle in just an oscillation in this field, a little packet
of energy held by the field. If the energy in a Quantum field is in the form of particles
and if space is expanding- as in our universe- then that energy gets more and more spread
over time. As these particles get dispersed, the energy density becomes low. A Quantum
field contains an intrinsic amount of energy, even without particles. In that case, it always
tries to drop to the lowest energy state, and that means it loses all energy besides
what is bound up in particles. If we take an example of a magnetic field, when we take
away electric current that created it, the magnetic field will quickly fade away. A field
doesn’t jump to the lowest energy state instantly, it does it at one step at a time. If
we graph Quantum field potential energy versus filed strength, it might look like this:-
Figure 1.1 If the field finds itself at a high energy
state, it would roll to the minimum and stay there. The lowest energy state pf the field
is called its vacuum state. [figure 1.2]
But sometimes the energy contained by a field has a more complex relationship with field
strength. The field could have a local energy minimum and if a Quantum field finds itself
near such a local minimum, it would roll down to the bottom and get stuck there, It would
have a large amount of energy but no particles. We call this a false vacuum, a temporary one
as the name suggests. It gives us exactly the constant energy density needs for Inflation.
This filed was called Inflaton Field. In the early universe, because of very high temperature,
this Inflaton field had a high field strength. It loses strength and energy with the cooling
of the universe. But is stuck in the local energy minimum.
[Figure 2.1] [Figure 2.2]
{} The universe keeps cooling, but the Inflaton
field can’t lose more strength. It would have to cross the local energy barrier to
do that. [Pause] Being stuck at a constant and very high-energy-density Inflation takes
hold and its exponential nature blows up the Universe, rendering it empty and cooling it
to a lower temperature or we can say it super cools the Inflaton field. It remains in a
vacuum state hat doesn’t match its temperature. Inflation would go on forever if the Inflaton
field stays stuck, but the Quantum fields have a tendency to randomly fluctuate to different
values, as is explained in the Heisenberg’s Uncertainty principle. And somewhere in the
Inflating universe, the Inflaton field fluctuated to the other side of the local minimum barrier,
it Quantum tunnelled there. [Figure 3]
And on the other side it sees a deeper, truer minimum, the true vacuum state, and starts
losing energy to reach there. Inflation stopped at that point and the entire Inflaton field
surged down in energy. The Energy that existed in the Inflaton field doesn’t just do away,
it remains there, but in the form of Inflaton Particles. It’s like the entire floor of
the field shifted down in space and converted into a stack of Inflaton particles.
[Figure 4.1] [Figure 4.2]
These particles are very unstable and dispersed their energy into other Quantum Fields and
decayed into Quarks, electrons etc.The vacuum of Inflation is converted to a hot ocean of
particles. The Universe was “rethermalized” by this process. This process heated the universe
to the extreme energies that we expect existed right after the Big Bang. T this point the
Universe should have evolved as the rest of the Big Bang story predicts.
While it may be too early to say that inflation is proved, I claim that the case for inflation
is compelling. It is hard to even conceive of an alternative theory that could explain
the basic features of the observed Universe. Not only does inflation produce just the kind
of special bang that matches the observed Universe, but quantum fluctuations during
inflation could have produced nonuniformities which served as the seeds of cosmic structure.
These nonuniformities can be observed directly in the cosmic background radiation, with an
amplitude of about one part in 100,000. So far the measurements of the spectrum have
been beautifully consistent with the predictions of inflation, although it must be admitted
that nonuniformities created by cosmic strings are also consistent with the observations.
Cosmic strings, however, cannot explain the large-scale homogeneity or the flatness of
the Universe. While the case for inflation is strong, it
should be stressed that inflation is really a paradigm and not a theory. The statement
that the Universe arose from inflation, if it is true, is not the end of the study of
cosmic origins - it is in fact closer to the beginning. The details of inflation depend
upon the details of the underlying particle physics, so cosmology and particle physics
become intimately linked together. While I cannot see any viable alternative to the general
idea of inflation, there is still much work to be done before a detailed picture is established.
And I suspect that there is room for many new important ideas.
So what do you think about the theory of Inflation? Does it really gives the answers
for Inflation? Did you know about this theory before? Let us know in the comment section
below. If you liked our video please like, subscribe and share it. We will keep answering
your questions in the coming future.