Origin of the Universe

From time immemorial, great minds have wandered around trying to find the truth behind everything. Some hypothesized about the origin of mankind, while others about the meaning of life. One such topic that they stumbled upon is ‘Who created this world’ or ‘How did universe came into being’.

The answers, more like conjectures, were often entangles with culture, religion and pseudo-science. It was later in the 20^th century that we had the technology to obtain observations, assess various models and come to a result.

Do mind that science is ever-changing and dynamic, and not constant. That is, a theory accepted by all today may not hold any significance tomorrow.

On this note, let’s understand various scientific models proposed to explain the origin of the universe.

It is the most well known and accepted theory. It also has solid evidence to support its claim. Georges Lemaître, a Catholic priest and a Belgian cosmologist, proposed this theory. The proof was further provided by Edwin Hubble, who discovered galaxies other than ours and also the expanding nature of our universe.

Origin of the Universe

Expansion, when reversed, is contraction and the end would be a point source. This is also known as singularity. For a singularity to expand to a universe, it is speculated to have taken about 13.8 billion years.

THE SINGULARITY :

This time period is called as the Planck epoch or the Singularity epoch. Here, the singularity ahs infinite density and temperatures that we can’t comprehend. One theory suggests that the four major physical forces – gravitational, electromagnetic, strong nuclear and weak nuclear – combined into one fundamental force still unknown to us. Another theory explains that quantum effects dominated over the physical forces.

Any law known to us is not applicable for this epoch. This is because no current theory can be applied on timescale shorter than the Planck time [5.39 x 10^-44 sec] and the Planck epoch describes about times shorter than 10^-43 sec.

THE GRAND UNIFICATION EPOCH :

This describes the activities during 10^-43 to 10^-36 sec. Here, the temperature starts to decrease [yet still very hot] and the single fundamental force starts breaking down into gravitational force and electrogauge force. Further, the electrogauge force separated into strong nuclear and electroweak force. This marks the end of this epoch.

A simple way to explain how this happened is to imagine different gases with high temperature in a container. As I lower the temperature, it is a fact that a gas with higher boiling point will convert into a liquid and settle down. As I further decrease the temperature, the gaseous mixture will condense and separate into different liquids until there is no gas left to cool down. The same is happening in this and the next epoch.

Using a more scientific terminology, the physical forces that we know propagate and interact using specific quanta. For example, it is hypothesized in the Quantum theory that gravitational force between two objects is the result of exchange of gravitons. On the other hand, it has been proven that quanta for electromagnetic force is photon, for weak force is W and Z boson, and for strong force is gluons.

So, during the Plank epoch, each of the respective quantum fields exist at a higher energy state. As the transition to the next epoch starts, the fields have a decrease in their energy, thus reaching a stable low energy configuration. As soon as this happens, the force separates from the singular fundamental force and starts functioning on its own.

THE ELECTROWEAK EPOCH :

The time period lasts from 10^-36 sec to 10^-32 sec after the big bang. Now the temperature has cooled down to 10²⁸ K for the electroweak force to separate into electromagnetic and weak nuclear force. This epoch marks the end of inflation.

THE INFLATIONARY EPOCH :

Time period till 10^-32 sec after the Big Bang. The singularity expanded by at least 10⁷⁸ times in volume or 10²⁶ times per spatial dimension. To wrap our minds around this number, it is equivalent to object of length 1 micrometer [width of an hair], expanding to one approximately 10,600 light-years (100,000 trillion kilometres) long in a tiny fraction of a second.

Seeing this rate of expansion, a question may arise in our mind. It is said that nothing can travel faster than the speed of light but the universe sure did expand exponentially faster than the speed of light [3x10⁸m/s].

Well, to be more precise, the Special Theory of Relativity states that neither information nor matter can travel faster than the speed of light in a vacuum. Here, the information travels in ‘space’ from one place to another with the speed of light. On the other hand, when the universe was expanding, it was not the matter that travelled, rather it was the ‘space’ itself that expanded. Thus, Special relativity was maintained.

After the inflation ended, the universe was reheated which further marked the emergence oh hot quantum plasma. From this point onwards, laws of physics were more understandable due to research performed in particle colliders.

THE QUANTUM EPOCH :

Time period of 10^-32 sec to 10 secs after the Big Bang, With the abundance of plasma containing various quantum particles, particles and antiparticles were continuously formed and annihilated by collisions. Along with the space expanding, the temperature started to decrease. As most particles and antiparticles were destroyed due to collisions, most of the mass-energy left took the form of neutrinos, photons and other particles.

THE PHOTON EPOCH :

The mass-energy now was dominated by photons. The photons interacted frequently with charged particles like protons and eventually with nuclei. This lasted from 10 secs to 370,000 years after the Big Bang.

MATTER DOMINATION :

Between 2 mins and 20 mins after the Big Bang, light nuclei began forming via nuclear fusion of protons and neutrons. Before this time period, the nuclei formed dissociated easily due to the surrounding energy to be higher that their binding energy. But as the universe started cooling down, nuclei started to become more state.

After 47,000 years after the Big Bang, the universe which was dominated by radiation shifted towards matter. According to the Lambda-CDM model, the matter in the universe was comprised of 15.5% ordinary matter and the rest was dark matter. The characteristics of dark matter are yet to be determined but it is speculated that dark matter played a pivotal role in structuring our universe.  

COSMIC MICROWAVE BACKGROUND :

The interactions between photon and matter were very frequent when hot plasma existed. Due to this, photons could not travel very far without any collision and the universe was opaque and foggy.

As everything cooled down and space expanded, neutral atoms started to form. As the subatomic particles existed in excited stage, they tended to lose energy by releasing photons and lower their configuration to a stable energy state. This meant that the mean free path of photons became infinite. This resulted in universe becoming transparent.

The photons were visible as pale yellow or soft white in color. As the space expanded, they became red shifted [ie lower frequency and longer wavelength]. This red shifting is an example of Doppler effect in which the frequency and wavelength changes due to relative speed between two locations.

As Edwin Hubble discovered that the universe is expanding, it can be speculated that the light we perceive from the early universe should be red shifted. This was proven to be correct as the light had shifted from being visible to radio waves.

This acts as a solid evidence that this theory is indeed legitimate.

DARK ENERGY :

It is an unknown form of energy that is not understood at all. The universe was first dominated by radiation, then matter and about 9.8 billion years after the BB, dark energy seems to be dominant. During these transitions, the rate at which space expanded also varied; starting from being extremely fast, then slowing down, and at last picking up its pace.

Thus, this results in the universe that we observe now.

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THE STEADY STATE MODEL

It is an obsolete model based on the cosmological principle – It is an assumption that spatial distribution of matter is homogeneous and isotropic when viewed on a large scale. The model states that the density of matter is constant, i.e. as the universe expands, matter is continuously created. It also claims that the universe has neither a beginning nor an end.

This theory was given by Sir James Jeans in 1920. It was further revised by Hermann Bondi and Thomas Gold in 1948. It was later developed by Sir Fred Hoyle.

As this theory was tested, none of their claims were found to be correct. The principle of isotropy was violated when the CMB [Cosmic microwave Background] was found to be anisotropic [uneven]. Many structures have been discovered that are larger than what the principle of homogeneity predicted.

Although this model was in the limelight for some time, it was eventually discarded due to large deviations from the actual observations.

THE BIG BOUNCE

The Big Bounce theory is a combination of the Big Bang and the Big Crunch [read more] theory. It essentially says that after the expansion of the Universe, until it comes to a stop. Then the opposite [contraction] will start, ending into a singularity.

The Theory then hypothesizes that after forming a new singularity, another Big Bang will happen and the cycle continues.

Dark energy is claimed to be the reason for contraction of the Universe.

In contrast to their claims, the current Universe is expanding at a faster pace due to the same dark energy which will cause contraction in theory.

There are other theories like the Eternal Inflation and the Incredible Bulk which stem out from the Big Bang theory into the realm of multiverse.

ORIGIN OF THE UNIVERSE - MY OPINION

Big Bang may very well be the start of our universe, but the theory still lacks quite a bit. For starters, the understanding of physics is still lacking and we are yet to develop quantum mechanics and integrate it into ‘The Theory of Everything’. There are a lot of unknown variables that constitute a major part of our universe that we know nothing about; namely dark matter and dark energy. Also, it only talks about what must have happened after the Big Bang, and not ‘why’ the Big Bang occurred. It also cannot answer if something existed before the Big Bang.

Time, in the theory, is assumed to be linearly going forward and the Big Bang to be the start of time. However, there are speculations if time is itself an illusion rather than a dimension.

So, I think the Big Bang theory is in its infancy and has a lot to develop.

Same with the Big Bounce theory, it lacks evidence about its claim that the Big Crunch would happen due to dark energy. This, in fact, stems from our inability to understand the characteristics and origin of dark energy and how it influences our universe.

I think that as we go beyond the Big Bang, we will enter the world of multiverse which will further connect us with other theories like the String theory, Black holes and many more. I believe that when this mystery is solved, it will turn into something we can’t even imagine in this age. I hope this development fastens its pace so that we can understand more about the place we live in.

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REFERENCES

https://www.universetoday.com/54756/what-is-the-big-bang-theory/

https://www.discovermagazine.com/the-sciences/3-theories-that-might-blow-up-the-big-bang

https://www.wikipedia.org/