In spite of numerous theories and scientific laws, humans have been gazing at the stars and wondering about the mysteries surrounding their existence. The Universe has always been a subject of debate and discussion of the scientific and religious people all over the world. What is this Universe? It includes everything we see, feel, sense and measure, from the microcosm to the macrocosm, such as stars, planets, galaxies, matter in its totality, space, time and light. With millions or billions of stars and galaxies, with empty spaces in between them, the Universe, since its evolution, has been expanding outwards every moment, the galaxies are moving apart, and everything is moving away from everything else.

Several renowned scientists like Albert Einstein, Edwin Hubble and Stephen Hawking have tried to reveal the secrets behind the Universe. There are different ranges of models that attempt to explain the development of the universe. One of the famous theories that has got wide acceptance by the scientific world is the Big-Bang theory.

The Big-Bang Theory

The Big-Bang theory is an attempt to describe what happened 13.7 billion years ago at the very beginning of the universe. Scientific discoveries have shown beyond doubt that our universe did have a beginning. During and after that crucial moment happened something; that was our Universe. But nothing is known about what was there before that moment, because we cannot reach there; all theories and laws of our science break down. The Big-Bang theory explains us what happened during that moment and after that.

13.7 billion years ago, our universe sprang into existence as a “Singularity”! Singularity means a zone infinitesimally small, extremely hot, and infinite density, within which all energy, matter and space were compressed. We do not know from where this singularity came from and why it appeared. At the beginning this singularity expanded rapidly (termed as the “Big Bang”), became less dense and cooled. From the infinitesimal size and extreme hot state, the universe expanded and cooled for 13.7 billion years and became what it is today.

The Big-Bang Theory - Misconceptions

One misconception about the Big-Bang is that it was a giant explosion; but, experts say that it was not an explosion, but an expansion of the universe, that still continues. It explains us about the development of the universe from a state of infinitesimal size, infinite density, and extreme temperature and into what it is today.

Another misconception is that the “singularity” appeared somewhere in space. But according to experts, there was no space prior to Big Bang. Space, time, energy and matter; everything began inside the “singularity”. If there was no space, where did the singularity appear and why it was there? (where?)!!

The Story Began in the First Second

• Due to limitations, science could not look into the instant universe came into existence. The earliest moment scientists could describe occurred at 1x10^-43 seconds after the universe came into being, after the Big Bang. This period is known as Plank Era. Only quantum physics will be able to explain these earliest moments of Big Bang. In this period, the universe was of incredibly small, extremely dense and hot, with temperature assumed to be around 10³² degrees Kelvin. The four primary forces, namely, electromagnetism, gravitational force, weak nuclear force and strong nuclear force were united into a single force.
• Between 1x10^-43 seconds and 1x10^-36 seconds, known as Grand Unification era, the gravitational forces were separated from other forces.
• At 1x10^-36 seconds the universe expanded rapidly, and this expansion is referred as inflation. In the inflationary era from 1x10^-36 seconds to 1x10^-32 seconds the universe expanded with an exponential growth and the volume increased to 1078 times the present size in as low as a hundredth fraction of a second. The temperature dropped below 1028 degrees Kelvin, and the strong force and the weak forces were separated.
• After the inflationary era, at 1x10^-32 seconds matter and energy were separated. Equal amount of matter and antimatter were formed, which destroyed each other; but some matter survived to form all the future matter in the universe.
• At 1x10^-11 seconds started the period of particle cosmology, the phase which the scientists would be able to create in laboratories with particle accelerators. The four basic forces separated out from the unified force. Photon particles were more than matter particles, but it was too dense for light to transmit.
• The phase of standard cosmology started at 0.01 seconds after the beginning of Big-Bang. Expansion and cooling of the universe continued, and neutrons and protons were formed. By the completion of one full second, the nuclei of light elements hydrogen, helium and lithium were formed, by the process known as nucleosynthesis.  

Major phases in the next 13.7 Billion Years

• After 100 seconds, temperature came down to 1 billion degrees Kelvin. Nuclei of hydrogen, helium and lithium continued to form. More photons were created but the universe was too dense for light to pass.
• After 324,000 years, temperature cooled down to 3000 degrees Kelvin, and the protons and neutrons combined to form neutral hydrogen atoms.
• After 380,000 years the universe became transparent enough for light to transmit throughout the universe.
• Universe continued to expand and cool for the next 100 million years. Due to gravity, particles of matter gathered together and gases fell into tight pockets and became dense and hot. Stars formed from these gas pockets. First stars were formed around 400 million years after the first event.
• Stars grouped together to form galaxies and the galaxies formed their own clusters. The first galaxies were formed 500 million years after the Big Bang. Stars exploded and emitted matter of all kind in the universe. From the remnants of the older stars, newer stars were formed.
• Our Solar System was formed about 4.6 billion years ago, that was about 9 billion years after the Big Bang.
• Today the temperature of the universe is 2.725 degrees Kelvin (-270 degrees Celsius), very close to Absolute Zero, the lower limit of thermodynamics temperature scale.

The Big Bang Theory – Supporting Factors

There are some major factors that support the Big Bang theory.

• Famous scientist Edwin Hubble discovered a phenomenon in 1929, known as “Hubble’s Law”. He observed that galaxies appeared to be moving away from us at the speeds proportional to their distance. It is an evidence for the expansion of the universe.
• In 1965, scientists Arno Penzias and Bob Wilson discovered a 2.725 degrees Kelvin Cosmic Microwave Background (CMB) radiation, when they registered a signal in their radio telescope. This radiation that was released soon after the Big Bang, considered as an echo of the Big Bang, has been travelling eternally through the universe. In 1978, Arno Penzias and Bob Wilson shared the Nobel Prize for Physics for their discovery.
• The light elements hydrogen and helium were found in the universe in large quantity that supports the Big bang theory.

Some Problems and Concerns

In spite of the wide popularity of the Big Bang theory, compared to the other different models, it needs to address several issues and questions of the scientific community. Some of the issues are highlighted below.

• What was there and what happened before Big Bang? This question cannot be answered based on science. All scientific laws break down, when there was no time and no space. The answer lies beyond time and space.
• The universe is expanding for last 13.7 billion years. Will the expansion continue forever? Will it stop after a definite time? Will it reverse the process? As per the general theory of relativity, the gravitational force between two objects depends upon their size and the distance between them. If there is not enough matter, the universe will expand forever. If there is enough matter, the expansion may slow down and may eventually reverse the process.
• What is the shape of the universe?  Shape of the universe continues to be a matter of debate. Some believe that the universe has no boundary and is flat. Scientists have been working on this to construct a mathematical model that portraits the shape of the universe. Big Bang theory does not give any specific answer to this issue.
• It is criticized that the Big Bang theory violates the first law of thermodynamics. As per the law, energy cannot be created or destroyed. The critics were replied that the Big Bang was all about the evolution of the universe, but not its creation. Also, the laws of science are not applicable here.
• The period of inflation of the Big Bang seems to have violated the theory that nothing can travel faster than the speed of light. One answer to this issue is that the theory of relativity is not applicable here. Another response to this issue is that space can expand faster than light because space is beyond the theory of gravitation.

Conclusion

In this crucial juncture of cosmogony, where science and philosophy meet with similar ideologies, we should be aware about our fabulous existence. We are living on a beautiful planet, which is rotating itself and encircling a great star gathered together with billions of stars in an amazing galaxy, moving through the space, inside a rapidly expanding universe that began its pace billions of years ago, originated from a miniscule “Singularity” that appeared from naught for unknown reasons.

Science confirms us that our universe has a beginning and everything in it is the manifestation of a Singularity that was beyond the conceptions of time, space and causation. It was a point of infinitesimal size and infinite density, where all laws of science would have broken down. To be honest, we do not know what exactly this singularity was, where it came from and why it appeared; except some mind blogging assumptions that defy our knowledge of physics. Intelligence is the nature of the universe and the nature of all manifestations in the universe. In the beginning there should be the cosmic intelligence that got involved and subsequently evolved itself to become microcosm and macrocosm. If so,….. was Intelligence the First Cause?! 

Image Source: http://en.wikipedia.org/wiki/Universe