Big Bang Theory

 The Big Bang Theory

How was the universe created? How did it come to be the seemingly infinite place we know of today? And what will it be, ages from now? These are few of the questions that have been puzzling philosophers and scholars since the beginning of time; these questions also led to some wild and interesting theories. Among them, Big Bang Theory is considered the best guess.

Big Bang Theory is a leading explanation of how the universe began. Other theories include 'Steady State Theory' and 'Oscillating Universe Theory'. This theory was proposed by Georges Lemaitre in 1927. The Big Bang Theory states that Universe started with an infinitely hot, infinitely dense singularity and then exploded, first at unimaginable speed, then at a  more measurable rate. Around 13.8 billion years ago, everything we know of was an infinitesimally small singularity, being very dense and hot. Then, explosive expansion began, ballooning our universe outwards faster than the speed of light. This was a period of 'cosmic inflation' that lasted mere fractions of a second (about 10^-32 of a second). The Big Bang not only created the majority of the matter but also the physical laws that govern our ever-expanding cosmos. This theory explains many things like the laws of physics, all of the known matter, large-scale structure of the universe, and it also accounts for the expansion of the universe along with a broad range of other phenomena.

According to this theory, if we look at the universe one second after the big bang, we could see a 10-billion-degree sea of neutrons, protons, electrons, anti-electrons (positrons), photons, and neutrions. As time went on, we would see the universe cool down; either neutrons decaying into protons and electrons or neutrons combining with protons to make deuterium (an isotope of hydrogen). This early soup would have been impossible to look at because light could not carry inside of it. The free electrons would have caused light (photons) to scatter the way light scatters from the water droplets in clouds. Over time, however, the free electrons met up with nuclei and created neutral atoms. This allowed light to shine through about 3,80,000  years after the Big Bang. Sometimes called the 'afterglow' of the Big Bang, this light is more properly known as the Cosmic Microwave Background (CMB).

As we've talked about 'cosmic inflation' in the second paragraph, let's learn more about it. When cosmic inflation came to a sudden and mysterious end, the more classic descriptions of the Big Bang took hold. A flood of matter and radiation, known as 'reheating', began the process of populating the universe with the stuff we know today: particles, atoms, stars, galaxies, etc.

During the years following Hubble and COBE, the picture of the Bog Bang gradually became clearer. But in 1996, observations of very distant supernovae required a dramatic change in the picture. It had always been assumed that matter in the universe would slow its rate of expansion. Mass creates gravity, gravity creates pull, the pulling must slow the expansion. But supernovae observations showed that the expansion of the universe is accelerating. Something, not like matter and not like ordinary energy, is pushing the galaxies apart. This stuff is named dark energy.