Big Bang Theory, Definition, Evidences, Expansion, Missions

Big Bang Theory

The Big Bang is the most acceptable answer to how the universe began. According to this theory, the universe came into existence around 13.8 billion years ago. It started as a single point called “singularity.” Singularity is infinite mass with zero volume; therefore, it has infinite density. Thus, the universe began as an infinitely hot and dense single point. This single point appeared from nowhere for reasons unknown.

During the “Big Bang,” the single point inflated and exploded violently, resulting in a massive universe expansion. The universe’s expansion was rapid during the initial seconds after the bang. Post a considerable time; the expansion slowed down. It is believed that the first atom was formed within 3 minutes of the Big Bang event. In the next 300,000 years, the temperature dropped to 4,500K and gave rise to atomic matter, which eventually became stars, planets, etc. The universe also became transparent to light.

The universe has been expanding since 13.8 billion years ago to attain its present form. Scientists believe that an undiscovered phenomenon called ‘dark energy’ is causing the Universe to grow. However, there is no concrete scientific explanation for dark energy.

Before The Big Bang

Nobody knows what the universe was like back then. The “inflationary universe” model, which is the best current theory, assumes that all of space is filled with an extremely concentrated, unstable form of energy that will be transformed into particles of matter at the instant of the Big Bang. However, no one knows how space and time came to be in the first place.

First Few Minutes to Next Thousand Years

The universe cooled sufficiently after the initial expansion to allow the formation of subatomic particles such as photons, electrons, protons, and neutrons. Though simple atomic nuclei formed within three minutes of the Big Bang, it took thousands of years for the first electrically neutral atoms to form. The majority of atoms created by the Big Bang are hydrogen, with traces of helium and lithium.

Earlier vs Later Universe

Early Universe was Opaque and later Universe was Transparent. Because photons (light) are elementary particles, they would have formed shortly after the Big Bang. However, the early electrons would have scattered these photons. The Universe would have eventually reached the temperature where electrons combined with nuclei to form neutral atoms as it continued to cool (recombination).

The Universe would have been opaque before this “recombination” occurred because free electrons would have caused light (photons) to scatter in the same way that sunlight scatters from water droplets in clouds. However, when free electrons were absorbed to form neutral atoms, the Universe became suddenly transparent. Those same photons can be seen today as Cosmic Background Radiation, the afterglow of the Big Bang.

The Big Bang Theories and Evidence

Some evidence helps us ascertain that the universe did have a beginning, and the Big Bang happened.

1. Red Shift and Expanding of Galaxies

In 1929, Edwin Hubble discovered that galaxies outside our own Milky Way were all moving away from us at a rate proportional to their distance from us. He quickly realised what this meant: there had to have been a point in time (now estimated to be around 14 billion years ago) when the entire Universe was contained in a single point in space. The Universe must have been created in a single violent event known as the “Big Bang.”

The first piece of evidence is the phenomenon called Red Shift discovered by Edwin Hubble. The galaxies appeared to be moving away at speeds proportional to their distance. This is called Hubble’s law, named after Edwin Hubble.

White light is formed from seven colours: VIBGYOR (violet, indigo, blue, green, yellow, orange, and red); red has the longest wavelength and the shortest frequency within the visible spectrum of colours. When white light emitted from a galaxy is captured as the red light in another galaxy, it means that the distance between the galaxies has increased. This is because white light has travelled a larger distance from the time of its origin, which has caused its wavelength to change over time. As a result, the light from these galaxies gets shifted to a redder wavelength – i.e., they are ‘red-shifted.’

2. Heat Left by the Big Bang

The second important piece of evidence is the heat left by the Big Bang. If the universe was initially extremely hot, as the Big Bang suggests, we should be able to find some heat signature of this event. In 1960, scientists discovered the “Cosmic Microwave Background Radiation” coming from the farthest reaches of the Universe.

3. Cosmic Background Explorer (COBE) Missions

NASA has launched two missions to study cosmic background radiation, taking “baby pictures” of the Universe only 400,000 years after it was born. The Cosmic Background Explorer was the first of these (COBE).

The Big Bang Missions to Study

1. Wilkinson Microware Anisotropy Probe (WMAP)

The Wilkinson Microware Anisotropy Probe (WMAP) was the second mission to investigate cosmic background radiation (WMAP). WMAP surveyed the entire sky with much higher resolution than COBE, measuring temperature differences in microwave radiation that is nearly uniformly distributed across the Universe.

By combining this evidence with theoretical models of the Universe, scientists have concluded that the Universe is “flat,” which means that the geometry of space satisfies the rules of Euclidean geometry on cosmological scales (e.g., parallel lines never meet, the ratio of circle circumference to diameter is pi, etc).

2. Planck

In 2009, the European Space Agency launched Planck, a third mission with significant participation from NASA. Planck is creating the most precise maps of microwave background radiation to date. It measures the fluctuations of the temperature of the CMB with an accuracy set by fundamental astrophysical limits, using instruments sensitive to temperature variations of a few millionths of a degree and mapping the entire sky over 9 wavelength bands.

Big Bang Theory UPSC

Cosmic Microwave Radiation is a faint glow of light present in the Universe. It falls on Earth from every direction with uniform intensity. The light arises from the heat radiation. The heat is supposed to be left over from the Big Bang event. This light is invisible to the naked eye. It was discovered in 1965 by American radio astronomers Arno Penzias and Robert Wilson.

The Big Bang Theory is critical concept for the UPSC science and technology section. Both Indian and global scientists are conducting extensive research in this field to determine how the universe began billions of years ago. In this article, you will learn about the various views of the origin of the earth in a nutshell in preparation for the UPSC IAS exam.

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