Origin of the Universe – Big Bang Unveiled – Geography Notes

The Big Bang Theory

• The Big Bang Theory, also known as the expanding universe hypothesis, is the prevailing explanation for the origin of the universe. In 1920, Edwin Hubble presented evidence that the universe is expanding, which means that galaxies are moving away from each other as time passes. This expansion is indicated by the increasing distance between galaxies. However, while the space between galaxies is expanding, scientists have not observed any expansion of individual galaxies.
• According to the Big Bang Theory, the development of the universe can be described in several stages. Initially, all the matter that now exists in the universe was concentrated in a single point, which scientists refer to as a “tiny ball.” This ball was incredibly small, with infinite temperature and density. Then, about 13.7 billion years ago, the “tiny ball” suddenly exploded, leading to a massive expansion. 
• This expansion has continued to this day. During the initial expansion, some of the energy was converted into matter, and there was a period of very rapid expansion. Over time, the rate of expansion has slowed down. Within the first few minutes after the Big Bang, the first atoms begin to form. Approximately 300,000 years after the Big Bang, the temperature of the universe had dropped to around 4,500 Kelvin, which allowed for the formation of atomic matter. As a result, the universe became transparent.

• The expansion of the universe refers to the increase in the space between galaxies.
• This concept is in contrast to Hoyle’s steady-state theory, which posits that the universe has remained relatively unchanged throughout time.
• However, as more evidence has become available, the scientific community now largely favors the idea of an expanding universe.

• According to this theory, the universe, ever since its birth, is expanding in all directions.

• The year 1964 marked a significant milestone in the development of the Big Bang theory when cosmic microwave background radiation was discovered, providing compelling evidence in support of the theory.
• Since then, other pieces of evidence have further strengthened the case for the Big Bang, including observations of cosmological redshift and the detection of gravitational waves. All of these lines of evidence support the idea that the universe began as a hot, dense state and has been expanding and cooling ever since.

Cosmic microwave background (CMD)

• When observed with a traditional optical telescope, the vast expanse of space between stars and galaxies appears pitch-black and empty. However, with the use of a highly sensitive radio telescope, a faint background glow can be detected. 
• This glow is most prominent in the microwave region of the radio spectrum, and it is known as the cosmic microwave background (CMB).
• The cosmic microwave background (CMB) radiation has evolved over time, shifting from high-energy gamma or X-ray photons to low-energy microwave photons as a result of the universe’s expansion and the associated redshift.
• The CMB, also known as relic radiation, appears nearly uniform in all directions and is not associated with any particular star, galaxy, or other object. 
• It is instead a type of thermal radiation that was left over from the “Big Bang” era of the universe’s development.
• Because the CMB represents the oldest light in the universe and can be observed in all directions, it is a crucial tool for observational cosmology.
• The discovery of the CMB was a landmark event in the history of cosmology because it provided strong support for the Big Bang model of the universe, which predicts the existence of this type of relic radiation.

Accelerating expansion of the universe

• Hubble’s law is the observation that the velocity at which galaxies are moving away from us is continuously increasing with time, indicating the ongoing expansion of the universe. 
• This expansion implies that matter in the universe is spreading out and becoming increasingly colder over time.
• It is believed that the accelerated expansion of the universe began approximately 5 billion years ago, during the dark-energy-dominated era. 
• This acceleration was first discovered in 1998 through the use of distant Type Ia supernovae, which were used to measure the acceleration of the universe.
• Type Ia supernovae are a specific type of supernova that occur in binary star systems, where one star is a white dwarf and the other star can be anything from a giant star to a smaller white dwarf. 
• All Type Ia supernovae are thought to have nearly the same maximum brightness when they explode, making them useful as standard candles to measure the rate of expansion of the universe. By observing the cosmological redshift of these supernovae, astronomers can determine their distance from Earth, with weaker light indicating greater distance.

Dark energy

• Dark energy is a hypothetical form of energy that is believed to exist throughout all of space, with the potential to accelerate the expansion of the universe.
• It is called “dark” because it is thought to be invisible and non-interacting with other forms of matter and radiation, making it extremely difficult to detect or observe directly.

The Units of Measuring Distances in the Universe

• The vast distances between celestial objects in the universe can be described using different units of measurement. Some commonly used units include:
• Astronomical Unit (AU): This is the average distance between the Earth and the Sun, and is equal to approximately 149.6 million kilometers or 1.5 x 10^8 kilometers.
• Light-year (ly): This is the distance that light travels in one year, and is equal to approximately 9.46 x 10^12 kilometers.
• Parsec (pc): This is a unit of distance used in astronomy, defined as the distance at which one astronomical unit subtends an angle of one arcsecond. One parsec is approximately equal to 3.26 light-years or 30.9 trillion kilometers.

Evidence in Support of the Big Bang Theory

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