Table of Contents
1. Astronomy
Astronomy is a natural science that studies celestial objects (stars, planets, comets, etc.) and the phenomena (such as the solar wind, gravitational waves, etc.) that occur in the cosmos.
2. Universe
The universe is everything that exists, has existed, and will exist, including all of space, time, energy, matter, and the physical laws that govern them. The universe also includes galaxies, stars, planets, moons, and the contents of intergalactic space.
The size of the whole Universe is not known and may be either finite or infinite.
The observable universe is about 28 billion parsecs (91 billion light-years) in diameter at the present time.
As for the age of the Universe, scientists agree that it is about 15 billion years old. (Big Bang)
The universe comprises a number of galaxies. Optical and radio telescope studies indicate the existence of between 100-200 billion galaxies in the visible universe. Each galaxy comprises an average of 100 billion stars.
The Big Bang Theory is most accepted for the origin of the Universe in comparison to the Steady State and the Pulsating Universe Theory.
The Universe consists of both physical (subatomic particles like electrons, protons to galactic superclusters) and non-physical (light, gravitation, space etc.) components.
The science dealing with the nature and origin of the Universe is known as Cosmology.
Cosmos: another word for the universe.
Cosmic: relating to the universe or cosmos.
Cosmic rays: highly energetic atomic nucleus or other particle travelling through space at speed approaching that of light. Direct exposure to cosmic rays can cause gene mutations resulting in cancer.
Cosmological: relating to the origin and development of the universe.
Celestial bodies – A celestial object is a natural physical entity that exists in the observable universe and is located outside of Earth’s atmosphere. The sun, the moon and all those objects shining in the night sky are called celestial bodies.
| Dark energy (10%) Dark energy is an unknown form of energy which is hypothesised to permeate (spread throughout) all of space, tending to accelerate the expansion of the universe. Dark matter (85%) Dark matter is a hypothetical form of matter that is thought to account for approximately 85% of the matter in the universe. Dark energy plus dark matter constitutes 95% of the total mass-energy content of the universe (the rest in the normal matter). In short, we are unsure about what’s there in 95% of the universe. The name dark matter refers to the fact that it does not appear to interact with observable electromagnetic radiation, such as light. It is thus invisible (or ‘dark’) to the entire electromagnetic spectrum, making it extremely difficult to detect. Dark matter interacts with the rest of the universe only through its gravity (that’s how we know it exists). Anti-Matter It is hypothesized that every elementary particle in the Universe has a partner particle, known as an ‘antiparticle’. The particle and its antiparticle share many similar characteristics, but many other properties are the exact opposite. The electron, for example, has as its antiparticle the antielectron. They both have the same masses, but they have exactly opposite electrical charges. When a matter particle meets its antimatter particle, they destroy each other completely (i.e. annihilation), releasing the energy equivalent of their masses (E = mc2). |
3. Formation and Evolution of the Universe
The three main theories put forward to explain the origin and evolution of the universe are:
- The Big Bang Theory
- The Steady State Theory
- The Pulsating Theory
3.1 The Big Bang Theory
The Big Bang theory is the prevailing cosmological model for the birth of the universe.
George Lemaitre and Gammow proposed this theory. The Big Bang Theory formed in 1972, according to this theory everything in the universe emerged from a point known as singularity, 15 billion years ago.
According to this theory, at the beginning of the universe, the whole matter of the universe was once concentrated in an extremely dense and hot (~10 32 degree Celsius) fireball. Then about 15 billion years ago a vast explosion (big bang) occurred. The matter was broken into pieces, which were thrown out with high speed in all directions forming stars and galaxies; which are still moving away from one another.
There was particularly rapid expansion within fractions of a second after the bang. Thereafter, the expansion has slowed down.
Within the first three minutes from the Big Bang event, the first atom began to form.
After the initial expansion (inflation), the universe cooled sufficiently to allow the formation of subatomic particles and later simple atoms. The majority of atoms produced by the Big Bang were hydrogen and helium along with trace amounts of lithium and beryllium.
At 380,000 years after the Big Bang, the universe was filled with a hot plasma of particles that scattered light everywhere, making it impossible for light to travel far without being absorbed.
As the universe cooled down, the plasma recombined into neutral atoms, allowing the light to travel freely through space.
Giant clouds of these primordial elements (hydrogen and helium) later coalesced through gravity to form stars and galaxies.
According to this theory, the universe, ever since its birth, is expanding in all directions. The galaxies moved apart from one another as the empty space between them expanded.
This theory by George Lemaitre was based on Albert Einstein’s famous theory of relativism.
3.2.1 Evidence of Big bang
In 1964, the cosmic microwave background radiation was discovered, which was crucial evidence in favour of the Big Bang model.
Other evidence such as cosmological redshift, gravitational waves, etc. have added weight to the big bang theory.
3.2.1.1 Cosmic microwave background (CMB):
The cosmic microwave background (CMB) is a type of light that fills the entire universe. It was first discovered in 1964 and is believed to be the afterglow of the Big Bang, which is the event that created the universe.
With a traditional optical telescope, the space between stars and galaxies is completely dark.
However, a sensitive radio telescope shows a faint background glow. This glow is strongest in the microwave region of the radio spectrum, and hence it is called a cosmic microwave background.
CMB, also known as relic radiation, is almost the same in all directions and it is not associated with any star, galaxy, or other objects. It is the thermal radiation left over from the “Big Bang”.
CMB has gone from high energy photons (gamma photons or X-ray photons) to low microwave photons today due to the redshift from the expanding Universe.
The CMB is fundamental to observational cosmology because it is the oldest light in the Universe and can be found in all directions.
As CMB is the radiation left over from an early stage in the development of the Universe, its discovery is considered a landmark test for the Big Bang model of the Universe.
By studying the CMB, scientists can learn about the conditions of the early universe and confirm that the Big Bang theory is correct. The CMB also provides evidence for the existence of dark matter and dark energy, which are still mysteries in modern physics.
3.2.1.2 Doppler-shift or Redshift and Blueshift:
American astronomer Edwin Hubble was the first to describe the redshift phenomenon (galactic redshift) and tie it to an expanding universe (galaxies are drifting apart).
Redshift and Blueshift describe how light changes as objects in space (such as stars or galaxies) move closer or farther away from us.
Imagine you are on a train platform, and a train passes by. As the train gets closer, the sound it makes gets louder, and as it moves away, the sound gets quieter. This is because the sound waves are compressed as the train moves towards you, and stretched out as it moves away.
The same thing happens with light from distant galaxies. The light waves get compressed or stretched out as the galaxy moves towards or away from us, and this affects the colour of the light we see. This effect is called redshift, and it is what Hubble used to discover that galaxies are moving away from us.
When an object moves away from us (Doppler-shifted to lower frequencies), the light is shifted to the red end of the spectrum, as its wavelengths get longer.
If an object moves closer (Doppler-shifted to higher frequencies), the light moves to the blue end of the spectrum, as its wavelength gets shorter.
Electromagnetic spectrum:
Electromagnetic radiation is a form of energy that is produced by oscillating electric and magnetic disturbance, or by the movement of electrically charged particles traveling through a vacuum or matter. The electromagnetic (EM) spectrum is the range of all types of EM radiation.
Hubble’s Law:
Hubble’s law tells us that the speed at which a galaxy is moving away from us is proportional to its distance from us. This means that the farther a galaxy is, the faster it is moving away from us. Also known as accelerating the expansion of the universe. This law was discovered by astronomer Edwin Hubble in the 1920s, and it is one of the most important discoveries in modern astronomy.
This discovery led to the idea of an expanding universe, which is now widely accepted in modern cosmology.
It is the observation that the expansion of the universe is such that the velocity at which a galaxy is moving away from the observer is continuously increasing with time. It implies that the universe will get increasingly colder as matter spreads across in space.
Observable Universe:
According to Hubble’s law, the velocity of recession of a galaxy becomes equal to the velocity of light at a distance equal to 20 billion light years. It means, the light rays from stars and galaxies, which are situated at a distance of 20 billion light years or more, can never reach us. Thus, this distance becomes the boundary of the observable universe.
On account of continuous recession, more and more galaxies will go beyond this boundary and they will be lost. As a result of this, the number of galaxies per unit volume will go on decreasing and ultimately a time may come when we may have an empty observable universe.
Hubble constant:
A unit of measurement that describes the rate at which the universe is expanding.
Two parameters that are essential to estimating the Hubble constant are the distance of the stars from Earth and how fast they are moving away from us (their velocity).
But to date, the most precise efforts have landed on very different values of the Hubble constant. Scientists have proposed a more accurate and independent way to measure the Hubble constant, using gravitational waves.
A flash of light would give an estimate of the system’s velocity (system: neutron stars or black holes orbiting each other), or how fast it is moving away from the Earth.
The emitted gravitational waves, if detected on Earth, should provide a precise measurement of the system’s distance. By knowing the system’s velocity and distance, a precise calculation of Hubble constant is possible.
3.2.1.3 Gravitational waves:
Gravitational waves are ‘ripples’ in the fabric of space-time caused by some of the most violent and energetic processes in the Universe. These ripples travel at the speed of light through the Universe, carrying with them information about their origins.
Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity.
He observed that massive accelerating objects (such as neutron stars or black holes orbiting each other) would disrupt space-time in such a way that ‘waves’ of distorted space would radiate from the source (like the movement of waves away from a stone thrown into a pond).
In 2015, First time, the LIGO (The Laser Interferometer Gravitational-Wave Observatory, USA) physically sensed the distortions in spacetime caused by passing gravitational waves generated by two colliding black holes nearly 1.3 billion light-years away.
While the processes that generate gravitational waves can be extremely violent and destructive, by the time the waves reach Earth, they are billions of times smaller.
3.2 Steady State Theory
Bondi, Gold and Fred Hoyle developed this theory.
According to this theory, the number of galaxies in the observable universe is constant and new galaxies are continuously being created out of empty space, which fill up the gaps caused by those galaxies, which have crossed the boundary of the observable universe.
As a result of it, the overall size of mass of the observable universe remains constant. Thus, a steady state of the universe is not disturbed at all.
3.3 The Pulsating Theory
According to this theory, the universe is supposed to be expanding and contracting alternately i.e., pulsating.
At present, the universe is expanding.
According to pulsating theory, it is possible that at a certain time, the expansion of the universe may be stopped by the gravitational pull and they may contract again. After it has been contracted to a certain size, an explosion again occurs and the universe will start expanding.
The alternate expansion and contraction of the universe give rise to a pulsating universe.
3.4 Big Crunch
Some Geographers assume that at some point of time, the universe would reach a maximum size and then begin to collapse. It would become denser and hotter again, ending with a state similar to that in which it started — a Big Crunch, the death of the universe.
4. Prelims PYQs on Formation and Evolution of the Universe – UPSC & Other Exams
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5. Mains PYQs on Formation and Evolution of the Universe – UPSC & Other Exams
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6. FAQs on Formation and Evolution of the Universe – UPSC & Other Exams
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