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1. According to the Big Bang theory of the origin of the Universe, the ag

According to the Big Bang theory of the origin of the Universe, the age of the Universe is estimated at about :

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0-3 million years
4 - 6 billion years
7 - 10 billion years
13 - 18 billion years
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UPSC CISF-AC-EXE – 2023
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According to the Big Bang theory, the age of the Universe is estimated at about 13 – 18 billion years, which corresponds to option D.
The standard cosmological model, which is based on the Big Bang theory, estimates the age of the Universe by observing the expansion rate (using the Hubble constant) and the composition of the Universe (from Cosmic Microwave Background data, e.g., from Planck or WMAP satellites). Current estimates based on these observations place the age of the Universe at approximately 13.8 billion years.
Early estimates varied, but increasingly precise measurements over the past couple of decades have converged on a value close to 13.8 billion years. Options A, B, and C represent ages that are significantly younger than the currently accepted scientific estimate for the age of the Universe.

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2. Consider the following statements : Statement-I : Giant stars live muc

Consider the following statements :
Statement-I :
Giant stars live much longer than dwarf stars.
Statement-II :
Compared to dwarf stars, giant stars have a greater rate of nuclear reactions.
Which one of the following is correct in respect of the above statements ?

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Both Statement-I and Statement-II are correct and Statement-II explains Statement-I .
Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I
Statement-I is correct, but Statement-II is incorrect
Statement-I is incorrect, but Statement-II is correct
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UPSC IAS – 2024
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The question asks about the lifespan and nuclear reactions in giant stars compared to dwarf stars.
Statement-I: “Giant stars live much longer than dwarf stars.” This statement is incorrect. Giant stars, being more massive than dwarf stars (like our Sun, a G-type dwarf), have much stronger gravitational forces. This results in higher temperatures and pressures in their cores, which accelerates the rate of nuclear fusion. Although they have more fuel, they burn it at a vastly higher rate, leading to significantly shorter lifespans compared to dwarf stars. Dwarf stars, with their slower rate of fusion, can live for billions or even trillions of years.
Statement-II: “Compared to dwarf stars, giant stars have a greater rate of nuclear reactions.” This statement is correct. As explained above, the higher core temperatures and pressures in giant stars lead to a much higher rate of nuclear fusion reactions (converting hydrogen to helium) compared to dwarf stars. This high reaction rate is responsible for their high luminosity.
Statement I is incorrect, and Statement II is correct. Statement II actually explains *why* Statement I is incorrect (higher reaction rate leads to shorter lifespan). Therefore, Option D is the correct choice.
A star’s lifespan is primarily determined by its mass and luminosity (rate of energy output, which is proportional to the rate of nuclear reactions). More massive stars have more fuel but burn it much faster due to higher core temperatures and pressures, resulting in shorter lives. Less massive stars burn their fuel slowly and live much longer. Giant stars are typically more massive and much more luminous than dwarf stars.
Stars evolve through different stages, including dwarf phases, giant phases (like red giants or supergiants), and eventually remnant stages (like white dwarfs, neutron stars, or black holes), depending on their initial mass. The term “dwarf star” usually refers to main-sequence stars (like the Sun), while “giant star” refers to later evolutionary stages after the star has exhausted the hydrogen in its core and expanded significantly.

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3. Recently, scientists observed the merger of giant ‘blackholes’ billion

Recently, scientists observed the merger of giant ‘blackholes’ billions of lightyears away from the Earth. What is the significance of this observation?

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Higgs boson particles' were detected.
'Gravitational waves' were detected.
Possibility of inter-galactic space travel through 'wormhole' was confirmed.
It enabled the scientists to understand 'singularity'.
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UPSC IAS – 2019
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The correct option is B. The observation of the merger of giant black holes billions of lightyears away from Earth led to the first direct detection of gravitational waves.
Gravitational waves are ripples in the fabric of spacetime caused by accelerating massive objects. Highly energetic events like the merger of black holes or neutron stars are strong sources of gravitational waves.
The LIGO and Virgo collaborations detected the first direct evidence of gravitational waves in 2015 (event GW150914), which originated from the merger of two black holes. This observation was a landmark discovery, confirming a major prediction of Einstein’s general theory of relativity and opening a new window for observing the universe through gravitational wave astronomy.
A) Higgs boson particles were detected at the Large Hadron Collider (LHC) at CERN, which is unrelated to black hole mergers.
C) While black holes and general relativity are related to the concept of wormholes, the detection of gravitational waves from a merger does not confirm the possibility of inter-galactic space travel through wormholes.
D) Observing black hole mergers and the resulting gravitational waves provides insights into the nature of gravity in extreme conditions, but it does not directly enable scientists to understand the singularity at the heart of a black hole, which remains a theoretical concept under current physics.

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4. Consider the following phenomena : 1. Light is affected by gravity.

Consider the following phenomena :

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  • 1. Light is affected by gravity.
  • 2. The Universe is constantly expanding.
  • 3. Matter warps its surrounding space-time.

Which of the above is/are the prediction/predictions of Albert Einstein’s General Theory of Relativity, often discussed in media ?

1 and 2 only
3 only
1 and 3 only
1, 2 and 3
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UPSC IAS – 2018
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Albert Einstein’s General Theory of Relativity describes gravity not as a force, but as a consequence of the curvature of spacetime caused by mass and energy. The theory makes several key predictions about the universe and gravity.
Statement 1 is correct. A prediction of General Relativity is that light is affected by gravity. Massive objects curve spacetime, and light follows this curvature. This phenomenon, known as gravitational lensing or the bending of light by gravity, was famously confirmed during a solar eclipse in 1919.
Statement 2 is correct. While Einstein initially favored a static universe, his field equations in General Relativity allow for dynamic solutions, including an expanding or contracting universe. The observation of the redshift of distant galaxies by Edwin Hubble in the 1920s provided strong evidence for an expanding universe, a phenomenon that is well-described by cosmological models based on General Relativity (like the Friedmann equations). Thus, the theory predicted the possibility of a non-static universe, which aligns with the observed expansion.
Statement 3 is correct. This is the fundamental principle of General Relativity: mass and energy warp the fabric of spacetime around them, and this warping is what we perceive as gravity.
All three statements describe predictions or fundamental aspects of Albert Einstein’s General Theory of Relativity that are often discussed in media and scientific discourse. Other predictions include gravitational time dilation, gravitational redshift, the precession of planetary orbits (like Mercury’s perihelion), and gravitational waves.

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5. The terms ‘Event Horizon’, ‘Singularity’, ‘String Theory’ and ‘Standar

The terms ‘Event Horizon’, ‘Singularity’, ‘String Theory’ and ‘Standard Model’ are sometimes seen in the news in the context of

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Observation and understanding of the Universe
Study of the solar and the lunar eclipses
Placing satellites in the orbit of the Earth
Origin and evolution of living organisms on the Earth
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UPSC IAS – 2017
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The correct answer is A) Observation and understanding of the Universe.
‘Event Horizon’ and ‘Singularity’ are terms associated with black holes, phenomena extensively studied in astrophysics and cosmology, related to the structure and evolution of the Universe. ‘String Theory’ is a theoretical framework in physics attempting to describe the fundamental constituents of the universe as tiny vibrating strings, aiming for a unified theory of everything. The ‘Standard Model’ is a theory describing the fundamental particles and forces (excluding gravity) that make up the Universe and how they interact. All these terms belong to the fields of cosmology, astrophysics, and theoretical particle physics, which are dedicated to observing and understanding the fundamental nature and workings of the Universe.
While related to astronomy, eclipses (B) are specific celestial events and do not directly involve these fundamental concepts. Satellite placement (C) is related to orbital mechanics and space technology, not these theoretical physics terms. Origin and evolution of living organisms (D) is the domain of biology, genetics, and evolutionary science, which are unrelated to these concepts from physics/cosmology.

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6. In the context of modern scientific research, consider the following s

In the context of modern scientific research, consider the following statements about ‘IceCube’, a particle detector located at South Pole, which was recently in the news :

  • It is the world’s largest neutrino detector, encompassing a cubic kilometre of ice.
  • It is a powerful telescope to search for dark matter.
  • It is buried deep in the ice.

Which of the statements given above is/are correct?

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1 only
2 and 3 only
1 and 3 only
1, 2 and 3
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UPSC IAS – 2015
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The correct option is C. Statements 1 and 3 about the IceCube particle detector are correct.
– Statement 1: IceCube is indeed the world’s largest neutrino detector. It consists of thousands of sensors embedded in a cubic kilometre of ice at the South Pole, designed to detect high-energy neutrinos.
– Statement 2: While neutrinos are fundamental particles relevant to various areas of physics, including cosmology and potential dark matter interactions, IceCube is primarily designed as a neutrino *telescope* to study astrophysical sources of high-energy neutrinos (like supernovae, gamma-ray bursts, active galactic nuclei). Searching for dark matter is not its primary or stated main purpose.
– Statement 3: The detector sensors (Digital Optical Modules or DOMs) are lowered into holes drilled deep into the Antarctic ice, at depths between 1450 and 2450 meters, making this statement correct.
By detecting the faint light (Cherenkov radiation) produced when neutrinos interact with the ice, IceCube scientists can infer the direction and energy of the neutrinos, opening a new window to observe the universe.

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7. Two planets orbit the Sun in circular orbits, with their radius of orb

Two planets orbit the Sun in circular orbits, with their radius of orbit as R₁ = R and R₂ = 4R. Ratio of their periods (T₁/T₂) around the Sun will be

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1/16
1/8
1/4
1/2
This question was previously asked in
UPSC NDA-2 – 2020
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This problem can be solved using Kepler’s Third Law of planetary motion, which states that the square of the orbital period (T) of a planet is directly proportional to the cube of the semi-major axis (R) of its orbit: T² ∝ R³. For circular orbits, the semi-major axis is simply the radius (R). Thus, (T₁/T₂)² = (R₁/R₂)³. Given R₁ = R and R₂ = 4R, we have (T₁/T₂)² = (R / 4R)³ = (1/4)³ = 1/64. Taking the square root of both sides, T₁/T₂ = √(1/64) = 1/8.
Kepler’s Third Law relates the orbital period and orbital radius of planets orbiting the same central body: T² ∝ R³.
Kepler’s Laws are empirical laws describing the motion of planets around the Sun. Newton’s Law of Universal Gravitation provides the theoretical basis for Kepler’s Laws. For circular orbits, the speed v is constant, and the period T = 2πR/v. The gravitational force provides the centripetal force: GMm/R² = mv²/R. Substituting v = 2πR/T gives GMm/R² = m(2πR/T)²/R, which simplifies to T² = (4π²/GM) R³, confirming T² ∝ R³.

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8. How long does light take to reach the Earth from the Sun ?

How long does light take to reach the Earth from the Sun ?

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About 4 minutes
About 8 minutes
About 24 minutes
About 24 hours
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UPSC NDA-2 – 2017
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The average distance from the Earth to the Sun is approximately 149.6 million kilometers, or about 1.5 x 10^11 meters. The speed of light in a vacuum is approximately 3 x 10^8 meters per second. The time taken for light to travel this distance can be calculated using the formula time = distance / speed.
Time ≈ (1.5 x 10^11 m) / (3 x 10^8 m/s) = 0.5 x 10^3 seconds = 500 seconds.
Converting seconds to minutes: 500 seconds / 60 seconds/minute ≈ 8.33 minutes.
Among the given options, “About 8 minutes” is the closest and most accurate approximation for the time light takes to travel from the Sun to the Earth.
– Distance from Sun to Earth is approximately 1.5 x 10^11 m.
– Speed of light is approximately 3 x 10^8 m/s.
– Time = Distance / Speed.
This travel time is often used to define the Astronomical Unit (AU), where 1 AU is the average distance between the Earth and the Sun. Observing distant celestial objects means looking back in time, as the light we see was emitted minutes, years, or even billions of years ago, depending on the distance.

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9. LIGO experiment confirmed one of the predictions of :

LIGO experiment confirmed one of the predictions of :

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String theory
Special theory of relativity
Quantum mechanics
General theory of relativity
This question was previously asked in
UPSC NDA-1 – 2024
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LIGO (Laser Interferometer Gravitational-Wave Observatory) is a large-scale physics experiment designed to detect cosmic gravitational waves. The existence of gravitational waves, which are ripples in spacetime caused by massive accelerating objects, was a major prediction of Albert Einstein’s General Theory of Relativity, published in 1915. LIGO made the first direct detection of gravitational waves in 2015, confirming this prediction.
– LIGO detects gravitational waves.
– Gravitational waves are a prediction of Einstein’s General Theory of Relativity.
– The first direct detection of gravitational waves by LIGO provided strong evidence for General Relativity.
String theory, Special Theory of Relativity, and Quantum Mechanics are other significant areas of modern physics, but the detection of gravitational waves is a direct verification of a specific prediction from General Relativity. General Relativity describes gravity as the curvature of spacetime caused by mass and energy.

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10. LIGO stands for

LIGO stands for

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Laser Interferometer Gravitational wave Observatory
Light Interferometer Gravitational wave Observatory
Light Induced Gravity Observer
Laser Induced Gascous Optics
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UPSC NDA-1 – 2019
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The correct option is A) Laser Interferometer Gravitational wave Observatory. LIGO is a major scientific collaboration dedicated to detecting gravitational waves.
– LIGO stands for Laser Interferometer Gravitational-Wave Observatory.
– It is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave science as an astronomical tool.
– LIGO consists of two large observatories in the United States (Livingston, Louisiana, and Hanford, Washington) that work in tandem.
LIGO achieved the first direct detection of gravitational waves on September 14, 2015, from the merger of two black holes. This detection, announced in February 2016, confirmed a major prediction of Einstein’s general theory of relativity and opened a new window on the universe, leading to the Nobel Prize in Physics in 2017.

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