Class 10 Science SEE Guide | Unit - 12 Universe Guide 2080

Class 10 Science SEE Guide

Unit - 12 Universe Guide

2. Differentiate between:

(a) Closed Universe and Open Universe

Answer 👉 Closed Universe:

A closed universe refers to a cosmological model where the spatial geometry of the universe is positively curved, like the surface of a sphere.
In a closed universe, if you were to travel in a straight line, you would eventually return to your starting point.
It suggests that the universe is finite and has a bounded size.

Open Universe:

An open universe refers to a cosmological model where the spatial geometry of the universe is negatively curved, like a saddle.
In an open universe, if you were to travel in a straight line, you would continue to move apart from your starting point indefinitely.
It suggests that the universe is infinite and has an unbounded size.

The key difference between a closed universe and an open universe lies in the curvature of space and the ultimate fate of the universe. A closed universe curves back on itself, while an open universe extends infinitely.

(b) Flat Universe and Closed Universe

Answer 👉 Flat Universe:

A flat universe refers to a cosmological model where the spatial geometry of the universe is flat, like a Euclidean plane.
In a flat universe, the geometry follows the rules of Euclidean geometry, where parallel lines never meet and the angles of a triangle add up to 180 degrees.
It suggests that the universe has a critical density where the expansion rate is just sufficient to balance the gravitational pull.

Closed Universe:

As mentioned earlier, a closed universe has a positively curved spatial geometry, like the surface of a sphere.
In a closed universe, space is curved in such a way that if you travel in a straight line, you eventually return to your starting point.
It suggests that the universe has a higher density than the critical density, causing gravitational forces to eventually halt the expansion and lead to a contraction.
The main difference between a flat universe and a closed universe lies in the curvature of space. In a flat universe, space is flat like a plane, while in a closed universe, space is curved like the surface of a sphere.

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3. Give reason:

(a) As the distance between celestial bodies increases their separating speed increases.

Answer 👉 As the distance between celestial bodies increases, their separating speed increases due to the expansion of the universe. This phenomenon is known as the Hubble's law. According to Hubble's law, galaxies and other celestial objects in the universe are receding from each other, and the recessional velocity is directly proportional to their distance. This means that the farther away a celestial body is, the faster it appears to be moving away from us. This observation led to the understanding that the universe is undergoing an expansion, and the rate of expansion is accelerating. Therefore, as the distance between celestial bodies increases, their separating speed increases.

(b) Celestial bodies continue to remain in their own place.

Answer 👉 Celestial bodies continue to remain in their own place due to the balance between gravitational forces and their own inertia. Gravitational forces between celestial bodies act as an attractive force, pulling them towards each other. However, the inertia of celestial bodies resists this gravitational pull. Inertia is the property of matter that makes objects tend to stay at rest or in uniform motion in a straight line. As a result, celestial bodies continue to move in their own orbits or follow their own trajectories unless acted upon by external forces. This balance between gravitational forces and inertia allows celestial bodies to maintain their position in space and continue their motion without being pulled or pushed away from their orbits or paths.

4. Answer the following questions:

(a) What is the universe?

Answer 👉 The universe refers to all matter, energy, space, and time as a whole. It encompasses everything that exists, including galaxies, stars, planets, and all other celestial objects.

(b) State the Big Bang theory.

Answer 👉 The Big Bang theory states that the universe originated from a singularity, an extremely hot and dense state, approximately 13.8 billion years ago. It suggests that the universe began expanding rapidly from this initial point and has been expanding ever since. The theory is supported by various lines of evidence, such as the observed cosmic microwave background radiation and the redshift of distant galaxies.

(c) Write the conclusion of Hubble's study.

Answer 👉 Hubble's study concluded that the recessional velocity of galaxies is directly proportional to their distance from us. This observation provided evidence for the expansion of the universe and led to the formulation of Hubble's law, which states that the velocity at which a galaxy or celestial object is moving away from us is proportional to its distance.

( d) According to the Big Bang theory, the universe is continuously expanding. Is there no limitation to the expansion of the universe? Explain your arguments.

Answer 👉 According to the Big Bang theory, the universe is continuously expanding. However, it is important to note that the concept of the expansion of the universe does not imply an unlimited or infinite expansion in all aspects. The expansion refers to the increasing distance between galaxies and celestial objects over time. The expansion is driven by the distribution of matter and energy in the universe and influenced by factors such as dark matter and dark energy. The expansion rate of the universe can change over time, and there are theoretical possibilities such as the "Big Freeze" or "Big Rip" scenarios, which describe potential future outcomes for the expansion of the universe.

( e) Write the importance of gravitational force in the position of celestial bodies in the universe.

Answer 👉 The gravitational force plays a crucial role in determining the positions of celestial bodies in the universe. Gravity is a fundamental force that attracts objects with mass towards each other. It acts as a binding force between celestial bodies, such as stars, planets, and galaxies. The gravitational force governs the motion and orbits of these celestial bodies. It keeps planets in orbit around stars, moons in orbit around planets, and holds galaxies together in clusters. Without the gravitational force, celestial bodies would not be able to maintain their positions and the structures we observe in the universe would not exist.

(f) Earth revolves around the Sun; Moon revolves around the Earth. They have their force of gravity as well as the gravitational force between them, but they never collide with each other. Clarify this with reasons.

Answer 👉 The reason Earth revolves around the Sun and the Moon revolves around the Earth without colliding is due to a combination of their respective orbits and the gravitational force. Both Earth and the Moon follow elliptical orbits around their common center of mass. The gravitational force between them acts as a centripetal force, continuously pulling them towards each other. However, the motion of both Earth and the Moon provides the necessary inertia to balance the gravitational force, allowing them to maintain their orbits without colliding. The combination of their orbital paths and the gravitational force results in a stable and consistent motion of celestial bodies in their respective systems.

Class 10 Science SEE Guide Unit - 12 Universe Guide

(g) Explain the concept of a flat universe.

Answer 👉 In the concept of a flat universe, the spatial geometry of the universe is considered to be flat, like a Euclidean plane. This means that the geometry of space obeys the rules of Euclidean geometry, where parallel lines never meet and the angles of a triangle add up to 180 degrees. In a flat universe, the expansion of space occurs uniformly in all directions. The curvature of space in a flat universe is zero, and the overall geometry is consistent with a flat surface. This concept is an important component of various cosmological models and is supported by observational data, including measurements of the cosmic microwave background radiation.

(h) In your opinion, what might be the future of the universe: open, flat or closed? Explain your answer with suitable arguments.

Answer 👉 The future of the universe is a topic of ongoing scientific research and theoretical speculation. There are several possible scenarios for the future based on current understanding and theories:

The "Big Freeze" or "Heat Death": If the expansion of the universe continues and accelerates, galaxies will move farther apart, leading to a gradual cooling and decrease in energy. Eventually, stars will burn out, and the universe will enter a state of low energy and entropy, known as the heat death, where no usable energy is available.
The "Big Crunch": If the density of matter and energy in the universe is high enough, the gravitational attraction could overcome the expansion, leading to a reverse process where the universe contracts. This could result in a "Big Crunch," where the universe collapses in on itself.
The "Big Rip": If dark energy, which is responsible for the accelerating expansion of the universe, continues to increase in strength, it could eventually overpower the gravitational forces holding structures together. This could result in a "Big Rip," where the expansion becomes so rapid that it tears apart galaxies, stars, and eventually even atoms.

It is important to note that these scenarios are based on current theories and understanding, and our knowledge of the universe is continually evolving. The future of the universe remains a subject of active scientific investigation and debate.