THE UNIVERSE

UNIT 12: UNIVERSE

Multiple Choice Question [1 mark each]

1.      What puts the planet around the sun despite the universe is expanding?

a) magnetic forces                b) dark energies           c) gravitation               d) expanding forces

2.      What’s the conclusion of Hubble’s Observation?

a) galaxies far away are red             b) galaxies travel faster

c) universe is expanding                   d) there are many galaxies around us

3.      How will our world end if the gravity produced by galaxies will slow down the expanding forces

a) Every matter in the universe will concentrate at a single point.

b) Every matter in the universe will spread out until they are all alone.

c) the universe will be flat

d) The universe will be divergent

4.      How will an open universe die?

a) It will end with a big crunch                    b) It will end as a hot ball of matter

c) It will be cold and dark               d) It will die in a big chill

5.      Which universe has negative curvatures?

a) Close universe      b) Open universe         c) Spherical universe   d) Flat universe

6.      What is the condition of the matter of the universe for an open universe in the future?

a) equal density to critical density               b) more density than critical density

c) less density than critical density              d) less or more density than critical density

7.      What percent of the universe is visible to us?

a) 25                         b) 15                            c) 10                            d) 5

8.      Which of the following is one of the findings of Hubble’s study about the motion of the heavenly body?

a) Galaxies are moving towards each other.

b) Galaxies are moving away from each other.

c) Galaxies are constant.

d) Milky way is only the galaxy in the universe which is moving.

9.      Which condition leads the universe to the big chill?

a)  Geometry of space time is shaped like the surface of a saddle.

b) Geometry of space time is shaped like a flat surface.

c) Geometry of space time is shaped like the surface of a sphere.

Geometry of space time is shaped like the surface of a cylinder.

10.  What is the value of 1 light year?

a) 1.4×10¹⁰ years      b) 9.46×10¹² Km         c) 1.4×10¹⁴ years         d) 1.4×10¹⁶ Km

11.  What happened after Big Bang?

12.  a) nothing                 b) the universe imploded        c) the universe shrank d) the universe expanded

Answers: 1(c), 2(c), 3(a), 4(d), 5(b), 6(c), 7(d), 8(b), 9(a), 10(b), 11(d)

Very Short Answer Question [1 mark each]

1.      What is a universe?

The universe is the infinite expansion of time, space and matter including planets, stars, satellite, meteors, comets, constellation, galaxies, dust and gases.

2.      Define red shift.

The displacement of spectral lines toward longer wavelengths (the red end of the spectrum) in radiation from distant galaxies and celestial objects is defined as red shift.

3.      Who purposed the theory of relativity?

Albert Einstein purposed the theory of relativity.

4.      What is the common in Big Bang theory and Hubble’s finding?

One of the key commonalities between the Big Bang theory and Hubble’s findings is the concept of an expanding universe.

5.      Define singularity.

A singularity is a point in space-time where the laws of physics as we know them does not work.  

6.      Give a point which supports that the universe is expanding.

The red shift indicated that galaxies were moving away from us, supporting the idea of an expanding universe.

7.      What is delicate equilibrium?

Delicate equilibrium refers to the state of balance that exists within a celestial object where the gravitational forces acting upon it are in precise balanced, allowing it to maintain its structure and composition without undergoing significant changes.

8.      What is the role of gravity during nuclear fusion in stars?

The immense gravity compresses the matter and produce excessive heat nearly 10⁷K to initiate nuclear fusion reaction. If the sufficient gravity is not supplied, the gaseous matter would expand and cool making it impossible to have nuclear fusion reaction.

9.      Mention the role of gravity in the death of stars.

Gravity plays crucial role in the death of star. When the star run out of fuel, The star starts to collapse under its own gravity forming White dwarf or supernova explosion may take place.

10. Define critical density of the universe.

Critical density is the average density of matter in the universe at which gravity is just sufficient to halt its expansion but only after an infinite.

11. Define black hole.

A black hole is a region of space time where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. 

12. What is close universe?

A closed universe is a model of the universe in which the curvature of space is roughly spherical, entailing that the universe has finite size. 

13. Write Big-bang theory.

According to the big bang theory, the universe began from a single high energy, high temperature, high pressure and high density matter. It suddenly exploded and expanded 13.8 billion years ago. Finally the explosion magnified to form the current universe.

14. What is open universe?

An open universe is a model of the universe in which the curvature of space is flat or curved away from itself, entailing that the size of the universe is infinite.

15. What is meant by flat universe?

A flat universe is a universe in which the geometry of space is flat, like a piece of paper. In a flat universe, parallel lines never meet, and the sum of the angles in a triangle is always 180 degrees.

16. What causes the satellite to revolve around a planet?

The gravitational force exerted by a planet on the satellite provides necessary centripetal force to revolve around a planet.

17. What is dark energy?

18. Dark energy is a hypothetical form of energy that is causing expansion of universe at an accelerating rate.

19. What kind of universe has positive curvature?

A closed universe has positive curvature.

20. When and who proposed the big bang theory?

The big bang theory was proposed in 1929 by Belgium astronomer George Lemaitre.

21. Which model of the universe allows particles to unite into a point?

Closed model of universe allows particles to unite into a point.

22. Which hypothesis on the origin of the universe is most valid yet?

The big-bang hypothesis on the origin of the universe is most valid yet.

23. What will the universe be like if the gravitation balance expansion just right?

The universe will be flat if the gravitation balance expansion just right.

24. Is our universe close, open or flat, What does the observation suggest?

The observation suggest that our universe is flat.

25. What is the meaning of H in Hubble’s law v=Hd?

26. The meaning of H in Hubble’s law V=Hd is Hubble constant whose value is 73km/sec/mega parsec.

27.                  What is Doppler shift?

28.                  The actual change in the frequency or wavelength of sound or light due to the relative motion of the source and observer is called Doppler shifT.

Short Answer Questions [2 marks each]

1.      How can we conclude that gravitation forms galaxies?

Gravitation brings matter together. The stars are heavenly bodies with huge quantity of matter. So, the stars can pull each other and stay as a cluster. Sometimes a dying massive star can change into black hole. Black hole are the celestial bodies with extensive gravity which has the tendency to bind stars around it. Thus, billions of stars attract each other forming a huge cluster called galaxy. Hence, we can conclude that gravitation forms galaxies.

2.      Compare between the open universe and close universe.

SN	Open Universe	SN	Close Universe
1	In this universe, the matter will continue to expand forever in divergent path.	1	In this universe, the matter will continue to converge.
2	The expanding force (big bang force) is greater than gravitation.	2	The gravitation is greater than expanding force (big bang force).
3	The open universe is curve like surface of the saddle.	3	The closed universe is spherical or eliptical

 

3.      Why are billions of stars present in a galaxy?

4.      The gravitational force among stars pull them close to form a huge cluster of stars called galaxy. Therefore, gravitational force is a factor due which billions of stars are present in a galaxy.

5.      Why does solar system exist?

6.      During the formation of solar system, the star (sun) of the solar system has excessive mass. This excessive mass created gravitational force which pulled the nearby heavenly objects to form solar system. Planets, millions of asteroids, meteors, comets, satellites, dwarf planets, etc. revolve around the sun in response to its gravity.

7.      Why were there no stars in the beginning of universe?

8.      There were no stars at the beginning of the universe because it took millions of years for hydrogen gases to accumulate into a nebula which could give birth to stars.

9.      Why do many scientists agree that the universe is expanding?

10. When light from distant galaxies is observed, it is found to be shifted towards the red end of the spectrum. This is known as redshift, and it is caused by the expansion of space. The farther away a galaxy is, the greater the redshift, which is a direct indication of the speed at which the galaxy is moving away from us.

11. The big theory is most reliable. Give reason.

12. The Big Bang Theory is the most reliable theory of the formation of the universe because  of the following evidences:

 a) Most of the galaxies appear red shifted, an indication that they are moving away from us and that the universe is expanding.

b) The remnant radiation from the Big Bang is observed today as the cosmic microwave background radiation (CMB), a low-level radiation with a temperature of 2.725 K,

c) The percentage of light elements such as hydrogen and helium agree with the idea that the universe started in a hot and dense phase.

13. Excessive gravitation can produce a close universe, why?

It is supposed that the effect of gravity on matter determines the shape of the universe. The critical density is the average density of the matter which is just sufficient to prevent it from expansion. But when the density of the universe is greater than critical density, gravitational force becomes strong enough to stop it from expansion, instead the universe starts to contract. So, excessive gravitation can produce a close universe.

14. Open universe is formed if gravitation is weaker. Why?

Open universe is the universe in which there is continuous expansion of universe occur. An open universe is only possible when the density of the matter in the universe is less than critical density then the galaxies continuous to move apart from each other since the gravitational force between them is not strong enough to halt them from expansion. Hence open universe is formed if the gravitation is weaker.

15. Balance between gravitation and expansion forces is key to a flat universe. Give reason.

A flat universe is the universe whose total density is equal to the critical density. When the gravitational force of the universe and the expansion force are equal, critical density is achieved. The geometry of the space time during the critical density can be thought of as being flat. So, balance between gravitation and expansion force is key to a flat universe.

16. A closed universe will end with s big crunch.

Big crunch is a hypothetical scenario for the ultimate fate of the universe where universe collapse into a point and restart forming universe with a big bang. A closed universe has density of matter greater than critical density which means that there is continuous collapsing and contracting of the matter due to immense gravity which ultimately end with a big crunch.

17. An open universe will end with big freeze. Give reason.

If the density of the universe is less than the critical density, the gravity will be too weak to halt It's expansive. As the universe continued to expand, all this star Galaxy will eventually lose their energy and the universe cool down ending in a big chill or big freeze.

18. A flat universe end with a big freeze.

A flat universe is the one which has gravity equal to the critical density of the universe. In this model of universe, there is a the expansion is very slow i.e. slower than the open universe. Thus it also has an expansion but slower than open universe. Therefore, the fate of flat universe end with big freeze.

19. Differentiate between close universe and open universe.

Closed universe	Open Universe
It has positive curvature resembling a sphere.	It has negative curvature resembling a saddle.
It ends with a big crunch.	It ends with a big chill.
It collapses on itself.	It continuously expands.

 

20. Compare Flat universe and close universe.

Flat Universe	Close universe
1. It is like a sheet of paper.	1. It is positive curve like a sphere.
2. It occurs when the density of the universe is equal to the critical density.	2. It occurs when the density of the universe is greater than critical density.
3. Its expansion is constant rate.	3. Its expansion first slow down, reaches maximum and then contracts.
4.It ends with infinite expansion with big chill.	4. It ends with a big crunch.

 

21. Write the differences between Gravitation and momentum from big bang.

Gravitation	Momentum
1. It's responsible for the formation and evolution of galaxies, stars, and planets.	1. It can be transferred between objects during collisions or interactions.
2. Emerged in the first moments of the Big Bang along with the other fundamental forces.	2. Imparted to the primordial particles and fields created in the Big Bang through the rapid expansion of space-time.
3. Has acted as a braking force, slowing down the expansion of the universe since its inception.	3. Initially responsible for the rapid expansion of the universe after the Big Bang.
4.  Its influence becomes stronger as the universe ages and matter clumps together.	4. As the universe expanded and cooled, the influence of momentum decreased, giving way to gravity's dominant role.

 

22. Enlist the effect of gravitation.

i)                    Gravitation pulls dust and gas together, forming stars, planets, galaxies, and clusters. It governs their orbits and motions within larger structures.

ii)                  It also played a role in determining the initial momentum and distribution of matter during the Big Bang.

iii)                Massive objects bend the fabric of spacetime, causing light from distant objects to be distorted and magnified. This allows us to study objects otherwise too faint or distant to see directly.

iv)                Massive objects can collapse under their own gravity, creating regions of spacetime where the gravitational pull is so strong that not even light can escape.

23. What is the role of gravity in the formation of solar system?

i)        As gravity tugged at the individual particles within the cloud, they started to clump together, snowballing into ever-larger masses. This slow but steady accretion was the first step towards forming the Sun, the central star of our solar system.

ii)                  As the central mass grew, its gravity intensified, pulling in more and more material. This intense gravitational pull also caused the cloud to spin faster, creating a flattened disk of debris around the nascent Sun. This swirling disk became the solar system's nursery, where the planets would eventually form.

iii)               Within the protoplanetary disk, gravity continued its work, pulling together dust and gas into clumps that we now call protoplanets. These protoplanets then went through their own gravitational growth spurts, sweeping up surrounding material and growing into the planets we know today.

iv)             The strength of the Sun's gravity determined the distance of each planet from it, influencing their temperatures and the types of materials they could hold onto. Collisions between protoplanets further shaped their final forms and compositions.

 

24. Is the universe expanding? Put your opinion with a suitable explanation.

Yes, the universe is expanding. The study of spectrum of galaxy reveals the red shift. This indicates that the galaxy is moving away from us. In fact, all the galaxies are receding from each other. This phenomenon proves that the universe is expanding.

25. What happens to the universe if the mass present in the universe produces gravitation stronger than the expansion forces? Explain.

If the mass present in the universe produces gravitational stronger than the expansion forces, The universe began to collapse slowly and gradually and converted into a spherical mass whose curve is positive and a triangle on it is greater than 180 degree. At this condition the universe condenses into a big crunch.

26. What happens to the universe if the mass present in the universe produces gravitation weaker than the expansion forces? Explain.

If the mass present in the universe produces gravitation weaker than the expansion forces, The shape of the universe will become saddle shape and the curvature will be negative. A triangle drawn on this type of universe will be less than 180 degree. The universe continued to expand until and unless all the energy present in the celestial bodies vanish. The universe at this condition, ends with a big chill.

Long Answer Questions [4 marks each]

1.      Answer the following question on the basis of the given figure.

a)      Which model of the universe does the above picture depict?

The above picture depicts flat model of universe.

b)      Under what condition does the above universe occur?

The universe become flat when the density of the universe is equal to the critical density.

c)     How will such universe come t o end?

Such universe comes to the end with a big chill.

d)     What is the relation between density of this universe and critical density?

The density of the universe is equal to the critical density.

2.      What is the proof of the big bang? How did the universe come to be based on the big bang theory?

The Big Bang theory isn't a single piece of evidence, but rather a collection of observations that paint a compelling picture of the universe's origin and evolution. Here are some key pieces of evidence supporting the Big Bang:

1. Cosmic Microwave Background (CMB): This faint radiation permeates the entire universe and is considered the "echo" of the Big Bang. Its nearly uniform temperature and specific properties strongly suggest it originated from a hot, dense state in the early universe.

2. Redshift of Galaxies: Distant galaxies appear redder than nearby ones, indicating they're moving away from us. This expansion of the universe, predicted by the Big Bang theory, is measured by the redshift phenomenon. The farther the galaxy, the faster it recedes and the redder its light appears.

3. Abundance of Light Elements: The observed abundance of light elements like hydrogen and helium in the universe closely matches the predictions of Big Bang nucleosynthesis, the process occurring in the first few minutes of the Big Bang.

4. Age of the Universe: Independent measurements of radioactive elements in meteorites and stars consistently point to a universe around 13.8 billion years old, which aligns well with the Big Bang's predicted timeline.