Our Picture of the Universe

-Stephen Hawking

Summary:

In the past, the world was considered as a flat plate supported by a big tortoise standing on an infinite tower of tortoises. People would take it as a ridiculous matter.  There were several questions related to the beginning, continuing and existence of the universe. New breakthroughs in physics would contribute more to solve these questions. The answers of these questions would be true as well as fantastic like the fact of earth orbiting the sun or as a tower of tortoise. Only time will tell regarding it.

The Greek philosopher Aristotle in his book On the Heavens put forward two arguments related to the shape of the earth. Firstly, he claimed that the eclipses occurred as the earth came in between the sun and the moon. When he saw the shadow of the earth spherical on the moon, he concluded that earth was round. Secondly, the North Star was nearby the earth in comparison to the stars seen on the equatorial side. It indicated the distance of the stars and earth is not same from all places.  

Aristotle thought that the earth was static; the sun, the moon, the planets and the stars orbited in circles around the earth. Ptolemy elaborated this idea in the 2^nd century AD. He also claimed that earth was the center of all the planets and he introduced some more planets like Mercury, Venus, Mars, Jupiter and Saturn rather than Aristotle. He claimed that the planets moved on smaller complicated circles in the space. Out of the circles of the planets some fixed stars would stay in fixed positions in the space. Beyond that their arguments remained silent as it was beyond the observation of the mankind of that time.

In 1514, Copernicus presented a simple model of the universe. He claimed that the sun was stationary at the center. The earth and other planets moved around in circular orbits. After a century passed, Kepler and Galileo supported the theory of Copernicus, yet they were wrong in the concept of orbits. Aristotelian-Ptolemaic theory was proved wrong when Galileo observed Jupiter with his telescope. Galileo found that several small satellites or moons orbited around the Jupiter. It proved that the earth was not the center of the universe. Later on Kepler modified the Copernican theory and suggested that planets moved in ellipses not in circles. However, Kepler couldn’t prove that the planets orbited the sun by magnetic forces. The detail explanation was given by Newton in 1687 that heavenly bodies moved in space and time in complicated circles. Newton introduced the theory of Gravitation which proved that each body attracted every other body by force which is stronger among massive bodies and in short distance. It was repulsive if the objects are farther. It was the same force that made things fell down to the earth. Newton also proved that moon and other planets went round the sun in an elliptical path due to gravitational force.

Newton also realized that stars would attract on another so they would move round the massive bodies at the center. There was suspicion that the planets and stars would fall together at the center with gravitational force. In response of it, Newton argued that there was no finite center in the space; the universe was divided into infinite number of stars; so there wouldn’t be any center.

There was some problem while talking about infinity. Every point can be regarded as center in an infinite universe. Every point has an infinite number of stars on each side of it. If we consider the finite universe in which all the stars would fall together, it would be wrong. There is a question what will happen if we add more stars in the universe? According to Newton’s theory it didn’t make any difference. We could add as many stars as we like because they would collapse within themselves. It is impossible to find infinite static model because gravity always affects them.

Till the 20^th century, there was debate among scientists whether the universe was expanding or contracting. There was also another argument either the universe existed forever or had it been created at a finite time in the past. The scholars who believed in Newton’s theory didn’t believe in that the world had been expanding. Rather they would try to prove that gravitational force would be repulsive if the bodies go far beyond. Such thought wouldn’t affect the predictions of the motions of the planets, but it established the belief that stars would remain in equilibrium. The attractive force would work with nearest bodies and the repulsive force worked with furthest bodies. Now we have advanced thought that the stars which are nearer to one another would work with attractive forces and they would collapse with one another. Similarly, stars which are farther away would be affected by repulsive forces and they would be driven farther away.

Theologians would believe in unchanging or static universe. According to these people the universe had created by the God and it would exist forever till the boon of God goes to humans. But in 1929, Edwin Hubble discovered that the distant galaxies are moving away from us. It meant that the universe has been expanding ever which meant that the universe was compact in the past. Before 10 or 20 thousand million years ago the density of the universe was infinite. This discovery introduced the beginning of the universe in the field of science.

Hubble named the time as Big Bang in which the earth was too small and too dense. Along with the introduction of Big Bang theory all the laws of science and predictions would break down. When we believed that time had begun at the time of Big Bang which was difficult to define. The beginning of time with the Big Bang was different from the concept developed previously. In the static universe, the beginning of time seemed to have imposed by some outside forces. Theologians could say that god created the universe in the past. On the other hand, physical reason of the earth needed the beginning of the universe. The writer argued that God’s creation of the universe was wrong. He also added that it was meaningless to imagine that the universe had been created before the Big Bang.

We need to be clear about the scientific theory to know about the beginning and end of the universe. The theory is just a model of the universe, or a restricted part, or a set of rules. It doesn’t have any other realities except to be existed in our mind. A good theory makes us satisfies in two ways: firstly, it must describe large number of observations with few arbitrary elements. Secondly, it must make definite predictions about future observations. Aristotle’s theory predicted that the earth was made up of earth, air, fire and water; so it didn’t make any definite predictions. Similarly, Newton’s theory was also simple but its predictions about gravitation were accurate.

The physical theories are provisional as they are hypothetical. Philosopher Karl Popper argued that a good theory is characterized by the facts that could be disproved or falsified by observations. New experiments would thrive on predictions that increased our confidence; if new observations would make it false we have to abandon or modify them. In practice, new theory is developed from the old one. For instance, Einstein’s theory of general relativity was developed from Newton’s theory of gravity.

The evaluation goal of science is to provide a single theory; but scientists would separate the problems into two parts. Firstly, there are the laws that tell us how the universe changes with time. Secondly, there is the question of the initial state of the universe. Some people would argue that science should follow the first question. They claimed that the initiation of the universe is the matter of religion. They also claimed that the omnipotent God had started the universe. These people would follow certain regular laws of the creator God. Certainly there are the laws that govern the initial state of the universe.

It is difficult to describe all the theories of the universe at a time. We need to break them apart and to develop partial theories. Each of these theories would describe certain limited class of observations with simple set of numbers. This approach is completely wrong because each part represents or solves single problem in isolation. Since universe depends on everything else we need to address all the issues together. We have made progression in the past regarding the theories of universe. The concept of Newtonian theory is that gravitational force depends on body; it’s mass but independent of what the bodies are made of. In the same way, we need not have the knowledge of structure and constitution of the sun and the planets to identify their orbits.

These days scientists describe the universe using the general theory of relativity and quantum mechanics. The general theory of relativity describes the force of gravity and the large-scale structure of the universe. The size of observable universe is million million million million miles in distance. Quantum mechanics deals with millionth of a millionth of an inch. These two theories are inconsistent with one other or both of them are not correct. One important endeavor in physics today is to incorporate them both. We don’t have a theory that can address all the issues related to the universe; it will have been developing till long in the future.

If you believe that the universe is arbitrary, it’s a different matter. We need to combine the partial theories into a unified theory that will solve all the problems. Partial theories of the past would make sufficient accurate predictions; however it’s difficult to unite them on practical grounds. The discovery of the unified theory may not contribute to the survival of our species, nor may it affect our lifestyle. However people won’t be contented with it as it has been happening since the dawn of civilization. We are keenly interested to know why we are here and where we came from. Humanity’s deepest desire is to quench the quest of their knowledge so that our goal should have been directed to get complete knowledge of the universe where we live.

Comprehension

A.    Read the given text carefully and answer the following questions briefly.

1.      What was Aristotle’s basis for believing that the earth was spherical?

He observed the eclipse of the moon at night time. It was spherical or round in shape so he concluded that the earth was spherical.

2.      What were Aristotle’s and Copernicus’ models of the universe and how was the latter supported by Galileo?

Aristotle’s model of universe was that the earth was the center of all the planets; the sun, the moon and other planets would go round the earth. Copernicus’ model was different than him and he claimed that sun was the center of the universe. The earth and other planets would move round the sun. Galileo supported the Copernicus when he observed Jupiter with his telescope he found that it was one of the planets in the solar system.

3.      What was the gist of Newton’s theory of gravity?

The magnetic force of gravity is attractive with bigger mass and short distance whereas it is repulsive with the distance of objects.

4.      Why does Stephen Hawking think there is need to develop a complete unified theory of the universe? Has it been done at all?

He argued that everything in this universe is related with everything else. The partial solution of such problem can’t address the collective problem. So the goal of science should be directed to develop a unified theory. It hasn’t been done till date.

5.      Which human yearning is justification enough for the continued search for this complete unified theory of the universe and why?

The yearning of knowledge from the beginning of human civilization has been the justification for the continued search of unified theory of the universe. It’s because human beings can’t be contented with limited means and resources.

B.     Choose from a, b or c and correct the endings to the following sentences.

1.      Aristotle realized that eclipses of the moon were caused by: the earth coming between the sun and the moon.

2.      Galileo’s observation of the planet Jupiter indicated that: the planets moved around Jupiter.

3.      Newton postulated a law of universal gravitation according to which: each body in the universe was attracted toward every other body by a strong force.

4.      A good theory must accurately describe a class of observations on the basis of a model and: it must be able to make observations based on past theories.

C.    Vocabulary

1.      List out antonyms of the following words that appear in the given text.

Perfect = imperfect           partial= full                 stationary= moving

Superior=inferior               major=minor                believing=distrust

Define=not define                        complicated=simple    expanding=contracting

Finite=infinite                   similar=different         accurately=inaccurately

Practical=impractical         general=specific          single=together          

2.      Write the pronunciation pattern and stress to the following words:

1.Fantastic=/fanˈtastɪk/; 2. tortoise/ˈtɔːtəs/; 3. Endeavour=/ɪnˈdɛvə/; 4. yearn

/’jəːn/; 5. Elliptical=/ɪˈlɪptɪk(ə)l/; 6. Principle=/ˈprɪnsɪp(ə)l/WORD 

3.      Fill in the blanks with the suitable words given below:

a.       Ahmed has run out of subjects to discuss with the man sitting next to him.

b.      The children’s imagination was run away with them, and their story sounded more and more incredible.

c.       Could this exercise be run through your language teacher, please?

d.      I run up against an interesting person today on my way to college.

e.       Shall we run across the schedule for the seminar before we leave?

f.       There are some of the problems that Sujata run by at the booking office tomorrow.

g.      The play runs on until very late last night.

-By Prem Prasad Sigdel