Category Archives: Science
– Pushpa Raj Adhikary
Former Dean and Controller of Examinations
We human beings live in a planetary system of a star which we call the Sun. Our sun is just one of the minor stars in the cluster of about 250 billion stars called the Milky Way. We live far from the bright and densely populated nucleus of the Milky Way. Earth is one of the nine planets which surround the Sun, and continuously revolves around the Sun in more or less a fixed path known as its orbit. The earth is surrounded by a gaseous ocean. We live on the bottom of this rather opaque gaseous ocean. The earth is also one of the billions of other planets in the universe, nothing more than a tiny speck of dust in the vast galactic island. What can we hope to learn of this universe from our galactic backwoods?
In our short history of the existence on earth we had hardly had time enough to take stock of our immediate surroundings. We have just begun to know and understand ourselves. Thousands of years of human civilization are but a fleeting instance as compared with the periods of time in which matter evolves on the universal scale. Less than 500 years have passed since man first proved that this planet is a globe by circumnavigating it. A century has passed since we discovered, at first by speculative reasoning, some of the laws connecting space, time, and motion. We have just begun to probe the secrets of the structure of the matter. Our knowledge of the universe is scanty indeed and we still have a lot more to learn. But we are inquisitive, have learned things step by step and continue to learn many more things about our universe by the same way and in course of time will unravel more mysteries of the universe.
Apart from the terrestrial landscape of mountains, valleys, flat plain, dense forest and oceans, man has been looking up at the twinkling dots in the sky for thousands of years. Some have compared these twinkling dots, known as stars, the twinkling eyes of the universe looking down on earth. Stars appear after the Sunset and must have looked very mysterious objects for early human beings. Beginning with idle stargazing, it has now turned to systematic observations, first with naked eyes, then with the simplest of instruments, and today with the help of giant telescope with lenses several feet in diameter and other sophisticated instruments. Now we can distinguish planets and stars.
In addition, we have identified various other objects scattered around the vast void of the universe. There are very big clusters of stars like our Milky Way. These clusters of stars are known as galaxies. The galaxies have hundreds of solar systems like ours. There are huge objects made of a gaseous material known as nebulae. Some objects are not visible to us but we feel their presence by detecting the noises they emit. These noises are known as radio waves and are detected and analyzed to understand about these noisy objects. We can measure how big a star is, how far one star is from another, and measure the distance of the farthest nebulae. So the old saying “Twinkle, twinkle little star, how I wonder what you are” is no longer true. Today we can say “Twinkle, twinkle little star, we know exactly what you are”. Stars are no wonders today and neither are they little. Other stars are several thousands to even hundreds of millions larger than our sun and are made of materials in plasma state.
The earth is surrounded by an ocean of colorless gases which we call air. Air mainly contains nitrogen and oxygen along with different other gases in traces. This air covering of our planet earth is known as the atmosphere and is spread up to 3,000 kilometers altitude above the earth. Clouds are usually observed at an altitude of about 80 kilometres. Somewhat higher, between 100 and 120 kilometres, meteors appear as shooting stars. A flying meteor is a complex phenomenon involving the interaction of a fast moving body carrying an electrical charge with the Surrounding air. Atmosphere gradually becomes less and less dense depending on the distance from the surface of the earth. Some strange lights (Northern and Southern lights) called Aurora Polaris occur in the uppermost layers of the atmosphere as high as 1,200 kilometres.
At an altitude of 3,000 kilometres above the surface of the earth, just outside the edge of the atmosphere, electrically charged particles from the outer space counter us. Earth is a huge magnet and its magnetic influence spreads in the surrounding space known as magnetic field. The charge particles which come from outer space towards earth are trapped by the earth’s electromagnetic field. They spiral along the earth forming three radiation belts. A disturbance in this belt causes disturbances in our radio, television and other means of communication.
From the surface of the earth we see the sky is blue and the stars twinkle. These phenomena do occur due to the earth’s atmosphere. So, how does the sky look when we watch it beyond the atmosphere? Astronauts and space travelers tell us that the sky looks totally dark and stars no longer twinkle. Rather they look like dull light-emitting objects. If we recall back, on March 18, 1965 an earth man named Alexei Leonov, citizen of the then Soviet Socialist Republic, first encountered the vast void of the universe face to face. Leonov became the first person from the planet earth to push himself away from his spaceship Voskhod 2 to drift out into the bottomless void known as space. Leonov was connected with a rope-like chord to keep from losing himself in the strange, weird void surrounding him.
Man is inquisitive by nature. As soon as we discover a new law of nature, we try to exploit it for our own ends. Having discovered the secret of lightning bolts we use it to produce electric light. By learning the laws of river flow we dug irrigation canals. We have harnessed the power of nuclear fission of uranium and will soon learn to tame the thermonuclear reaction which heats the sun and stars. No sooner do we discover the laws of the universe than we surely put them to work and make them serve us. We have understood the terrestrial laws and phenomena and made them serve us. So we can hope that by becoming the master of the universe one day we may be able to reconstruct the planetary systems, move stars about and regulate their brightness at our will.
– Pushpa Raj Adhikary
We call the pull of the earth on the bodies the force of gravity. The measure of this pull is called the weight of the body. There is no escape from the gravity and its eternal laws are valid even in the remotest parts of the universe. It equally pervades vacuum and the densest substance. There is no way of shielding from it or acting on it. Its action is less and less when we move away from earth but does not vanish completely. Gravity makes rivers flow down to the sea, keeps the atmosphere around the earth, and is the cause of tides in the oceans. We have to use force to overcome gravity if we want to move away from the earth.
Since time immemorial, living beings had to reckon with gravity, and learned to adapt to it. The force of gravity, which makes everything move towards it, was unexplained for ages. The first man to develop a scientific theory of gravity and apply it to study of the universe was the great Englishman, Sir Isaac Newton.
The anecdote that Newton discovered the law of gravity by watching an apple fall from a tree may or may not be true. It has been said that he invented this story to get rid of people demanding explanation of just how he discovered the great law. Today, any high school student knows this law with such an ease that it seems strange indeed that there was a time when learned men had not the slightest idea about it. However, it is not as it may appear to us and it took the genius of Newton to discover it.
Newton’s studies convinced him that not only earth attracts an apple but an apple also attracts the earth. In fact, every material body attracts other material bodies towards it. But then why the apple moves towards the earth but not the earth towards the apple? This attraction or pull or force exists between the earth and all heavenly bodies too. This is known as the force of gravitation.Any material object attracts all other material objects and this attraction is in proportion to the weight of an object. The heavier a body, the stronger is the attraction. The weight of the earth is enormous compared to the weight of an apple or a man. Hence, the attraction exerted by the earth on other objects is also very strong compared to the attraction of an apple on earth or by a man on earth. This attraction of the earth makes every body move towards earth. The attraction between two material bodies increases if they come closer or if their weights are increased.
About seventy years before Newton’s time, the great German Scientist Johannes Kepler discovered the law as how planets moved around the sun. But in Kepler’s time nobody knew why the planets moved as explained by him. Newton, with the help of the law of universal gravitation, could explain why the planets moved around the sun as explained by Kepler. The universal law of gravitation found another brilliant confirmation in the discovery of the planet Neptune. Astronomers had long discovered that the planet Uranus occasionally appeared to stray from its orbit. Sometimes it would slow down its motion and again it would go faster as if drawn by some invisible force. The law of gravitation predicted that the anomaly in the motion of Uranus was due to the presence of another planet farther from Uranus and soon astronomers discovered a new planet Neptune.
For many decades Newton’s theory of Gravitation appeared perfect. But then facts began to accumulate which could not be explained by the law of universal gravitation alone. One of these is the Seeliger paradox. This paradox goes this way. The universe is infinite and is infinitely variable. Its lifetime too, is unlimited. It is more or less filled with material bodies and so can be assumed to possess some mean density of matter. Seelinger decided to apply the universal law of gravitation to determine the gravitational force which an infinite universe would exert at any point within it. This force was found proportional to the radius of the universe. As the radius of the universe is infinite, so the force would be. But this is not the case. Does it mean that the law of Universal gravitation is not valid on universal scale?
Another phenomenon in which the conclusions of gravitational theory did not quite agree with observations was found in the displacement of the orbit if the planet Mercury. Very accurate calculations of the orbit of Mercury reveal that the point closer to the sun suffers a precession or displacement. For a long time this precession of the orbits of Mercury remained unexplained. It took a revolution in science to explain it, and the revolution was carried out by a young German Scientist, Albert Einstein.
It is a long known fact that if a gun fires at a distance we see the flash of light some time before we hear the sound. This tells us that sound travels in a far less speed that the light. It was possible to measure the speed of sound in the surface of the earth as 330 meters per second. But it is much harder to measure the speed of light because light travels with an incredible speed of 3,00000 kilometers per second. A ray of light can circle the earth in just over 0.1 second i.e. one tenth of a second. For a long time people were unable to measure the speed of light. It was finally measured by observing the eclipses of the satellites of the planet Jupiter from two points on earth’s orbit around the sun, when the earth was closed and farther from Jupiter. Today it is measured in laboratory conditions to a high degree of precession by means of rotating mirrors. In fact, not only light but all electromagnetic waves travel with light’s speed as the electromagnetic field moves through space.
But how do electromagnetic fields propagate through space? Does gravitational force also propagate through space in the form of gravitational field? If so, how fast does a gravitational field travel? As fast as sound in air, light in vacuum or with some other speed? Can the attraction between the bodies happen directly without the participation of the intervening medium? Do the gravitational force and gravitational field also propagate with the same speed of light or have a finite velocity? A new scientific theory was needed to explain the propagation of electromagnetic field through space and its foundation was laid in 1905-1915 by Albert Einstein in his special and general theories of relativity based on the geometries of Lobachevski and Riemann.
One of the fundamental conclusions of the special theory of relativity, which defines the interconnection between space and time, is the equivalence of mass and energy. The theory states that a moving body carries kinetic energy, hence its mass is greater than when it is at rest. The greater a body’s latent energy is, the greater is its mass. A cup of hot coffee is heavier than cold coffee in the same cup. The famous equation E=mc2 is Einstein’s formula of mass-energy equivalence.
But what is meant by a body’s mass? The mechanical concept of mass states that mass is a measure of a body’s inertia. Hence, mass can be expressed in terms of force and the acceleration which it imparts to the body. In physics, mass measured in this way is known as inertial mass. But mass can also be measured from Newton’s formula of gravitation. This mass of bodies which may be at rest relative to one another is known as gravitational mass. The physical interpretation of inertial and gravitational mass are different but quantitatively have, to date, been found to be the same no matter how they are measured. This led Einstein to think that inertia and gravitation must have a common origin. So, if a body’s inertial mass varies with the velocity of motion, then, he reasoned, the gravitational mass should also vary with the velocity of motion.
Einstein’s identification of inertia and gravity on the basis of the equality of inertial and gravitational mass of great significance. It enabled him, in 1915, to develop the general theory of relativity, which is the modern theory of gravitation. This modern theory offers a much more exact and profound explanation of the properties of the bodies than Newton’s theory. Einstein’s theory was a revolution in physics which provided explanation for many hitherto unexplained phenomena. But it would hardly be useful to present the theory in common language as it contains largely mathematical, extremely complicated equations belonging to the class of non-linear differential equations in spite of the clarity of its physical meaning.