Newton’s Laws Of Gravitation
According to Newton’s law, every particle attracts every other particle in the universe. For instance, between the sun and the earth and between the earth and the moon, there are respective attractive forces. His law states that the gravitational force can act upon an object no matter how far the distance is. However, the farther the two objects, the weaker the gravitational force between them. Also, no matter how great the mass of one object, if the other has no mass, there will be no attractive force between them. (One point to note here is that the term “mass” is different from the term “volume.” Although small iron marble may be smaller in volume than a balloon, the marble has a lot greater mass than the balloon. This is because they have different densities. In this way, if we want to change Newton’s gravitational law into a form of proportion, the equation will come out like this. The attractive force between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
The above facts are familiar for most of us. The interesting ones are coming….
Suppose I tie an apple and an orange with a string. If I hold the apple and spin it, the orange will not move away. This is because of the bond between the apple and the orange. This bond is made by the string I tied. If the string is cut accidentally or intentionally, the orange will definitely move far away from the apple. The same way goes for the process of the earth revolving around the earth. Newton suggested that the earth is not going anywhere away from the sun due to the invisible string-like bond between the sun and the earth. He named that bond “gravity”. In a way, he suggested that gravity is the force which exists between the objects with mass.
In fact, Newton’s law is incomplete and could not explain some of the phenomena in the universe. For example, the phenomenon of Gravitational Lensing, Mercury’s unusual orbit.
Gravitational Lensing Phenomenon
Gravitational Lensing is the bending of light rays when light passes near the massive objects due to the attraction of those masses. Let me explain. Rays of light emitted from the very far away galaxy have to pass near the stars before they reach the earth. As a result, the light is refracted so that when observing with a telescope the images of the Galaxy appear distorted. It can also result in the multiple images of light-emitting galaxies. Light actually has no mass. (mass=zero). Considering Newton’s law, big stars should not act force upon the light with zero mass. SO WHY DO ALL THOSE LIGHT RAYS BEND EVEN THOUGH THEY HAVE NO MASS???
Newton’s law could not explain this phenomenon for he considered Space and Time as absolute. On the other hand, he regarded time and space only as a matrix of universal phenomena or as a fixed and constant existence.
This is not actually surprising. Until the 20th century, physicists considered time and space as a matrix which has nothing to do with universal phenomena. However, one person found out that time and space are the main of the universal phenomena rather than mere matrix in the 20th century. Yes!!! He is the one who is regarded as the most intelligent person of the 20th century. He is Albert Einstein. His theories of general relativity and special relativity are complicated. Among these theories, I will point out the facts concerning gravity only.
Einstein’s general relativity states that space and time are not uniform. They may be bending in some spaces and straight in others. Space and time near massive objects are bending. As a result, a massive object will draw other particles near it. Let’s read a little more to get explained!!!
Imagine the person reading now and I are holding tightly a very wide fabric from each end. If we put a very massive metal sphere onto the middle of the fabric, the surface will certainly become depressed. If someone rolls a glass marble from the corner of the fabric, it will move into the metal sphere just as the curved surface of the fabric. Remember that there is no bond between the metal sphere and the glass marble. The metal sphere makes the surface of the fabric curve. The marble moves along the curved surface and reaches near to the metal sphere. This is what gravity meant by Einstein. Our sun takes space in the fabric-like space-time. The space is curved due to the mass of the sun. As the earth and the other planets just follow the structure of curved space-time, they automatically revolve around the sun.
In the gravitational lensing phenomenon, the reason why the light bends is that as the space it passes is curved, it has to pass that curved space.
In the nutshell, there is no bond or attractive force in modern considerations. Matter tells space-time how to curve and space-time tells matter how to move.
This is the comparison of Newton’s Laws of Gravitation and Einstein’s theory. We cannot say Newton’s law is completely false. His law is still accurate and right in some ways. It is still used in taking off the planes. Einstein’s theory is still being used for measuring the geography of space-time and it was the first step for studying “Black Holes.”