On the Idea of Gravitational Field in Physics

“ If we pick up a stone and then let it go, why does it fall to the ground? ” The usual answer to the question is: “ Because it is attracted by the Earth ”.  Modern physics formulates the answer rather differently for the following reason. As a result of the more careful study of electromagnetic phenomena, we have come to regard action at a distance as a process impossible without the intervention of some intermediary medium. If , for instance, a manget attracts a piece of iron, we cannot be content to regard this as meaning that the magnet acts directly on the iron through the intermediate empty space, but we are constrained to imagine — after the manner of Faraday — that the magnet always calls into being something physically real in the space around it, that something being what we call a  “ magnetic field ”.

In its turn this magnetic field operates on the piece of iron, so that the latter strives to move towards the magnet. We shall not discuss here the justification for this incidental conception, which is indeed a somewhat arbitrary one. We shall only mention that with its aid electromagnetic phenomena can be theoretically represented much more satisfactorily than without it, and this applies particularly to the transmission of electromagnetic waves. The effects of gravitation also are regarded in an analogous manner. 

The action of the earth on the stone takes place indirectly. The earth produces in its surrounding a gravitational field, which acts on the stone and produces its motion of fall. As we know from experience, the intensity of the action on the body diminishes according to a quite definite law, as we proceed farther and farther away from the earth. From our point of view this mean: The law governing the properties of the gravitational field in space must be a perfectly definite one, in order correctly to represent the diminution of the gravitational action with the distance from operative bodies. It is something like this: The body ( e.g. the earth ) produces a field in its immediate neighbourhood directly; the intensity and direction of the field at the points farther removed from the body are thence determined by the law which governs the properties in space of the gravitational fields themselves. 

In contrast to electric and magnetic fields, the gravitational field exhibits a most remarkable property, which is of fundamental importance for what follows. Bodies which are moving under the sole influence of a gravitational field receive an acceleration, which does not in the least depend either on the material or on the physical state of the body . For instance, a piece of lead and piece of wood fall in exactly the same manner in a gravitational field in ( in vacuo ), when they start off from rest or with the same initial velocity. This law, which holds most accurately, can be expressed in a different from in the light of the following consideration. 

According to Newton's law of motion, we have: 

( Force ) = ( inertial mass ) × ( acceleration ) 

Where the “ inertial mass ” is a characteristic constant of the accelerated body. If now gravitation is the cause of the acceleration, we then have:

( Force ) = ( gravitational mass ) × ( intensity of                                                  the gravitational field ) 

where the “ gravitational mass ” is likewise a characteristic constant for the body. From these two relations follows: 

( Acceleration ) =  ( gravitational mass ) /                                                  ( inertial mass) × ( intensity                                            of the gravitational field )

If now, as we find from experience, the acceleration is to be independent of the nature and the condition of the body and always the same for a given gravitational field, then the ratio of the gravitational to the inertial mass must likewise be the same for all bodies. By a suitable choice of units we can thus make this ratio equal to unity.  We then have the following law:  The gravitational  mass of a body is equal to its inertial law  .

 It is true that this important law had hitherto been recorded in mechanics, but it had not been interpreted. A satisfactory interpretation can be obtained only if we recognise the following  fact:  The same quality of the body manifests itself according to circumstances as “ inertia ” or as    “ weight ” ( lit “  heaviness ” ). In the following section we shall show to what extent this is actually the case, and how this question is connected with the general postulate of relativity...

Galileo Galilei ( Italian astronomer, physicist )

Galileo di Vincenzo Bonaiuti de' Galilei was born on February 15, 1564 in Pisa, Italy. His father was a musician and wool trader. He wanted his son to study medicine. Galileo began his education in   Jesuit monastery  at the age of eleven. By the time he was seventeen, he was enrolled with the University of Pisa to learn medicine.

In University, mathematics became his favourite subject, so much so that he shunned other subjects and began studying only mathematics. Later, to earn his living, he began mathematics tution for other students.

GALILEO, Perhaps more than any other single person, was responsible for the birth of modern science. His renowned conflict with the Catholic Church was central to his philosophy, for Galileo was one of the first to argue that man could hope understand how the world works and, moreover, that we could do this by observing the real world. 

Galileo had believed Copernican theory ( that the planets orbited the sun ) since early on, but it was only when he found the evidence needed to support the idea that he started to publicly espouse it. He wrote about Copernicus's theory in Italian ( not the usual academic Latin ), and soon his views became widely adopted outside the Universities. This annoyed the Aristotlelian professors, who united against him, seeking to persuade the Catholic Church to ban Copernicanism.

Galileo, worried by this, travelled to Rome to speak to the ecclesiastical authorities. He argued that the Bible was not intended to tell us anything about scientific theories and that it was usual to assume that, where the Bible conflicted with common sense, it was being allegorical.

But the Church was afraid of a scandal that might undermine its fight against Protestantism, and so took repressive measures. It declared Copernicanism “  false and erroneous ” in 1616, and commanded Galileo never again to “  defend or hold ” the doctrine. Galileo acquiesced.

In 1623, a longtime friend of Galileo's became the pope. Immediately Galileo tried to get 1616 decree revoked. He failed, but he did manage to get permission to write a book discussing both Aristotlelian and Copernican theories, on two conditions: he would not take sides, and he would how the world worked because God could not place restrictions on God's omnipotence.

The book, “ Dialogue Concerning the Two Chief World Systems ”, was completed and published in 1632, with the full backing of the censors—and was immediately greeted throughout Europe as a literary and philosophical masterpiece. Soon the pope, realizing that people were seeing the book as a convincing argument in favour of Copernicanism, regretted having allowed its publication. The pope argued that although the book had nevertheless contravened the 1616 decree. He brought Galileo before the Inquisition, which sentenced him to house arrest for life and commanded him to publicly renounce Copernicanism. For a second time, Galileo acquiesced.

Galileo remained a faithful Catholic, but his belief in the independence of science had not been crushed. Four years before his death in 1642, while he was still under house arrest, the manuscript of his second major book was smuggled to a publisher in Holland . It was this, referred to as Two New Sciences, even more his support for Copernicus, that was not to be the genesis of modern physics. 

♦ Did You Know?

                      ♣ Galileo wanted to be a monk when he came back from the  Jesuit monastery . His father got angry and withdrew him from there.

                      ♣ Galileo built his first telescope in 1609, which featured three times magnification. Later, he developed models that could see up to 30 times magnification.

                       ♣ Galileo was a well-known and accomplished musician.

Galileo Galilei died on March 8, 1642 following a prolonged illness...

Issac Newton ( English mathematican, physicist )

Sir Isaac Newton was born on December 25, 1642 in Lincolnshire, England. Newton was named after his father — Isaac Newton, who died three months before his birth. He was a premature child and was raised by his maternal grandmother. Newton went to The King's School, Grantham; When he turned twelve. In 1661, he enrolled with the Trinity College, Cambridge. He obtained his degree in 1665. Later, he joined the same college as a mathematics professor. 

Sir Isaac Newton was not a pleasant man. His relations with other academics were notorious, with most of his later life spent embroiled in heated disputes. Following publication of  Principia Mathematica  (1687) —  surely the most influential book ever written in physics —  Newton had risen rapidly into public prominence. He was appointed president of the Royal Society and became the first scientist ever to be knighted. 

Newton soon clashed with the Astronomer Royal, John Flamsteed, who had earlier provided Newton with much needed data for  Principia, but was now withholding information that Newton wanted. Newton would not take no for an answer:  he had himself appointed to the governing body of the Royal Observatory and then tried to force immediate publication of the data. Eventually he arranged for Flamsteed's work to be seized and prepared for publication by Flamsteed's mortal enemy, Edmond Halley. But Flamsteed took the case to court and, in the nick of time, won a court order preventing distribution of the stolen work. Newton was incensed and sought his revenge by systematically deleting all references to Flamsteed in later editions of  Principia. 

A more serious dispute arose with the German philosopher Gottfried  Leibniz. Both Leibniz and Newton had independently developed a branch of mathematics called calculus, which underlies most of modern physics. Although we now know that Newton discovered calculus years before Leibniz, he published his work much later. A major row ensued over who had been first, with scientists vigorously defending both contenders. It is remarkable, however, that most of the articles appearing in defense of Newton were originally written by his own hand — and only published in the name of friends!  As the row grew, Leibniz made the mistake of appealing to the Royal Society to resolve the dispute. Newton, as president, appointed an " impartial " committee to investigate, coincidentally consisting entirely of Newton's friends!  But that was not all: Newton then wrote the committee's report himself and had the Royal Society published it, officially accusing Leibniz of plagiarism. Still unsatisfied, he then wrote an anonymous review of the report in the Royal society's own periodical. Following the death of Leibniz, Newton is reported to have declared that he had taken great satisfaction in " breaking Leibniz's heart ". He also did some important work in optics.

During the period of these two disputes Newton had already left Cambridge and academe. He had been active in anti-Catholic politics at Cambridge, and later in Parliament, and was rewarded eventually with the lucrative post of  " Warden of the Royal Mint ". Here he used his talents for deviousness and vitriol in a more socially acceptable way, successfully conducting a major campaign against counterfeiting, even sending several men to their death on the gallows. 

Sir Isaac Newton died on March 31, 1727 during his sleep...

Albert Einstein ( German—born Theoretical physicist )

Albert Einstein was regarded as the founder of modern physics, Albert Einstein was born to Hermann Einstein,a salesman and an engineer,and Pauline Kochon on 14 March 1879, in Ulm, Kingdom of Württemberg, German Empire. He received his education at the Luitpold Gymnasium in Munich. His grades in physics and mathematics were always excellent. He completed his schooling at the Argovian Cantonal School, Aarau, Switzerland, and at the age of seventeen he joined the Zürich Polytechnic for a physics and mathematics teaching diploma programme.

Einstein received his degree in 1900 but failed to get a suitable teaching job. With his friend's help, he joined the Federal Office for Intellectual Property as an assistant examiner – level lll .

Einstein secured a permanent position at the Swiss Patent Office in 1903. His conclusions about the space-time connection and the nature of light were aided by his work and experiments during this job.

Einstein completed his Ph.D. from the University of Zürich in 1905 and published four papers in the scientific journal named ″ Annalen der Physik ". The year was miraculous for him as these papers on photoelectric effect, Brownian motion, special relativity, and mass-energy equivalence ( E= mc² ) were significant contributors to the foundation of modern physics. They reformed the views on time ,  space, and matter. In the next few years, Einstein came to be recognized as a major scientist.

In 1908 he joined the University of Bern as a lecturer and the next year he was appointed as an associate professor at the University of Zürich. Two years later, in 1911, he was appointed as a professor at the Charles-Ferdinand University, Prague. Here he wrote several scientific works. Einstein returned to Zürich the next year, and for the two years that followed, he joined ETH Zurich as a professor of theoretical physics.

Einstein was appointed as the director of Kaiser Wilhelm Institute of Physics in the year 1914 and as the president of the German Physical Society in 1916. He developed the general theory of relativity between 1907 and 1915. It was published in 1915. In 1916, Einstein published " Relativity: The Special and the General Theory " in German. Its first English translation was published in 1920. Divided into three parts, the special theory of relativity, the general theory of relativity, and the consideration on the universe as a whole. It is considered a groundbreaking scientific work.

In 1921, Einstein was awarded the Nobel prize in physics " for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect. " 

 In the year that followed, he travelled extensively. In 1933, he joined the Institute for Advanced Study in the United States, and by 1940 he became an American citizen.

Einstein published numerous scientific and non-scientific works. Some of his published works include: Sidelights on Relativity (1922), Cosmic Religion: With Other Opinions and Aphorisms (1931), Essays in Science (1934), The World as I see It (1949), Out of My Later Years (1950), and Ideas and Opinions (1954). 

Einstein died on 18 April 1955, aged seventy-six, in Princeton, New Jersey.