"Every great advance in science has issued from the audacity of the imagination."

When man crawled out of his cave and started wondering about the world around him, it is reasonable that astronomy should have been the first to command his interest. As you look up at the night sky, especially on a dark night away from the lights of civilization, there, spread out before you is a most amazing sight. As far as the eye can see, a multitude of twinkling stars and barely perceptible nebulae burst into view. It must have filled ancient man with amazement and awe much as it does with us today.

Even now when you look at a cathedral-like clear night sky, away from city lights, a sense of reverence is hard to resist. Yet, as we have seen, ancient man slowly overcame his initial intimidation and began to make some sense of it all. In time he succeeded in extracting the basic laws of physics that appeared to govern even such a vast mechanism as the universe above his head. Fanciful beliefs in a pantheon of gods gave way to basic rules that made much of the universe predictable and understandable.

It's the law
It's easy, today to speak of the laws of physics that govern even the universe. To early man these physical laws were no more obvious than his understanding of the night sky itself. What controls the motion of objects—a rock or a stick tossed idly through the air? Why do they stop? How do birds manage to fly and why can't we? Why is fire warm? Why does ice float? Why do objects fall? When man first began to ask the questions, the answers did not come easily and he often got it wrong.

Ancient theories in physics were rarely more than philosophical musings and this was reflected in the terminology. Also they were rarely tested by systematic experiment. As a result many of them were pretty wide of the mark. Yet, some of them were surprisingly good. As far back as the 9th century B.C.E., an Indian astronomer, Yajnavalkya, proposed a spherical earth as part of a sun-centered universe. Also in India we find early versions of the atomic theory of matter.

Then there were the early attempts by the Greeks to understand the nature of matter. For example, our "old friend" Archimedes (287 – 212 BCE) not only discovered the concept of displacement, but also the Archimedes screw and the properties of levers. Much earlier a fellow by name of Empedocles (c.490 - 430 BCE) came up with the idea that all matter was made up of four "elements": Fire, Earth, Air, and Water. A number of Greek thinkers including Plato and Aristotle had a heyday with that idea and this notion lingered in Europe well into modern times.

Through the efforts of Thomas Aquinas and the other scholastics who turned Aristotle's Greek philosophy into a Christian science, the "physics" of Aristotle became part of church doctrine. Predictably, this retarded the birth of modern science. Galileo, for instance, got into some difficulty because he tried to convince the people of his day that all bodies fall to earth at exactly the same rate of speed regardless of their weight or size, something he had discovered through experiment. He was accused of impiety because after all, Aristotle had plainly stated the opposite was true.

Fire, earth, air, and water comprising the four building blocks of matter also led to some rather strange conclusions related to medicine. For example, according to classic medicine, the state of one's health was controlled by yellow bile, black bile, blood, and phlegm. These were called the four humors. Speaking of blood, another notable Greek, Galen (c.129 - 199 BCE) of Pergamon got that a little mixed up. He had the idea that food was converted into blood which was then used up to power the body.

A fellow by the name of William Harvey (1578 - 1657) finally cleared that up with his discovery that blood remained more or less intact in the body and instead circulated in an endless loop. Like most new ideas this was instantly dismissed by most of the knowledgeable people of his day. After all it totally contradicted Galen, who's authority even then was so pervasive that most new theories relating to the human body faced an uphill battle.

In spite of this attitude, more and more breakthroughs in physiology and physics were proposed and in time accepted. This came about because people began testing ancient beliefs to see if they held any water so to speak. We can only imagine the kind of bravery and perseverance involved. By questioning established notions you not only ran the risk of a little unpopularity, you actually put your life on the line. New ideas weren't just a novelty, they were a crime!

Sofar, we've mentioned Galileo and William Harvey. Who were some of the other fearless pioneers? Well, there was Robert Boyle who delved into the mystery of gases and in the process formulated the laws that described their behavior. There was Christiaan Huygens (1629 - 1695) who, among many other accomplishments determined a key property of light. There was Anton van Leeuwenhoek who created his marvellous little microscopes and discovered some amazing biology. And of course, Isaac Newton's contributions go without saying.

But we're getting ahead of ourselves a little. It's probably safe to say that modern physics got a real boost from magnetism and static electricity. Even in the 16th and 17th centuries when they began to be seriously studied these were mysterious forces that were known but not understood. The ancient Greeks were familliar with some of the effects produced by amber and lodestone and as early as the 13th century, Roger Bacon and a Peter Peregrinus had made a study of sorts.

By the late 1500's there was a serious attempt at understanding what these forces were all about. The property of magnetism was the subject of an extensive work by William Gilbert entitled De Magnete, published in 1600. The first electrostatic generator, a machine which rubbed a cloth against a rotating ball of sulphur, was invented by Otto von Guerike (1602-86). A means of storing the resulting charge, the Leiden jar, was invented by Pieter van Muschenbroek (1692-1761).

Then there was nothing...
With this and the work carried out by Galileo on falling bodies we begin to see the beginnings of modern "physics". From here the story becomes increasingly more fascinating. Some of the attempts to create acceptance for modern discoveries that challenged the revered convictions of the faithful bordered on farce. Otto von Guericke was the mayor of Magdeburg, in present day Germany, from 1646 to 1676. In the mid 1600's he mounted a dramatic demonstration of the existence and power of a vacuum.

He had joined two copper hemispheres and pumped the air out of the enclosure. He then hooked a team of horses to each hemisphere and showed that try as they might, they could not pull the ball apart. Then when air was let back into the ball, they were easily separated. Theatrics aside, this was a pretty important demonstration. You see, the possibility of a vacuum was widely disputed and in fact raised some serious theological issues.

In the Middle Ages, Christians held the idea of a vacuum to be immoral or even heretical. The absence of anything, implied the absence of God, and harkened back to the void prior to the creation in Genesis. Even an intellectual giant like René Descartes ultimately fell victim to this religious bias and he substituted the aether for the complete absense of matter, the vacuum. So you see, when the mayor of Magdeburg demonstrated so dramatically what could only be interpreted as a near vacuum, he struck a major blow for modern science.

A related development was the concept of inertia, the tendency for a moving body to continue to travel in a straight line unless acted on by another force, as defined by one of Newton's laws of motion. This was first proposed in the 14th century by a fellow named Jean Buridan. Understandibly this initial attempt lacked the sophistication of the Newtonian explanation and it was called impetus, not inertia. Buridan reasoned that some force was imparted to an object when it was set in motion which caused it to continue in the same trajectory as it began, straight or curved.

In the 14th century this was pretty daring stuff because it was a direct challenge to the church-sanctioned aristotelian beliefs of the day. Roughly stated, this went something like this: Objects set in motion do tend to continue for awhile. On earth this force came from the surrounding air which continued to "push" the object along. In the heavens, the sun and the planets were pushed along by angels. Buridan's impetus did away with the need for such an outside force. Also by noting that objects tended to plummet back to earth in an arc when slowed by the friction of the air, he disputed the notion that objects no longer pushed along by Aristotle's "force" dropped straight down to the earth.

There's a lot more to be said on the subject, but for now we'll reflect on the unbelievable amount of courage shown by those who were willing to challenge the established beliefs of their day. René Descartes, in spite of his waffling on the subject of the vacuum did in fact develop the idea of momentum a little further. Little by little, Aristotle's stranglehold on the science of the 16th century and beyond, was being whittled away. Slowly but surely the idea that the Bible was the last word on all matters of science was successfully challenged.

In future essays we'll continue to deal with the development of modern physics where for example, repeatable experiment became the arbiter of scientific fact.

• History of Physics Newsletter. American Institute of Physics.
• History of Physics. From Wikipedia.

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