"The study of an idea is, of necessity, the story of many things. Ideas, like large rivers, never have just one source. Just as the water of a river near its mouth, in its final form, is composed largely of many tributaries, so an idea, in its final form, is composed largely of Iater additions." -Willy Ley (1906-1969)
When the Greek scientist Archimedes screamed "Eureka! I have found it!" he was running through the streets of Syracuse naked. His exuberance came about when he realized how to measure whether King Heiros’s crown was pure gold or a mix of gold and silver. He’d conceived of a test while in the bath, after observing that his body displaced water. Since gold is denser than silver, he reasoned, a mixed crown would displace less water, and that’s what happened when he tested the method that became known as Archimedes’ Principle. Although the idea was new, it was not a fluke. The big ideas that guide science come from a combination of careful observation and the thought processes that interpret the observation.
The history of science is filled with big ideas that become the starting point of a series of research projects that may span centuries. Each researcher adds another observation, another hypothesis, a new test, or even a new theory about the idea. The ideas in this chapter are not necessarily more important or encompassing than other big ideas. They are presented as examples of how science grows from an initial idea to one or more major theories.
Atoms
At the heart of our understanding of matter is the concept of the atom—the smallest particle of an element that has the properties of the element. The word "atom" is of Greek derivation, from atomos, meaning "indivisible," or more specifically a meaning "not" and tomos meaning "cuttable."
One ancient Greek view of the atom was proposed by the philosopher Democritus. According to Democritus, any substance could be cut in half, and then halved again and again, until the point where no further division was possible. Since these atoms were thus "uncuttable," they held the basic nature of each substance. An atom of gold, for example, when revealed in its essence, would be dense, malleable, and smooth to the touch, like anything made of pure gold. The atom might also have edges, so that it would fit together with like atoms and thus form a solid metal. Atoms of air, in contrast, would be spaced widely apart and rather insubstantial in construction.
Democritus believed that everything in nature formed by random collisions of unseen atoms. There were atoms, and where there were no atoms, there was a void. The idea was not universally accepted among Greek philosophers. Aristotle, for example, thought that everything observable was composed of four elements: Earth, Air, Fire, and Water. These things had no atoms but were instead continuous. If the void existed, it would violate basic physical principles.
The Greek concept of the atom was not, however, a theory in the way that we use the term today. The tools and techniques to build experiments to test the idea did not exist. The ideas of Democritus and Aristotle competed, but they were essentially thought exercises. There were no scientific tests to support one over the other.
The "uncuttable" atom that the Greeks could not measure is now known to be about 300 millionths of an inch across. To put this in human and metric terms, the width of a human hair is about one-tenth of a millimeter, and the width of an atom is a millionth of the width of a hair.
Dalton’s Model of the Atom
In 1801, John Dalton presented a series of "Experimental Essays" to the Manchester Literary and Philosophical Society, of which he was a secretary. The papers were about the nature of gases. While studying properties of a wide range of materials, he determined that the ratio of elements in a compound is always the same, no matter how much of the material was analyzed. Dalton concluded that these fixed chemical combinations resulted from the interactions of atoms of various elements, each of which had a specific weight. He published a table of atomic weights, listing carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulphur, with the lightest atom, hydrogen, given the weight of 1.
Dalton proposed that all elements are composed of a basic unit, which he called an atom, from the Greek concept of a smallest unit of matter. All of the atoms of a given element are identical and had the same mass. When atoms of particular elements combined in specific ratios, compounds are formed. Chemical reactions involve the rearrangement of combinations of atoms. Although our understanding of atoms differs significantly from Dalton’s, his theory of atoms provides the basic concepts of modern atomic theory.
"The elements of oxygen may combine with a certain portion of nitrous gas or with twice that portion, but with no intermediate quantity."
Compared to the ancient Greeks, Dalton had a couple of advantages in developing his idea. The first was the development of the scientific method, which provided a structure to his investigations and a way to support his theory. The second was that a number of elements had been identified and methods to isolate and identify these elements had been developed. His idea of atoms of different elements being distinguishable by respective relative weights was a new and supportable concept.
How Atoms Look Today
Obviously, atoms in ancient times never looked any different than they do in the present, but the model began to change when Dalton proposed his atomic theory. Further developments in the modern view of atomic structure occurred in 1897 at Cambridge University in England when J. J. Thompson discovered the electron with its negative electrical charge. In 1913, Ernest Rutherford discovered that each atom has a positively charged core, or nucleus, which comprises 99 percent of the mass of the atom. The nucleus is itself made up of positively charged particles called protons and neutral particles (not electrically charged) called neutrons. A cloud of negatively charged electrons swirl around the nucleus. Each electron is around 2,000 times lighter than the lightest element, hydrogen.
According to the modern atomic theory, bonding between atoms is electrical, and separation between atoms is maintained by the balance of the forces of attraction and repulsion, similar to those demonstrated by the poles of magnets. When electrons are shared between atoms, a "covalent bond" is formed—"co" meaning "together" and "valent" referring to "valence," which is derived from the Latin valentia, meaning "strength or capacity."
The modern atomic model was further developed by Danish scientist Niels Bohr, who received the Nobel Prize in Physics in 1922 for the development of quantum mechanics. Bohr and others established the concept of the atomic orbital, which is a confined region of space around the nucleus. According to the Bohr model, there are clearly defined orbitals, representing different levels of energy, that an electron can occupy. For an electron to move from one orbital to another it must either absorb or emit a particle of light known as a photon. Chemical properties of an element are determined by the electrons orbiting the nucleus. Since the electrons are in constant movement, atoms cannot be thought of as "solid" in the sense of a wall in your house, but because the electrons move so fast, they can be modeled as a solid shell. In contrast to the indivisible solid atoms envisioned by Greek philosophers and by John Dalton, "modern" atoms are characterized by constant movement and change!
In Although a few gaseous elements, including helium and argon, normally exist as individual atoms, most of the elements do not. Some, such as hydrogen and oxygen, form molecules of two (or sometimes more) atoms. Most metals exist as arrays of many atoms arranged in a three-dimensional pattern.
Motion—Everything Moves Like Clockwork
While the Greek philosopher Aristotle made many discoveries through careful observation, his description of motion was later proved to be flawed. He proposed that a force is necessary to keep an object in motion and that the speed of a falling object is proportional to its weight. Although these ideas were accepted for almost 2,000 years, they were both disproved by the seventeenth century.
The first crack came with observations of objects in the sky by Polish nobleman Nicolaus Copernicus. His On the Revolution of the Celestial Spheres, often credited with beginning the Scientific Revolution, was published in 1543. In it Copernicus proposed that the sun, not Earth, was the center of the solar system. Based on this idea and careful observation of the planets, German astronomer Johannes Kepler developed his laws of planetary motion:
1. The orbit of every planet is an ellipse with the sun at one of the foci (foci being "focal points").
2. A line joining a planet and the sun sweeps out equal areas during equal intervals of time.
3. The squares of the orbital periods of planets are directly proportional to the cubes of the semi-major axis of the orbits.
Our modern understanding of motion came together with the publication in 1687 of Isaac Newton’s three laws of motion in his Philosophiae Naturalis Principia Mathematica:
1. Every object in a state of uniform motion remains in motion unless an external force is applied to it.
2. The acceleration of an object is equal to the force applied divided by the mass of the object.
3. When one object exerts a force on a second object, the second object exerts an equal and opposite force.
Fast Facts
Newton’s equation for motion is: Fnet = m x a. Fnet represents the total of all forces acting on an object. Mass is represented by m and acceleration is a. Thus, if you multiply the mass times the acceleration, you know the total of forces in play. This is important because to apply any of Newton’s laws of motion you need to know the net force.
These three laws form the basis of all of the science and engineering principles of motion. Newton’s laws of motion completely supplanted the idea that a force is needed to keep something moving.
Some people still believe, like Aristotle, that a force is necessary to keep an object in motion. This is directly contradictory to Newton’s first law of motion. For example, a meteor falling into Earth’s atmosphere does not run out of energy. The presence of the force of friction with Earth’s atmosphere causes it to slow. If our planet had no atmosphere, the meteor would not slow at all.
Gravity
It was Galileo Galilei who disproved Aristotle’s idea that heavier objects fall faster than lighter objects. Although most historians discount the story that he dropped objects of different masses from the Tower of Pisa, Galileo did determine that falling objects accelerate at the same rate, regardless of their mass. Isaac Newton later proposed an attractive force between Earth and other objects, which also acted between the sun and the planets.
The famous story of Newton under the apple tree and an apple falling on his head is probably not true, but by observing an apple fall he realized it went from zero acceleration to the speed when it hit the ground. What force caused the acceleration? It was not, as the ancient Greeks felt, a solid body seeking its "natural place." Newton realized that because of gravitational attraction, the moon was continually falling toward Earth, but its acceleration in orbit formed a balance. Based on these attractions between bodies, Newton developed the law of universal gravitation.
Gravitational force between two bodies whose masses were known was first measured by Henry Cavendish in 1798. Cavendish also discovered hydrogen, which he called "inflammable air" in his treatise "On Factitious Airs" in 1766. From 1797 to 1798, a Cavendish experiment was the first to measure gravity between masses—two 350-pound lead spheres and two 1.61-pound lead spheres. His aim was to determine the density of Earth. Although he did not get an accurate measurement, his work allowed others to do so later.
If you ever wondered why astronauts in orbit are weightless, it’s simple—they’re falling at the same speed of their spacecraft. The acceleration of the craft counterbalances the pull of gravity. And without the balance that gravity affords to objects in motion, the universe simply would not hold together. Had Newton not demonstrated that all bodies attract each other gravitationally and that the force depends on the product of two masses divided by the square of the distance separating them, no one would have ever had a space program.
There is a difference between the mass of an object and its weight. Mass is a measure of the amount of material that an object has. Weight is a measure of the gravitational pull on the object, so weight is proportional to mass. However, the weight of an object depends on its relationship to Earth or some other body. The weight of a person standing on the moon is about one-sixth the weight of the same person on Earth. The person’s mass, however, does not change.
Germ Theory
If you were to ask a number of medical experts to name the most important theory ever developed in medical science, it is likely that you would get the same answer from all of them: the germ theory of disease. While it may seem obvious today that many diseases are caused by microorganisms, the germ theory is actually a fairly recent concept.
As recently as 200 years ago, doctors had to work with no real understanding of the cause of illness or how it is transmitted from one person to another. Ancient explanations relied on the supernatural. Later explanations relied on spontaneous generation, the idea that living things can rise from nonliving matter. In this view disease was spontaneously generated instead of being created by microorganisms that grow and reproduce.
Although
it has been more than 150 years since Ignaz Semmelweis found that hand washing reduces the spread of infection, the message must be repeated frequently. A Johns Hopkins research team reported the results of a study in 2004, recommending that doctors wash their hands frequently and thoroughly in order to control the spread of methicillin resistant staph infections (MRSA).
Microorganisms were first directly observed by Anton van Leeuwenhoek, who is considered the father of microbiology, in the 1670s. The connection to disease did not come about for quite some time after his discovery, though. A major breakthrough occurred in 1847 when Ignaz Semmelweis, a Hungarian obstetrician, observed a high incidence of death from puerperal fever among women who delivered babies in hospitals, while the disease was relatively rare for home births. Recognizing that some sort of contagion was at work and that doctors might be transmitting the disease, he began insisting the doctors wash their hands before examining their patients. Fatalities from the disease dropped from 30 percent of births to 2 percent.
In the 1860s, Louis Pasteur demonstrated that fermentation and the growth of microorganisms in nutrient broths did not proceed by spontaneous generation. By heating the broth, he destroyed microorganisms and found that they did not begin growing again if the broth was sealed from contact with air. This process, known as pasteurization, is still used in the food industry. Further research led Pasteur to the discovery that certain diseases are caused by microorganisms.
About 10 years later, Robert Koch devised a series of experiments to verify the germ theory of disease. Koch demonstrated that anthrax was caused by the bacterium Bacillus anthracis.
The germ theory of disease proposes that microorganisms are the cause of many diseases. Although highly controversial when first proposed, it is now a cornerstone of modern medicine and clinical microbiology, leading to such important innovations as antibiotics and hygienic practices.
Even today, some diseases previously thought to be of genetic or environmental causes have been discovered to be caused by microorganisms. The human papilloma virus (HPV) is now known to be capable of causing cervical cancer. Hepatitis B or C has been shown to be a cause of liver cancer. The discovery that stomach ulcers are caused by a bacterium revolutionized the treatment of this disease.
The Gardasil vaccine, first approved for American use in 2006, was tested on 11,000 females aged 9 to 26 around the world before its release. Contrary to emotional opinions that arose when Governor Rick Perry of Texas made the human papilloma virus-fighting vaccination mandatory for girl students, there were no serious side effects noted during testing. In October of 2007 Great Britain made the HPV vaccine free for all women over age 12.
Evolutionary biologist Paul Ewald hypothesizes that many diseases not currently considered infectious are caused by microorganisms. For example, heart disease can be linked to Chlamydia pneumoniae, a bacterium known to cause pneumonia and bronchitis. He thinks that someday, many diseases currently thought to have a genetic cause may be curable by isolating and eradicating bacterial agents at the root of the problem.
"Surprisingly, neglect of the germ’s-eye view of the world is not restricted to the average person; it extends to medicine as a whole for most of its history. Only during the past twenty years have researchers emphasized the importance of looking at a germ’s evolutionary scorecard. This scrutiny is suggesting solutions to the most damaging problems of medicine as well as the most irritating. Both categories of problems are important."
Plate Tectonics
In 1912, Alfred Wegener, a German meteorologist, proposed that all the continents of Earth had once been joined in a supercontinent he named Pangaea. He presented various evidence including the ancient fern Glossopteris, which could be found in Africa, Australia, India, and South America. He showed rock strata similarities in these continents, as well as glaciation markings, and posited that shifts in the southern magnetic pole could only be accounted for by the gradual splitting of this giant land mass.
In 1962 it was proposed that Earth’s continents were composed of lithospheric (solid outermost layer) plates that move slowly across the asthenosphere, the hot rock zone in the upper mantle below Earth’s crust. Scientists determined that at midocean ridges, long cracks from which lava rises, the two sides move apart and thus plates diverge and have new material added to them.
In 1965, Canadian geophysicist J. Tuzo Wilson introduced the term "plate" to describe the broken segments of the former supercontinent. Two years later, American geologist W. Jason Morgan suggested that there are 12 plates making up Earth’s surface, and shortly thereafter French geophysicist Xavier Le Pichon published a paper revealing the location and type of plates and the direction in which they are moving.
The Big Bang
According to the most widely accepted theory of the beginning of the universe, the Big Bang theory, the universe began when all the matter of the universe exploded instantaneously from a single point. The "big bang" expansion from this point set in motion the process in which the universe expands and matter cools along the way. The big bang should not be conceived, however, as a phenomenon akin to a bomb going off. Instead it is an expansion that has been going on for billions of years and continues today. For the first million years or so of the universe’s existence, it was too hot for atoms to form. As the universe expanded, matter condensed into atoms which were pulled together by gravity to form the first stars and galaxies. Along with the expansion, the universe as a whole became cooler.
A fairly recent piece of evidence for the big bang is cosmic microwave background (CMB) radiation. CMB is a form of electromagnetic radiation that fills the whole universe. Characterization of the CMB indicates that the average temperature of the universe is about 3 degrees above absolute zero. This information has helped scientists determine that the universe is about 14 billion years old. Interestingly, the term "big bang" was first used in 1950 by astronomer Fred Hoyle, a critic of the theory. While he intended it to be a derisive term, it has since been adopted as the consensus name of the theory.
