History of Science
ca. 800 BC-500 AD
|Thales (fundamental substance);
Aristotle (geocentric universe) > Ptolemy (refined Aristotelian universe)
|Dark Age stagnation;
later medieval recovery of Greek learning and absorption of Asian learning
Galileo (telescope observations, mechanics), Kepler (laws of planetary motion);
Newton (complete formulation of classical mechanics)
|modern atomic theory (Dalton),
|Lavoisier (precise measurement)||Darwin (evolution),
|subatomic chemistry||tiny-scale biology|
Science can be defined as "the study of how something works". The term generally denotes the natural sciences, which are concerned with the physical world (as opposed to the social sciences, which are concerned with human interaction). "Science" is a young term; until the nineteenth century, the field was referred to as natural philosophy.
Scientific knowledge is accumulated via the scientific method, which consists of three parts: observation (one sees something working), hypothesis (one formulates a logical theory about how it works), and testing (one searches for objective evidence of the theory). Evidence is objective if it can be physically observed or measured; any other sort of evidence (e.g. scripture, traditional belief) is unacceptable. Although the scientific method seems obvious today, pre-modern science was burdened with an abundance of false theories, due to lack of rigorous demand for objective evidence.
The mature scientific method only emerged during the Enlightenment (ca. 1650-1800; see Enlightenment), which overlaps with the final decades of the Scientific Revolution (ca. 1500-1700). Though earlier Western science (dating back to ancient Greece) featured observation and hypothesis, rigorous testing was not conducted, allowing many evidence-less theories to persist.A309-12,4
Technology may be defined as "the practical application of science".
The natural sciences are often divided into two branches: physical sciences and life sciences.
|life sciences (biology)|
The physical sciences are often divided into four branches: physics, chemistry, astronomy, and earth sciences. Physics is the study of matter and energy; thus, all science is ultimately physics. Chemistry is the study of pure substances (elements and compounds) and how they react.
The other two branches of physical science are defined by the region they investigate. The earth sciences study everything that comprises our planet, while astronomy is the study of everything outside Earth's atmosphere; thus, astronomy and earth sciences are simply the application of physics and chemistry to their respective regions. Earth sciences may be divided into three types: geology (solid earth), hydrology (water), and atmospheric sciences (the atmosphere).
Biology (aka the "life sciences") is the study of life. More specifically, biology is the application of physics and chemistry to life forms.
Biology can be divided into anatomy (the study of the structure of living things) and physiology (the study of the functioning of living things). Alternatively, the field can be organized by taxonomic kingdom: zoology (the study of animals), botany (the study of plants), mycology (the study of fungi), and so on. The most immediately practical life science is medicine (the study of health and healing).
For the amateur scholar, mathematics may be defined as "the study of numbers". Numbers are not part of the physical world; they are simply a way of describing it. Mathematics is therefore the abstract science, rather than a natural science. Mathematics serves as the language of all other sciences.
Mathematics can be reduced to three basic fields: algebra, geometry, and calculus. Algebra is the study of generalized operations. (An operation is the production of a new number from input numbers, e.g. 2+2=4; algebra generalizes operations by using symbols to represent numbers, e.g. a+a=2a.)
Geometry is the study of shapes and spaces. Calculus is the study of continuous change (e.g. the changing position of a moving object, or the changing speed of an accelerating object). While algebra and geometry date to antiquity, calculus was only invented during the Scientific Revolution (by Isaac Newton and Gottfried Leibniz, independently).
The Math-Physics Foundation
From antiquity to the Scientific Revolution (ca. 1500-1700), most scientific progress took place in mathematics and physics.A308 These two fields naturally flourished together, as ancient and medieval thinkers observed physical phenomena (e.g. planetary motion) and attempted to describe them with numbers. This symbiosis culminated in the Scientific Revolution, during which understanding of physics and mathematics surged to unprecedented heights, cresting with Newton's formulation of classical mechanics and invention of calculus.
The mature scientific method finally emerged amidst the mathematics and physics of the Scientific Revolution, causing progress to become permanently rapid in all scientific fields. Thus did mathematics and physics serve as the launchpad of modern science. This fact is reflected in the structure of this article, which focuses mainly on physics up until the Scientific Revolution, then branches out to include chemistry and biology.
Astronomy and mathematics were the first sciences of all ancient civilizations. The great astronomer-mathematicians of antiquity included the Mesopotamians, Chinese, Indians, Greeks, and Maya.4
Two kinds of science emerged in the pre-modern world. The most common was observational science, in which natural phenomena are carefully observed and described, but not logically explained. (In other words, only one part of the scientific method is practised: observation.) While observational science enabled profound scientific discoveries and impressive technological advances, explanations for natural events (if developed at all) were limited to arbitrary supernatural forces.4
Theoretical science, on the other hand, takes the additional step of providing logical explanations for natural phenomena. (Thus, hypothesis is practised in addition to observation.) Natural events are described in terms of universal laws; if gods or magic are included in the description, they are nonetheless subject to these laws. Only once in history did theoretical science firmly develop: in ancient Greece (see Greek Awakening).4
The equivalent is true of mathematics: while various civilizations garnered impressive mathematical knowledge, theoretical mathematics was only devised by the ancient Greeks. In theoretical mathematics, a set of axioms (fundamental assumptions) is established, from which general theories are logically derived. In non-theoretical mathematics, mathematical laws are only guessed at via repeated observations; they cannot be proven.26
Consider the Pythagorean theorem, which states that for a right angle triangle with sides a, b, and c (c being the diagonal), a2+b2=c2. This relationship might be noticed via repeated observation, by drawing several triangles of different sizes, then measuring and comparing the sides of each. Yet it would remain unknown whether the relationship always holds true; this knowledge can only be obtained through the reasoned proofs of theoretical mathematics.
It should be emphasized that the ingenuity and technological advances of non-Western science, and their importance for Western progress, were immense; this was indeed true from the very start, given that the ancient Greeks inherited a large body of mathematical and astronomical knowledge from Mesopotamia. The most extraordinary non-Western technological achievements are those of China, which early in its history rose to global technological supremacy, remaining there until the Early Modern age.4 During the medieval period, Europe tapped an invaluable flow of technology and mathematical/scientific knowledge from China, India, and the Islamic world.
The birth of Western science (i.e. theoretical science) can be traced to the Archaic period (ca. 800-500 BC) of ancient Greece, when thinkers began to ponder a simple question: "is there a fundamental substance from which all matter is composed?". The first person to explore this question was apparently Thales, who argued that this substance is water.4 Thales, who we would describe today as a physicist, mathematician, astronomer, and engineer, thus founded the field of physics, and is known as the father of Western science.
Thales was followed by other philosophers who argued in favour of other elements. Eventually, the notion of a single fundamental substance was joined by various multiple-element systems, including the four classical elements (air, water, earth, fire), which remained an influential theory until the Scientific Revolution. The degree to which something is hot/cold and wet/dry was explained by the proportions of these elements.4
Some Greek theorists even argued that the material world is made up of tiny particles called atoms, and that the various materials and phenomena of the material world are explained by simple differences among these particles (e.g. size, motion, configuration). Atomism would remain a minority scientific position, however, until it was conclusively proven in the modern age.
Greek science continued to develop throughout the Classical period, then peaked during the Hellenistic age and early Roman period. (During the Hellenistic and Roman periods, the leading centre of Greek science was Alexandria.) Major fields of inquiry included geometry, algebra, astronomy, mechanics, anatomy, and medicine; thus was the foundation of Western science established. (The Romans showed little interest in theoretical science, though they did eagerly pursue technological advances.)4
The leading scientific figure of Classical Greece was Aristotle, who performed detailed studies of animals and developed a refined system of classifying life, such that he is often considered the father of biology.4 He also developed a model of the universe based on the four classical elements. According to this model, the elements naturally strive to occupy different levels: earth at the centre, water above earth, air above water, and fire above air.15
The heavenly bodies are made of a fifth, divine substance called ether.15 Aristotle reasoned that a divine substance could only have “perfect motion”, which he defined as a circle; therefore, the heavenly bodies must have circular orbits around the Earth.4 His model is thus geocentric (“Earth-centred”).
Though Aristotle’s model gained widespread acceptance, it clashed with astronomical observation. Ptolemy, a Roman-age Greek scientist, addressed this problem by introducing several embellishments; for instance, he argued that each planet moves in a small circle (an epicycle) while moving along its orbit (see topmost animation). The Ptolemaic model, which had much-improved predictive power, would not be overturned until the Scientific Revolution.
In the Dark Ages (ca. 500-1000), scientific progress essentially ceased in Europe, as the continent became overwhelmingly preoccupied with religious matters. Some ancient knowledge was preserved in the monasteries of Western Europe and more in the libraries of the Byzantine Empire, but the true successor to classical science was the Islamic world, which absorbed much Greek learning (particularly from Alexandria) and proceeded to expand upon it in every field. Islamic advances in mathematics and chemistry, for instance, are reflected in the familiar terms “algebra” and “alkali”, both from Arabic.2,4
With the recovery of Western Europe in the later Middle Ages (ca. 1000-1500), Islamic advances (as well as much original Greek work that had only survived among the Arabs) were absorbed.4 Europe also enjoyed the transmission of East and South Asian advances via the Muslim world. The Hindu-Arabic numeral system originated in India, where the invention of zero had made the system possible; the name “Hindu-Arabic” reflects the development of the system in India and the subsequent modification of its ten symbols as it passed through the Arab world. From China, two critical inventions arrived: gunpowder and paper, both of which dramatically accelerated the course of Western history.1
In Western Europe itself, theoretical science was stifled during the later Middle Ages by obsession with making scientific theory compatible with theology. On the other hand, various important practical advances were made, including the mechanical clock, wind and water mills, and the printing press. Indeed, without the printing press (to rapidly distribute scientific advances to thinkers across Europe), modern science might never have emerged. By the end of the Middle Ages, the stage was set for the Scientific Revolution.2,3,4
The overarching triumph of the Scientific Revolution was the development of the mature scientific method. This period also gave rise to the first scientific societies, most notably the Royal Society of London and the Académie des Sciences of Paris.4
The leading figures of the Scientific Revolution (ca. 1500-1700) are four astronomers. Copernicus lived at the beginning of this period, while Galileo and Kepler are found in the middle. The late Scientific Revolution is crowned with the career of Isaac Newton.
The birth of the Scientific Revolution is often traced to Copernicus, who finally refuted the Ptolemaic universe with the first convincing model of heliocentrism, thereby becoming the “father of modern astronomy”.3 Heliocentrism asserts that the Earth orbits the sun (causing the seasons) and rotates (causing day and night). This model was only gradually accepted, meeting with both scientific and (especially) theological resistance.
Theologically, the heliocentric model was considered unacceptable as it diminished Earth’s apparent importance in the universe. If Copernicus was right, not only was the Earth not at the centre of everything, it was also a tiny ball of matter in the midst of staggeringly vast space. If the Earth is in constant motion around the sun, then at night the stars should appear to be constantly moving; the only alternative explanation is that the stars are so incredibly far away that they don’t appear to move.4
The chief scientific objection to the heliocentric model was that if the Earth is spinning, everything on the planet’s surface should be hurled into space.4 The answer to this argument is, of course, gravity: the gravitational pull of the Earth far exceeds the outward force exerted by the planet’s rotation. But the force of gravity would not be identified until Newton.
The first person to study the heavens via telescope was Galileo Galilei.12 Galileo’s observations helped to further discredit the Ptolemaic model by demonstrating that other heavenly bodies are not so unlike the Earth: they have their own geography (e.g. the moon has rugged craters; it is not a smooth sphere of divine substance), and other planets have moons of their own (e.g. Galileo discovered the moons of Jupiter; this conflicted with the Ptolemaic model, in which all heavenly bodies orbit the Earth). Galileo also observed the phases of Venus, proving that this planet orbits the sun.K266-67,4
Galileo was also the leading scientist in the field of mechanics (the study of moving bodies) prior to Newton. Most famously, he demonstrated that weight does not affect how fast an object falls. He also proved that the path of a projectile is a parabola, thus overturning the prevailing belief that a projectile moves in a straight line until it runs out of momentum, then falls straight down.16
Johannes Kepler advanced the heliocentric model by finally developing an accurate description of planetary orbits, summarized in three laws.4 One: the path of each planet’s orbit around the sun is an ellipse (not a circle). Two: the speed of a planet’s orbit increases as it gets closer to the sun. Kepler’s third law is the proportional relationship between the size and period of a planet’s orbit.
Yet the very force that causes planets to orbit the sun (gravity) remained a mystery. The most influential theory prior to Newton was that space is filled with some kind of invisible matter (which, borrowing Aristotle’s term, was referred to as “ether”) and that whirlpools in this matter sweep the planets along. This explanation was dispelled by Isaac Newton, whose three laws of motion and universal law of gravitation explained not only the motion of the planets, but of all physical objects.4
Newton’s laws provide a complete description of the mechanics of everyday experience, also known as classical mechanics. They only cease to hold true at extreme physical scales, whether very large (when relativity applies) or very small (when quantum theory applies).
|first law||a stationary object will remain stationary, and a moving object will continue
to move (at the same constant speed), unless a force is applied
|second law||applying force to an object will cause the object to accelerate
(at a rate equal to force divided by mass)
|third law||for any exerted force, an equal and opposite force is exerted|
|all objects exert attracting force on other objects, the strength of which increases
with the mass of each object and decreases with the distance between them
Newton described these laws in the Philosophiae Naturalis Principia Mathematica (often referred to simply as the Principia), arguably the most important scientific document ever written. It contains the laws described above, as well as descriptions of those laws using calculus, which Newton was compelled to invent.
In addition to revolutionizing physics and mathematics, Newton was a leading figure in developing and propagating the mature scientific method. (Francis Bacon, it may be noted, was another key English proponent of meticulous observation and experiment.) In short, Isaac Newton is the leading figure of the Scientific Revolution, and is often considered the foremost scientist of all time.4,13
Wave Theory of Light
Newton did eventually lose support for one major argument, however, when his assertion that light is composed of particles was superseded by the wave theory of light.1
A wave is simply a “moving disturbance” (see video). Imagine a sealed transparent tube filled with marbles (with a small amount of wiggle room); if one end of the tube is struck, the marbles at that end of the tube will strike the marbles next to them, which strike the marbles next to them, and so on. The disturbance will travel the full length of the tube, though the particles (represented by the marbles) will return to their original positions after the wave has passed. This is how sound waves travel through the air; the air particles are like marbles (see topmost animation).
All waves obey a number of physical laws (e.g. reflection, refraction); as it became clear that light obeys these laws, the wave theory of light prevailed. Yet a wave cannot exist without a medium to travel through, and scientists needed an explanation for how light could travel through space. Thus, even though the theory of swirling ether (to explain the motion of the planets) had been abandoned, the notion of ether itself (an invisible form of matter filling all space) was retained.
The notion of light as a disturbance travelling through ether persisted all the way to the twentieth century. Today, light waves are understood to be disturbances in an electromagnetic field; the waves themselves generate this electromagnetic field, such that are self-propagating. (As an analogy, consider a wave travelling along the surface of the ocean. This wave can only travel as far as the ocean lasts; when it reaches the shore, it will crash. If it were self-propagating, however, it would constantly generate a stretch of water in front of itself, allowing it to travel an infinite distance.)
During the classical age of science (ca. 1700-1900), scientific fields matured into their recognizably modern forms. The profession of scientist finally emerged, with the development of educational programs devoted to science and sharp increases in government funding; previously, scientific progress had depended mainly on the work of independently wealthy individuals. The Industrial Revolution played a central role in driving scientific progress, as scientists took up the challenges of developing new technologies (and new technologies, in turn, allowed the natural world to be explored more deeply and accurately than ever before).4
Classical physics can be summed up in three primary advances: modern atomic theory, thermodynamics, and electromagnetism.
The easiest to explain is modern atomic theory, founded by John Dalton. Dalton proved that all matter is made up of elements (which cannot be separated into simpler substances), and that atoms of these elements differ by mass alone.4
Thermodynamics is the study of the conversion of heat into work. This field, which emerged as scientists attempted to improve the efficiency of steam engines, gave rise to the three laws of thermodynamics. The first two were worked out during the classical age, while the third was added in the twentieth century.24
|first law||the total amount of energy in an isolated system is constant
(energy cannot be created or destroyed)
|second law||the entropy of an isolated system increases over time,
until its temperature is the same throughout
|third law||if heat is extracted from a system, its entropy decreases, approaching zero
entropy as the temperature of the system approaches absolute zero
An isolated system is a region of the universe which is sealed off, such that no matter or energy can enter or escape. It is simply a helpful imaginary concept, though it does describe the universe as a whole.
One property of a system is entropy, which denotes the amount of “chaos” in the system. There are two ways of looking at physical chaos. One is total energy: the more energy a system has (i.e. the hotter it is), the more violently particles bounce around, and thus the higher the system’s entropy. The other is the degree to which energy is evenly spread throughout a system. When energy is neatly organized into distinct sections (e.g. a cold ice cube in a warm glass of water), entropy is low. As this organization breaks down (e.g. as the ice cube melts) and energy becomes more evenly spread, entropy rises.
Electromagnetism is the relationship between electricity, magnetism, and light. It was worked out by various scientists during the classical age of science, especially James Clerk Maxwell, who produced a set of four equations (known as “Maxwell’s equations”) that describe this relationship.1 Maxwell is thus often hailed as the “Newton” of the classical age of science.
One of the fundamental properties of nature is that an object can have an electric charge. Objects with opposite charges attract one another, while objects with like charges repel one another. This force of attraction/repulsion is referred to as electric force; the region in which this force can be felt is called an electric field.
When a charged object moves, it generates a magnetic field (in addition to its electric field). A magnetic field, which is neither positive or negative, has a north pole and a south pole; when two magnetic fields come into contact, opposite poles attract while like poles repel. This force of attraction/repulsion is magnetic force.
The nature of electromagnetism may be summed up in three statements. One: a stationary charged object generates an electric field. Two: a moving charged object generates a magnetic field, which combines with the electric field to form an electromagnetic field. Three: light waves are disturbances in an electromagnetic field; these disturbances are caused when a moving charged object changes speed (i.e. accelerates or decelerates).
Due to heat energy, all particles constantly vibrate. A charged vibrating particle constantly produces disturbances in its electromagnetic field; thus, all matter constantly emits light, though most is not visible to the human eye. The hotter particles are, the faster they vibrate, and the higher frequency light they produce.
Frequency refers to the spaces between waves. When waves are emitted rapidly, the spaces between them are small, and thus their frequency is high (e.g. X-rays); likewise, when waves are emitted slowly, their frequency is low (e.g. radio waves). Visible light lies in a narrow range of frequencies toward the middle of the spectrum.
Classical Chemistry and Biology
The leading figure of classical chemistry is Antoine Lavoisier, the "father of modern chemistry", who led the charge in making chemistry a field of precise measurement. This allowed him to discover the law of conservation of mass, which states that the mass of the products of a chemical reaction is equal to the mass of the reactants. Perhaps his other most famous discovery is that combustion is a reaction between a substance and oxygen.4
Classical biology, meanwhile, featured two exceptional figures.
Louis Pasteur, the "father of microbiology", proved that microscopic life only arises from reproduction; it does not arise from non-living matter, as claimed by the prevailing theory of "spontaneous generation". He demonstrated that both fermentation and food spoilage is caused by microscopic organisms, and showed that heat treatment (aka pasteurization) could prevent the latter. He also played a leading role in the development of germ theory (which asserts that diseases are caused by microscopic life) and vaccinations.1
Meanwhile, Charles Darwin founded evolution theory. While evolution was an old concept (dating back, like so many things, to ancient Greece), Darwin gave it a scientific basis via meticulous observational studies and identification of a mechanism by which evolution could occur. This mechanism was natural selection, which asserts that a species evolves more favourable characteristics over time as individuals with better-adapted characteristics survive to reproduce.4
As the classical age of science drew to a close, it was beginning to look as though scientists had completely unravelled the workings of the physical world. This illusion was shattered ca. 1900, when the discovery of the electron advanced science to the subatomic level; soon after came the discovery of radioactivity (unstable atoms that crumble into smaller atoms, giving off energy in the process).4 Further exploration into the subatomic world has yielded the standard model, which asserts that all matter is comprised of quarks, leptons, and bosons.
During the early twentieth century, two pillars of modern physics were erected: quantum theory and relativity. While the former was developed by numerous scientists, the latter was primarily the work of Albert Einstein, the indisputable "Newton" of modern science.1
Quantum theory is the current explanation of how the universe works at extremely small scales. The theory asserts that energy exists in discrete packets, each of which is called a quantum (plural quanta). This was discovered when experiments showed that light (a form of energy) can only be absorbed/emitted (by an object) in discrete amounts; it cannot be absorbed/emitted continuously.
In this respect, light behaves as though it were composed of particles. Indeed, light is now described as having wave-particle duality, since it behaves like waves in some ways and like particles in others. It has since been discovered that all particles, and indeed all objects, exhibit wave-particle duality (although wave-like properties are negligible in all but the tiniest objects).9
The theory of relativity encompasses a number of unintuitive ideas, including that physical perception is relative to the speed of the observer (except for the speed of light in a vacuum, which remains constant for all observers), that time and space are connected (together forming the unified phenomenon of spacetime), and that energy and mass are convertible (expressed in the equation E=mc2).
Modern chemistry and biology have been dominated by advances at very small scales. Understanding of the subatomic level has allowed chemical reactions to be explained in terms of the formation and breakage of electromagnetic bonds between particles.1 Biology has also been extended to extremely small scales, enabling the rise of molecular biology (including the discovery of DNA) and exploration of the world's tiniest life forms (including viruses).
2 - "Science", Encarta 2004.
3 - "Physical science", Encyclopedia Britannica. Accessed March 2010.
4 - "History of science", Encyclopedia Britannica. Accessed March 2010.
5 - "Sir Isaac Newton", Encyclopedia Britannica. Accessed March 2010.
6 - "Galileo Galilei", Encyclopedia Britannica. Accessed March 2010.
7 - "Relativity", Encarta 2004.
8 - "Quantum theory", Columbia Encyclopedia. Accessed March 2010.
9 - "Quantum theory", Encarta 2004.
10 - "Energy", Encyclopedia Britannica. Accessed March 2010.
11 - "Four Great Inventions of ancient China", Wikipedia. Accessed March 2010.
12 - "Telescope," Encyclopedia Britannica. Accessed March 2010.
13 - "Sir Isaac Newton", Columbia Encyclopedia. Accessed March 2010.
14 - "Robert Boyle," Encyclopedia Britannica. Accessed March 2010.
15 - "Aristotle", Wikipedia. Accessed March 2010.
16 - "Galileo", Columbia Encyclopedia. Accessed March 2010.
17 - "Robert Boyle," Columbia Encyclopedia. Accessed March 2010.
18 - "Microbiology", Encarta 2004.
19 - "Heat," Encyclopedia Britannica. Accessed March 2010.
20 - "Entropy", Columbia Encyclopedia. Accessed March 2010.
21 - "Archimedes", Encarta 2004.
22 - "Galen", Encarta 2004.
23 - "Robert Boyle", Encarta 2004.
24 - "Thermodynamics", Wikipedia. Accessed March 2010.
25 - "Philosophy", Encarta 2004.
26 - "Mathematics," Encyclopedia Britannica. Accessed March 2010.