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Democritus (l. c. 460 - c. 370 BCE) was a Greek philosopher and younger contemporary of Socrates , born in Abdera (though other sources cite Miletus) who, with his teacher Leucippus (l. 5th century BCE), was the first to propose an atomic universe. Democritus claimed that everything is made of tiny uncuttable building blocks known as atoms.

Very little is known of Leucippus, and almost none of his work has survived, but he is known by ancient writers as Democritus' teacher and apparently wrote on many subjects besides atomism. Democritus is known as the 'laughing philosopher' because of the importance he placed on cheerfulness. His work, like that of Leucippus, has been mostly lost, but later writers claim he wrote 70 books on topics ranging from farming to geometry, human origins, ethics, astronomy as well as poetry and literature , and fragments of his work are cited by later philosophers (notably Aristotle of Stagira (l. 384-322 BCE) who regarded him highly.

He was the first philosopher to claim that what people refer to as the 'Milky Way' was the light of stars naturally occurring and not the result of the actions of the gods, although, at the same time, he does not seem to deny the existence of spirits or the soul. Although his atomic theory makes clear that all things happen out of necessity – that one event naturally leads to the next – he maintained that people are responsible for their actions, that one must first consider the good of one’s soul over any other consideration, and that it was free will, not determinism, that directed one’s course in life.

He is considered one of the most important Pre-Socratic Philosophers (so-called because they pre-date and influenced Socrates of Athens (l. 470/469 - 399 BCE) who directly inspired Plato (l. 428/427-348/347 BCE) and the development of Western Philosophy . Democritus’ influence on Socrates is apparent in the fragments regarding ethics, but his concept of the atomic universe is also thought to have helped form Plato’s belief in an unchanging, eternal realm of which the visible world was only a reflection, at the same time his materialism challenged this very concept.

Democritus, in turn, was influenced by those who came before him, especially Parmenides of Elea (l. c. 485 BCE), Zeno of Elea (l. c. 465 BCE), and Empedocles (l. c. 484-424 BCE). The philosopher thought to make the greatest impression on him, however, besides his teacher Leucippus, was Anaxagoras (l. c. 500 - c. 428 BCE) who first proposed that all things are made up of "seeds" which cause them to be what they are. Democritus developed this "seed" theory into the concept of the atomic universe.

Travels & Reputation

Almost nothing is known of Democritus’ life. He is said to have been born and raised in Abdera and came from a wealthy family who was able to provide him with a good education. His father may have been Thracian nobility and was at least of the upper class. He may have studied with the philosopher Anaxagoras, though this is doubtful, but acquired a far-ranging education through travel and study with many masters.

When his father died, Democritus took his inheritance and left Abdera, traveling throughout the Mediterranean world and spending at least five years in Egypt studying mathematics before going south to Meroe . He is also believed to have stayed in Babylon and, according to the historian Diogenes Laertius (l. c. 180-240 CE), studied with the priests there. His association with Babylon, where the philosopher Thales of Miletus (l. c. 585 BCE) also studied, may be the reason why later writers claimed Democritus was from Miletus.

The precise route and order of his travels is unknown, but he said to have also studied in India and possibly in Persia before returning to Abdera. Once he was back home, he devoted himself to further study, research of the natural world, and writing . He was a prolific writer (over 300 fragments have been identified as his work) who is said to have authored 70 books which were all well-received. Scholar Robin Waterfield comments:

Democritus covered not only familiar Presocratic chestnuts such as embryology and why magnets attract iron, but also wrote books on mathematics and geometry, geography, medicine , astronomy, and the calendar, Pythagoreanism, acoustics and other scientific topics, the origins of humans and animals, and even literature and prosody. Importantly, it is also clear that not only did he cover this wide range of topics, but he covered them in some depth – for instance, by raising and answering possible objections. He was therefore an important bridge between the dogmatism of many of the Presocratics and the fully fledged philosophy of Plato. (164)

As Democritus himself would say, “nothing comes from nothing” and he was clearly influenced by the Presocratic Philosophers who came before him. It is unclear how deeply Leucippus influenced him as nothing is known of this philosopher outside of his association with Democritus. Only two fragments of Leucippus’ work have survived, and the only complete sentence is his famous “Nothing happens at random; everything happens out of reason and by necessity” (Baird, 39). As this concept is later echoed by Democritus, it is probable Leucippus had a significant impact on his thought, but it is certain he, and most likely Leucippus, was influenced by Parmenides, Zeno of Elea, Empedocles, and Anaxagoras.

Philosophic Influences

Parmenides claimed that all of reality was of single substance and people only recognized duality in the world because they trusted in sense experience, which was faulty and could lead one into error. Trusting in one’s senses, one accepted changes and differences in life as the true nature of reality but this, according to Parmenides, would be a serious error because change was an illusion. One’s outward appearance might change and one’s circumstances but not one’s essence.

To Parmenides, that which is has always been and is unchangeable in its actual underlying form. That which is perceived as mutability, and change is a lie of the senses which separate one from knowledge of the self and true reality. Parmenides’ student Zeno of Elea defended his master’s claim through 40 mathematical paradoxes proving that change, and even motion, was an illusion. Zeno proved, mathematically, that if one wished to walk from Point A to Point B, one would first have to walk halfway and, before one reached the halfway mark , one would have to walk halfway to that and so on. One could never, therefore, actually walk from Point A to Point B, and the claim that one could was simply a lie of the senses.

Zeno used this paradox to show how reliance on sense perception separated one from actual reality, from the essence of what makes the world what it is and allows it to operate as it does. To these two philosophers, there did not need to be a First Cause for existence or a 'meaning' to any of it; that which was had always been and would always be.

Empedocles drew on this concept in claiming that the underlying form of the universe was love, a transformative and regenerating force expressed in the coming together and pulling apart of natural forces which produced the four elements that then informed everything else. Empedocles’ insistence on a single, unifying, force inspired Anaxagoras’ claim that all things are comprised of particles (which he called "seeds") which were all of the same substance but, arranged differently, produced different results, sometimes a human, sometimes an animal, a tree, grass, a mountain, a bird.

Like Parmenides, Anaxagoras believed the essence of reality was One, but this One was expressed in Many. For this to be so, there had to be something underlying every single aspect of the visible world and this "something" was "seeds" which, in a given arrangement, produced now one and now another visible phenomenon.

Anaxagoras and his seed-theory is the immediate inspiration for the atomic theory of Leucippus and Democritus. Waterfield explains:

Anaxagoras had argued that the natural substances which are the basic building-blocks of things were infinitely divisible: however much you divide a piece of wood, it will remain wood all the way. But it was presumably Leucippus, as the earliest of the atomists, who made an intuitive leap of genius and proposed that the world was ultimately made up of things which do not have qualities, as wood does. He said that if you were to continue to divide anything, at some point you would reach things which are not further divisible – they are atoma , indivisible. (165-166)

Waterfield credits Leucippus with this realization in keeping with the tradition that Leucippus was Democritus’ teacher – and it may well be that it was Leucippus who first came to this conclusion – but, if so, it was Democritus who developed it fully.

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The Atomic Universe

In response to Parmenides' claim that change is impossible, and all is One, and Anaxagoras’ seed theory, Democritus tried to find a way to show how change and motion can be while still maintaining the unity of the underlying essence of the physical world. Democritus argued that everything, including human beings, is composed of very small particles which he called atomos ("uncuttables" in Greek), and that these atoms make up everything we see and are. Atoms were all of the same essence, but when "hooked together" in different ways, they formed different entities and visible phenomena.

Democritus claimed that, when one is born, one’s atoms are held together by a body shape with a soul inside, also composed of atoms, and while one lives, one perceives all that one does by an apprehension of atoms outside of the body being received and interpreted by the soul inside of the body. So when atoms have been combined into one certain form, a person looks at that form and says "That is a book", and when they have been combined in another, a person says "That is a tree", but however these atoms combine, they are all One, "uncuttable", and indestructible. When one dies, one’s body shape loses energy and one’s atoms disperse as there is no longer a soul inside the corpse to generate the heat that holds the body-shape atoms together. According to Aristotle, Democritus claimed the soul was composed of fire-atoms while the body was of earth-atoms and the earth-atoms needed the energy of the fire for cohesion. Still, Aristotle also asserts, this did not mean these atoms were different atoms, rather that they were like letters of the alphabet which, though they are all letters, stand for different sounds and, combined in various ways, spell different words. To use a very simple example, the letters 'N', 'D' 'A' can be combined to spell the word 'and' or, with a different combination, spell the name 'Dan', which, while it has a different and distinct meaning from 'and' is still made up of the same letters.

Though there have been some claims made by materialists that Democritus' atomic view of human life denies the possibility of an afterlife, this is not necessarily true. As Democritus seems to have viewed the soul as causing motion and even life and that thought was the physical movement of indestructible, "uncuttable" atoms, it is possible a soul, even defined along materialist lines, would survive bodily death .

Democritus nowhere speaks of a "meaning" to life, however, outside of maintaining a cheerful disposition. Life, for him, did not need to be given a meaning whether while one lived it or in another realm that followed because the essence of life had always been and would always be; the meaning of existence was simply existence.

In Democritus’ philosophy, one was born, lived, and died according to the coming together and dispersal of atoms. One might ask "What caused this event to happen?" and then define the cause of, say, an accident, but one was not encouraged to ask "Why did this happen?" in hope of some higher meaning. The famous line by Leucippus ("Nothing happens at random; everything happens out of reason and by necessity") is a concept which informs a great deal of Democritus' own writing especially his claim that "Everything happens according to necessity" in that atoms operate in one certain way and so, of course, that which happens in life does so out of the necessity of this operation whether one likes it or not.

While this claim would seem to deny the possibility of human free will, Democritus wrote extensively on ethics and clearly believed one could make free-will choices within the parameters of atomic determinism. Even though one was formed of these indivisible particles, both outwardly as a body, and inwardly as a soul, and these atoms came together and broke apart according to their own natural function, one still had control over one’s choices in life and was responsible for those choices. Professor Forest E. Baird comments:

Both the soul and the body are made up of atoms. Perception occurs when atoms from objects outside the person strike the sense organs inside the person which, in turn, strike the atoms of the soul further inside. Death, in turn, is simply the dissipation of the soul atoms when the body atoms no longer hold them together. Such an understanding of the person seems to eliminate all possibility of freedom of choice and, indeed, the only known saying of Leucippus is "Nothing happens at random; everything happens out of reason and necessity." Such a position would seem to eliminate all ethics: if you must act a certain way, it seems futile to talk about what you ought to do. (39)

Democritus addresses this objection, however, in stipulating that one is still responsible for what one does with one’s body and soul because a human being is able to distinguish between “right” – which Democritus associates with pleasures of the mind – and “wrong” – defined as sensual pleasures pursued without regard for consequences. Democritus recommended setting moderation in all things as one’s guide in order to maintain a balanced life. There was nothing inherently wrong in pursuing sensual pleasure, money, or power but one needed to recognize that these pleasures were fleeting and, if pursued without that recognition or without moderation, would lead to suffering.

Ethics, to Democritus, seems to have been primarily a means by which one lived a contented and composed life by recognizing the ultimate futility of trying to make life more than it is. In recognizing that everything is made of atoms which one has no control over, and responding to others in the same situation with compassion and cheerfulness, one could live free of the worry over "meaning" in life and concentrate on simply living.

The circumstances and precise date of Democritus’ death are as unclear as most of the events of his life, but it is well-established that he was highly regarded as an original thinker and writer while he lived and was clearly respected and often cited afterwards. He contributed significantly to the philosophical foundation which would be developed by Plato and did so by synthesizing and defining concepts previously suggested by other philosophers. Democritus did this in such a way that he is regarded by many in the present day as the "first scientist" as his thought and apparent method contributed to the development of that discipline.

His influence over the Greek and Roman writers who followed him is apparent not only in their philosophies but their references to him and his influence was clearly far-reaching and significant. Baird notes:

Democritus’ philosophy is important for at least two reasons. First, while atomism represents still another pluralistic answer to Parmenides, and while Leucippus was a Pre-Socratic, nevertheless Democritus was actually a slightly younger contemporary of Socrates and an older contemporary of Plato. Hence, Democritus’ atomistic materialism may be viewed as an important alternative to Plato’s idealism. Second, Democritus’ thought continued to have an impact, being taken up first by Epicurus and then, in Roman times, by Lucretius. (40)

The famous hedonist philosopher Epicurus (l. 341-270 BCE), in fact, drew on Democritus’ thoughts on pleasure in claiming that it was the chief good and end one should pursue in life. Democritus’ insistence on cheerfulness as the best response to life is mirrored in Epicurus’ philosophy, and both advocated moderation as the best means by which pleasures should be pursued and life lived to its fullest.

Epicurus, however, is only one of many who were influenced by Democritus’ work from ancient times to the present. Thinkers and writers in the modern day have expressed their admiration for Democritus as well as acknowledging their debt to him, and he remains as highly regarded today as he was during his own time.

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Bibliography

• Baird, F. E. Philosophic Classics: Ancient Philosophy . Routledge, 2010.
• Diogenes Laertius. Diogenes Laertius. Loeb Classical Library, 1925.
• Freeman, K. Ancilla to Pre-Socratic Philosophers. Harvard University Press, 1983.
• Guthrie, W.K.C. A History of Greek Philosophy. Cambridge University Press, 1979.
• Robinson, J. M. An Introduction to Early Greek Philosophy. Houghton Mifflin School, 1968.
• Waterfield, R. The First Philosophers: The Presocratics and the Sophists. Oxford University Press, 2009.

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Mark, J. J. (2021, May 26). Democritus . World History Encyclopedia . Retrieved from https://www.worldhistory.org/Democritus/

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Mark, Joshua J.. " Democritus ." World History Encyclopedia . Last modified May 26, 2021. https://www.worldhistory.org/Democritus/.

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The atomic philosophy of the early Greeks

The emergence of experimental science.

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Development of atomic theory

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• Table Of Contents

The concept of the atom that Western scientists accepted in broad outline from the 1600s until about 1900 originated with Greek philosophers in the 5th century bce . Their speculation about a hard, indivisible fundamental particle of nature was replaced slowly by a scientific theory supported by experiment and mathematical deduction. It was more than 2,000 years before modern physicists realized that the atom is indeed divisible and that it is not hard, solid , or immutable.

Leucippus of Miletus (5th century bce ) is thought to have originated the atomic philosophy. His famous disciple , Democritus of Abdera, named the building blocks of matter atomos , meaning literally “indivisible,” about 430 bce . Democritus believed that atoms were uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped. Differences in atomic shape and size determined the various properties of matter. In Democritus’s philosophy, atoms existed not only for matter but also for such qualities as perception and the human soul . For example, sourness was caused by needle-shaped atoms, while the colour white was composed of smooth-surfaced atoms. The atoms of the soul were considered to be particularly fine. Democritus developed his atomic philosophy as a middle ground between two opposing Greek theories about reality and the illusion of change. He argued that matter was subdivided into indivisible and immutable particles that created the appearance of change when they joined and separated from others.

The philosopher Epicurus of Samos (341–270 bce ) used Democritus’s ideas to try to quiet the fears of superstitious Greeks. According to Epicurus’s materialistic philosophy, the entire universe was composed exclusively of atoms and void, and so even the gods were subject to natural laws.

Most of what is known about the atomic philosophy of the early Greeks comes from Aristotle ’s attacks on it and from a long poem, De rerum natura (“On the Nature of Things”), which Latin poet and philosopher Titus Lucretius Carus ( c. 95–55 bce ) wrote to popularize its ideas. The Greek atomic theory is significant historically and philosophically, but it has no scientific value. It was not based on observations of nature, measurements, tests, or experiments. Instead, the Greeks used mathematics and reason almost exclusively when they wrote about physics . Like the later theologians of the Middle Ages , they wanted an all-encompassing theory to explain the universe, not merely a detailed experimental view of a tiny portion of it. Science constituted only one aspect of their broad philosophical system. Thus, Plato and Aristotle attacked Democritus’s atomic theory on philosophical grounds rather than on scientific ones. Plato valued abstract ideas more than the physical world and rejected the notion that attributes such as goodness and beauty were “mechanical manifestations of material atoms.” Where Democritus believed that matter could not move through space without a vacuum and that light was the rapid movement of particles through a void, Aristotle rejected the existence of vacuums because he could not conceive of bodies falling equally fast through a void. Aristotle’s conception prevailed in medieval Christian Europe; its science was based on revelation and reason, and the Roman Catholic theologians rejected Democritus as materialistic and atheistic.

De rerum natura , which was rediscovered in the 15th century, helped fuel a 17th-century debate between orthodox Aristotelian views and the new experimental science. The poem was printed in 1649 and popularized by Pierre Gassendi , a French priest who tried to separate Epicurus’s atomism from its materialistic background by arguing that God created atoms.

Soon after Italian scientist Galileo Galilei expressed his belief that vacuums can exist (1638), scientists began studying the properties of air and partial vacuums to test the relative merits of Aristotelian orthodoxy and the atomic theory. The experimental evidence about air was only gradually separated from this philosophical controversy.

Anglo-Irish chemist Robert Boyle began his systematic study of air in 1658 after he learned that Otto von Guericke , a German physicist and engineer, had invented an improved air pump four years earlier. In 1662 Boyle published the first physical law expressed in the form of an equation that describes the functional dependence of two variable quantities. This formulation became known as Boyle’s law . From the beginning, Boyle wanted to analyze the elasticity of air quantitatively, not just qualitatively, and to separate the particular experimental problem about air’s “spring” from the surrounding philosophical issues. Pouring mercury into the open end of a closed J-shaped tube, Boyle forced the air in the short side of the tube to contract under the pressure of the mercury on top. By doubling the height of the mercury column, he roughly doubled the pressure and halved the volume of air. By tripling the pressure, he cut the volume of air to a third, and so on.

This behaviour can be formulated mathematically in the relation P V = P ′ V ′, where P and V are the pressure and volume under one set of conditions and P ′ and V ′ represent them under different conditions. Boyle’s law says that pressure and volume are inversely related for a given quantity of gas . Although it is only approximately true for real gases, Boyle’s law is an extremely useful idealization that played an important role in the development of atomic theory.

Soon after his air-pressure experiments, Boyle wrote that all matter is composed of solid particles arranged into molecules to give material its different properties. He explained that all things are

made of one Catholick Matter common to them all, and…differ but in the shape, size, motion or rest, and texture of the small parts they consist of.

In France Boyle’s law is called Mariotte’s law after physicist Edme Mariotte , who discovered the empirical relationship independently in 1676. Mariotte realized that the law holds true only under constant temperatures; otherwise, the volume of gas expands when heated or contracts when cooled.

Forty years later Isaac Newton expressed a typical 18th-century view of the atom that was similar to that of Democritus, Gassendi, and Boyle. In the last query in his book Opticks (1704), Newton stated:

All these things being considered, it seems probable to me that God in the Beginning form’d Matter in solid, massy, hard, impenetrable, moveable Particles, of such Sizes and Figures, and with such other Properties, and in such Proportion to Space, as most conduced to the End for which he form’d them; and that these primitive Particles being Solids, are incomparably harder than any porous Bodies compounded of them; even so very hard, as never to wear or break in pieces; no ordinary Power being able to divide what God himself made one in the first Creation.

By the end of the 18th century, chemists were just beginning to learn how chemicals combine. In 1794 Joseph-Louis Proust of France published his law of definite proportions (also known as Proust’s law). He stated that the components of chemical compounds always combine in the same proportions by weight. For example, Proust found that no matter where he obtained his samples of the compound copper carbonate, they were composed by weight of five parts copper , four parts oxygen , and one part carbon .

Early Ideas about Matter: From Democritus to Dalton

by Anthony Carpi, Ph.D.

Listen to this reading

Did you know that some ancient Greeks believed that all matter was made up of four substances: fire, air, water, and earth? They believed that rabbits were soft because they had more water than earth. Although this idea seems silly now, it contains a fundamental principle of atomic theory: that matter is made up of a small number of fundamental elements.

Early humans easily distinguished between materials that were used for making clothes, those that could be shaped into tools, or those that were good to eat. Then they gave these things the names, such as "fur," "stone," or "rabbit." However, these people did not have our current understanding of the substances that made up those objects. Empedocles , a Greek philosopher and scientist who lived on the south coast of Sicily between 492 BCE and 432 BCE, proposed one of the first theories that attempted to describe the things around us. Empedocles argued that all matter was composed of four elements: fire, air, water, and earth. The ratio of these four elements affected the properties of the matter. Stone was thought to contain a high amount of earth, while a rabbit was thought to have a higher ratio of both water and fire, thus making it soft and giving it life.

Empedocles's theory was quite popular, but it had a number of problems. For example, regardless of how many times you break a stone in half, the pieces never resemble any of the core elements of fire, air, water, or earth. Despite these problems, Empedocles 's theory was an important development in scientific thinking because it was among the first to suggest that some substances that looked like pure materials, like stone, were actually made up of a combination of different "elements."

• The atom is proposed

A few decades after Empedocles , Democritus (460 BCE - 370 BCE), who was also Greek, developed a new theory of matter that attempted to overcome the problems of his predecessor. Democritus's ideas were based on reasoning rather than science, and drew on the teachings of two Greek philosophers who came before him: Leucippus and Anaxagoras . Democritus knew that if you took a stone and cut it in half, each half had the same properties as the original stone. He reasoned that if you continued to cut the stone into smaller and smaller pieces, at some point you would reach a piece so tiny that it could no longer be divided. Democritus called these infinitesimally small pieces of matter atomos , meaning 'indivisible'. He suggested that atomos were eternal and could not be destroyed. Democritus theorized that atomos were specific to the material that they made up, meaning that the atomos of stone were unique to stone and different from the atomos of other materials, such as fur. This was a remarkable theory that attempted to explain the whole physical world in terms of a small number of ideas.

Ultimately, though, Aristotle and Plato, two of the best-known philosophers of Ancient Greece, rejected the theories of Democritus . Aristotle accepted the theory of Empedocles , adding his own (incorrect) idea that the four core elements could be transformed into one another. Because of Aristotle's great influence, Democritus's theory would have to wait almost 2,000 years before being rediscovered.

In the 17 th and 18 th centuries CE , several key events helped revive the theory that matter was made of small, indivisible particles . In 1643, Evangelista Torricelli , an Italian mathematician and pupil of Galileo, showed that air had weight and was capable of pushing down on a column of liquid mercury (thus inventing the barometer). This was a startling finding. If air – this substance that we could not see, feel, or smell – had weight, it must be made of something physical. But how could something have a physical presence, yet not respond to human touch or sight? Daniel Bernoulli , a Swiss mathematician, proposed an answer. He developed a theory that air and other gases consist of tiny particles that are too small to be seen, and are loosely packed in an empty volume of space. The particles could not be felt because unlike a solid stone wall that does not move, the tiny particles move aside when a human hand or body moves through them. Bernoulli reasoned that if these particles were not in constant motion, they would settle to the ground like dust particles; therefore, he pictured air and other gases as loose collections of tiny billiard-ball-like particles that are continuously moving around and bouncing off one another.

• Law of Conservation of Mass

Many scientists were busy studying the natural world at this time. Shortly after Bernoulli proposed his theory , the Englishman Joseph Priestley began to experiment with red mercury calx in 1773. Mercury calx, a red solid stone, had been known and coveted for thousands of years because when it is heated, it appears to turn into mercury, a silver liquid metal. Priestley had observed that it does not just turn into mercury; it actually breaks down into two substances when it is heated, liquid mercury and a strange gas . Priestley carefully collected this gas in glass jars and studied it. After many long days and nights in the laboratory, Priestley said of the strange gas, "What surprised me more than I can well express was that a candle burned in this air with a remarkably vigorous flame." Not only did flames burn strongly in this gas, but a mouse placed in a sealed container of this gas lived for a longer period of time than a mouse placed in a sealed container of ordinary air. Priestley's discovery revealed that substances could combine together or break apart to form new substances with different properties. For example, a colorless, odorless gas could combine with mercury, a silver metal, to form mercury calx, a red mineral .

Priestley called the gas he discovered dephlogisticated air , but this name would not stick. In 1778, Antoine Lavoisier , a French scientist, conducted many experiments with dephlogisticated air and theorized that the gas made some substances acidic. He renamed Priestley's gas oxygen , from the Greek words that loosely translate as 'acid maker'. While Lavoisier's theory about oxygen and acids proved incorrect, his name stuck. Lavoisier knew from other scientists before him that acids react with some metals to release another strange and highly flammable gas called phlogiston . Lavoisier mixed the two gases, phlogiston and the newly renamed oxygen, in a closed glass container and inserted a match. He saw that phlogiston immediately burned in the presence of oxygen, and afterwards he observed droplets of water on the glass container. After careful testing, Lavoisier realized that the water was formed by the reaction of phlogiston and oxygen, and so he renamed phlogiston hydrogen , from the Greek words for 'water maker'.

Lavoisier also burned other substances such as phosphorus and sulfur in air, and showed that they combined with air to make new materials. These new materials weighed more than the original substances, and Lavoisier showed that the weight gained by the new materials was lost from the air in which the substances were burned. From these observations , Lavoisier established the Law of Conservation of Mass , which says that mass is not lost or gained during a chemical reaction .

Comprehension Checkpoint

• Modern atomic theory

Priestley, Lavoisier, and others had laid the foundations of the field of chemistry. Their experiments showed that some substances could combine with others to form new materials, other substances could be broken apart to form simpler ones, and a few key "elements" could not be broken down any further. But what could explain this complex set of observations? John Dalton , an exceptional British teacher and scientist, put together the pieces and developed the first modern atomic theory in 1803. To learn more about Priestley's and Lavoisier's experiments and how they formed the basis of Dalton's theories , try the interactive experiment Dalton's Playhouse , linked to below.

Interactive Animation: Dalton's Playhouse

Dalton made it a regular habit to track and record the weather in his hometown of Manchester, England. Through his observations of morning fog and other weather patterns, Dalton realized that water could exist as a gas that mixed with air and occupied the same space as air. Solids could not occupy the same space as each other; for example, ice could not mix with air. So what could allow water to sometimes behave as a solid and sometimes as a gas? Dalton realized that all matter must be composed of tiny particles . In the gas state, those particles floated freely around and could mix with other gases, as Bernoulli had proposed. But Dalton extended this idea to apply to all matter – gases, solids, and liquids . Dalton first proposed part of his atomic theory in 1803 and later refined these concepts in his classic 1808 paper A New System of Chemical Philosophy (which you can access through a link under the Resources tab).

All matter is composed of indivisible particles called atoms . Bernoulli, Dalton, and others pictured atoms as tiny billiard-ball-like particles in various states of motion. While this concept is useful to help us understand atoms, it is not correct as we will see in later modules on atomic theory linked to at the bottom of this module.

All atoms of a given element are identical; atoms of different elements have different properties. Dalton's theory suggested that every single atom of an element such as oxygen is identical to every other oxygen atom; furthermore, atoms of different elements, such as oxygen and mercury, are different from each other. Dalton characterized elements according to their atomic weight ; however, when isotopes of elements were discovered in the late 1800s, this concept changed.

Chemical reactions involve the combination of atoms, not the destruction of atoms. Atoms are indestructible and unchangeable, so compounds , such as water and mercury calx, are formed when one atom chemically combines with other atoms. This was an extremely advanced concept for its time; while Dalton's theory implied that atoms bonded together, it would be more than 100 years before scientists began to explain the concept of chemical bonding .

When elements react to form compounds, they react in defined, whole-number ratios . The experiments that Dalton and others performed showed that reactions are not random events; they proceed according to precise and well-defined formulas . This important concept in chemistry is discussed in more detail below.

Some of the details of Dalton's atomic theory require more explanation.

Elements: As early as 1660, Robert Boyle recognized that the Greek definition of element (earth, fire, air, and water) was not correct. Boyle proposed a new definition of an element as a fundamental substance, and we now define elements as fundamental substances that cannot be broken down further by chemical means . Elements are the building blocks of the universe . They are pure substances that form the basis of all of the materials around us. Some elements can be seen in pure form, such as mercury in a thermometer; some we see mainly in chemical combination with others, such as oxygen and hydrogen in water. We now know of approximately 116 different elements. Each of the elements is given a name and a one- or two-letter abbreviation. Often this abbreviation is simply the first letter of the element; for example, hydrogen is abbreviated as H, and oxygen as O. Sometimes an element is given a two-letter abbreviation; for example, helium is He. When writing the abbreviation for an element, the first letter is always capitalized and the second letter (if there is one) is always lowercase.

Atoms: A single unit of an element is called an atom . The atom is the most basic unit of matter , which makes up everything in the world around us. Each atom retains all of the chemical and physical properties of its parent element. At the end of the nineteenth century, scientists would show that atoms were actually made up of smaller, "subatomic" pieces, which smashed the billiard-ball concept of the atom (see our Atomic Theory I: The Early Days module).

Compounds: Most of the materials we come into contact with are compounds, substances formed by the chemical combination of two or more atoms of the elements. A single "particle" of a compound is called a molecule . Dalton incorrectly imagined that atoms "hooked" together to form molecules. However, Dalton correctly realized that compounds have precise formulas . Water, for example, is always made up of two parts hydrogen and one part oxygen. The chemical formula of a compound is written by listing the symbols of the elements together, without any spaces between them. If a molecule contains more than one atom of an element, a number is subscripted after the symbol to show the number of atoms of that element in the molecule. Thus the formula for water is H 2 O, never HO or H 2 O 2 .

• Law of Definite Proportions

The idea that compounds have defined chemical formulas was first proposed in the late 1700s by the French chemist Joseph Proust . Proust performed a number of experiments and observed that no matter how he caused different elements to react with oxygen, they always reacted in defined proportions. For example, two parts of hydrogen always reacts with one part oxygen when forming water; one part mercury always reacts with one part oxygen when forming mercury calx. Dalton used Proust's Law of Definite Proportions in developing his atomic theory .

The law also applies to multiples of the fundamental proportion, for example:

In both of these examples, the ratio of hydrogen to oxygen to water is 2 to 1 to 1. When reactants are present in excess of the fundamental proportions, some reactants will remain unchanged after the chemical reaction has occurred.

The story of the development of modern atomic theory is one in which scientists built upon the work of others to produce a more accurate explanation of the world around them. This process is common in science, and even incorrect theories can contribute to important scientific discoveries. Dalton, Priestley, and others laid the foundation of atomic theory, and many of their hypotheses are still useful. However, in the decades after their work, other scientists would show that atoms are not solid billiard balls, but complex systems of particles . Thus, they would smash apart a bit of Dalton's atomic theory in an effort to build a more complete view of the world around us.

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Ancient physics: How Democritus predicted the atom

Credit: vinap via Adobe Stock / Public Domain via Wikimedia

• The idea of the atom goes as far back as the ancient Greek philosopher Democritus in about 400 B.C.E.
• This led to his “theory of eidôla” to explain how our minds create the illusion of reality.
• Democritus was one of the first determinists, arguing that a world made only of atoms and controlled by the laws of physics left no room for free will.

Philosophers love “The Matrix”.

It’s the perfect introduction to the ideas of big names such as Plato and Descartes but with leather trench coats, bullet time, and a brooding Keanu Reeves. One of the most memorable moments in the movie comes near the end when the protagonist, Neo, finally understands the Matrix for the illusionary simulation that it is. Now, he can see the numbers underpinning everything. He can see the source code of the world.

With only the slightest of modifications, Neo’s epiphany is no science fiction at all. This is how the world is made. But, where Neo saw green, floating numbers, we now know the universe is actually made up of tiny, imperceptible objects. Rather than code, we have atoms—the building blocks of everything there is, ever was, and ever will be.

We know atoms exist thanks to scientists and electron microscopes, but the idea goes much further back than that. It goes back to the ancient Greeks. Their output was prodigious. Almost every discipline you can study, the Greeks turned their minds to first. Pythagoras laid the foundation for math and geometry, Aristotle contemplated biology and physics, Plato thought about governance, Herodotus was a historian, and Hippocrates gave doctors his eponymous oath. But one of the most ingenious “firsts” must come with the atomists, like Democritus or Epicurus.

It’s odd to think that millennia ago, a few bearded men in togas, strolling around a sun-bleached agora, used philosophy to establish the fundamental fabric of the universe.

Although the idea of “the atom” had been floating around the Peloponnese for a while, Democritus was the first to articulate it fully. He argued that atoms must exist because the alternative is sheer nonsense. If we could constantly divide or cut a thing into two then we would go on forever. We’d get smaller and smaller all the way to infinity, and there’d be no end point. But the universe can’t be built without foundations. Nothing can come from nothing. So, there must be a fundamental unit to the world from which everything else is made, and for this, Democritus coined the term “atom” (which literally means uncuttable, although 20th Century scientists learned how to split one, rather ruining the definition).

The question now facing Democritus was how these basic, imperceptible atoms came to make the objects we all see, touch, and love. He noted how, when we look at the world around us, we can see it constantly changing, shifting, dying, and growing. The world flows. So atoms, which make up everything there is, must themselves be moving. They can’t just be inert or still.

Democritus argued that atoms come together in various combinations, and then emit something called an “ eidôla. ” These composite blobs of atoms radiate eidôla outward, like ripples in water. The eidôla are then picked up by us as the subjective experiencer and we translate this atomic radiation into ideas or sensations.

For example, let’s imagine a group of atoms come together and, with a special wiggle, emit their eidôla . This flies through the space (or “void,” as Democritus called it) to our eyes. Our eyes then whizz this eidôla along to our understanding, where it’s converted into “blue” or “round” or “big.”

There were two big implications to Democritus’ theory.

First, the world as we know it doesn’t actually exist. Just like the code in the Matrix, the world is really just incomprehensible atoms. Our minds create “reality” out of these atoms, and everything is just an illusion we play on ourselves.

Second, the world is entirely made up of atoms. The tree outside, your pet turtle, your feeling of love, and even the mind that processes eidôla are all made up of atoms.

The upshot of this is that Democritus was one of the first “determinists” in that he thought there could be no free will or choice. We’re all just marbles, bouncing around to the laws of physics.

We might think this a pretty depressing place to finish, yet Democritus was actually known as “the laughing philosopher.” He simply refused to take anything seriously. If reality was ultimately the invented story of our minds, and the universe was just physical laws, what’s the point in getting wound up by things? Why stress about that email from your boss, or that mean thing a friend said when there’s nothing we can do anyway? If the world is an illusion, and a boringly scripted one at that, why not laugh?

The first “atomist,” Democritus, of course got a lot wrong, but it’s remarkable how much he got right. By reflecting on reality long enough, he came to conclusions that scientists proved millennia later. If nothing else, he offers a shining example of the power of contemplation.

Jonny Thomson teaches philosophy in Oxford. He runs a popular Instagram account called Mini Philosophy (@ philosophyminis ). His first book is Mini Philosophy: A Small Book of Big Ideas .

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Sight and the Philosophy of Vision: Classical Greek Theories of Seeing between Democritus and Aristotle

2015, Sight and the Ancient Senses

This essay examines the theories of vision in Democritus, Plato and Aristotle. These philosophers offered different accounts of how a person (or the eye) can see things in the visible world. Each philosopher's theory of vision reflects his specific views of the physical world, the human body, and the psyche. The essay also discusses the notion of attention and the cultural contexts in which one chooses to attend to some things and not to others.

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Kelli Rudolph

Nancy Rabinowitz

Ruth Bielfeldt

Journal of Hellenic Studies 131: 67-83

Democritus’ theory of vision combines the notions of images (eidola) streaming from objects and air imprints, which gives him the resources to account for the perception of the relative size and distance of objects, not just their characteristics. This perspectival explanation of the visual theory accommodates important but overlooked evidence from Vitruvius. By comparing Democritus’ theory with ancient developments in visual representation, my analysis provides a new approach to the evidence of atomist vision. I begin with the process of vision before turning to the Peripatetic objections, showing how a unified theory of vision takes into account all of the ancient testimony and provides possible atomist responses to the criticisms raised against it. I also identify the importance of vision via air imprints as an important metaphor for the conventionality of sensible qualities. Understanding these fundamental issues puts us in a better position to assess Democritus’ place in the development of ancient optics and of atomist approaches to sense perception.

Democritus' Perspectival Theory of Vision

Doruk Tatlıdil

Examined closely in this paper, Democritus's perspective theory of vision is a crucial but sometimes overlooked aspect of his more general philosophical contributions. Democritus suggested that vision arises via the interaction of eidola (effluences from objects) with the eye, mediated by air imprints containing information about the qualities of the object. This thesis connects with his atomistic ontology to propose that visual experience is dynamically shaped by microstructural interactions of atoms and light. Dealing with objections from thinkers like Theophrastus and looking at the potential of illusion and error in sensory experience, the paper cautiously investigates the aspects and implications of Democritus's theory. Furthermore underlining the ongoing relevance of Democritus's views on perspective and reality, it ties to philosophical developments of the 20th century like phenomenology and logical positivism. Through this study, the basic role of early atomist concepts in the ongoing philosophical inquiry on the nature of vision and knowledge is underlined.

Debra Hawhee

Oxford Handbooks Online

Victor Caston

Laval théologique et philosophique

Paolo Biondi

Current Approaches to Religion in Ancient Greece. Papers Presented at a Symposium at the Swedish Institute of Athens, 17-19 April 2008. Edited by Matthew Haysom and Jenny Wallensten. Stockholm

Nassos Papalexandrou

A fruitful, but insufficiently explored, domain of Greek religious practice has to do with vision in the nexus of religious experiences. Drawing on recent studies on the theory and anthropology of vision and visual culture, this paper is based on the premise that vision is a culturally conditioned category of human behavior. The exploration of the cognitive and psychological dimensions of active vision and its objects involves the consideration of the multiple ways of seeing and being seen. The Homeric corpus, for example, points to the complexity of phenomena of vision in a period of intensive contacts and dialogues with the cultures of the Near East. Moreover, the importance of material culture in this inquiry can not be emphasized enough. It is of primary importance to ask how material objects were meant to be seen, by whom, under what circumstances, and to what ends.

Phenomenology and the Metaphysics of Sight. Edited by Antonio Cimino and Pavlos Kontos. Leiden: Brill.

Jussi Backman

The paper outlines a tentative genealogy of the Platonic metaphysics of sight by thematizing pre-Platonic thought, particularly Heraclitus and Parmenides. By “metaphysics of sight” it understands the features of Platonic-Aristotelian metaphysics expressed with the help of visual metaphors. It is argued that the Platonic metaphysics of sight can be regarded as the result of a synthesis of the Heraclitean and Parmenidean approaches. In pre-Platonic thought, the visual paradigm is still marginal. For Heraclitus, the basic structure of being is its discursive articulation (logos) into conceptual pairs of binary opposites, an articulation that at the same time binds differences together into a tensional unity. The fundamental grasping of this ultimate unity-in-difference is conceived primarily through acoustic terms as a non-sensory “hearing.” For Parmenides, the ultimate unity of contraries is based on the capacity of thinking (noos) to intend anything as present; in fragment B 4, the exclusive relationship of thinking to intelligible presence is finally visualized in terms of a seeing or looking (leusso).

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Democritus, known in antiquity as the ‘laughing philosopher’ because of his emphasis on the value of ‘cheerfulness,’ was one of the two founders of ancient atomist theory. He elaborated a system originated by his teacher Leucippus into a materialist account of the natural world. The atomists held that there are smallest indivisible bodies from which everything else is composed, and that these move about in an infinite void space. Of the ancient materialist accounts of the natural world which did not rely on some kind of teleology or purpose to account for the apparent order and regularity found in the world, atomism was the most influential. Even its chief critic, Aristotle, praised Democritus for arguing from sound considerations appropriate to natural philosophy.

1. Life and Works

2. atomist doctrine, 3. theory of perception, 4. the soul and the nature of living things, 5. theory of knowledge, 6. indivisibility and mathematics, 8. anthropology, bibliography, other internet resources, related entries.

According to ancient reports, Democritus was born about 460 BCE (thus, he was a younger contemporary of Socrates) and was a citizen of Abdera, although some reports mention Miletus. As well as his associate or teacher Leucippus, Democritus is said to have known Anaxagoras, and to have been forty years younger than the latter (DK 68A1). A number of anecdotes concern his life, but their authenticity is uncertain.

The work of Democritus has survived only in secondhand reports, sometimes unreliable or conflicting. Much of the best evidence is that reported by Aristotle, who regarded him as an important rival in natural philosophy. Aristotle wrote a monograph on Democritus, of which only a few passages quoted in other sources have survived. Democritus seems to have taken over and systematized the views of Leucippus, of whom little is known. Although it is possible to distinguish some contributions as those of Leucippus, the overwhelming majority of reports refer either to both figures, or to Democritus alone; the developed atomist system is often regarded as essentially Democritus'.

Diogenes Laertius lists a large number of works by Democritus on many fields, including ethics, physics, mathematics, music and cosmology. Two works, the Great World System and the Little World System , are sometimes ascribed to Democritus, although Theophrastus reports that the former is by Leucippus (DK 68A33). There is more uncertainty concerning the authenticity of the reports of Democritus' ethical sayings. Two collections of sayings are recorded in the fifth-century anthology of Stobaeus, one ascribed to Democritus and another ascribed to an otherwise unknown philosopher ‘Democrates’. DK accepts both as relating to Democritus, but the authenticity of sayings in both collections is a matter of scholarly discussion, as is the relationship between Democritus' atomism and his ethics.

Ancient sources describe atomism as one of a number of attempts by early Greek natural philosophers to respond to the challenge offered by Parmenides. Parmenides had argued that it is impossible for there to be change without something coming from nothing. Since the idea that something could come from nothing was generally agreed to be impossible, Parmenides argued that change is merely illusory. In response, Leucippus and Democritus, along with other Presocratic pluralists such as Empedocles and Anaxagoras, developed systems that made change possible by showing that it does not require that something should come to be from nothing. These responses to Parmenides suppose that there are multiple unchanging material principles, which persist and merely rearrange themselves to form the changing world of appearances. In the atomist version, these unchanging material principles are indivisible particles, the atoms: the atomists are said to have taken the idea that there is a lower limit to divisibility to answer Zeno's paradoxes about the impossibility of traversing infinitely divisible magnitudes.

The atomists held that there are two fundamentally different kinds of realities composing the natural world, atoms and void. Atoms, from the Greek adjective atomos or atomon , ‘indivisible,’ are infinite in number and various in size and shape, and perfectly solid, with no internal gaps. They move about in an infinite void, repelling one another when they collide or combining into clusters by means of tiny hooks and barbs on their surfaces, which become entangled. Other than changing place, they are unchangeable, ungenerated and indestructible. All changes in the visible objects of the world of appearance are brought about by relocations of these atoms: in Aristotelian terms, the atomists reduce all change to change of place. Macroscopic objects in the world that we experience are really clusters of these atoms; changes in the objects we see—qualitative changes or growth, say—are caused by rearrangements or additions to the atoms composing them. While the atoms are eternal, the objects compounded out of them are not. Clusters of atoms moving in the infinite void come to form kosmoi or worlds as a result of a circular motion that gathers atoms up into a whirl, creating clusters within it (DK 68B167); these kosmoi are impermanent. Our world and the species within it have arisen from the collision of atoms moving about in such a whirl, and will likewise disintegrate in time.

In supposing that void exists, the atomists deliberately embraced an apparent contradiction, claiming that ‘what is not’ exists. Apparently addressing an argument by Melissus, a follower of Parmenides, the atomists paired the term for ‘nothing’ with what it negates, ‘thing,’ and claimed that—in a phrase typical of the atomists—the one ‘no more’ exists than the other (DK 67A6). By putting the full (or solid) and the void ontologically on a par, the atomists were apparently denying the impossibility of void. Void they considered to be a necessary condition for local motion: if there were no unoccupied places, where could bodies move into? Melissus had argued from the logical impossibility of void to the impossibility of motion; the atomists apparently reasoned in reverse, arguing from the fact that motion exists to the necessity for void space to exist (DK 67A7). It has been suggested that Democritus' conception of void is that of the (temporarily) unfilled regions between atoms rather than a concept of absolute space (Sedley 1982). Void does not impede the motion of atoms because its essential quality is that of ‘yielding,’ in contrast to the mutual resistance of atoms. Later atomist accounts attest that this ‘yielding’ explains the tendency of bodies to drift into emptier spaces, driven out by collision from more densely packed regions (Lucretius DRN 6.906-1089).

Some controversy surrounds the properties of the atoms. They vary in size: one report—which some scholars question—suggests that atoms could, in principle, be as large as a cosmos, although at least in this cosmos they all seem to be too small to perceive (DK 68A47). They can take on an infinite variety of shapes: there are reports of an argument that there is ‘no more’ reason for the atoms to be one shape than another. Many kinds of atoms can interlock with one another because of their irregular shapes and hooks at their surface, accounting for the cohesiveness of some compounds. It is not clear whether the early atomists regarded atoms as conceptually indivisible or merely physically indivisible (Furley 1967). The idea that there is a smallest possible magnitude seems to suggest that this is the lower limit of size for atoms, although notions like being in contact or having shape seem to entail that even the smallest atoms have parts in some sense, if only mathematically or conceptually.

There are conflicting reports on whether atoms move in a particular direction as a result of their weight: a number of scholars have tried to reconcile these by supposing that weight is not intrinsic to the atoms, but is a result of the centripetal tendencies set up in the cosmic whirl (cf. O'Brien 1981; Furley 1989, pp. 91-102). Atoms may have an inherent tendency to a kind of vibratory motion, although the evidence for this is uncertain (McDiarmid 1956). However, their primary movement seems to result from collision with other atoms, wherein their mutual resistance or antitupia causes them to move away from one another when struck. Democritus is criticized by Aristotle for supposing that the sequence of colliding atoms has no beginning, and thus for not offering an explanation of the existence of atomic motion per se , even though the prior collision with another atom can account for the direction of each individual atomic motion (see O'Keefe 1996). Although the ancient atomists are often compared to modern ‘mechanistic’ theories, Balme warned of the danger of assuming that the atomists share modern ideas about the nature of atomic motion, particularly the idea that motion is inertial (Balme 1941).

According to different reports, Democritus ascribed the causes of things to necessity, and also to chance. Probably the latter term should be understood as ‘absence of purpose’ rather than a denial of necessity (Barnes 1982, pp. 423-6). Democritus apparently recognized a need to account for the fact that the disorderly motion of individual distinct atoms could produce an orderly cosmos in which atoms are not just randomly scattered, but cluster to form masses of distinct types. He is reported to have relied on a tendency of ‘like to like’ which exists in nature: just as animals of a kind cluster together, so atoms of similar kinds cluster by size and shape. He compares this to the winnowing of grains in a sieve, or the sorting of pebbles riffled by the tide: it is as if there were a kind of attraction of like to like (DK 68B164). Although this claim has been interpreted differently (e.g. Taylor 1999b p. 188), it seems to be an attempt to show how an apparently ordered arrangement can arise automatically, as a byproduct of the random collisions of bodies in motion (Furley 1989, p. 79). No attractive forces or purposes need be introduced to explain the sorting by the tide or in the sieve: it is probable that this is an attempt to show how apparently orderly effects can be produced without goal-directioned forces or purpose.

Democritus regards the properties of atoms in combination as sufficient to account for the multitude of differences among the objects in the world that appears to us. Aristotle cites an analogy to the letters of the alphabet, which can produce a multitude of different words from a few elements in combinations; the differences all stem from the shape ( schêma ) of the letters, as A differs from N; by their arrangement ( taxis ), as AN differs from NA; and by their positional orientation ( thesis ), as N differs from Z (DK 67A6). These terms are Aristotle's interpretation of Democritus' own terminology, which has a more dynamic sense (Mourelatos 2004). This passage omits differences of size, perhaps because it is focused on the analogy to letters of the alphabet: it is quite clear from other texts that Democritus thinks that atoms also differ in size.

He famously denies that perceptible qualities other than shape and size (and, perhaps, weight) really exist in the atoms themselves: one direct quotation surviving from Democritus claims that ‘by convention sweet and by convention bitter, by convention hot, by convention cold, by convention color; but in reality atoms and void’ (DK 68B9, trans. Taylor 1999a). As Furley argues, the translation ‘convention’ should not be taken to suggest that there is anything arbitrary about the perception of certain colors, say: the same configuration of atoms may be regularly associated with a given color. The contrast here is intended to be that between real and unreal properties (Furley 1993; cf. Barnes 1982, pp. 370-7). What Democritus rejects as ‘merely conventional’ is, perhaps, the imputation of the qualities in question to the atoms, or perhaps even to macroscopic bodies.

While several reports of Democritus' view, apparently direct quotations, mention exclusively sensible qualities as being unreal, a report of Plutarch includes in the list of things that exist only by convention the notion of ‘combination’ or sunkrisis . If this report is genuinely Democritean, it would broaden the scope of the claim considerably: the idea that any combination—by which he presumably means any cluster of atoms—is ‘unreal’ or merely ‘conventional’ suggests that Democritus is drawing a more radical distinction than that between sensible and nonsensible qualities. The implication would be that anything perceived, because it is a perception of combinations of atoms and not atoms themselves, would count as ‘unreal,’ not merely the qualia experienced by means of individual sense organs. One report indeed attributes to Democritus a denial that two things could become one, or vice versa (DK 68A42), thus suggesting that combinations are regarded as conventional. Commentators differ as to the authenticity of Plutarch's report. As the word sunkrisis does not occur in other reports, Furley (following Sandbach) suggests that it is most likely an error for pikron , ‘bitter’ which occurs instead in another report. However, Furley concedes that Plutarch at least understands the earliest atomists to be committed to the view that all combinations of atoms, as much as sensible qualities, should be understood as conventional rather than real (Furley 1993 pp. 76-7n7). This would suggest that everything at the macroscopic level—or, strictly, everything available to perception—is regarded as unreal. If we take the ‘conventionality’ thesis to be restricted to sensible qualities, there is still an open question about Democritus' reason for denying their ‘reality’ (Wardy 1988; O'Keefe 1997; Ganson 1999).

Democritus' theory of perception depends on the claim that eidôla or images, thin layers of atoms, are constantly sloughed off from the surfaces of macroscopic bodies and carried through the air. Later atomists cite as evidence for this the gradual erosion of bodies over time. These films of atoms shrink and expand; only those that shrink sufficiently can enter the eye. It is the impact of these on our sense organs that enables us to perceive. Visible properties of macroscopic objects, like their size and shape, are conveyed to us by these films, which tend to be distorted as they pass through greater distances in the air, since they are subject to more collisions with air atoms. A different or complementary account claims that the object seen impresses the air by the eidôla , and the compacted air thus conveys the image to the eye (DK 68A135; Baldes 1975). The properties perceived by other senses are also conveyed by contact of some kind. Democritus' theory of taste, for example, shows how different taste sensations are regularly produced by contact with different shapes of atoms: some atoms are jagged and tear the tongue, creating bitter sensations, or are smooth and thus roll easily over the tongue, causing sensations of sweetness.

Theophrastus, who gives us the most thorough report of Democritus' theory, criticizes it for raising the expectation that the same kinds of atoms would always cause similar appearances. However, it may be that most explanations are directed towards the normal case of a typical observer, and that a different account is given as to the perceptions of a nontypical observer, such as someone who is ill. Democritus' account why honey sometimes tastes bitter to people who are ill depends on two factors, neither of which undercut the notion that certain atomic shapes regularly affect us in a given way. One is that a given substance like honey is not quite homogeneous, but contains atoms of different shapes. While it takes its normal character from the predominant type of atom present, there are other atom-types present within. The other is that our sense-organs need to be suitably harmonized to admit a given atom-type, and the disposition of our passageways can be affected by illness or other conditions. Thus someone who is ill may become unusually receptive to an atom-type that is only a small part of honey's overall constitution.

Other observed effects, however, require a theory whereby the same atoms can produce different effects without supposing that the observer has changed. The change must then occur in the object seen. The explanation of color seems to be of this variety: Aristotle reports that things acquire their color by ‘turning,’ tropê ( GC 1.2, 315b34). This is the Democritean term that Aristotle had translated as ‘position,’ thesis , i.e. one of the three fundamental ways in which atoms can appear differently to us. Aristotle gives this as the reason why color is not ascribed to the atoms themselves. Lucretius' account of why color cannot belong to atoms may help clarify the point here. We are told that if the sea's atoms were really blue, they could not undergo some change and look white ( DRN 2.774-5), as when we observe the sea's surface changing from blue to white. This seems to assume that, while an appearance of a property P can be produced by something that is neither P nor not-P, nonetheless something P cannot appear not-P. Since atoms do not change their intrinsic properties, it seems that change in a relational property, such as the relative position of atoms, is most likely to be the cause of differing perceptions. In the shifting surface of the sea or the flutter of the pigeon with its irridescent neck, it is evident that the parts of the object are moving and shifting in their positional relations.

By ascribing the causes of sensible qualities to relational properties of atoms, Democritus forfeits the prima facie plausibility of claiming that things seem P because they are P. Much of Theophrastus' report seems to focus on the need to make it plausible that a composite can produce an appearance of properties it does not have. Democritus is flying in the face of at least one strand of commonsense when he claims that textures produce the appearance of hot or cold, impacts cause colour sensations. The lists of examples offered, drawing on commonsense associations or anecdotal experience, are attempts to make such claims persuasive. Heat is said to be caused by spherical atoms, because these move freely: the commonsense association of quick movement with heating is employed. The jagged atoms associated with bitter taste are also said to be heat-producing: there, the association of heat with friction is invoked. It is not so much the specific intrinsic qualities—smooth or jagged shape—as the motion of those shapes that provides the explanation.

Aristotle sometimes criticizes Democritus for claiming that visible, audible, olfactory and gustatory sensations are all caused by touch (DK 68A119). Quite how this affects the account of perception is not clear, as the sources tells us little about how touch is thought to work. Democritus does not, however, seem to distinguish between touch and contact, and may take it to be unproblematic that bodies communicate their size, shape and surface texture by physical impact.

In common with other early ancient theories of living things, Democritus seems to have used the term psychê to refer to that distinctive feature of living things that accounts for their ability to perform their life-functions. According to Aristotle, Democritus regarded the soul as composed of one kind of atom, in particular fire atoms. This seems to have been because of the association of life with heat, and because spherical fire atoms are readily mobile, and the soul is regarded as causing motion. Democritus seems to have considered thought to be caused by physical movements of atoms also. This is sometimes taken as evidence that Democritus denied the survival of a personal soul after death, although the reports are not univocal on this.

One difficulty faced by materialist theories of living things is to account for the existence and regular reproduction of functionally adapted forms in the natural world. Although the atomists have considerable success in making it plausible that a simple ontology of atoms and void, with the minimal properties of the former, can account for a wide variety of differences in the objects in the perceptible world, and also that a number of apparently orderly effects can be produced as a byproduct of disorderly atomic collisions, the kind of functional organization found in organisms is much harder to explain.

Democritus seems to have developed a view of reproduction according to which all parts of the body contribute to the seed from which the new animal grows, and that both parents contribute seed (DK 68A141; 143). The theory seems to presuppose that the presence of some material from each organ in the seed accounts for the development of that organ in the new organism. Parental characteristics are inherited when the contribution of one or other parent predominates in supplying the appropriate part. The offspring is male or female according to which of the two seeds predominates in contributing material from the genitals. In an atomist cosmos, the existence of particular species is not considered to be eternal. Like some other early materialist accounts, Democritus held that human beings arose from the earth (DK 68A139), although the reports give little detail.

One report credits Democritus and Leucippus with the view that thought as well as sensation are caused by images impinging on the body from outside, and that thought as much as perception depends on images (DK 67A30). Thought as well as perception are described as changes in the body. Democritus apparently recognized that his view gives rise to an epistemological problem: it takes our knowledge of the world to be derived from our sense experience, but the senses themselves not to be in direct contact with the nature of things, thus leaving room for omission or error. A famous fragment may be responding to such a skeptical line of thought by accusing the mind of overthrowing the senses, though those are its only access to the truth (DK68B125). Other passages talk of a gap between what we can perceive and what really exists (DK 68B6-10; 117). But the fact that atoms are not perceptible means that our knowledge of their properties is always based on analogy from the things of the visible world. Moreover, the senses report properties that the atoms don't really possess, like colors and tastes. Thus the potential for doubt about our knowledge of the external world looms large.

Later philosophers adapted a Democritean phrase ou mallon or ‘no more’ in the argument that something that seems both P and not-P is ‘no more’ P than not-P. Arguments of this form were used for sceptical purposes, citing the conflicting evidence of the senses in order to raise concern about our knowledge of the world (de Lacy 1958). Democritus does not seem to be pursuing a consistently skeptical program, although he does express concern about the basis for our knowledge.

The idea that our knowledge is based on the reception of images from outside us is employed in Democritus' discussion of the gods, wherein it is clear that our knowledge of the gods comes from eidôla or giant films of atoms with the characteristics we attribute to the gods, although Democritus denies that they are immortal. Some scholars take this to be a deflationary attack on traditional theology as based on mere images (Barnes 1982, pp. 456-61), but others suppose that the theory posits that these eidôla are really living beings (Taylor 1999a, pp. 211-6). Although atomism is often identified as an atheist doctrine in later times, it is not clear whether this is really Democritus' view.

The reasons for supposing that there are indivisible magnitudes apparently stem from the problems posed by Zeno of Elea. Some of Zeno's paradoxes concern the difficulty of crossing a finite magnitude if it is understood to be infinitely divisible, i.e. composed of an infinite number of parts. The atomists may have sought to avoid these paradoxes by supposing that there is a limit to divisibility.

It is not clear, however, in what sense the atoms are said to be indivisible, and how the need for smallest magnitudes is related to the claim that atoms are indivisible. Furley suggests that the atomists may not have distinguished between physical and theoretical indivisibility of the atoms (Furley 1967, p. 94). The physical indivisibility of the atoms seems to be independent of the argument for indivisible magnitudes, since the solidity of atoms—the fact that there is no void within them—is said to be the reason why they cannot be split. The existence of void space between atoms is cited as the reason why they can be separated: one late source, Philoponus, even suggests that atoms could never actually touch, lest they fuse (DK 67A7). Whether or not Democritus himself saw this consequence, it seems that atoms are taken to be indivisible whatever their size. Presumably, though, there is a smallest size of atom, and this is thought to be enough to avoid the paradoxes of infinite divisibility.

A reductio ad absurdum argument reported by Aristotle suggests that the atomists argued from the assumption that, if a magnitude is infinitely divisible, nothing prevents it actually having been divided at every point. The atomist then asks what would remain: if the answer is some extended particles, such as dust, then the hypothesized division has not yet been completed. If the answer is nothing or points, then the question is how an extended magnitude could be composed from what does not have extension (DK 68A48b, 123).

Democritus is also said to have contributed to mathematics, and to have posed a problem about the nature of the cone. He argues that if a cone is sliced anywhere parallel to its base, the two faces thus produced must either be the same in size or different. If they are the same, however, the cone would seem to be a cylinder; but if they are different, the cone would turn out to have step-like rather than continuous sides. Although it is not clear from Plutarch's report how (or if) Democritus solved the problem, it does seem that he was conscious of questions about the relationship between atomism as a physical theory and the nature of mathematical objects.

The reports concerning Democritus' ethical views pose a number of interpretative problems, including the difficulty of deciding which fragments are genuinely Democritean (see above, section 1). In contrast to the evidence for his physical theories, many of the ethical fragments are lists of sayings quoted without context, rather than critical philosophical discussions of atomist views. Many seem like commonsense platitudes that would be consistent with quite different philosophical positions. Thus, despite the large number of ethical sayings, it is difficult to construct a coherent account of his ethical views. Annas notes the Socratic character of a number of the sayings, and thinks there is a consistent theme about the role of one's own intellect in happiness (Annas 2002). The sayings contain elements that can be seen as anticipating the more developed ethical views of Epicurus (Warren 2002).

It is also a matter of controversy whether any conceptual link can be found between atomist physics and the ethical commitments attributed to Democritus. Vlastos argued that a number of features of Democritus' naturalistic ethics can be traced to his materialist account of the soul and his rejection of a supernatural grounding for ethics (Vlastos 1975). Taylor is more sceptical about the closeness of the connection between Democritus' ethical views and his atomist physics (Taylor 1999a, pp. 232-4).

The reports indicate that Democritus was committed to a kind of enlightened hedonism, in which the good was held to be an internal state of mind rather than something external to it. The good is given many names, amongst them euthymia or cheerfulness, as well as privative terms, e.g. for the absence of fear. Some fragments suggest that moderation and mindfulness in one's pursuit of pleasures is beneficial; others focus on the need to free oneself from dependence on fortune by moderating desire. Several passages focus on the human ability to act on nature by means of teaching and art, and on a notion of balance and moderation that suggests that ethics is conceived as an art of caring for the soul analogous to medicine's care for the body (Vlastos 1975, pp. 386-94). Others discuss political community, suggesting that there is a natural tendency to form communities.

Although the evidence is not certain, Democritus may be the originator of an ancient theory about the historical development of human communities. In contrast to the Hesiodic view that the human past included a golden age from which the present day is a decline, an alternative tradition that may derive from Democritus suggests that human life was originally like that of animals; it describes the gradual development of human communities for purposes of mutual aid, the origin of language, crafts and agriculture. Although the text in question does not mention Democritus by name, he is the most plausible source (Cole 1967; Cartledge 1997).

If Democritus is the source for this theory, it suggests that he took seriously the need to account for the origin of all aspects of the world of our experience. Human institutions could not be assumed to be permanent features or divine gifts. The explanations offered suggest that human culture developed as a response to necessity and the hardships of our environment. It has been suggested that the sheer infinite size of the atomist universe and thus the number of possible combinations and arrangements that would occur by chance alone are important in the development of an account that can show how human institutions arise without assuming teleological or theological origins (Cole 1967). Although here, as on other questions, the evidence is less than certain, it is plausible that Democritus developed a powerful and consistent explanation of much of the natural world from a very few fundamentals.

For the reception and subsequent history of Democritean atomism, see the related entry on ancient atomism.

The standard scholarly edition of the ancient evidence concerning the views of the Presocratic philosophers is Diels-Kranz’ work (cited as DK):

• Diels, H. and W. Kranz, 1951, Die Fragmente der Vorsokratiker , 6 th ed. (Berlin).

A fuller presentation of the evidence for Democritus, with commentary in Russian:

• Luria, Solomon, 1970, Demokrit (Leningrad).

English translation and commentary:

• Taylor, C.C.W., 1999a, The Atomists: Leucippus and Democritus. Fragments, A Text and Translation with Commentary (Toronto).

See also the report on Democritus in:

• Diogenes Laertius. Lives of Eminent Philosophers , tr. R.D. Hicks (Loeb Classical Library: Cambridge Mass 1925), book 9.34-49.
• Barnes, Jonathan, 1982, The Presocratic Philosophers , rev. ed. (London and New York).
• Cartledge, Paul, 1997, Democritus , The Great Philosophers (London).
• Furley, David J., 1987, The Greek Cosmologists vol 1: The Formation of the Atomic Theory and its Earliest Critics (Cambridge).
• Kirk, G.S., J.E. Raven and Malcolm Schofield, 1957, The Presocratic Philosophers , second edition (Cambridge).
• McKirahan, Jr., Richard D., 1994, Philosophy Before Socrates: An Introduction with Texts and Commentary (Indianapolis).
• Taylor, C.C.W., 1999b, ‘The atomists,’ 181-204 in A.A. Long (ed.), The Cambridge Companion to Early Greek Philosophy (Cambridge).

Secondary Sources

• Annas, Julia, 2002, ‘Democritus and Eudaimonism,’ 169-82 in V. Caston and D. Graham (eds.), Presocratic Philosophy: Essays in Honour of Alexander Mourelatos (London).
• Baldes, Richard W., 1975, ‘Democritus on Visual Perception: Two Theories or One?,’ Phronesis 20: 93-105.
• Balme, David, 1941, ‘Greek Science and Mechanism II. The Atomists,’ Classical Quarterly 35: 23-8.
• Benakis, Linos G. (ed.)., 1984, Proceedings of the Ist International Congress on Democritus (Xanthi).
• Berryman, Sylvia, 2002, ‘Democritus and the explanatory power of the void,’ in V. Caston and D. Graham (eds.), Presocratic Philosophy: Essays in Honour of Alexander Mourelatos (London).
• Cherniss, Harold, 1935, Aristotle's Criticism of Presocratic Philosophy (Baltimore).
• Cole, Thomas, 1967, Democritus and the Sources of Greek Anthropology (Cleveland).
• de Lacy, Phillip, 1958, ‘ Ou mallon and the Antecedents of Ancient Scepticism,’ Phronesis 3: 59-71.
• Edmunds, Lowell, 1972, ‘Necessity, Chance, and Freedom in the Early Atomists,’ Phoenix 26: 342-57
• Furley, David J., 1967, Two Studies in the Greek Atomists (Princeton).
• -----, 1989, Cosmic Problems: Essays on Greek and Roman Philosophy of Nature (Cambridge).
• -----, 1993, ‘Democritus and Epicurus on Sensible Qualities,’ 72-94 in J. Brunschwig and M.C. Nussbaum (eds), Passions and Perceptions (Cambridge).
• Ganson, Todd, 1999, ‘Democritus against Reducing Sensible Qualities,’ Ancient Philosophy 19: 201-15.
• Hankinson, R.J., 1998, Cause and Explanation in Ancient Greek Thought (Oxford).
• Hirsch, Ulrike, 1990, ‘War Demokrits Weltbild mechanistisch und antiteleologisch?’ Phronesis 35: 225-44.
• McDiarmid, J.B., 1956, ‘Phantoms in Democritean Terminology: PERIPALAJIS and PERIPALASSESYAI ,’ Hermes 89: 291-8.
• Mourelatos, Alexander P.D., 2004, ‘Intrinsic and Relational Properties of Atoms in the Democritean Ontology,’ in Ricardo Salles (ed.), Metaphysics, Soul, and Ethics: Themes from the work of Richard Sorabji (forthcoming).
• O'Brien, Denis, 1981, Democritus, weight and size: an exercise in the reconstruction of early Greek philosophy, Theories of Weight in the Ancient World vol. 1 (Leiden).
• O'Keefe, Timothy, 1996, ‘Does Epicurus Need the Swerve as an archê of Collisions?,’ Phronesis 41: 305-17.
• -----, 1997, ‘The Ontological Status of Sensible Qualities for Democritus and Epicurus,’ Ancient Philosophy 17: 119-34.
• Sedley, David, 1982, ‘Two Conceptions of Vacuum,’ Phronesis 27: 175-93.
• Sorabji, Richard, 1983, Time, Creation and the Continuum (Ithaca and London).
• Vlastos, G., 1975, ‘Ethics and physics in Democritus,’ 381-408 in D.J. Furley and R.E. Allen (eds), Studies in Presocratic Philosophy, vol. 2: Eleatics and Pluralists (London).
• Wardy, Robert, 1988, ‘Eleatic Pluralism,’ Archiv für Geschichte der Philosophie 70: 125-46.
• Warren, James, 2002, Epicurus and Democritean Ethics: An Archaeology of Ataraxia (Cambridge).

[Please contact the author with suggestions.]

atomism: ancient | Epicurus | Leucippus | Lucretius | -->Melissus --> | Parmenides | Zeno of Elea | Zeno of Elea: Zeno's paradoxes

Acknowledgments

I wish to thank the ancient philosophy editor John Cooper, A.P.D. Mourelatos and Tim O'Keefe for helpful comments and suggestions.

A History of the Atomic Theory: From Democritus to Dalton

Werner Forssmann: The Nobel Prize winner who “touched his own heart”

The history of the atomic theory is a fascinating journey that spans over two millennia. It involves the contributions of numerous scientists and philosophers who sought to understand the fundamental building blocks of matter.

Throughout history, the atomic theory has evolved and deepened our understanding of matter and its fundamental properties. It has played a central role in the development of modern chemistry and physics, with applications in various scientific and technological fields.

Although we know an atom as a particle that is made up of various subatomic particles, like the proton, neutron and electron, this was not known for over 2,000 years when Democritus, the Ancient Greek philosopher, first defined an atom as an indivisible particle around the year 400 B.C. 

It was not until 1808 that the English scientist, John Dalton, came up with what we now know as the Modern Atomic Theory.

Ancient History of the Atom

The concept of the atomic theory dates back to Ancient Greece, with philosophers like Leucippus and his student Democritus proposing that matter is composed of indivisible particles called atomos (meaning “indivisible” in Greek) around the fifth century B.C. Democritus believed that atoms were too small to be seen. However, their ideas were philosophical and lacked empirical evidence.

Aristotle , a prominent philosopher of the time, rejected the atomic theory in favour of his own ideas, which dominated scientific thought for centuries. Aristotle believed in the continuous and infinitely divisible nature of matter. Aristotle postulated that all matter was made of only four elements – Earth, Air, Water and Fire.

Unfortunately, the atomic ideas of Democritus had no lasting effects on other Greek philosophers, including Aristotle. In fact, Aristotle dismissed the atomic idea as worthless. Ancient Greeks considered Aristotle’s opinions as “very important” and if Aristotle thought the atomic idea had no merit, then most of these Greeks thought the same as well.

During the Middle Ages and the Renaissance, scientists pursued various goals, including the transmutation of base metals into gold and the discovery of the philosopher’s stone. This was known as alchemy . These pursuits contributed to early chemical knowledge but were often shrouded in mysticism and superstition.

However, philosophers are not scientists nor do they test their ideas. Instead, they use reasoning to back up their beliefs. To them, human reasoning was superior to experimentation.  Democritus created the first atomic model (a round sphere with no electrons, protons, or neutrons). His contribution helped people understand the idea of an atom and helped other scientists further look into the science of the atom and its generic makeup.

Due to a lack of evidence and experiments, their views on what atoms look like and how they behave were incorrect. Its actual existence was not established until the 19th century when the idea was accepted and refined by scientists. So, for the next 2,000 years, the world depended on the theories of Democritus and Aristotle, until the year 1808, when John Dalton came up with the Modern Atomic Theory.

Due to a lack of evidence and experiments, their views on what atoms look like and how they behave were incorrect. Its actual existence was not established until the 19th century when the idea was accepted and refined by scientists. So, for the next two thousand years, the world depended on the theories of Democritus and Aristotle, until the year 1808, when John Dalton came up with the Modern Atomic Theory .

Modern Atomic Theory

John Dalton (1766–1844) , an English Chemist, put forward a theory to describe the nature of the atom. The atom is now considered to be the basic unit of simple substances or elements. He was a schoolteacher who performed many experiments on atoms. His atomic theory had five statements:

1. Atoms are tiny, indivisible particles.

2. Atoms can neither be created nor destroyed.

3. Atoms of one element are all the same.

4. Atoms of different elements are different.

5. Compounds form by combining atoms.

The really awesome thing about Dalton’s model of the atom is that he came up with it without ever seeing the atom! He had no concept of protons, neutrons or electrons. His model was created solely on experiments that were macroscopic, or seen with the unaided eye.

Although the two theories that proposed atoms couldn’t be divided were not true, John Dalton added significantly to the developments of atomic theory, and would greatly influence J.J. Thomson in his own.

Cathode Ray Tube

Joseph John Thomson (1856–1940) , the son of an English bookseller, had wanted to be an engineer and was already admitted to college at an unusually young age of 14 to study engineering. But in 1873, his father died and due to lack of funds changed his major to physics.

In 1897, as Cavendish Professor of Physics at Cambridge, Thomson discovered the electron which he had originally named as corpuscle. He was also the first scientist to show that the atom is made of other smaller particles and ended up contributing to more than the atomic theory. He helped to indirectly create the television and the computer.

Using his research on Cathode Ray Tube technology, Thomson showed that when a potential difference of 5000 volts was applied across a glass tube containing a gas at a very low pressure of about 0.0001 atmospheric pressure, the tube began to glow. When the potential difference was increased to 15000 volts, a bright green glow appeared on the glass.

Thomson was able to prove that the glow was due to some kind of rays which travelled in straight lines from the cathode. He called these rays, cathode rays, which showed that they are composed of only negatively charged particles which he called electrons, because they are attracted by the positive plate of the tube and repelled by the negative plate of the same tube. Hundreds of years earlier, Dalton had proposed that atoms were neutral, solid spheres but Thomson’s experiment disproved Dalton’s theory.

In 1898, Thomson proposed his model of the atom, which advocated that electrons and protons were haphazardly placed all through the atom. He called the theory, the Plum Pudding Model . This theory was not accurate, but subsequently led to the discovery of the nucleus, made by Ernest Rutherford.

Gold foil experiment

Ernest Rutherford (1871–1937) , a New Zealander, was the second of eleven children born to his parents. After college, he travelled to England to work as a researcher at the University of Manchester. He was a student of J.J Thomson.

In 1911, Rutherford, along with Hans Geiger (1882–1945) and Ernest Marsden (1889–1970) , conducted the gold foil experiment using Thomson’s model as a reference. In order to find out what is inside an atom, they used positively charged particles called alpha (α) particles from a radioactive source to bombard the atom (a thin gold foil). They found out that most of the alpha particles followed a straight path through the gold foil, some of them were scattered through wide angles while a few were even scattered in the backward direction.

Studying the experimental results, Rutherford proposed a nuclear theory of the atom which states that atom consists of a positive core called the nucleus, where most of the mass of the atom is contained and electrons move around the nucleus.

Quantum Theory

In 1913, Niels Bohr (1885–1962) proposed his theory of the atom using the Quantum Theory. Agreeing with Rutherford’s model of the atom, he suggested that electrons are arranged in up to seven specific energy levels and that each spectral line is caused by an electron.  Bohr postulated that circular orbits of the electrons were quantized (orbiting of electrons at certain specific energy levels within the atom).

Bohr determined that different energy levels could be found by using mathematical formulas, which measured the wavelengths of the different energy levels. He also went on to suggest that electrons would only occupy the lowest possible energy level on the respective level they were on. Moreover, electrons would only move up a level (increasing energy) if the lower levels were full. Bohr’s model was not entirely correct but it would lead to Schrödinger’s idea of the modern atomic model.

The Wave Mechanics Model

In 1926, Erwin Schrödinger (1887–1961) introduced the Wave Mechanics Model which describes the behaviour of the tiny particles that make up matter in terms of waves. Schrödinger formulated the Schrödinger wave equation to describe the behaviour of electrons (tiny, negatively charged particles) in atoms. He developed the equation which is used today to understand atoms and molecules.

The complex mathematics behind Schrödinger’s wave equation makes it extremely difficult to solve for any system more complicated than a hydrogen atom, which has only one proton and one electron.

In 1932, James Chadwick (1891–1974) , a student of Rutherford, discovered a sub-particle of the atom called the neutron through the bombardment of a thin sheet of beryllium with alpha particles. The neutron carried no charge and its discovery indicated that the atomic nucleus was made up of protons and neutrons. It also explained the existence of isotopes of an element.

Further experiments pertaining to the atomic theory are still being carried out by scientists with the hope of new ideas, theories and pieces of evidence being introduced. The scientific world is looking forward to seeing more scientists unravel more mysteries concerning the model of the atom and subsequently the modern atomic theory.

The atom is made up of three main sub-particles – electrons, protons, and neutrons with positive, negative, and zero charges respectively.

An atom consists of a positively charged core called the nucleus, where most of the mass of the atom is contained and electrons move around the nucleus.

When an electron is excited, it will jump from a level of lower energy to a level of higher energy.

The Wave Mechanics Model of the atom makes the electron elusive and indicates a region around the nucleus called an orbital.

Other scientists who have contributed to the Atomic Theory include Antoine Lavoisier (1743–1794), Isaac Newton (1642–1727), Dmitri Mendeleev (1834–1907), Wilhelm Roentgen (1845–1923), Robert A. Millikan (1868– 963), Marie Curie (1867–1934), Henry Moseley (1887–1915), Max Planck (1858–1947), Albert Einstein (1879–1955), Werner Heisenberg (1901–1976), Louis de Broglie (1892–1987) and Enrico Fermi (1901–1954).

We always have more stories to tell, so make sure you are subscribed to our YouTube Channel and have pressed the bell button for interesting historical videos. You can also follow us on all our social media handles and don’t hesitate to share this article with your friends as well.

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How Jabir Ibn Hayyan Became the Father of Modern Chemistry

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Dalton's Atomic Theory vs. Democritus' Atomic Theory

What's the difference.

Dalton's Atomic Theory, proposed in the early 19th century, revolutionized the understanding of atoms. According to Dalton, atoms are indivisible and indestructible particles that combine in fixed ratios to form compounds. He also introduced the concept of different elements having different types of atoms. On the other hand, Democritus' Atomic Theory, proposed in ancient Greece, suggested that atoms are the fundamental building blocks of matter and are indivisible. However, Democritus did not provide any experimental evidence to support his theory, whereas Dalton's theory was based on extensive experimentation and observation. Despite their differences, both theories laid the foundation for the modern understanding of atoms and their role in chemistry.

Further Detail

Introduction.

Atomic theory is a fundamental concept in the field of chemistry, providing a framework for understanding the nature of matter and its behavior. Two prominent figures in the development of atomic theory are John Dalton and Democritus. While Democritus proposed his atomic theory in ancient Greece, Dalton's atomic theory emerged during the early 19th century. This article aims to compare the attributes of Dalton's Atomic Theory and Democritus' Atomic Theory, highlighting their similarities and differences.

Democritus' Atomic Theory

Democritus, an ancient Greek philosopher, was one of the first to propose the concept of atoms. According to Democritus' Atomic Theory:

• All matter is composed of tiny, indivisible particles called atoms.
• Atoms are eternal, indestructible, and indivisible.
• Atoms are constantly moving and can combine to form different substances.
• Atoms have different shapes and sizes, which determine their properties.
• Changes in matter occur due to the rearrangement of atoms.

Democritus' theory laid the foundation for understanding the existence of discrete particles that make up matter. However, it lacked experimental evidence and mathematical support, limiting its acceptance and development.

Dalton's Atomic Theory

John Dalton, an English chemist, expanded upon Democritus' ideas and formulated his own atomic theory, which became widely accepted in the scientific community. Dalton's Atomic Theory consists of the following postulates:

• All matter is composed of indivisible particles called atoms.
• Atoms of the same element are identical in size, mass, and chemical properties.
• Atoms of different elements have different sizes, masses, and chemical properties.
• Atoms combine in simple whole-number ratios to form compounds.
• Chemical reactions involve the rearrangement of atoms, but no atoms are created, destroyed, or changed into atoms of another element.

Dalton's theory introduced the concept of atomic masses and provided a quantitative explanation for chemical reactions. It also emphasized the conservation of matter during chemical transformations. Dalton's Atomic Theory formed the basis for further advancements in atomic structure and the development of modern atomic theory.

Comparison of Attributes

While both Democritus' and Dalton's atomic theories share the fundamental concept of atoms, there are notable differences in their attributes:

1. Indivisibility of Atoms

Democritus believed that atoms are indivisible and indestructible, while Dalton's theory stated that atoms are indivisible but can combine to form compounds. Dalton's view was supported by experimental evidence, such as the law of definite proportions, which demonstrated that elements combine in fixed ratios to form compounds.

2. Uniformity of Atoms

Democritus proposed that atoms have different shapes and sizes, leading to variations in their properties. In contrast, Dalton's theory asserted that atoms of the same element are identical in size, mass, and chemical properties. This idea was later refined with the discovery of isotopes, which are atoms of the same element with different masses.

3. Mathematical Explanation

Dalton's Atomic Theory provided a mathematical explanation for chemical reactions by introducing the concept of atomic masses and simple whole-number ratios. This quantitative approach allowed for the prediction and calculation of reactant and product masses, providing a more comprehensive understanding of chemical transformations. Democritus' theory, on the other hand, lacked mathematical support and relied primarily on philosophical reasoning.

4. Experimental Evidence

Dalton's Atomic Theory was supported by various experimental observations, such as the law of multiple proportions and the law of conservation of mass. These experimental findings provided strong evidence for the existence of atoms and their behavior during chemical reactions. In contrast, Democritus' theory lacked experimental evidence and was primarily based on logical reasoning and philosophical arguments.

5. Influence and Acceptance

Democritus' Atomic Theory had limited influence and acceptance during his time due to the lack of experimental evidence and the dominance of other philosophical schools of thought. In contrast, Dalton's Atomic Theory gained widespread acceptance and significantly influenced the development of modern chemistry. Dalton's theory provided a solid foundation for further research and discoveries in atomic structure and the understanding of matter.

Both Democritus' and Dalton's atomic theories played crucial roles in shaping our understanding of matter and its composition. While Democritus proposed the concept of atoms in ancient Greece, Dalton's Atomic Theory emerged during the 19th century and provided a more comprehensive and quantitative explanation for chemical behavior. Dalton's theory, supported by experimental evidence and mathematical reasoning, gained widespread acceptance and laid the groundwork for further advancements in atomic theory. Despite their differences, both theories contributed significantly to the development of modern chemistry and our understanding of the microscopic world.

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A good question, with a fascinating history. I'll answer from the perspective of electronic materials in materials science. In short, In fact, we can even manipulate individual atoms for potentially useful things (more on this later)! But this was not always the case. One of the earliest records we have on the atom came from Democritus, an ancient Greek philosopher (others like Plato and Aristotle had similar trains of thought). Democritus had a thought experiment. The idea was if you took a material and divided it half, you would have a smaller but identical chunk. If you keep dividing your material, there should eventually be a point where you've reached the smallest representative element of your material. That element is the In fact "atom" is derived from the Greek word "atomos," which roughly translates to indivisible (it turns out there are even smaller components that make up an atom, but the name stuck; see ). It wasn't until much later in the 18th and 19th centuries that significant progress towards understanding the atom was made. Our understanding of the structure of the atom has vastly changed from the model John Dalton first proposed with the development and advancement of quantum mechanics. It is the interplay between theory (e.g., quantum mechanics) and experiment that let's us characterize and engineer materials at the atomic level. Both are part of a feedback loop where e.g., experiment confirms a theoretical prediction or theory explains what is observed experimentally. Read more about the history and how our understanding of the atom changed ) (several seminal experiments that contributed to this are described). The coolest part is the fact that , and even manipulate them! is the famous image of using a scanning tunneling microscope. Each dot you see is an . Read more and . (you might have heard of nanotechnology, for instance). For example, here at UCSB, there is active research on growing materials with atomically sharp interfaces. Here is an . Each of the balls you see corresponds to a or atom; the other elements are harder to see because they are smaller/lighter, though you might be able to see the >b>Al and if you squint hard enough). This material was carefully grown using a technique called , and is being studied for its rich physics and as the next big electronic material for things like your computer and phone. Hope this helps! Best,

Nowadays we can indeed see atoms using advanced technology, like . This technology allows us to observe, or even move an individual atom. Here is a picture of the silicon atoms that scientists see using STM:

We can't see them with our eyes because they're too small, but we can build machines that can see them. In particular, , so using an x-ray camera and shining x-rays through something with an orderly arrangement of atoms (like a crystal), we can see the atoms inside of it by seeing how the x-rays scatter.

Great question. At first, scientists were not sure about what matter looked like on a very small scale. Atoms were just a theory. But scientists made a lot of other theories in chemistry that fit with the idea that matter is made up of atoms. Even though we couldn't prove these theories, many of them were useful. For example, atoms can explain why chemicals always react in the same ratios, since these chemicals are made up of atoms that must group together in the same numbers every time. We can use the STM to see details smaller than one nanometer, including atoms. has some interesting images made using the STM. We even have machines that can arrange atoms in simple patterns--many early examples of this technology show atoms arranged to spell out words or company names, like and to return to the search form. 262 IMAGES Atomic Models/Experiments PPT PPT Democritus Atomic Model Experiment Democritus and Aristotle Atomic Theory by Catherine Holtz on Prezi Aristotle, Democritus, Mendeleev & the Chemical Elements COMMENTS Democritus Democritus. First published Sun Aug 15, 2004; substantive revision Sat Jan 7, 2023. Democritus, known in antiquity as the 'laughing philosopher' because of his emphasis on the value of 'cheerfulness,' was one of the two founders of ancient atomist theory. He elaborated a system originated by his teacher Leucippus into a materialist ... Democritus Democritus (born c. 460 bce —died c. 370) was an ancient Greek philosopher, a central figure in the development of philosophical atomism and of the atomic theory of the universe. Knowledge of Democritus's life is largely limited to untrustworthy tradition. It seems that he was a wealthy citizen of Abdera, in Thrace; that he traveled widely ... Ancient Atomism Because Epicurus made some significant changes in atomist theory, it is often thought that his reformulation of the physical theory is an attempt to respond to Aristotle's criticisms of Democritus. Even more significant, however, is the increasing centrality of ethical concerns to Epicurus' atomism, and the importance of the view that ... Democritus Democritus (/ d ɪ ˈ m ɒ k r ɪ t ə s /, dim-OCK-rit-əs; Greek: Δημόκριτος, Dēmókritos, meaning "chosen of the people"; c. 460 - c. 370 BC) was an Ancient Greek pre-Socratic philosopher from Abdera, primarily remembered today for his formulation of an atomic theory of the universe. [2] Democritus wrote extensively on a wide variety of topics. [3] Democritus Democritus (l. c. 460 - c. 370 BCE) was a Greek philosopher and younger contemporary of Socrates, born in Abdera (though other sources cite Miletus) who, with his teacher Leucippus (l. 5th century BCE), was the first to propose an atomic universe.Democritus claimed that everything is made of tiny uncuttable building blocks known as atoms. Very little is known of Leucippus, and almost none of ... Atom Atom - Development, Theory, Structure: The concept of the atom that Western scientists accepted in broad outline from the 1600s until about 1900 originated with Greek philosophers in the 5th century bce. Their speculation about a hard, indivisible fundamental particle of nature was replaced slowly by a scientific theory supported by experiment and mathematical deduction. Early Ideas about Matter Ultimately, though, Aristotle and Plato, two of the best-known philosophers of Ancient Greece, rejected the theories of Democritus.Aristotle accepted the theory of Empedocles, adding his own (incorrect) idea that the four core elements could be transformed into one another. Because of Aristotle's great influence, Democritus's theory would have to wait almost 2,000 years before being rediscovered. Ancient physics: How Democritus predicted the atom The idea of the atom goes as far back as the ancient Greek philosopher Democritus in about 400 B.C.E. This led to his "theory of eidôla" to explain how our minds create the illusion of ... Leucippus and Democritus LEUCIPPUS AND DEMOCRITUS. Leucippus and Democritus were the earliest Greek atomists. The originator of the atomic theory, Leucippus (fifth century BCE), must be considered a speculative thinker of the first order, but to Democritus (c. 460 - c. 370 BCE) must go the credit for working out the detailed application of the theory and supporting it with a subtle epistemology. The Atomist Philosophers of Ancient Greece: Leucippus, Democritus, and The fourth-century BC Greek philosopher Aristotle and his student Theophrastus made references to Democritus in their works. Aristotle wrote a monograph of Democritus, of which only fragments survive, but he viewed him as a rival in natural philosophy. ... In addition to the "slight swerve" of the atoms introduced to Democritus's theory ... Democritus' Idea of the Atom Aristotle disagreed with Democritus and offered his own idea of the composition of matter. According to Aristotle, everything was composed of four elements: earth, air, fire, and water. The theory of Democritus explained things better, but Aristotle was more influential, so his ideas prevailed. ... (PDF) Sight and the Philosophy of Vision: Classical Greek Theories of This essay examines the theories of vision in Democritus, Plato and Aristotle. These philosophers offered different accounts of how a person (or the eye) can see things in the visible world. Each philosopher's theory of vision reflects his ... Democritus' theory of vision combines the notions of images (eidola) streaming from objects and air ... Democritus' Idea of the Atom Aristotle disagreed with Democritus and offered his own idea of the composition of matter. According to Aristotle, everything was composed of four elements: earth, air, fire, and water. The theory of Democritus explained things better, but Aristotle was more influential, so his ideas prevailed. We had to wait almost two thousand years before ... Democritus Democritus. First published Sun Aug 15, 2004. Democritus, known in antiquity as the 'laughing philosopher' because of his emphasis on the value of 'cheerfulness,' was one of the two founders of ancient atomist theory. He elaborated a system originated by his teacher Leucippus into a materialist account of the natural world. Democritus' Idea of the Atom According to this theory, atoms of matter are in constant random motion. This motion is greater in , and it is greater in liquids than in solids. But even in solids, atoms are constantly vibrating in place. Democritus thought that different kinds of matter vary because of the size, shape, and arrangement of their atoms. A History of the Atomic Theory: From Democritus to Dalton So, for the next 2,000 years, the world depended on the theories of Democritus and Aristotle, until the year 1808, when John Dalton came up with the Modern Atomic Theory. Due to a lack of evidence and experiments, their views on what atoms look like and how they behave were incorrect. Its actual existence was not established until the 19th ... Democritus Interestingly, many scientists denied the atomic theory of Democritus all the way until Einstein's famous theory in 1905 and Rutherford's famous experiment in 1909. PDF 10. Leucippus and Democritus: Fifth-century Atomism (Simplicius, Commentary on Aristotle's Physics 28.4-26) 7. (67A7) Leucippus and Democritus have accounted for all things very systematically and in a single theory, taking the natural start-ing point as their own. For some of the early philosophers held that what-is is necessarily one and immovable. For the void is not, Dalton's Atomic Theory vs. Democritus' Atomic Theory Democritus believed that atoms are indivisible and indestructible, while Dalton's theory stated that atoms are indivisible but can combine to form compounds. Dalton's view was supported by experimental evidence, such as the law of definite proportions, which demonstrated that elements combine in fixed ratios to form compounds. 2. UCSB Science Line But this was not always the case. One of the earliest records we have on the atom came from Democritus, an ancient Greek philosopher (others like Plato and Aristotle had similar trains of thought). Democritus had a thought experiment. The idea was if you took a material and divided it half, you would have a smaller but identical chunk. Democritus vs. Aristotle by Andre Thompson on Prezi Democritus: He thought that all matter is composed of atoms. Matter in an empty space has a different appearence. Atoms determine properties. Believed atoms were mechanically bound. Aristotle: He rejected Democritus atomic theroy and didn't think atoms move through empty spaces because he didn't think that empty spaces existed. He believed that ... essay homework paper phd project resume review study thesis