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: Democritus

Born: c. 460 BCE in Abdera, Thrace

Died: c. 370 BCE

Experiment/Discovery

Democritus and his mentor, Leucippus, were rationalist and materialist philosophers who used thought experiments and logical reasoning rather than physical experiments to develop their ideas

Democritus proposed the radical idea that all matter is composed of minute, indivisible particles called atoms that exist in an infinite void. His theory transformed the understanding of matter by suggesting that all the diversity of the physical world could be explained by the arrangements and movements of these eternal, fundamental building blocks, challenging the dominant ancient Greek belief that matter could be endlessly divided. For over 2,000 years, his atomist theory was largely rejected in favor of Aristotle's rival elemental theory, which claimed that matter was continuous and composed of four elements.

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Aristotle disagreed with Democritus’ theory. He was also a philosopher, not a scientist. He believed you could understand and figure out things by simply thinking about them. He also believed…

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Aristotle (384–322 BC). He was born in Stagira, a Greek seaport on the northern coast of Greece.

Aristotle is not known for any experiments or discoveries related to atomic theory. In fact, he opposed the idea of indivisible particles proposed by other Greek philosophers like Democritus

Aristotle did not contribute to atomic theory but actively challenged and delayed its acceptance for nearly 2,000 years. His theory held that all matter was a continuum made of four basic elements—earth, air, fire, and water—and could be divided indefinitely. This idea fundamentally influenced scientific thought by redirecting focus toward a philosophical understanding of matter rather than an anatomist one

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John Dalton (1766-1844)

Dalton's research on gases led to his groundbreaking atomic theory, published in 1808 in his work A New System of Chemical Philosophy. His theory is based on several key ideas

Dalton's atomic theory was the first comprehensive, evidence-based attempt to describe matter in terms of atoms and their properties. It established that all matter is made of indivisible atoms, and that atoms of different elements have unique masses and properties. This work fundamentally changed chemistry by laying the groundwork for quantitative analysis and providing a theoretical framework for understanding chemical reactions as the rearrangement of atoms.

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Antoine Lavoisier (1743-1794)

Elucidated the role of oxygen: Beginning his investigations in 1772, Lavoisier conducted experiments on combustion and calcification (the heating of metals). He heated mercury in a sealed container, observed the formation of a red calx (mercury oxide), and found that the air inside was reduced by a fifth. When he later heated the red calyx, he was able to collect a gas—oxygen—that weighed the same as the mass the mercury gained during calcification.

Lavoisier is known as the "father of modern chemistry" for his emphasis on quantitative, experimental-based chemistry. By meticulously measuring the mass of reactants and products, he established the Law of Conservation of Mass and proved the true nature of combustion as a reaction with oxygen, effectively refuting the phlogiston theory. His work fundamentally changed the understanding of matter by showing that it is neither created nor destroyed in chemical reactions, which laid the groundwork for future atomic theories.

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Lived 1743 - 1794.
Antoine Lavoisier revolutionized chemistry. He named the elements carbon, hydrogen and oxygen; discovered oxygen's role in combustion and respiration; established that water is a compound of hydrogen and oxygen; discovered that sulfur is an element, and helped continue the transformation of chemistry from a qualitative science into a quantitative one.

Beginnings

Antoine-Laurent Lavoisier was born into a privileged family on August 26, 1743 in France's capital city, Paris.

His father was Jean-Antoine Lavoisier, a lawyer in the Paris Parliament.

His mother was Émilie Punctis, whose family wealth had come from a butchery business. She died when Antoine was five years old, leaving him a large amount of money.

Between the ages of 11 and 18, Antoine was educated at Collège des Quatre-Nations, a college of the University of Paris. He studied general subjects there, including the sciences in his final two years.

Although he was very attracted to the sciences, he enrolled in the college's law school at age 18, aiming to pursue the same career as his father. (His father had encouraged him to believe that science was merely a hobby, not a serious profession.)

After two years studying law, Antoine Lavoisier was awarded a bachelor's degree. A year later, in 1764, he obtained a license to practice as a lawyer, but decided against this.

Antoine Lavoisier's Lifetime in Context

Antoine Lavoisier's Science

While studying for his law degree Lavoisier maintained his interest in science, attending science lectures in addition to law lectures.

In 1764, the year he obtained his license to practice law, he also published his first scientific paper. In the same year he read a paper to the elite French Academy of Sciences. He was elected to the French Academy of Sciences in 1769, aged just 26.

Forms of Carbon

In 1772 Lavoisier and other chemists bought a diamond and placed it in a closed glass jar. They used a remarkable giant magnifying glass to focus the sun's rays on the diamond. The diamond burned and disappeared.

Lavoisier noted the overall weight of the jar was unchanged, even though all of the diamond had disappeared. This observation would later be part of the evidence convincing him that his law of mass conservation was correct.

Whether diamond or charcoal were burned by the giant lens, the same gas was produced - we now call it carbon dioxide. Lavoisier realized that diamond and charcoal are different forms of the same element.

He gave this element the name carbon.

Oxygen and Combustion

In 1772 people did not understand the process of burning. They had inconsistent and confused theories, chief of which was the theory of phlogiston, an undetectable substance which sometimes had negative mass!

We now know that combustion happens when substances react with oxygen at high temperatures. In 1772, however, when Lavoisier began working in this field, oxygen's discovery by Joseph Priestley still lay two years in the future.

Lavoisier's work enjoyed a great advantage over many other scientists, namely his great passion for making accurate measurements. He pursued quantitative rather than qualitative science.

In 1772 Lavoisier discovered that when phosphorus or sulfur are burned in air the products are acidic. The products also weigh more than the original phosphorus or sulfur, suggesting the elements combine with something in the air to produce acids. But what?

In 1774 Joseph Priestley visited Paris. He told Lavoisier about the gas produced when he decomposed the compound we now called mercury oxide. This gas supported combustion much more powerfully than normal air. Priestley believed the gas was a particularly pure version of air. He started calling it dephlogisticated air, believing its unusual properties were caused by the absence of phlogiston.

Lavoisier did not believe it was dephlogisticated anything, because he did not believe in phlogiston.

In 1779 Lavoisier coined the name oxygen for the element released by mercury oxide. He found oxygen made up 20 percent of air and was vital for combustion and respiration. He also concluded that when phosphorus or sulfur are burned in air, the products are formed by the reaction of these elements with oxygen.

"Sulfur, when burning, absorbs oxygen gas; the resulting acid is considerably heavier than the sulfur burned; its weight is equal to the sum of weights of the sulfur burned and the oxygen absorbed."

Elementary Treatise on Chemistry

Sulfur is an element

In 1777 Lavoisier correctly identified sulfur as an element. He had carried out extensive experiments involving this substance and observed that it could not be broken down into any simpler substances.

The Conservation of Mass

In 1778 Lavoisier found that when mercury oxide is heated its weight decreases. The oxygen gas it releases has exactly the same weight as the weight lost by the mercury oxide.

While this may seem obvious to us today, it was less so in those days (hence the general support for the phlogiston theory). After carrying out work with a number of different substances, and recalling earlier work such as his work in 1772 with carbon, Lavoisier announced a new fundamental law of nature: the law of conservation of mass:

matter is conserved in chemical reactions

or stated in another way:

the total mass of a chemical reaction's products is identical to the total mass of the starting materials

It is often said that Lavoisier was the first scientist to state the principle of mass conservation. This is not strictly incorrect. In 1630 Jean Rey had formulated a similar law; in 1755 Joseph Black had assumed the law was true in his work discovering magnesium; and in 1760 Mikhail Lomonosov had published a statement of the law.

The law of mass conservation only became firmly established after Lavoisier independently discovered it.

"In performing experiments, it is necessary... that they be simplified as much as possible, and that every circumstance that could complicate the results should be completely removed."

Elementary Treatise on Chemistry

Combustion and respiration

Lavoisier suspected that combustion and respiration are chemically the same. He demonstrated this with the help of Pierre-Simon Laplace. The pair measured the amount of carbon dioxide and heat given off by a guinea pig as it breathed. They compared this to the amount of heat produced when they burned carbon to produce the same amount of carbon dioxide as had been exhaled by the guinea pig.

The results allowed Lavoisier to conclude that respiration is a form of combustion. The heat produced by mammals during respiration keeps their bodies above room temperature.

Water is not an element

In 1783 Lavoisier coined the name 'hydrogen' for the gas which Henry Cavendish had recognized as a new element in 1766; Cavendish had called the gas inflammable air.

Working again with Pierre-Simon Laplace, Lavoisier burned hydrogen with oxygen and found that water was produced, establishing that water is not an element, but is actually a compound made from the elements hydrogen and oxygen. This result astonished many people, because at that time 'everyone knew' that water was itself one of the 'indivisible' elements.

Hydrogen means water former in Greek.

"It required 85 parts by weight of oxygen and 15 parts of hydrogen to compose 100 parts of water."

Elementary Treatise on Chemistry

There is no such thing as phlogiston!

Lavoisier's work with oxygen and his demonstration of mass conservation had made it absolutely clear to him that phlogiston was fictitious. In 1783 his paper Reflections on Phlogiston marked the beginning of the end for phlogiston and a triumph for Lavoisier's oxygen theory and quantitative chemistry.

Lavoisier's list of elements

In 1789 Lavoisier published his groundbreaking Elementary Treatise on Chemistry.

Aristotle's elements of earth, water, air, fire and quintessence had been abandoned by medieval alchemists, and Lavoisier now abandoned their tria prima of sulfur, mercury and salt.

Elementary Treatise on Chemistry detailed his oxygen theory of chemistry (banishing phlogiston), made clear the difference between a compound and an element, and contained a list of chemical elements. The list included oxygen, nitrogen, hydrogen, sulfur, phosphorus, carbon, antimony, cobalt, copper, gold, iron, manganese, molybdenum, nickel, platinum, silver, tin, tungsten, and zinc.

Curiously, and consistent with chemistry's infancy, Lavoisier included light as one of the chemical elements.

He also included a substance called caloric, which was later shown, like phlogiston, to be fictitious. In fact, so much of Elementary Treatise on Chemistry involves caloric in explanations that it slightly spoils the work. Again though, we must remember that chemistry was still in its infancy, and Lavoisier was largely responsible for pulling it up on to firmer ground.

"Experiments upon vegetation give reason to believe that light combines with certain parts of vegetables, and that the green of their leaves, and the various colors of flowers, is chiefly owing to this combination."

Elementary Treatise on Chemistry

The Metric System

Starting in 1791, Lavoisier served on the committee of the French Academy of Sciences which developed the metric system of measurement. Other members of the committee included the well-known mathematicians Pierre-Simon Laplace and Adrien-Marie Legendre.

Some Personal Details and The End

In addition to his scientific research, Lavoisier was industrious in other fields. At the age of 26 he bought into a company that gathered tax for the French government. Having done this, he tried to reform tax law to help poorer taxpayers. He also served on the government's gunpowder commission, improving the quality of French gunpowder considerably.

Lavoisier married Marie-Anne Pierrette Paulze in 1771. He was 28 and she was just 13. In marrying Marie-Anne so young, he was acting at the request of her father, who was a senior member of the tax company Lavoisier had bought into. The Count d'Amerval, who was about 40, had made a proposal of marriage to Marie-Anne and her father had been threatened with dismissal from the tax company if she did not say yes. Lavoisier stepped in and married her to provide Marie-Anne and her father with a suitable excuse for her not marrying The Count.

Marie-Anne was a skilled artist and well-educated. She helped Lavoisier considerably with his work, translating scientific papers from English into French, adding her own notes and scientific criticisms of papers, helping with laboratory work, making accurate drawings of laboratory apparatus for Lavoisier's scientific publications, and keeping accurate written records of Lavoisier's experiments.

During the French Revolution, which began in 1789, wealthy people and anyone who had worked for the government were under threat. In 1793 the revolutionaries put an end to the French Academy of Sciences and other academic societies.

In 1794 Lavoisier was branded a traitor because of his involvement with taxation. He was also unpopular with revolutionaries because he had supported foreign scientists whom the revolutionaries wished to strip of their assets.

Lavoisier was sentenced to death by the revolutionaries. Trumped-up charges against him included stealing money from France's Treasury and giving it to France's enemies.

Antoine Lavoisier died by the guillotine at the age of 50 on May 8, 1794 in Paris. Marie-Anne's father and 26 other people were executed on the same occasion.

At the end of 1795, in a U-turn, the French government found Lavoisier innocent of all charges. By then, of course, it was too late: he was just another innocent victim of the revolution's Reign of Terror.

Lavoisier's wife and his tremendous contributions to chemistry survived. Ironically Marie-Anne later married Benjamin Thompson, who played a key role in establishing that caloric, like phlogiston, was merely a figment of people's imaginations.

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Further Reading
Antoine-Laurent Lavoisier
Elements of Chemistry
Dover Publications Inc, 1965

Robert D. Whitaker
An Historical Note on the Conservation of Mass
J. Chem. Educ., 1975, 52 (10), p 658

Arthur Donovan
Antoine Lavoisier: Science, Administration and Revolution
Cambridge University Press, 1996

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Lived 1743 - 1794. Antoine Lavoisier revolutionized chemistry. He named the elements carbon, hydrogen and oxygen; discovered oxygen's role in combustion and respiration; established that water is a compound of hydrogen and oxygen; discovered that sulfur is an element, and helped continue the transformation of chemistry from a qualitative science into a quantitative one.

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J.J. Thomson (1856-1940)

In 1897, Thomson conducted a series of experiments using cathode ray tubes. A cathode ray tube is a sealed glass tube from which most of the air has been removed. When voltage is applied across the tube, a glowing beam travels from the cathode to the anode.

J.J. Thomson's work proved that the atom was not the indivisible particle that John Dalton had proposed. Through his cathode ray experiments, he discovered the electron, a subatomic particle with a negative charge. His "plum pudding" model fundamentally changed the understanding of matter by suggesting that atoms were composed of charged, smaller components, a concept that paved the way for future atomic models.

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J.J. Thomson | Biography, Nobel Prize, & Facts | Britannica

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J.J. Thomson, English physicist who helped revolutionize the knowledge of atomic structure by his discovery of the electron (1897). He received the Nobel Prize for Physics in 1906 and was knighted two years later. Learn more about his life, career, and legacy.

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Ernest Rutherford (1871-1937)

Discovery of the atomic nucleus: While most of the alpha particles passed straight through the foil as expected, a small number were deflected at large angles, and some even bounced directly back. This indicated the presence of a tiny, dense, positively charged region at the center of the atom, which Rutherford called the nucleus

Rutherford's gold foil experiment revolutionized the understanding of atomic structure by discovering the nucleus. The unexpected deflection of alpha particles showed that an atom is not a uniform "plum pudding" but is mostly empty space surrounding a tiny, dense, positively charged core. This fundamental insight paved the way for the modern understanding of the atom and led to the development of nuclear physics.

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Through his inventive experimental work Rutherford made many new discoveries in both radioactivity and nuclear physics.

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Robert Millikan (1868-1953)

Experiment/Discovery: The Oil Drop Experiment

In 1909, Robert Millikan and his graduate student, Harvey Fletcher, developed the oil drop experiment to precisely measure the elementary unit of electric charge (the charge of a single electron). The experiment built upon previous attempts to measure the charge of an electron that used charged water droplets but was a major improvement in accuracy.

Millikan's oil drop experiment determined the fundamental unit of electric charge, confirming that the charge of an electron is a discrete, quantifiable value rather than a variable amount. By proving that all electric charges were simple multiples of this single number, his findings established the quantization of electric charge and enabled scientists to calculate the mass of the electron with much greater accuracy. This work solidified the existence of the electron as a fundamental particle and contributed to the development of the modern atomic model.

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Director, Norman Bridge Laboratory of Physics, California Institute of Technology, Pasadena, CA, USA. Nobel laureate in Physics, 1923

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Niels Bohr (1885-1962)

Bohr's major contribution was the Bohr model of the atom, proposed in 1913. He built upon Ernest Rutherford's nuclear model, which described a dense, positively charged nucleus with electrons orbiting it, similar to planets around the sun.

Niels Bohr's model revolutionized the understanding of atomic structure by introducing the concept of quantized energy levels. His work explained why atoms are stable and produce specific spectral lines, which classical physics could not. The Bohr model served as a crucial stepping stone toward the modern quantum mechanical model of the atom, demonstrating that matter and energy behave differently at the atomic scale.

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Niels Henrik David Bohr Nobel Prize in Physics 1922 Affiliation at the time of the award: Copenhagen University, Copenhagen, Denmark Prize motivation: "for his services in the investigation of the structure of atoms and of the radiation emanating from them" Prize share: 1/1 Niels Bohr was born and raised in Copenhagen.

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Max Planck (1858-1947)

Planck, a theoretical physicist, did not conduct experiments himself for his most famous discovery. Instead, he focused on solving the theoretical black-body radiation problem, which was based on experimental data collected by others, like Heinrich Rubens and Ferdinand Kurlbaum in Berlin.

Max Planck's groundbreaking work on black-body radiation introduced the revolutionary concept of quantized energy, laying the foundation for quantum theory. By proposing that energy is emitted in discrete packets called "quanta," he resolved inconsistencies that classical physics could not explain. This discovery completely changed the understanding of matter at the atomic and subatomic level, paving the way for a new era of modern physics.

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Early life

Max Karl Ernst Ludwig Planck was the sixth child of a distinguished jurist and professor of law at the University of Kiel. The long family tradition of devotion to church and state, excellence in scholarship, incorruptibility, conservatism, idealism, reliability, and generosity became deeply ingrained in Planck's own life and work. When Planck was nine years old, his father received an appointment at the University of Munich, and Planck entered the city's renowned Maximilian Gymnasium, where a teacher, Hermann Müller, stimulated his interest in physics and mathematics. But Planck excelled in all subjects, and after graduation at age 17 he faced a difficult career decision. He ultimately chose physics over classical philology or music because he had dispassionately reached the conclusion that it was in physics that his greatest originality lay. Music, nonetheless, remained an integral part of his life. He possessed the gift of absolute pitch and was an excellent pianist who daily found serenity and delight at the keyboard, enjoying especially the works of Schubert and Brahms. He also loved the outdoors, taking long walks each day and hiking and climbing in the mountains on vacations, even in advanced old age.

Planck entered the University of Munich in the fall of 1874 but found little encouragement there from physics professor Philipp von Jolly. During a year spent at the University of Berlin (1877-78), he was unimpressed by the lectures of Hermann von Helmholtz and Gustav Robert Kirchhoff, despite their eminence as research scientists. His intellectual capacities were, however, brought to a focus as the result of his independent study, especially of Rudolf Clausius's writings on thermodynamics. Returning to Munich, he received his doctoral degree in July 1879 (the year of Einstein's birth) at the unusually young age of 21. The following year he completed his Habilitationsschrift (qualifying dissertation) at Munich and became a Privatdozent (lecturer). In 1885, with the help of his father's professional connections, he was appointed ausserordentlicher Professor (associate professor) at the University of Kiel. In 1889, after the death of Kirchhoff, Planck received an appointment to the University of Berlin, where he came to venerate Helmholtz as a mentor and colleague. In 1892 he was promoted to ordentlicher Professor (full professor). He had only nine doctoral students altogether, but his Berlin lectures on all branches of theoretical physics went through many editions and exerted great influence. He remained in Berlin for the rest of his active life.

Planck recalled that his "original decision to devote myself to science was a direct result of the discovery...that the laws of human reasoning coincide with the laws governing the sequences of the impressions we receive from the world about us; that, therefore, pure reasoning can enable man to gain an insight into the mechanism of the [world]...." He deliberately decided, in other words, to become a theoretical physicist at a time when theoretical physics was not yet recognized as a discipline in its own right. But he went further: he concluded that the existence of physical laws presupposes that the "outside world is something independent from man, something absolute, and the quest for the laws which apply to this absolute appeared...as the most sublime scientific pursuit in life."

The first instance of an absolute in nature that impressed Planck deeply, even as a Gymnasium student, was the law of the conservation of energy, the first law of thermodynamics. Later, during his university years, he became equally convinced that the entropy law, the second law of thermodynamics, was also an absolute law of nature. The second law became the subject of his doctoral dissertation at Munich, and it lay at the core of the researches that led him to discover the quantum of action, now known as Planck's constant h, in 1900.

In 1859-60 Kirchhoff had defined a blackbody as an object that reemits all of the radiant energy incident upon it; i.e., it is a perfect emitter and absorber of radiation. There was, therefore, something absolute about blackbody radiation, and by the 1890s various experimental and theoretical attempts had been made to determine its spectral energy distribution-the curve displaying how much radiant energy is emitted at different frequencies for a given temperature of the blackbody. Planck was particularly attracted to the formula found in 1896 by his colleague Wilhelm Wien at the Physikalisch-Technische Reichsanstalt (PTR) in Berlin-Charlottenburg, and he subsequently made a series of attempts to derive " Wien's law " on the basis of the second law of thermodynamics. By October 1900, however, other colleagues at the PTR, the experimentalists Otto Richard Lummer, Ernst Pringsheim, Heinrich Rubens, and Ferdinand Kurlbaum, had found definite indications that Wien's law, while valid at high frequencies, broke down completely at low frequencies.

Planck learned of these results just before a meeting of the German Physical Society on October 19. He knew how the entropy of the radiation had to depend mathematically upon its energy in the high-frequency region if Wien's law held there. He also saw what this dependence had to be in the low-frequency region in order to reproduce the experimental results there. Planck guessed, therefore, that he should try to combine these two expressions in the simplest way possible, and to transform the result into a formula relating the energy of the radiation to its frequency.

The result, which is known as Planck's radiation law, was hailed as indisputably correct. To Planck, however, it was simply a guess, a "lucky intuition." If it was to be taken seriously, it had to be derived somehow from first principles. That was the task to which Planck immediately directed his energies, and by December 14, 1900, he had succeeded-but at great cost. To achieve his goal, Planck found that he had to relinquish one of his own most cherished beliefs, that the second law of thermodynamics was an absolute law of nature. Instead he had to embrace Ludwig Boltzmann's interpretation, that the second law was a statistical law. In addition, Planck had to assume that the oscillators comprising the blackbody and re-emitting the radiant energy incident upon them could not absorb this energy continuously but only in discrete amounts, in quanta of energy; only by statistically distributing these quanta, each containing an amount of energy hν proportional to its frequency, over all of the oscillators present in the blackbody could Planck derive the formula he had hit upon two months earlier. He adduced additional evidence for the importance of his formula by using it to evaluate the constant h (his value was 6.55 × 10 −27 erg-second, close to the modern value of 6.626 × 10 −27 erg-second), as well as the so-called Boltzmann constant (the fundamental constant in kinetic theory and statistical mechanics), Avogadro's number, and the charge of the electron. As time went on physicists recognized ever more clearly that-because Planck's constant was not zero but had a small but finite value-the microphysical world, the world of atomic dimensions, could not in principle be described by ordinary classical mechanics. A profound revolution in physical theory was in the making.

Planck's concept of energy quanta, in other words, conflicted fundamentally with all past physical theory. He was driven to introduce it strictly by the force of his logic; he was, as one historian put it, a reluctant revolutionary. Indeed, it was years before the far-reaching consequences of Planck's achievement were generally recognized, and in this Einstein played a central role. In 1905, independently of Planck's work, Einstein argued that under certain circumstances radiant energy itself seemed to consist of quanta (light quanta, later called photons), and in 1907 he showed the generality of the quantum hypothesis by using it to interpret the temperature dependence of the specific heats of solids. In 1909 Einstein introduced the wave-particle duality into physics. In October 1911 Planck and Einstein were among the group of prominent physicists who attended the first Solvay conference in Brussels. The discussions there stimulated Henri Poincaré to provide a mathematical proof that Planck's radiation law necessarily required the introduction of quanta-a proof that converted James Jeans and others into supporters of the quantum theory. In 1913 Niels Bohr also contributed greatly to its establishment through his quantum theory of the hydrogen atom. Ironically, Planck himself was one of the last to struggle for a return to classical theory, a stance he later regarded not with regret but as a means by which he had thoroughly convinced himself of the necessity of the quantum theory. Opposition to Einstein's radical light quantum hypothesis of 1905 persisted until after the discovery of the Compton effect in 1922.

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Max Planck | Biography, Discoveries, & Quantum Theory | Britannica

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Max Planck, German theoretical physicist who originated quantum theory, one of the fundamental theories of modern physics, for which he won the 1918 Nobel Prize for Physics. Learn about Max Planck's life and his physics discoveries with this article.

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Marie Curie (1867-1934)

Discovery of Radioactivity: Following Henri Becquerel's discovery that uranium salts emitted rays, Marie Curie used an electrometer to show that the radiation was directly proportional to the amount of uranium present in a compound. This led her to propose that radiation was an atomic property, not a molecular one. She also found that the mineral pitchblende was more radioactive than could be explained by its uranium content, suggesting it contained other, more active elements.

Marie Curie's research on radioactivity proved that atoms are not solid, indivisible particles, as their instability causes them to release energy and decay into other elements. Her discovery of polonium and radium provided definitive proof of subatomic processes and opened up entirely new fields of physics and chemistry. Her work laid the foundation for modern nuclear physics and medicine, including the development of radiotherapy for cancer treatment.

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Marie Curie: Facts About the Pioneering Chemist | HISTORY

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“Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fea…

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Louis de Broglie (1892-1987)

De Broglie proposed the theory of wave-particle duality for all matter in his 1924 doctoral thesis

Louis de Broglie is best known for his 1924 proposal that all matter, not just light, exhibits wave-like properties. This hypothesis of wave-particle duality for electrons and all other matter was pivotal in the development of wave mechanics and quantum theory. His work fundamentally changed the scientific view of the physical world, revealing that particles and waves were not mutually exclusive concepts but two manifestations of the same phenomenon.

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Louis de Broglie: Research and Atomic Theories

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Louis de Broglie, a French physicist, revolutionized our understanding of atomic physics with his theory that all types…

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Erwin Schrodinger (1905-1961)

Schrödinger is best known for his 1926 development of the Schrödinger wave equation, a fundamental result in quantum mechanics. Influenced by Louis de Broglie's idea that particles like electrons could also behave as waves, Schrödinger theorized that the behavior of electrons within atoms could be described by treating them as matter waves. He did not perform a physical experiment for this theory but instead formulated the mathematical framework of wave mechanics.

Erwin Schrödinger's main contribution was his development of the wave equation in 1926, which formed the basis for the modern quantum mechanical model of the atom. This model shifted the understanding of electrons from distinct particles in fixed orbits to matter waves existing in probable regions of space, called orbitals. By mathematically predicting the probable locations and energy levels of electrons, Schrödinger provided a more flexible and accurate description of atomic structure that replaced the simpler Bohr model.

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Schrödinger’s atomic model (1926 AD) - Rincón educativo

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It is known as the ‘Quantum-Ondulatory Model’ and was proposed by Erwin Schrödinger in 1926, based on the studies of De Broglie, Bohr and Sommerfeld. His model conceives of electrons as ripples of matter, i.e. it describes the wave-like behaviour of the electron.

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James Chadwick (1891-1974)

Chadwick discovered the neutron, an elementary particle with no electrical charge and a mass approximately equal to that of a proton. He made this groundbreaking discovery in 1932 while working at the Cavendish Laboratory at the University of Cambridge.

James Chadwick's 1932 discovery of the neutron completed the modern picture of the atom, revealing a neutral particle within the nucleus alongside protons. This revelation explained why atoms of the same element could have different atomic masses (isotopes) and provided a powerful new tool for nuclear physics, as uncharged neutrons could be used to probe and split atomic nuclei. His work fundamentally changed atomic theory and enabled the later discovery of nuclear fission, paving the way for nuclear energy and weapons.

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James Chadwick - Biography, Facts and Pictures

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Lived 1891 - 1974. James Chadwick discovered the neutron in 1932 and was awarded the Nobel Prize for Physics in 1935. Held in a German prison camp for all of World War 1, he led the British team in the Manhattan Project, in which the UK and Canada supported the USA’s World War 2 effort

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Werner Heisenberg (1901-1976)

Heisenberg is best known for developing the Uncertainty Principle, which he published in 1927. This principle states that it is impossible to know with complete accuracy both a particle's position and its momentum at the same time. The more precisely one of these properties is measured, the less precisely the other can be known.

Heisenberg's development of quantum mechanics and the Uncertainty Principle revolutionized atomic theory by proving that a particle's position and momentum cannot be known simultaneously with perfect accuracy. This fundamentally changed the understanding of matter by showing that absolute, deterministic certainty is impossible at the subatomic level, and that reality must be described in terms of probabilities. His work, alongside Schrödinger's, replaced the older, deterministic Bohr model with the probabilistic electron cloud model, which is the foundation of the modern understanding of the atom.

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Werner Heisenberg

German physicist

Born: December 5, 1901; Würzburg, Germany

Died: February 1, 1976; Munich, Germany

Twentieth-century German theoretical physicist Werner Heisenberg won the Nobel Prize in Physics in 1932 and is best remembered as one of the founders of quantum mechanics. His most important contribution to quantum mechanical ideas is the Heisenberg uncertainty principle, which has become a cornerstone of modern physics.
Primary field: Physics

Specialties: Theoretical physics; quantum mechanics; nuclear physics

Early Life

Werner Karl Heisenberg was born on December 5, 1901, in Würzburg, Germany, to August Heisenberg and Anna Wecklein Heisenberg. August was a scholar of ancient Greek language and literature and was a stern and demanding teacher. He encouraged his children to take academics seriously, and Werner excelled in his studies, particularly in science and math.

When his father received a teaching appointment at the University of Munich in 1910, Heisenberg entered the Maximilians Gymnasium (an academically rigorous secondary school) in the fall of 1911. He impressed his teachers with his intelligence and ambition, and he also developed interests in music and languages. Heisenberg graduated in 1920 and had already begun to focus on physics and mathematics, teaching himself calculus and the principles of Einstein's theory of relativity while in high school.

Following the end of World War I in 1918, Heisenberg became part of a nationalistic youth movement and accepted a leadership position of a group of young male activists who spent time discussing politics, philosophy, and science.

Heisenberg entered the University of Munich in 1920 and began to focus primarily on theoretical physics. Professor Arnold Sommerfeld was Heisenberg's mentor and encouraged his interest in atomic theory (the study of the parts and structure of the atom) and introduced him to two luminaries in the field, Max Born and Niels Bohr, both of whom would later mentor Heisenberg and collaborate on the formation of the theory of quantum mechanics and the uncertainty principle.

Heisenberg received his doctoral degree in 1923 and enrolled at the University of Göttingen to study physics under Max Born. In the fall of 1924, he travelled to the University Institute for Theoretical Physics in Copenhagen to study under Niels Bohr. In 1927, at the age of twenty-five, Heisenberg was appointed professor of theoretical physics and head of the physics department at the University of Leipzig.

Heisenberg met his future wife, Elisabeth Schumacher, at a private music recital in 1937. They were married four months later and had seven children, one of whom became a physics professor at the University of New Hampshire.

Life's Work

When Heisenberg became a theoretical physicist, the current hypothesis surrounding atomic structure was known as quantum theory, which was pioneered by Bohr and Sommerfeld. They held that atoms were composed of a positively charged center called a nucleus. The nucleus, containing most of the physical substance of the atom, was continuously being circled by negatively-charged particles called electrons. Quantum theory came from the idea that the amount of electrical energy an electron could possess was limited to a number of specific quantities, called quanta.

Although quantum theory was an important breakthrough, experimental results showed that it was flawed. Heisenberg set out to devise a new quantum theory that was based solely on observable information. He was unhappy with the imagined picture of electrons orbiting an atomic nucleus, since this behavior could not be seen or proven with existing technology. Instead, Heisenberg concentrated on what could be seen: the light reflecting off and being absorbed by atoms.

By 1925, Heisenberg published a paper that would help to win him the Nobel Prize in Physics seven years later. The paper described a new set of equations for calculating the position and momentum of subatomic particles (particles, like electrons, that are smaller than the atom). However, it was difficult for many scientists to give up the image of electrons moving in orbits around the nucleus.

At the same time, physicist Erwin Schrödinger came up with a competing theory of wave mechanics. This theory gave the same mathematical results as Heisenberg's theory and was also consistent with the electrons-in-orbit idea. The scientific community fell into an argument over the theories.

Since both sets of equations gave the same results, Heisenberg set out to determine what the particles were doing in reality, not just in numbers; in other words, he wanted to explain the physical basis for the mathematics, which would lead him toward what would be called the Heisenberg uncertainty principle. The uncertainty principle states that it is impossible to know with great precision both a particle's position (where it is in space) and its velocity (how fast it is moving). Before the uncertainty principle, physics had been a deterministic science: Physicists believed that if enough information was known about a particle, its past behavior and future actions could be determined. Heisenberg's principle showed this to be impossible and concluded that only an estimate of the probability of past or future particle behavior could be determined.

When World War II began in 1939, Heisenberg belonged to a German military reserve unit, but rather than being sent to the front lines to fight, he and other scientists were ordered instead to conduct research on the recently advanced field of nuclear fission. Nuclear fission involved the splitting of nuclei, which in turn released enormous amounts of energy.

Heisenberg and his colleagues were asked to investigate nuclear fission as a means to create an atomic bomb for the Nazis. Such a device would be capable of causing more destruction than any weapon previously built, and the German government felt the cause was urgent since they were not the only country working on the problem. The United States, which would join the Allies in the battle to defeat Germany, created its own nuclear research facility during the war, and eventually succeeded in developing the atomic bomb.

Heisenberg's scientific expertise was important to the Nazis, who moved him from his small lab in Leipzig to their main research center in Berlin halfway through the war. He was heavily involved in the German nuclear effort, but Germany never managed to develop a bomb. Many were fascinated by a private conversation Heisenberg had with his old mentor Bohr in 1941, in which it was known that the atomic bomb was discussed. Some thought that Heisenberg had identified a method for building the bomb, but hid it because he did not want to help the Nazis. Most historians now believe that Heisenberg did his best to solve the problem of how to build an atomic bomb, but as a theoretical physicist, he did not have much experience with experimental work, and he simply failed to make the necessary discoveries.

Heisenberg and the other scientists were taken prisoner at the end of the war and held in Cambridge, England, for six months. After their release, Heisenberg returned to Germany, where he continued research on high-energy particle physics and joined various scientific foundations and committees. He headed the Institute for Physics at Göttingen, which was moved to Munich and renamed the Max Planck Institute for Physics and Astrophysics in 1958. He also taught at the University of Munich.

Heisenberg retired from active research in 1970 and died of cancer on February 1, 1976.

Impact

Heisenberg helped to establish the modern science of quantum mechanics and contributed significant refinements to a conceptual understanding of the atomic nucleus, ferromagnetism, cosmic rays, and elementary particles. Heisenberg's work continues to stimulate questions in the philosophy of science involving the certainty and probability of scientific knowledge. In addition to receiving the Nobel Prize in Physics in 1932, Heisenberg earned such honors as the Max Planck Medal, the Matteucci Medal, and the Barnard College Medal of Columbia University.

Bibliography

Dardo, Mauro. Nobel Laureates and Twentieth-Century Physics. Cambridge: Cambridge UP, 2004. Print. Provides a history of physics and the physicists who were instrumental in advancing the field.

Heisenberg, Elisabeth. Inner Exile: Recollections of a Life with Werner Heisenberg. Trans. S. Cappelari and C. Morris. Boston: Birkhäuser, 1984. Print. Heisenberg's wife provides insight into her husband's personal and professional life.

Heisenberg, Werner. Physics and Philosophy: The Revolution in Modern Science. New York: HarperCollins, 2007. Print. Heisenberg examines the effect of scientific advances on society and explains that science allows for cultural change only when society accepts the philosophical assumptions underlying the science.

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Werner Heisenberg | Research Starters | EBSCO Research

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Werner Karl Heisenberg (1901-1976) was a prominent German theoretical physicist best known for his foundational contributions to quantum mechanics, particularly the uncertainty principle, which asserts the inherent limitations in simultaneously knowing a particle's position and momentum.