Center For Integrating Research and Learning

Arrow1900 - 1909


The dawn of the 20th century brought paradigm-shifting insights to physics that resulted in profound changes in the way people perceived and lived in the world. Scientists chipped away at the concept of the indivisible atom, gained a new understanding of matter and energy and began to see that, at the atomic level, physics was a whole new ballgame that had little in common with classical mechanics. The field of quantum mechanics was born.

In 1900, German physicist Max Planck published a theory suggesting that atoms did not release their energy in a continuous flow, as scientists had thought, but in discrete increments he called quanta. It was a radical idea, but Planck did not recognize its true scope and implications, and for several years neither did most of his peers.

It took the genius of Albert Einstein to comprehend the consequences of his compatriot’s idea. Seizing Planck’s concept and running with it, Einstein, working at the time in a Swiss patent office, developed a theory positing that light was both a wave and a particle. This brilliant notion, which flabbergasted Einstein’s fellow physicists, held that light was made up of quanta (later called photons), thus accounting for the photoelectric effect, in which light ejects electrons from metals.

In this same “miraculous year” of 1905, Einstein introduced his special theory of relativity. Featuring the famed equation E = mc2, the theory solved the connection between electromagnetic theory and ordinary motion, offering the radical concept that mass and energy were one and the same.

Many others shed light on the basic building blocks of matter. German physicist Philipp Lenard, based on his cathode ray research, suggested that most of an atom is empty space, with its mass taking up a tiny percentage of its volume. In his ingenious oil drop experiment, American physicist Robert Millikan established the charge of an electron with greater accuracy than ever before. German physicist Hans Geiger moved the field forward with the prototype of a chamber specialized for counting particles of radiation.

In his studies on magnetism, French physicist Pierre-Ernest Weiss developed a theory of domain structure known as mean field theory. Weiss suggested that atoms in ferromagnetic materials such as iron and nickel (unlike those in paramagnetic materials) group themselves into “domains,” inside which they share the same magnetic orientation. When these materials come into contact with a strong magnetic field, domains that had been oriented in different directions align with the field.

Average citizens with no knowledge of physics watched electricity and magnetism begin to change their lives. More and more appliances were invented to exploit electricity, including, in the first years of the new century, the vacuum cleaner, toaster, flashlight and iron. Inventors continued developing the radio, still in its infancy. The shipping industry adopted “wireless telegraphy” for transmitting signals in Morse code. In 1906, American engineer Lee De Forest created a three-electrode tube (triode) that could detect wireless signals better than existing instruments. Later that year, for the first time, rapt listeners heard a human voice and music broadcast over “the wireless.” Not until the 1920s, however, would radio broadcasting truly get off the ground.

1900 - 1909


French husband-and-wife physicists Pierre and Marie Curie produce evidence that beta rays are a form of radiation identical to cathode rays.


German physicist Max Planck introduces his radiation law, the fundamental physical constant that bears his name, and his concept of energy quanta. German physicist Max Planck introduces his radiation law, the fundamental physical constant that bears his name, and his concept of energy quanta.


After thousands of experiments, American inventor Thomas Edison successfully develops the nickel-alkaline storage battery.


Following reports of Guglielmo Marconi’s transmission of radio signals across the Atlantic Ocean (1901), Oliver Heaviside of Britain conjectures that an electrically conductive layer located in the upper atmosphere of the earth enables such waves to propagate over expansive distances despite the curvature of the planet. In the United States, electrical engineer Arthur Kennelly independently arrives at the same conclusion and the hypothetical atmospheric stratum comes to be referred to as the Kennelly–Heaviside layer or the ionosphere.


German physicist Philipp Lenard suggests that the majority of an atom’s mass is confined to only a small portion of the atom’s volume based on the results of electron scattering experiments he carried out with a Crookes tube and thin metal foils.


Willem Einthoven, a Dutch physiologist, invents a device known as the Einthoven galvanometer that allows him to produce the first electrocardiogram, a graphical record of the electrical activity of the heart.


Kristian Birkeland of Norway introduces the concept of polar magnetic storms, a form of intense, localized magnetic disturbance associated with auroras.


First successful gas turbine is built in France.


Hendrik Lorentz develops a set of equations known as the Lorentz transformations in his attempt to explain the results of the Michelson-Morley experiment searching for evidence of the ether thought to pervade the atmosphere. The Dutch physicist’s equations would serve as the foundation upon which Albert Einstein would build his special theory of relativity.


The International Electrotechnical Commission is founded and assumes responsibility for the standardization of nomenclature relating to electricity and magnetism.


English physicist and engineer John Ambrose Fleming harnesses the Edison effect to develop the Fleming oscillation valve, a thermionic tube with two electrodes (diode) that functioned as a signal detector and rectifier.


German physicist Albert Einstein formulates his special theory of relativity and indicates that electricity and magnetism are two aspects of a single phenomenon.


French physicist Paul Langevin utilizes statistics to explain the correlation between paramagnetism and temperature.


Lee De Forest, an American engineer, invents the Audion, a three-electrode thermionic tube (triode) that could detect wireless signals much better than could Fleming’s valve and which would come to play an important role in early electronic devices.


French physicist Pierre-Ernest Weiss develops a mean field theory to explain the behavior of iron and other ferromagnetic materials.


German physicist Hans Geiger develops an early version of the Geiger counter, a chamber specialized for counting particles of radiation. Significant improvements to the device would be made by Geiger and his student Walther Mueller in 1928.


George Hale, an American astronomer, publishes a report arguing that sunspots possess magnetic fields.


Australian explorers Douglas Mawson and Edgeworth David complete the first successful journey to the south magnetic pole.


American physicist Robert Millikan performs his famous oil-drop experiment and establishes the charge of an electron with greater accuracy than ever before.

Next Section Arrow1910-1929

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