Physics Timeline

ANTIQUITY

Thales Theorem

6th century BCE - Thales's Theorem
A line through the diameter a circle (AC) and any point on the circle (B) will form a right angle (special case of the 31th proposition of Euclid's Elements). Thales of Miletus (626-545BCE), a pre-Socratic Greek Philosopher, is noted for breaking away from mythology to explain the world by using mathematics, science (natural philosophy) and deductive reasoning to explain the world. Thales's view that all of nature is based on the existence of a single ultimate substance (water) is an early expression of 'first principle' (arche) - the a priori effort of decomposing things down to fundamental axioms or postulates. One of the earliest known reference to lodestone's magnetic properties was made by Thales which later led to the development of compasses using magnetic needles.

Archmedes2

C 245 BCE - Archimedes' Principle
Any object, totally or partially immersed in a fluid or liquid, is buoyed up by a force equal to the weight of the fluid displaced by the object. King Hiero II of Syracuse suspected his crown was not of pure gold. Archimedes, while taking a bath and noticing the rising water level, determined that he could determine the crown's volume (and if silver was mixed in with the gold).  According to legend, Archimedes jump out of the bathtub and ran down the streets crying 'Eureka!' - "I have found it!".

11th CENTURY

Alhazen
1021 - Theory of Vision
Alhazen Hasan Ibn al-Haytham (965-1040) was the first to correctly explain the theory of vision ('Book of Vision').  Alhazen's publications were frequently citied by Isaac Newton Johannes Kepler Christiaan Huygens and Galileo Galilei. He is known as the 'father of modern optics',

16th CENTURY
1543 - Heliocentrism
Nicolaus Copernicus (1473-1543) develops the model of the solar system where the Sun is its center ("De revolutionibus orbium coelestium" - "On the Revolutions of the Celestial Spheres", 1543). Major event in the history of science, triggering the Copernican Revolutions and pioneering the way to the Scientific Revolution.

1589 - Leaning Tower of Pisa Experiment
Galileo Galilei (1564–1642) dropped two spheres of different masses from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass.

17th CENTURY

Electroscope
1600 - Electroscope

British physician William Gilbert (1544-1603) invented the electroscope, the first electrical measuring instrument (to detect the presence of electric charge on a body).

1609 - Kepler's Laws of Planetary Motion

1662 - Boyle's Law  

Robert Boyle (1627-1691) confirmed that the pressure of a gas tends to increase as the volume of the container decreases (constant temperature). In short, pressure is inversely proportional to the volume (P=k/V). Boyle’s experiments were not conceivable until air was recognized as an elastic fluid to which all the elaborate concepts of hydrostatics could be applied (theoretical commitment ruled over the ‘Baconian method’ – examining measurements for their own sake). Sir Francis Bacon (1561-1626) is known as the father of empiricism (John Locke is the father of 'modern' empiricism). Bacon advocated inductive reasoning ('bottom up’ reasoning) where general principles are developed from observations. Sir Isaac Newton credited much of his work in Principia to the Baconian method.  Bacon has been referred to as the ‘prophet’ whose prophesies were redeemed by Newton. 

 Huygen Principle

1678 – Huygens's Principle
Christiaan Huygens (1629-1695) proposed that light was made up of waves vibrating up and down perpendicular to the direction of the wave propagation. Huygens's Principle proposed that every point reached by a luminous disturbance becomes a source of a spherical wave. The sum of these secondary waves determines the form of the wave at any subsequent time. In 1704 Sir Isaac Newton advanced the particle theory of light ('Opticks') where light is made of up of small discrete particles - forerunner to the modern understanding of the photon.

1687 - Isaac Newton's (1642–1727) Laws of Motion & Universal Gravitation
1st Law: an object at rest will stay at rest. An object in motion will stay in motion unless acted on by a net external force.
2nd Law: the rate of change of momentum (mv) of a body over time is directly proportional to the force applied. Constant mass: F=ma (mass times acceleration).
The important point is that Newton told the world that a constant force produces a constant acceleration. Not a constant velocity – that was the big surprise.
3rd Law: all forces between two objects exist in equal magnitude and opposite direction. "For every action, there is an equal and opposite reaction".
Universal Gravitation Law: every particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

18th CENTURY

Leyden Jar
1745 – Leyden Jar
The ‘Leyden Jar’ independently discovered by German cleric Ewald Georg von Kleist (1700-1748) and by Dutch scientist Pieter van Musschenbroek of Leiden (1692-1761), Netherlands. The ‘Kleistian’ or ‘Leyden’ Jar, the original form of a capacitor, or condenser, consists of a glass jar with metal foil on the inside and outside surfaces. The Leyden Jar was the first means of storing electric charge in large quantities which greatly expanded early electrical research. Over a half-century later the 'voltaic pile' was invented (1799).

“The Structure of Scientific Revolutions” (Thomas Kuhn, 1962): “The Leyden jar belongs to a class that may be described as theory-induced…Not all theories are paradigm theories.  Both during pre-paradigm periods and during the crises that lead to large-scale changes of paradigm, scientists usually develop many speculative and unarticulated theories that can themselves point the way to discovery…Only as experiment and tentative theory are together articulated to match does the discovery emerge and the theory becomes a paradigm. The discovery of the Leyden Jar displays all these features. When it began there was no single paradigm for electrical research.  One of the competing schools of electricians took electricity to be a fluid and that conception led a number of men to attempt bottling the fluid by holding a water-filled glass vial in their hands and touching the water to a conductor suspended from an active electrostatic generator.  The initial attempts to store electrical fluid worked only because investigators held the vial in their hands while stand upon the ground.  Electricians still had to learn that the jar required an outer as well as an inner conducting coating and that the fluid is not really stored in the jar at all.”

1782 - Conservation of Matter
Antoine Lavoisier (1743-1794) demonstrated the principle of conservation of mass with experiments of the combustion of masses. Influences John Dalton’s on discovery of the law of multiple proportions regarding elements and later atomic theory of matter.

1799 – Electric Battery
Alessandro Volta (1745-1827) invents the 'voltaic pile'. Volta proves that electricity cold be generated chemically and debunked the theory that electricity was generated solely by living beings. The SI unit of electric potential is named in his honor as the volt.

19th CENTURY

Double Slit

1801 - Double-Slit Experiment
Thomas Young (1773-1829) establishes the wave theory of light with the double-slit experiment.. His work influenced that of William Herschel, Hermann von Helmholtz, James Clerk Maxwell and Albert Einstein.

1803 - Atomic Theory of Matter
John Dalton (1766–1844) observed that chemical substances seemed to combine and break down into other substances by weight in proportions that suggested that each chemical element is ultimately made up of tiny indivisible particles of consistent weight. The amazing upshot: elements only exist in discrete packets of matter! ('quantization' was later to be observed with energy - see "1900-Black-body Radiation Law”).

 

1827 - Electrical Resistance
Georg Simon Ohm (1789-1854) develops Ohm's law: the potential difference (voltage) applied across a conductor is proportional to the resultant current (E=IR).

1831 - Faraday's Law of Induction
Michael Faraday's (1791–1867) Law of Electromagnetism predicts how a magnetic field will interact with an electric circuit to product an electromotive force (voltage).

Mechanical Heat

1843 - Mechanical Equivalent of Heat
James Prescott Joule’s (1818-1889) best-known experiment to determine the mechanical equivalent of heat involved the use of a falling weight which spun a paddle wheel in an insulated barrel of water which increased the temperature. After further experimental refinements Joule declared that 1 BTU is equivalent to 778 foot-pounds of work (3,412kWh). Joule's work led to the law of conservation of energy which in turn led to the development of the first law of thermodynamics. Understanding the underpinnings of Joule's work requires one to believe that the collisions of molecules are perfectly elastic. The scientific community's slow acceptance to Joule's ground breaking idea, which challenged the Caloric theory, now obsolete, was that the very existence of atoms and molecules was not widely accepted for another 50 years. The SI unit of energy, the Joule (J), is named after him.

2nd Law of Thermo

1850 - Clausius Formalizes the 2nd Law of Thermodynamics
The German scientist Rudolf Clausius (1822-1888) laid the foundation for the second law of thermodynamics in 1850 with the publication of "On the Moving Force of Heat" (1850).  Clausius restated Sadi Carnot's principle (Carnot Cycle) by providing a truer and sounder explanation of the relation between heat transfer and work: "Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time". In 1865 Clausius introduced the concept of entropy.
1) Heat cannot flow from a cold source to a hotter source, unless work is provided.
2) 100% conversion of heat into mechanical work is not possible.
3) No process is possible in which the entropy decreases. (entropy relates to the 'quality' of heat).
4) There is no principle of conservation of entropy (unlike energy, linear and angular momentum).
 

1861 - Maxwell's Equations
Partial differential (space-time) equations that form the foundation of classical electromagnetism. The equations provide a mathematical model for electric, optical and radio technologies. They describe how electric and magnetic fields are generated by charges, currents and changes of the fields. The equations are named after James Clerk Maxwell (1831–1879) who published them, including the Lorentz force law, in 1861 and 1862. The important consequence of Maxwell's equations is that they demonstrate how fluctuating electric and magnetic currents propagate at a constant speed (c) in a vacuum - known as electromagnetic radiation.

1887 - Statistical Mechanics
Ludwig Boltzmann (1844–1906) develops statistical mechanics to describe how macroscopic observations of temperature or pressure are correlated to microscopic parameters that fluctuate around an average. Boltzman also provides the definition of entropy: S = kBln(W) (kB = Boltzmann’s constant = 1.308 x 10-23 J-K-1).

1887 - Electromagnetic Waves
Heinrich Rudolf Hertz (1857-1894) proves the existence of electromagnetic waves predicted by James Clerk Maxwell's equations of electromagnetism. The unit of frequency, cycle per second, is named the "hertz" in his honor.

1895 - X-Rays
Wilhelm Rontgen (1845-1923) produced and detected electromagnetic radiation in a wavelength range known as X-rays (Rontgen rays). An achievement that earned him the Nobel Prize in Physics (1901).
X-rays are a classic case of discovery through accident – an event that occurs more frequently than the layman realizes (and where the impersonal standards of scientific reporting reluctant to disclose). During a normal investigation of cathode rays Roentgen noticed that the barium platino-cyanide screen at some distance from his shielded apparatus glowed when the discharge was in process. The cause of the glow came in straight lines from the cathode ray tube, that the radiation cast shadows and could not be deflected by a magnet. The effect was not due to the cathode rays but to an agent with some similarity to light. X-rays were greeted not only with surprise but with shock.  Lord Kelvin at first pronounced them an elaborate hoax.  X-rays were not prohibited by theory, however they violated deeply entrenched expectations based on established laboratory procedures.  X-rays opened up a new field of scientific investigation and its discovery not only expanded the domain of normal science but revealed the importance of how anomalies can seriously challenge existing scientific achievements or ‘paradigms’ in the words of Thomas Kuhn (“The Structure of Scientific Revolutions”,1962). Rontgen discovered x-rays’ medical use when he took a picture of his wife's hand. When she saw the picture, she said "I have seen my death."

Radioactivity

1896 – Discovery of Radioactivity
After learning about Rontgen's x-ray discovery, Antoine Henri Becquerel (1852-1908) investigated whether if phosphorescence material emitted x-rays (it did not). In an experiment with non-phosphorescent uranium salts Becquerel discovered that the salts emitted radiation. Becquerel shared the 1903 Nobel Prize in Physics with Marie Curie and Pierre Curie for his discovery of radioactivity.

 

1897 - Electron Discovered
Sir Joseph John Thomson (1856-1940) discovers the first subatomic 'particle' - the electron. Thomson showed that cathode rays were composed of previously unknow negatively charged particles (electrons).

20th CENTURY

1900 - Plank's Blackbody Radiation Law
Max Karl Ernst Ludwig Plank (1858–1947) modified Wien's radiation law to develop a mathematical expression (formalism) for black-body radiation. Unlike the Wien approximation, Planck's law accurately describes the complete spectrum of thermal radiation. Plank's formalism also relied on Boltzmann's statistical interpretation of the second law of thermodynamics which led to the Plank's Postulate - that the energy of oscillators in a black body is quantized (E=nhv; n = integer, h = Plank's constant, v = oscillator frequency). hv is referred to as the energy of quanta photons. Quantization of energy later gave birth to quantum physics. For the discovery of energy quanta Plank won the Nobel Prize in Physics (1818).
 
1905 - Einstein Proves that Atoms Exist
Albert Einstein (1879–1955) publishes a paper where he modeled the motion of the pollen particles as being moved by individual water molecules. The formalization of the Brownian motion served as convincing evidence that atoms and molecules exist.

1905 - Einstein's Photoelectric Effect
Classical electromagnetism predicts that continuous light waves transfer energy to electrons and that the energy should be proportional to the intensity of the light, regardless of the light’s color. Electric currents are generated in metals (or particles emitted) when they are illuminated by blue or ultraviolet light (photoelectric effect). Physicists were surprised to learn that a red or green light, even a bright beam of red or green light, failed to generate this effect. Albert Einstein created a new definition of light - that light is made of individual quantum particles. He proposed that a beam of light is not a propagating wave, but a swarm of discrete energy packets, known as photons, and that electrons are dislodged only as a function of the light's frequency and not its intensity. Einstein’s new model (‘truth’) of light is controversial – the dawn of the wave-particle duality: light is both a wave and a particle. To this day physicists have failed to devise an experiment to catch light’s true nature. If an experiment is set up to measure light’s wave properties, light behaves as a wave. If the experiment is set up to measure light’s particle properties, light behaves as particles. Einstein was awarded the Nobel Prize in Physics (1921) for discovery of the law of the Photoelectric Effect.

1905 - Einstein's Mass-Energy Equivalence
Albert Einstein accepted Maxwell’s postulate that the speed of light is a constant. His grand insight was that time and mass must change as you approached the speed of light (1905). Albert Einstein's develops the famous formula for mass-energy equivalence: E=mc2. The energy of a particle in its rest frame is the product of mass and the speed of light squared. The Space-Time concept is born. During Einstein’s time people assumed that time was like a watch on God’s hand – that it beat at a steady rate throughout the universe, no matter where you were. Einstein disagreed with classical physics. The tick, tick of the wristwatch is actually the click, click of electricity turning into magnetism, turning back into electricity – the steady pace of light itself. When you approach the speed of light the energy that’s contributing to speed gets put into mass (since c is constant). Mass gets heavier. The equivalence principle implies that when energy is lost in chemical reactions, nuclear reactions and other energy transformations, the system will also lose a corresponding amount of mass. The energy, and mass, can be released to the environment as radiant energy (light) or as thermal energy.
The scientific community was very slow to respond this radical idea (‘
truth’). Max Planck recognizes Einstein pioneering work and is appointed professor in Zurich University. Einstein becomes the ‘father’ of modern physics’.

1905 - Einstein's Special Relativity
Special relativity was proposed by Albert Einstein in a 1905 paper titled "On the Electrodynamics of Moving Bodies". Einstein reasoned that the hypothesized luminiferous aether, the postulated medium for the propagation of light, could not exist due to the incompatibility of Newtonian mechanics with Maxwell's equations of electromagnetism (the negative outcome of the Michelson–Morley experiment (1887) suggested that the aether did not exist). Einstein's development of special relativity corrected the mechanics to handle situations involving all motions and especially those at a speed close to that of light (known as relativistic velocities). Today, special relativity is proven to be the most accurate model of motion at any speed when gravitational and quantum effects are negligible.

Cloud Chamber

1911 - Cloud Chamber
Charles Wilson (1869-1959) invented the cloud chamber (or Wilson Chamber) from researching the effects of the Brocken spectre (shadow of an observer cast in mid air upon any type of cloud opposite a strong light source). Refinement of the design permitted the chamber to be a particle detector for visualizing the passage of ionizing radiation. Wilson received half the Nobel Prize in Physics in 1927 for his work on the cloud chamber.

Superconductivity

1912 - Discovery of Superconductivity
By using liquid helium Dutch experimental physicist Heike Onnes (1853-1926) discovered that the electrical resistance of solid mercury vanishes at 4.2K. Onnes was awarded the Nobel Prize in Physics in 1913.

1913 – Bohr’s Model of the Atom
Niels Bohr (1885–1962) and Ernest Rutherford (1871–1937) develops the "Rutherford-Bohr" atomic model. A 'planetary' model that consisted of a small, dense nucleus surrounded by orbiting electrons (electrostatic forces took the place of gravity).  The Rutherford-Bohr model typically is called the Bohr model for short.  The Bohr model gave a successful theoretical underpinning of the Rydberg formula which calculated the wavelengths of hydrogen spectral series.  Today the Bohr model is considered an obsolete scientific theory. Besides providing an adequate first-order approximation of the hydrogen atom, the Bohr model is commonly taught to introduce students to quantum mechanics or energy level diagrams before moving on to the more accurate, but more complex, valence shell atom. Bohr was awarded the Nobel Prize in Physics (1922) for his investigation of the structure of atoms and of the radiation emanating from them.

General Relativity

1915 - General Relativity
Albert Einstein publishes "Einstein's theory of gravity", known as the general theory of relativity, which is the current description of gravitation in modern physics. General relativity provides a unified description of gravity as a geometric property of space and time, or four-dimensional spacetime, where the curvature of spacetime is directly related to the energy and momentum of whatever is present, including matter and radiation. General relativity has held up well to various tests scientists have thrown at it, however it is at a lost to explain the physics inside a black hole.

1920 – Rutherford Isolates the Proton
Initially Ernest Rutherford only knew about electrons and the positively charged nucleus. When he shot heavy alpha particles through very thin gold foil, he was astonished to find that a small fraction of particles ricocheted back 180 degrees – as if they had hit a brick wall. Thomson’s plum pudding model could not explain this (where negatively charged electrons were sprinkled like prunes through a sponge dough of positive charge). Rutherford assumes that the nucleus was made up of a mix of protons – positively charged particles that he discovered (1918) by isolated the nuclei of hydrogen. Hydrogen contains just one proton and one electron orbiting it. In 1919 he discovered the emission of a subatomic particle which he called the "hydrogen atom" but, in 1920, he more accurately named the proton.

1924 - DeBrogle Waves
In his PhD thesis French physicist Louis de Broglie (1892–1987) proposed that just as light has both wave-like and particle-like properties, electrons also have wave-like properties. Wave-like behavior of matter has been confirmed with various metal diffraction experiments using electrons and experiments using other elementary particles.

1925-1927 - Quantum Mechanics
Quantum mechanics arose gradually from theories to explain observations which could not be reconciled with classical physics, such as Max Planck's 'quantum oscillator' solution in the black-body radiation problem and Albert Einstein's observation between energy and frequency in the photoelectric effect. The modern development of quantum mechanics began in the mid-1920s by Niels Bohr, Werner Heisenberg, Erwin Schrodinger, Max Born and others.
Since its inception, the many counter-intuitive aspects and results of quantum mechanics have provoked strong philosophical debates and many interpretations. The arguments center on the probabilistic nature of quantum mechanics, the difficulties with wavefunction collapse and the related measurement problem, and quantum nonlocality. Theoretical physicists Richard Feynman once said, "I think I can safely say that nobody understands quantum mechanics." According to Steven Weinberg, theoretical physicist and Nobel laureate in Physics, "There is now in my opinion no entirely satisfactory interpretation of quantum mechanics."  The views of Niels Bohr, Werner Heisenberg and other physicists are often grouped together as the "Copenhagen interpretation".

1926 - Schrodinger Equation
Erwin Schrodinger published the paper "Quantization as an Eigenvalue Problem" ("Quantisierung als Eigenwertproblem") now known as the Schrodinger Equation. It is a linear partial differential equation that governs the wave function of a quantum-mechanical system and gives the correct energy eigenvalues for a hydrogen-like atom. It is important to note that the Schrodinger Equation uses the imaginary number i.
Electrons are wave-particle duality.  Just like with a single string producing multiple notes on a guitar an electron can exist in different number of harmonics. In physics, a standing wave, also known as a stationary wave, is a wave which oscillates in time but whose peak amplitude profile does not move in space. The locations at which the absolute value of the amplitude is minimum are called nodes, and the locations where the absolute value of the amplitude is maximum are called antinodes.  A standing wave must have whole number repeats of 1/2 wavelengths.  A standing wave must have whole number repeats of 1/2 wavelengths. Since the electron is held fixed by the atractive force of the nucleus, it is similar to a standing wave whose ends are also fixed (like the guitar string).  A standing wave must have whole number repeats of 1/2 wavelengths.
Erwin Schrodinger developed a mathematical model where the electron was assumed to be a standing wave.  Schrodinger's paper has been universally celebrated as one of the most important achievements of the twentieth century and created a revolution in quantum mechanics as well as physics and chemistry in general. The philosophical issues raised by Schrodinger's cat are still debated today and remain his most enduring legacy in popular science. Schrodinger was awarded the Nobel Prize in Physics (1933).


1927 - Heisenberg's Uncertainty Principle
Werner Heisenberg's (1901–1976) Uncertainty Principle asserts a fundamental limit to the accuracy with which the values for certain pairs of physical quantities of a particle, such as position and momentum can be predicted from initial conditions.

1927 - The Big Bang
Astronomer Georges Lemaitre (1894-1966) first noted in 1927 that an expanding universe could be traced back in time to an originating single point, which he called the "primeval atom". Edwin Hubble (1889–1953) confirmed through analysis of galactic redshifts in 1929 that galaxies were drifting apart - an important observational evidence for an expanding universe. For several decades, the scientific community was divided between supporters of the Big Bang and the rival steady-state model which stipulated an eternal universe in contrast to the Big Bang's finite age. In 1965, the Cosmic Microwave Background (CMB) was discovered, which convinced many cosmologists that the steady-state theory was falsified, since, unlike the steady-state theory, the hot Big Bang predicted a uniform background radiation throughout the universe caused by the high temperatures and densities in the distant past. A wide range of empirical evidence strongly favors the Big Bang, which is now essentially universally accepted.

Positron

1928 – Dirac derives the Existence of Antimatter
Theoretical physicist Paul Dirac (1902–1984) published a paper (1928) proposing that electrons can have both a positive and negative charge. In 1931 Dirac predicted the existence of  an as-yet-unobserved particle that he called an "anti-electron" ('positron') that would have the same mass and the opposite charge as an electron and that would mutually annihilate upon contact with an electron. In 1932 particle physicist Carl Anderson (1905-1991) discovered the positron for which he won the Nobel Prized for Physics in 1936.

1929 – Hubble Confirms the Expansion of the Universe
1912: Vesto Slipher (1875-1969) discovers that light from remote galaxies was redshifted, indicating that galaxies were receding from the Earth.
1922: Using Einstein’s field equations Alexander Friedmann used Einstein field equations to provide theoretical evidence that the universe is expanding.
1927: Georges Lemaitre independently reached a similar conclusion to Friedmann on a theoretical basis, and also presented the first observational evidence for a linear relationship between distance to galaxies and their recessional velocity.
1929: Edwin Hubble observationally confirmed Lemaitre findings. Assuming the cosmological principle, these findings would imply that all galaxies are moving away from each other.

1930 - Cyclotron Developed
Ernest O. Lawrence (1901–1958) develops the cyclotron particle accelerator at the University of California, Berkeley (patented in 1932). A cyclotron accelerates charged particles, via a static magnetic field and a varying radio frequency, outwards from the center of a cylindrical vacuum chamber along a spiral path. The cyclotron was an important improvement over linear accelerators (linacs) which provided higher energy particles, with a smaller footprint and lower cost. Particle physicists were able to generate particle energies over 700MeV. In the 1950s, the cyclotron was replaced with the synchrotron particle accelerator. The largest synchrotron-type accelerator is the 27km circumference (17mi) Large Hadron Collider (near Geneva, Switzerland) which can accelerate beams of protons to an energy of 6.5TeV. Lawrence was awarded the Nobel Prize in Physics (1939) for the invention and development of the cyclotron and for the results obtained in regard to artificial radioactive elements.

1932 – Chadwick Discovers the Neutron
Cambridge physicist James Chadwick (1891-1974) discovered a new type of “radiation” which was heavy enough to free protons from paraffin, but with no charge.  Chadwick showed that the new radiation was a neutral particle with the same mass as the proton.  Neutral proton or ‘neutron’.  Neutrons and protons are known as nucleons.  The nucleus is a hundred thousand times smaller than an atom (few femtometers – 10-15 m).  If the atom were scaled to the size of the earth, the nucleus at the center would be just 10km wide, or the length of Manhattan.  The nucleus harbors practically all the mass of the atom in one tiny spot.  The strong nuclear forces hold the protons and neutrons together (which has to overcome the electrostatic repulsion of the neutron’s positive charges – inverse square law).  The strong force only appears at very small separations.  In 1934, Hideki Yukawa proposed that the nuclear force was carried by special particles called mesons.  Protons and neutrons are glued together by exchanging mesons. Chadwick was awarded the Noble Prize in Physics for the discovery of the neutron (1935).

1933 – Zwicky measure Dark Matter
Swiss astronomer Fritz Zwicky (1898-1974) realized that a nearby giant cluster of galaxies was behaving in a way that implied it mass was much greater than the weight of all the stars in all the galaxies within it.  He inferred that some unknown dark matter accounted for 400 times as much material as luminous matter, glowing stars and hot gas, across the entire cluster.  The sheer amount of dark matter was a big surprise, implying that most of the universe was not in the form of stars and gas but something else.
Mass is also missing from individual spiral galaxies.  Gas in the outer regions rotates faster than it should if the galaxy was only as heavy as the combine mass of stars within it.  So such galaxies are more massive than expected by looking at the light alone.  Again, the extra dark matter needs to be hundreds of times more abundant than the visible stars and gass.  Dark matter is not only spread throughout galaxies but its mass is so great it dominates the motions of every star within them. Dark matter even extends beyond the stars, filing a spherical “halo” or bubble around every flattened spiral galaxy disk.
Dark matter is made up of MACHOS or WiMPs
MACHOS – Massive Compact Halo Objects – dark gas clouds, dime stars or unlit planets.  In terms of relativity theory, the MACHO planets distort space-time, like a heavy ball depressing a rubber sheet, which curves the light’s wavefront around it.
WIMPs – Weakly Interacting Massive Particles – shouldn’t have any effect on matter or light.  Difficult to detect.  One candidate is the neutrino.  Not enough neutrinos in the universe to balance out the extra mass required.  Suggest other exotic particles to be detected (axions, photinos).

Superfluid

1937 - Discovery of Superfluidity
Pyotr Kapitsa (1894-1984) discovered superfluidity in helium-4 where the viscosity drops to zero and the fluid flows without any loss of kinetic energy. When stirred, a superfluid forms vortices than continue to rotate indefinitely.

 

1938 – Atomic Fission is Observed
German scientists Otto Hahn (1879-1968) and Fritz Strassmann (1902-1980) shot neutrons into the heavy element uranium, attempting to create new heavier metals.  They got much lighter elements, some half the mass of uranium.  It was like a watermelon splitting in two when hit by a cherry.  Colleagues Lise Meitner and Otto Frisch (living in Sweden during fascist Germany) realized that energy would be released as the nucleus split because the two halves took up less energy overall. Meitner and Frisch’s paper introduced the word “fission” after the division of a biological cell.  Later, Enrico Fermi obtained the first chain reaction in 1942 (University of Chicago, beneath the football stadium).  In 1967 Otto Frisch comments,  “…gradually we came to the idea that perhaps one should not think of the nucleus being cleaved in half as with a chisel, but rather that perhaps there was something in Bohr’s idea that the nucleus was like a liquid drop.”

“The Structure of Scientific Revolutions” (Thomas Kuhn, 1962): “One reason why that nuclear reaction proved especially difficult to recognize was that men who knew what to expect when bombarding uranium chose chemical tests aimed mainly at elements from the upper end of the periodic table. Paradigm procedures and applications are as necessary to science as paradigm laws and theories and they have the same effects.  Inevitably they restrict the phenomenological field accessible for scientific investigation at any given time… The discovery of X-rays could seem to open a strange new world to many scientists and could thus participate so effectively in the crisis that led to 20th century physics.”

1948 - Development of the Transistor
John Bardeen (1908–1991), Walter Brattain (1902–1987) and William Shockley develop point-contact (1947) and bipolar junction (1948) transistors at AT&T's Bell Labs (Murray Hill, NJ). The transistor revolutionized the electronics industry, making possible the development of almost every modern electronic device, from telephones to computers, and ushering in the Information Age.  Shockley, Bardeen, and Brattain were jointly awarded the 1956 Nobel Prize in Physics.

1956 – Neutrinos are Detected

Quark

1964 - Quark Model
The quark model was independently proposed by physicists Murray Gell-Mann (1929–2019) and George Zweig in 1964. Quarks were introduced as parts of an ordering scheme for hadrons, and there was little evidence for their physical existence until deep inelastic scattering experiments at the Stanford Linear Accelerator Center (1968) where electrons were scattering from each other more widely than calculations suggested — indicating that protons and neutrons were made of even smaller particles. The name "quark" was coined by Gell-Mann who borrowed the line "Three quarks for Muster Mark!" (the hypothetical particles came in threes) from the James Joyce's novel Finnegans Wake.
According to physicists, quarks first appeared 10-12 seconds after the Big Bang when two of four fundamental forces (the weak force and the electromagnetic force) separated.  The antiparticles of quarks, or antiquarks, also appeared around this time.  There are six different “flavors” of quarks: up, down, strange, charm, bottom, and top, each with different masses and charges. Quarks can never be seen alone due to a property known as color confinement.  The energy required to remove a quark from a proton or separate two quarks immediately produces an antiquark, which quickly turns a single quark back into a hadron.  Computer models have to be used to determine their mass by simulating the interaction between quarks and gluons — the particles that glue quarks together.

1965 – Cosmic Microwave Background Discovered by Arno Penzias (1933-2024) and Robert Wilson

1965 - Quantum Electrodynamics
In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved. Shin'ichirō Tomonaga (1906-1979), Julian Schwinger (1918-1994), Richard Feynman (1918–1988) and Freeman Dyson (1923–2020) produced fully covariant formulations that were finite at any order in a perturbation series of quantum electrodynamics. Tomonaga, Schwinger, and Feynman were jointly awarded the 1965 Nobel Prize in Physics.

1980 – Quantum Computing
Theoretical physicist Richard Feynman and mathematician Yuri Manin (1937–2023) suggested that a quantum computer had the potential to simulate things a classical computer could not. Quantum computing is the exploitation of collective properties of quantum states, such as superposition and entanglement, to perform fast, complex computation such as integer factorization for RSA encryption. In 1994, Peter Shor developed a quantum algorithm for factoring integers with the potential to decrypt RSA-encrypted communications. Quantum computing is likely to find applications in pharmaceutical, biomedicine, data security, machine learning, autonomous vehicle systems and other applications.

1998 – Supernova Data suggests Dark Energy

21st CENTURY

2012 - Higgs Boson Particle Detected
The Higgs boson (the ‘God Particle’) is the fundamental particle associated with the Higgs field, a field that gives mass to other fundamental particles such as electrons and quarks. A particle’s mass determines how much it resists changing its speed or position when it encounters a force. Not all fundamental particles have mass. The photon, which is the particle of light and carries the electromagnetic force, has no mass at all.  The Higgs boson was proposed in 1964 by Peter Higgs, François Englert, and four other theorists to explain why certain particles have mass. Scientists confirmed its existence in 2012 through the ATLAS (A Toroidal LHC Apparatus) and CMS (Compact Muon Solenoid) experiments at the Large Hadron Collider (LHC) at CERN in Switzerland. The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a field of 4 tesla, about 100,000 times the magnetic field of the Earth. The field is confined by a steel “yoke” that forms the bulk of the detector’s 14,000-tonne weight. This discovery led to the 2013 Nobel Prize in Physics being awarded to Higgs and Englert.

Sidenote: as of AUG20 mysteries remain, such as why particles have different masses. To answer the 'mysteries' more precise measurements are necessary and the need to build a more powerful collider.

2015 - Gravitational Waves Detected
The first direct observation of gravitational waves was made in 2015, when a signal generated by the merger of two black holes was received by the LIGO (Laser Interferometer Gravitational-Wave Observatory) gravitational wave detectors in Livingston and in Hanford. The 2017 Nobel Prize in Physics was subsequently awarded to Rainer Weiss, Kip Thorne and Barry Barish for their role in the direct detection of gravitational waves.

2019 - 1st Image of a Black Hole
Using the Event Horizon Telescope, scientists obtained an image of the black hole at the center of the galaxy M87. Messier 87 (also known as Virgo A or NGC 4486, generally abbreviated to M87) is a supergiant elliptical galaxy with several trillion stars in the constellation Virgo. M87 is about 16.4 million parsecs (53 million light-years) from Earth and is the second-brightest galaxy within the northern Virgo Cluster, having many satellite galaxies. One of the most massive galaxies in the local universe, it has a large population of globular clusters—about 15,000 compared with the 150–200 orbiting the Milky Way—and a jet of energetic plasma that originates at the core and extends at least 1,500 parsecs (4,900 light-years), traveling at a relativistic speed. It is one of the brightest radio sources in the sky and a popular target for both amateur and professional astronomers.