Physics Timeline
c245 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.
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 dropped two spheres of different masses from the
Leaning Tower of Pisa to demonstrate that their time of descent was independent of their
mass.
1609 - Kepler's Laws of
Planetary Motion
1662 - Boyle's
Law
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).
1687 - Isaac
Newton's 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.
1782 - Conservation of Matter
Antoine Lavoisier 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 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.
1801 - Wave Theory of Light
Thomas Young establishes the waver theory of light, in contrast to the particle theory of Isaac
Newton. His work influenced that of William Herschel,
Hermann von Helmholtz, James Clerk Maxwell and Albert Einstein.
1803 - Atomic Theory of Matter
John Dalton 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 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
Law of electromagnetism predicting how a magnetic field will interact with an electric circuit to
product an electromotive force (voltage).
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 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 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 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 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). Rontgen discovered their medical use when
he took a picture of his wife's hand on a photographic plate formed due to X-rays. When she saw the picture,
she said "I have seen my death."
1897 - Electron Discovered
Sir Joseph John Thomson discovers the first subatomic 'particle' - the electron. Thomson showed that
cathode rays were composed of previously unknow negatively charged particles
(electrons).
1900 - Plank's Blackbody Radiation Law
Max Karl Ernst Ludwig Plank modifies 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 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.
1913 – Bohr’s Model of the
Atom
Niels Bohr and Ernest Rutherford 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.
1920 – Rutherford
Isolates the Proton
Initially
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 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.
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 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 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 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.
1928 – Dirac Derives the Existence of
Antimatter
1929 – Hubble Confirms the Expansion of the
Universe
1912: Vesto Slipher 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 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 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 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).
1938 – Atomic
Fission is Observed
German scientists Otto Hahn and Fritz
Strassmann 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.”
1948 - Development of the Transistor
John Bardeen, Walter Brattain 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
1965 – Cosmic Microwave Background Discovered by Penzias
and Wilson
1980 – Quantum Computing
Theoretical physicist Richard Feynman and mathematician Yuri Manin 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
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.
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