timeline of fundamental physics discoveries

A TRIBUTE TO DEPARTMENT OF PHYSICS D E I

Timeline of fundamental physics discoveries


Advances in the knowledge of the laws of nature consisting either of

experimental discoveries or theoretical proposals that were

confirmed experimentally.


250 BCE ~ Archimedes principle: Archimedes

• the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces.


1514~ Heliocentrism: Nicholas Copernicus

• “Heliothe”- astronomical model in which the Earth and planets revolve around a relatively stationary Sun at the center of the Solar System.

• The word comes from the Greek (ἥλιος helios "sun" and κέντρον kentron "center").


1589 ~Galileo's Leaning Tower of Pisa experiment:

Galileo Galilei• He predicted - bodies of the same material

falling through the same medium would fall at the same speed.


THE EXPERIMENT-Imagine two objects, one light and one heavier than the other one, are connected to each other by a string. Drop this system of objects from the top of a tower. If we

assume heavier objects do indeed fall faster than lighter ones (and conversely, lighter objects fall

slower), the string will soon pull taut as the lighter object retards the fall of the heavier

object. But the system considered as a whole is heavier than the heavy object alone, and

therefore should fall faster. This contradiction leads one to conclude the assumption is false.


₰ The larger ball, being less susceptible to the effects of what Galileo recognized as air resistance, fell faster. The fact that it fell only

fractionally faster gave Galileo scant advantage.

₰ You find, on making the test, that the larger ball beats the smaller one by two inches.


1600 ~Earth's magnetic field discovered : William

Gilbert

• also known as the geomagnetic field• the magnetic field that extends from

the Earth's interior to where it meets the solar wind (a stream of charged particles emanating from the Sun).


Its magnitude at the Earth's surface ranges from 25 to 65 micro Tesla (0.25 to 0.65 Gauss). It is approximately the field of a magnetic dipole

tilted at an angle of 10 degrees with respect to the rotational axis—as if there were a bar

magnet placed at that angle at the center of the Earth. However, unlike the field of a bar magnet,

Earth's field changes over time because it is generated by the motion of molten iron alloys in

the Earth's outer core (the geodynamo).


1613 ~Inertia: Galileo Galilei

• Inertia is the resistance of any physical object to any change in its state of motion (including a change in direction).

• Inertia comes from the Latin word, iners, meaning idle, sluggish.


₰ Isaac Newton defined inertia as his first law in his Philosophiæ Naturalis Principia

Mathematica.₰On the surface of the Earth inertia is often masked by the effects of friction

and air resistance, both of which tend to decrease the speed of moving objects (commonly to the point of rest), and

gravity.


1621 ~Snell's law: Willebrord Snellius

• Snell–Descartes law/the law of refraction• is a formula used to describe the relationship between the

angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass and air.

• The law follows from Fermat's principle of least time, which in turn follows from the propagation of light as waves.


1660 ~Pascal's Principle: Blaise Pascal

• Pascal's principle- A change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points in the fluid.

• Pascal's law applies only for fluids.• Mathematically,

is the hydrostatic pressure

height of fluid above the point of measurement


1660 ~Hooke's law: Robert Hooke

• states -force F needed to extend or compress a spring by some distance X is proportional to that distance

F = k X,

where k is a constant factor characteristic of the spring, its stiffness.• An elastic body or material for which this

equation can be assumed is said to be linear-elastic or Hookean.


1687 ~Laws of motion and law of gravity: Newton

First law : When viewed in an inertial reference frame, an object either is at rest or moves at a constant velocity, unless acted upon by an external force.


Second law: the acceleration of a body is directly proportional to, and in the same direction as, the net force acting on the body, and inversely proportional to its

mass.


Third law: When one body exerts a force on a second

body, the second body simultaneously exerts a force

equal in magnitude and opposite in direction to that of

the first body.


1785 ~Inverse square law for electric charges confirmed: Coulomb

• a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity. In equation form:

• Newton's law of universal gravitation follows inverse-square law, effects of electric, magnetic, light, sound, and radiation phenomena.


1803 ~Atomic theory of matter: Dalton

• matter is composed of discrete units called atoms.

• It began as a philosophical concept in ancient Greece (Democritus) and entered the scientific mainstream in the early 19th century.


1806 ~Kinetic energy: Young

• It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity.

• The same amount of work is done by the body in decelerating from its current speed to a state of rest.


1827 ~Electrical resistance, etc.: Ohm

Ohm's law said that the voltage between any two points in a conductor changes directly as the current between the two points, given the temperature remains the same.

R -resistance , ohms (Ω)

V -voltage ,volts (V)

I -current ,amperes (A)


1838 ~Lines of force, fields: Michael Faraday

Electric field -The alteration of the properties of space around a charged body that will affect a test charge with a force, F. The direction of the net electric field is defined to be in the direction of the force acting on a positive test charge.

Figure 1(a) pair of unlike charges Figure 1(b) pair of like charges.


Lines of force -Imaginary lines used in visualizing

fields such as electric fields.The lines emanate from positive

charges and terminate on negative charges.

The density of the lines in a region indicates the strength of the field

there.


1838 ~Earth's magnetic field: Weber

• is thought to be associated with electrical currents produced by the coupling of convective effects and rotation in the spinning liquid metallic outer core of iron and nickel. This mechanism is termed the dynamo effect.

• Earth's magnetic field reverses itself every million years or so (the north and south magnetic poles switch). This is but one detail of the magnetic field that is not well understood.


1842–3 ~Conservation of energy: Mayer, Kelvin

• the total energy of an isolated system cannot change—it is said to be conserved over time.

• Energy can be neither created nor destroyed, but can change form

• A consequence of the law of conservation of energy is that no system without an external energy supply can deliver an unlimited amount of energy to its surroundings.


1842 ~Doppler effect: Kelvin

• is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession.

• For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium.

• For waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered.


Doppler_effect_diagrammatic


Doppler frequenz


1842–3 ~Conservation of energy: Mayer, Kelvin

• the total energy of an isolated system cannot change—it is said to be conserved over time.

• Energy can be neither created nor destroyed, but can change form

• A consequence of the law of conservation of energy is that no system without an external energy supply can deliver an unlimited amount of energy to its surroundings.


1845 ~Faraday rotation (light and electromagnetic):

Faraday• The Faraday effect causes a rotation of

the plane of polarization which is linearly proportional to the component of the magnetic field in the direction of propagation.

• It was the first experimental evidence that light and electromagnetism are related.


1850–1 ~Second law of thermodynamics: Clausius,

Kelvin• states- the entropy of an isolated system never decreases, because isolated systems spontaneously evolve toward thermodynamic equilibrium—the state of maximum entropy. Equivalently, perpetual motion machines of the second kind are impossible.


1857–9 ~Kinetic theory: Clausius, Maxwell

• describes a gas as a large number of small particles (atoms or molecules), all of which are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container.

• Kinetic theory explains macroscopic properties of gases, such as pressure, temperature, viscosity, thermal conductivity, and volume, by considering their molecular composition and motion.

• The theory posits that gas pressure is due to the impacts, on the walls of a container, of molecules or atoms moving at different velocities.


1861~Black body: Kirchhoff• is an idealized physical body that absorbs all incident

electromagnetic radiation, regardless of frequency or angle of incidence.

• A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black-body radiation. The radiation is emitted according to Planck's law, meaning that it has a spectrum that is determined by the temperature alone not by the body's shape or composition.

• An approximate realization of a black surface is a hole in the wall of a large enclosure (see below). Any light entering the hole is reflected indefinitely or absorbed inside and is unlikely to re-emerge, making the hole a nearly perfect absorber. The radiation confined in such an enclosure may or may not be in thermal equilibrium, depending upon the nature of the walls and the other contents of the enclosure.


1863~Entropy: Clausius• a measure of the number of specific ways in which

a thermodynamic system may be arranged, often taken to be a measure of disorder, or a measure of progressing towards thermodynamic equilibrium.

• The entropy of an isolated system never decreases, because isolated systems spontaneously evolve towards thermodynamic equilibrium, which is the state of maximum entropy.

• The change in entropy (ΔS) was originally defined for a thermodynamically reversible process as


1867~Dynamic theory of gases, Maxwell

• The molecular friction between two components is proportional to their difference in speed and their mole fractions. In the simplest case, the gradient of chemical potential is the driving force of diffusion. For complex systems, such as electrolytic solutions, and other drivers, such as a pressure gradient, the equation must be expanded to include additional terms for interactions.


1871–89 ~Statistical mechanics: Boltzmann,

Gibbs• Statistical mechanics is a branch of mathematical physics that studies, using probability theory, the average behaviour of a mechanical system where the state of the system is uncertain.


1905~Special relativity: Einstein

Photoelectric effect: EinsteinBrownian motion: Einstein


Special relativity

It is based on two postulates: (1) that the laws of physics are invariant (i.e., identical) in all

inertial systems (non-accelerating frames of reference) (2) that the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source.

It was originally proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".

corrects classical mechanics to handle situations involving motions nearing the speed of light.

the most accurate model of motion at any speed. a wide range of consequences(have been experimentally verified )-

length contraction, time dilation, relativistic mass, mass–energy equivalence, a universal speed limit, invariant spacetime interval,

and relativity of simultaneity.The theory is called "special" because it applied the principle of relativity only to the special case of inertial reference frames.


photoelectric effect-electrons are emitted from atoms when they

absorb energy from light. In 1905 Albert Einstein published a paper that

explained experimental data from the photoelectric effect as being the result of light

energy being carried in discrete quantized packets. This discovery led to the quantum revolution. Einstein was awarded the Nobel Prize in 1921 for "his discovery of the law of

the photoelectric effect".


Brownian motion or pedesis -

is the random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the quick atoms or molecules in the gas or liquid.

Albert Einstein published a paper in 1905 that explained in precise detail how the motion that Brown had observed was a result of the pollen being moved

by individual water molecules The direction of the force of atomic bombardment is

constantly changing, and at different times the particle is hit more on one side than another, leading

to the seemingly random nature of the motion.


1911~equivalence principleDiscovery of the Atomic

nucleus: RutherfordSuperconductivity: Kamerlingh Onnes


Equivalence principle

In the physics of general relativity, the equivalence principle is any of several related concepts dealing with the

equivalence of gravitational and inertial mass, and to Albert Einstein's observation that the gravitational "force" as experienced locally while standing on a massive body

(such as the Earth) is actually the same as the pseudo-force experienced by an observer in a non-inertial

(accelerated) frame of reference.

It is only when there is numerical equality between the inertial and gravitational mass that the acceleration is independent of the

nature of the body. —

Albert Einstein


Discovery of the Atomic nucleus It was discovered in 1911 as a result of Ernest Rutherford's interpretation of the

1909 Geiger–Marsden gold foil experiment performed by Hans Geiger and Ernest Marsden under Rutherford's direction.

The diameter of the nucleus is in the range of 1.75 fm (1.75×10−15 m) for hydrogen (the diameter of a single proton) to about 15 fm for the heaviest atoms, such as uranium.


Superconductivity- is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields

occurring in certain materials when cooled below a characteristic critical temperature.

*superconductivity cannot be understood simply as the idealization of perfect conductivity in classical

physics.


1913 ~Bohr model of the atom: Bohr

• In atomic physics, the Bohr model, introduced by Niels Bohr in 1913, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with attraction provided by electrostatic forces rather than gravity. After the cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911) came the Rutherford–Bohr model or just Bohr model for short (1913). The improvement to the Rutherford model is mostly a quantum physical interpretation of it. The Bohr model has been superseded, but the quantum theory remains sound.


1916~General relativity: Einstein

• General relativity, or the general theory of relativity, is the geometric theory of gravitation published by Albert Einstein in 1916[1] and the current description of gravitation in modern physics. General relativity generalizes special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations.


Some predictions of general relativity differ significantly from those of classical physics, especially concerning the

passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light. Examples

of such differences include gravitational time dilation, gravitational lensing, the gravitational redshift of light, and

the gravitational time delay. The predictions of general relativity have been confirmed in all observations and

experiments to date. Although general relativity is not the only relativistic theory of gravity, it is the simplest theory

that is consistent with experimental data. However, unanswered questions remain, the most fundamental being how general relativity can be reconciled with the

laws of quantum physics to produce a complete and self-consistent theory of quantum gravity.


Einstein's theory has important astrophysical implications. For example, it implies the existence of black holes—regions of space in which space and time are distorted in such a way that nothing, not

even light, can escape—as an end-state for massive stars. There is ample evidence that the intense radiation emitted by certain kinds of

astronomical objects is due to black holes; for example, microquasars and active galactic nuclei result from the presence of stellar black holes

and black holes of a much more massive type, respectively. The bending of light by gravity can lead to the phenomenon of gravitational

lensing, in which multiple images of the same distant astronomical object are visible in the sky. General relativity also predicts the

existence of gravitational waves, which since have been observed indirectly; a direct measurement is the aim of projects such as LIGO

and NASA/ESA Laser Interferometer Space Antenna and various pulsar timing arrays. In addition, general relativity is the basis of current

cosmological models of a consistently expanding universe.


1923 ~Stern-Gerlach experiment

Matter wavesGalaxies

Particle nature of photons confirmed


The Stern–Gerlach experiment

This experiment, performed in 1922, is often used to illustrate basic principles of quantum

mechanics.It can be used to demonstrate that electrons

and atoms have intrinsically quantum properties, and how measurement in

quantum mechanics affects the system being measured.


Matter waves or de Broglie waves-

₰ The de Broglie relations show that the wavelength is inversely proportional to the

momentum of a particle and is also called de Broglie wavelength.

₰ Also the frequency of matter waves, as deduced by de Broglie, is directly

proportional to the total energy E (sum of its rest energy and the kinetic energy) of a

particle.


Galaxy- is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of

gas and dust, and dark matter, an important but poorly understood component

₰ Galaxies contain varying numbers of planets, star systems, star clusters and types of interstellar clouds.

₰ In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays.

₰ Supermassive black holes reside at the center of most galaxies.

₰ The Milky Way galaxy is known to harbor at least one such object.


₰ There are probably more than 170 billion galaxies in the observable universe.

₰ Most are 1,000 to 100,000 parsecs in diameter and usually separated by distances on the order of millions of

parsecs (or megaparsecs). ₰ Intergalactic space (the space between galaxies) is filled

with a tenuous gas of an average density less than one atom per cubic meter.

₰ The majority of galaxies are organized into a hierarchy of associations known as galaxy groups and clusters, which, in turn usually form larger superclusters. At the largest scale, these associations are generally arranged into sheets and

filaments, which are surrounded by immense voids.


1925–7 ~Quantum mechanics

• Is a branch of physics which deals with physical phenomena at nanoscopic scales, where the action is on the order of the Planck constant.

• Quantum mechanics provides a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It is the non-relativistic limit of quantum field theory (QFT), a theory that was developed later that combined quantum mechanics with relativity.


The name quantum mechanics derives from the observation that some physical quantities can change only in discrete amounts (Latin quanta), and not in a continuous (cf. analog) way. For example, the angular momentum of an electron bound to an atom or molecule is quantized.


The mathematical formulations of quantum mechanics are abstract.

A mathematical function known as the wavefunction provides information about the probability amplitude of position, momentum, and other physical properties of a

particle. Mathematical manipulations of the wavefunction usually involve the bra-ket notation,

which requires an understanding of complex numbers and linear functionals. The wavefunction treats the object as a quantum harmonic oscillator, and the mathematics is akin to that describing acoustic

resonance.


Early quantum theory was significantly reformulated in the mid-1920s by Werner

Heisenberg, Max Born and Pascual Jordan, who created matrix mechanics; Louis de Broglie and

Erwin Schrödinger (wave mechanics); and Wolfgang Pauli and Satyendra Nath Bose

(statistics of subatomic particles). Moreover, the Copenhagen interpretation of Niels Bohr became

widely accepted.


Quantum mechanics has since branched out into almost every aspect of 20th-century physics and other disciplines, such as

quantum chemistry, quantum electronics, quantum optics, and quantum information science. Much 19th-century physics has

been re-evaluated as the "classical limit" of quantum mechanics, and its more advanced

developments in terms of quantum field theory, string theory, and speculative

quantum gravity theories.


1927~Big Bang: Lemaître

• the Big Bang occurred approximately 13.798 ± 0.037 billion years ago,which is thus considered the age of the universe.

• At this time, the Universe was in an extremely hot and dense state and began expanding rapidly.

• After the initial expansion, the Universe cooled sufficiently to allow energy to be converted into various subatomic particles, including protons, neutrons, and electrons.


₰ Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed

before the first electrically neutral atoms formed.

₰ The majority of atoms that were produced by the Big Bang are

hydrogen, along with helium and traces of lithium.


₰ Giant clouds of these primordial elements later coalesced through gravity to form stars

and galaxies, and the heavier elements were synthesized either within stars or

during supernovae.₰ offers a comprehensive explanation for a

broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background, large scale structure, and the Hubble diagram.


1928~Antimatter predicted: Dirac

• In particle physics, antimatter is material composed of antiparticles, which have the same mass as particles of ordinary matter but have opposite charge and other particle properties such as lepton and baryon number.


₰ Encounters between particles and antiparticles lead to the annihilation of both,

giving rise to varying proportions of high-energy photons (gamma rays), neutrinos,

and lower-mass particle–antiparticle pairs. ₰ Antiparticles bind with each other to form antimatter just as ordinary particles bind to

form normal matter. For example, a positron (the antiparticle of the electron) and an

antiproton can form an antihydrogen atom.


₰ To date, however, anti-atoms more complex than antihelium have neither been artificially produced nor

observed in nature. ₰ There is considerable speculation as to why the

observable universe is apparently composed almost entirely of ordinary matter.

₰ This asymmetry of matter and antimatter in the visible universe is one of the greatest unsolved

problems in physics.₰The process by which this asymmetry between

particles and antiparticles developed is called baryogenesis.

₰ Antimatter is commonly produced by particle accelerators and in some types of radioactive decay.


1932~Antimatter discovered: AndersonNeutron discovered:

Chadwick

.


Neutron

₰ While the bound neutrons in nuclei can be stable (depending on the nuclide, (there are many more unstable (radioactive) isotopes

than stable ones)), free neutrons are unstable; they undergo beta decay with a

mean lifetime of just under 15 minutes (881.5±1.5 s).

₰ Free neutrons are produced in nuclear fission and fusion.


Neutron


1933 ~Invention of the electron microscope: Ernst

Ruska• An electron microscope (EM) is a type of

microscope that uses an electron beam to illuminate a specimen and produce a magnified image.

• The electron microscope uses electrostatic and electromagnetic lenses to control the electron beam and focus it to form an image. These electron optical lenses are analogous to the glass lenses of a light optical microscope.


₰ has greater resolving power ,because electrons have wavelengths about

100,000 times shorter than visible light photons.

₰ can achieve better than 50 pm resolution and magnifications of up to about 10,000,000x whereas ordinary, non-confocal light microscopes are

limited by diffraction to about 200 nm resolution and useful magnifications

below 2000x.


1937~Muon discovered: Anderson & Neddermeyer

• an elementary particle similar to the electron, unitary negative electric charge and a spin of 1⁄2, but with much more mass (105.7 MeV/c2).

• no sub-structure at all• Unstable, mean lifetime of 2.2 µs. • antiparticle -the antimuon /positive muon


1938~Superfluidity discovered

Energy production in stars understood


Superfluiditya state of matter in which the

matter behaves like a fluid with zero viscosity; appears to exhibit the ability to self-propel and travel in a way that defies the forces of

gravity and surface tension.


Energy Production in Stars There are two possible sources of such

energy: (1) gravitational contraction and

(2) thermonuclear reactions that convert mass to energy.

Both play important roles in producing energy over the lifetime of a star, but the primary energy source for the long stable

period of a star's life is thermonuclear fusion.


1944~Theory of magnetism in 2D: Ising model

• a mathematical model of ferromagnetism in statistical mechanics.

• The model consists of discrete variables that represent magnetic dipole moments of atomic spins that can be in one of two states (+1 or −1). The spins are arranged in a graph, usually, a lattice, allowing each spin to interact with its neighbors.


1948~Quantum electrodynamics

• represents the quantum counterpart of classical electromagnetism giving a complete account of matter and light interaction.

• Feynman called it "the jewel of physics" for its extremely accurate predictions of quantities like the anomalous magnetic moment of the electron and the Lamb shift of the energy levels of hydrogen.


1948~Invention of the Maser and Laser - Charles

Townes


Maser

A maser is a device that produces coherent electromagnetic waves

through amplification by stimulated emission.

MASER: "Microwave Amplification by Stimulated Emission of Radiation".


Laser₰ emits light through a process of optical

amplification based on the stimulated emission of electromagnetic radiation.

₰ "light amplification by stimulated emission of radiation".

₰ differ from other sources of light because they emit light coherently.


₰ important applications- DVD players, laser printers, and

barcode scanners,in medicine for laser surgery and various skin treatments,

and in industry for cutting and welding materials,military and law enforcement

devices for marking targets and measuring range and

speed,entertainment medium,scientific research.


1956~Electron neutrino discovered

• is a subatomic lepton elementary particle which has no net electric charge. Together with the electron it forms the first generation of leptons, hence its name electron neutrino.


1956–7~Parity found violated

• In quantum physics, a parity transformation (also called parity inversion) is the flip in the sign of one spatial coordinate. In three dimensions, it is also commonly described by the simultaneous flip in the sign of all three spatial coordinates:


Parity violation

₰ It turns out to be violated in weak interactions.

₰ This implies that parity is not a symmetry of our universe, unless a hidden mirror sector exists in which

parity is violated in the opposite way.


1959–60~Role of topology in quantum physics,

predicted and confirmed• A topological quantum field theory (or

topological field theory or TQFT) is a quantum field theory which computes topological invariants.

• In cosmology, topology can be used to describe the overall shape of the universe. This area is known as spacetime topology.


1962~SU(3) theory of strong interactions

Muon neutrino found• The Standard Model of particle physics is

a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles.

• sometimes regarded as a "theory of almost everything". Mathematically, the standard model is a quantized Yang–Mills theory.


1963 ~Quarks predicted ;Murray Gell-Mann

and George Zweig• an elementary particle and a fundamental constituent of

matter. • combine to form hadrons(protons ,neutrons etc) • never directly observed or found in isolation.• There are six types of quarks, known as flavors: up, down,

strange, charm, bottom, and top.• Quarks are the only elementary particles in the Standard

Model of particle physics to experience all four fundamental interactions, also known as fundamental forces (electromagnetism, gravitation, strong interaction, and weak interaction), as well as the only known particles whose electric charges are not integer multiples of the elementary charge.

• Antiparticle-antiquark


1967~Unification of weak and electromagnetic interactionsSolar neutrino problem found

Pulsars (neutron stars) discovered


Unification of weak and electromagnetic interactions

₰ the theory models them as two different aspects of the same force.

₰ above the unification energy, on the order of 100 GeV, they would merge into a single

electroweak force. ₰ Thus if the universe is hot enough

(approximately 1015 K, a temperature exceeded until shortly after the Big Bang) then the

electromagnetic force and weak force merge into a combined electroweak force.


Solar neutrino problem₰ The solar neutrino problem was a major

discrepancy between measurements of the numbers of neutrinos flowing through the Earth and

theoretical models of the solar interior.₰ The discrepancy has since been resolved by new

understanding of neutrino physics, requiring a modification of the Standard Model of particle

physics – specifically, neutrino oscillation. ₰ Essentially, as neutrinos have mass, they can

change from the type that had been expected to be produced in the Sun's interior into two types that

would not be caught by the detectors in use at the time.


Pulsar₰ A pulsar (pulsating star) is a highly

magnetized, rotating neutron star that emits a beam of electromagnetic radiation.

₰ This radiation can only be observed when the beam of emission is pointing toward the Earth, much the way a lighthouse can only

be seen when the light is pointed in the direction of an observer, and is responsible

for the pulsed appearance of emission.


1974 ~Black hole radiation predicted

Renormalization groupCharmed quark found


Black hole radiation₰ aka Hawking radiation

₰ named after the physicist Stephen Hawking, who provided a theoretical argument for its existence and sometimes also after Jacob

Bekenstein, who predicted that black holes should have a finite, non-zero temperature and entropy.

₰according to the quantum mechanical uncertainty principle, rotating black holes should

create and emit particles.


Renormalization group₰ a mathematical apparatus that allows

systematic investigation of the changes of a physical system as viewed at different

distance scales. ₰ In particle physics, it reflects the changes in the underlying force laws as the energy scale at which physical processes occur varies(energy/momentum and resolution

distance scales being effectively conjugate under the uncertainty principle )


Charmed quark₰ the third most massive of all quarks, a

type of elementary particle. ₰ an elementary fermion with spin-1⁄2, and

experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. ₰ antiparticle- charm antiquark (sometimes

called anticharm quark or simply anticharm)


1975~Tau lepton found

• an elementary particle similar to the electron, with negative electric charge and a spin of 1⁄2.

• classified as a lepton• antiparticle -antitau /positive tau• Tau leptons have a lifetime of 2.9×10−13 s

and a mass of 1776.82 MeV/c2 (compared to 105.7 MeV/c2 for muons and 0.511 MeV/c2 for electrons).

• has an associated tau neutrino.


1977~Bottom quark found

• bottom quark /b quark/beauty quark• is a third-generation quark with a

charge of −1⁄3 e. • mass -four times the mass of a proton• a frequent decay product for the

Higgs boson.


1980~Quantum Hall effect• quantum-mechanical version of the Hall effect,

observed in two-dimensional electron systems subjected to low temperatures and strong magnetic fields.

• The integer quantum Hall effect is very well understood, and can be simply explained in terms of single-particle orbitals of an electron in a magnetic field.

• The fractional quantum Hall effect is more complicated, as its existence relies fundamentally on electron–electron interactions.


1981~Theory of cosmic inflation proposed

• The term "inflation" is used to refer to the hypothesis that inflation occurred, to the theory of inflation, or to the inflationary epoch.

• While the detailed particle physics mechanism responsible for inflation is not known, the basic picture makes a number of predictions that have been confirmed by observation.


1982~Fractional quantum Hall effect

• FQHE-a physical phenomenon in which the Hall conductance of 2D electrons shows precisely quantised plateaus at fractional values of e^2/h.

• It is a property of a collective state in which electrons bind magnetic flux lines to make new quasiparticles, and excitations have a fractional elementary charge and possibly also fractional statistics.


1995~Bose–Einstein condensate found : Wolfgang Ketterle

• BEC-a state of matter of a dilute gas of bosons cooled to temperatures very close to absolute zero

• Under such conditions, a large fraction of the bosons occupy the lowest quantum state, at which point quantum effects become apparent on a macroscopic scale. These effects are called macroscopic quantum phenomena.


1995~Top quark found

• top quark/ t quark / truth quark• an elementary particle and a fundamental constituent of

matter. • an elementary fermion with spin-1⁄2, and experiences all

four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions.

• It has an electric charge of +2⁄3 e,[2] and is the most massive of all observed elementary particles. It has a mass of 173.07 ± 0.52 (stat) ± 0.72 (syst) GeV/c2,[1] which is about the same mass as an atom of tungsten.

• antiparticle -top antiquark


1998~Accelerating expansion of universe found• is the observation that the universe

appears to be expanding at an increasing rate.


1999~Slow light experimentally

demonstrated : Lene Vestergaard Hau• Slow light occurs when a propagating pulse is

substantially slowed down by the interaction with the medium in which the propagation takes place.

• This was in an effort to develop computers that will use only a fraction of the energy of today's machines.

• In 2005, IBM created a microchip fashioned of fairly standard materials, potentially paving the way toward commercial adoption.


2000~Tau neutrino found

• a subatomic elementary particle• no net electric charge. • Together with the tau, it forms the third

generation of leptons, hence its name tau neutrino.


2003~WMAP observations of Cosmic microwave

background• The Wilkinson Microwave Anisotropy Probe

(WMAP) – also known as the Microwave Anisotropy Probe (MAP), and Explorer 80 – a spacecraft which measures differences in the temperature of the Big Bang's remnant radiant heat – the Cosmic Microwave Background Radiation – across the full sky,headed by Professor Charles L. Bennett, Johns Hopkins University.


2012~Higgs Boson found

• The Higgs boson or Higgs particle is an elementary particle initially theorised in 1964

• On 4 July 2012, it was announced that a previously unknown particle with a mass between 125 and 127 GeV/c2 (134.2 and 136.3 amu) had been detected.

• positive parity and zero spin,two fundamental attributes of a Higgs boson.

• appears to be the first elementary scalar particle discovered in nature.


In mainstream media the Higgs boson has often been called the

"God particle", from a 1993 book on the topic; the nickname is strongly

disliked by many physicists, including Higgs, who regard it as

inappropriate sensationalism.

timeline of fundamental physics discoveries

Documents

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heavier objects

earths field changes

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galileo galileihe