An X-ray generator is a device that produces X-rays. Together with an X-ray detector, it is commonly used in a variety of applications including medicine, fluorescence, electronic assembly inspection, and measurement of material thickness in manufacturing operations. In medical applications, X-ray generators are used by radiographers to acquire x-ray images of the internal structures (e.g., bones) of living organisms, and also in sterilization.
Structure

An X-ray generator generally contains an X-ray tube to produce the X-rays. Possibly, radioisotopes can also be used to generate X-rays.[1]
An X-ray tube is a simple vacuum tube that contains a cathode, which directs a stream of electrons into a vacuum, and an anode, which collects the electrons and is made of tungsten to evacuate the heat generated by the collision. When the electrons collide with the target, about 1% of the resulting energy is emitted as X-rays, with the remaining 99% released as heat. Due to the high energy of the electrons that reach relativistic speeds the target is usually made of tungsten even if other material can be used particularly in XRF applications.
An X-ray generator also needs to contain a cooling system to cool the anode; many X-ray generators use water or oil recirculating systems.[2]
Medical imaging

In medical imaging applications, an x-ray machine has a control console that is used by a radiologic technologist to select x-ray attributes suitable for the specific exam, a power supply that creates and produces the desired kVp (peak kilovoltage), mA (milliamperes, sometimes referred to as mAs which is actually mA multiplied by the desired exposure length) for the x-ray tube, and the x-ray tube itself.
History
The discovery of X-rays came from experimenting with Crookes tubes, an early experimental electrical discharge tube invented by English physicist William Crookes around 1869-1875. In 1895, Wilhelm Röntgen discovered X-rays emanating from Crookes tubes and the many uses for X-rays were immediately apparent. One of the first X-ray photographs was made of the hand of Röntgen's wife. The image displayed both her wedding ring and bones. On January 18, 1896 an X-ray machine was formally displayed by Henry Louis Smith. A fully functioning unit was introduced to the public at the 1904 World's Fair by Clarence Dally.[3]
In the 1940s and 1950s, X-ray machines were used in stores to help sell footwear. These were known as Shoe-fitting fluoroscopes. However, as the harmful effects of X-ray radiation were properly considered, they finally fell out of use. Shoe-fitting use of the device was first banned by the state of Pennsylvania in 1957. (They were more a clever marketing tool to attract customers, rather than a fitting aid.) Together with Robert J. Van de Graaff, John G. Trump developed one of the first million-volt X-ray generators.
Overview
An X-ray imaging system consists of a generator control console where the operator selects desired techniques to obtain a quality readable image(kVp, mA and exposure time), an x-ray generator which controls the x-ray tube current, x-ray tube kilovoltage and x-ray emitting exposure time, an X-ray tube that converts the kilovoltage and mA into actual x-rays and an image detection system which can be either a film (analog technology) or a digital capture system and a PACS.
Applications
X-ray machines are used in health care for visualising bone structures, during surgeries (especially orthopedic) to assist surgeons in reattaching broken bones with screws or structural plates, assisting cardiologists in locating blocked arteries and guiding stent placements or performing angioplasties and for other dense tissues such as tumours. Non-medicinal applications include security and material analysis.
Medicine

The main fields in which x-ray machines are used in medicine are radiography, radiotherapy, and fluoroscopic type procedures.
Radiography is generally used for fast, highly penetrating images, and is usually used in areas with a high bone content but can also be used to look for tumors such as with mammography imaging.  Some forms of radiography include:
orthopantomogram — a panoramic x-ray of the jaw showing all the teeth at once
mammography — x-rays of breast tissue
tomography — x-ray imaging in sections
In fluoroscopy, imaging of the digestive tract is done with the help of a radiocontrast agent such as barium sulfate, which is opaque to X-rays.
Radiotherapy — the use of x-ray radiation to treat malignant and benign cancer cells, a non-imaging application
Fluoroscopy is used in cases where real-time visualization is necessary (and is most commonly encountered in everyday life at airport security). Some medical applications of fluoroscopy include:
angiography — used to examine blood vessels in real time along with the placement of stents and other procedures to repair blocked arteries.
barium enema — a procedure used to examine problems of the colon and lower gastrointestinal tract
barium swallow — similar to a barium enema, but used to examine the upper gastrointestinal tract
biopsy — the removal of tissue for examination
X-rays are highly penetrating, ionizing radiation, therefore X-ray machines are used to take pictures of dense tissues such as bones and teeth. This is because bones absorb the radiation more than the less dense soft tissue. X-rays from a source pass through the body and onto a photographic cassette.  Areas where radiation is absorbed show up as lighter shades of grey (closer to white). This can be used to diagnose broken or fractured bones.
Security

X-ray machines are used to screen objects non-invasively. Luggage at airports and student baggage at some schools are examined for possible weapons, including bombs. Prices of these Luggage X-rays vary from $50,000 to $300,000. The main parts of an X-ray Baggage Inspection System are the generator used to generate x-rays, the detector to detect radiation after passing through the baggage, signal processor unit (usually a PC) to process the incoming signal from the detector, and a conveyor system for moving baggage into the system. Portable pulsed X-ray Battery Powered X-ray Generator used in Security as shown in the figure provides EOD responders safer analysis of any possible target hazard.
Operation
When baggage is placed on the conveyor, it is moved into the machine by the operator. There is an infrared transmitter and receiver assembly to detect the baggage when it enters the tunnel. This assembly gives the signal to switch on the generator and signal processing system. The signal processing system processes incoming signals from the detector and reproduce an image based upon the type of material and material density inside the baggage. This image is then sent to the display unit.
Color classification

The colour of the image displayed depends upon the material and material density: organic material such as paper, clothes and most explosives are displayed in orange. Mixed materials such as aluminum are displayed in green. Inorganic materials such as copper are displayed in blue and non-penetrable items are displayed in black (some machines display this as a yellowish green or red). The darkness of the color depends upon the density or thickness of the material.
The material density determination is achieved by two-layer detector. The layers of the detector pixels are separated with a strip of metal. The metal absorbs soft rays, letting the shorter, more penetrating wavelengths through to the bottom layer of detectors, turning the detector to a crude two-band spectrometer.
Advances in X-ray technology

A film of carbon nanotubes (as a cathode) that emits electrons at room temperature when exposed to an electrical field has been fashioned into an X-ray device. An array of these emitters can be placed around a target item to be scanned and the images from each emitter can be assembled by computer software to provide a 3-dimensional image of the target in a fraction of the time it takes using a conventional X-ray device. The system also allows rapid, precise control, enabling prospective physiological gated imaging.[5]
Engineers at the University of Missouri (MU), Columbia, have invented a compact source of x-rays and other forms of radiation.
The radiation source is the size of a stick of gum and could be used to create portable x-ray scanners. A prototype handheld x-ray scanner using the source could be manufactured in as soon as three years.[6]
See also
Fluoroscope
Backscatter X-ray e.g., for security scanning passengers (rather than baggage)
X-ray crystallography
Radiography
X-ray fluorescence
X-ray astronomy Just detectors.
Notes

Cite uses deprecated parameter |dead-url= (help)CS1 maint: multiple names: authors list (link) 2. Chris Salberg owner of


The reconstruction of Germany after World War II was a long process. Germany had suffered heavy losses during the war, both in lives and industrial power. 6.9 to 7.5 million Germans had been killed, roughly 8.26 to 8.86 percent of the population (see also World War II casualties).[1][2] The country's cities were severely damaged from heavy bombing in the closing chapters of the War and agricultural production was only 35 percent of what it was before the war.
At the Potsdam Conference, the victorious Allies ceded roughly 25 percent of Germany's pre-Anschluss territory to Poland and the Soviet Union. The German population in this area was expelled, together with the Germans of the Sudetenland and the German populations scattered throughout the rest of Eastern Europe. Between 1.5 and 2 million are said to have died in the process, depending on source. As a result, the population density grew in the "new" Germany that remained after the dismemberment.
As agreed at Potsdam, an attempt was made to convert Germany into a pastoral and agricultural nation, allowed only light industry.  Many factories were dismantled as reparations or were simply destroyed (see also the Morgenthau Plan). Millions of German prisoners of war were for several years used as forced labor, both by the Western Allies and the Soviet Union.
Beginning immediately after the German surrender and continuing for the next two years, the United States pursued a vigorous program to harvest all technological and scientific know-how, as well as all patents in Germany. John Gimbel comes to the conclusion in his book, Science Technology and Reparations: Exploitation and Plunder in Post-war Germany, that the "intellectual reparations" taken by the U.S. and the UK amounted to close to 10 billion dollars, equivalent to around 100 billion dollars in 2006.[3][4] (see also Operation Paperclip).
As soon as 1945, the Allied forces worked heavily on removing Nazi influence from Germany in a process dubbed as "denazification".[5]
By mid-1947, the success of denazification and the start of the Cold War had led to a re-consideration of policy, as the Germans were seen as possible allies in the conflict and the dawning realization that the economic recovery of Europe was dependent on the reactivation of German industry. With the repudiation of the U.S. occupation directive JCS 1067 in July 1947, the Western Allies were able to start planning for the introduction of a currency reform to halt the rampant inflation. This type of action to help the German economy had been prohibited by the directive and its execution also led to the setting up of a Soviet controlled puppet state in the eastern zone, to maintain Soviet control there.
In 1948, the Deutsche Mark replaced the occupation currency as the currency of the Western occupation zones, leading to their eventual economic recovery.[6]
In 1947, the Marshall Plan, initially known as the  "European Recovery Program" was initiated. In the years 1947–1952,  some $13 billion of economic and technical assistance—-equivalent to around $140 billion in 2017—were allocated to Western Europe. Despite protests from many beneficiaries, the Marshall Plan, although in the less generous form of loans, was in 1949 extended to also include the newly formed West Germany.  In the years 1949–1952, West Germany received loans which totaled $1.45 billion, equivalent to around $14.5 billion in 2006.
The country subsequently began a slow but continuous improvement of its standard of living, with the export of local products, a reduction in unemployment, increased food production, and a reduced black market.
By 1950, the UK and France were finally induced to follow the U.S. lead, and stop the dismantling of German heavy industry.[7] The country's economic recovery under the newly formed democratic government was, once it was permitted, swift and effective. During the mid-1950s, the unemployment rate in Germany was so low that it led to the influx of Turkish immigrants into the country's labor force. Germany's economy continued to improve until the 1973 oil crisis. (see also Wirtschaftswunder)
Rehabilitation Milestones
In 1946, the US Secretary of State (foreign minister) made the speech Restatement of Policy on Germany, repudiating the Morgenthau Plan policies.[8]
In 1947, the JCS 1067 was rescinded.[9]
In 1948, the Deutsche Mark replaced the almost worthless Reichsmark in the Allied western occupation zones initiating the start of economic recovery in western Germany.[6]
In 1949, West Germany is formed from the Western occupation zones, with the exception of the Saarland.
In 1949, the Marshall Plan is extended to include West Germany.
In 1950, the dismantling of West German heavy industry ends.
In 1955, the military occupation of West Germany ends.
In 1955, NATO, which was formed in 1948, allowed West Germany to join.
In 1957, France returned the Saarland to West Germany.
In 1957, West Germany was one of the founding nations of the European Economic Community.
In 1973, West Germany joined the United Nations (formed in 1945).
In 1991, a unified Germany was allowed by the Allies of World War II to become fully sovereign after signing the Treaty on the Final Settlement with Respect to Germany.
See also
GARIOA
Allied plans for German industry after World War II
Restatement of Policy on Germany
The President's Economic Mission to Germany and Austria
Vergangenheitsbewältigung


This is an incomplete list of notable avalanches.

See also
Avalanche
List of natural disasters by death toll

How many people die in avalanches each year?


Many passenger trains (usually medium and long-distance) have toilet facilities, often at the ends of carriages. Toilets suitable for wheelchair users are larger, and hence trains with such facilities may not have toilets in each carriage.
Hopper toilet
The traditional method of disposing human waste from trains is to deposit the waste onto the tracks or, more often, onto nearby ground using what is known as a hopper toilet. This ranges from a hole in the floor to a full-flush system (possibly with sterilization). The hole in the floor (also known as a drop chute toilet) system is still in use in many parts of the world, particularly on older rolling stock. The principal disadvantage is that it can be considered crude or unhygienic and dangerous to health and the environment – it litters the railway lines and can convey serious health risks when the train passes over or under a navigable waterway. Passengers may be discouraged from flushing or using toilets while the train is at a station or standing at a red signal. To enforce this limitation, toilets may be automatically locked when the train pulls into a station or stops at a red signal. In the United States, railway employees were required to lock the toilets closed whenever a passenger train stood in a station or at any other location designated by instructions in the timetable. Toilets would promptly be unlocked upon departure.
Properly-designed drop chute toilets will draw air like a chimney, pulling air through the lavatory door vents and down and out through the toilet, reducing odor.[1]
Hopper toilets are similar to old-fashioned sea toilets in that they release the excreta directly to the environment, untreated.
In October 2017, it was announced that the United Kingdom would phase out hopper toilets on all timetabled passenger services, to protect rail workers and reduce health risks.[2]
Chemical holding tank
Chemical holding tanks (retention tanks) are usually included on newer carriages and railcars in wealthier and more densely populated parts of the world. One issue is that the tanks need to be regularly emptied, often at a terminal station or prolonged stop-over. If a train needs to be used again quickly, the tanks may not get emptied. In this case, toilets may back up, which can result in toilets being closed.
Vacuum toilet
Vacuum systems used in the newest carriages are similar to those in airliners: waste is pulled into a holding tank with a high pressure pump. Their disadvantages are the same as of chemical holding tanks, in addition they require stable power supply for working, and flushing of anything else but water and human waste (e.g. toilet paper) can easily break the pump.
Composting toilet
Some trains may have composting toilet tanks, which use bacterial action to break down solid and liquid waste before releasing it to the trackbed by way of a chlorine sanitizing tank.
Cultural references
In the United States, Dvořák's tune "Humoresque Number 7" became the setting for a series of mildly scatological humorous verses,[3] regarding passenger train toilets, beginning:
Passengers will please refrain

From flushing toilets while the train

Is standing in the station (I love you)...

In The Good Soldier Svejk, author Jaroslav Hašek used hypocatastasis to indicate the fruit of hopper toilets, while conveying soldiers' envy and contempt for their general officer:[4]
In the station restaurant the general began to speak again about the latrines and to say how ugly it looked when there were cactuses everywhere on the track. Meanwhile he ate beef steak and all of them imagined that he had a cactus in his mouth.

Gallery

Traditional hole in the floor system, operated by a pedal
The basics: paper towels, toilet roll and soap dispenser
Squat toilet in Chinese train
Toilet in Taiwan high speed rail train
"DO NOT USE the toilet while the train is stopped at the station" notice in Polish, German, French, and English, displayed by Polish State Railways
Vacuum waste tank on a China Railways 25T coach
This is one of several restrooms on the lower level of Superliner #34960
A restroom on Amtrak's Acela Express
Universal access toilet of Japanese Keisei AE series
Wheelchair-accessible toilet of Japanese Shinkansen（E6 Series）


The invention of the communication medium commonly known as radio, although generally attributed to Guglielmo Marconi in the 1890s, spanned many decades, from theoretical underpinnings, through proof of the phenomenon's existence, development of technical means, to its final use in signalling.
The idea that the wires needed for electrical telegraphy could be eliminated, creating a wireless telegraph, had been around for a while before radio based communication. Inventors attempted to build systems based on electric conduction, electromagnetic induction, or on their own theoretical ideas. Several inventors/experimenters came across radio waves before they were proven to exist but it was written off as electromagnetic induction at the time.
The discovery of electromagnetic waves, including radio waves, by Heinrich Rudolf Hertz in the 1880s came about after over a half century theoretical development on the connection between electricity and magnetism starting in the early 1800s and culminated in a theory of electromagnetism developed by James Clerk Maxwell by 1873, which Hertz finally proved.
The development of radio waves into a communication medium did not follow immediately afterwards. After their discovery Hertz considered them of little practical value and other experimenters who explored the physical properties of the new phenomenon, such as Oliver Lodge and Jagadish Chandra Bose, while transmitting radio waves some distance, did not seem to see any value in developing a communication system based on them. In their experiments they did develop electronic components and methods to improve the transmission and detection of electromagnetic waves.
In the mid 1890s, building on techniques physicists were using to study electromagnetic waves, Guglielmo Marconi developed the first apparatus for long distance radio communication.[1] On 23 December 1900, the Canadian inventor Reginald A. Fessenden became the first person to send audio (wireless telephony) by means of electromagnetic waves, successfully transmitting over a distance of about 1.6 kilometers, and six years later on Christmas Eve 1906 he became the first person to make a public radio broadcast.[2][3]
By 1910 these various wireless systems had come to be referred to by the common name "radio".
Wireless communication theories and methods previous to radio

Before the discovery of electromagnetic waves and the development of radio communication there were many wireless telegraph systems proposed or tried out.[4] Early researchers may not have understood or disclosed which physical effects were responsible for transmitting signals. These experimenters used the existing theories of the day or novel theories of their own on how wireless signals could be transmitted.
In April 1872 William Henry Ward received  for a wireless telegraphy system where he theorized that convection currents in the atmosphere could carry signals like a telegraph wire.[5] A few months after Ward received his patent, Mahlon Loomis of West Virginia received  for a "wireless telegraph" in July 1872. The patented system claimed to utilize atmospheric electricity to eliminate the overhead wire used by the existing telegraph systems. It did not contain diagrams or specific methods and it did not refer to or incorporate any known scientific theory. It was similar to William Henry Ward's patent.[6][7]

In the United States, Thomas Edison, in the mid-1880s, patented an electromagnetic induction system he called "grasshopper telegraphy", which allowed telegraphic signals to jump the short distance between a running train and telegraph wires running parallel to the tracks.[8] In the United Kingdom, William Preece was able to develop an electromagnetic induction telegraph system that, with antenna wires many kilometers long, could transmit across gaps of about 5 kilometres (3.1 miles). Inventor Nathan Stubblefield, between 1885 and 1892,[9] also worked on an induction transmission system.
Forms of Wireless telephony is recorded in four patents for the photophone, invented jointly by Alexander Graham Bell and Charles Sumner Tainter in 1880. The  photophone allowed for the transmission of sound on a beam of light, and on June 3, 1880 Bell and Tainter transmitted the world's first wireless telephone message on their newly invented form of light telecommunication.[10][11]
In the early 1890s Nikola Tesla began his research into high frequency electricity. Tesla was aware of Hertz's experiments with electromagnetic waves from 1889 on[12][13] but, (like many scientists of that time) thought, even if radio waves existed, they would probably only travel in straight lines making them useless for long range transmission.[14]
Tesla's primary interest in wireless phenomenon was as a power distribution system[14] although he proposed by 1893 that it could also incorporate communication. His laboratory work and later large scale experiments at Colorado Springs led him to the conclusion that he could build a conduction based worldwide wireless system that would use the Earth itself (via injecting very large amounts of electric current into the ground) as the means to conduct the signal very long distances (across the Earth), overcoming the perceived limitations of other systems.[15] He went on to try to implement his ideas of power transmission and wireless telecommunication  in his very large but unsuccessful Wardenclyffe Tower project.[16]
Development of electromagnetism

Experiments and Theory

Joseph Henry
Michael Faraday
Hans Christian Ørsted

Various scientists proposed that electricity and magnetism were linked. Around 1800 Alessandro Volta developed the first means of producing an electric current.   In 1802 Gian Domenico Romagnosi may have suggested a relationship between electricity and magnetism but his reports went unnoticed.[17][18] In 1820 Hans Christian Ørsted performed a simple and today widely known experiment on  electric current and magnetism. He demonstrated that a wire carrying a current could deflect a magnetized compass needle.[19] Ørsted's work influenced André-Marie Ampère to produce a theory of electromagnetism.  Several scientists speculated that light might be connected with electricity or magnetism.
In 1831, Michael Faraday began a series of experiments in which he discovered electromagnetic induction. The relation was mathematically modelled by Faraday's law, which subsequently became one of the four Maxwell equations. Faraday proposed that electromagnetic forces extended into the empty space around the conductor, but did not complete his work involving that proposal. In 1846 Michael Faraday speculated that light was a wave disturbance in a force field".[20]
Expanding upon a series of experiments by Felix Savary,[21][22][23][24] between 1842 and 1850 Joseph Henry performed experiments detecting inductive magnetic effects over a distance of 200 feet (61m).[25][26][27] He was the first (1838–42) to produce high frequency AC electrical oscillations, and to point out and experimentally demonstrate that the discharge of a capacitor under certain conditions is oscillatory, or, as he puts it, consists "of a principal discharge in one direction and then several reflex actions backward and forward, each more feeble than the preceding until equilibrium is attained". This view was also later adopted by Helmholtz,[28] the mathematical demonstration of this fact was first given by Lord Kelvin in his paper on "Transient Electric Currents".[29][30]
Maxwell and the theoretical prediction of electromagnetic waves

Maxwell and electromagnetic waves

James Clerk Maxwell
Oliver Heaviside

Between 1861 and 1865, based on the earlier experimental work of Faraday and other scientists and on his own modification to Ampere's law, James Clerk Maxwell developed his theory of electromagnetism, which predicted the existence of electromagnetic waves. In 1873 Maxwell described the theoretical basis of the propagation of electromagnetic waves in his paper to the Royal Society, "A Dynamical Theory of the Electromagnetic Field."  This theory united all previously unrelated observations, experiments and equations of electricity, magnetism, and optics into a consistent theory.[31] His set of equations—Maxwell's equations—demonstrated that electricity, magnetism, and light are all manifestations of the same phenomenon, the electromagnetic field. Subsequently, all other classic laws or equations of these disciplines were special cases of Maxwell's equations. Maxwell's work in electromagnetism has been called the "second great unification in physics".[32]
Oliver Heaviside, later reformulated Maxwell's original equations into the set of four vector equations that are generally known today as Maxwell's equations.[33]  Neither Maxwell nor Heaviside transmitted or received radio waves; however, their equations for electromagnetic fields established principles for radio design, and remain the standard expression of classical electromagnetism.
Of Maxwell's work, Albert Einstein wrote:[34]
"Imagine [Maxwell's] feelings when the differential equations he had formulated proved to him that electromagnetic fields spread in the form of polarised waves, and at the speed of light!  To few men in the world has such an experience been vouchsafed... it took physicists some decades to grasp the full significance of Maxwell's discovery, so bold was the leap that his genius forced upon the conceptions of his fellow-workers."
Other physicists were equally impressed with Maxwell's work, such as Richard Feynman who commented:[35]
"From a long view of the history of the world—seen from, say, ten thousand years from now—there can be little doubt that the most significant event of the 19th century will be judged as Maxwell's discovery of the laws of electromagnetism.  The American Civil War will pale into provincial insignificance in comparison with this important scientific event of the same decade."
Experiments and proposals
Berend Wilhelm Feddersen,[36] a German physicist, in 1859, as a private scholar in Leipzig, succeeded in experiments with the Leyden jar to prove that electric sparks were composed of damped oscillations.
In 1870 the German physicist Wilhelm von Bezold discovered and demonstrated the fact that the advancing and reflected oscillations produced in conductors by a capacitor discharge gave rise to interference phenomena.[37][38] Professors Elihu Thomson and E. J. Houston in 1876 made a number of experiments and observations on high frequency oscillatory discharges.[39] In 1883 George FitzGerald suggested[40] at a British Association meeting that electromagnetic waves could be generated by the discharge of a capacitor, but the suggestion was not followed up, possibly because no means was known for detecting the waves.[30]
Hertz experimentally verifies Maxwell's theory

It had been proposed in 1879 to German physicist Heinrich Rudolf Hertz that he try to prove Maxwell's theory of electromagnetism but he could not see any way to build an apparatus to experimentally test the theory.[41] His observation, in the autumn of 1886, of discharging a Leyden jar into a large coil producing a spark in an adjacent coil gave him the idea of how to build a test apparatus.[42][43] Between 1886 and 1888 Hertz conducted scientific experiments that validated Maxwell's theory.[44] He designed a method of detecting spark-gap radio waves by observing that another unpowered spark-gap, acting as an antenna, would absorb the radio energy and convert it back into an electric spark. Hertz published his results in a series of papers between 1887 and 1890,[45] and again in complete book form in 1893.[46]
The first of the papers published, "On Very Rapid Electric Oscillations", gives an account of the chronological course of his investigation, as far as it was carried out up to the end of the year 1886 and the beginning of 1887.[47]
For the first time, electromagnetic radio waves ("Hertzian waves")[48] were intentionally and unequivocally proven to have been transmitted through free space by a spark-gap device, and detected over a short distance.[49]

Hertz was able to have some control over the frequencies of his radiated waves by altering the inductance and capacitance of his transmitting and receiving antennas. He focused the electromagnetic waves using a corner reflector and a parabolic reflector, to demonstrate that radio behaved the same as light, as Maxwell's electromagnetic theory had predicted more than 20 years earlier.[30]
Hertz did not devise a system for practical utilization of electromagnetic waves, nor did he describe any potential applications of the technology. Hertz was asked by his students at the University of Bonn what use there might be for these waves. He replied, “It's of no use whatsoever. This is just an experiment that proves Maestro Maxwell was right, we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there."[50]
Hertz died in 1894, and the art of radio wave communication was left to others to implement into a practical form. After Hertz's experiments, Sir William Crookes published an article in February 1892 in The Fortnightly Review on 'Some possibilities of electricity' with his thoughts on possibility of wireless communication based on the research of Lodge and Hertz,[51] and the American physicist Amos Emerson Dolbear brought similar attention to the idea.[52]
Pre-Hertz radio wave detection

Towards the end of 1875, while experimenting with the telegraph, Thomas Edison noted a phenomenon that he termed "etheric force", announcing it to the press on November 28. He abandoned this research when Elihu Thomson, among others, ridiculed the idea, claiming it was electromagnetic induction.
In 1879 the experimenter and inventor David Edward Hughes working in London discovered that a bad contact in a Bell telephone he was using in his experiments seemed to be sparking when he worked on a nearby induction balance (an early form of metal detector).[53][54] He developed an improved detector to pick up this unknown "extra current" based on his new microphone design (similar to later detectors known as coherers or crystal detectors)[53][55] and developed a way to interrupt his induction balance to produce a series of sparks. By trial and error experiments he eventually found he could pick up these "aerial waves" as he carried his telephone device down the street out to a range of 500 yards (460m).
On February 20, 1880, he demonstrated his experiment to representatives of the Royal Society including Thomas Henry Huxley, Sir George Gabriel Stokes, and William Spottiswoode, then president of the Society. Stokes was convinced the phenomenon Hughes was demonstrating was merely electromagnetic induction, not a type of conduction through the air.[56][57][58] Hughes was not a physicist and seems to have accepted Stokes observations and did not pursue the experiments any further.[57] His work may have been mentioned in William Crookes' 1892 Fortnightly Review review of  'Some possibilities of electricity' article as an unnamed individual whose experiment Crookes participate in.[51]
Development of radio waves

Early experimenters

Édouard Branly
Oliver Joseph Lodge

Jagadish Chandra Bose

The Branly detector
In 1890, Édouard Branly[59][60][61] demonstrated what he later called the "radio-conductor,"[62] which Lodge in 1893 named the coherer, the first sensitive device for detecting radio waves.[63] Shortly after the experiments of Hertz, Branly discovered that loose metal filings, which in a normal state have a high electrical resistance, lose this resistance in the presence of electric oscillations and become practically conductors of electricity. This Branly showed by placing metal filings in a glass box or tube, and making them part of an ordinary electric circuit. According to the common explanation, when electric waves are set up in the neighborhood of this circuit, electromotive forces are generated in it which appear to bring the filings more closely together, that is, to cohere, and thus their electrical resistance decreases, from which cause this piece of apparatus was termed by Sir Oliver Lodge a coherer.[64] Hence the receiving instrument, which may be a telegraph relay, that normally would not indicate any sign of current from the small battery, can be operated when electric oscillations are set up.[65] Branly further found that when the filings had once cohered they retained their low resistance until shaken apart, for instance, by tapping on the tube.[66] The coherer, however, was not sensitive enough to be used reliably as radio developed.[67]
Lodge's demonstrations
British physicist and writer Sir Oliver Lodge came close to being the first to prove the existence of Maxwell's electromagnetic waves. In a series spring of 1888 experiments conducted with a Leyden jar connected to a length of wire with spaced spark gaps he noticed he was getting different size sparks and a glow pattern along the wire that seemed to be a function of wavelength.[68][69] Before he could present his own findings he learned of Hertz' series of proofs on the same subject.
On 1 June 1894, at a meeting of the British Association for the Advancement of Science at Oxford University, Lodge gave a memorial lecture on the work of Hertz (recently deceased) and the German physicist's proof of the existence of electromagnetic waves 6 years earlier. Lodge set up a demonstration on the quasi-optical nature of "Hertzian waves" (radio waves) and demonstrated their similarity to light and vision including reflection and transmission.[70] Later in June and on 14 August 1894 he did similar experiments, increasing the distance of transmission up to 55 meters.[68] In these lectures Lodge demonstrated a detector that would become standard in radio work, an improved version of Branly's detector which Lodge dubbed the coherer. It consisted of a glass tube containing metal filings between two electrodes. When the small electrical charge from waves from an antenna were applied to the electrodes, the metal particles would cling together or "cohere" causing the device to become conductive allowing the current from a battery to pass through it. In Lodge's setup the slight impulses from the coherer were picked up by a mirror galvanometer which would deflect a beam of light being projected on it, giving a visual signal that the impulse was received. After receiving a signal the metal filings in the coherer were broken apart or "decohered" by a manually operated vibrator or by the vibrations of a bell placed on the table near by that rang every time a transmission was received.[70] Lodge also demonstrated tuning using a pair of Leyden jars that could be brought into resonance.[71] Lodges lectures were widely publicized and his techniques influenced and were expanded on by other radio pioneers including Augusto Righi and his student Guglielmo Marconi, Alexander Popov, Lee de Forest, and Jagadish Chandra Bose.[72][73][74]
Lodge at the time seemed to see no value in using radio waves for signalling or wireless telegraphy and there is debate as to whether he even bothered to demonstrate communication during his lectures.[75] Physicist John Ambrose Fleming, pointed out that Lodge's lecture was a physics experiment, not a demonstration of telegraphic signaling.[76] After radio communication was developed Lodge's lecture would become the focus of priority disputes over who invented wireless telegraphy (radio). His early demonstration and later development of radio tuning (his 1898 Syntonic tuning patent) would lead to patent disputes with the Marconi Company. When Lodge's syntonic patent was extended in 1911 for another 7 years Marconi agreed to settle the patent dispute and purchase the patent.[77]
J. C. Bose
In November 1894, the Indian physicist, Jagadish Chandra Bose, demonstrated publicly the use of radio waves in Calcutta, but he was not interested in patenting his work.[78] Bose ignited gunpowder and rang a bell at a distance using electromagnetic waves,[79] confirming that communication signals can be sent without using wires. He sent and received radio waves over distance but did not commercially exploit this achievement.
Bose demonstrated the ability of the signal to travel from the lecture room, and through an intervening room and passage, to a third room 75 feet (23m) distant from the radiator, thus passing through three solid walls on the way, as well as the body of the chairman (who happened to be the Lieutenant-Governor). The receiver at this distance still had energy enough to make a contact which set a bell ringing, discharged a pistol, and exploded a miniature mine. To get this result from his small radiator, Bose set up an apparatus which curiously anticipated the lofty 'antennae' of modern wireless telegraphy—a circular metal plate at the top of a pole, 20 feet (6.1m) high, being put in connection with the radiator and a similar one with the receiving apparatus.[80]
The form of 'Coherer' devised by Professor Bose, and described by him at the end of his paper 'On a new Electro Polariscope' allowed for the sensibility and range to appear to leave little to be desired at the time.[80] In 1896, the British, Daily Chronicle reported on his UHF experiments: "The inventor (J. C. Bose) has transmitted signals to a distance of nearly a mile and herein lies the first and obvious and exceedingly valuable application of this new theoretical marvel."
After Bose's Friday Evening Discourses at the Royal Institution, The Electric Engineer expressed 'surprise that no secret was at any time made as to its construction, so that it has been open to all the world to adopt it for practical and possibly money-making purposes.'
Bose was sometimes criticised as unpractical for making no profit from his inventions.[80]
In 1899, Bose announced the development of an "iron-mercury-iron coherer with telephone detector" in a paper presented at the Royal Society, London.[81] Later he received , "Detector for electrical disturbances" (1904), for a specific electromagnetic receiver. Bose would continue with his research and made other contributions to the development of radio.[82]
Adaptations of radio waves
Popov's lightning detector

In 1894-95 the Russian physicist Alexander Stepanovich Popov conducted experiments developing a radio receiver, an improved version of coherer-based design by Oliver Lodge. His design with coherer auto-tapping mechanism was designed as a lightning detector to help the forest service track lightning strikes that could start fires. His receiver proved to be able to sense lightning strikes at distances of up to 30km. Popov built a version of the receiver that was capable of automatically recording lightning strikes on paper rolls. Popov presented his radio receiver to the Russian Physical and Chemical Society on May 7, 1895— the day has been celebrated in the Russian Federation as "Radio Day" promoted in eastern European countries as the inventor of radio.[83][84][85] The paper on his findings was published the same year (December 15, 1895). Popov had recorded, at the end of 1895, that he was hoping for distant signaling with radio waves.[86] He did not apply for a patent for this invention.
Tesla's boat
In 1898 Nikola Tesla developed a radio/coherer based remote-controlled boat, with a form of secure communication[87][88] between transmitter and receiver,[89] which he demonstrated in 1898. Tesla called his invention a "teleautomaton" and he hoped to sell it as a guided naval torpedo.[90]
Radio based wireless telegraphy
Marconi

Guglielmo Marconi studied at the Leghorn Technical School, and acquainted himself with the published writings of Professor Augusto Righi of the University of Bologna.[91] In 1894, Sir William Preece delivered a paper to the Royal Institution in London on electric signalling without wires.[92][93] In 1894 at the Royal Institution lectures, Lodge delivered "The Work of Hertz and Some of His Successors".[94] Marconi is said to have read, while on vacation in 1894, about the experiments that Hertz did in the 1880s. Marconi also read about Tesla's work.[95] It was at this time that Marconi began to understand that radio waves could be used for wireless communications. Marconi's early apparatus was a development of Hertz’s laboratory apparatus into a system designed for communications purposes. At first Marconi used a transmitter to ring a bell in a receiver in his attic laboratory. He then moved his experiments out-of-doors on the family estate near Bologna, Italy, to communicate further. He replaced Hertz’s vertical dipole with a vertical wire topped by a metal sheet, with an opposing terminal connected to the ground. On the receiver side, Marconi replaced the spark gap with a metal powder coherer, a detector developed by Edouard Branly and other experimenters. Marconi transmitted radio signals for about 1.5 miles (2.4km) at the end of 1895.[96]
Marconi was awarded a patent for radio with British patent , Improvements in Transmitting Electrical Impulses and Signals and in Apparatus There-for. The complete specification was filed March 2, 1897. This was Marconi's initial patent for the radio, though it used various earlier techniques of various other experimenters and resembled the instrument demonstrated by others (including Popov). During this time spark-gap wireless telegraphy was widely researched. In July, 1896, Marconi got his invention and new method of telegraphy to the attention of Preece, then engineer-in-chief to the British Government Telegraph Service, who had for the previous twelve years interested himself in the development of wireless telegraphy by the inductive-conductive method. On June 4, 1897, he delivered "Signalling through Space without Wires".[97] Preece devoted considerable time to exhibiting and explaining the Marconi apparatus at the Royal Institution in London, stating that Marconi invented a new relay which had high sensitiveness and delicacy.[98]

The Marconi Company Ltd. was founded by Marconi in 1897, known as the Wireless Telegraph Trading Signal Company. Also in 1897, Marconi established the radio station at Niton, Isle of Wight, England. Marconi's wireless telegraphy was inspected by the Post Office Telegraph authorities; they made a series of experiments with Marconi's system of telegraphy without connecting wires, in the Bristol Channel. The October wireless signals of 1897 were sent from Salisbury Plain to Bath, a distance of  34 miles (55km).[101]  Around 1900 Marconi developed an empirical law that, for simple vertical sending and receiving antennas of equal height, the maximum working telegraphic distance varied as the square of the height of the antenna.[102]  This became known as Marconi's law.
Other experimental stations were established at Lavernock Point, near Penarth; on the Flat Holmes, an island in mid-channel, and at Brean Down, a promontory on the Somerset side. Signals were obtained between the first and last-named points, a distance of, approximately, 8 miles (13km). The receiving instrument used was a Morse inkwriter[103] of the Post Office pattern.[104][105] In 1898, Marconi opened a radio factory in Hall Street, Chelmsford, England, employing around 50 people. In 1899, Marconi announced his invention of the "iron-mercury-iron coherer with telephone detector" in a paper presented at Royal Society, London.
In May, 1898, communication was established for the Corporation of Lloyds between Ballycastle and the Lighthouse on Rathlin Island in the North of Ireland. In July 1898, the Marconi telegraphy was employed to report the results of yacht races at the Kingstown Regatta for the Dublin Express newspaper. A set of instruments were fitted up in a room at Kingstown, and another on board a steamer, the Flying Huntress. The aerial conductor on shore was a strip of wire netting attached to a mast 40 feet (12m) high, and several hundred messages were sent and correctly received during the progress of the races.
At this time His Majesty King Edward VII, then Prince of Wales, had the misfortune to injure his knee, and was confined on board the royal yacht Osltorm in Cowes Bay.[106]
Marconi fitted up his apparatus on board the royal yacht by request, and also at Osborne House, Isle of Wight, and kept up wireless communication for three weeks between these stations. The distances covered were small; but as the yacht moved about, on some occasions high hills were interposed so that the aerial wires were overtopped by hundreds of feet, yet this was no obstacle to communication. These demonstrations led the Corporation of Trinity House to afford an opportunity for testing the system in practice between the South Foreland Lighthouse, near Dover, and the East Goodwin Lightship, on the Goodwin Sands. This installation was set in operation on December 24, 1898, and proved to be of value. It was shown that when once the apparatus was set up it could be worked by ordinary seamen with very little training.
At the end of 1898 electric wave telegraphy established by Marconi had demonstrated its utility, especially for communication between ship and ship and ship and shore.[107]
The Haven Hotel station and Wireless Telegraph Mast was where much of Marconi's research work on wireless telegraphy was carried out after 1898.[108] In 1899, he transmitted messages across the English Channel. Also in 1899, Marconi delivered "Wireless Telegraphy" to the Institution of Electrical Engineers.[107] In addition, in 1899, W. H. Preece delivered "Aetheric Telegraphy", stating that the experimental stage in wireless telegraphy had been passed in 1894 and inventors were then entering the commercial stage.[109] Preece, continuing in the lecture, details the work of Marconi and other British inventors. In April 1899, Marconi's experiments were repeated for the first time in the United States, by Jerome Green at the University of Notre Dame.[110][111] In October, 1899, the progress of the yachts in the international race between the Columbia and Shamrock was successfully reported by aerial telegraphy, as many as 4,000 words having been (as is said) despatched from the two ship stations to the shore stations. Immediately afterward the apparatus was placed by request at the service of the United States Navy Board, and some highly interesting experiments followed under Marconi's personal supervision.[112] The Marconi Company was renamed Marconi's Wireless Telegraph Company in 1900.

In 1901, Marconi claimed to have received daytime transatlantic radio frequency signals at a wavelength of 366metres (820kHz).[114][115][116] Marconi established a wireless transmitting station at Marconi House, Rosslare Strand, Co. Wexford in 1901 to act as a link between Poldhu in Cornwall and Clifden in Co. Galway. His announcement on 12 December 1901, using a 152.4-metre (500ft) kite-supported antenna for reception, stated that the message was received at Signal Hill in St John's, Newfoundland (now part of Canada) via signals transmitted by the company's new high-power station at Poldhu, Cornwall. The message received had been prearranged and was known to Marconi, consisting of the Morse letter 'S' - three dots. Bradford has recently contested the reported success, however, based on theoretical work as well as a reenactment of the experiment. It is now well known that long-distance transmission at a wavelength of 366 meters is not possible during the daytime, because the skywave is heavily absorbed by the ionosphere. It is possible that what was heard was only random atmospheric noise, which was mistaken for a signal, or that Marconi may have heard a shortwave harmonic of the signal.[115][116] The distance between the two points was about 3,500 kilometres (2,200mi).
The Poldhu to Newfoundland transmission claim has been criticized.[117] There are various science historians, such as Belrose and Bradford, who have cast doubt that the Atlantic was bridged in 1901, but other science historians have taken the position that this was the first transatlantic radio transmission. Critics have claimed that it is more likely that Marconi received stray atmospheric noise from atmospheric electricity in this experiment.[118] The transmitting station in Poldhu, Cornwall used a spark-gap transmitter that could produce a signal in the medium frequency range and with high power levels.
Marconi transmitted from England to Canada and the United States.[119] In this period, a particular electromagnetic receiver, called the Marconi magnetic detector[120] or hysteresis magnetic detector,[121] was developed further by Marconi and was successfully used in his early transatlantic work (1902) and in many of the smaller stations for a number of years.[122][123] In 1902, a Marconi station was established in the village of Crookhaven, County Cork, Ireland to provide marine radio communications to ships arriving from the Americas. A ship's master could contact shipping line agents ashore to enquire which port was to receive their cargo without the need to come ashore at what was the first port of landfall.[124] Ireland was also, due to its western location, to play a key role in early efforts to send trans-Atlantic messages. Marconi transmitted from his station in Glace Bay, Nova Scotia, Canada across the Atlantic, and on 18 January 1903 a Marconi station sent a message of greetings from Theodore Roosevelt, the President of the United States, to the King of the United Kingdom, marking the first transatlantic radio transmission originating in the United States

In 1904, Marconi inaugurated an ocean daily newspaper, the Cunard Daily Bulletin, on the R.M.S. "Campania."  At the start, passing events were printed in a little pamphlet of four pages called the Cunard Bulletin. The title would read Cunard Daily Bulletin, with subheads for "Marconigrams Direct to the Ship."[125] All the passenger ships of the Cunard Company were fitted with Marconi's system of wireless telegraphy, by means of which constant communication was kept up, either with other ships or with land stations on the eastern or western hemisphere. The RMS Lucania, in October 1903, with Marconi on board, was the first vessel to hold communications with both sides of the Atlantic. The Cunard Daily Bulletin, a thirty-two page illustrated paper published on board these boats recorded news received by wireless telegraphy, and was the first ocean newspaper. In August 1903, in agreement was made with the British Government by which the Cunard Co. were to build two steamers, to be, with all other Cunard ships, at the disposal of the British Admiralty for hire or purchase whenever they might be required, the Government lending the company £2,600,000 to build the ships and granting them a subsidy of £150,000 a year. One was the RMS Lusitania and another was the RMS Mauritania.[126]
In June and July 1923, Marconi's shortwave transmissions took place at night on 97 meters from Poldhu Wireless Station, Cornwall, to his yacht Elettra in the Cape Verde Islands. In September 1924, Marconi transmitted during daytime and nighttime on 32 meters from Poldhu to his yacht in Beirut. In July 1924, Marconi entered into contracts with the British General Post Office (GPO) to install telegraphy circuits from London to Australia, India, South Africa and Canada as the main element of the Imperial Wireless Chain. The UK-to-Canada shortwave "Beam Wireless Service" went into commercial operation on 25 October 1926. Beam Wireless Services from the UK to Australia, South Africa and India went into service in 1927. Electronic components for the system were built at Marconi's New Street wireless factory in Chelmsford.[127]
Marconi was awarded the 1909 Nobel Prize in Physics with Karl Ferdinand Braun for contributions to radio sciences. Marconi's demonstrations of the use of radio for wireless communications, equipping ships with life saving wireless communications,[128] establishing the first transatlantic radio service,[119] and building the first stations for the British shortwave service, have marked his place in history. Shortly after the turn of the 20th century, the US Patent Office re-awarded Marconi a patent for radio. The  was granted on June 4, 1901. Marconi's  was awarded on June 11, 1901, also. This system was more advanced than his previous works. The United States Supreme Court, decision of MARCONI WIRELESS T. CO. OF AMERICA v. U.S., 320 U.S. 1 (1943) stated that “Marconi's reputation as the man who first achieved successful radio transmission … is not here in question” this statement is followed by “Marconi's patent involved no invention over Lodge, Tesla, and Stone”. The 1943 decision didn't overturn Marconi's original patents, or his reputation as the first person to develop practical radiotelegraphic communication. It just said that the adoption of adjustable transformers in the transmitting and receiving circuits, which was an improvement of the initial invention, was anticipated by patents issued to Oliver Lodge and John Stone. (This decision wasn't unanimous).[129]
Braun

Ferdinand Braun's major contributions were the introduction of a closed tuned circuit in the generating part of the transmitter, and its separation from the radiating part (the antenna) by means of inductive coupling, and later on the usage of crystals for receiving purposes. Braun experimented at first at the University of Strasbourg. Braun had written extensively on wireless subjects and was well known through his many contributions to the Electrician and other scientific journals.[130] In 1899, he would apply for the patents, Electro telegraphy by means of condensers and induction coils and Wireless electro transmission of signals over surfaces.[131]
Pioneers working on wireless devices eventually came to a limit of distance they could cover.  Connecting the antenna directly to the spark gap produced only a heavily damped pulse train. There were only a few cycles before oscillations ceased. Braun's circuit afforded a much longer sustained oscillation because the energy encountered less loss swinging between coil and Leyden Jars. Also, by means of inductive antenna coupling[132] the radiator was matched to the generator.
In spring 1899 Braun, accompanied by his colleagues Cantor and Zenneck, went to Cuxhaven to continue their experiments at the North Sea. On February 6, 1899, he would apply for the United States Patent, .  Not before long he bridged a distance of 42km to the city of Mutzing. On 24 September 1900 radio telegraphy signals were exchanged regularly with the island of Heligoland over a distance of 62km. Lightvessels in the river Elbe and a coast station at Cuxhaven commenced a regular radio telegraph service. On August 6, 1901, he would apply for .
By 1904, the closed circuit system of wireless telegraphy, connected with the name of Braun, was well known and generally adopted in principle. The results of Braun's experiments, published in the Electrician, possess interest, apart from the method employed. Braun showed how the problem could be satisfactorily and economically solved.[133] The closed circuit oscillator has the advantage, as was known, of being able to draw upon the kinetic energy in the oscillator circuit, and thus, because such a circuit can be given a much greater capacity than can be obtained with a radiating aerial alone, much more energy can be stored up and radiated by its employment.[133] The emission is also prolonged, both results tending towards the attainment of the much desired train of undamped waves. The energy available, though greater than with the open system, was still inconsiderable unless very high potentials, with the attendant drawbacks, were used.[133][134] Braun avoided the use of extremely high potentials for charging the gap and also makes use of a less wasteful gap by sub-dividing it.[133][135] The chief point in his new arrangement, however, is not the sub-division of the gap merely but their arrangement, by which they are charged in parallel, at low voltages, and discharge in series. The Nobel Prize awarded to Braun in 1909 depicts this design.[136]
Stone Stone

John Stone Stone labored as an early telephone engineer and was influential in developing wireless communication technology, and holds dozens of key patents in the field of "space telegraphy". Patents of Stone for radio, together with their equivalents in other countries, form a very voluminous contribution to the patent literature of the subject. More than seventy United States patents have been granted to this patentee alone. In many cases these specifications are learned contributions to the literature of the subject, filled with valuable references to other sources of information.[137]
Stone has had issued to him a large number of patents embracing a method for impressing oscillations on a radiator system and emitting the energy in the form of waves of predetermined length whatever may be the electrical dimensions of the oscillator.[138] On February 8, 1900, he filed for a selective system in . In this system, two simple circuits are associated inductively, each having an independent degree of freedom, and in which the restoration of electric oscillations to zero potential the currents are superimposed, giving rise to compound harmonic currents which permit the resonator system to be syntonized with precision to the oscillator.[138] Stone's system, as stated in , developed free or unguided simple harmonic electromagnetic signal waves of a definite frequency to the exclusion of the energy of signal waves of other frequencies, and an elevated conductor and means for developing therein forced simple electric vibrations of corresponding frequency.[139] In these patents Stone devised a multiple inductive oscillation circuit with the object of forcing on the antenna circuit a single oscillation of definite frequency. In the system for receiving the energy of free or unguided simple harmonic electromagnetic signal waves of a definite frequency to the exclusion of the energy of signal waves of other frequencies, he claimed an elevated conductor and a resonant circuit associated with said conductor and attuned to the frequency of the waves, the energy of which is to be received.[139] A coherer made on what is called the Stone system[140] was employed in some of the portable wireless outfits of the United States Army. The Stone Coherer has two small steel plugs between which are placed loosely packed carbon granules. This is a self-decohering device; though not as sensitive as other forms of detectors it is well suited to the rough usage of portable outfits.[140]
Naval wireless
US Navy
In 1899 the United States Navy Board issued a report on the results of investigations of the Marconi system of wireless telegraphy.[141]  The report noted that the system was well adapted for use in squadron signalling, under conditions of rain, fog, darkness and motion of speed although dampness affected the performance.[142] They also noted that when two stations were transmitting simultaneously both would be received and that the system had the potential to affect the compass.  They reported ranges from 85 miles (137km) for large ships with tall masts (43 metres, 141ft) to 7 miles (11km) for smaller vessels.  The board recommended that the system was given a trial by the United States Navy.
Royal Navy

In 1897, recently promoted Royal Navy Captain Henry Jackson  became the first person to achieve ship-to-ship wireless communications and demonstrated continuous communication with another vessel up to three miles away.[143] HMS<i>Hector became the first British warship to have wireless telegraphy installed when she conducted the first trials of the new equipment for the Royal Navy.[144][145] Starting in December 1899, HMS Hector and HMS<i>Jaseur were outfitted with wireless equipment.[146] On 25 January 1901, HMS Jaseur received signals from the Marconi transmitter on the Isle of Wight and from HMS Hector (25 January).[147]
Wireless telephony

Fessenden
In late 1886, Reginald A. Fessenden began working directly for Thomas Edison at the inventor's new laboratory in West Orange, New Jersey. Fessenden quickly made major advances, especially in receiver design, as he worked to develop audio reception of signals. The United States Weather Bureau began, early in 1900, a systematic course of experimentation in wireless telegraphy, employing him as a specialist.[148] Fessenden evolved the heterodyne principle here where two signals combined to produce a third signal.
In 1900, construction began on a large radio transmitting alternator. Fessenden, experimenting with a high-frequency spark transmitter, successfully transmitted speech on December 23, 1900, over a distance of about 1.6 kilometres (0.99mi), the first audio radio transmission. Early in 1901 the Weather Bureau officially installed Fessenden at Wier's Point, Roanoke Island, North Carolina, and he made experimental transmissions across water to a station located about 5 miles (8.0km) west of Cape Hatteras, the distance between the two stations being almost exactly 50 miles (80km).[148] An alternator of 1kW output at 10 kilohertz was built in 1902. The credit for the development of this machine is due to Charles Proteus Steinmetz, Caryl D. Haskins, Ernst Alexanderson, John T. H. Dempster, Henry Geisenhoner, Adam Stein, Jr., and F. P. Mansbendel.[30]
In a paper written by Fessenden in 1902, it was asserted that important advances had been made, one of which was overcoming largely the loss of energy experienced in other systems.  In an interview with a New York Journal correspondent, Fessenden stated that in his early apparatus he did not use an air transformer at the sending end, nor a concentric cylinder for emitters and antennae,[148][149] and had used capacity, but arranged in a manner entirely different from that in other systems, and that he did not employ a coherer or any form of imperfect contact.  Fessenden asserted that he had paid particular attention to selective and multiplex systems, and was well satisfied with the results in that direction.[148] On August 12, 1902, 13 patents were issued to Fessenden, covering various methods, devices, and systems for signaling without wires.[148] These patents involved many new principles, the chef-d'oeuvre of which was a method for distributing capacity and inductance instead of localizing these coefficients of the oscillator as in previous systems.[138]

By the summer of 1906, a machine producing 50 kilohertz was installed at the Brant Rock station, and in the fall of 1906, what was called an electric alternating dynamo was working regularly at 75 kilohertz, with an output of 0.5kW.[30] Fessenden[150] used this for wireless telephoning to Plymouth, Massachusetts, a distance of approximately 11 miles (18km).[30] In the following year machines were constructed having a frequency of 96 kilohertz[151] and outputs of 1kW and 2kW. Fessenden believed that the damped wave-coherer system was essentially and fundamentally incapable of development into a practical system.[30] He would employ a two-phase high frequency alternator method[152] and the continuous production of waves[153] with changing constants of sending circuit.[30][154] Fessenden would also use duplex and multiplex commutator methods.[155] On December 11, 1906, operation of the wireless transmission in conjunction with the wire lines took place.[156][30] In July 1907 the range was considerably extended and speech was successfully transmitted between Brant Rock and Jamaica, on Long Island, a distance of nearly 200 miles (320km), in daylight and mostly over land,[157] the mast at Jamaica being approximately 180 feet (55m) high.[30]
Fleming
In November 1904, the English physicist John Ambrose Fleming invented the two-electrode vacuum-tube rectifier, which he called the Fleming oscillation valve.[158] for which he obtained GB patent 24850 and .[159] This "Fleming Valve" was sensitive and reliable, and so it replaced the crystal diode used in receivers used for long-distance wireless communication. It had an advantage, that it could not be permanently injured or set out of adjustment by any exceptionally strong stray signal, such as those due to atmospheric electricity.[160] Fleming earned a Hughes Medal in 1910 for his electronic achievements. Marconi used this device as a radio detector.
The Supreme Court of the United States would eventually invalidate the US patent because of an improper disclaimer and, additionally, maintained the technology in the patent was known art when filed.[161] This invention was the first vacuum tube. Fleming's diode was used in radio receivers for many decades afterward, until it was superseded by improved solid state electronic technology more than 50 years later.
De Forest
Lee De Forest[162][163][164] had an interest in wireless telegraphy and he invented the Audion in 1906. He was president and secretary of the De Forest Radio Telephone and Telegraph Company (1913).[165][166] The De Forest System was adopted by the United States Government, and had been demonstrated to other Governments including those of Great Britain, Denmark, Germany, Russia, and British Indies, all of which purchased De Forest apparatus previous to the Great War. De Forest is one of the fathers of the "electronic age", as the Audion helped to usher in the widespread use of electronics.[167]
De Forest made the Audion tube from a vacuum tube. He also made the "Oscillion", an undamped wave transmitter. He developed the De Forest method of wireless telegraphy and founded the American De Forest Wireless Telegraph Company. De Forest was a distinguished electrical engineer and the foremost American contributor to the development of wireless telegraphy and telephony. The elements of his device takes relatively weak electrical signals and amplifies them. The Audion Detector, Audion Amplifier, and the "Oscillion" transmitter had furthered the radio art and the transmission of written or audible speech. In World War I, the De Forest system was a factor in the efficiency of the United States Signal Service, and was also installed by the United States Government in Alaska.[167]
Radio invention timeline

Below is a brief selection of important events and individuals related to the development of radio, from 1860 to 1910.[168]

See also

PeopleEdwin Howard Armstrong, Greenleaf Whittier Pickard, Ernst Alexanderson, Archie Frederick Collins, Alexander Stepanovich Popov
RadioRadio communication system, Timeline of radio, Oldest radio station, Birth of public radio broadcasting, Crystal radio
CategoriesRadio People, Radio Pioneers, Discovery and invention controversies
OtherList of persons considered father or mother of a field, Radiotelegraph and Spark-Gap Transmitters, The Great Radio Controversy, Induction coil, Ruhmkorff coil, Poldhu, Alexanderson alternator, De Forest tube
Footnotes

Further reading
Anderson, L.I., "Priority in the Invention of Radio: Tesla vs. Marconi", Antique Wireless Association Monograph No. 4, March, 1980.
Anderson, L.I., "John Stone Stone on Nikola Tesla's Priority in Radio and Continuous-Wave Radiofrequency Apparatus", The AWA Review, Vol. 1, 1986, pp.18–41.
Brand, W.E., "Rereading the Supreme Court: Tesla's Invention of Radio", Antenna, Volume 11 No. 2, May 1998, Society for the History of Technology
Lauer, H., & Brown, H. L. (1919). . New York: McGraw-Hill book company; [etc., etc.]
Rockman, H. B. (2004). . New York [u.a.: IEEE Press].

United States Court case
", 320 U.S. 1 (U.S. 1943)", 320 U.S. 1, 63 S. Ct. 1393, 87 L. Ed. 1731 Argued April 9,12, 1943. Decided June 21, 1943.
Books and articleslisted by date, earliest first
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Fahie, J. J. (1900). . Edinburgh: W. Blackwood and Sons.
Thompson, S. P., Homans, J. E., & Tesla, N. (1903). Polyphase electric currents and alternate-current motors. "". The library of electrical science, v. 6. New York: P.F. Collier & Son.
Sewall, C. H. (1904). . New York: D. Van Nostrand.
Trevert, E. (1904). . Lynn, Mass: Bubier Pub.
Collins, A. F. (1905). . New York: McGraw Pub.
Mazzotto, D., & Bottone, S. R. (1906). . London: Whittaker & Co.
Erskine-Murray, J. (1907). . London: Crosby Lockwood and Son. (ed., also available in the  version).
Murray, J. E. (1907). . New York: D. Van Nostrand Co.; [etc.]
Simmons, H. H. (1908). "", . London: Cassell and Co.
Fleming, J. A. (1908). . London: New York and Co.
Twining, H. L. V., & Dubilier, W. (1909). . Los Angeles, Cal: The author.
Bottone, S. R. (1910). . London: Whittaker & Co.
Bishop, L. W. (1911).  Lynn, Mass: Bubier Pub. Co.; [etc., etc.].
Massie, W. W., & Underhill, C. R. (1911). . New York: D. Van Nostrand.
Ashley, C. G., & Hayward, C. B. (1912). : an understandable presentation of the science of wireless transmission of intelligence. Chicago: American School of Correspondence.
Stanley, R. (1914). . London: Longmans, Green.
Thompson, S. P. (1915). . New York: Macmillan
Bucher, E. E. (1917). : A complete text book for students of radio communication. New York: Wireless Press, Inc.
American Institute of Electrical Engineers. (1919). . New York: American Institute of Electrical Engineers. (ed., Contains Radio Telephony— By E. B. Craft and E. H. Colpitts (Illustrated). )
Stanley, R. (1919). . London: Longmans, Green.
Encyclopedias
Chisholm, H. (1910). The encyclopædia britannica: A dictionary of arts, sciences, literature and general information. Cambridge, Eng: At the University press. "Telegraph", "".
American Technical Society. (1914). Cyclopedia of applied electricity: A general reference work on direct-current generators and motors, storage batteries, electrochemistry, welding, electric wiring, meters, electric light transmission, alternating-current machinery, telegraphy, etc. . . Chicago: American technical society.
Colby, F. M., Williams, T., & Wade, H. T. (1922). "", . New York: Dodd, Mead and Co.
"", . (1922). London: Encyclopædia Britannica.
Gutenberg project
 by Lucien Poincaré, eBook #15207, released February 28, 2005.
Websites

Howeth, Captain H.S. , published 1963, GPO, 657 pages. Free online public domain US government published book.
Wunsch, A.D., ",” Antenna, Volume 11 No. 1, November 1998, Society for the History of Technology
Katz, Randy H., "". History of Communications Infrastructures* .


Standard Model of particle physicsElementary particles of the Standard Model
BackgroundParticle physics
Standard Model
Quantum field theory
 Gauge theory
 Spontaneous symmetry breaking
 Higgs mechanism
ConstituentsElectroweak interaction
 Quantum chromodynamics
 CKM matrix
Standard Model mathematics
LimitationsStrong CP problem
Hierarchy problem
Neutrino oscillations
Physics beyond the Standard Model
ScientistsRutherford·Thomson·Chadwick·Bose·Sudarshan·Koshiba·Davis Jr.·Anderson·Fermi·Dirac·Feynman·Rubbia·Gell-Mann·Kendall·Taylor· Friedman·Powell·P. W. Anderson·Glashow·Iliopoulos·Maiani·Meer· Cowan·Nambu·Chamberlain·Cabibbo·Schwartz·Perl· Majorana·Weinberg·Lee·Ward·Salam·Kobayashi·Maskawa·Yang·Yukawa·'t Hooft·Veltman·Gross·Politzer·Wilczek· Cronin· Fitch· Vleck·Higgs·Englert·Brout·Hagen·Guralnik ·Kibble · Ting· Richtervt

In particle physics, the weak interaction (the weak force or weak nuclear force) is the mechanism of interaction between subatomic particles that causes radioactive decay and thus plays an essential role in nuclear fission. The theory of the weak interaction is sometimes called quantum flavordynamics (QFD), in analogy with the terms quantum chromodynamics (QCD) dealing with the strong interaction and quantum electrodynamics (QED) dealing with the electromagnetic force. However, the term QFD is rarely used because the weak force is best understood in terms of electroweak theory (EWT).[1]
The weak interaction takes place only at very small, sub-atomic distances, less than the diameter of a proton. It is one of the four known fundamental interactions of nature, alongside the strong interaction, electromagnetism, and gravitation.
Background
The Standard Model of particle physics provides a uniform framework for understanding the electromagnetic, weak, and strong interactions. An interaction occurs when two particles (typically but not necessarily half-integer spin fermions) exchange integer-spin, force-carrying bosons. The fermions involved in such exchanges can be either elementary (e.g. electrons or quarks) or composite (e.g. protons or neutrons), although at the deepest levels, all weak interactions ultimately are between elementary particles.
In the case of the weak interaction, fermions can exchange three distinct types of force carriers known as the W+, W−, and Z bosons. The mass of each of these bosons is far greater than the mass of a proton or neutron, which is consistent with the short range of the weak force. The force is in fact termed weak because its field strength over a given distance is typically several orders of magnitude less than that of the strong nuclear force or electromagnetic force.
Quarks, which make up composite particles like neutrons and protons, come in six "flavors" – up, down, strange, charm, top and bottom – which give those composite particles their properties. The weak interaction is unique in that it allows for quarks to swap their flavor for another. The swapping of those properties is mediated by the force carrier bosons. For example, during beta minus decay, a down quark within a neutron is changed into an up quark, thus converting the neutron to a proton and resulting in the emission of an electron and an electron antineutrino.
The weak interaction is the only fundamental interaction that breaks parity-symmetry, and similarly, the only one to break charge parity symmetry.
Other important examples of phenomena involving the weak interaction include beta decay, and the fusion of hydrogen into helium that powers the Sun's thermonuclear process. Most fermions will decay by a weak interaction over time. Such decay makes radiocarbon dating possible, as carbon-14 decays through the weak interaction to nitrogen-14. It can also create radioluminescence, commonly used in tritium illumination, and in the related field of betavoltaics.[2]
During the quark epoch of the early universe, the electroweak force separated into the electromagnetic and weak forces.
History
In 1933, Enrico Fermi proposed the first theory of the weak interaction, known as Fermi's interaction. He suggested that beta decay could be explained by a four-fermion interaction, involving a contact force with no range.[3][4]
However, it is better described as a non-contact force field having a finite range, albeit very short. In 1968, Sheldon Glashow, Abdus Salam and Steven Weinberg unified the electromagnetic force and the weak interaction by showing them to be two aspects of a single force, now termed the electroweak force.[5][6]
The existence of the W and Z bosons was not directly confirmed until 1983.[7]
Properties

The weak interaction is unique in a number of respects:
It is the only interaction capable of changing the flavor of quarks (i.e., of changing one type of quark into another).
It is the only interaction that violates P or parity-symmetry. It is also the only one that violates charge-parity CP symmetry.
It is mediated (propagated) by force carrier particles that have significant masses, an unusual feature which is explained in the Standard Model by the Higgs mechanism.
Due to their large mass (approximately 90GeV/c2[8]) these carrier particles, termed the W and Z bosons, are short-lived with a lifetime of under 10−24seconds.[9] The weak interaction has a coupling constant (an indicator of interaction strength) of between 10−7 and 10−6, compared to the strong interaction's coupling constant of 1 and the electromagnetic coupling constant of about 10−2;[10] consequently the weak interaction is weak in terms of strength.[11] The weak interaction has a very short range (around 10−17 to 10−16m[11]).[10] At distances around 10−18 meters, the weak interaction has a strength of a similar magnitude to the electromagnetic force, but this starts to decrease exponentially with increasing distance.  At distances of around 3×10−17 m, a distance which is scaled up by just one and a half decimal orders of magnitude from before, the weak interaction is 10,000 times weaker than the electromagnetic.[12]
The weak interaction affects all the fermions of the Standard Model, as well as the Higgs boson; neutrinos interact through gravity and the weak interaction only, and neutrinos were the original reason for the name weak force.[11] The weak interaction does not produce bound states nor does it involve binding energy – something that gravity does on an astronomical scale, that the electromagnetic force does at the atomic level, and that the strong nuclear force does inside nuclei.[13]
Its most noticeable effect is due to its first unique feature: flavor changing. A neutron, for example, is heavier than a proton (its sister nucleon), but it cannot decay into a proton without changing the flavor (type) of one of its two down quarks to an up quark. Neither the strong interaction nor electromagnetism permit flavor changing, so this proceeds by weak decay; without weak decay, quark properties such as strangeness and charm (associated with the quarks of the same name) would also be conserved across all interactions.
All mesons are unstable because of weak decay.[14] In the process known as beta decay, a down quark in the neutron can change into an up quark by emitting a virtual W−
 boson which is then converted into an electron and an electron antineutrino.[15] Another example is the electron capture, a common variant of radioactive decay, wherein a proton and an electron within an atom interact, and are changed to a neutron (an up quark is changed to a down quark) and an electron neutrino is emitted.
Due to the large masses of the W bosons, particle transformations or decays (e.g., flavor change) that depend on the weak interaction typically occur much more slowly than transformations or decays that depend only on the strong or electromagnetic forces. For example, a neutral pion decays electromagnetically, and so has a life of only about 10−16seconds. In contrast, a charged pion can only decay through the weak interaction, and so lives about 10−8seconds, or a hundred million times longer than a neutral pion.[16] A particularly extreme example is the weak-force decay of a free neutron, which takes about 15minutes.[15]
Weak isospin and weak hypercharge

All particles have a property called weak isospin (symbol T3), which serves as a quantum number and governs how that particle behaves in the weak interaction. Weak isospin plays the same role in the weak interaction as does electric charge in electromagnetism, and color charge in the strong interaction. All left-handed fermions have a weak isospin value of either +1⁄2 or −1⁄2. For example, the up quark has a T3 of +1⁄2 and the down quark −1⁄2. A quark never decays through the weak interaction into a quark of the same T3: Quarks with a T3 of +1⁄2 only decay into quarks with a T3 of −1⁄2 and vice versa.

In any given interaction, weak isospin is conserved: the sum of the weak isospin numbers of the particles entering the interaction equals the sum of the weak isospin numbers of the particles exiting that interaction. For example, a (left-handed) π+
, with a weak isospin of 1 normally decays into a ν
μ (+1⁄2) and a μ+
 (as a right-handed antiparticle, +1⁄2).[16]
Following the development of the electroweak theory, another property, weak hypercharge, was developed. It is dependent on a particle's electrical charge and weak isospin, and is defined by:

Y

W

=
2
(
Q
−

T

3

)

{\displaystyle \qquad Y_{W}=2(Q-T_{3})}

where YW is the weak hypercharge of a given type of particle, Q is its electrical charge (in elementary charge units) and T3 is its weak isospin. Whereas some particles have a weak isospin of zero, all spin-1⁄2 particles have non-zero weak hypercharge.
Weak hypercharge is the generator of the U(1) component of the electroweak gauge group.
Interaction types
There are two types of weak interaction (called vertices). The first type is called the "charged-current interaction" because it is mediated by particles that carry an electric charge (the W+
 or W−
 bosons), and is responsible for the beta decay phenomenon. The second type is called the "neutral-current interaction" because it is mediated by a neutral particle, the Z boson.
Charged-current interaction

In one type of charged current interaction, a charged lepton (such as an electron or a muon, having a charge of −1) can absorb a W+
 boson (a particle with a charge of +1) and be thereby converted into a corresponding neutrino (with a charge of 0), where the type ("flavor") of neutrino (electron, muon or tau) is the same as the type of lepton in the interaction, for example:

μ

−

+

W

+

→

ν

μ

{\displaystyle \mu ^{-}+W^{+}\to \nu _{\mu }}

Similarly, a down-type quark (d with a charge of −1⁄3) can be converted into an up-type quark (u, with a charge of +2⁄3), by emitting a W−
 boson or by absorbing a W+
 boson. More precisely, the down-type quark becomes a quantum superposition of up-type quarks: that is to say, it has a possibility of becoming any one of the three up-type quarks, with the probabilities given in the CKM matrix tables. Conversely, an up-type quark can emit a W+
 boson, or absorb a W−
 boson, and thereby be converted into a down-type quark, for example:

d

→
u
+

W

−

d
+

W

+

→
u

c

→
s
+

W

+

c
+

W

−

→
s

{\displaystyle {\begin{aligned}d&\to u+W^{-}\\d+W^{+}&\to u\\c&\to s+W^{+}\\c+W^{-}&\to s\end{aligned}}}

The W boson is unstable so will rapidly decay, with a very short lifetime. For example:

W

−

→

e

−

+

ν
¯

e

W

+

→

e

+

+

ν

e

{\displaystyle {\begin{aligned}W^{-}&\to e^{-}+{\bar {\nu }}_{e}~\\W^{+}&\to e^{+}+\nu _{e}~\end{aligned}}}

Decay of the W boson to other products can happen, with varying probabilities.[18]
In the so-called beta decay of a neutron (see picture, above), a down quark within the neutron emits a virtual W−
 boson and is thereby converted into an up quark, converting the neutron into a proton. Because of the energy involved in the process (i.e., the mass difference between the down quark and the up quark), the W−
 boson can only be converted into an electron and an electron-antineutrino.[19] At the quark level, the process can be represented as:

d
→
u
+

e

−

+

ν
¯

e

{\displaystyle d\to u+e^{-}+{\bar {\nu }}_{e}~}

Neutral-current interaction
In neutral current interactions, a quark or a lepton (e.g., an electron or a muon) emits or absorbs a neutral Z boson. For example:

e

−

→

e

−

+

Z

0

{\displaystyle e^{-}\to e^{-}+Z^{0}}

Like the W boson, the Z boson also decays rapidly,[18] for example:

Z

0

→
b
+

b
¯

{\displaystyle Z^{0}\to b+{\bar {b}}}

Electroweak theory

The Standard Model of particle physics describes the electromagnetic interaction and the weak interaction as two different aspects of a single electroweak interaction. This theory was developed around 1968 by Sheldon Glashow, Abdus Salam and Steven Weinberg, and they were awarded the 1979 Nobel Prize in Physics for their work.[20] The Higgs mechanism provides an explanation for the presence of three massive gauge bosons (W+
, W−
, Z0
, the three carriers of the weak interaction) and the massless photon (γ, the carrier of the electromagnetic interaction).[21]
According to the electroweak theory, at very high energies, the universe has four components of the Higgs field whose interactions are carried by four massless gauge bosons – each similar to the photon – forming a complex scalar Higgs field doublet. However, at low energies, this gauge symmetry is spontaneously broken down to the U(1) symmetry of electromagnetism, since one of the Higgs fields acquires a vacuum expectation value. This symmetry-breaking would be expected to produce three massless bosons, but instead they become integrated by the other three fields and acquire mass through the Higgs mechanism. These three boson integrations produce the W+
, W−
 and Z0
 bosons of the weak interaction. The fourth gauge boson is the photon of electromagnetism, and remains massless.[21]
This theory has made a number of predictions, including a prediction of the masses of the Z and W-bosons before their discovery. On 4July 2012, the CMS and the ATLAS experimental teams at the Large Hadron Collider independently announced that they had confirmed the formal discovery of a previously unknown boson of mass between 125–127GeV/c2, whose behaviour so far was "consistent with" a Higgs boson, while adding a cautious note that further data and analysis were needed before positively identifying the new boson as being a Higgs boson of some type. By 14March 2013, the Higgs boson was tentatively confirmed to exist.[22]
Violation of symmetry

The laws of nature were long thought to remain the same under mirror reflection. The results of an experiment viewed via a mirror were expected to be identical to the results of a mirror-reflected copy of the experimental apparatus. This so-called law of parity conservation was known to be respected by classical gravitation, electromagnetism and the strong interaction; it was assumed to be a universal law.[23] However, in the mid-1950s Chen-Ning Yang and Tsung-Dao Lee suggested that the weak interaction might violate this law. Chien Shiung Wu and collaborators in 1957 discovered that the weak interaction violates parity, earning Yang and Lee the 1957 Nobel Prize in Physics.[24]
Although the weak interaction was once described by Fermi's theory, the discovery of parity violation and renormalization theory suggested that a new approach was needed. In 1957, Robert Marshak and George Sudarshan and, somewhat later, Richard Feynman and Murray Gell-Mann proposed a V−A (vector minus axial vector or left-handed) Lagrangian for weak interactions. In this theory, the weak interaction acts only on left-handed particles (and right-handed antiparticles). Since the mirror reflection of a left-handed particle is right-handed, this explains the maximal violation of parity. The V−A theory was developed before the discovery of the Zboson, so it did not include the right-handed fields that enter in the neutral current interaction.
However, this theory allowed a compound symmetry CP to be conserved. CP combines parity P (switching left to right) with charge conjugation C (switching particles with antiparticles). Physicists were again surprised when in 1964, James Cronin and Val Fitch provided clear evidence in kaon decays that CP symmetry could be broken too, winning them the 1980 Nobel Prize in Physics.[25] In 1973, Makoto Kobayashi and Toshihide Maskawa showed that CP violation in the weak interaction required more than two generations of particles,[26] effectively predicting the existence of a then unknown third generation. This discovery earned them half of the 2008 Nobel Prize in Physics.[27]
Unlike parity violation, CPviolation occurs only in limited circumstances. Despite its rarity, it is widely believed to be the reason that there is much more matter than antimatter in the universe, and thus forms one of Andrei Sakharov's three conditions for baryogenesis.[28]
See also

Weakless Universe – the postulate that weak interactions are not anthropically necessary
Gravity
Nuclear force
Electromagnetism

Citations

General readers

Texts

Harry Cheung,  @
 @, Georgia State University.