AcharyaChanakya/simple-wikipedia huggingface dataset:
In Australia and Europe SUVs are often called 4 wheel drives (4X4) or 4WDs.
Substance is the material, or matter, of which something is made. Substances are physical things that can be seen, touched, or measured. They are made up of one or more elemental parts. Iron, aluminium, water and air are examples of substances.
The main problem of a clear definition of what the substance is that if, for example, to consider not just the universe (cosmos), being and non-being, and in general all, the question arises, what is the constant basic principle (attribute) is the basis of the substance, which generally consists of all (that is, matter, mind, senses, space, soul, and so on).
The Latin word "substantia" - a translation of the Greek word for the essence ("ousia"), and in Latin to describe the essence of using the word "essentia". In ancient philosophy substance is treated as a substrate, the first principle of all things (for example, "water" of Thales, the "fire" of Heraclitus).
In modern times, the concept of substance is treated and spread widely. The first view is connected with an ontological understanding of substance as ultimate bases being (Francis Bacon, Benedict Spinoza, Gottfried Wilhelm Leibniz). Central category of metaphysics in philosophy substance is identified as with God and with nature and determined as the cause of itself (Latin, "causa sui"). The main characteristics (attributes) of a substance from Benedict Spinoza are thinking and stretch. By analogy with the philosophy of Benedict Spinoza substance considered in the light of the concept of René Descartes and Leibniz. The first substance is a unity of subject and object, and the second - the same atoms are simple beings who lose their stretch, but receive attribute aspirations (French, "appetitio"n) and multiplicity. Thanks Leibniz substance begins to associate with matter.
The second point of view on the substance - an epistemological understanding of the concept, its capabilities and the need for scientific knowledge (John Locke, David Hume). Immanuel Kant believed that the law under which any change in the substance of events and the number of stored it in nature remains the same, can be attributed to the "analogies of experience." Georg Wilhelm Friedrich Hegel defined substance as the integrity of changing, transient side of things, as a "major step in the development of the will." For Arthur Schopenhauer substance - matter for David Hume - a fiction, the coexistence properties.
A symbol is a drawing, shape, or object that represents an idea, object, or amount of something.
The most common symbols are letters, which are symbols of words and sounds. A symbol can be an actual object (such as the cross, a symbol of Christianity or a scepter, a symbol of royalty and power), or a certain color or pattern. Symbols are used often in poetry and other types of literature, sometimes as metaphors or similes.
A national emblem is a symbol for a certain country.
There are thousands of symbols that are recognized by most people all over the world, and many more that are limited to certain regions, religions, sciences, etc.. Some of the best known ones are listed below.
September (Sep.) is the ninth month of the year in the Gregorian calendar, coming between August and October. It has 30 days. Its name comes from the Latin word "sept" for "seven" (it was the seventh month of the year, before January and February were added to the beginning of the year.)
September always begins on the same day of the week as December, but never ends on the same day of the week as any other month.
In the old Roman calendar, September was the seventh month, which is where it got its name ("Septem" means "seventh"). The ninth month at the time was November ("Novem" means "ninth"). With Julius Caesar's calendar reform, September became the ninth month, with 30 days. September comes after August and before October.
September begins on the same day of week as December every year, as each other's first days are 13 weeks (91 days) apart. No other month of any year, common or leap year, ends on the same day of the week as September.
In common years, September starts on the same day of the week as April and July of the previous year, and in leap years, October of the previous year. In common years, September finishes on the same day of the week as April and December of the previous year, and in leap years, July of the previous year. In leap years and years immediately after that, September starts on the same day of the week as January of the previous year.
In years immediately before common years, September starts on the same day of the week as June of the following year, and in years immediately before leap years, March and November of the following year. In years immediately before common years, September finishes on the same day of the week as March and June of the following year, and in years immediately before leap years, August and November of the following year.
September is one of two months to have an equinox (the other is March, its seasonal equivalent in both hemispheres), where both day and night are roughly of equal length, occurring either on the 22nd or 23rd, halfway between the June and December solstices. In the Northern Hemisphere, Autumn (Fall) begins in this month, while in the Southern Hemisphere, this is the beginning of Spring. For meteorologists, the people who study the weather, these seasons begin on September 1 in those hemispheres. In most Northern Hemisphere countries, school starts in this month, following the summer holidays.
In Ancient Greece, September was called "Boedromion". The Anglo-Saxons called it "Gerstmonath", meaning "Barley month", referring to the harvest. In other countries, it is referred to as "Autumn Month", such as in Finland (Syyskuu) and German-speaking parts of Switzerland (Herbstmonat).
Ethiopian New Year occurs in September. Jewish New Year also often occurs in this month.
Sound is caused by sound waves. It can be heard when goes through a medium to the ear. All sounds are made by vibrations of molecules. For example, when a person hits a drum or a cymbal the object vibrates. These vibrations make air molecules move. Sound waves move away from where they came from. When the vibrating air molecules reach our ears, the eardrum vibrates, too. The bones of the ear vibrate in way the object that started the sound wave vibrated.
There are three different mediums. They are solids, liquids and gas. Sound travels the fastest through solids because the air particles are closer together than gas and liquids.
These vibrations let you hear different things. Even music is vibrations. Irregular vibrations are noise. People can make very complex sounds. We use them for speech.
Sound waves are longitudinal waves with two parts: "compression" and "rarefaction". Compression is the part of the sound waves where the molecules of air are pushed ("compressed") together. Rarefaction is the part of the waves where the molecules are far away from each other. Sound waves are a sequence of compression and rarefaction.
There are some things that sound can't travel through like vacuum. Vacuum is when there is no air. So if a sound made it would not be able to travel. A vacuum is a space that has no matter. The word comes from the Latin adjective "vacuus" for "vacant" or "void".
Sound waves can travel through solids, liquids, and gases. The thicker the medium, the faster it goes, but they cannot travel through a vacuum (a place with nothing in it). This is why astronauts cannot talk to each other in space: they need a radio to hear each other. Sound can travel through water faster than through air; and even faster in solids like stone, iron, and steel. Sound travels at 335 metres (1,100 feet) per second in the air.
"Pitch" is the highness or lowness of sound. Pitch is how humans hear different frequencies. Frequency is determined by the number of vibrations per second. The highest key on a piano, for instance, vibrates 4,000 times per second. It has a frequency of 4000 hertz (Hz), or 4 kilohertz (kHz). Lower keys have lower frequencies. A note an octave higher than another note has twice the frequency of that note.
The intensity of a sound is how much sound energy goes through a square meter in one second. Sound waves with higher amplitude (bigger vibration) have higher intensity. The intensity of a sound is higher closer to the sound source. Farther away, it's less intense. The inverse-square law shows how sound intensity becomes smaller, farther from the source. "Inverse square" says that when distance gets multiplied by a number, sound intensity gets divided by that number squared (the number times itself). Thus, twice the distance means a quarter the intensity.
Sound intensities can be very different. They can range from 0.000000000001, which are barely heard, to 1 W/m (painfully loud). The decibel scale makes sound intensity numbers easier to work with. A 0.000000000001 W/m intensity is 0 dB (decibels). It is an exponential scale, so when the decibel number increases by 10, the intensity is ten times as much. So, a 1 W/m intensity is 120 dB.
Loudness is how people sense the intensity of sound. Loudness depends on sound intensity, sound frequency, and the person's hearing.
Audible sound has frequencies between 20 Hz to 20 kHz. Human beings can hear audible sound. Sound waves with frequency above 20 kHz are called ultrasound waves. Sound waves with frequency below 20 Hz are called infrasound waves. Human beings cannot hear ultrasound waves and infrasound waves, but some animals, like bats and dolphins, use them. Older people have an even smaller hearing range. People are best at hearing sounds between 1000 Hz and 6000 Hz.
When a sound source is moving towards someone, the frequency seems to increase. The same thing happens when someone moves toward the sound source. Frequency seems to decrease when someone moves away from a sound source. It also seems to decrease when the sound source moves away from someone. This is called the Doppler effect.
Halpern, Alvin, Erich Erlbach (1998). "Beginning Physics II: Waves, Electromagnetism, Optics, and Modern Physics," pg. 50-56
Society is the term to describe human beings together (collective, the sum of their social networks and social interactions). The term comes from the Latin idea of "societas", or the connection between friends or allies (friend or ally being "socius"). It can also mean a specific group of people who interact, as well as a wider society of which they are members. People form societies in order to gain greater benefits as a group than would be possible separately. Many animals beside humans also do this, such as wolves or eusocial insects. Sociology is the name for the study of society.
A society is often considered in terms of citizenship, rights, and ethics. The strength and unity of any society's members' willingness to help each other is to be measured can be called social capital.
A social contract sets out the rules and roles for this kind of cooperation. One kind of social contract is a constitution – which outlines to some extent what society in a given state is intended to look like.
A suggestion is an idea that one suggests, or says is good for another (or others) to follow. Some people may agree to it, and some may disagree. If they disagree or have a different suggestion, the person who first suggested the idea will usually discuss with the other people and find a good conclusion that satisfies both and is good.
Spache Readability Formula
Spache Readability Formula is one method of finding out how hard a piece of writing is (its textual difficulty).
The method compares words in a text to a list of words which are familiar in everyday writing. The words that are not on the list are called "unfamiliar". The number of words per sentence are counted. This number and the percentage of unfamiliar words is put into a formula. The result is a reading age. Someone of this age should be able to read the text.
Spache works best on texts that are for children under the age of eight.
the formula; (0.141 * average sentence length)+(0.086 * percentage of difficult words)+0.839 = grade level
According to Oleander Solutions (), the revised Spache Formula is:
Where:
Sport is commonly defined as an athletic activity that involves a degree of competition, such as netball or basketball. Some games and many kinds of racing are called sports. A professional at a sport is called an athlete. Many people play sports with their friends. They need coaches to teach or train teams or individuals how to do better. Sports can be played indoors or outdoors and by individuals or teams.
Sports is needed for health and can help reduce diseases such as heart attacks, many types of cancer, depression and anxiety, and dementia. Different types of sports help our body in different ways. For children, sports play an extremely important part in their lives by providing all round development of the child, physically, mentally and emotionally.
Some people like to watch other people play sports. Those who watch others playing sports are called "fans". While some fans watch sports on television, others actually go to stadiums or other places where people pay to watch them in person. These fans are called "spectators".
People engage in many kinds of sports, for example:
Science is what we do to find out about the natural world. Natural sciences include, chemistry, biology, geology, astronomy, and physics. Science uses mathematics and logic, which are sometimes called "formal sciences". Natural science makes observations and experiments. Science produces accurate facts, scientific laws and theories. 'Science' also refers to the large amount of knowledge that has been found using this process.
Research uses the scientific method. Scientific research uses hypotheses based on ideas or earlier knowledge, which can be categorized through different topics. Then those hypotheses are tested by experiments.
People who study and research science and try to find out everything about it are called scientists. Scientists study things by looking at them very carefully, by measuring them, and by doing experiments and tests. Scientists try to explain why things act the way they do, and predict what will happen.
Today, "science" usually refers to a way of pursuing knowledge, not just the knowledge itself. It is mainly about the phenomena of the material world. In the 17th and 18th centuries scientists increasingly sought to formulate knowledge in terms of "laws of nature" such as Newton's laws of motion. And over the course of the 19th century, the word "science" became increasingly associated with the scientific method itself, as a way to study the natural world, including physics, chemistry, geology and biology.
It was in the 19th century also that the term "scientist" was created by William Whewell. He meant it to distinguish those who sought knowledge on nature from those who sought other types of knowledge.
The scientific method is the name given to the methods used by scientists to find knowledge. The main features of the scientific method are:
A famous example of science in action was the expedition led by Arthur Eddington to Principe Island in Africa in 1919. He went there to record the positions of stars around the Sun during a solar eclipse. The observation of star positions showed that the apparent star positions close to the Sun were changed. In effect, the light passing the Sun was pulled towards the Sun by gravitation. This confirmed predictions of gravitational lensing made by Albert Einstein in the general theory of relativity, published in 1915. Eddington's observations were considered to be the first solid evidence in favour of Einstein's theory. Had the observations resulted differently, this would have counted against Einstein's theory, and perhaps refuted it (shown it was wrong).
Discoveries in fundamental science can be world-changing. For example:
Not everyone completely agrees about how science works. Some philosophers and scientists say that scientific theories are only accepted for the time being. They last so long as they are the best explanation. When theories no longer explain the data, they are discarded and replaced. Or, sometimes scientists will make a theory better rather than discard it, or they will keep on using the theory hoping that it will be made better eventually.
Science is a way to get knowledge by discarding what is not true.
Scientists must be very careful to make explanations that fit well with what they observe and measure. They compete to provide better explanations. An explanation might be interesting or pleasing, but if it does not agree with what other scientists really see and measure, they will try to find a better explanation.
Before a scientific article is published, other scientists read the article and decide whether the explanations make sense from the data. This is called peer review. After articles are published, other scientists will also check if the same experiments, observations or tests produce the same data again. Peer review and repeating experiments are the only way to be sure the knowledge is correct.
Science makes models of nature, models of our universe, and medicine. There are many different sciences with their own names. However it is not right to say "science says" any one thing. Science is a process, not just the facts and rules believed at one time.
Saint Lawrence River
The Saint Lawrence River (; Tuscarora: "Kahnawáʼkye"; Mohawk: "Kaniatarowanenneh", meaning "big waterway") is a big river in eastern North America. It flows between the Canadian province of Quebec & Ontario and the American state of New York, and through the major canadian city of Montreal. It is the third largest river in Canada.
The river drains water from the Great Lakes into the Atlantic Ocean. It is more than three thousand kilometres long. The river meets the Atlantic Ocean in a big "estuary" or bay, the biggest in the world; this is called the Gulf of Saint Lawrence.
The Canadian cities of Kingston, Montreal, Trois-Rivières and Quebec City are on this river. The Saint Lawrence Seaway allows ships to go up the river and through the Great Lakes right into the middle of North America.
Seville
Seville () is a big city in the South of Spain, in Europe. A big river called the Guadalquivir River goes through Seville.
The city of Seville is the capital of the Spanish region called Andalusia and of the province of Sevilla. The people who live in the city are called "Sevillanos" and there are almost a million of them: 700,000.
A very old story says that the city was started by the famous hero of Greece, named Hercules. The Romans when they came to Spain gave it the Latin name of Hispalis. Over time this changed to be spelled in English as "Seville". The Arab Moors took the city when they invaded the country, and you can still see a lot of the buildings they built during their 800-year stay in Spain (711-1492).
In 1992 Seville was the place for the Expo 92. There is a beautiful bridge across the Guadalquivir River called "Puente del Alamillo". It was thought up by Santiago Calatrava a famous building expert.
Seville is famous for its hot summer weather.
Seville is the home town of two soccer teams, Sevilla FC (often simply called "El Sevilla") and Real Betis Balompié (often called "El Betis").
Salami
Salami is a sausage that first came from Italy. The name comes from the Italian salare meaning to make something salty.
The original salami was made from a mix of chopped pork and salt which was dried using air in a casing. Jews & Muslims are not allowed to eat this type of salami for religious reasons. Now there are many types of salamis made in some countries. Nearly all are seasoned with a combination of herbs and spices in addition to salt. Salamis are now sometimes smoked or cooked before air drying. Some kinds are made of beef while others mix beef and pork. Most, if not all Italian salamis have garlic in them, but few German kinds do, for example. Some, like a few salamis from Spain, include paprika or chili. The difference between some types is in how coarse or fine the meat is chopped. Some "light" salami might add turkey or chicken to reduce both fat and calories.
Many salamis are named after the city or region where they come from. Some examples are Arles, Genoese, Hungarian, and Milano salamis.
Special English is a simple form of the English language. It is used by a public radio station called Voice of America, run by the United States government in Special English programs every day. Its news and feature programs are read more slowly than usual, using fewer English words and simple grammar.
The contents of Special English programs are much easier to understand. Special English is clearer and simpler, and it uses shorter sentences. It can also help someone whose English is weak to improve his or her English. In some countries, for example China, Special English is popular among people learning English.
Special English was first used on October 19, 1959. Special English started in that year as one of radio programs by the Voice of America. This broadcasts adopt slow space and simple English in order to increase understanding for millions of listeners. It is now also known as "Learning English".
Special English started in 1959. It was developed as an experimental radio program to spread information on news and culture to people outside the United States. Programs on VOA use a simpler English within about 1,500 words. And reports are paced 1/3 slower than regular English in order to allow listeners to increase a better understanding. This means broadcasters speak at about two-thirds the speed of conversational English. But far from sounding like a record played at the wrong speed. It now deals with various topics to keep interest of listeners, such as news, business, science, and culture. Stories are written in clear.
To be a Special English broadcaster, he or she needs a complicated skill that takes months of training. The training includes a professional voice trainer who teaches how to breathe properly and pronounce clearly. A chief of Special English at VOA said, "People in this country have likely never heard of Special English," and also said, "and, if they have, they often don't understand the significance of it to people in other countries."
One VOA staff explains that the main goal of Special English is for the listener to understand the content of what is being broadcast, and to make steady progress in English. “There is a fine line between being simplified and simplistic,” he says. “We never want to cross that line.” So when necessary, more “advanced” English words are used and the meanings made clear, so the stories never suffer from incomplete information.
Students and teachers in other countries say Special English is a good learning tool.
Some of popular programs on VOA follow.
VOA broadcast a program titled 'Willis Conover, the Voice of Jazz, Is Now Online" in the past, as Willis Conover became a famous host at Music USA.
Sausage is a food made of ground-up or chopped-up meat. It often has spices in it and is covered in a casing. Traditionally, a sausage casing is made of animal intestine, but can sometimes be made of plastic. There are many forms of sausages, including hot dog, pepperoni, bologna, and salami.
Sausages often have meat from the animal's head, lips, cheeks, ears and other parts. Some have blood in them. Irish and English sausages normally have a lot of "rusk," or bread crumbs, and they are less meaty than sausages from other countries. Vegetarian or vegan sausages are often made of products other than animal products, such as tofu.
Sausages may be used as a meal, in a sandwich, or in other foods like stews. Sausages can be eaten as whole pieces, or they can be chopped up as already cooked pieces.
Many countries and regions have special kinds of sausage. Sausages are some of the oldest foods.
The word "sausage" was first used in English in the mid-15th century. During the mid-15th century, the word "sausage" was spelled as "sawsyge". The word "sawsyge" came from Old North French "saussiche" (Modern French "saucisse")". The French word came from Vulgar Latin "salsica" (sausage), from "salsicus" (seasoned with salt).
Slang are words that are informal. Usually each generation or social group has its own slang - for example, older people can have trouble understanding the slang of younger people. On the other hand, younger people often understand, but find silly or old-fashioned, the slang of older people.
Over time, language tends to get more complex, since new words enter much faster than old words leave. Over time, slang almost always becomes part of the language, and approved for use by all.
It has also happened that some words used in Anglo-Saxon for bodily functions became thought of as profanity or rude after they were replaced by Latinate words like "urinate", "defecate" and "copulate" - which polite people were supposed to use after the Norman conquest of England in 1066. This was in part a way of making poor people (who spoke Anglo-Saxon) all appear to be rude, while more powerful people (who spoke Norman) appeared to be polite - one way that etiquette can develop, and reinforce power structure. This is only one example from history of how racism can be a reason for defining one group's language as 'slang' and another as 'correct'.
Wanting to have rules of grammar that do not change and the same vocabulary used by everyone for better communication is another reason that is often given for defining one group's language as correct.
An "idiom" can be slang, but it can also be a metaphor that becomes part of the culture.
Two examples of slang are 'wassup' and 'dunnow'. 'Wassup' usually means 'What is up?' (as in, 'How are you?'), and 'dunnow' usually means 'I don't know'.
Social contract
A social contract or political contract is a perceived agreement among the people of a state about the rules that will define their government. These rules are usually called laws. Laws help to make sure people have rights and that their rights are protected. One kind of social contract is a constitution. A constitution says how decisions are made, and sets limits on the powers of leaders and other people who have authority.
In the Age of Enlightenment, philosophers Thomas Hobbes, John Locke and Jean-Jacques Rousseau wrote books about social contracts. They saw good government as coming from social contracts. Rousseau wrote a book called "The Social Contract". Both the United States Declaration of Independence and United States Constitution use the theory of social contracts.
Social capital is the willingness of people to help each other.
It often replaces money which people would use to buy the same help.
Society works best when there is plenty of social capital. The less social capital there is, the more social problems there usually are. If there is no social capital, war and revolution often results.
People who have no money and cannot get help from society may have to agree to do things they do not want to do, or force others to do things they do not want to. Organized crime grows in this way, and so do forced labour and slavery.
Most ways of measuring social capital have to do with trust - people who trust that favours and help will be available when they need it will favour and help others more. Those who are seen as trying to get a free ride will get much less help. A social climber tries to earn social capital by making friends with those who have it but without actually helping. Some call this kind of person a social parasite. They are very hard to detect, unlike people who cheat or commit fraud. When there are too many of these kinds of people, especially when they are politicians, people begin to mistrust their government. Rather than work with a political party to change law, they may start to look for direct revenge for things.
Social capital is a lot like real capital. The more money a person or a society has, the easier it is to do things and the better off people are. The less money, the more difficult things become and the worse people feel.
The Social Capital Foundation
A site is a real fixed physical location where something will or has happened or a place where something is.
It is used very often in building trades to mean the place where a building will go up.
A gravesite is a place where a person will be buried after they die.
The words onsite and offsite refer to work that must take place on the site, or which can take place somewhere else. For instance, a prefabricated building can be "built offsite" and then "moved onsite".
"Site" is also a common abbreviation in net jargon for "website". In this case no real physical location exists other than the place where the computers are, and one "goes to the site" simply by using a web browser to "go to" that URL. This is a conceptual metaphor. It can be confusing. Someone who uses it is also likely using other jargon.
Subtraction is the arithmetic operation for finding the difference between two numbers, though it can also be generalized to other mathematical objects such as vectors and matrices. The special names of the numbers in a subtraction expression are, minuend - subtrahend = difference. For example, the expression 7 - 4 = 3 can be read as "seven minus four equals three," "seven take away four leaves three," or "four from seven leaves three."
If the minuend is less than the subtrahend, the difference will be a negative number. For example, 17 - 25 = -8 . This can be read as "Seventeen minus twenty-five equals negative eight."
Subtraction is how cash registers determine the change a buyer receives, when the buyer pays with more money than the purchase cost.
String theory tries to model the four known fundamental interactions—gravitation, electromagnetism, strong nuclear force, weak nuclear force—together in one theory. This tries to resolve the alleged conflict between classical physics and quantum physics by "elementary units"—the one classical force: gravity, and a new quantum field theory of the other three fundamental forces.
Einstein had sought a unified field theory, a single model to explain the fundamental interactions or mechanics of the universe. Today's search is for a unified field theory that is "quantized" and that explains matter's structure, too. This is called the search for a theory of everything (TOE). The most prominent contender as a TOE is string theory converted into superstring theory with its six higher dimensions in addition to the four common dimensions (3D + time).
Some superstring theories seem to come together on a shared range of geometry that, according to string theorists, is apparently the geometry of space. The mathematical framework that unifies the multiple superstring theories upon that shared geometrical range is M-theory. Many string theorists are optimistic that M-theory explains our universe's very structure and perhaps explains how other universes, if they exist, are structured as part of a greater "multiverse". M theory/supergravity theory has 7 higher dimensions + 4D.
Introductions to string theory that are designed for the general public must first explain physics. Some of the controversies over string theory result from misunderstandings about physics. A common misunderstanding even for scientists is the presumption that a theory is proved true in its "explanation" of the natural world wherever its "predictions" are successful. Another misunderstanding is that earlier physical scientists, including chemists, have already explained the world. This leads to the misunderstanding that string theorists began making strange hypotheses after they became unaccountably "set free from truth".
Newton's law of universal gravitation (UG), added to the three Galilean laws of motion and some other presumptions, was published in 1687. Newton's theory successfully modeled interactions among objects of a size we can see, a range of phenomena now called the "classical realm". Coulomb's law modeled electric attraction. Maxwell's electromagnetic field theory unified electricity and magnetism, while optics emerged from this field.
Light's speed remained about the same when measured by an observer traveling in its field, however, although "addition of velocities" predicted the field to be slower or faster "relative" to the observer traveling with or against it. So, versus the electromagnetic field, the observer kept losing speed. Still, this did not violate Galileo’s Principle of relativity that says the laws of mechanics work the same for all objects showing inertia.
By law of inertia, when no force is applied to an object, the object holds its velocity, which is speed "and" direction. An object either in "uniform motion", which is constant speed in an unchanging direction, or staying at rest, which is zero velocity, experiences inertia. This exhibits Galilean invariance—its mechanical interactions proceeding without variation—also called Galilean relativity since one cannot perceive whether one is at rest or in uniform motion.
In 1905, Einstein's special theory of relativity explained the accuracy of both Maxwell's electromagnetic field and Galilean relativity by stating that the field's speed is absolute—a universal constant—whereas both space and time are local phenomena "relative" to the object's energy. Thus, an object in relative motion shortens along the direction of its momentum (Lorentz contraction), and its unfolding of events slows (time dilation). A passenger on the object cannot detect the change, as all measuring devices aboard that vehicle have experienced length contraction and time dilation. Only an external observer experiencing relative rest measures the object in relative motion to be shortened along its travel pathway and its events slowed. Special relativity left Newton's theory—which states space and time as "absolute"—unable to explain gravitation.
By the equivalence principle, Einstein inferred that being under either gravitation or constant acceleration are indistinguishable experiences that might share a physical mechanism. The suggested mechanism was "progressive" length contraction and time dilation—a consequence of the local energy density within 3D space—establishing a progressive tension within a rigid object, relieving its tension by moving toward the location of greatest energy density. Special relativity would be a limited case of a gravitational field. Special relativity would apply when the energy density across 3D space is uniform, and so the gravitational field is scaled uniformly from location to location, why an object experiences no acceleration and thus no gravitation.
In 1915, Einstein's general theory of relativity newly explained gravitation with 4D spacetime modeled as a Lorentzian manifold. Time is one dimension merged with the three space dimensions, as every "event" in 3D space—2D horizontally and 1D vertically—entails a point along a 1D time axis. Even in everyday life, one states or implies both. One says or at least means, "Meet me at building 123 Main Street intersecting Franklin Street in apartment 3D on 10 October 2012 at 9:00PM". By omitting or missing the time coordinate, one arrives at the correct location in space when the sought event is absent—it is in the past or future at perhaps 6:00PM or 12:00AM.
By converging space and time and presuming both relative to the energy density in the vicinity, and by setting the only "constant" or absolute as not even mass but as light speed in a vacuum, general relativity revealed the natural world's previously unimagined balance and symmetry. Every object is always moving at light speed along a straight line—its equivalent, on a curved surface, called "geodesic" or "worldline"—the one pathway of least resistance like a free fall through 4D spacetime whose geometry "curves" in the vicinity of mass/energy.
An object at light speed in a vacuum is moving at maximal rate through 3D space but exhibits no evolution of events—it is frozen in time—whereas an object motionless in 3D space flows fully along 1D time, experiencing the maximal rate of events' unfolding. The displayed universe is relative to a given location, yet once the mass/energy in that vicinity is stated, Einstein's equations predict what is occurring—or did occur or will occur—anywhere in the universe. The popularized notion that "relative" in Einstein's theory suggests "subjective" or "arbitrary" was to some regret of Einstein, who later thought he ought have to named it "general theory".
The electromagnetic field's messenger particles, photons, carry an image timelessly across the universe while observers within this field have enough flow through time to decode this image and react by moving within 3D space, yet can never outrun this timeless image. The universe's state under 400 000 years after the presumed big bang that began our universe is thought to be displayed as the cosmic microwave background (CMB).
In 1915, the universe was thought to be entirely what we now call the Milky Way galaxy and to be static. Einstein operated his recently published equations of the gravitational field, and discovered the consequence that the universe was expanding or shrinking. (The theory is operable in either direction—time invariance.) He revised the theory add a "cosmological constant" to arbitrarily balance the universe. Nearing 1930, Edwin Hubble's telescopic data, interpreted through general relativity, revealed the universe was expanding.
In 1916 while on a World War I battlefield, Karl Schwarzschild operated Einstein's equations, and the Schwarzschild solution predicted black holes. Decades later, astrophysicists identified a supermassive black hole in the center of perhaps every galaxy. Black holes seem to lead galaxy formation and maintenance by regulating star formation and destruction.
In the 1930s, it was noticed that according to general relativity, galaxies would fall apart unless surrounded by invisible matter holding a galaxy together, and by the 1970s dark matter began to be accepted. In 1998 it was inferred that the universe's expansion, not slowing, is accelerating, indicating a vast energy density—enough to accelerate both visible matter and dark matter—throughout the universe, a vast field of dark energy. Apparently, under 5% of the universe's composition is known, while the other 95% is mysterious—dark matter and dark energy.
By the 1920s, to probe the operating of the electromagnetic field at minuscule scales of space and time, quantum mechanics (QM) was developed. Yet electrons—the matter particles that interact with the photons that are the electromagnetic field's force carriers—would appear to defy mechanical principles altogether. None could predict a quantum particle's location from moment to moment.
In the slit experiment, an electron would travel through one hole placed in front of it. Yet a single electron would travel simultaneously though multiple holes, however many were placed in front of it. The single electron would leave on the detection board an interference pattern as if the single particle were a wave that had passed through all the holes simultaneously. And yet this occurred only when unobserved. If light were shone on the expected event, the photon's interaction with the field would set the electron to a single position.
By the uncertainty principle, any quantum particle's exact location and momentum cannot be determined with certainty, however. The particle's interaction with the observation/measurement instrument deflects the particle such that greater determination of its position yields lower determination of its momentum, and vice versa.
By extending quantum mechanics across a field, a consistent pattern emerged. From location to adjacent location, the probability of the particle existing there would rise and fall like a wave of probability—a rising and falling probability density. When unobserved, any quantum particle enters superposition, such that even a single particle fills the entire field, however large. Yet the particle is not "definitely" anywhere in the field, but there at a definite "probability" in relation to whether it was had been at the adjacent location. The waveform of Maxwell's electromagnetic field was generated by an accumulation of probabilistic events. Not the particles, but the mathematical form, was constant.
Setting the field to special relativity permitted prediction of the complete electromagnetic field. Thus arose relativistic quantum field theory (QFT). Of the electromagnetic field, it is relativistic quantum electrodynamics (QED). Of the weak and electromagnetic fields together, it is relativistic electroweak theory (EWT). Of the strong field, it is relativistic quantum chromodynamics (QCD). Altogether, this became the Standard Model of particle physics.
When the Standard Model is set to general relativity in order to include mass, probability densities of infinity appear. This is presumed incorrect, as probability ordinarily ranges from 0 to 1—0% to 100% probability. Some theoretical physicists suspect that the problem is in the Standard Model, which represents each particle by a zero-dimensional point that in principle can be infinitely small. Yet in quantum physics, the Planck's constant is the minimum energy unit that a field can be divided into, perhaps a clue to the smallest size a particle can be. So there is a quest to "quantize" gravity—to develop a theory of quantum gravity.
String conjectures that on the microscopic scale, Einstein's 4D spacetime is a field of Calabi-Yau manifolds, each containing 6 space dimensions curled up, thus not extended into the 3 space dimensions presented to the classical realm. In string theory, each quantum particle is replaced by a 1D string of vibrating energy whose length is the Planck length. As the string moves, it traces width, and thus becomes 2D, a worldsheet. As a string vibrates and moves within the 6D Calabi-Yau space, the string becomes a quantum particle. With this approach, the hypothetical graviton—predicted to explain general relativity—emerges easily.
String theory began as bosonic string theory, whose 26 dimensions act as many fewer. Yet this modeled only bosons, which are energy particles, while omitting fermions, which are matter particles. So bosonic string theory could not explain matter. Yet by adding supersymmetry to bosonic string theory, fermions were achieved, and string theory became "super"string theory, explaining matter, too.
String theory's claim that all molecules are "strings of energy" has drawn harsh criticism. There are many versions of string theory, none quite successfully predicting the observational data explained by the Standard Model. M theory is now known to have countless solutions, often predicting things strange and unknown to exist. Some allege that string theorists select only the desired predictions.
The allegation that string theory makes no testable predictions is false, as it makes many. No theory—a predictive and perhaps explanatory model of some domain of natural phenomena—is verifiable. All conventional physical theories until the Standard Model have made claims about unobservable aspects of the natural world. Even the Standard Model has various interpretations as to the natural world. When the Standard Model is operated, it is often made a version with supersymmetry, doubling the number of particle species so far identified by particle physicists.
None can literally measure space, yet Newton postulated absolute space and time, and Newton's theory made explicit predictions, highly testable and predictively successful for 200 years, but the theory was still falsified as explanatory of nature. Physicists accept that there exists no such attractive force directly attracting matter to matter, let alone that the force traverses the universe instantly. Nevertheless, Newton's theory is still paradigmatic of science.
The idea of hidden dimensionality of space can seem occult. Some theorists of loop quantum gravity—a contender for quantum gravity—regard string theory as fundamentally misguided by presuming that space even has a shape until particles shape it. That is, they do not doubt that space takes various shapes, simply regard the particles as determining space's shape, not the other way around. The spacetime vortex predicted by general relativity is apparently confirmed.
If interpreted as naturally true, the Standard Model, representing a quantum particle as a 0D point, already indicates that spacetime is a sea of roiling shapes, quantum foam. String theorists tend to believe nature more elegant, a belief that loop theorist Lee Smolin dismisses as romantic while using biology's Modern Synthesis as a rhetorical device. Experiments to detect added spatial dimensions have so far failed, yet there is still the possibility that signs of them can emerge.
M theory has many trillions of solutions. Leonard Susskind, a leader of string theory, interprets string theory's plasticity of solutions as paradoxical support resolving the mystery of why "this" universe exists, as M theory shows it but a variant of a general pattern that always approximately results.
General relativity has brought many discoveries that in 1915 were all but unimaginable except in fiction. A solution of Einstein's equations that sought to explain quantum particles' dynamics, the Einstein-Rosen Bridge predicts a shortcut connecting two distant points in spacetime. Commonly called a wormhole, the Einstein-Rosen Bridge is doubted but not disproved, showing either that not all consequences of a theory must be accurate or that reality is quite bizarre in ways unobservable.
Even the Standard Model of particle physics suggests bizarre possibilities that populist accounts of science either omit or mention as unexplained curiosities. The theory conventionally receives the Copenhagen interpretation, whereby the field is only "possibilities", none real until an observer or instrument interacts with the field, whose wavefunction then collapses and leaves only its particle function, only the particles being real. Yet wavefunction collapse was merely assumed—neither experimentally confirmed nor even mathematically modeled—and no variance from either the wavefunction in the quantum realm or the particle function in the classical realm has been found.
In 1957 Hugh Everett described his "Relative state" interpretation. Everett maintained that the wavefunction does not collapse, and since all matter and interactions are presumed to be built up from quantum waveparticles, all possible variations of the quantum field—indicated by the mathematical equations—are "real" and simultaneously occurring but different courses of history. By this interpretation, whatever interacts with the field joins the field's state that is "relative" to the observer's state—itself a waveform in its own quantum field—while the two simply interact in a universal waveform never collapsing. By now, many physicists' interpretation of the apparent transition from the quantum to the classical realms is not wavefunction collapse, but quantum decoherence.
In decoherence, an interaction with the field takes the observer into only one determinant constellation of the quantum field, and so all observations align with that new, combined quantum state. Everett's thesis has inspired Many worlds interpretation, whereby within our universe are predicted to be virtually or potentially infinite parallel worlds that are real, yet each a minuscule distance from the other worlds. As each world's waveform is universal—not collapsing—and its mathematical relations are invariant, parallel worlds simply fill the gaps and do not touch.
Einstein doubted that black holes, as predicted by the Schwarzschild solution, are real. Some now conjecture that black holes do not exist as such but are dark energy, or that our universe is both—a black hole and dark energy. The Schwarzschild solution of Einstein's equations can be maximally extended to predict a black hole having a flip side—another universe emerging from a white hole. Perhaps our universe's big bang was half of a "big bounce", something's collapse down to a black hole, and our universe popping out its other side as a white hole.