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Portland Institute for Contemporary Art

The Portland Institute for Contemporary Art (PICA) is a contemporary performance and visual arts organization in Portland in the U.S. state of Oregon. PICA was founded in 1995 by Kristy Edmunds. Since 2003, it has presented the annual Time-Based Art Festival (TBA) every September in Portland, featuring contemporary and experimental visual art, dance, theatre, film/video, music, and educational and public programs from local, national, and international artists. As of November 2017, it is led by Executive Director Victoria Frey and Artistic Directors Roya Amirsoleymani, Erin Boberg Doughton, and Kristan Kennedy.

History
PICA was founded in 1995 by Kristy Edmunds, at the time the Director of the Portland Art Museum's "Art on the Edge" program. The organization's exhibition and performance program was built largely around an itinerant model, utilizing vacant space or rented venues throughout the city of Portland rather than programming a single gallery or theatre year-round. The majority of PICA's performance programming was grouped into its annual performance seasons, which it produced for seven years before the organization began presenting the Time-Based Art Festival in 2003. The organization's signature event during this time was an annual costume party fundraiser known as the Dada Ball, which it held from 1996 until 2001 in a variety of vacant spaces throughout the city.

PICA's offices were housed at Boora Architects from its founding until about 2001, and then moved to the headquarters of Wieden+Kennedy in Northwest Portland. PICA housed its offices within those of Wieden & Kennedy until 2012, and operated an additional 2200 ft2 exhibition space in the building until 2004.

In September 2003, PICA began presenting its annual Time-Based Art Festival, a ten-day international festival of contemporary performance and visual art modeled after those in Edinburgh and Adelaide (Fringe or main Festival?). The TBA Festival built upon PICA's itinerant model of utilizing multiple venues around the city, including sites such as the former Washington High School building in Southeast Portland, which would later become Revolution Hall.

In 2012, PICA moved to a leased third floor space on Southwest 10th Avenue, allowing the organization's offices and resource library to also be used a gallery and performance space when programs required it.

On April 19, 2016, PICA announced that the organization was gifted a 20-year no-rent lease on a 16000 ft2 building along the North Williams Avenue corridor by donor Allie Furlotti and the Calligram Foundation. In September 2016, PICA began utilizing this space as a box office, performance venue, and gallery for their 2016 TBA Festival while maintaining offices in downtown Portland. In November 2017, PICA's offices were relocated to the renovated Northeast Portland space.

Leadership
Founder Kristy Edmunds left PICA in 2005 to become artistic director for the Melbourne International Arts Festival. She is now Artistic & Executive Director of the Center for the Art of Performance (CAP) at University of California, Los Angeles (UCLA). Mark Russell (producer of The Public Theater's Under the Radar Festival and former director of P.S.122) and Cathy Edwards (former director of programming for the International Festival of Arts and Ideas) operated as the organization's two guest artistic directors from 2006 until 2011. Angela Mattox, the former Performing Arts Curator at Yerba Buena Center for the Arts, was hired as the organization's permanent artistic director in 2011. Mattox left PICA in 2017 following the end of that year's Time-Based Art Festival, her sixth as artistic director.

PICA announced on November 28, 2017, that long-time programming staff members Roya Amirsoleymani (previously Director of Community Engagement), Erin Boberg Doughton (previously Performing Arts Program Director), and Kristan Kennedy (previously Visual Art Curator) had been selected as the organization's Artistic Directors.

Performance
PICA has presented works from performance artists and musicians such as Philip Glass, Laurie Anderson, Karen Finley, Spalding Gray, Marina Abramović, Miranda July, Mike Daisey, and Reggie Watts, among others.

Since its inception, PICA has programmed both performances and exhibitions, while also hosting educational events such as lectures, public conversations, and artist-led workshops. Its first performance series ran from 1995-1996. PICA ceased its seasonal performance series when it began presenting the Time-Based Art Festival in 2003, though still presents some performances during other parts of the year.

Visual Art
PICA has presented work by visual artists such as William Pope.L, Matthew Day Jackson, Francis Alÿs, Emily Roysdon, A.L. Steiner, Erika Vogt, Abigail DeVille, Carlos Motta and others. Since 2005, PICA's visual art programming has been curated by Kristan Kennedy.

As with PICA's itinerant model to performance presentation, the organization has not had a single exhibition space for most of its history. From 2000–2004, PICA did run a year-round gallery out of a corner of the Wieden+Kennedy Building in Northwest Portland's Pearl District, designed by early PICA supporter Brad Cloepfil. During that time, visual art curator Stuart Horodner presented work from artists such as Janine Antoni, Dana Schutz, and Melanie Manchot in the space. Horodner left the organization in 2004.

The Time-Based Art Festival has included visual art curated by Kennedy as part of its artistic program since 2006 under the "On Sight" program strand. On Sight exhibition programs often include performance-based or otherwise non-conventional visual art modes in addition to traditional gallery spaces. The exhibition-based visual art projects are generally exhibited for two to four weeks after the conclusion of each year's TBA. In 2016, the On Sight exhibition was titled "Makeup on Empty Space" and included a multi-channel video installation by A.K. Burns, a performance art piece by Keijaun Thomas, a performance by Dylan Mira, and an exhibition-turned-artist-residency by Bunny Brains and collaborators.

Community Engagement, Education and Public Programs
PICA offers a variety of education, outreach, contextual and public programs, often presented in tandem with its artistic programs but sometimes independent of them. As part of the annual TBA Festival, PICA offers an education, engagement, and public programs strand called the "Institute" that brings festival artists, guest scholars, and writers into dialogue. Institute programming includes workshops, discussions, panels, lectures, and (since 2013) the Field Guide series, in which expert facilitates engage in focused workshops and dialogues with members of the public about a particular performance or program.

Precipice Fund
In 2011, PICA announced that the organization had received money from the Andy Warhol Foundation for the Visual Arts' Regional Regranting Program to create a regranting program for small, artist-led visual art projects that do not otherwise qualify for project support through traditional granting mechanisms. Dubbed the Precipice Fund, PICA began distributing its first round of grants in 2013. As of 2016, $225,000 has been redistributed over three grant periods to 57 projects in the region.

Resource Room
Since 2000, PICA's offices have included a public reference library known as the Resource Room. The PICA Resource Room collects a variety of art publications, housing over 4,000 books and periodicals on its shelves. The Resource Room also collects video documentation from the organization's 20-year history of artistic presentation. From 2012–2015, the Resource Room Residency gave artists the opportunity to engage with the space and collection of archival materials.

title: Portland Institute for Contemporary Art


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User:Jqt

Welcome to wikipedia!

 * Are you the JQT whom I know, or some other JQT? -- Marj Tiefert, Thursday, May 2, 2002

Hi Marj. No, I am not. There are only about 15,000 three-letter sequences so I guess that this is not surprising. Anyway, nice to meet you. ;-)

Hi. I made a few edits to your Balazs Gyorffy page. I noticed you used the past tense - I hope that doesn't indicate he's no longer around. It's probably a good idea if you could add some references to the article, or it's highly likely to be flagged for deletion as unverifiable. I would try, but am still very new here and not entirely sure how to go about it. Blythrir (talk) 18:28, 6 April 2008 (UTC)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: User:Jqt


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SoftICE

SoftICE is a kernel mode debugger for DOS and Windows up to Windows XP. It is designed to run underneath Windows, so that the operating system is unaware of its presence. Unlike an application debugger, SoftICE is capable of suspending all operations in Windows when instructed. Due to its low-level capabilities, SoftICE is also popular as a software cracking tool.

Microsoft offers two kernel-mode debuggers, WinDbg and KD, without charges. However, the full capabilities of WinDbg and KD are available only when two interlinked computers are used. SoftICE, therefore, is an exceptionally useful tool for difficult driver-related development. The last released version was for Windows XP.

Older versions exist for DOS and compatible operating systems. SoftICE was originally produced by the company NuMega, and was subsequently acquired by Compuware in 1997, which in turn sold the property to Micro Focus in 2009. Currently, Micro Focus owns the source code and patents, but is not actively maintaining SoftICE.

Naming
"Soft" refers to software, and "ICE" is an allusion to in-circuit emulator.

History
The original SoftICE for DOS was written in 1987 by NuMega founders Frank Grossman and Jim Moskun. The program, written in 80386 assembly language, played the role of an operating system and ran software in virtual 8086 mode. It sold for $386.

SoftICE/W (for Windows) was developed in the 1990s, and was instrumental in the Writing of "Undocumented Windows", by Andrew Schulman, David Maxey and Matt Pietrek. SoftICE/W was derived from an earlier, lesser known product, SoftICE for NetWare (32-bit protected mode). One of the key advantages it had over Microsoft's debuggers is that it enabled single machine debugging, rather than requiring a second machine to be connected over a serial port.

The principal developers of SoftICE were Dom Basile ('Mr. SoftICE'), Tom Guinther (Kitchen Sink, Symbol Engine), Gerald Ryckman (Video drivers and Kitchen Sink), Ray Hsu (Video drivers for Windows 95), and Dan Babcock (SoftICE/NT 3.1/3.5: Universal video driver, symbol engine), with contributions by a variety of NuMega developers including Frank Grossman, Jim Moskun and Matt Pietrek.

In 1998, the codebase for SoftICE/95 was ported to run on the Windows NT platform.

Newer versions of SoftICE patch deep into Microsoft Windows. As such, old versions of SoftICE are rarely compatible with new versions of Windows. Compuware therefore offered SoftICE as a subscription so that it could be kept up to date and in sync with the latest Microsoft Windows version.

SoftICE was previously offered as part of Compuware's DriverStudio package, but was discontinued in April 2006.

Termination
As of April 3, 2006, the DriverStudio product family has been discontinued because of "a variety of technical and business issues as well as general market conditions". Maintenance support was offered until March 31, 2007.

Anti-SoftICE measures
Software vendors have put in place a wide range of countermeasures to protect themselves from people employing SoftICE as a tool to analyse software.

For example, here is code some vendors used to detect the presence of SoftICE running in the same machine as an early countermeasure:

More and better such measures have evolved since. While most of them can only deter the less experienced and determined hackers, SoftICE is no longer a tool of choice for someone new to analysing software.

Modern software anti-analysis methods are based on more sophisticated packers/protectors, e.g. Themida, Armadillo or ASProtect which pack the program code and tamper with entry point addresses so it is hard to find the program's original entry point (OEP). That is also true for the program's import address table (IAT). However, tools for hiding SoftICE are also available, such as IceStealth and IceExt for Windows NT, or Icedump and IcePatch for Windows 9x.

Reception
In 1989, BYTE listed Soft-ICE among the "Distinction" winners of the BYTE Awards, stating that, "If you're developing 8086-based applications on an 80386 machine, this is an essential and affordable tool".

Alternatives
A commercial kernel-level debugger called Syser claims to continue where SoftICE left off.

A shareware debugger, but free to use, OllyDbg is a 32-bit assembler-level debugger from Oleh Yuschuk. However, it can only be used for user-mode debugging.

An open source kernel debugger similar to SoftICE named Rasta Ring 0 Debugger (RR0D) is available. It provides low-level debugging for Microsoft Windows, Linux, OpenBSD, NetBSD, and FreeBSD. This project does not seem to be actively maintained. , the last change in its GitHub source code repository occurred in December 2008.

A debugger called BugChecker is a 32-bit single-host kernel debugger for Windows 2000 and XP, developed and made available as open source for educational purposes. BugChecker allows users to trace into both user and kernel code, both on uniprocessor and multiprocessor versions of Windows 2000 and XP.

A modern successor to SoftICE named BugChecker (unrelated to the one mentioned above) was released by Vito Plantamura in 2023. Unlike the other local kernel debuggers, it supports Windows XP to Windows 11, both 32-bit and 64-bit. To achieve this, the debugger spoofs the machine as being debugged by a second system by intercepting serial cable communication, and then and draws its display directly to the framebuffer. This method significantly improves stability and compatibility compared to previous approaches, including that of SoftICE itself.

Many hypervisors allow debugging the kernel running in the virtual machine through exposing some kind of debugger interface that can control the virtualized processor directly. This allows debugging even if the kernel does not have native debugging facilities.

title: SoftICE


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Mail

The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal systems have generally been established as a government monopoly, with a fee on the article prepaid. Proof of payment is usually in the form of an adhesive postage stamp, but a postage meter is also used for bulk mailing.

Postal authorities often have functions aside from transporting letters. In some countries, a postal, telegraph and telephone (PTT) service oversees the postal system, in addition to telephone and telegraph systems. Some countries' postal systems allow for savings accounts and handle applications for passports.

The Universal Postal Union (UPU), established in 1874, includes 192 member countries and sets the rules for international mail exchanges as a Specialized Agency of the United Nations.

Etymology
The word mail comes from the Middle English word male, referring to a travelling bag or pack. It was spelled in that manner until the 17th century and is distinct from the word male. The French have a similar word, malle, for a trunk or large box, and mála is the Irish term for a bag. In the 17th century, the word mail began to appear as a reference for a bag that contained letters: "bag full of letter" (1654). Over the next hundred years the word mail began to be applied strictly to the letters themselves and the sack as the mailbag. In the 19th century, the British typically used mail to refer to letters being sent abroad (i.e. on a ship) and post to refer to letters for domestic delivery. The word Post is derived from Old French poste, which ultimately stems from the past participle of the Latin verb ponere 'to lay down or place'. So in the U.K., the Royal Mail delivers the post, while in North America both the U.S. Postal Service and Canada Post deliver the mail.

The term email, short for "electronic mail", first appeared in the 1970s. The term snail mail is a retronym to distinguish it from the quicker email. Various dates have been given for its first use.

History
The practice of communication by written documents carried by an intermediary from one person or place to another almost certainly dates back nearly to the invention of writing. However, the development of formal postal systems occurred much later. The first documented use of an organized courier service for the dissemination of written documents is in Egypt, where Pharaohs used couriers to send out decrees throughout the territory of the state (2400 BCE). The earliest surviving piece of mail is also Egyptian, dating to 255 BCE.

Persia (Iran)
The first credible claim for the development of a real postal system comes from Ancient Persia. The best-documented claim (Xenophon) attributes the invention to the Persian King Cyrus the Great (550 BCE), who mandated that every province in his kingdom would organize reception and delivery of post to each of its citizens. Other writers credit his successor Darius I of Persia (521 BCE). Other sources claim much earlier dates for an Assyrian postal system, with credit given to Hammurabi (1700 BCE) and Sargon II (722 BCE). Mail may not have been the primary mission of this postal service, however. The role of the system as an intelligence gathering apparatus is well documented, and the service was (later) called angariae, a term that in time came to indicate a tax system. The Old Testament (Esther, VIII) makes mention of this system: Ahasuerus, king of Medes, used couriers for communicating his decisions.

The Persian system worked using stations (called Chapar-Khaneh), whence the message carrier (called Chapar) would ride to the next post, whereupon he would swap his horse with a fresh one for maximum performance and delivery speed. Herodotus described the system in this way: "It is said that as many days as there are in the whole journey, so many are the men and horses that stand along the road, each horse and man at the interval of a day's journey; and these are stayed neither by snow nor rain nor heat nor darkness from accomplishing their appointed course with all speed". The verse prominently features on New York's James Farley Post Office, although it uses the translation "Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds".

India

The economic growth and political stability under the Mauryan Empire (322–185 BCE) stimulated sustained development of civil infrastructure in ancient India. The Mauryans developed early Indian mail service as well as public wells, rest houses, and other facilities for the public. Common chariots called Dagana were sometimes used as mail chariots in ancient India. Couriers were used militarily by kings and local rulers to deliver information through runners and other carriers. The postmaster, the head of the intelligence service, was responsible for ensuring the maintenance of the courier system. Couriers were also used to deliver personal letters.

In South India, the Wodeyar dynasty (1399–1947) of the Kingdom of Mysore used mail service for espionage purposes thereby acquiring knowledge related to matters that took place at great distances.

By the end of the 18th century, a postal system in India was in operation. Later this system underwent complete modernization when the British Raj established its control over most of India. The Post Office Act XVII of 1837 provided that the Governor-General of India in Council had the exclusive right of conveying letters by post for hire within the territories of the East India Company. The mails were available to certain officials without charge, which became a controversial privilege as the years passed. On this basis the Indian Post Office was established on October 1, 1837.

Rome
The first well-documented postal service was that of Rome. Organized at the time of Augustus Caesar (62 BCE – 14 CE), the service was called cursus publicus and was provided with light carriages (rhedæ) pulled by fast horses. By the time of Diocletian, a parallel service was established with two-wheeled carts (birotæ) pulled by oxen. This service was reserved for government correspondence. Yet another service for citizens was later added.

Vietnam
In 1802, the first Vietnamese postal service was established under the Nguyen dynasty, under the Ministry of Rites. During the Nguyen dynasty, official documents were transported by horse and other primitive means to stations built about 25-30 kilometers apart. In 1904, three wireless communication offices were established, and in early 1906 they were merged with the postal service to form the Post and Wireless Office. In 1945, after the August Revolution, the Post and Wireless Office was renamed the Post Office under the Ministry of Transportation. In 1955, the Post Office was upgraded to the Ministry of Post.

China
Some Chinese sources claim mail or postal systems dating back to the Xia or Shang dynasties, which would be the oldest mailing service in the world. The earliest credible system of couriers was initiated by the Han dynasty (206 BCE – 220 CE), who had relay stations every 30 li (about 15km) along major routes.

The Tang dynasty (618 to 907 AD) operated a recorded 1,639 posthouses, including maritime offices, employing around 20,000 people. The system was administered by the Ministry of War and private correspondence was forbidden from the network. The Ming dynasty (1368 to 1644) sought a postal system to deliver mail quickly, securely, and cheaply. Adequate speed was always a problem, because of the slow overland transportation system, and underfunding. Its network had 1,936 posthouses every 60 li along major routes, with fresh horses available every 10 li between them. The Qing operated 1,785 posthouses throughout their lands. More efficient, however, was the system linking the international settlements, centered around Shanghai and the Treaty ports. It was the main communication system for China's international trade.

Mongol Empire
Genghis Khan installed an empire-wide messenger and postal station system named Örtöö within the Mongol Empire. During the Yuan dynasty under Kublai Khan, this system also covered the territory of China. Postal stations were used not only for the transmission and delivery of official mail but were also available for travelling officials, military men, and foreign dignitaries. These stations aided and facilitated the transport of foreign and domestic tribute specifically and the conduct of trade in general.

By the end of Kublai Khan's rule, there were more than 1400 postal stations in China alone, which in turn had at their disposal about 50,000 horses, 1,400 oxen, 6,700 mules, 400 carts, 6,000 boats, more than 200 dogs, and 1,150 sheep.

The stations were 25 to 65 km apart and had reliable attendants working for the mail service. Foreign observers, such as Marco Polo, have attested to the efficiency of this early postal system.

Each station was maintained by up to twenty five families. Work for postal service counted as military service. The system was still operational in 18th century when 64 stations were required for a message to cross Mongolia from the Altai Mountains to China.

Japan
The modern Japanese system was developed in the mid-19th century, closely copying European models. Japan was highly innovative in developing the world's largest and most successful postal savings system and later a postal life insurance system as well. Postmasters play a key role in linking the Japanese political system to local politics. The postmasters are high prestige, and are often hereditary. To a large extent, the postal system generated the enormous funding necessary to rapidly industrialize Japan in the late 19th century.

Korea
The postal service was one of Korea's first attempts at modernization. The Joseon Post Office was established in 1884.

Other systems
Another important postal service was created in the Islamic world by the caliph Mu'awiyya; the service was called barid, for the name of the towers built to protect the roads by which couriers travelled.

By 3000 BC, Egypt was using homing pigeons for pigeon post, taking advantage of a singular quality of this bird, which when taken far from its nest is able to find its way home due to a particularly developed sense of orientation. Messages were then tied around the legs of the pigeon, which was freed and could reach its original nest. By the 19th century, homing pigeons were used extensively for military communications.

Charlemagne extended to the whole territory of his empire the system used by Franks in northern Gaul and connected this service with that of missi dominici.

In the mid-11th century, flax traders known as the Cairo Geniza Merchants from Fustat, Egypt wrote about using a postal service known as the kutubi. The kutubi system managed routes between the cities of Jerusalem, Ramla, Tyre, Ascalon, Damascus, Aleppo, and Fustat with year-round, regular mail delivery.

Many religious orders had a private mail service. Notably, the Cistercians had one which connected more than 6,000 abbeys, monasteries, and churches. The best organization, however, was created by the Knights Templar.

In 1716, Correos y Telégrafos was established in Spain as public mail service, available to all citizens. Delivery postmen were first employed in 1756 and post boxes were installed firstly in 1762.

Thurn und Taxis
In 1505, Holy Roman Emperor Maximilian I established a postal system in the Empire, appointing Franz von Taxis to run it. This system, originally the Kaiserliche Reichspost, is often considered the first modern postal service in the world, which initiated a revolution in communication in Europe. The system combined contemporary technical and organization means to create a stable transcontinental service which was also the first to offer (fee-based) public access. The Thurn und Taxis family, then known as Tassis, had operated postal services between Italian city-states from 1290 onward. For 500 years the postal business based in Brussels and in Frankfurt was passed from one generation to another. Following the abolition of the Empire in 1806, the Thurn-und-Taxis Post system continued as a private organization into the postage stamp era before being absorbed into the postal system of the new German Empire after 1871. 1867 July 1 the State of Prussia had to make a compensation payment of 3.000.000 Thalers reinvested by Helene von Thurn & Taxis, daughter-in-law of the last postmaster, Maximilian Karl, 6th Prince of Thurn and Taxis, into real estate, most of it continuing to exist today.

The Phone Book of the World has its roots in the long history of the avant-garde telecommunications family Thurn & Taxis. The directory is the result of Johannes, 11th Prince of Thurn & Taxis transmitting PTT culture to a student and helping with the opening of a small Telephone Boutique next to a historic Postal mansion his ancestors used to go to centuries earlier. Several European Post Carriers like Deutsche Post or Österreichische Post continue to use the Thurn & Taxis Post Horn in their company logo just like the global Phone Book of the World based in the old Postal mansion of King Louis XIV in Paris.

Postal reforms

In the United Kingdom, prior to 1840 letters were paid for by the recipient and the cost was determined by the distance from sender to recipient and the number of sheets of paper rather than by a countrywide flat rate with weight restrictions. Sir Rowland Hill reformed the postal system based on the concepts of penny postage and prepayment. In his proposal, Hill also called for official pre-printed envelopes and adhesive postage stamps as alternative ways of getting the sender to pay for the postage, at a time when prepayment was optional, which led to the invention of the postage stamp, the Penny Black.

Modern transport and technology
The postal system was important in the development of modern transportation. Railways carried railway post offices. During the 20th century, air mail became the transport of choice for inter-continental mail. Postmen started to use mail trucks. The handling of mail became increasingly automated.

The Internet came to change the conditions for physical mail. Email (and in recent years social networking sites) became a fierce competitor to physical mail systems, but online auctions and Internet shopping opened new business opportunities as people often get items bought online through the mail.

Modern mail
Modern mail is organized by national and privatized services, which are reciprocally connected by international regulations, organizations and international agreements. Paper letters and parcels can be sent to almost any country in the world relatively easily and cheaply. The Internet has made the process of sending letter-like messages nearly instantaneous, and in many cases and situations correspondents use email where they previously would have used letters. The volume of paper mail sent through the U.S. Postal Service has declined by more than 15% since its peak at 213 billion pieces per annum in 2006.

Organization
Some countries have organized their mail services as public limited liability corporations without a legal monopoly.

The worldwide postal system constituting the individual national postal systems of the world's self-governing states is coordinated by the Universal Postal Union, which among other things sets international postage rates, defines standards for postage stamps and operates the system of international reply coupons.

In most countries a system of codes has been created (referred to as ZIP codes in the United States, postcodes in the United Kingdom and Australia, eircodes in Ireland and postal codes in most other countries) in order to facilitate the automation of operations. This also includes placing additional marks on the address portion of the letter or mailed object, called "bar coding". Bar coding of mail for delivery is usually expressed either by a series of vertical bars, usually called POSTNET coding or a block of dots as a two-dimensional barcode. The "block of dots" method allows for the encoding of proof of payment of postage, exact routing for delivery, and other features.

The ordinary mail service was improved in the 20th century with the use of planes for a quicker delivery. The world's first scheduled airmail post service took place in the United Kingdom between the London suburbs of Hendon and Windsor, Berkshire, on 9 September 1911. Some methods of airmail proved ineffective, however, including the United States Postal Service's experiment with rocket mail.

Receipt services were made available in order to grant the sender a confirmation of effective delivery.

Payment
Before about the mid-nineteenth century, in regions where postal systems existed, the payment models varied, but most mail was sent unpaid requiring the recipient to pay the postage fee. In some regions a partial payment was made by the sender. Today, worldwide, the most common method of prepaying postage is by buying an adhesive postage stamp to be applied to the envelope before mailing; a much less common method is to use a postage-prepaid envelope. Franking is a method of creating postage-prepaid envelopes under licence using a special machine. They are used by companies with large mail programs, such as banks and direct mail companies.

In 1998, the U.S. Postal Service authorised the first tests of a secure system of sending digital franks via the Internet to be printed out on a PC printer, obviating the necessity to license a dedicated franking machine and allowing companies with smaller mail programs to make use of the option; this was later expanded to test the use of personalized postage. The service provided by the U.S. Postal Service in 2003 allows the franks to be printed out on special adhesive-backed labels.

In 2004 the Royal Mail in the United Kingdom introduced its SmartStamp Internet-based system, allowing printing on ordinary adhesive labels or envelopes. Similar systems are being considered by postal administrations around the world.

When the pre-paid envelope or package is accepted into the mail by an agent of the postal service, the agent usually indicates by means of a cancellation that it is no longer valid for pre-payment of postage. The exceptions are when the agent forgets or neglects to cancel the mailpiece, for stamps that are pre-cancelled and thus do not require cancellation and for, in most cases, metered mail. (The "personalized stamps" authorized by the USPS and manufactured by Zazzle and other companies are in fact a form of meter label and thus do not need to be cancelled.)

Privacy and censorship
Documents should generally not be read by anyone other than the addressee; for example, in the United States of America it is a violation of federal law for anyone other than the addressee and the government to open mail. There are exceptions however: executives often assign secretaries or assistants the task of handling their mail; and postcards do not require opening and can be read by anyone. For mail contained within an envelope, there are legal provisions in some jurisdictions allowing the recording of identities of sender and recipient.

The privacy of correspondence is guaranteed by the constitutions of Mexico, Colombia, Brazil and Venezuela, and is alluded to in the European Convention on Human Rights and the Universal Declaration of Human Rights. The control of the contents inside private citizens' mail is censorship and concerns social, political, and legal aspects of civil rights. International mail and packages are subject to customs control, with the mail and packages often surveyed and their contents sometimes edited out (or even in).

There have been cases over the millennia of governments opening and copying or photographing the contents of private mail. Subject to the laws in the relevant jurisdiction, correspondence may be openly or covertly opened, or the contents determined via some other method, by the police or other authorities in some cases relating to a suspected criminal conspiracy, although black chambers (largely in the past, though there is apparently some continuance of their use today) opened extralegally.

The mail service may be allowed to open the mail if neither addressee nor sender can be located, in order to attempt to locate either. Mail service may also open the mail to inspect if it contains materials that are hazardous to transport or violate local laws.

While in most cases mail censorship is exceptional, military mail to and from soldiers is often subject to surveillance. The mail is censored to prevent leaking tactical secrets, such as troop movements or weather conditions. Depending on the country, civilian mail containing military secrets can also be monitored and censored.

Mail sent to and from inmates in jails or prisons within the United States is subject to opening and review by jail or prison staff to determine if the mail has any criminal action dictated or provides means for an escape. The only mail that is not able to be read is attorney client mail, which is covered under the attorney-client confidentiality laws in the United States.

Rise of electronic correspondence
Modern alternatives, such as the telegraph, telephone, telex, facsimile, and email, have reduced the attractiveness of paper mail for many applications. These modern alternatives have some advantages: in addition to their speed, they may be more secure, e.g., because the general public cannot learn the address of the sender or recipient from the envelope, and occasionally traditional items of mail may fail to arrive, e.g. due to vandalism to mailboxes, unfriendly pets, and adverse weather conditions. Mail carriers due to perceived hazards or inconveniences, may refuse, officially or otherwise, to deliver mail to a particular address (for instance, if there is no clear path to the door or mailbox). On the other hand, traditional mail avoids the possibility of computer malfunctions and malware, and the recipient does not need to print it out if they wish to have a paper copy, though scanning is required to make a digital copy.

Physical mail is still widely used in business and personal communications for such reasons as legal requirements for signatures, requirements of etiquette, and the requirement to enclose small physical objects.

Since the advent of email, which is almost always much faster, the postal system has come to be referred to in Internet slang by the retronym "snail mail". Occasionally, the term "white mail" has also been used as a neutral term for postal mail.

Mainly during the 20th century, experimentation with hybrid mail has combined electronic and paper delivery. Electronic mechanisms include telegram, telex, facsimile (fax), email, and short message service (SMS). There have been methods which have combined mail and some of these newer methods, such as temporary emails, that combine facsimile transmission with overnight delivery. These vehicles commonly use a mechanical or electro-mechanical standardised writing (typing), that on the one hand makes for more efficient communication, while on the other hand makes impossible characteristics and practices that traditionally were in conventional mail, such as calligraphy.

This epoch is undoubtedly mainly dominated by mechanical writing, with a general use of no more of half a dozen standard typographic fonts from standard keyboards. However, the increased use of typewritten or computer-printed letters for personal communication and the advent of email have sparked renewed interest in calligraphy, as a letter has become more of a "special event". Long before email and computer-printed letters, however, decorated envelopes, rubber stamps and artistamps formed part of the medium of mail art.

In the 2000s (decade) with the advent of eBay and other online auction sites and online stores, postal services in industrialized nations have seen a major shift to item shipping. This has been seen as a boost to the system's usage in the wake of lower paper mail volume due to the accessibility of email.

Online post offices have emerged to give recipients a means of receiving traditional correspondence mail in a scanned electronic format.

Collecting
Postage stamps are also object of a particular form of collecting. Stamp collecting has been a very popular hobby. In some cases, when demand greatly exceeds supply, their commercial value on this specific market may become enormously greater than face value, even after use. For some postal services the sale of stamps to collectors who will never use them is a significant source of revenue; for example, stamps from Tokelau, South Georgia & South Sandwich Islands, Tristan da Cunha, Niuafoʻou and many others. Stamp collecting is commonly known as philately, although strictly the latter term refers to the study of stamps.

Another form of collecting regards postcards, a document written on a single robust sheet of paper, usually decorated with photographic pictures or artistic drawings on one of the sides, and short messages on a small part of the other side, that also contained the space for the address. In strict philatelic usage, the postcard is to be distinguished from the postal card, which has a pre-printed postage on the card. The fact that this communication is visible by other than the receiver often causes the messages to be written in jargon.

Letters are often studied as an example of literature, and also in biography in the case of a famous person. A portion of the New Testament of the Bible is composed of the Apostle Paul's epistles to Christian congregations in various parts of the Roman Empire. See below for a list of famous letters.

A style of writing, called epistolary, tells a fictional story in the form of the correspondence between two or more characters.

A makeshift mail method after stranding on a deserted island is a message in a bottle.

Deregulation
Numerous countries, including Sweden (1 January 1993), New Zealand (1998 and 2003), Germany (2005 and 2007), Argentina and Chile opened up the postal services market to new entrants. In the case of New Zealand Post Limited, this included (from 2003) its right to be the sole New Zealand postal administration member of the Universal Postal Union, thus the ending of its monopoly on stamps bearing the name New Zealand.

Letters
Letter-sized mail constitutes the bulk of the contents sent through most postal services. These are usually documents printed on A4 (210×297 mm), Letter-sized (8.5×11 inches), or smaller paper and placed in envelopes.

Handwritten correspondence, while once a major means of communications between distant people, is now used less frequently due to the advent of more immediate forms of communication, such as the telephone or email. Traditional letters, however, are often considered to hark back to a "simpler time" and are still used when someone wishes to be deliberate and thoughtful about their communication. An example would be a letter of sympathy to a bereaved person.

Bills and invoices are often sent through the mail, like regular billing correspondence from utility companies and other service providers. These letters often contain a self-addressed envelope that allows the receiver to remit payment back to the company easily. While still very common, many people now opt to use online bill payment services, which eliminate the need to receive bills through the mail. Paperwork for the confirmation of large financial transactions is often sent through the mail. Many tax documents are as well.

New credit cards and their corresponding personal identification numbers are sent to their owners through the mail. The card and number are usually mailed separately several days or weeks apart for security reasons.

Bulk mail is mail that is prepared for bulk mailing, often by presorting, and processing at reduced rates. It is often used in direct marketing and other advertising mail, although it has other uses as well. The senders of these messages sometimes purchase lists of addresses (which are sometimes targeted towards certain demographics) and then send letters advertising their product or service to all recipients. Other times, commercial solicitations are sent by local companies advertising local products, like a restaurant delivery service advertising to their delivery area or a retail store sending their weekly advertising circular to a general area. Bulk mail is also often sent to companies' existing subscriber bases, advertising new products or services.

First-Class
First-Class Mail in the U.S. includes postcards, letters, large envelopes (flats), and small packages, providing each piece weighs 13 oz or less. Delivery is given priority over second-class (newspapers and magazines), third class (bulk advertisements), and fourth-class mail (books and media packages). First-Class Mail prices are based on both the shape and weight of the item being mailed. Pieces over 13 ounces can be sent as Priority Mail. As of 2011 42% of First-Class Mail arrived the next day, 27% in two days, and 31% in three. The USPS expected that changes to the service in 2012 would cause about 51% to arrive in two days and most of the rest in three. The Canada Post counterpart is Lettermail.

The British Royal Mail's 1st Class, as it is styled, is simply a priority option over 2nd Class, at a slightly higher cost. Royal Mail aims (but does not guarantee) to deliver all 1st Class letters the day after posting.

In Austria priority delivery mail is called Prio, in Switzerland A-Post.

Registered and recorded mail
Registered mail allows the location and in particular the correct delivery of a letter to be tracked. It is usually considerably more expensive than regular mail, and is typically used for valuable items. Registered mail is constantly tracked through the system.

Recorded mail is handled just like ordinary mail with the exception that it has to be signed for on receipt. This is useful for legal documents where proof of delivery is required.

In the United Kingdom recorded delivery mail (branded as signed for by the Royal Mail) is covered by The Recorded Delivery Services Act 1962. Under this legislation any document which its relevant law requires service by registered post can also be lawfully served by recorded delivery.

Repositionable notes
The United States Postal Service introduced a test allowing "repositionable notes" (for example, 3M's Post-it notes) to be attached to the outside of envelopes and bulk mailings, afterwards extending the test for an unspecified period. The repositionable note may be fixed directly to the address side of First-Class Mail and Standard Mail letter-size mailpieces. These mailpieces must meet the standards in 7.2 through 7.6. The note is included as an integral part of the mailpiece for weight and postage rate and must be accounted for in pricing.

Postal cards and postcards
Postal cards and postcards are small message cards that are sent by mail unenveloped; the distinction often, though not invariably and reliably, drawn between them is that "postal cards" are issued by the postal authority or entity with the "postal indicia" (or "stamp") preprinted on them, while postcards are privately issued and require affixing an adhesive stamp (though there have been some cases of a postal authority's issuing non-stamped postcards). Postcards are often printed to promote tourism, with pictures of resorts, tourist attractions or humorous messages on the front and allowing for a short message from the sender to be written on the back. The postage required for postcards is generally less than postage required for standard letters; however, certain technicalities such as their being oversized or having cut-outs, may result in payment of the first-class rate being required.

Postcards are also used by magazines for new subscriptions. Inside many magazines are postage-paid subscription cards that a reader can fill out and mail back to the publishing company to be billed for a subscription to the magazine. In this fashion, magazines also use postcards for other purposes, including reader surveys, contests or information requests.

Postcards are sometimes sent by charities to their members with a message to be signed and sent to a politician (e.g. to promote fair trade or third world debt cancellation).

Other mail services

Small packets are usually less than 2 kg (4 lb).

Larger envelopes are also sent through the mail. These are often composed of a stronger material than standard envelopes and are often used by businesses to transport documents that may not be folded or damaged, such as legal documents and contracts. Due to their size, larger envelopes are sometimes charged additional postage.

Packages are often sent through some postal services, usually requiring additional postage than an average letter or postcard. Many postal services have limitations as to what a package may or may not contain, usually placing limits or bans on perishable, hazardous or flammable materials. Some hazardous materials in limited quantities may be shipped with appropriate markings and packaging, like an ORM-D label. Additionally, as a result of terrorism concerns, the U.S. Postal Service subjects their packages to numerous security tests, often scanning or x-raying packages for materials that might be found in biological materials or mail bombs.

Newspapers and magazines are also sent through postal services. Many magazines are simply placed in the mail normally (but in the U.S., they are printed with a special bar code that acts as pre-paid postage – see POSTNET), but many are now shipped in shrinkwrap to protect the loose contents of the magazine. During the second half of the 19th century and the first half of the 20th century, newspapers and magazines were normally posted using wrappers with a stamp imprint.

Hybrid mail, sometimes referred to as L-mail, is the electronic lodgement of mail from the mail generator's computer directly to a Postal Service provider. The Postal Service provider is then able to use electronic means to have the mail piece sorted, routed and physically produced at a site closest to the delivery point. It is a type of mail growing in popularity with some Post Office operations and individual businesses venturing into this market. In some countries, these services are available to print and deliver emails to those who are unable to receive email, such as the elderly or infirm. Services provided by Hybrid mail providers are closely related to that of mail forwarding service providers.

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William Riker

William Thomas "Will" Riker is a fictional character in the Star Trek universe appearing primarily as a main character in Star Trek: The Next Generation, portrayed by Jonathan Frakes. Throughout the series and its accompanying films, he is the Enterprise's first officer, and briefly captain, until he accepts command of the USS Titan at the end of Star Trek: Nemesis. He is the husband of Deanna Troi.

Casting
Frakes went to seven auditions over six weeks before being cast as Riker. Frakes stated: "I started with the cattle call, then the casting director, the producer, then other directors, to Gene Roddenberry, and then through the Paramount execs, including the vice-president himself and the heads of television."Frakes was not the first choice for the part of Riker, Patrick Stewart was the number one choice when casting began.

Star Trek: The Next Generation
Riker is usually referred to as "Will". He is also usually (and informally) called "Number One" by Captain Picard, because of his position as first officer on the Enterprise.

Riker was originally scripted as a much more serious, by-the-book officer, but by the middle episodes of the first season, it was felt that he was too "official", and his character was toned down and became more of a ladies' man. For the first two seasons, Riker is portrayed as a bold, confident and sometimes arrogant, ambitious young officer; however, over time he becomes more reserved, as experience teaches him the wisdom of a patient, careful approach. He becomes comfortable on the Enterprise, repeatedly turning down offers of his own command, and he learns to cherish his fellow officers' company. Nonetheless, he retains a willingness to occasionally disregard the chain of command.

Although Riker was clean-shaven for the first season, he grew a beard at the start of the second season that later became something of a trademark. Between sessions, Frakes grew a beard for his role in the Civil War miniseries North and South, and Gene Roddenberry asked him to keep it because he thought it made Riker look more nautical. Because Frakes' beard coincided with what fans and critics perceived as an improvement of the show's writing quality, "growing the beard" has become an internet colloquialism for a once subpar television series achieving a dramatic level of improvement. Riker did shave his mustache and beard during the events of Star Trek Insurrection, to the amusement of Data.

Riker's background is first explored in the second-season episode "The Icarus Factor". In the episode, Riker's estranged father, Kyle, visits the Enterprise to offer his son the command of the USS Aries, which Riker refuses. We learn that Riker grew up in Alaska; that his mother, Elizabeth (Betty), died when he was two; and that he was raised by his father until age 15, when he left home. In the episode, Riker had not spoken with his father for 15 years, but they manage to partially mend their relationship over a game of martial-arts sparring called Anbo-jitsu. In the episode "Lower Decks", a waiter at Ten Forward mistakenly states that Riker is Canadian, and in the same episode Riker clarifies that he grew up in Alaska. According to the Voyager episode "Death Wish" (in which Riker made a guest appearance), Riker's distant ancestors also lived in the United States: During the American Civil War, his ancestor Colonel Thaddeus Riker fought on the Union side as an officer in the 102nd New York Infantry Regiment during the Atlanta Campaign.

In the two-part episode "The Best of Both Worlds" Riker takes command of the Enterprise, promoted to the rank of captain through a field promotion, and orchestrates Picard's rescue. This episode also explores the idea of Riker being unwilling to take chances since he had grown comfortable in his role as First Officer aboard the Enterprise. By the end of the episode, when he orders the Enterprise to fire on former Captain Picard, now Locutus of Borg, Riker has grown into a more confident leader. The sixth-season episode "Second Chances" reveals that Will Riker was duplicated long ago by a transporter malfunction. The "second" Riker takes the name "Thomas", which is revealed to be William Riker's middle name. In the seventh-season episode "The Pegasus", Riker must confront his former commanding officer, Admiral Erik Pressman, over a cover-up related to the destruction of the USS Pegasus. The Pegasus had illegally developed a radically different type of cloaking device that also allowed it to phase through matter, resulting in it becoming fused within an asteroid when unstable power consumption forced the cloaking device offline. In the Enterprise series finale, Riker appears as a never before seen cook discussing matters of life, duty, and sacrifice with the crew. It is revealed that his presence is part of a holodeck simulation of historic events that Riker initiated to help himself make the decision to inform Captain Picard of the illegal research once conducted by Admiral Pressman aboard the Pegasus.

Before the beginning of the series, Riker was involved in a romantic relationship with Counselor Troi on her home planet Betazed. They often refer to each other as imzadi, a Betazoid term of endearment meaning "soulmate". The novel Imzadi takes place before the beginning of the series and explores the history of the relationship between the two characters. The two characters are close friends throughout the series, but their relationship does not resume until Star Trek: Insurrection, the third Star Trek film set in the Next Generation era, although Thomas Riker, the duplicate created by a transporter malfunction, attempts to respark their relationship in "Second Chances". The following movie, Star Trek: Nemesis, begins with their wedding reception on board the Enterprise-E. At the start of the film, Riker finally accepts a promotion to captain and an offer to command the USS Titan; during the movie's final scenes he bids Picard, and the Enterprise, farewell.

Star Trek: Voyager
Riker guest-starred along with Q in the Star Trek: Voyager episode "Death Wish".

Star Trek: Enterprise
Frakes reprised his role of Commander Riker in the 2005 Enterprise series finale, "These Are the Voyages...".

Star Trek: Picard
Riker returns to the screen in the "Nepenthe" episode of Star Trek: Picard. In that episode, taking place in 2399, Riker is married to Deanna Troi; they have two children, Thad (now deceased) and Kestra. Picard and his gynoid companion Soji visit the Rikers' home, a National Parks-style lodge on the planet Nepenthe, and are welcomed with open arms. Will and Deanna are retired from Starfleet although Will describes his status as being on "active reserve."

Riker makes another Picard appearance in the Season 1 finale "Et in Arcadia Ego, Part II". In that episode, Riker has been reinstated to active duty. He is temporarily in command of the USS Zheng He, the lead ship in a Starfleet squadron sent to the planet Coppelius to protect its inhabitants from imminent Romulan attack.

Riker, along with other former members of the crew of the USS Enterprise-D, return for an extended story arc in the third and final season of Picard, wherein they fight a rogue Changeling conspiracy against the Federation. Riker appears from the season premiere onward (as of the fourth episode), and is acting captain of the USS Titan (NCC-80102-A) – successor to the ship he was given command of at the end of Star Trek: Nemesis, continuing in Star Trek: Lower Decks – in the third and fourth episodes. While conducting a heist at the advanced research center the Daystrom Institute on Picard's behalf, Riker is captured by the rogue Changelings, and reunited with Deanna in the sixth episode. Riker had fallen into an existential crisis after Thad's death, and their relationship had turned into one of toxic codependency and longing for adventure, necessitating their temporary separation and Picard's help. Their former crewmate Worf rescues the couple and brings them aboard the Titan in the eighth episode, reuniting the crew of the Enterprise.

Star Trek: Lower Decks
Riker appears in "No Small Parts", the 2020 finale of the first season of Star Trek: Lower Decks, as captain of the USS Titan (NCC-80102) alongside his wife Deanna Troi – continuing a posting announced in dialogue at the end of Star Trek: Nemesis (2002). Riker appeared in the second season's first and second episodes.

Alternate versions
Frakes appeared in dual roles in "Second Chances", a TNG episode where it was established that a duplicate of him was created years earlier by a transporter malfunction. Frakes appeared as the duplicate, Thomas Riker, in the Star Trek: Deep Space Nine episode "Defiant", where Thomas impersonates William in order to commandeer the USS Defiant on behalf of the Maquis.

Popular culture
In 1993, mainframe software company Boole & Babbage announced that it had signed a two-year licensing agreement, paying Paramount Pictures $75,000 a year, to use Star Trek imagery in advertising for its products. Boole & Babbage's campaign used actor Jonathan Frakes, playing his character of Commander William Riker, in their Star Trek-themed advertisements.

Reception
In 2009, IGN rated William Riker the 22nd best character of all Star Trek up to that time.

In 2016, Wired magazine ranked First Officer Riker as the 6th most important character of Starfleet within the Star Trek science fiction universe.

In 2017, IndieWire ranked Riker as the 2nd best character on Star Trek:The Next Generation.

In March 2018, TheWrap placed William Riker as 5th out 39 in a ranking of main cast characters of the Star Trek franchise. In October 2018, CBR ranked Riker as the 12th best Starfleet character of Star Trek.

In 2019, CinemaBlend ranked Riker the fifth best Starfleet character of all time. They point out he is good at his job as "Number One", first officer to Captain Picard on the starship USS Enterprise 1701-D.

title: William Riker


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Giant-impact hypothesis

The giant-impact hypothesis, sometimes called the Theia Impact, is an astrogeology hypothesis for the formation of the Moon first proposed in 1946 by Canadian geologist Reginald Daly. The hypothesis suggests that the Early Earth collided with a Mars-sized protoplanet of the same orbit approximately 4.5 billion years ago in the early Hadean eon (about 20 to 100 million years after the Solar System coalesced), and the ejecta of the impact event later accreted to form the Moon. The impactor planet is sometimes called Theia, named after the mythical Greek Titan who was the mother of Selene, the goddess of the Moon.

Analysis of lunar rocks published in a 2016 report suggests that the impact might have been a direct hit, causing a fragmentation and thorough mixing of both parent bodies.

The giant-impact hypothesis is currently the favored hypothesis for lunar formation among astronomers. Evidence that supports this hypothesis include:
 * The Moon's orbit has a similar orientation to Earth's rotation, both of which are at a similar angle to the ecliptic plane of the Solar System.
 * The stable isotope ratios of lunar and terrestrial rock are identical, implying a common origin.
 * The Earth–Moon system contains an anomalously high angular momentum, meaning the momentum contained in Earth's rotation, the Moon's rotation and the Moon revolving around Earth is significantly higher than the other terrestrial planets. A giant impact might have supplied this excess momentum.
 * Moon samples indicate that the Moon was once molten to a substantial, but unknown, depth. This might have required much more energy than predicted to be available from the accretion of a celestial body of the Moon's size and mass. An extremely energetic process, such as a giant impact, could provide this energy.
 * The Moon has a relatively small iron core, which gives it a much lower density than Earth. Computer models of a giant impact of a Mars-sized body with Earth indicate the impactor's core would likely penetrate deep into Earth and fuse with its own core. This would leave the Moon, which was formed from the ejecta of lighter crust and mantle fragments that went beyond the Roche limit and were not pulled back by gravity to re-fuse with Earth, with less remaining metallic iron than other planetary bodies.
 * The Moon is depleted in volatile elements compared to Earth. Vaporizing at comparably lower temperatures, they could be lost in a high-energy event, with the Moon's smaller gravity unable to recapture them while Earth did.
 * There is evidence in other star systems of similar collisions, resulting in debris discs.
 * Giant collisions are consistent with the leading theory of the formation of the Solar System.

However, several questions remain concerning the best current models of the giant-impact hypothesis. The energy of such a giant impact is predicted to have heated Earth to produce a global magma ocean, and evidence of the resultant planetary differentiation of the heavier material sinking into Earth's mantle has been documented. However, there is no self-consistent model that starts with the giant-impact event and follows the evolution of the debris into a single moon. Other remaining questions include when the Moon lost its share of volatile elements and why Venus – which experienced giant impacts during its formation – does not host a similar moon.

History
In 1898, George Darwin made the suggestion that Earth and the Moon were once a single body. Darwin's hypothesis was that a molten Moon had been spun from Earth because of centrifugal forces, and this became the dominant academic explanation. Using Newtonian mechanics, he calculated that the Moon had orbited much more closely in the past and was drifting away from Earth. This drifting was later confirmed by American and Soviet experiments, using laser ranging targets placed on the Moon.

Nonetheless, Darwin's calculations could not resolve the mechanics required to trace the Moon back to the surface of Earth. In 1946, Reginald Aldworth Daly of Harvard University challenged Darwin's explanation, adjusting it to postulate that the creation of the Moon was caused by an impact rather than centrifugal forces. Little attention was paid to Professor Daly's challenge until a conference on satellites in 1974, during which the idea was reintroduced and later published and discussed in Icarus in 1975 by William K. Hartmann and Donald R. Davis. Their models suggested that, at the end of the planet formation period, several satellite-sized bodies had formed that could collide with the planets or be captured. They proposed that one of these objects might have collided with Earth, ejecting refractory, volatile-poor dust that could coalesce to form the Moon. This collision could potentially explain the unique geological and geochemical properties of the Moon.

A similar approach was taken by Canadian astronomer Alastair G. W. Cameron and American astronomer William R. Ward, who suggested that the Moon was formed by the tangential impact upon Earth of a body the size of Mars. It is hypothesized that most of the outer silicates of the colliding body would be vaporized, whereas a metallic core would not. Hence, most of the collisional material sent into orbit would consist of silicates, leaving the coalescing Moon deficient in iron. The more volatile materials that were emitted during the collision probably would escape the Solar System, whereas silicates would tend to coalesce.

Eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, and Jeff Taylor challenged fellow lunar scientists: "You have eighteen months. Go back to your Apollo data, go back to your computer, and do whatever you have to, but make up your mind. Don't come to our conference unless you have something to say about the Moon's birth." At the 1984 conference at Kona, Hawaii, the giant-impact hypothesis emerged as the most favored hypothesis. "Before the conference, there were partisans of the three 'traditional' theories, plus a few people who were starting to take the giant impact seriously, and there was a huge apathetic middle who didn't think the debate would ever be resolved. Afterward, there were essentially only two groups: the giant impact camp and the agnostics."

Theia
The name of the hypothesised protoplanet is derived from the mythical Greek titan Theia, who gave birth to the Moon goddess Selene. This designation was proposed initially by the English geochemist Alex N. Halliday in 2000 and has become accepted in the scientific community. According to modern theories of planet formation, Theia was part of a population of Mars-sized bodies that existed in the Solar System 4.5 billion years ago. One of the attractive features of the giant-impact hypothesis is that the formation of the Moon and Earth align; during the course of its formation, Earth is thought to have experienced dozens of collisions with planet-sized bodies. The Moon-forming collision would have been only one such "giant impact" but certainly the last significant impactor event. The Late Heavy Bombardment by much smaller asteroids may have occurred later – approximately 3.9 billion years ago.

Basic model

Astronomers think the collision between Earth and Theia happened at about 4.4 to 4.45 billion years ago (bya); about 0.1 billion years after the Solar System began to form. In astronomical terms, the impact would have been of moderate velocity. Theia is thought to have struck Earth at an oblique angle when Earth was nearly fully formed. Computer simulations of this "late-impact" scenario suggest an initial impactor velocity below 4 km/s at "infinity" (far enough that gravitational attraction is not a factor), increasing as it approached to over 9.3 km/s at impact, and an impact angle of about 45°. However, oxygen isotope abundance in lunar rock suggests "vigorous mixing" of Theia and Earth, indicating a steep impact angle. Theia's iron core would have sunk into the young Earth's core, and most of Theia's mantle accreted onto Earth's mantle. However, a significant portion of the mantle material from both Theia and Earth would have been ejected into orbit around Earth (if ejected with velocities between orbital velocity and escape velocity) or into individual orbits around the Sun (if ejected at higher velocities).

Modelling has hypothesised that material in orbit around Earth may have accreted to form the Moon in three consecutive phases; accreting first from the bodies initially present outside Earth's Roche limit, which acted to confine the inner disk material within the Roche limit. The inner disk slowly and viscously spread back out to Earth's Roche limit, pushing along outer bodies via resonant interactions. After several tens of years, the disk spread beyond the Roche limit, and started producing new objects that continued the growth of the Moon, until the inner disk was depleted in mass after several hundreds of years. Material in stable Kepler orbits was thus likely to hit the Earth–Moon system sometime later (because the Earth–Moon system's Kepler orbit around the Sun also remains stable). Estimates based on computer simulations of such an event suggest that some twenty percent of the original mass of Theia would have ended up as an orbiting ring of debris around Earth, and about half of this matter coalesced into the Moon. Earth would have gained significant amounts of angular momentum and mass from such a collision. Regardless of the speed and tilt of Earth's rotation before the impact, it would have experienced a day some five hours long after the impact, and Earth's equator and the Moon's orbit would have become coplanar.

Not all of the ring material need have been swept up right away: the thickened crust of the Moon's far side suggests the possibility that a second moon about 1,000 km in diameter formed in a Lagrange point of the Moon. The smaller moon may have remained in orbit for tens of millions of years. As the two moons migrated outward from Earth, solar tidal effects would have made the Lagrange orbit unstable, resulting in a slow-velocity collision that "pancaked" the smaller moon onto what is now the far side of the Moon, adding material to its crust. Lunar magma cannot pierce through the thick crust of the far side, causing fewer lunar maria, while the near side has a thin crust displaying the large maria visible from Earth.

Above a high resolution threshold for simulations, a study published in 2022 finds that giant impacts can immediately place a satellite with similar mass and iron content to the Moon into orbit far outside Earth's Roche limit. Even satellites that initially pass within the Roche limit can reliably and predictably survive, by being partially stripped and then torqued onto wider, stable orbits. Furthermore, the outer layers of these directly formed satellites are molten over cooler interiors and are composed of around 60% proto-Earth material. This could alleviate the tension between the Moon's Earth-like isotopic composition and the different signature expected for the impactor. Immediate formation opens up new options for the Moon's early orbit and evolution, including the possibility of a highly tilted orbit to explain the lunar inclination, and offers a simpler, single-stage scenario for the origin of the Moon.

Composition
In 2001, a team at the Carnegie Institution of Washington reported that the rocks from the Apollo program carried an isotopic signature that was identical with rocks from Earth, and were different from almost all other bodies in the Solar System.

In 2014, a team in Germany reported that the Apollo samples had a slightly different isotopic signature from Earth rocks. The difference was slight, but statistically significant. One possible explanation is that Theia formed near Earth.

This empirical data showing close similarity of composition can be explained only by the standard giant-impact hypothesis, as it is extremely unlikely that two bodies prior to collision had such similar composition.

Equilibration hypothesis
In 2007, researchers from the California Institute of Technology showed that the likelihood of Theia having an identical isotopic signature as Earth was very small (less than 1 percent). They proposed that in the aftermath of the giant impact, while Earth and the proto-lunar disc were molten and vaporised, the two reservoirs were connected by a common silicate vapor atmosphere and that the Earth–Moon system became homogenised by convective stirring while the system existed in the form of a continuous fluid. Such an "equilibration" between the post-impact Earth and the proto-lunar disc is the only proposed scenario that explains the isotopic similarities of the Apollo rocks with rocks from Earth's interior. For this scenario to be viable, however, the proto-lunar disc would have to endure for about 100 years. Work is ongoing to determine whether or not this is possible.

Direct collision hypothesis
According to research (2012) to explain similar compositions of the Earth and the Moon based on simulations at the University of Bern by physicist Andreas Reufer and his colleagues, Theia collided directly with Earth instead of barely swiping it. The collision speed may have been higher than originally assumed, and this higher velocity may have totally destroyed Theia. According to this modification, the composition of Theia is not so restricted, making a composition of up to 50% water ice possible.

Synestia hypothesis
One effort, in 2018, to homogenise the products of the collision was to energise the primary body by way of a greater pre-collision rotational speed. This way, more material from the primary body would be spun off to form the Moon. Further computer modelling determined that the observed result could be obtained by having the pre-Earth body spinning very rapidly, so much so that it formed a new celestial object which was given the name 'synestia'. This is an unstable state that could have been generated by yet another collision to get the rotation spinning fast enough. Further modelling of this transient structure has shown that the primary body spinning as a doughnut-shaped object (the synestia) existed for about a century (a very short time) before it cooled down and gave birth to Earth and the Moon.

Terrestrial magma ocean hypothesis
Another model, in 2019, to explain the similarity of Earth and the Moon's compositions posits that shortly after Earth formed, it was covered by a sea of hot magma, while the impacting object was likely made of solid material. Modelling suggests that this would lead to the impact heating the magma much more than solids from the impacting object, leading to more material being ejected from the proto-Earth, so that about 80% of the Moon-forming debris originated from the proto-Earth. Many prior models had suggested 80% of the Moon coming from the impactor.

Evidence
Indirect evidence for the giant impact scenario comes from rocks collected during the Apollo Moon landings, which show oxygen isotope ratios nearly identical to those of Earth. The highly anorthositic composition of the lunar crust, as well as the existence of KREEP-rich samples, suggest that a large portion of the Moon once was molten; and a giant impact scenario could easily have supplied the energy needed to form such a magma ocean. Several lines of evidence show that if the Moon has an iron-rich core, it must be a small one. In particular, the mean density, moment of inertia, rotational signature, and magnetic induction response of the Moon all suggest that the radius of its core is less than about 25% the radius of the Moon, in contrast to about 50% for most of the other terrestrial bodies. Appropriate impact conditions satisfying the angular momentum constraints of the Earth–Moon system yield a Moon formed mostly from the mantles of Earth and the impactor, while the core of the impactor accretes to Earth. Earth has the highest density of all the planets in the Solar System; the absorption of the core of the impactor body explains this observation, given the proposed properties of the early Earth and Theia.

Comparison of the zinc isotopic composition of lunar samples with that of Earth and Mars rocks provides further evidence for the impact hypothesis. Zinc is strongly fractionated when volatilised in planetary rocks, but not during normal igneous processes, so zinc abundance and isotopic composition can distinguish the two geological processes. Moon rocks contain more heavy isotopes of zinc, and overall less zinc, than corresponding igneous Earth or Mars rocks, which is consistent with zinc being depleted from the Moon through evaporation, as expected for the giant impact origin.

Collisions between ejecta escaping Earth's gravity and asteroids would have left impact heating signatures in stony meteorites; analysis based on assuming the existence of this effect has been used to date the impact event to 4.47 billion years ago, in agreement with the date obtained by other means.

Warm silica-rich dust and abundant SiO gas, products of high velocity impacts – over 10 km/s – between rocky bodies, have been detected by the Spitzer Space Telescope around the nearby (29 pc distant) young (~12 My old) star HD 172555 in the Beta Pictoris moving group. A belt of warm dust in a zone between 0.25AU and 2AU from the young star HD 23514 in the Pleiades cluster appears similar to the predicted results of Theia's collision with the embryonic Earth, and has been interpreted as the result of planet-sized objects colliding with each other. A similar belt of warm dust was detected around the star BD+20°307 (HIP 8920, SAO 75016).

On 1 November 2023, scientists reported that, according to computer simulations, remnants of Theia could be still visible inside the Earth as two giant anomalies of the Earth's mantle.

Difficulties
This lunar origin hypothesis has some difficulties that have yet to be resolved. For example, the giant-impact hypothesis implies that a surface magma ocean would have formed following the impact. Yet there is no evidence that Earth ever had such a magma ocean and it is likely there exists material that has never been processed in a magma ocean.

Composition
A number of compositional inconsistencies need to be addressed.

 * The ratios of the Moon's volatile elements are not explained by the giant-impact hypothesis. If the giant-impact hypothesis is correct, these ratios must be due to some other cause.
 * The presence of volatiles such as water trapped in lunar basalts and carbon emissions from the lunar surface is more difficult to explain if the Moon was caused by a high-temperature impact.
 * The iron oxide (FeO) content (13%) of the Moon, intermediate between that of Mars (18%) and the terrestrial mantle (8%), rules out most of the source of the proto-lunar material from Earth's mantle.
 * If the bulk of the proto-lunar material had come from an impactor, the Moon should be enriched in siderophilic elements, when, in fact, it is deficient in them.
 * The Moon's oxygen isotopic ratios are essentially identical to those of Earth. Oxygen isotopic ratios, which may be measured very precisely, yield a unique and distinct signature for each Solar System body. If a separate proto-planet Theia had existed, it probably would have had a different oxygen isotopic signature than Earth, as would the ejected mixed material.
 * The Moon's titanium isotope ratio (50Ti/47Ti) appears so close to Earth's (within 4 ppm), that little if any of the colliding body's mass could likely have been part of the Moon.

Lack of a Venusian moon
If the Moon was formed by such an impact, it is possible that other inner planets also may have been subjected to comparable impacts. A moon that formed around Venus by this process would have been unlikely to escape. If such a moon-forming event had occurred there, a possible explanation of why the planet does not have such a moon might be that a second collision occurred that countered the angular momentum from the first impact. Another possibility is that the strong tidal forces from the Sun would tend to destabilise the orbits of moons around close-in planets. For this reason, if Venus's slow rotation rate began early in its history, any satellites larger than a few kilometers in diameter would likely have spiraled inwards and collided with Venus.

Simulations of the chaotic period of terrestrial planet formation suggest that impacts like those hypothesised to have formed the Moon were common. For typical terrestrial planets with a mass of 0.5 to 1 Earth masses, such an impact typically results in a single moon containing 4% of the host planet's mass. The inclination of the resulting moon's orbit is random, but this tilt affects the subsequent dynamic evolution of the system. For example, some orbits may cause the moon to spiral back into the planet. Likewise, the proximity of the planet to the star will also affect the orbital evolution. The net effect is that it is more likely for impact-generated moons to survive when they orbit more distant terrestrial planets and are aligned with the planetary orbit.

Possible origin of Theia
In 2004, Princeton University mathematician Edward Belbruno and astrophysicist J. Richard Gott III proposed that Theia coalesced at the or  Lagrangian point relative to Earth (in about the same orbit and about 60° ahead or behind),  similar to a trojan asteroid. Two-dimensional computer models suggest that the stability of Theia's proposed trojan orbit would have been affected when its growing mass exceeded a threshold of approximately 10% of Earth's mass (the mass of Mars). In this scenario, gravitational perturbations by planetesimals caused Theia to depart from its stable Lagrangian location, and subsequent interactions with proto-Earth led to a collision between the two bodies.

In 2008, evidence was presented that suggests that the collision might have occurred later than the accepted value of 4.53 Gya, at approximately 4.48 Gya. A 2014 comparison of computer simulations with elemental abundance measurements in Earth's mantle indicated that the collision occurred approximately 95 My after the formation of the Solar System.

It has been suggested that other significant objects might have been created by the impact, which could have remained in orbit between Earth and the Moon, stuck in Lagrangian points. Such objects might have stayed within the Earth–Moon system for as long as 100 million years, until the gravitational tugs of other planets destabilised the system enough to free the objects. A study published in 2011 suggested that a subsequent collision between the Moon and one of these smaller bodies caused the notable differences in physical characteristics between the two hemispheres of the Moon. This collision, simulations have supported, would have been at a low enough velocity so as not to form a crater; instead, the material from the smaller body would have spread out across the Moon (in what would become its far side), adding a thick layer of highlands crust. The resulting mass irregularities would subsequently produce a gravity gradient that resulted in tidal locking of the Moon so that today, only the near side remains visible from Earth. However, mapping by the GRAIL mission has ruled out this scenario.

In 2019, a team at the University of Münster reported that the molybdenum isotopic composition in Earth's primitive mantle originates from the outer Solar System, hinting at the source of water on Earth. One possible explanation is that Theia originated in the outer Solar System.

Alternative hypotheses
Other mechanisms that have been suggested at various times for the Moon's origin are that the Moon was spun off from Earth's molten surface by centrifugal force; that it was formed elsewhere and was subsequently captured by Earth's gravitational field; or that Earth and the Moon formed at the same time and place from the same accretion disk. None of these hypotheses can account for the high angular momentum of the Earth–Moon system.

Another hypothesis attributes the formation of the Moon to the impact of a large asteroid with Earth much later than previously thought, creating the satellite primarily from debris from Earth. In this hypothesis, the formation of the Moon occurs 60–140 million years after the formation of the Solar System (as compared to hypothesized Theia impact at 4.527 ± 0.010 billion years). The asteroid impact in this scenario would have created a magma ocean on Earth and the proto-Moon with both bodies sharing a common plasma metal vapor atmosphere. The shared metal vapor bridge would have allowed material from Earth and the proto-Moon to exchange and equilibrate into a more common composition.

Yet another hypothesis proposes that the Moon and Earth formed together, not from the collision of once-distant bodies. This model, published in 2012 by Robin M. Canup, suggests that the Moon and Earth formed from a massive collision of two planetary bodies, each larger than Mars, which then re-collided to form what is now called Earth. After the re-collision, Earth was surrounded by a disk of material which accreted to form the Moon. This hypothesis could explain evidence that others do not.

title: Giant-impact hypothesis


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Scat singing

Originating in vocal jazz, scat singing or scatting is vocal improvisation with wordless vocables, nonsense syllables or without words at all. In scat singing, the singer improvises melodies and rhythms using the voice solely as an instrument rather than a speaking medium. This is different from vocalese, which uses recognizable lyrics that are sung to pre-existing instrumental solos.

Structure and syllable choice
Though scat singing is improvised, the melodic lines are often variations on scale and arpeggio fragments, stock patterns and riffs, as is the case with instrumental improvisers. As well, scatting usually incorporates musical structure. All of Ella Fitzgerald's scat performances of "How High the Moon", for instance, use the same tempo, begin with a chorus of a straight reading of the lyric, move to a "specialty chorus" introducing the scat chorus, and then the scat itself. Will Friedwald has compared Ella Fitzgerald to Chuck Jones directing his Roadrunner cartoon—each uses predetermined formulas in innovative ways.

The deliberate choice of scat syllables is also a key element in vocal jazz improvisation. Syllable choice influences the pitch, articulation, coloration, and resonance of the performance. Syllable choice also differentiated jazz singers' personal styles: Betty Carter was inclined to use sounds like "louie-ooie-la-la-la" (soft-tongued sounds or liquids) while Sarah Vaughan would prefer "shoo-doo-shoo-bee-ooo-bee" (fricatives, plosives, and open vowels). The choice of scat syllables can also be used to reflect the sounds of different instruments. The comparison of the scatting styles of Ella Fitzgerald and Sarah Vaughan reveals that Fitzgerald's improvisation mimics the sounds of swing-era big bands with which she performed, while Vaughan's mimics that of her accompanying bop-era small combos.

Humor and quotation
Humor is another important element of scat singing. Bandleader Cab Calloway exemplified the use of humorous scatting. Other examples of humorous scatting include Slim Gaillard, Leo Watson, and Bam Brown's 1945 song "Avocado Seed Soup Symphony," in which the singers scat variations on the word "avocado" for much of the recording.

In addition to such nonsensical uses of language, humor is communicated in scat singing through the use of musical quotation. Leo Watson, who performed before the canon of American popular music, frequently drew on nursery rhymes in his scatting. This is called using a compression. Similarly, Ella Fitzgerald's scatting, for example, drew extensively on popular music. In her 1960 recording of "How High the Moon" live in Berlin, she quotes over a dozen songs, including "The Peanut Vendor," "Heat Wave," "A-Tisket, A-Tasket," and "Smoke Gets in Your Eyes."

Origins
Improvisational singing of nonsense syllables occurs in many cultures, such as diddling or lilting in Ireland, German yodeling, Sámi joik, and speaking in tongues in various religious traditions.

Although Louis Armstrong's 1926 recording of "Heebie Jeebies" is often cited as the first modern song to employ scatting, there are many earlier examples. One early master of ragtime scat singing was Gene Greene who recorded scat choruses in his song "King of the Bungaloos" and several others between 1911 and 1917. Entertainer Al Jolson scatted through a few bars in the middle of his 1911 recording of "That Haunting Melody." Gene Greene's 1917 "From Here to Shanghai," which featured faux-Chinese scatting, and Gene Rodemich's 1924 "Scissor Grinder Joe" and "Some of These Days" also pre-date Armstrong. Cliff "Ukulele Ike" Edwards scatted an interlude on his 1923 "Old Fashioned Love" in lieu of using an instrumental soloist. One of the early female singers to use scat was Aileen Stanley, who included it at the end of a duet with Billy Murray in their hit 1924 recording of "It Had To Be You" (Victor 19373).

Jazz pianist Jelly Roll Morton credited Joe Sims of Vicksburg, Mississippi, as the creator of scat around the turn of the 20th century. In a conversation between Alan Lomax and Jelly Roll Morton, Morton recounted the history of scat: Lomax: "Well, what about some more scat songs, that you used to sing way back then?"

Morton: "Oh, I'll sing you some scat songs. That was way before Louis Armstrong's time. By the way, scat is something that a lot of people don't understand, and they begin to believe that the first scat numbers was ever done, was done by one of my hometown boys, Louis Armstrong. But I must take the credit away, since I know better. The first man that ever did a scat number in history of this country was a man from Vicksburg, Mississippi, by the name of Joe Sims, an old comedian. And from that, Tony Jackson and myself, and several more grabbed it in New Orleans. And found it was pretty good for an introduction of a song."

Lomax: "What does scat mean?"

Morton: "Scat doesn't mean anything but just something to give a song a flavor."

Morton also once boasted, "Tony Jackson and myself were using scat for novelty back in 1906 and 1907 when Louis Armstrong was still in the orphan's home." Don Redman and Fletcher Henderson also featured scat vocals in their 1925 recording of "My Papa Doesn't Two-Time No Time" five months prior to Armstrong's 1926 recording of "Heebie Jeebies."

Heebie Jeebies
It was Armstrong's February 1926 performance of "Heebie Jeebies," however, that is considered the turning point for the medium. From the 1926 recording of "Heebie Jeebies" arose the techniques that would form the foundation of modern scat. In a possibly apocryphal story, Armstrong claimed that, when he was recording "Heebie Jeebies" with his band The Hot Five, his sheet music fell off the stand and onto the ground. Not knowing the lyrics to the song, he invented a gibberish melody to fill time, expecting the cut to be thrown out in the end, but that take of the song was the one released:

""I dropped the paper with the lyrics—right in the middle of the tune. . . And I did not want to stop and spoil the record which was moving along so wonderfully. . . So when I dropped the paper, I immediately turned back into the horn and started to scatting. . . Just as nothing had happened. . . When I finished the record I just knew the recording people would throw it out. . . And to my surprise they all came running out of the controlling booth and said—'Leave That In.'""

Armstrong's "Heebie Jeebies" became a national bestseller and, consequently, the practice of scatting "became closely associated with Armstrong." The song would serve as a model for Cab Calloway, whose 1930s scat solos inspired George Gershwin's use of the medium in his 1935 opera Porgy and Bess.

Widespread adoption
Following the success of Armstrong's "Heebie Jeebies," a number of popular songs featured scat singing. In June 1927, Harry Barris and Bing Crosby of bandleader Paul Whiteman's "The Rhythm Boys" scatted on several songs including "Mississippi Mud," which Barris had composed.

On October 26, 1927, Duke Ellington's Orchestra recorded "Creole Love Call" featuring Adelaide Hall singing wordlessly. Hall's wordless vocals and "evocative growls" were hailed as serving as "another instrument." Although creativity must be shared between Ellington and Hall as he knew the style of performance he wanted, Hall was the one who was able to produce the sound. A year later, in October 1928, Ellington repeated the experiment in one of his versions of "The Mooche," with Getrude "Baby" Cox singing scat after a muted similar trombone solo by Joe "Tricky Sam" Nanton.

During the Great Depression, acts such as The Boswell Sisters regularly employed scatting on their records, including the high complexity of scatting at the same time, in harmony. An example is their version of "It Don't Mean a Thing (If It Ain't Got That Swing)." The Boswell Sisters' "inventive use of scat singing was a source for Ella Fitzgerald." As a young girl, Fitzgerald often practiced imitating Connee Boswell's scatting for hours.

Fitzgerald herself would become a talented scat singer and later claimed to be the "best vocal improviser jazz has ever had," and critics since then have been in almost universal agreement with her. During this 1930s era, other famous scat singers included Scatman Crothers —who would go on to movie and television fame —and British dance band trumpeter and vocalist Nat Gonella whose scat-singing recordings were banned in Nazi Germany.

Later development
Over the years, as jazz music developed and grew in complexity, scat singing did as well. During the bop era of the 1940s, more highly developed vocal improvisation surged in popularity. Annie Ross, a bop singer, expressed a common sentiment among vocalists at the time: "The [scat] music was so exciting, everyone wanted to do it." And many did: Eddie Jefferson, Betty Carter, Anita O'Day, Joe Carroll, Sarah Vaughan, Carmen McRae, Jon Hendricks, Babs Gonzales, Mel Torme and Dizzy Gillespie were all singers in the idiom.

Free jazz and the influence of world musicians on the medium pushed jazz singing nearer to avant-garde art music. In the 1960s Ward Swingle was the product of an unusually liberal musical education. He took the scat singing idea and applied it to the works of Bach, creating The Swingle Singers. Scat singing was also used by Louis Prima and others in the song "I Wan'na Be Like You" in Disney's The Jungle Book (1967).

The bop revival of the 1970s renewed interest in bop scat singing, and young scat singers viewed themselves as a continuation of the classic bop tradition. The medium continues to evolve, and vocal improvisation now often develops independently of changes in instrumental jazz.

During the mid-1990s, jazz artist John Paul Larkin (better known as Scatman John) renewed interest in the genre briefly when he began fusing jazz singing with pop music and electronica, scoring a world-wide hit with the song "Scatman (Ski Ba Bop Ba Dop Bop)" in 1994. Vocal improviser Bobby McFerrin's performances have shown that "wordless singing has traveled far from the concepts demonstrated by Louis Armstrong, Gladys Bentley, Cab Calloway, Anita O'Day, and Leo Watson."

Vocal bass
Vocal bass is a form of scat singing that is intended to vocally simulate instrumental basslines that are typically performed by bass players. A technique most commonly used by bass singers in a cappella groups is to simulate an instrumental rhythm section, often alongside a vocal percussionist or beatboxer. Some notable vocal bass artists are Tim Foust, Adam Chance, Bobby McFerrin, Al Jarreau, Reggie Watts, Alvin Chea, Joe Santoni, Avi Kaplan, Matt Sallee, Chris Morey, Geoff Castellucci.

Use in hip hop
Many hip hop artists and rappers use scat singing to come up with the rhythms of their raps. Tajai of the group Souls of Mischief states the following in the book How to Rap: "Sometimes my rhythms come from scatting. I usually make a scat kind of skeleton and then fill in the words. I make a skeleton of the flow first, and then I put words into it." The group Lifesavas describe a similar process. Rapper Tech N9ne has been recorded demonstrating exactly how this method works, and gangsta rapper Eazy-E used it extensively in his song "Eazy Street."

Historical theories

Some writers have proposed that scat has its roots in African musical traditions. In much African music, "human voice and instruments assume a kind of musical parity" and are "at times so close in timbre and so inextricably interwoven within the music's fabric as to be nearly indistinguishable." Dick Higgins likewise attributes scat singing to traditions of sound poetry in African-American music. In West African music, it is typical to convert drum rhythms into vocal melodies; common rhythmic patterns are assigned specific syllabic translations. However, this theory fails to account for the existence—even in the earliest recorded examples of scatting—of free improvisation by the vocalist. It is therefore more likely that scat singing evolved independently in the United States.

Others have proposed that scat singing arose from jazz musicians' practice of formulating riffs vocally before performing them instrumentally. (The adage "If you can't sing it, you can't play it" was common in the early New Orleans jazz scene. ) In this manner, soloists like Louis Armstrong became able to double as vocalists, switching effortlessly between instrumental solos and scatting.

Scat singing also resembles the Irish/Scottish practice of lilting or diddling, a type of vocal music that involves using nonsensical syllables to sing non-vocal dance tunes.

Critical assessment
Scat singing can allow jazz singers to have the same improvisational opportunities as jazz instrumentalists: scatting can be rhythmically and harmonically improvisational without concern about the lyric. Especially when bebop was developing, singers found scat to be the best way to adequately engage in the performance of jazz.

Scatting may be desirable because it does not "taint the music with the impurity of denotation." Instead of conveying linguistic content and pointing to something outside itself, scat music—like instrumental music—is self-referential and "d[oes] what it mean[s]." Through this wordlessness, commentators have written, scat singing can describe matters beyond words. Music critic Will Friedwald has written that Louis Armstrong's scatting, for example, "has tapped into his own core of emotion," releasing emotions "so deep, so real" that they are unspeakable; his words "bypass our ears and our brains and go directly for our hearts and souls."

Scat singing has never been universally accepted, even by jazz enthusiasts. Writer and critic Leonard Feather offers an extreme view; he once said that "scat singing—with only a couple exceptions—should be banned." He also wrote the lyrics to the jazz song "Whisper Not," which Ella Fitzgerald then recorded on her 1966 Verve release of the same name. Many jazz singers, including Bessie Smith, Billie Holiday, Jimmy Rushing, and Dinah Washington, have avoided scat entirely.

title: Scat singing