History of Central Asia

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Contemporary political map of Central Asia

The history of Central Asia concerns the history of the various peoples that have inhabited Central Asia. The lifestyle of such people has been determined primarily by the area's climate and geography. The aridity of the region makes agriculture difficult and distance from the sea cut it off from much trade. Thus, few major cities developed in the region. Nomadic horse peoples of the steppe dominated the area for millennia. 

Relations between the steppe nomads and the settled people in and around Central Asia were marked by conflict. The nomadic lifestyle was well suited to warfare, and the steppe horse riders became some of the most militarily potent people in the world, due to the devastating techniques and ability of their horse archers. Periodically, tribal leaders or changing conditions would cause several tribes to organize themselves into a single military force, which would then often launch campaigns of conquest, especially into more 'civilized' areas. A few of these types of tribal coalitions included the Huns' invasion of Europe, various Turkic migrations into Transoxiana, the Wu Hu attacks on China and most notably the Mongol conquest of much of Eurasia.

The dominance of the nomads ended in the 16th century as firearms allowed settled people to gain control of the region. The Russian Empire, the Qing dynasty of China, and other powers expanded into the area and seized the bulk of Central Asia by the end of the 19th century. After the Russian Revolution of 1917, the Soviet Union incorporated most of Central Asia; only Mongolia and Afghanistan remained nominally independent, although Mongolia existed as a Soviet satellite state and Soviet troops invaded Afghanistan in the late 20th century. The Soviet areas of Central Asia saw much industrialization and construction of infrastructure, but also the suppression of local cultures and a lasting legacy of ethnic tensions and environmental problems.

With the collapse of the Soviet Union in 1991, five Central Asian countries gained independence — Kazakhstan, Uzbekistan, Turkmenistan, Kyrgyzstan, and Tajikistan. In all of the new states, former Communist Party officials retained power as local strongmen.

Prehistory

Top image: The Sampul tapestry, a woolen wall hanging from Lop County, Hotan Prefecture, Xinjiang, China, showing a possibly Greek soldier from the Greco-Bactrian kingdom (250–125 BC), with blue eyes, wielding a spear, and wearing what appears to be a diadem headband; depicted above him is a centaur, from Greek mythology, a common motif in Hellenistic art
Bottom image: painted clay and alabaster head of a Zoroastrian priest wearing a distinctive Bactrian-style headdress, Takhti-Sangin, Tajikistan, 3rd–2nd century BC

 

A Sogdian silk brocade textile fragment, dated c. 700 AD (left image), and a Sogdian silver wine cup with mercury gilding, 7th century (right image)

 

Anatomically modern humans (Homo sapiens) reached Central Asia by 50,000 to 40,000 years ago. The Tibetan Plateau is thought to have been reached by 38,000 years ago. Populations who lived in Siberia during the Last Glacial Maximum have also contributed significantly to the populations of both Europe and the Americas.

The term Ceramic Mesolithic is used of late Mesolithic cultures of Central Asia, during the 6th to 5th millennia BC (in Russian archaeology, these cultures are described as Neolithic even though farming is absent). It is characterized by its distinctive type of pottery, with point or knob base and flared rims, manufactured by methods not used by the Neolithic farmers. The earliest manifestation of this type of pottery may be in the region around Lake Baikal in Siberia. It appears in the Elshan or Yelshanka or Samara culture on the Volga in Russia by about 7000 BC. and from there spread via the Dnieper-Donets culture to the Narva culture of the Eastern Baltic.

In the Pontic-Caspian steppe, Chalcolithic cultures develop in the second half of the 5th millennium BC, small communities in permanent settlements which began to engage in agricultural practices as well as herding. Around this time, some of these communities began the domestication of the horse. According to the Kurgan hypothesis, the north-west of the region is also considered to be the source of the root of the Indo-European languages. The horse-drawn chariot appears in the 3rd millennium BC, by 2000 BC, in the form of war chariots with spoked wheels, thus being made more maneuverable, and dominated the battlefields. The growing use of the horse, combined with the failure, roughly around 2000 BC, of the always precarious irrigation systems that had allowed for extensive agriculture in the region, gave rise and dominance of pastoral nomadism by 1000 BC, a way of life that would dominate the region for the next several millennia, giving rise to the Scythian expansion of the Iron Age. 

Scattered nomadic groups maintained herds of sheep, goats, horses, and camels, and conducted annual migrations to find new pastures (a practice known as transhumance). The people lived in yurts (or gers) – tents made of hides and wood that could be disassembled and transported. Each group had several yurts, each accommodating about five people.

While the semi-arid plains were dominated by the nomads, small city-states and sedentary agrarian societies arose in the more humid areas of Central Asia. The Bactria-Margiana Archaeological Complex of the early 2nd millennium BC was the first sedentary civilization of the region, practicing irrigation farming of wheat and barley and possibly a form of writing. Bactria-Margiana probably interacted with the contemporary Bronze Age nomads of the Andronovo culture, the originators of the spoke-wheeled chariot, who lived to their north in western Siberia, Russia, and parts of Kazakhstan, and survived as a culture until the 1st millennium BC. These cultures, particularly Bactria-Margiana, have been posited as possible representatives of the hypothetical Aryan culture ancestral to the speakers of the Indo-Iranian languages.

Later the strongest of Sogdian city-states of the Fergana Valley rose to prominence. After the 1st century BC, these cities became home to the traders of the Silk Road and grew wealthy from this trade. The steppe nomads were dependent on these settled people for a wide array of goods that were impossible for transient populations to produce. The nomads traded for these when they could, but because they generally did not produce goods of interest to sedentary people, the popular alternative was to carry out raids.

A wide variety of people came to populate the steppes. Nomadic groups in Central Asia included the Huns and other Turks, as well as Indo-Europeans such as the Tocharians, Persians, Scythians, Saka, Yuezhi, Wusun, and others, and a number of Mongol groups. Despite these ethnic and linguistic differences, the steppe lifestyle led to the adoption of very similar culture across the region.

Ancient era

Tetradrachm of the Greco-Bactrian King Eucratides (171–145 BC).

 

A monumental Sogdian wall mural of Samarkand, dated c. 650 AD, known as the Ambassadors' Painting, found in the hall of the ruin of an aristocratic house in Afrasiab, commissioned by the Sogdian king of Samarkand, Varkhuman

 

Two Buddhist monks on a mural of the Bezeklik Thousand Buddha Caves near Turpan, Xinjiang, China, 9th century AD; although Albert von Le Coq (1913) assumed the blue-eyed, red-haired monk was a Tocharian, modern scholarship has identified similar Caucasian figures of the same cave temple (No. 9) as ethnic Sogdians, an Eastern Iranian people who inhabited Turfan as an ethnic minority community during the phases of Tang Chinese (7th–8th century) and Uyghur rule (9th–13th century).

 

In the 2nd and 1st millennia BC, a series of large and powerful states developed on the southern periphery of Central Asia (the Ancient Near East). These empires launched several attempts to conquer the steppe people but met with only mixed success. The Median Empire and Achaemenid Empire both ruled parts of Central Asia. The Xiongnu Empire (209 BC-93 (156) AD) may be seen as the first central Asian empire which set an example for later Göktürk and Mongol empires. Xiongnu's ancestor Xianyu tribe founded Zhongshan state (c. 6th century BC – c. 296 BC) in Hebei province, China. The title chanyu was used by the Xiongnu rulers before Modun Chanyu so it is possible that statehood history of the Xiongnu began long before Modun's rule.

Following the success of the Han–Xiongnu War, Chinese states would also regularly strive to extend their power westwards. Despite their military might, these states found it difficult to conquer the whole region.

When faced by a stronger force, the nomads could simply retreat deep into the steppe and wait for the invaders to leave. With no cities and little wealth other than the herds they took with them, the nomads had nothing they could be forced to defend. An example of this is given by Herodotus's detailed account of the futile Persian campaigns against the Scythians. The Scythians, like most nomad empires, had permanent settlements of various sizes, representing various degrees of civilisation. The vast fortified settlement of Kamenka on the Dnieper River, settled since the end of the 5th century BC, became the centre of the Scythian kingdom ruled by Ateas, who lost his life in a battle against Philip II of Macedon in 339 BC.

Some empires, such as the Persian and Macedonian empires, did make deep inroads into Central Asia by founding cities and gaining control of the trading centres. Alexander the Great's conquests spread Hellenistic civilisation all the way to Alexandria Eschate (Lit. “Alexandria the Furthest”), established in 329 BC in modern Tajikistan. After Alexander's death in 323 BC, his Central Asian territory fell to the Seleucid Empire during the Wars of the Diadochi.

In 250 BC, the Central Asian portion of the empire (Bactria) seceded as the Greco-Bactrian Kingdom, which had extensive contacts with India and China until its end in 125 BC. The Indo-Greek Kingdom, mostly based in the Punjab region but controlling a fair part of Afghanistan, pioneered the development of Greco-Buddhism. The Kushan Kingdom thrived across a wide swath of the region from the 2nd century BC to the 4th century AD, and continued Hellenistic and Buddhist traditions. These states prospered from their position on the Silk Road linking China and Europe.

Likewise, in eastern Central Asia, the Chinese Han Dynasty expanded into the region at the height of its imperial power. From roughly 115 to 60 BC, Han forces fought the Xiongnu over control of the oasis city-states in the Tarim Basin. The Han was eventually victorious and established the Protectorate of the Western Regions in 60 BC, which dealt with the region's defence and foreign affairs. Chinese rule in Tarim Basin was replaced successively with Kushans and Hephthalites.

Later, external powers such as the Sassanid Empire would come to dominate this trade. One of those powers, the Parthian Empire, was of Central Asian origin, but adopted Persian-Greek cultural traditions. This is an early example of a recurring theme of Central Asian history: occasionally nomads of Central Asian origin would conquer the kingdoms and empires surrounding the region, but quickly merge into the culture of the conquered peoples.

At this time Central Asia was a heterogeneous region with a mixture of cultures and religions. Buddhism remained the largest religion, but was concentrated in the east. Around Persia, Zoroastrianism became important. Nestorian Christianity entered the area, but was never more than a minority faith. More successful was Manichaeism, which became the third largest faith.

Turkic expansion began in the 6th century; the Turkic speaking Uyghurs were one of many distinct cultural groups brought together by the trade of the Silk Route at Turfan, which was then ruled by China's Tang Dynasty. The Uyghurs, primarily pastoral nomads, observed a number of religions including Manichaeism, Buddhism, and Nestorian Christianity. Many of the artefacts from this period were found in the 19th century in this remote desert region.

Medieval

Sui and early Tang Dynasty

A Tang period gilt-silver jar, shaped in the style of northern nomad's leather bag decorated with a horse dancing with a cup of wine in its mouth, as the horses of Emperor Xuanzong were trained to do.

 

The monumental Sogdian wall murals of Panjakent (modern Tajikistan), showing cavalry and horse riders, dated c. 740 AD

 

It was during the Sui and Tang dynasties that China expanded into eastern Central Asia. Chinese foreign policy to the north and west now had to deal with Turkic nomads, who were becoming the most dominant ethnic group in Central Asia. To handle and avoid any threats posed by the Turks, the Sui government repaired fortifications and received their trade and tribute missions. They sent royal princesses off to marry Turkic clan leaders, a total of four of them in 597, 599, 614, and 617. The Sui stirred trouble and conflict amongst ethnic groups against the Turks.

As early as the Sui Dynasty, the Turks had become a major militarised force employed by the Chinese. When the Khitans began raiding north-east China in 605, a Chinese general led 20,000 Turks against them, distributing Khitan livestock and women to the Turks as a reward. On two occasions between 635 and 636, Tang royal princesses were married to Turk mercenaries or generals in Chinese service.

Throughout the Tang Dynasty until the end of 755, there were approximately ten Turkic generals serving under the Tang. While most of the Tang army was made of fubing(府兵) Chinese conscripts, the majority of the troops led by Turkic generals were of non-Chinese origin, campaigning largely in the western frontier where the presence of fubing(府兵) troops was low. Some "Turkic" troops were nomadisized Han Chinese, a desinicized people.

Civil war in China was almost totally diminished by 626, along with the defeat in 628 of the Ordos Chinese warlord Liang Shidu; after these internal conflicts, the Tang began an offensive against the Turks. In the year 630, Tang armies captured areas of the Ordos Desert, modern-day Inner Mongolia province, and southern Mongolia from the Turks.

After this military victory, Emperor Taizong won the title of Great Khan amongst the various Turks in the region who pledged their allegiance to him and the Chinese empire (with several thousand Turks traveling into China to live at Chang'an). On June 11, 631, Emperor Taizong also sent envoys to the Xueyantuo bearing gold and silk in order to persuade the release of enslaved Chinese prisoners who were captured during the transition from Sui to Tang from the northern frontier; this embassy succeeded in freeing 80,000 Chinese men and women who were then returned to China.

While the Turks were settled in the Ordos region (former territory of the Xiongnu), the Tang government took on the military policy of dominating the central steppe. Like the earlier Han Dynasty, the Tang Dynasty, along with Turkic allies like the Uyghurs, conquered and subdued Central Asia during the 640s and 650s. During Emperor Taizong's reign alone, large campaigns were launched against not only the Göktürks, but also separate campaigns against the Tuyuhun, and the Xueyantuo. Taizong also launched campaigns against the oasis states of the Tarim Basin, beginning with the annexation of Gaochang in 640. The nearby kingdom of Karasahr was captured by the Tang in 644 and the kingdom of Kucha was conquered in 649.

The expansion into Central Asia continued under Taizong's successor, Emperor Gaozong, who invaded the Western Turks ruled by the qaghan Ashina Helu in 657 with an army led by Su Dingfang. Ashina was defeated and the khaganate was absorbed into the Tang empire. The territory was administered through the Anxi Protectorate and the Four Garrisons of Anxi. Tang hegemony beyond the Pamir Mountains in modern Tajikistan and Afghanistan ended with revolts by the Turks, but the Tang retained a military presence in Xinjiang. These holdings were later invaded by the Tibetan Empire to the south in 670. For the remainder of the Tang Dynasty, the Tarim Basin alternated between Tang and Tibetan rule as they competed for control of Central Asia.

Tang rivalry with the Tibetan Empire

A lion motif on Sogdian polychrome silk, 8th century AD, most likely from Bukhara

 

The Tang Empire competed with the Tibetan Empire for control of areas in Inner and Central Asia, which was at times settled with marriage alliances such as the marrying of Princess Wencheng (d. 680) to Songtsän Gampo (d. 649). A Tibetan tradition mentions that after Songtsän Gampo's death in 649 AD, Chinese troops captured Lhasa. The Tibetan scholar Tsepon W. D. Shakabpa believes that the tradition is in error and that "those histories reporting the arrival of Chinese troops are not correct" and claims that the event is mentioned neither in the Chinese annals nor in the manuscripts of Dunhuang.

There was a long string of conflicts with Tibet over territories in the Tarim Basin between 670–692 and in 763 the Tibetans even captured the capital of China, Chang'an, for fifteen days during the An Shi Rebellion. In fact, it was during this rebellion that the Tang withdrew its western garrisons stationed in what is now Gansu and Qinghai, which the Tibetans then occupied along with the territory of what is now Xinjiang. Hostilities between the Tang and Tibet continued until they signed a formal peace treaty in 821. The terms of this treaty, including the fixed borders between the two countries, are recorded in a bilingual inscription on a stone pillar outside the Jokhang temple in Lhasa.

Islamic empires

In the 8th century, Islam began to penetrate the region, the desert nomads of Arabia could militarily match the nomads of the steppe, and the early Arab Empire gained control over parts of Central Asia. The early conquests under Qutayba ibn Muslim (705–715) were soon reversed by a combination of native uprisings and invasion by the Turgesh, but the collapse of the Turgesh khaganate after 738 opened the way for the re-imposition of Muslim authority under Nasr ibn Sayyar.

The Arab invasion also saw Chinese influence expelled from western Central Asia. At the Battle of Talas in 751 an Arab army decisively defeated a Tang Dynasty force, and for the next several centuries Middle Eastern influences would dominate the region. Large-scale Islamization however did not begin until the 9th century, running parallel with the fragmentation of Abbasid political authority and the emergence of local Iranian and Turkic dynasties like the Samanids.

Steppe empires

A map showing the major trade routes of Central Asia in the 13th century.

 

Mongol invasions and conquests seriously depopulated large areas of Muslim Central Asia

 

Over time, as new technologies were introduced, the nomadic horsemen grew in power. The Scythians developed the saddle, and by the time of the Alans the use of the stirrup had begun. Horses continued to grow larger and sturdier so that chariots were no longer needed as the horses could carry men with ease. This greatly increased the mobility of the nomads; it also freed their hands, allowing them to use the bow from horseback.

Using small but powerful composite bows, the steppe people gradually became the most powerful military force in the world. From a young age, almost the entire male population was trained in riding and archery, both of which were necessary skills for survival on the steppe. By adulthood, these activities were second nature. These mounted archers were more mobile than any other force at the time, being able to travel forty miles per day with ease.

The steppe peoples quickly came to dominate Central Asia, forcing the scattered city states and kingdoms to pay them tribute or face annihilation. The martial ability of the steppe peoples was limited, however, by the lack of political structure within the tribes. Confederations of various groups would sometimes form under a ruler known as a khan. When large numbers of nomads acted in unison they could be devastating, as when the Huns arrived in Western Europe. However, tradition dictated that any dominion conquered in such wars should be divided among all of the khan's sons, so these empires often declined as quickly as they formed.

Once the foreign powers were expelled, several indigenous empires formed in Central Asia. The Hephthalites were the most powerful of these nomad groups in the 6th and 7th century and controlled much of the region. In the 10th and 11th centuries the region was divided between several powerful states including the Samanid dynasty, that of the Seljuk Turks, and the Khwarezmid Empire.

The most spectacular power to rise out of Central Asia developed when Genghis Khan united the tribes of Mongolia. Using superior military techniques, the Mongol Empire spread to comprise all of Central Asia and China as well as large parts of Russia, and the Middle East. After Genghis Khan died in 1227, most of Central Asia continued to be dominated by the successor Chagatai Khanate. This state proved to be short lived, as in 1369 Timur, a Turkic leader in the Mongol military tradition, conquered most of the region.

Even harder than keeping a steppe empire together was governing conquered lands outside the region. While the steppe peoples of Central Asia found conquest of these areas easy, they found governing almost impossible. The diffuse political structure of the steppe confederacies was maladapted to the complex states of the settled peoples. Moreover, the armies of the nomads were based upon large numbers of horses, generally three or four for each warrior. Maintaining these forces required large stretches of grazing land, not present outside the steppe. Any extended time away from the homeland would thus cause the steppe armies to gradually disintegrate. To govern settled peoples the steppe peoples were forced to rely on the local bureaucracy, a factor that would lead to the rapid assimilation of the nomads into the culture of those they had conquered. Another important limit was that the armies, for the most part, were unable to penetrate the forested regions to the north; thus, such states as Novgorod and Muscovy began to grow in power.

In the 14th century much of Central Asia, and many areas beyond it, were conquered by Timur (1336–1405) who is known in the west as Tamerlane. It was during Timur's reign that the nomadic steppe culture of Central Asia fused with the settled culture of Iran. One of its consequences was an entirely new visual language that glorified Timur and subsequent Timurid rulers. This visual language was also used to articulate their commitment to Islam. Timur's large empire collapsed soon after his death, however. The region then became divided among a series of smaller Khanates, including the Khanate of Khiva, the Khanate of Bukhara, the Khanate of Kokand, and the Khanate of Kashgar.

Early modern period (16th to 19th centuries)

The lifestyle that had existed largely unchanged since 500 BCE began to disappear after 1500. Important changes to the world economy in the 14th and 15th century reflected the impact of the development of nautical technology. Ocean trade routes were pioneered by the Europeans, who had been cut off from the Silk Road by the Muslim states that controlled its western termini. The long-distance trade linking East Asia and India to Western Europe increasingly began to move over the seas and not through Central Asia. However, the emergence of Russia as a world power enabled Central Asia to continue its role as a conduit for overland trade of other sorts, now linking India with Russia on a north–south axis.

A native Turkmen man in traditional dress with his dromedary camel in Turkmenistan, c. 1915.

An even more important development was the introduction of gunpowder-based weapons. The gunpowder revolution allowed settled peoples to defeat the steppe horsemen in open battle for the first time. Construction of these weapons required the infrastructure and economies of large societies and were thus impractical for nomadic peoples to produce. The domain of the nomads began to shrink as, beginning in the 15th century, the settled powers gradually began to conquer Central Asia.

The last steppe empire to emerge was that of the Dzungars who conquered much of East Turkestan and Mongolia. However, in a sign of the changed times they proved unable to match the Chinese and were decisively defeated by the forces of the Qing Dynasty. In the 18th century the Qing emperors, themselves originally from the far eastern edge of the steppe, campaigned in the west and in Mongolia, with the Qianlong Emperor taking control of Xinjiang in 1758. The Mongol threat was overcome and much of Inner Mongolia was annexed to China.

The Chinese dominions stretched into the heart of Central Asia and included the Khanate of Kokand, which paid tribute to Beijing. Outer Mongolia and Xinjiang did not become provinces of the Chinese empire, but rather were directly administered by the Qing dynasty. The fact that there was no provincial governor meant that the local rulers retained most of their powers and this special status also prevented emigration from the rest of China into the region. Persia also began to expand north, especially under the rule of Nadir Shah, who extended Persian dominion well past the Oxus. After his death, however, the Persian empire rapidly crumbled.

Russian expansion into Central Asia (19th century)

Russian wars of conquest in Turkestan

The Russians also expanded south, first with the transformation of the Ukrainian steppe into an agricultural heartland, and subsequently onto the fringe of the Kazakh steppes, beginning with the foundation of the fortress of Orenburg. The slow Russian conquest of the heart of Central Asia began in the early 19th century, although Peter the Great had sent a failed expedition under Prince Bekovitch-Cherkassky against Khiva as early as the 1720s.

By the 1800s, the locals could do little to resist the Russian advance, although the Kazakhs of the Great Horde under Kenesary Kasimov rose in rebellion from 1837–46. Until the 1870s, for the most part, Russian interference was minimal, leaving native ways of life intact and local government structures in place. With the conquest of Turkestan after 1865 and the consequent securing of the frontier, the Russians gradually expropriated large parts of the steppe and gave these lands to Russian farmers, who began to arrive in large numbers. This process was initially limited to the northern fringes of the steppe and it was only in the 1890s that significant numbers of Russians began to settle farther south, especially in Zhetysu (Semirechye).

The Great Game

Russian campaigns

Prisoners in a zindan, a traditional Central Asian prison, in the Bukharan Protectorate under Imperial Russia, ca. 1910

 

The forces of the khanates were poorly equipped and could do little to resist Russia's advances, although the Kokandian commander Alimqul led a quixotic campaign before being killed outside Chimkent. The main opposition to Russian expansion into Turkestan came from the British, who felt that Russia was growing too powerful and threatening the northwest frontiers of British India. This rivalry came to be known as The Great Game, where both powers competed to advance their own interests in the region. It did little to slow the pace of conquest north of the Oxus, but did ensure that Afghanistan remained independent as a buffer state between the two Empires.

After the fall of Tashkent to General Cherniaev in 1865, Khodjend, Djizak, and Samarkand fell to the Russians in quick succession over the next three years as the Khanate of Kokand and the Emirate of Bukhara were repeatedly defeated. In 1867 the Governor-Generalship of Russian Turkestan was established under General Konstantin Petrovich Von Kaufman, with its headquarters at Tashkent. In 1881–85 the Transcaspian region was annexed in the course of a campaign led by Generals Mikhail Annenkov and Mikhail Skobelev, and Ashkhabad (from Persia), Merv and Pendjeh (from Afghanistan) all came under Russian control. 

Russian expansion was halted in 1887 when Russia and Great Britain delineated the northern border of Afghanistan. Bukhara and the Khanate of Khiva remained quasi-independent, but were essentially protectorates along the lines of the Princely States of British India. Although the conquest was prompted by almost purely military concerns, in the 1870s and 1880s Turkestan came to play a reasonably important economic role within the Russian Empire.

Because of the American Civil War, cotton shot up in price in the 1860s, becoming an increasingly important commodity in the region, although its cultivation was on a much lesser scale than during the Soviet period. The cotton trade led to improvements: the Transcaspian Railway from Krasnovodsk to Samarkand and Tashkent, and the Trans-Aral Railway from Orenburg to Tashkent were constructed. In the long term the development of a cotton monoculture would render Turkestan dependent on food imports from Western Siberia, and the Turkestan-Siberia Railway was already planned when the First World War broke out.

Russian rule still remained distant from the local populace, mostly concerning itself with the small minority of Russian inhabitants of the region. The local Muslims were not considered full Russian citizens. They did not have the full privileges of Russians, but nor did they have the same obligations, such as military service. The Tsarist regime left substantial elements of the previous regimes (such as Muslim religious courts) intact, and local self-government at the village level was quite extensive.

Qing Dynasty

During the 17th and 18th centuries the Qing Dynasty made several campaigns to conquer the Dzungar Mongols. In the meantime, they incorporated parts of Central Asia into the Chinese Empire. Internal turmoil largely halted Chinese expansion in the 19th century. In 1867 Yakub Beg led a rebellion that saw Kashgar declaring its independence as the Taiping and Nian Rebellions in the heartland of the Empire prevented the Chinese from reasserting their control.

Instead, the Russians expanded, annexing the Chu and Ili Valleys and the city of Kuldja from the Chinese Empire. After Yakub Beg's death at Korla in 1877 his state collapsed as the area was reconquered by China. After lengthy negotiations Kuldja was returned to Beijing by Russia in 1884.

Revolution and revolt

During the First World War the Muslim exemption from conscription was removed by the Russians, sparking the Central Asian Revolt of 1916. When the Russian Revolution of 1917 occurred, a provisional Government of Jadid Reformers, also known as the Turkestan Muslim Council met in Kokand and declared Turkestan's autonomy. This new government was quickly crushed by the forces of the Tashkent Soviet, and the semi-autonomous states of Bukhara and Khiva were also invaded. The main independence forces were rapidly crushed, but guerrillas known as basmachi continued to fight the Communists until 1924. Mongolia was also swept up by the Russian Revolution and, though it never became a Soviet republic, it became a communist People's Republic in 1924.

The creation of the Republic of China in 1911 and the general turmoil in China affected the Qing Dynasty's holdings in Central Asia. Republic of China's control of the region was relegated to southern Xinjiang and there was a dual threat from Islamic separatists and communists. Eventually the region became largely independent under the control of the provincial governor. Rather than invade, the Soviet Union established a network of consulates in the region and sent aid and technical advisors.

By the 1930s, the governor of Xinjiang's relationship with Moscow was far more important than that with Nanking. The Chinese Civil War further destabilised the region and saw Turkic nationalists make attempts at independence. In 1933, the First East Turkestan Republic was declared, but it was destroyed soon after with the aid of the Soviet troops.

After the German invasion of the Soviet Union in 1941, Governor Sheng Shicai of Xinjiang gambled and broke his links to Moscow, moving to ally himself with the Kuomintang. This led to a civil war within the region. Sheng was eventually forced to flee and the Soviet-backed Second East Turkestan Republic was formed in northern Dzungaria, while the Republic of China retained control of southern Xinjiang. Both states were annexed by the People's Republic of China in 1949.

Soviet era (1918–1991)

After being conquered by Bolshevik forces, Soviet Central Asia experienced a flurry of administrative reorganisation. In 1918 the Bolsheviks set up the Turkestan Autonomous Soviet Socialist Republic, and Bukhara and Khiva also became SSRs. In 1919 the Conciliatory Commission for Turkestan Affairs was established, to try to improve relations between the locals and the Communists. New policies were introduced, respecting local customs and religion. In 1920, the Kirghiz Autonomous Soviet Socialist Republic, covering modern Kazakhstan, was set up. It was renamed the Kazakh Autonomous Soviet Socialist Republic in 1925. In 1924, the Soviets created the Uzbek SSR and the Turkmen SSR. In 1929 the Tajik SSR was split from the Uzbek SSR. The Kyrgyz Autonomous Oblast became an SSR in 1936.

These borders had little to do with ethnic make-up, but the Soviets felt it important to divide the region. They saw both Pan-Turkism and Pan-Islamism as threats, which dividing Turkestan would limit. Under the Soviets, the local languages and cultures were systematised and codified, and their differences clearly demarcated and encouraged. New Cyrillic writing systems were introduced, to break links with Turkey and Iran. Under the Soviets the southern border was almost completely closed and all travel and trade was directed north through Russia.

During the period of forced collectivisation under Joseph Stalin at least a million persons died, mostly in the Kazakh SSR. Islam, as well as other religions, were also attacked. In the Second World War several million refugees and hundreds of factories were moved to the relative security of Central Asia; and the region permanently became an important part of the Soviet industrial complex. Several important military facilities were also located in the region, including nuclear testing facilities and the Baikonur Cosmodrome. The Virgin Lands Campaign, starting in 1954, was a massive Soviet agricultural resettlement program that brought more than 300,000 individuals, mostly from the Ukraine, to the northern Kazakh SSR and the Altai region of the Russian SFSR. This was a major change in the ethnicity of the region.

Similar processes occurred in Xinjiang and the rest of Western China where the PRC quickly established control from the Second East Turkestan Republic that controlled northern Xinjiang and the Republic of China forces that controlled southern Xinjiang after the Qing Dynasty. The area was subject to a number of development schemes and, like Soviet Central Asia, one focus was on the growing of the cotton cash crop. These efforts were overseen by the Xinjiang Production and Construction Corps. The XPCC also encouraged Han Chinese to return to Xinjiang after many had migrated out during the Muslim revolts against the Qing Dynasty.

Political turmoil has led to major demographic shifts in the region: During the Qing Dynasty there were 60% Turkic and 30% Han Chinese in the region, after the Muslim revolts the percentage of Han Chinese dropped to as low as 7%, and by the year 2000 some 40% of the population of Xinjiang were Han. As with the Soviet Union local languages and cultures were mostly encouraged and Xinjiang was granted autonomous status. However, Islam was much persecuted, especially during the Cultural Revolution. Many people from other parts of China fled to Xinjiang due to the failed agricultural policies of the Great Leap Forward in other provinces. However, the Great Leap Forward did not affect much of Xinjiang due to its geographical isolation from other parts of China.

Soviet Evacuation and Population Deportations During World War II

The Second World War sparked the widespread migration of Soviet citizens to the rear of the USSR. Much of this movement was directed to Soviet Central Asia. These migrations included official, state-organised evacuations and deportations as well as the non-sanctioned, panicked flight from the front by both general citizenry and important officials. The evacuation of Soviet citizens and industry during World War II was an essential element of their overall success in the war, and Central Asia served as a main destination for evacuees.

The German invasion of the Soviet Union began on June 22, 1941. A decree from the Presidium of the Executive Committee on the same day forbade the entry or exit from the USSR's border regions, which were under a state of martial law. Such mandates demonstrated the Soviets' fear of spreading panic and their commitment to asserting direct state control over wartime relocations to maintain order. Soviet wartime population policy consisted of two distinct operations: deportation and evacuation. Deportation aimed to clear regions near the front of potentially insidious anti-Soviet elements that could hamper the war effort, while evacuation policy aimed to move Soviet industry and intelligentsia to the rear, where they would be safe.

Deportations along ethnic lines

Soviet officials organised their wartime deportation policy largely along ethnic lines. As a response to the German invasion, Soviet citizens of German descent in border regions were targeted for deportation to the rear where Soviet authorities had no need to worry of their conspiring with the enemy. Such dubious ethnically-derived logic was not reserved for Germans. Many Finns were also forcibly relocated in the first year of the war simply for their heritage, though they were mainly sent to remote areas in the northern rear, such as Siberia, rather than Central Asia. A large portion of the German deportees, however, were sent to Kazakhstan. The remobilisation of relocated human resources into the labour force was pivotal to Soviet wartime production policy, and to that end many able-bodied deportees were conscripted into a “labour army” with military style discipline.

By early 1942 as many as 20,800 ethnic Germans had been organised into battalions in this labour army, though this number would grow to as much as 222,000 by early 1944 as conscription criteria were broadened. The NKVD employed about 101,000 members of the labour army at construction sites to develop infrastructure for the war effort. Those who were not assigned to the labour army were used for timber harvesting, the construction of railways and other infrastructure, or sent to collective farms.

As the tide turned in the war, and the Soviets began to reclaim the territories they lost to the initial German advance, they began a new wave of deportations of unfavoured ethnic groups. Karachais, Kalmyks, Chechens, Ingushetians, Kabardians, and Crimean Tatars were all deported to Central Asia for their supposed fraternisation with occupying German forces. These groups were sent mostly to Kazakhstan, Kyrgyzstan, and Uzbekistan for their infidelity. These punitive deportations were also conducted to keep “anti-Soviet elements” far from the border – where the Soviet offensive against Germany was progressing – for fear of spying or sabotage.

Evacuation of Soviet citizens to Central Asia

Many Soviet citizens ended up in Central Asia during World War II, not as a result of deportation, but evacuation. The evacuation focused on the movement of critical wartime industry and the factory workers responsible for overseeing such production. Whole factories and their employees were moved together via railway eastward to cities like Tashkent, which received a lion's share of the evacuees.

The initial attempts at evacuation while the war was still in its early stages through early 1942 were a far cry from the organised affair that the Soviet central bureaucracy envisaged. Throughout the summer and fall of 1941, numerous Soviet frontier cities evacuated in a haphazard and panicked fashion before the German onslaught. A number of factors led to this lack of organisation. For one, the Soviet evacuation plans were thrown together fairly hurriedly, and a lot of the logistical planning was done on the fly as the German advance was already sweeping through the Soviet border zone. The German invasion also hampered the effectiveness of the Soviet response by shattering their communications in the war's early stages; many Soviet leaders were unable to gather reliable information about the positions of German forces until it was too late to effect an orderly evacuation.

There was also a desire on the part of Soviet officials to forestall any evacuations until it was absolutely necessary, the marching orders were often to continue factory production until the eve of occupation before hurriedly dismantling and transporting factory equipment, and destroying what couldn't be moved in time. As a result of the delay in evacuations, they were often carried out under German aerial bombardment, which led to additional confusion among the frightened citizenry. Historian Rebecca Manley describes these early evacuations as being charactered by “three phenomena: the 'flight' of officials, the flight of the population, and 'panic'”.

The early flight of Soviet officials who were supposed to manage the evacuation was roundly condemned by Soviet leaders, but often their retreat resulted from a realisation that evacuation procedures had started too late, and that there was no way to effectively execute it. Additionally, Soviet officials who remained in a city captured by German forces feared execution by Nazis on the hunt for communists. Avoiding that, the officials knew that they would be subject to intense interrogation as to what happened by suspicious Soviets upon returning to the fold.

Despite these setbacks in the implementation of evacuation policy early in the war, around 12 million Soviet citizens successfully evacuated in 1941, even if a number of these were the result of disorganised, “spontaneous self-evacuation,” and another 4.5 million evacuated the following year. In addition, the factories that were successfully evacuated to the Central Asian rear would help provide the productive capacity the Soviets needed to eventually win the war, as well as preventing the Germans from acquiring additional industrial resources. By providing a safe haven from the German advance for Soviet citizens, Central Asia played a critical role in securing Allied victory. The evacuation itself was only part of the difficulty, however, as evacuees arriving in Central Asia faced many trials and tribulations.

Due to the haphazard nature of evacuation, many labourers did not arrive with their factory, and had to find labour on their own, though jobs were hard to come by. Additionally, cities like Tashkent became overwhelmed at the sheer volume of people arriving at its gates and had great difficulty supplying the food and shelter necessary for evacuees. Upon arrival, many evacuees died of illness or starvation in extreme poverty in Central Asia. Uzbek officials set up aid stations at Tashkent, which were mirrored at other railway stations to help combat the poverty, but they could only do so much as little could be spared economically for the war effort. Despite these troubles, the ability of Central Asia to absorb Soviet industry and population to the extent that it did and in the harried manner that it did was impressive. The Germans certainly didn't foresee the preparedness of Soviet Central Asia, and in the end they paid dearly for it.

Since 1991

From 1988 to 1992, a free press and multi-party system developed in the Central Asian republics as perestroika pressured the local Communist parties to open up. What Svat Soucek calls the "Central Asian Spring" was very short-lived, as soon after independence former Communist Party officials recast themselves as local strongmen. Political stability in the region has mostly been maintained, with the major exception of the Tajik Civil War that lasted from 1992 to 1997. 2005 also saw the largely peaceful ousting of Kyrgyz president Askar Akayev in the Tulip Revolution and an outbreak of violence in Andijan, Uzbekistan. 

The independent states of Central Asia with their Soviet-drawn borders.

Much of the population of Soviet Central Asia was indifferent to the collapse of the Soviet Union, even the large Russian populations in Kazakhstan (roughly 40% of the total) and Tashkent, Uzbekistan. Aid from the Kremlin had also been central to the economies of Central Asia, each of the republics receiving massive transfers of funds from Moscow.

Independence largely resulted from the efforts of the small groups of nationalistic, mostly local intellectuals, and from little interest in Moscow for retaining the expensive region. While never a part of the Soviet Union, Mongolia followed a somewhat similar path. Often acting as the unofficial sixteenth Soviet republic, it shed the communist system only in 1996, but quickly ran into economic problems. See: History of independent Mongolia.

The economic performance of the region since independence has been mixed. It contains some of the largest reserves of natural resources in the world, but there are important difficulties in transporting them. Since it lies farther from the ocean than anywhere else in the world, and its southern borders lay closed for decades, the main trade routes and pipelines run through Russia. As a result, Russia still exerts more influence over the region than in any other former Soviet republics. Nevertheless, the rising energy importance of the Caspian Sea entails a great involvement in the region by the US. The former Soviet republics of the Caucasus now have their own US Special Envoy and inter-agency working groups. Former US Secretary of Energy Bill Richardson had claimed that "the Caspian region will hopefully save us [the US] from total dependence on Middle East oil".

Some analysts, such as Myers Jaffe and Robert A. Manning, estimate however that US' entry into the region (with initiatives such as the US-favored Baku-Tbilisi-Ceyhan pipeline) as a major actor may complicate Moscow's chances of making a decisive break with its past economic mistakes and geopolitical excesses in Central Asia. They also regard as a myth the assertion that Caspian oil and gas will be a cheaper and more secure alternative to supplies from the Persian Gulf.

Despite these reservations and fears, since the late 1980s, Azerbaijan, Kazakhstan, and Turkmenistan have gradually moved to centre stage in the global energy markets and are now regarded as key factors of the international energy security. Azerbaijan and Kazakhstan in particular have succeeded in attracting massive foreign investment to their oil and gas sectors. According to Gawdat Bahgat, the investment flow suggests that the geological potential of the Caspian region as a major source of oil and gas is not in doubt.

Russia and Kazakhstan started a closer energy co-operation in 1998, which was further consolidated in May 2002, when Presidents Vladimir Putin and Nursultan Nazarbayev signed a protocol dividing three gas fields – Kurmangazy, Tsentralnoye, and Khvalynskoye – on an equal basis. Following the ratification of bilateral treaties, Russia, Kazakhstan and Azerbaijan declared that the northern Caspian was open for business and investment as they had reached a consensus on the legal status of the basin. Iran and Turkmenistan refused however to recognise the validity of these bilateral agreements; Iran is rejecting any bilateral agreement to divide the Caspian. On the other hand, US' choices in the region (within the framework of the so-called "pipeline diplomacy"), such as the strong support of the Baku pipeline (the project was eventually approved and was completed in 2005), reflect a political desire to avoid both Russia and Iran.

Increasingly, other powers have begun to involve themselves in Central Asia. Soon after the Central Asian states won their independence, Turkey began to look east, and a number of organizations are attempting to build links between the western and eastern Turks. Iran, which for millennia had close links with the region, has also been working to build ties and the Central Asian states now have good relations with the Islamic Republic. One important player in the new Central Asia has been Saudi Arabia, which has been funding the Islamic revival in the region. Olcott notes that soon after independence Saudi money paid for massive shipments of Qur'ans to the region and for the construction and repair of a large number of mosques. In Tajikistan alone an estimated 500 mosques per year have been erected with Saudi money.

The formerly atheistic Communist Party leaders have mostly converted to Islam. Small Islamist groups have formed in several of the countries, but radical Islam has little history in the region; the Central Asian societies have remained largely secular and all five states enjoy good relations with Israel. Central Asia is still home to a large Jewish population, the largest group being the Bukharan Jews, and important trade and business links have developed between those that left for Israel after independence and those remaining. 

The People's Republic of China sees the region as an essential future source of raw materials; most Central Asian countries are members of the Shanghai Cooperation Organization. This has affected Xinjiang and other parts of western China that have seen infrastructure programs building new links and also new military facilities. Chinese Central Asia has been far from the centre of that country's economic boom and the area has remained considerably poorer than the coast. China also sees a threat in the potential of the new states to support separatist movements among its own Turkic minorities. 

One important Soviet legacy that has only gradually been appreciated is the vast ecological destruction. Most notable is the gradual drying of the Aral Sea. During the Soviet era, it was decided that the traditional crops of melons and vegetables would be replaced by water-intensive growing of cotton for Soviet textile mills. Massive irrigation efforts were launched that diverted a considerable percentage of the annual inflow to the sea, causing it to shrink steadily. Furthermore, vast tracts of Kazakhstan were used for nuclear testing, and there exists a plethora of decrepit factories and mines.

In the first part of 2008 Central Asia experienced a severe energy crisis, a shortage of both electricity and fuel, aggravated by abnormally cold temperatures, failing infrastructure, and a shortage of food in which aid from the west began to assist the region.

As of 2019, despite its common cultural and historical past Central Asia has been "one of the least integrated regions in the world".

Newcomb's paradox

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Newcomb%27s_paradox 

 

In philosophy and mathematics, Newcomb's paradox, also referred to as Newcomb's problem, is a thought experiment involving a game between two players, one of whom is able to predict the future.
Newcomb's paradox was created by William Newcomb of the University of California's Lawrence Livermore Laboratory. However, it was first analyzed in a philosophy paper by Robert Nozick in 1969, and appeared in the March 1973 issue of Scientific American, in Martin Gardner's "Mathematical Games." Today it is a much debated problem in the philosophical branch of decision theory.

The problem

There is an infallible predictor, a player, and two boxes designated A and B. The player is given a choice between taking only box B, or taking both boxes A and B. The player knows the following:^[4]

• Box A is clear, and always contains a visible $1,000.
• Box B is opaque, and its content has already been set by the predictor:
  • If the predictor has predicted the player will take both boxes A and B, then box B contains nothing.
  • If the predictor has predicted that the player will take only box B, then box B contains $1,000,000.

The player does not know what the predictor predicted or what box B contains while making his/her choice.

Game theory strategies

Predicted choice	Actual choice	Payout
A + B	A + B	$1,000
A + B	B	$0
B	A + B	$1,001,000
B	B	$1,000,000

In his 1969 article, Nozick noted that "To almost everyone, it is perfectly clear and obvious what should be done. The difficulty is that these people seem to divide almost evenly on the problem, with large numbers thinking that the opposing half is just being silly." The problem continues to divide philosophers today.

Game theory offers two strategies for this game that rely on different principles: the expected utility principle and the strategic dominance principle. The problem is called a paradox because two analyses that both sound intuitively logical give conflicting answers to the question of what choice maximizes the player's payout.

• Considering the expected utility when the probability of the predictor being right is almost certain or certain, the player should choose box B. This choice statistically maximizes the player's winnings, setting them at about $1,000,000 per game.
• Under the dominance principle, the player should choose the strategy that is always better; choosing both boxes A and B will always yield $1,000 more than only choosing B. However, the expected utility of "always $1,000 more than B" depends on the statistical payout of the game; when the predictor's prediction is almost certain or certain, choosing both A and B sets player's winnings at about $1,000 per game.

David Wolpert and Gregory Benford point out that paradoxes arise when not all relevant details of a problem are specified, and there is more than one "intuitively obvious" way to fill in those missing details. They suggest that in the case of Newcomb's paradox, the conflict over which of the two strategies is "obviously correct" reflects the fact that filling in the details in Newcomb's problem can result in two different noncooperative games, and each of the strategies is reasonable for one game but not the other. They then derive the optimal strategies for both of the games, which turn out to be independent of the predictor's infallibility, questions of causality, determinism, and free will.

Causality and free will

Predicted choice	Actual choice	Payout
A + B	A + B	$1,000
B	B	$1,000,000

Causality issues arise when the predictor is posited as infallible and incapable of error; Nozick avoids this issue by positing that the predictor's predictions are "almost certainly" correct, thus sidestepping any issues of infallibility and causality. Nozick also stipulates that if the predictor predicts that the player will choose randomly, then box B will contain nothing. This assumes that inherently random or unpredictable events would not come into play anyway during the process of making the choice, such as free will or quantum mind processes. However, these issues can still be explored in the case of an infallible predictor. Under this condition, it seems that taking only B is the correct option. This analysis argues that we can ignore the possibilities that return $0 and $1,001,000, as they both require that the predictor has made an incorrect prediction, and the problem states that the predictor is never wrong. Thus, the choice becomes whether to take both boxes with $1,000 or to take only box B with $1,000,000—so taking only box B is always better.

William Lane Craig has suggested that, in a world with perfect predictors (or time machines, because a time machine could be used as a mechanism for making a prediction), retrocausality can occur. If a person truly knows the future, and that knowledge affects their actions, then events in the future will be causing effects in the past. The chooser's choice will have already caused the predictor's action. Some have concluded that if time machines or perfect predictors can exist, then there can be no free will and choosers will do whatever they're fated to do. Taken together, the paradox is a restatement of the old contention that free will and determinism are incompatible, since determinism enables the existence of perfect predictors. Put another way, this paradox can be equivalent to the grandfather paradox; the paradox presupposes a perfect predictor, implying the "chooser" is not free to choose, yet simultaneously presumes a choice can be debated and decided. This suggests to some that the paradox is an artifact of these contradictory assumptions.

Gary Drescher argues in his book Good and Real that the correct decision is to take only box B, by appealing to a situation he argues is analogous—a rational agent in a deterministic universe deciding whether or not to cross a potentially busy street.

Andrew Irvine argues that the problem is structurally isomorphic to Braess' paradox, a non-intuitive but ultimately non-paradoxical result concerning equilibrium points in physical systems of various kinds.

Simon Burgess has argued that the problem can be divided into two stages: the stage before the predictor has gained all the information on which the prediction will be based, and the stage after it. While the player is still in the first stage, they are presumably able to influence the predictor's prediction, for example by committing to taking only one box. Burgess argues that after the first stage is done, the player can decide to take both boxes A and B without influencing the predictor, thus reaching the maximum payout. This assumes that the predictor cannot predict the player's thought process in the second stage, and that the player can change their mind at the second stage without influencing the predictor's prediction. Burgess says that given his analysis, Newcomb's problem is akin to the toxin puzzle. This is because both problems highlight the fact that one can have a reason to intend to do something without having a reason to actually do it.

Consciousness

Newcomb's paradox can also be related to the question of machine consciousness, specifically if a perfect simulation of a person's brain will generate the consciousness of that person. Suppose we take the predictor to be a machine that arrives at its prediction by simulating the brain of the chooser when confronted with the problem of which box to choose. If that simulation generates the consciousness of the chooser, then the chooser cannot tell whether they are standing in front of the boxes in the real world or in the virtual world generated by the simulation in the past. The "virtual" chooser would thus tell the predictor which choice the "real" chooser is going to make.

Fatalism

Newcomb's paradox is related to logical fatalism in that they both suppose absolute certainty of the future. In logical fatalism, this assumption of certainty creates circular reasoning ("a future event is certain to happen, therefore it is certain to happen"), while Newcomb's paradox considers whether the participants of its game are able to affect a predestined outcome.

Extensions to Newcomb's problem

Many thought experiments similar to or based on Newcomb's problem have been discussed in the literature. For example, a quantum-theoretical version of Newcomb's problem in which box B is entangled with box A has been proposed.

The meta-Newcomb problem

Another related problem is the meta-Newcomb problem. The setup of this problem is similar to the original Newcomb problem. However, the twist here is that the predictor may elect to decide whether to fill box B after the player has made a choice, and the player does not know whether box B has already been filled. There is also another predictor: a "meta-predictor" who has reliably predicted both the players and the predictor in the past, and who predicts the following: "Either you will choose both boxes, and the predictor will make its decision after you, or you will choose only box B, and the predictor will already have made its decision."

In this situation, a proponent of choosing both boxes is faced with the following dilemma: if the player chooses both boxes, the predictor will not yet have made its decision, and therefore a more rational choice would be for the player to choose box B only. But if the player so chooses, the predictor will already have made its decision, making it impossible for the player's decision to affect the predictor's decision.

Ensemble interpretation

From Wikipedia, the free encyclopedia

 https://en.wikipedia.org/wiki/Ensemble_interpretation

 

The ensemble interpretation of quantum mechanics considers the quantum state description to apply only to an ensemble of similarly prepared systems, rather than supposing that it exhaustively represents an individual physical system.

The advocates of the ensemble interpretation of quantum mechanics claim that it is minimalist, making the fewest physical assumptions about the meaning of the standard mathematical formalism. It proposes to take to the fullest extent the statistical interpretation of Max Born, for which he won the Nobel Prize in Physics. For example, a new version of the ensemble interpretation that relies on a new formulation of probability theory was introduced by Raed Shaiia, which showed that the laws of quantum mechanics are the inevitable result of this new formulation. On the face of it, the ensemble interpretation might appear to contradict the doctrine proposed by Niels Bohr, that the wave function describes an individual system or particle, not an ensemble, though he accepted Born's statistical interpretation of quantum mechanics. It is not quite clear exactly what kind of ensemble Bohr intended to exclude, since he did not describe probability in terms of ensembles. The ensemble interpretation is sometimes, especially by its proponents, called "the statistical interpretation", but it seems perhaps different from Born's statistical interpretation.

As is the case for "the" Copenhagen interpretation, "the" ensemble interpretation might not be uniquely defined. In one view, the ensemble interpretation may be defined as that advocated by Leslie E. Ballentine, Professor at Simon Fraser University. His interpretation does not attempt to justify, or otherwise derive, or explain quantum mechanics from any deterministic process, or make any other statement about the real nature of quantum phenomena; it intends simply to interpret the wave function. It does not propose to lead to actual results that differ from orthodox interpretations. It makes the statistical operator primary in reading the wave function, deriving the notion of a pure state from that. In the opinion of Ballentine, perhaps the most notable supporter of such an interpretation was Albert Einstein:

The attempt to conceive the quantum-theoretical description as the complete description of the individual systems leads to unnatural theoretical interpretations, which become immediately unnecessary if one accepts the interpretation that the description refers to ensembles of systems and not to individual systems.

— Albert Einstein

Nevertheless, one may doubt as to whether Einstein, over the years, had in mind one definite kind of ensemble.

Meaning of "ensemble" and "system"

Perhaps the first expression of an ensemble interpretation was that of Max Born. In a 1968 article, he used the German words 'Haufen gleicher', which are often translated into English, in this context, as 'ensemble' or 'assembly'. The atoms in his assembly were uncoupled, meaning that they were an imaginary set of independent atoms that defines its observable statistical properties. Born did not mean an ensemble of instances of a certain kind of wave function, nor one composed of instances of a certain kind of state vector. There may be room here for confusion or miscommunication.

An example of an ensemble is composed by preparing and observing many copies of one and the same kind of quantum system. This is referred to as an ensemble of systems. It is not, for example, a single preparation and observation of one simultaneous set ("ensemble") of particles. A single body of many particles, as in a gas, is not an "ensemble" of particles in the sense of the "ensemble interpretation", although a repeated preparation and observation of many copies of one and the same kind of body of particles may constitute an "ensemble" of systems, each system being a body of many particles. The ensemble is not in principle confined to such a laboratory paradigm, but may be a natural system conceived of as occurring repeatedly in nature; it is not quite clear whether or how this might be realized.

The members of the ensemble are said to be in the same state, and this defines the term 'state'. The state is mathematically denoted by a mathematical object called a statistical operator. Such an operator is a map from a certain corresponding Hilbert space to itself, and may be written as a density matrix. It is characteristic of the ensemble interpretation to define the state by the statistical operator. Other interpretations may instead define the state by the corresponding Hilbert space. Such a difference between the modes of definition of state seems to make no difference to the physical meaning. Indeed, according to Ballentine, one can define the state by an ensemble of identically prepared systems, denoted by a point in the Hilbert space, as is perhaps more customary. The link is established by making the observing procedure a copy of the preparative procedure; mathematically the corresponding Hilbert spaces are mutually dual. Since Bohr's concern was that the specimen phenomena are joint preparation-observation occasions, it is not evident that the Copenhagen and ensemble interpretations differ substantially in this respect.

According to Ballentine, the distinguishing difference between the Copenhagen interpretation (CI) and the ensemble interpretation (EI) is the following:

CI: A pure state ${\displaystyle |y\rangle }$ provides a "complete" description of an individual system, in the sense that a dynamical variable represented by the operator ${\displaystyle \operatorname {Q} }$ has a definite value (${\displaystyle q}$, say) if and only if ${\displaystyle \operatorname {Q} |y\rangle =q|y\rangle }$. 

EI: A pure state describes the statistical properties of an ensemble of identically prepared systems, of which the statistical operator is idempotent. 

Ballentine emphasizes that the meaning of the "Quantum State" or "State Vector" may be described, essentially, by a one-to-one correspondence to the probability distributions of measurement results, not the individual measurement results themselves. A mixed state is a description only of the probabilities, ${\displaystyle {\mathcal {P}}(\chi _{1})}$ and ${\displaystyle {\mathcal {P}}(\chi _{2})}$ of positions, not a description of actual individual positions. A mixed state is a mixture of probabilities of physical states, not a coherent superposition of physical states.

Ensemble interpretation applied to single systems

The statement that the quantum mechanical wave function itself does not apply to a single system in one sense does not imply that the ensemble interpretation itself does not apply to single systems in the sense meant by the ensemble interpretation. The condition is that there is not a direct one-to-one correspondence of the wave function with an individual system that might imply, for example, that an object might physically exist in two states simultaneously. The ensemble interpretation may well be applied to a single system or particle, and predict what is the probability that that single system will have for a value of one of its properties, on repeated measurements. 

Consider the throwing of two dice simultaneously on a craps table. The system in this case would consist of only the two dice. There are probabilities of various results, e.g. two fives, two twos, a one and a six etc. Throwing the pair of dice 100 times, would result in an ensemble of 100 trials. Classical statistics would then be able predict what typically would be the number of times that certain results would occur. However, classical statistics would not be able to predict what definite single result would occur with a single throw of the pair of dice. That is, probabilities applied to single one off events are, essentially, meaningless, except in the case of a probability equal to 0 or 1. It is in this way that the ensemble interpretation states that the wave function does not apply to an individual system. That is, by individual system, it is meant a single experiment or single throw of the dice, of that system. 

The Craps throws could equally well have been of only one dice, that is, a single system or particle. Classical statistics would also equally account for repeated throws of this single dice. It is in this manner, that the ensemble interpretation is quite able to deal with "single" or individual systems on a probabilistic basis. The standard Copenhagen Interpretation (CI) is no different in this respect. A fundamental principle of QM is that only probabilistic statements may be made, whether for individual systems/particles, a simultaneous group of systems/particles, or a collection (ensemble) of systems/particles. An identification that the wave function applies to an individual system in standard CI QM, does not defeat the inherent probabilistic nature of any statement that can be made within standard QM. To verify the probabilities of quantum mechanical predictions, however interpreted, inherently requires the repetition of experiments, i.e. an ensemble of systems in the sense meant by the ensemble interpretation. QM cannot state that a single particle will definitely be in a certain position, with a certain momentum at a later time, irrespective of whether or not the wave function is taken to apply to that single particle. In this way, the standard CI also "fails" to completely describe "single" systems. 

However, it should be stressed that, in contrast to classical systems and older ensemble interpretations, the modern ensemble interpretation as discussed here, does not assume, nor require, that there exist specific values for the properties of the objects of the ensemble, prior to measurement.

Preparative and observing devices as origins of quantum randomness

An isolated quantum mechanical system, specified by a wave function, evolves in time in a deterministic way according to the Schrödinger equation that is characteristic of the system. Though the wave function can generate probabilities, no randomness or probability is involved in the temporal evolution of the wave function itself. This is agreed, for example, by Born, Dirac, von Neumann, London & Bauer, Messiah, and Feynman & Hibbs. An isolated system is not subject to observation; in quantum theory, this is because observation is an intervention that violates isolation.

The system's initial state is defined by the preparative procedure; this is recognized in the ensemble interpretation, as well as in the Copenhagen approach. The system's state as prepared, however, does not entirely fix all properties of the system. The fixing of properties goes only as far as is physically possible, and is not physically exhaustive; it is, however, physically complete in the sense that no physical procedure can make it more detailed. This is stated clearly by Heisenberg in his 1927 paper. It leaves room for further unspecified properties. For example, if the system is prepared with a definite energy, then the quantum mechanical phase of the wave function is left undetermined by the mode of preparation. The ensemble of prepared systems, in a definite pure state, then consists of a set of individual systems, all having one and the same the definite energy, but each having a different quantum mechanical phase, regarded as probabilistically random. The wave function, however, does have a definite phase, and thus specification by a wave function is more detailed than specification by state as prepared. The members of the ensemble are logically distinguishable by their distinct phases, though the phases are not defined by the preparative procedure. The wave function can be multiplied by a complex number of unit magnitude without changing the state as defined by the preparative procedure. 

The preparative state, with unspecified phase, leaves room for the several members of the ensemble to interact in respectively several various ways with other systems. An example is when an individual system is passed to an observing device so as to interact with it. Individual systems with various phases are scattered in various respective directions in the analyzing part of the observing device, in a probabilistic way. In each such direction, a detector is placed, in order to complete the observation. When the system hits the analyzing part of the observing device, that scatters it, it ceases to be adequately described by its own wave function in isolation. Instead it interacts with the observing device in ways partly determined by the properties of the observing device. In particular, there is in general no phase coherence between system and observing device. This lack of coherence introduces an element of probabilistic randomness to the system–device interaction. It is this randomness that is described by the probability calculated by the Born rule. There are two independent originative random processes, one that of preparative phase, the other that of the phase of the observing device. The random process that is actually observed, however, is neither of those originative ones. It is the phase difference between them, a single derived random process. 

The Born rule describes that derived random process, the observation of a single member of the preparative ensemble. In the ordinary language of classical or Aristotelian scholarship, the preparative ensemble consists of many specimens of a species. The quantum mechanical technical term 'system' refers to a single specimen, a particular object that may be prepared or observed. Such an object, as is generally so for objects, is in a sense a conceptual abstraction, because, according to the Copenhagen approach, it is defined, not in its own right as an actual entity, but by the two macroscopic devices that should prepare and observe it. The random variability of the prepared specimens does not exhaust the randomness of a detected specimen. Further randomness is injected by the quantum randomness of the observing device. It is this further randomness that makes Bohr emphasize that there is randomness in the observation that is not fully described by the randomness of the preparation. This is what Bohr means when he says that the wave function describes "a single system". He is focusing on the phenomenon as a whole, recognizing that the preparative state leaves the phase unfixed, and therefore does not exhaust the properties of the individual system. The phase of the wave function encodes further detail of the properties of the individual system. The interaction with the observing device reveals that further encoded detail. It seems that this point, emphasized by Bohr, is not explicitly recognized by the ensemble interpretation, and this may be what distinguishes the two interpretations. It seems, however, that this point is not explicitly denied by the ensemble interpretation. 

Einstein perhaps sometimes seemed to interpret the probabilistic "ensemble" as a preparative ensemble, recognizing that the preparative procedure does not exhaustively fix the properties of the system; therefore he said that the theory is "incomplete". Bohr, however, insisted that the physically important probabilistic "ensemble" was the combined prepared-and-observed one. Bohr expressed this by demanding that an actually observed single fact should be a complete "phenomenon", not a system alone, but always with reference to both the preparing and the observing devices. The Einstein–Podolsky–Rosen criterion of "completeness" is clearly and importantly different from Bohr's. Bohr regarded his concept of "phenomenon" as a major contribution that he offered for quantum theoretical understanding. The decisive randomness comes from both preparation and observation, and may be summarized in a single randomness, that of the phase difference between preparative and observing devices. The distinction between these two devices is an important point of agreement between Copenhagen and ensemble interpretations. Though Ballentine claims that Einstein advocated "the ensemble approach", a detached scholar would not necessarily be convinced by that claim of Ballentine. There is room for confusion about how "the ensemble" might be defined.

"Each photon interferes only with itself"

Niels Bohr famously insisted that the wave function refers to a single individual quantum system. He was expressing the idea that Dirac expressed when he famously wrote: "Each photon then interferes only with itself. Interference between different photons never occurs.". Dirac clarified this by writing: "This, of course, is true only provided the two states that are superposed refer to the same beam of light, i.e. all that is known about the position and momentum of a photon in either of these states must be the same for each." Bohr wanted to emphasize that a superposition is different from a mixture. He seemed to think that those who spoke of a "statistical interpretation" were not taking that into account. To create, by a superposition experiment, a new and different pure state, from an original pure beam, one can put absorbers and phase-shifters into some of the sub-beams, so as to alter the composition of the re-constituted superposition. But one cannot do so by mixing a fragment of the original unsplit beam with component split sub-beams. That is because one photon cannot both go into the unsplit fragment and go into the split component sub-beams. Bohr felt that talk in statistical terms might hide this fact. 

The physics here is that the effect of the randomness contributed by the observing apparatus depends on whether the detector is in the path of a component sub-beam, or in the path of the single superposed beam. This is not explained by the randomness contributed by the preparative device.

Measurement and collapse

Bras and kets

The ensemble interpretation is notable for its relative de-emphasis on the duality and theoretical symmetry between bras and kets. The approach emphasizes the ket as signifying a physical preparation procedure. There is little or no expression of the dual role of the bra as signifying a physical observational procedure. The bra is mostly regarded as a mere mathematical object, without very much physical significance. It is the absence of the physical interpretation of the bra that allows the ensemble approach to by-pass the notion of "collapse". Instead, the density operator expresses the observational side of the ensemble interpretation. It hardly needs saying that this account could be expressed in a dual way, with bras and kets interchanged, mutatis mutandis. In the ensemble approach, the notion of the pure state is conceptually derived by analysis of the density operator, rather than the density operator being conceived as conceptually synthesized from the notion of the pure state. 

An attraction of the ensemble interpretation is that it appears to dispense with the metaphysical issues associated with reduction of the state vector, Schrödinger cat states, and other issues related to the concepts of multiple simultaneous states. The ensemble interpretation postulates that the wave function only applies to an ensemble of systems as prepared, but not observed. There is no recognition of the notion that a single specimen system could manifest more than one state at a time, as assumed, for example, by Dirac. Hence, the wave function is not envisaged as being physically required to be "reduced". This can be illustrated by an example:

Consider a quantum die. If this is expressed in Dirac notation, the "state" of the die can be represented by a "wave" function describing the probability of an outcome given by:

${\displaystyle |\psi \rangle ={\frac {|1\rangle +|2\rangle +|3\rangle +|4\rangle +|5\rangle +|6\rangle }{\sqrt {6}}}}$

Where the "+" sign of a probabilistic equation is not an addition operator, it is a standard probabilistic or Boolean logical OR operator. The state vector is inherently defined as a probabilistic mathematical object such that the result of a measurement is one outcome OR another outcome. 

It is clear that on each throw, only one of the states will be observed, but this is not expressed by a bra. Consequently, there appears to be no requirement for a notion of collapse of the wave function/reduction of the state vector, or for the die to physically exist in the summed state. In the ensemble interpretation, wave function collapse would make as much sense as saying that the number of children a couple produced, collapsed to 3 from its average value of 2.4.

The state function is not taken to be physically real, or be a literal summation of states. The wave function, is taken to be an abstract statistical function, only applicable to the statistics of repeated preparation procedures. The ket does not directly apply to a single particle detection, but only the statistical results of many. This is why the account does not refer to bras, and mentions only kets.

Diffraction

The ensemble approach differs significantly from the Copenhagen approach in its view of diffraction. The Copenhagen interpretation of diffraction, especially in the viewpoint of Niels Bohr, puts weight on the doctrine of wave–particle duality. In this view, a particle that is diffracted by a diffractive object, such as for example a crystal, is regarded as really and physically behaving like a wave, split into components, more or less corresponding to the peaks of intensity in the diffraction pattern. Though Dirac does not speak of wave–particle duality, he does speak of "conflict" between wave and particle conceptions. He indeed does describe a particle, before it is detected, as being somehow simultaneously and jointly or partly present in the several beams into which the original beam is diffracted. So does Feynman, who speaks of this as "mysterious".

The ensemble approach points out that this seems perhaps reasonable for a wave function that describes a single particle, but hardly makes sense for a wave function that describes a system of several particles. The ensemble approach demystifies this situation along the lines advocated by Alfred Landé, accepting Duane's hypothesis. In this view, the particle really and definitely goes into one or other of the beams, according to a probability given by the wave function appropriately interpreted. There is definite quantal transfer of translative momentum between particle and diffractive object. This is recognized also in Heisenberg's 1930 textbook, though usually not recognized as part of the doctrine of the so-called "Copenhagen interpretation". This gives a clear and utterly non-mysterious physical or direct explanation instead of the debated concept of wave function "collapse". It is presented in terms of quantum mechanics by other present day writers also, for example, Van Vliet. For those who prefer physical clarity rather than mysterianism, this is an advantage of the ensemble approach, though it is not the sole property of the ensemble approach. With a few exceptions, this demystification is not recognized or emphasized in many textbooks and journal articles.

Criticism

David Mermin sees the ensemble interpretation as being motivated by an adherence ("not always acknowledged") to classical principles.

"[...] the notion that probabilistic theories must be about ensembles implicitly assumes that probability is about ignorance. (The 'hidden variables' are whatever it is that we are ignorant of.) But in a non-deterministic world probability has nothing to do with incomplete knowledge, and ought not to require an ensemble of systems for its interpretation".

However, according to Einstein and others, a key motivation for the ensemble interpretation is not about any alleged, implicitly assumed probabilistic ignorance, but the removal of "…unnatural theoretical interpretations…". A specific example being the Schrödinger cat problem stated above, but this concept applies to any system where there is an interpretation that postulates, for example, that an object might exist in two positions at once. 

Mermin also emphasises the importance of describing single systems, rather than ensembles.

"The second motivation for an ensemble interpretation is the intuition that because quantum mechanics is inherently probabilistic, it only needs to make sense as a theory of ensembles. Whether or not probabilities can be given a sensible meaning for individual systems, this motivation is not compelling. For a theory ought to be able to describe as well as predict the behavior of the world. The fact that physics cannot make deterministic predictions about individual systems does not excuse us from pursuing the goal of being able to describe them as they currently are."

Single particles

According to proponents of this interpretation, no single system is ever required to be postulated to exist in a physical mixed state so the state vector does not need to collapse.

It can also be argued that this notion is consistent with the standard interpretation in that, in the Copenhagen interpretation, statements about the exact system state prior to measurement cannot be made. That is, if it were possible to absolutely, physically measure say, a particle in two positions at once, then quantum mechanics would be falsified as quantum mechanics explicitly postulates that the result of any measurement must be a single eigenvalue of a single eigenstate.

Criticism

Arnold Neumaier finds limitations with the applicability of the ensemble interpretation to small systems.

"Among the traditional interpretations, the statistical interpretation discussed by Ballentine in Rev. Mod. Phys. 42, 358-381 (1970) is the least demanding (assumes less than the Copenhagen interpretation and the Many Worlds interpretation) and the most consistent one. It explains almost everything, and only has the disadvantage that it explicitly excludes the applicability of QM to single systems or very small ensembles (such as the few solar neutrinos or top quarks actually detected so far), and does not bridge the gulf between the classical domain (for the description of detectors) and the quantum domain (for the description of the microscopic system)".
(spelling amended)

However, the "ensemble" of the ensemble interpretation is not directly related to a real, existing collection of actual particles, such as a few solar neutrinos, but it is concerned with the ensemble collection of a virtual set of experimental preparations repeated many times. This ensemble of experiments may include just one particle/one system or many particles/many systems. In this light, it is arguably, difficult to understand Neumaier's criticism, other than that Neumaier possibly misunderstands the basic premise of the ensemble interpretation itself.

Schrödinger's cat

The ensemble interpretation states that superpositions are nothing but subensembles of a larger statistical ensemble. That being the case, the state vector would not apply to individual cat experiments, but only to the statistics of many similar prepared cat experiments. Proponents of this interpretation state that this makes the Schrödinger's cat paradox a trivial non-issue. However, the application of state vectors to individual systems, rather than ensembles, has claimed explanatory benefits, in areas like single-particle twin-slit experiments and quantum computing. As an avowedly minimalist approach, the ensemble interpretation does not offer any specific alternative explanation for these phenomena.

The frequentist probability variation

The claim that the wave functional approach fails to apply to single particle experiments cannot be taken as a claim that quantum mechanics fails in describing single-particle phenomena. In fact, it gives correct results within the limits of a probabilistic or stochastic theory.

Probability always requires a set of multiple data, and thus single-particle experiments are really part of an ensemble — an ensemble of individual experiments that are performed one after the other over time. In particular, the interference fringes seen in the double-slit experiment require repeated trials to be observed.

The quantum Zeno effect

Leslie Ballentine promoted the ensemble interpretation in his book Quantum Mechanics, A Modern Development. In it, he described what he called the "Watched Pot Experiment". His argument was that, under certain circumstances, a repeatedly measured system, such as an unstable nucleus, would be prevented from decaying by the act of measurement itself. He initially presented this as a kind of reductio ad absurdum of wave function collapse.

The effect has been shown to be real. Ballentine later wrote papers claiming that it could be explained without wave function collapse.

Classical ensemble ideas

These views regard the randomness of the ensemble as fully defined by the preparation, neglecting the subsequent random contribution of the observing process. This neglect was particularly criticized by Bohr.

Einstein

Early proponents, for example Einstein, of statistical approaches regarded quantum mechanics as an approximation to a classical theory. John Gribbin writes:

"The basic idea is that each quantum entity (such as an electron or a photon) has precise quantum properties (such as position or momentum) and the quantum wavefunction is related to the probability of getting a particular experimental result when one member (or many members) of the ensemble is selected by an experiment"

But hopes for turning quantum mechanics back into a classical theory were dashed. Gribbin continues:

"There are many difficulties with the idea, but the killer blow was struck when individual quantum entities such as photons were observed behaving in experiments in line with the quantum wave function description. The Ensemble interpretation is now only of historical interest."

In 1936 Einstein wrote a paper, in German, in which, amongst other matters, he considered quantum mechanics in general conspectus.

He asked "How far does the ψ-function describe a real state of a mechanical system?" Following this, Einstein offers some argument that leads him to infer that "It seems to be clear, therefore, that the Born statistical interpretation of the quantum theory is the only possible one." At this point a neutral student may ask do Heisenberg and Bohr, considered respectively in their own rights, agree with that result? Born in 1971 wrote about the situation in 1936: "All theoretical physicists were in fact working with the statistical concept by then; this was particularly true of Niels Bohr and his school, who also made a vital contribution to the clarification of the concept."

Where, then, is to be found disagreement between Bohr and Einstein on the statistical interpretation? Not in the basic link between theory and experiment; they agree on the Born "statistical" interpretation". They disagree on the metaphysical question of the determinism or indeterminism of evolution of the natural world. Einstein believed in determinism while Bohr (and it seems many physicists) believed in indeterminism; the context is atomic and sub-atomic physics. It seems that this is a fine question. Physicists generally believe that the Schrödinger equation describes deterministic evolution for atomic and sub-atomic physics. Exactly how that might relate to the evolution of the natural world may be a fine question.

Objective-realist version

Willem de Muynck describes an "objective-realist" version of the ensemble interpretation featuring counterfactual definiteness and the "possessed values principle", in which values of the quantum mechanical observables may be attributed to the object as objective properties the object possesses independent of observation. He states that there are "strong indications, if not proofs" that neither is a possible assumption.

Causal loop

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Causal_loop

Top: original billiard ball trajectory.Middle: the ball emerges from the future at a different trajectory from the original, and collides with its past self, changing its trajectory.Bottom: the changed trajectory causes the ball to enter and exit the time machine in exactly the same way that changed its trajectory. The changed trajectory is its own cause, without an origin.

 

A causal loop is a theoretical proposition in which, by means of either retrocausality or time travel, a sequence of events (actions, information, objects, people) is among the causes of another event, which is in turn among the causes of the first-mentioned event. Such causally looped events then exist in spacetime, but their origin cannot be determined. A hypothetical example of a causality loop is given of a billiard ball striking its past self: the billiard ball moves in a path towards a time machine, and the future self of the billiard ball emerges from the time machine before its past self enters it, giving its past self a glancing blow, altering the past ball's path and causing it to enter the time machine at an angle that would cause its future self to strike its past self the very glancing blow that altered its path. So, the question here in this paradox is, how was the ball struck in the first place? 

Terminology in physics, philosophy, and fiction

Backwards time travel would allow for causal loops involving events, information, people or objects whose histories form a closed loop, and thus seem to "come from nowhere." The notion of objects or information that are "self-existing" in this way is often viewed as paradoxical, with several authors referring to a causal loop involving information or objects without origin as a bootstrap paradox, an information paradox, or an ontological paradox. The use of "bootstrap" in this context refers to the expression "pulling yourself up by your bootstraps" and to Robert A. Heinlein's time travel story "By His Bootstraps". The term "time loop" is sometimes used to refer to a causal loop, but although they appear similar, causal loops are unchanging and self-originating, whereas time loops are constantly resetting.

An example of a causal loop paradox involving information is given by Everett: suppose a time traveler copies a mathematical proof from a textbook, then travels back in time to meet the mathematician who first published the proof, at a date prior to publication, and allows the mathematician to simply copy the proof. In this case, the information in the proof has no origin. A similar example is given in the television series Doctor Who of a hypothetical time-traveler who copies Beethoven's music from the future and publishes it in Beethoven's time in Beethoven's name. Everett gives the movie Somewhere in Time as an example involving an object with no origin: an old woman gives a watch to a playwright who later travels back in time and meets the same woman when she was young, and gives her the same watch that she will later give to him.

Krasnikov writes that these bootstrap paradoxes – information or an object looping through time – are the same; the primary apparent paradox is a physical system evolving into a state in a way that is not governed by its laws. He does not find this paradoxical, and attributes problems regarding the validity of time travel to other factors in the interpretation of general relativity.

A 1992 paper by physicists Andrei Lossev and Igor Novikov labeled such items without origin as Jinn, with the singular term Jinnee. This terminology was inspired by the Jinn of the Quran, which are described as leaving no trace when they disappear. Lossev and Novikov allowed the term "Jinn" to cover both objects and information with reflexive origin; they called the former "Jinn of the first kind", and the latter "Jinn of the second kind". They point out that an object making circular passage through time must be identical whenever it is brought back to the past, otherwise it would create an inconsistency; the second law of thermodynamics seems to require that the object become more disordered over the course of its history, and such objects that are identical in repeating points in their history seem to contradict this, but Lossev and Novikov argued that since the second law only requires disorder to increase in closed systems, a Jinnee could interact with its environment in such a way as to regain lost order. They emphasize that there is no "strict difference" between Jinn of the first and second kind. Krasnikov equivocates between "Jinn", "self-sufficient loops", and "self-existing objects", calling them "lions" or "looping or intruding objects", and asserts that they are no less physical than conventional objects, "which, after all, also could appear only from either infinity, or a singularity."

The term predestination paradox is used in the Star Trek franchise to mean "a time loop in which a time traveler who has gone into the past causes an event that ultimately causes the original future version of the person to go back into the past." This use of the phrase was created for a sequence in a 1996 episode of Star Trek: Deep Space Nine titled "Trials and Tribble-ations", although the phrase had been used previously to refer to belief systems such as Calvinism and some forms of Marxism that encouraged followers to strive to produce certain outcomes while at the same time teaching that the outcomes were predetermined. Smeenk and Morgenstern use the term "predestination paradox" to refer specifically to situations in which a time traveler goes back in time to try to prevent some event in the past, but ends up helping to cause that same event.

Self-fulfilling prophecy

A self-fulfilling prophecy may be a form of causality loop, only when the prophecy can be said to be truly known to occur, since only then events in the future will be causing effects in the past. Otherwise, it would be a simple case of events in the past causing events in the future. Predestination does not necessarily involve a supernatural power, and could be the result of other "infallible foreknowledge" mechanisms. Problems arising from infallibility and influencing the future are explored in Newcomb's paradox. A notable fictional example of a self-fulfilling prophecy occurs in the classical play Oedipus Rex, in which Oedipus becomes the king of Thebes and in the process unwittingly fulfills a prophecy that he would kill his father and marry his mother. The prophecy itself serves as the impetus for his actions, and thus it is self-fulfilling. The movie 12 Monkeys heavily deals with themes of predestination and the Cassandra complex, where the protagonist who travels back in time explains that he can't change the past.

Novikov self-consistency principle

General relativity permits some exact solutions that allow for time travel. Some of these exact solutions describe universes that contain closed timelike curves, or world lines that lead back to the same point in spacetime. Physicist Igor Dmitriyevich Novikov discussed the possibility of closed timelike curves in his books in 1975 and 1983, offering the opinion that only self-consistent trips back in time would be permitted. In a 1990 paper by Novikov and several others, "Cauchy problem in spacetimes with closed timelike curves", the authors suggested the principle of self-consistency, which states that the only solutions to the laws of physics that can occur locally in the real Universe are those which are globally self-consistent. The authors later concluded that time travel need not lead to unresolvable paradoxes, regardless of what type of object was sent to the past.

Physicist Joseph Polchinski argued that one could avoid questions of free will by considering a potentially paradoxical situation involving a billiard ball sent back in time. In this situation, the ball is fired into a wormhole at an angle such that, if it continues along its course, it will exit in the past at just the right angle to hit its earlier self, knocking it off course, which would stop it from entering the wormhole in the first place. Thorne referred to this problem as "Polchinski's paradox". Two students at Caltech, Fernando Echeverria and Gunnar Klinkhammer, went on to find a solution that avoided any inconsistencies. In the revised scenario, the ball would emerge from the future at a different angle than the one that had generated the paradox, and delivers its past self a glancing blow instead of knocking it completely away from the wormhole. This blow changes its trajectory by just the right degree, meaning it will travel back in time with the angle required to deliver its younger self the necessary glancing blow. Echeverria and Klinkhammer actually found that there was more than one self-consistent solution, with slightly different angles for the glancing blow in each case. Later analysis by Thorne and Robert Forward showed that for certain initial trajectories of the billiard ball, there could actually be an infinite number of self-consistent solutions.

Echeverria, Klinkhammer and Thorne published a paper discussing these results in 1991; in addition, they reported that they had tried to see if they could find any initial conditions for the billiard ball for which there were no self-consistent extensions, but were unable to do so. Thus it is plausible that there exist self-consistent extensions for every possible initial trajectory, although this has not been proven. The lack of constraints on initial conditions only applies to spacetime outside of the chronology-violating region of spacetime; the constraints on the chronology-violating region might prove to be paradoxical, but this is not yet known.

Novikov's views are not widely accepted. Visser views causal loops and Novikov's self-consistency principle as an ad hoc solution, and supposes that there are far more damaging implications of time travel. Krasnikov similarly finds no inherent fault in causal loops, but finds other problems with time travel in general relativity.

Quantum computation with negative delay

Physicist David Deutsch shows in a 1991 paper that quantum computation with a negative delay—backwards time travel—could solve NP problems in polynomial time, and Scott Aaronson later extended this result to show that the model could also be used to solve PSPACE problems in polynomial time. Deutsch shows that quantum computation with a negative delay produces only self-consistent solutions, and the chronology-violating region imposes constraints that are not apparent through classical reasoning. Researchers published in 2014 a simulation validating Deutsch's model with photons. However, it was shown in an article by Tolksdorf and Verch that Deutsch's CTC (closed timelike curve, or a causal loop) fixed point condition can be fulfilled to arbitrary precision in any quantum system described according to relativistic quantum field theory on spacetimes where CTCs are excluded, casting doubts on whether Deutsch's condition is really characteristic of quantum processes mimicking CTCs in the sense of general relativity.