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🔗 Russia 🔗 Physics 🔗 Physics/relativity 🔗 Russia/science and education in Russia

The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture and Larry Niven's law of conservation of history, is a principle developed by Russian physicist Igor Dmitriyevich Novikov in the mid-1980s. Novikov intended it to solve the problem of paradoxes in time travel, which is theoretically permitted in certain solutions of general relativity that contain what are known as closed timelike curves. The principle asserts that if an event exists that would cause a paradox or any "change" to the past whatsoever, then the probability of that event is zero. It would thus be impossible to create time paradoxes.

🔗 Philosophy 🔗 Philosophy/Aesthetics 🔗 Constructed languages

Zaum (Russian: за́умь, lit. 'transrational') are the linguistic experiments in sound symbolism and language creation of Russian Cubo-Futurist poets such as Velimir Khlebnikov and Aleksei Kruchenykh. Zaum is a non-referential phonetic entity with its own ontology. The language consists of neologisms that mean nothing. Zaum is a language organized through phonetic analogy and rhythm. Zaum literature cannot contain any onomatopoeia or psychopathological states.

🔗 Novels 🔗 Novels/Science fiction

Ready Player One is a 2011 science fiction novel, and the debut novel of American author Ernest Cline. The story, set in a dystopia in 2045, follows protagonist Wade Watts on his search for an Easter egg in a worldwide virtual reality game, the discovery of which would lead him to inherit the game creator's fortune. Cline sold the rights to publish the novel in June 2010, in a bidding war to the Crown Publishing Group (a division of Random House). The book was published on August 16, 2011. An audiobook was released the same day; it was narrated by Wil Wheaton, who was mentioned briefly in one of the chapters.^{Ch. 20} In 2012, the book received an Alex Award from the Young Adult Library Services Association division of the American Library Association and won the 2012 Prometheus Award. A film adaptation, screenwritten by Cline and Zak Penn and directed by Steven Spielberg, was released on March 29, 2018.

🔗 Physics

When using the term 'the speed of light' it is sometimes necessary to make the distinction between its one-way speed and its two-way speed. The "one-way" speed of light, from a source to a detector, cannot be measured independently of a convention as to how to synchronize the clocks at the source and the detector. What can however be experimentally measured is the round-trip speed (or "two-way" speed of light) from the source to a mirror (or other method of reflection) and back again to detector. Albert Einstein chose a synchronization convention (see Einstein synchronization) that made the one-way speed equal to the two-way speed. The constancy of the one-way speed in any given inertial frame is the basis of his special theory of relativity, although all experimentally verifiable predictions of this theory do not depend on that convention.

Experiments that attempt to directly probe the one-way speed of light independent of synchronization have been proposed, but none have succeeded in doing so. Those experiments directly establish that synchronization with slow clock-transport is equivalent to Einstein synchronization, which is an important feature of special relativity. However, those experiments cannot directly establish the isotropy of the one-way speed of light since it has been shown that slow clock-transport, the laws of motion, and the way inertial reference frames are defined already involve the assumption of isotropic one-way speeds and thus, are equally conventional. In general, it was shown that these experiments are consistent with anisotropic one-way light speed as long as the two-way light speed is isotropic.

The 'speed of light' in this article refers to the speed of all electromagnetic radiation in vacuum.

🔗 Philosophy 🔗 Philosophy/Ancient philosophy 🔗 Philosophy/Ethics

The Tetrapharmakos (τετραφάρμακος) "four-part remedy" is a summary of the first four of the Κύριαι Δόξαι (Kuriai Doxai, the forty Epicurean Principal Doctrines given by Diogenes Laërtius in his Life of Epicurus) in Epicureanism, a recipe for leading the happiest possible life. They are recommendations to avoid anxiety or existential dread.

The "tetrapharmakos" was originally a compound of four drugs (wax, tallow, pitch and resin); the word has been used metaphorically by Roman-era Epicureans. to refer to the four remedies for healing the soul.

🔗 Plants 🔗 Forestry 🔗 Ecology

Pioneer species are resilient species that are the first to colonize barren environments, or to repopulate disrupted biodiverse steady-state ecosystems as part of ecological succession. A number of kinds of events can create good conditions for pioneers, including disruption by natural disasters, such as wildfire, flood, mudslide, lava flow or a climate-related extinction event or by anthropogenic habitat destruction, such as through land clearance for agriculture or construction or industrial damage. Pioneer species play an important role in creating soil in primary succession, and stabilizing soil and nutrients in secondary succession.

For humans, because pioneer species quickly occupy disrupted spaces they are sometimes treated as weeds or nuisance wildlife, such as the common dandelion or stinging nettle. Even though humans have mixed relationships with these plants, these species tend to help improve the ecosystem because they can break up compacted soils and accumulate nutrients that help with a transition back to a more mature ecosystem. In human managed ecological restoration or agroforestry, trees and herbaceous pioneers can be used to restore soil qualities and provide shelter for slower growing or more demanding plants. Some systems use introduced species to restore the ecosystem, or for environmental remediation. The durability of pioneer species can also make them potential invasive species.

🔗 Military history 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Cold War 🔗 Military history/Asian military history 🔗 Military history/Southeast Asian military history 🔗 Vietnam

The Fall of Saigon, also known as the Liberation of Saigon by North Vietnamese, was the capture of Saigon, the capital of South Vietnam, by the People's Army of Vietnam (PAVN) and the Viet Cong on 30 April 1975. The event marked the end of the Vietnam War and the start of a transition period to the formal reunification of Vietnam into the Socialist Republic of Vietnam.

The PAVN, under the command of General Văn Tiến Dũng, began their final attack on Saigon on 29 April 1975, with the Army of the Republic of Vietnam (ARVN) forces commanded by General Nguyễn Văn Toàn suffering a heavy artillery bombardment. By the afternoon of the next day, the PAVN had occupied the important points of the city and raised their flag over the South Vietnamese presidential palace. The city was renamed Hồ Chí Minh City, after the late North Vietnamese President Hồ Chí Minh.

The capture of the city was preceded by Operation Frequent Wind, the evacuation of almost all American civilian and military personnel in Saigon, along with tens of thousands of South Vietnamese civilians who had been associated with the Republic of Vietnam. A few Americans chose not to be evacuated. United States ground combat units had left South Vietnam more than two years prior to the fall of Saigon and were not available to assist with either the defense of Saigon or the evacuation. The evacuation was the largest helicopter evacuation in history. In addition to the flight of refugees, the end of the war and the institution of new rules by the communists contributed to a decline in the city's population.

🔗 Mathematics

Graham's number is an immense number that arises as an upper bound on the answer of a problem in the mathematical field of Ramsey theory. It is named after mathematician Ronald Graham, who used the number in conversations with popular science writer Martin Gardner as a simplified explanation of the upper bounds of the problem he was working on. In 1977, Gardner described the number in Scientific American, introducing it to the general public. At the time of its introduction, it was the largest specific positive integer ever to have been used in a published mathematical proof. The number was published in the 1980 Guinness Book of World Records, adding to its popular interest. Other specific integers (such as TREE(3)) known to be far larger than Graham's number have since appeared in many serious mathematical proofs, for example in connection with Harvey Friedman's various finite forms of Kruskal's theorem. Additionally, smaller upper bounds on the Ramsey theory problem from which Graham's number derived have since been proven to be valid.

Graham's number is much larger than many other large numbers such as Skewes' number and Moser's number, both of which are in turn much larger than a googolplex. As with these, it is so large that the observable universe is far too small to contain an ordinary digital representation of Graham's number, assuming that each digit occupies one Planck volume, possibly the smallest measurable space. But even the number of digits in this digital representation of Graham's number would itself be a number so large that its digital representation cannot be represented in the observable universe. Nor even can the number of digits of that number—and so forth, for a number of times far exceeding the total number of Planck volumes in the observable universe. Thus Graham's number cannot be expressed even by power towers of the form ${\displaystyle a^{b^{c^{\cdot ^{\cdot ^{\cdot }}}}}}$.

However, Graham's number can be explicitly given by computable recursive formulas using Knuth's up-arrow notation or equivalent, as was done by Graham. As there is a recursive formula to define it, it is much smaller than typical busy beaver numbers. Though too large to be computed in full, the sequence of digits of Graham's number can be computed explicitly through simple algorithms. The last 12 digits are ...262464195387. With Knuth's up-arrow notation, Graham's number is ${\displaystyle g_{64}}$, where

🔗 Elements

Alternative periodic tables are tabulations of chemical elements differing in their organization from the traditional depiction of the periodic system.

Over a thousand have been devised, often for didactic reasons, as not all correlations between the chemical elements are effectively captured by the standard periodic table.

🔗 Cryptography 🔗 Cryptography/Computer science

In cryptography, power analysis is a form of side channel attack in which the attacker studies the power consumption of a cryptographic hardware device (such as a smart card, tamper-resistant "black box", or integrated circuit). The attack can non-invasively extract cryptographic keys and other secret information from the device.

Simple power analysis (SPA) involves visually interpreting power traces, or graphs of electrical activity over time. Differential power analysis (DPA) is a more advanced form of power analysis, which can allow an attacker to compute the intermediate values within cryptographic computations through statistical analysis of data collected from multiple cryptographic operations. SPA and DPA were introduced to the open cryptology community in 1998 by Paul Kocher, Joshua Jaffe and Benjamin Jun.