Category: User-created public domain images An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. ... The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and the verb γράφω gráfo write) is the study of message secrecy. ... In physical cosmology, cosmic inflation is the idea that the nascent universe passed through a phase of exponential expansion that was driven by a negative-pressure vacuum energy density. ... Doctor Who novel, see Cold Fusion (Doctor Who). ... In astronomy, a corona is the luminous plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... In astrophysics and cosmology, dark matter is matter, not directly observed and of unknown composition, that does not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter. ... General relativity (GR) [also called the general theory of relativity (GTR) and general relativity theory (GRT)] is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... The decay of a proton, a baryon, into non-baryonic matter, does not occur perturbatively in the Standard Model. ... Fig. ... The Bloch sphere is a representation of a qubit, the fundamental building block of quantum computers. ... Quantum chromodynamics (QCD) is the theory of the strong interaction, a fundamental force describing the interactions of the quarks and gluons found in nucleons (such as the proton and neutron). ... This article or section does not adequately cite its references or sources. ... Unsolved problems in mathematics: Is the real part of a non-trivial zero of the Riemann zeta function always ½? In mathematics, the Riemann hypothesis (also called the Riemann zeta-hypothesis), first formulated by Bernhard Riemann in 1859, is one of the most famous unsolved problems. ... Superstring theory is an attempt to explain all of the particles and fundamental forces of nature in one theory by modeling them as vibrations of tiny supersymmetric strings. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... This article or section is in need of attention from an expert on the subject. ... Time travel is a concept that has long fascinated humanity&#8212;whether it is Merlin experiencing time backwards, or religious traditions like Mohammeds trip to Jerusalem and ascent to heaven, returning before a glass knocked over had spilt its contents. ... The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as part of his theory of general relativity to achieve a stationary universe. ... Beggar-My-Neighbour, also known as Beat Jack out of Doors, Beat Your Neighbour out of Doors and Strip Jack Naked, is a simple card game somewhat similar in nature to War, and has spawned a more complicated variant, Egyptian Ratscrew. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... It has been suggested that Date magic square be merged into this article or section. ... Unsolved problems in physics: Is it possible to construct a practical electronic device that operates on the spin of the electron, rather than its charge? Spintronics (a neologism for spin-based electronics), also known as magnetoelectronics, is an emergent technology which exploits a quantum property of electrons known as spin... According to the Book of Genesis and 1 Chronicles, Amalek (עֲמָלֵק; Standard Hebrew , Tiberian Hebrew ) was the son of Eliphaz and the grandson of Esau (Gen. ... In physics, the zero-point energy is the lowest possible energy that a quantum mechanical physical system may possess; it is the energy of the ground state of the system. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and has strong negative pressure. ... The Land of Punt, which the Ancient Egyptians called Ta Netjeru, meaning Land of the Gods, was a fabled and exotic site in eastern Africa, which carried on extensive trade with Ancient Egypt, China and Arabia. ... Artists conception of a binary star system with one black hole and one main sequence star An accretion disc (or accretion disk) is a structure formed by diffuse material in orbital motion around a central body. ... The Hyksos (Egyptian heka khasewet meaning foreign rulers, Greek ) were an ethnically mixed group of Southwest Asiatic or Semitic people who appeared in the eastern Nile Delta during the Second Intermediate Period. ... Look up Cognition in Wiktionary, the free dictionary. ... CP-symmetry is a symmetry obtained by a combination of the C-symmetry and the P-symmetry. ... T-symmetry is the symmetry of physical laws under a time-reversal transformation— The universe is not symmetric under time reversal, although in restricted contexts one may find this symmetry. ... One of the oldest open problems in group theory was first posed by William Burnside in a paper published in 1902. ... In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic, stochastic property changes. ... Unsolved problems in mathematics: For every ε > 0, does there exist a K>0 such that for every triple of coprime positive integers a+b=c, with product d of their distinct prime factors, |a|+|b|+|c| < Kd1+ε? The abc conjecture in number theory was first proposed by Joseph Oesterlé and... In physics, a magnetic monopole is a hypothetical particle that may be loosely described as a magnet with only one pole (see electromagnetic theory for more on magnetic poles). ... The Greisen-Zatsepin-Kuzmin limit (GZK limit) is a theoretical upper limit on the energy of cosmic rays from distant sources. ... This article or section is in need of attention from an expert on the subject. ... Sporadic E propagation is a relatively rare form of propagation where a radio wave bounces off a sporadic E cloud, notated as Es in the E layer region of the ionosphere. ... Unsolved problems in Egyptology: Does the Story of Sinuhe recount real events? If so, did Sinuhe abandon his duty or was he a hero? The Tale of Sinuhe is an Ancient Egyptian work of literature. ... Unsolved problems in computer science: Do one-way functions exist? A one-way function is a function that is easy to compute but hard to invert — given the output of the function it is difficult to find any input which yields this output. ... Baryogenesis is the generic designation for the physical processes that generate matter (more specifically, a class of fundamental particle called baryon) from an otherwise matter-empty state (such as it is generally believed to be the state of the Universe at its onset, the so-called Big Bang). ... Unsolved problems in physics: Why is it that some cosmic rays appear to possess energies that are theoretically too high? In high-energy physics, an ultra-high-energy cosmic ray (UHECR) is a cosmic ray (subatomic particle) which appears to have extreme kinetic energy, far beyond both its rest mass... The Pioneer anomaly or Pioneer effect refers to the observed deviation from expectations of the trajectories of various unmanned spacecraft visiting the outer solar system, notably Pioneer 10 and 11. ... In mathematics, an Euler Brick, named after the famous mathematician Leonhard Euler, is a cuboid with integer edges and also integer face diagonals. ... A polar jet is a phenomenon often seen in astronomy. ... Unsolved problems in Egyptology: Did Egyptians have some form of understanding of electricity? Did the Egyptians use batteries? What is the relief at Dendera? The Dendera light is a stone relief located in the Hathor temple at the Dendera Temple complex in Egypt. ... Quark matter or QCD matter refers to any of a number of phases of matter whose degrees of freedom include quarks and gluons. ... The QCD vacuum is the vacuum state of quantum chromodynamics (QCD). ... // Definition and origin The C-value enigma is a term used to describe the complex puzzle surrounding the extensive variation in nuclear genome size among eukaryotic species. ... Unsolved problems in mathematics: How many colors are needed to color the plane so that no two points at unit distance are the same color? In mathematics, more specifically in geometric graph theory, the Hadwiger–Nelson problem asks for the minimum number of colors required to color the plane such... Wikipedia does not have an article with this exact name. ... Unsolved problems in physics: Arrow of time: Why did the universe have such low entropy in the past, resulting in the distinction between past and future and the second law of thermodynamics? Entropy is the only quantity in the physical sciences that picks a particular direction for time, sometimes called... The Petersen graph is a unit distance graph: it can be drawn in the plane with each edge having unit length. ... In physics, a gravitational wave is a fluctuation in the curvature of spacetime which propagates as a wave, traveling outward from a moving object or system of objects. ... Typical coronal loops observed by TRACE Coronal loops form the basic structure of the lower corona and transition region of the Sun. ...