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An exotic atom is an otherwise normal atom in which one or more sub-atomic particles have been replaced by other particles of the same charge. For example, electrons may be replaced by other negatively charged particles such as muons (muonic atoms) or pions (pionic atoms). Because these substitute particles are usually unstable, exotic atoms typically have very short lifetimes and all currently observed atoms cannot persist under normal conditions.

Fluidics, or fluidic logic, is the use of a fluid to perform analog or digital operations similar to those performed with electronics.

The physical basis of fluidics is pneumatics and hydraulics, based on the theoretical foundation of fluid dynamics. The term fluidics is normally used when devices have no moving parts, so ordinary hydraulic components such as hydraulic cylinders and spool valves are not considered or referred to as fluidic devices.

A jet of fluid can be deflected by a weaker jet striking it at the side. This provides nonlinear amplification, similar to the transistor used in electronic digital logic. It is used mostly in environments where electronic digital logic would be unreliable, as in systems exposed to high levels of electromagnetic interference or ionizing radiation.

Nanotechnology considers fluidics as one of its instruments. In this domain, effects such as fluid-solid and fluid-fluid interface forces are often highly significant. Fluidics have also been used for military applications.

In condensed matter physics, Hofstadter's butterfly describes the spectral properties of non-interacting two dimensional electrons in a magnetic field. The fractal, self-similar, nature of the spectrum was discovered in the 1976 Ph.D. work of Douglas Hofstadter and is one of the early examples of computer graphics. The name reflects the visual resemblance of the figure on the right to a swarm of butterflies flying to infinity.

The Hofstadter butterfly plays an important role in the theory of the integer quantum Hall effect, and D.J. Thouless has been awarded the Nobel prize in physics in 2016 for the discovery that the wings of the butterfly are characterized by Chern integers, the quantized Hall conductances discovered in 1980 by Klaus von Klitzing for which he has been awarded the Nobel prize in 1985. The colors in the diagram reflect the different Chern numbers.

A Van Allen radiation belt is a zone of energetic charged particles, most of which originate from the solar wind, that are captured by and held around a planet by that planet's magnetic field. Earth has two such belts and sometimes others may be temporarily created. The discovery of the belts is credited to James Van Allen, and as a result, Earth's belts are known as the Van Allen belts. Earth's two main belts extend from an altitude of about 640 to 58,000 km (400 to 36,040 mi) above the surface in which region radiation levels vary. Most of the particles that form the belts are thought to come from solar wind and other particles by cosmic rays. By trapping the solar wind, the magnetic field deflects those energetic particles and protects the atmosphere from destruction.

The belts are located in the inner region of Earth's magnetosphere. The belts trap energetic electrons and protons. Other nuclei, such as alpha particles, are less prevalent. The belts endanger satellites, which must have their sensitive components protected with adequate shielding if they spend significant time near that zone. In 2013, NASA reported that the Van Allen Probes had discovered a transient, third radiation belt, which was observed for four weeks until it was destroyed by a powerful, interplanetary shock wave from the Sun.

Ernst Florens Friedrich Chladni (German: [ˈɛʁnst ˈfloːʁɛns ˈfʁiːdʁɪç ˈkladnɪ]; 30 November 1756 – 3 April 1827) was a German physicist and musician. His most important work, for which he is sometimes labeled the father of acoustics, included research on vibrating plates and the calculation of the speed of sound for different gases. He also undertook pioneering work in the study of meteorites and is regarded by some as the father of meteoritics.

Polywater was a hypothesized polymerized form of water that was the subject of much scientific controversy during the late 1960s. By 1969 the popular press had taken notice and sparked fears of a "polywater gap" in the US.

Increased press attention also brought with it increased scientific attention, and as early as 1970 doubts about its authenticity were being circulated. By 1973 it was found to be illusory, being just water with any number of common organic compounds contaminating it.

Today, polywater is best known as an example of pathological science.

Wigner's friend is a thought experiment in theoretical quantum physics, first conceived by the physicist Eugene Wigner in 1961., and developed into a thought experiment by David Deutsch in 1985. The scenario involves an indirect observation of a quantum measurement: An observer W observes another observer F who performs a quantum measurement on a physical system. The two observers then formulate a statement about the physical system's state after the measurement according to the laws of quantum theory. However, in most of the interpretations of quantum theory, the resulting statements of the two observers contradict each other. This reflects a seeming incompatibility of two laws in quantum theory: the deterministic and continuous time evolution of the state of a closed system and the probabilistic, discontinuous collapse of the state of a system upon measurement. Wigner's friend is therefore directly linked to the measurement problem in quantum mechanics with its famous Schrödinger's cat paradox.

Separation of isotopes by laser excitation (SILEX) is a process for isotope separation that is being investigated to produce enriched uranium on an industrial scale using lasers. It was developed in the 1990s and is a variant of molecular laser isotope separation (MLIS). For uranium, it uses a cold molecular beam with UF₆ in a carrier cas, in which the ²³⁵UF₆ is selectively excited by an infrared laser near 16 µm. But in contrast to earlier MLIS techniques developed since the 1970s, it does not dissociate the molecule.

The green flash and green ray are meteorological optical phenomena that sometimes occur transiently around the moment of sunset or sunrise. When the conditions are right, a distinct green spot is briefly visible above the upper rim of the Sun's disk; the green appearance usually lasts for no more than two seconds. Rarely, the green flash can resemble a green ray shooting up from the sunset or sunrise point.

Green flashes occur because the earth's atmosphere can cause the light from the Sun to separate out into different colors. Green flashes are a group of similar phenomena that stem from slightly different causes, and therefore, some types of green flashes are more common than others.

Isaac Newton's rotating bucket argument (also known as Newton's bucket) was designed to demonstrate that true rotational motion cannot be defined as the relative rotation of the body with respect to the immediately surrounding bodies. It is one of five arguments from the "properties, causes, and effects" of "true motion and rest" that support his contention that, in general, true motion and rest cannot be defined as special instances of motion or rest relative to other bodies, but instead can be defined only by reference to absolute space. Alternatively, these experiments provide an operational definition of what is meant by "absolute rotation", and do not pretend to address the question of "rotation relative to what?" General relativity dispenses with absolute space and with physics whose cause is external to the system, with the concept of geodesics of spacetime.