Hubble Space TelescopeThe Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versatile, renowned both as a vital research tool and as a public relations boon for astronomy. The Hubble telescope is named after astronomer Edwin Hubble and is one of NASA's Great Observatories.
Primordial fluctuationsPrimordial fluctuations are density variations in the early universe which are considered the seeds of all structure in the universe. Currently, the most widely accepted explanation for their origin is in the context of cosmic inflation. According to the inflationary paradigm, the exponential growth of the scale factor during inflation caused quantum fluctuations of the inflation field to be stretched to macroscopic scales, and, upon leaving the horizon, to "freeze in".
Pulsar timing arrayA pulsar timing array (PTA) is a set of galactic pulsars that is monitored and analysed to search for correlated signatures in the pulse arrival times on Earth. As such, they are galactic-sized detectors. Although there are many applications for pulsar timing arrays, the best known is the use of an array of millisecond pulsars to detect and analyse long-wavelength (i.e., low-frequency) gravitational wave background.
Timeline of gravitational physics and relativityThe following is a timeline of gravitational physics and general relativity. 3rd century BC – Aristarchus of Samos proposes heliocentric model, measures the distance to the Moon and its size 1543 – Nicolaus Copernicus places the Sun at the gravitational center, starting a revolution in science 1583 – Galileo Galilei induces the period relationship of a pendulum from observations (according to later biographer). 1586 – Simon Stevin demonstrates that two objects of different mass accelerate at the same rate when dropped.
ObservableIn physics, an observable is a physical property or physical quantity that can be measured. Examples include position and momentum. In systems governed by classical mechanics, it is a real-valued "function" on the set of all possible system states. In quantum physics, it is an operator, or gauge, where the property of the quantum state can be determined by some sequence of operations. For example, these operations might involve submitting the system to various electromagnetic fields and eventually reading a value.
HyperinflationIn economics, hyperinflation is a very high and typically accelerating inflation. It quickly erodes the real value of the local currency, as the prices of all goods increase. This causes people to minimize their holdings in that currency as they usually switch to more stable foreign currencies. When measured in stable foreign currencies, prices typically remain stable. Unlike low inflation, where the process of rising prices is protracted and not generally noticeable except by studying past market prices, hyperinflation sees a rapid and continuing increase in nominal prices, the nominal cost of goods, and in the supply of currency.
Speed of gravityIn classical theories of gravitation, the changes in a gravitational field propagate. A change in the distribution of energy and momentum of matter results in subsequent alteration, at a distance, of the gravitational field which it produces. In the relativistic sense, the "speed of gravity" refers to the speed of a gravitational wave, which, as predicted by general relativity and confirmed by observation of the GW170817 neutron star merger, is the same speed as the speed of light (c).
DeflationIn economics, deflation is a decrease in the general price level of goods and services. Deflation occurs when the inflation rate falls below 0% (a negative inflation rate). Inflation reduces the value of currency over time, but sudden deflation increases it. This allows more goods and services to be bought than before with the same amount of currency. Deflation is distinct from disinflation, a slow-down in the inflation rate, i.e. when inflation declines to a lower rate but is still positive.
SeigniorageSeigniorage ˈseɪnjərɪdʒ, also spelled seignorage or seigneurage (from the Old French seigneuriage, "right of the lord (seigneur) to mint money"), is the difference between the value of money and the cost to produce and distribute it. The term can be applied in two ways: Seigniorage derived from specie (metal coins) is a tax added to the total cost of a coin (metal content and production costs) that a customer of the mint had to pay, and which was sent to the sovereign of the political region.
