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In the late 1990s, observations of supernovae [1] determined that not only is the universe expanding, it is expanding at an increasing rate. A better understanding of the acceleration of the universe, or dark energy, has become one of the most important questions in cosmology today. In order to understand the nature of the dark energy, it is ...
Sound waves that have frequencies below 16 Hz are called infrasonic and those above 20 kHz are called ultrasonic. Sound is a mechanical wave and as such consists physically in oscillatory elastic compression and in oscillatory displacement of a fluid .
To create an electron-positron pair, the total energy of the photons, in the rest frame, must be at least 2m e c 2 = 2 × 0.511 MeV = 1.022 MeV (m e is the mass of one electron and c is the speed of light in vacuum), an energy value that corresponds to soft gamma ray photons.
Gravitational energy from visible matter accounts for 26–37% of the observed total mass–energy density. [15] Therefore, to fit the concept of a "zero-energy universe" to the observed universe, other negative energy reservoirs besides gravity from baryonic matter are necessary. These reservoirs are frequently assumed to be dark matter. [16]
Sound waves may be viewed using parabolic mirrors and objects that produce sound. [9] The energy carried by an oscillating sound wave converts back and forth between the potential energy of the extra compression (in case of longitudinal waves) or lateral displacement strain (in case of transverse waves) of the matter, and the kinetic energy of ...
For example, d-wave or triplet superconductor, or a Fulde–Ferrell–Larkin–Ovchinnikov superconductor. Ferromagnetic superconductor: Materials that display intrinsic coexistence of ferromagnetism and superconductivity. Charge-4e superconductor: A proposed state in which electrons are not bound as Cooper pairs but as quadruplets of electrons.
Gerson Goldhaber (1924–2010) used supernova observations to measure the energy density of the universe; J. Richard Gott (1947–) proposed the use of cosmic strings for time travel; Alan Guth (1947–) explained the isotropy of the universe by theorizing a phase of exponential cosmic inflation soon after the big bang
The appearance of these distorted galaxies depends on the distribution of matter in the lens and on the relative geometry of the lens and the distant galaxies, as well as on the effect of dark energy on the geometry of the Universe. In astronomy and cosmology, baryonic dark matter is hypothetical dark matter composed of baryons. Only a small ...