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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 .
As the universe expanded, the plasma cooled to below 3000 K—a low enough energy such that the electrons and protons in the plasma could combine to form neutral hydrogen atoms. This recombination happened when the universe was around 379,000 years old, or at a redshift of z = 1089 . [ 4 ]
Hugh Everett's universal wavefunction supports the idea that observed and observer are all mixed together: . If we try to limit the applicability so as to exclude the measuring apparatus, or in general systems of macroscopic size, we are faced with the difficulty of sharply defining the region of validity.
In the widely accepted ΛCDM cosmological model, dark matter accounts for about 25.8% ± 1.1% of the mass and energy in the universe while about 69.2% ± 1.2% is dark energy, a mysterious form of energy responsible for the acceleration of the expansion of the universe. [17] Ordinary ('baryonic') matter therefore composes only 4.84% ± 0.1% of ...
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
A visual representation of the division order of universal forces. In physical cosmology, the quark epoch was the period in the evolution of the early universe when the fundamental interactions of gravitation, electromagnetism, the strong interaction and the weak interaction had taken their present forms, but the temperature of the universe was still too high to allow quarks to bind together ...
Dark energy, however, is a substance or force responsible for the accelerating expansion of the universe over time. [2] The significant focus of The 4 Percent Universe is on the developments of astronomical science in the 20th century, including the formation of the expanding universe theory by Edwin Hubble in the 1930s.
The discovery of cosmic microwave background radiation constitutes a major development in modern physical cosmology.In 1964, US physicist Arno Allan Penzias and radio-astronomer Robert Woodrow Wilson discovered the cosmic microwave background (CMB), estimating its temperature as 3.5 K, as they experimented with the Holmdel Horn Antenna.