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In physics, sound energy is a form of energy that can be heard by living things. Only those waves that have a frequency of 16 ...
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.
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
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 ]
On March 6, 2008, the United States Postal Service released a 41-cent stamp honoring Hubble on a sheet titled "American Scientists" designed by artist Victor Stabin. [46] His citation reads: [ 61 ] Often called a "pioneer of the distant stars", astronomer Edwin Hubble (1889–1953) played a pivotal role in deciphering the vast and complex ...
Based on the 2013 data, the universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy. On 5 February 2015, new data was released by the Planck mission, according to which the age of the universe is 13.799 ± 0.021 billion years old and the Hubble constant was measured to be 67.74 ± 0.46 (km/s)/Mpc .
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.
The scale factor is dimensionless, with counted from the birth of the universe and set to the present age of the universe: [4] giving the current value of as () or . The evolution of the scale factor is a dynamical question, determined by the equations of general relativity , which are presented in the case of a locally isotropic, locally ...