Hubble constant and expansion of the universe | |||||||||||||||||||||||||||||
Expansion of the universe | Automatic translation | Updated June 03, 2014 | |||||||||||||||||||||||||||
When you look in the past the universe is becoming smaller, denser and hotter. In other words, all objects in the Universe are approaching each other when we go back in time. Astronomy has two major areas of science, cosmology and particle physics. Which connects the two domains is Big Bang theory. In 1923 Edwin Hubble (1889-1953) uses the Hooker telescope 250 cm, the most powerful telescope time. Observations made with the Hubble telescope allow to establish that the nebulae previously observed with less powerful telescopes are not part of our Galaxy. Indeed, it determines the distance of the Andromeda galaxy (M31), which he estimated at 800,000 light-years, which places it outside our galaxy. Thus, Hubble terminates long debate on the nature of diffuse objects that now call galaxies. A little later in 1929, Hubble analysis radial velocities of galaxies, previously measured by Vesto Slipher (1875-1969), from redshifts of spectral lines. He limits himself to the first galaxies at least 6 million light years and finds that the speed-distance relationship is approximately linear. Along with Milton Humason (1891-1972), he extended his study of distant galaxies within 100 million light years, the relationship remains linear. Hubble then enunciate his famous law, "The galaxies are receding from each other at a speed proportional to their distance." In other words, plus a galaxy is away from us, more it seems to move away quickly. So he created the concept of expansion of the Universe. Galaxies are receding, but it is not a true motion of galaxies, is the Universe expands and gives the apparent velocity to galaxies. It is the space between galaxies increases, in fact it is the space-time expands. The rate of expansion of galaxies between them corresponds to the Hubble constant (Hο) calculated by Edwin Hubble and George Lemaitre in 1930. The inverse of the Hubble constant is called the "Hubble time" corresponds to the time since the Big Bang, so at the age of the universe. The CMB was discovered in 1965, is a real "Rosetta Stone" for cosmologists, as it allows to decipher the thermal history of the universe since the Big Bang. | Map of the cosmic microwave background (image opposite) represents the electromagnetic radiation from the first moments of the observable Universe. These photons detectable today in the range of radio waves, kept the traces of major emerging structures which are then transported by inflation. NB: The three units of measurement useful in astronomy to express the distances:
| Image: These small fluctuations in temperature are the first glimmers of the observable universe seen by the Planck mission (March 2013). Since 2013, European astronomers, Canadian and U.S. have refined the composition of the Universe. This false-color composite image represents the traces of the first moments of creation, about 380,000 years after the Big Bang, there are 13,800,000,000 years (≈ 1%). The universe is composed of 69.4% dark energy, 25.8% of cold dark matter and 4.8% of atoms, i.e. ordinary matter. Credit image: ESA. |