Hubble constant and expansion of the universe

Expansion of the universe

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.
What is the value of the Hubble constant?
The value of the Hubble constant (Hο) is not known with precision. All measurements made since the 2000s, giving a value between 63 km/s/Mpc and 73 km/s/Mpc. In March 2013, the Planck satellite whose mission is to reconstruct the thermal history of the Universe, calculated a value of 67 km/s/Mpc.
In other words a bubble of 1 Mpc, i.e. 3.26 light-years, inflates of 67 km per second, a 10 Mpc bubble inflates 670 km every second, a bubble inflates 100 Mpc of 6700 km every second...
What is the effect of the expansion of the Universe on the Earth-Sun distance?
The expansion of the universe is only applicable to very large spaces, i.e. between entities such as galaxy clusters and super clusters. In the solar system, objects are "connected" by the gravitational force of the Sun and the whole can be seen as a compact system. Objects, with a mass and with a speed relative to the other is less than the escape velocity, are part of a gravitational system. As long as the system is gravitationally bound, the space between objects can not swell up under the effect of an antigravitational force. The entire system is decoupled from the expansion of the observable universe. It is the same for the Sun inside the Galaxy.

NB: The three units of measurement useful in astronomy to express the distances:
- light year (a.l.) A light year is a unit of distance used in astronomy. A light-year is equal to the distance that light travels in a vacuum in the space of one year (31,557,600 seconds), about 10,000 billion kilometers. is the 63242.17881 au, is exactly equal to 9 460 895 288 762 850 m.
- parsec (pc The parsec is the distance at which one astronomical unit subtends an angle of one arcsecond.) is equal to 206 AU or 270.6904 3.2616 years-light or 30 857 656 073 828 900 m.
- astronomical unit (au (symbol: ua ou au) Créée en 1958, c’est l'unité de distance utilisée pour mesurer les distances des objets du système solaire, cette distance est égale à la distance de la Terre au Soleil. La valeur de l'unité astronomique représente exactement 149 597 870 700 m, lors de son assemblée générale tenue à Pékin, du 20 au 31 août 2012, l'Union astronomique internationale (UAI) a adopté une nouvelle définition de l'unité astronomique, unité de longueur utilisée par les astronomes du monde entier pour exprimer les dimensions du Système solaire et de l’Univers. On retiendra environ 150 millions de kilomètres. Une année-lumière vaut approximativement 63 242 ua. Mercure: 0,38 ua, Vénus: 0,72 ua, Terre: 1,00 ua, Mars: 1,52 ua, Ceinture d’astéroïdes: 2 à 3,5 ua, Jupiter: 5,21 ua, Saturne: 9,54 ua, Uranus: 19,18 ua, Neptune: 30,11 ua, Ceinture de Kuiper: 30 à 55 ua, Nuage d’Oort: 50 000 ua.) is from August 30, 2012, exactly 149 597 870 700 meters.

Table of equivalences on units of distances.