Cosmic timeline 03

How do we know how old the Universe is?
The answer depends on the rate of the expansion of the Universe and the calculation by Edwin Hubble of what is called Hubble’s constant. Hubble’s law of for the expansion of the Universe says that the speed at which any galaxy is moving away from us is equal to the distance from our own Milky Way galaxy multiplied by Hubble’s constant.

Using this calculation it is possible to work out when all the galaxies were close together at the beginning of the Universe. Current observations put Hubble’s constant, or H, at around 60 km (37 miles) per second per million parsecs. A parsec is a unit of astronomical distance of 3.26 light years, and a light year is the distance light travels in a year at the speed of 186,000 miles per second.

This gives an age of the Universe of about 15 billion years.

Modern scientific cosmology begins in 1917 with Albert Einstein‘s publication of his final modification of The General Theory of Relativity. General relativity prompted cosmogonists such as Willem de Sitter, Karl Schwarzschild and Arthur Eddington to explore the astronomical consequences of the theory, through the study of very distant objects using powerful telescopes. Prior to this physicists assumed that the Universe was static and unchanging.

In parallel to this dynamic approach to cosmology, a debate was unfolding regarding the nature of the cosmos itself. On the one hand, Mount Wilson astronomer Harlow Shapley championed the model of a cosmos made up of the Milky Way star system only.

Heber D. Curtis, on the other hand, suggested spiral nebulae were star systems in their own right, island universes. This difference of ideas came to a climax with the organization of the Great Debate at the meeting of the (US) National Academy of Sciences in Washington on 26 April 1920.

The resolution of the debate on the structure of the cosmos came with the detection of novae in the Andromeda galaxy by Edwin Hubble in 1923 and 1924. Their distance established spiral nebulae well beyond the edge of the Milky Way.

Subsequent modeling of the universe explored the possibility that the cosmological constant introduced by Einstein in his 1917 paper may result in an expanding universe, depending on its value.

Thus the big bang theory was proposed by the Belgian priest Georges Lemaître in 1927 which was subsequently corroborated by Edwin Hubble‘s discovery of the red shift in 1929 and later by the discovery of the cosmic microwave background radiation by Arno Penzias and Robert Woodrow Wilson in 1964.

So what happens after the so-called big bang?
The Universe underwent the second major cosmic phase transition just a tiny fraction of time after its beginning. The strong nuclear force separated from the superforce to become a fundamental universal entity, while electromagnetism and the weak nuclear force remain as the so-called electroweak force.

This phase gives rise to the next stage, the super-rapid expansion of space.

Grand Unification Epoch
Of course this still just a theory, part of what is currently called Grand Unification, grand unified theory, or GUT and refers to any of several similar unified field theories or models in particle physics in which at high energies, the gauge interactions of the standard model, namely the electromagnetic, weak nuclear, and strong nuclear interactions are unified into a single interaction. The grand unification epoch was the period in the evolution of the early universe following the Planck epoch, starting at about 0.0000000000000000000000000000000000000000001 seconds after the Big Bang, in which the temperature of the universe was comparable to the characteristic temperatures of grand unified theories


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