The Big Bang

The Science connexions field of study begins 13,799,000,000 years ago with the "Big Bang". This cosmological model, which is now universally adopted, was proposed in 1927 by Georges Lemaître. In 1929, Edwin Hubble demonstrated the expansion of the universe and created the law of Hubble. 

It was in 1965 that the existence of the Big Bang was experimentally demonstrated with the discovery of the cosmological background by Arno Allan Penzia and Robert Woodrow Wilson.   

Before we do not know what was there or if there was something. The Big Bang is the most distant horizon that can be apprehended. is a mathematical singularity and the equations of physics are not valid. 

The world that we can think of using physics begins 10-43 seconds after the Big Bang. This is called the Planck era. It was during the Big Bang that all the material contained in the universe was created. In fact, there is not just the material that was created during the Big Bang: Antimatter and dark matter were also created.

It was also during the Big Bang that space-time appeared the forces and the particles. We will return to the forces and particles a little later. Let's focus on the particles first.

At first, the universe was too hot for atoms to form. At first, the universe consisted of a sea of quarks and electrons.

At some point (T = X), temperature and density decreased sufficiently for quarks to combine to form protons and some neutrons.

When the temperature dropped to (T = Y), the electrons were able to combine with the protons to form the first atoms. Thus, hydrogen and primordial helium were created (along with a small amount of lithium).

This event occurred 300 000 years after the Big Bang. Previously, the universe was only a plasma of proton particles and electrons opaque to light. As soon as a photon was emitted, it was reabsorbed when it encountered another electron or proton floating in the plasma.

When the electrons combined with the protons, the photons could begin to circulate freely: the universe became transparent to electromagnetic radiation.

This radiation can still be detected today and is called the cosmological diffuse background. A few years ago, we could even see it in our living room: part of the snow we saw on our analog TVs was actually the cosmic background that was captured by the television antennas.

The particles we know are described by what is called the Standard Model. It has 20 elementary particles, the last of which, the Higgs boson, has only been discovered very recently.

Each particle is also a wave that has a probability of distribution in space.

This wave-particle duality is one of the foundations of quantum mechanics. In some cases, an electron can behave like a particle and in other cases the same electron can behave like a wave.

The simplest atom is the hydrogen atom that is composed at the base of a proton and an electron. There are also other variants of the hydrogen atom called isotopes that possess either a neutron (deuterium) or two neutrons (tritium).

During recombination, our hydrogen atom is found in a huge molecular cloud that contains a literally astronomical amount of hydrogen and helium atoms. Quickly, under the force of gravity, the cloud collapses around a slightly denser point in order to form a first-generation star.

The first stars, that the James Webb Space Telescope, which will be launched in 2020, should allow us to see was very massive and much larger than the sun.

Generally, the more a star is massive, the more it "burns" its nuclear fuel quickly. Stars that are more than 8 times larger than the sun end their lives in an extraordinary "explosion" called supernovae.

The mapping of the diffuse background of cosmological radiation shows very slight variations in the density of the primordial universe. These slight variations were sufficient for gravity to begin to do its work and begin to compress the atoms.

The more the attraction is effective, the more gravity accelerates the particles and quickly, the molecular cloud begins to collapse on itself.

The more the cloud collapses, the more the heart temperature increases. When the temperature reaches 10 million degrees, the star lights up and the thermonuclear reactions begin. The hydrogen atoms merge to create new helium atoms.

Chain of thermonuclear reactions for hydrogen fusion in helium

The mass of the resulting helium atom being slightly smaller than the mass of the 2 hydrogen atoms, the difference is converted to energy according to the famous Einstein formula: E = mc2.

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