The Last Scattering

The Last Scattering? New to this tour in physics? Start at THE BIG BANG. 

This is the last post about the events of The Big Bang.

The Last Scattering is another term for the Cosmic Microwave Background Radiation, CMB. This is how far we can look back in time with our telescopes. Before that time photons could not escape the soup of energy. The escape of photons is also called recombination.

Recombination from Wikipedia:

“Ca. 377,000 years after the Big Bang

Hydrogen and helium atoms begin to form as the density of the universe falls. This is thought to have occurred about 377,000 years after the Big Bang.

Hydrogen and helium are at the beginning ionized, i.e., no electrons are bound to the nuclei, which (containing positively charged protons) are therefore electrically charged (+1 and +2 respectively).

As the universe cools down, the electrons get captured by the ions, forming electrically neutral atoms.

This process is relatively fast (actually faster for the helium than for the hydrogen) and is known as recombination.

At the end of recombination, most of the protons in the universe are bound up in neutral atoms. Therefore, the photons’ mean free path becomes effectively infinite and the photons can now travel freely, the universe has become transparent.

The photons present at this time are the same photons that we see in the cosmic microwave background (CMB) radiation, after being greatly cooled by the expansion of the Universe.

The cosmic microwave background is a picture of the universe at the end of this epoch including the tiny fluctuations generated during inflation, and the spread of objects such as galaxies in the universe is an indication of the scale and size of the universe as it developed over time.”

After The Last Scattering, stars and galaxies were formed., out of  hydrogen and helium.

This ends the educational Tour throough The Big Bang, but you are not finished yet. Now we will continue with quantum physics, relativistic physics and classical physics.

Next lecture  on THE PHYSICS TOUR.

The Last Scattering

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