1.1.1 The timeline of the universe
The timeline of the universe is presently thought to be the following:
- 10exp-43 second: this is known as the Plank Era and it is at close as scientists know about what happened at the Big Bang. At that time the universe -for what it was then- was very hot, dense and turbulent. The four fundamental forces -gravity, electromagnetism, weak and strong nuclear forces- were unified in a single "superforce."
- 10exp-35 second: this is called the grand Unification Era at the end of which the superforce broke apart into three forces, gravity, strong nuclear force and the combination of electromagnetism and weak nuclear forces. Moreover inflationary energy triggered the expansion of the universe from something smaller that a subatomic particle to at least the universe as we know it now. The primordial wrinkles in space-time were also smoothed out.
- 10exp-32 second: energy was dumped in the universe at the end of the inflation and particles of matter and antimatter were formed according to Einstein's law E=mc². These particles and antiparticles annihilated each other releasing radiation s well as some scattered matter.
- 10exp-11 second: in this so-called Electroweak Era electromagnetism and weak nuclear force split apart too.
- 10exp-6 second: the universe is still expanding and become cool enough for the protons and neutrons to form from their sub particles known as quarks.
- 200 seconds: the temperature is now of the order of one billion degrees Celsius allow protons and neutrons to combine into nucleus. After about twenty minutes this process stops because the temperature is too low and the formation of hydrogen and helium nuclei begins. All the other elements -including carbon, oxygen and nitrogen needed for life- will appear with the first big stars millions of years later.
- 300,000 years: in this recombination Era the temperature is now about 1,000C and the electrons can join the nuclei to form the first atoms. At the end of this era, the universe is made of about 75% hydrogen and 25% helium. The universe is now transparent to light and this is as far as we can see today.
- 200m years: small, dense region of cosmic gas collapse under their own gravity becoming hot enough to start nuclear fusion reactions between the hydrogen atoms. The lightning up of the universe has started.
- 0.5bn to 1bn years: gravity begins to pull together the dense cosmic gas forming the stars that group in galaxies and clusters of galaxies as we know them.
- 9bn years: gravity is now trying to stop the cosmic expansion but it is loosing the battle with the anti-gravitational effect of "dark energy2 that has been accelerating the cosmic expansion since then.
- 9.1bn years: gas and dust from exploding stars in the Milky Way galaxy collapse under their own gravity forming a small star -the sun- surrounded by a disk of rocks and gas. Debris from the disk collides and merges forming the earth, the moon and the other planets.