La teoria del big bang y la formacion del Universo

• The Big Bang theory is the prevailing cosmological model for the early development of the universe.

• The key idea is that the universe is expanding. Consequently, the universe was denser and hotter in the past. Moreover, the Big Bang model suggests that at some moment all matter in the universe was contained in a single point, which is considered the beginning of the universe.

• Modern measurements place this moment at approximately ~13.8 billion years ago, which is thus considered the age of the universe.

• After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, including protons, neutrons, and electrons. Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed.

• The majority of atoms that were produced by the Big Bang are hydrogen, along with helium and traces of lithium. Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies, and the heavier elements were synthesized either within stars or during supernovae.

Background radiation left over from the Big Bang

free electrons met up with nuclei and created neutral atoms. This allowed light to shine through about 380,000 years after the Big Bang.

• Most of this matter, which formed from the pure energy of the Big Bang, took the form of hydrogen and helium atoms within about 300,000 years.

• So where did all of the other elements like carbon, oxygen, and iron come from? -> Elements larger than hydrogen and helium formed during the last supernova stage of dying stars.

• Within a few hundred million years after the Big Bang, the hydrogen and helium had pulled together under the force of gravity to form stars, which shine because hydrogen atoms are fusing together to make helium atoms, releasing radiation energy in the process.

• When the hydrogen runs out, the stars go through a rapid sequence of fusion stages called a supernova that produces heavier elements and then ejects them into space.

• This means that most of Earth, including your body, is made of the exploded ashes of a dead star.

The matter of our planet was primarily made through two very different mechanisms: the Big Bang and the supernovae of dying stars.

- The moment the Big Bang occurred, the universe immediately began to expand at speeds on the order of the speed of light. The energy and matter expanded outward, pulling the universe with it.

- Soon after the Big Bang, energy began converting into matter according to Einstein’s well-known equation E = mc2 .

Predicted timeline of the Big Bang

• 1) At the start of the Big Bang, all four of the fundamental forces were unified as a single force (weak nuclear, strong nuclear, electromagnetism and gravity).

• 2) By 10-43 seconds after the Big Bang the single unified force began to split apart.

• 3) By 10-34 seconds, the universe entered into a period of inflationary expansion, moving faster than the speed of light.

• 4) By 10-32 seconds, the first subatomic particles were forming. The universe was 30 centimeters in diameter and had a temperature of 3x1026 K.

• 5) By 10-11 seconds, the four forces had finally separated with the split of the electromagnetic and weak nuclear forces.

• 6) By 10-5 seconds, protons and neutrons had formed, though it was still too hot for stable atoms to form. The universe was 0.002 light-years in size (100 times the earth-sun distance) and had a temperature of 1013 K.

• 7) By one second, electrons had formed and were annihilating positrons. The universe was three light-years in size with a temperature of 1010 K.

• 8) By three minutes, hydrogen atoms were forming, though it was still too hot for stable atoms to form. The universe was 50 lightyears in size with a temperature of 1 billion degrees Kelvin.

• 9) By 10,000 years, matter began to dominate over radiation. The universe was two million light-years in size with a temperature of 30,000 K.

• 10) By 1 billion years, protogalaxies and the first stars were forming. The universe was 10 billion light-years in size with a temperature of only 10 K.

• 11) By 5 billion years, full galactic disks were forming. The universe was 20 billion light-years in size with a temperature of 5 K.

• 12) Currently, 13.7 billion years after the Big Bang, the universe is 40 billion light-years in size with a temperature of 2.7 K

• (- 270.42° C).

• The fate of the universe depends upon the amount of mass it contains.

• 1. If there is too much mass, the universe will stop expanding and eventually collapse;

• 2. if there is too little mass, the universe will continue to expand forever.

• It currently seems as if the rate of expansion of the universe is actually increasing.

Gravity

• The force of gravity is responsible for the formation of galaxies. Galaxies contain between tens of millions and a trillion stars. Stars are more plentiful and tend to be much larger near the centers of galaxies.

• Stars are born when there is enough hydrogen that the intense pressure causes hydrogen atoms to fuse together to form helium, emitting light in the process. This process is called nuclear fusion.

Near the end of a star’s life, hydrogen fusion occurs in theouter layer of the star, and the star swells in size to become a red giant or supergiant.

In the final stages of a star, when the hydrogen runs low, the helium begins fusing to start a series of fusion reactions that creates elements larger than helium.

• Stars follow a life cycle that is variable depending upon the size of the star.

• 1. Low-mass stars, at the end of their lifetimes, go through a sequence of becoming red giants, planetary nebulae, and then white or black dwarves; small stars can last for many billions of years.

• High-mass stars go through a final sequence of being a red supergiant, a supernova, and either a neutron star or black hole; very large stars can burn out in only thousands of years.

• The fact that our solar system contains planets means that our sun must be a second-generation star. A previous star had to die for the planet

• Earth to be formed from its remains.