THE BIG BANG THEORY
The Big Bang theory is the most widely accepted explanation of how the universe formed. He was a Belgian Catholic priest, theoretical physicist, mathematician, astronomer, and professor of physics at the Catholic University of Louvain.
According to the Big Bang theory, the universe began as an incredibly dense, hot, primordial fireball of expanding space, energy, and matter. Before this explosion, or the Big Bang, there was no universe as we know it, and space and time as we now know them did not exist. How long this state existed is unknown: but, according to astronomers' best estimates, about 13 to 14 billion years ago the event known as the Big Bang occurred. This explosion marks the beginning of the universe, including time, space, and the perception of the changes that have occurred from the time of the Big Bang to the present.
The Big Bang Theory
Abbé Georges Lemaître, a Belgian who was both a cleric and a scientist, was the father of the big bang model. Lemaître proposed a theory that is consistent both with Hubble’s observation that the universe is expanding and with the theological idea that the universe had a definite beginning point.
According to the Big Bang theory, the universe had a moment of formation when it appeared as an initial fireball. What caused this primeval fireball and what existed before the fireball came into existence is beyond the realm of questions science can answer. The fireball caused everything we can see in the universe today to expand away from the site of the fireball; we still observe that the universe is expanding.
This expanding fireball is often presented as a giant explosion, but this needs some rethinking. In an explosion, such as a bomb or firecracker, matter expands to fill up space that is already there.
In the expanding universe, space is expanding so that the galaxies in space are moving farther apart.
A better analogy than an explosion is a loaf of raisin bread. The raisins are spread throughout the bread and move farther apart as the dough rises.
As the universe continued to expand and cool, matter began to clump. Large clumps formed galaxies, such as our own Milky Way galaxy, which contains hundreds of billions of stars. We think all galaxies were formed about the same time during the early history of the universe. When galaxies are young, they often go through very energetic stages when they emit far more energy from their nuclei than can easily be explained.
Galaxies in this stage are quasars. The energy source for quasars, which is probably a supermassive black hole, tends to reduce the amount of energy it emits as it ages. Hence quasars existed only during the early history of the universe. Because of light travel time from the far reaches of the universe, we only see quasars at great distances. Closer galaxies have finished with the quasar stage.
The first generation of stars that formed in our galaxy were mostly hydrogen and helium because that was what was made during the Big Bang.
The nuclear fusion reactions that create stars fuse these lighter elements into heavier elements. When stars run out of hydrogen fuel in their cores, they expand into red giants, which might be about the size of Earth’s orbit around the Sun (or larger).
Stars of about the Sun’s mass can then fuse helium to carbon, and some oxygen, in their cores. These stars will then collapse into slowly cooling, burned-out stars about the size of Earth that are called white dwarfs.
If the white dwarf is more than 1.4 times the mass of the Sun, it can not be a stable white dwarf and collapses into a neutron star.
The protons and electrons are squeezed together into neutrons, and the neutron star collapses to about the size of a city. During the transition from red giant to white dwarf, many stars gently blow off their outer layers to form a planetary nebula, which is a shell of gas around a dying star.
Stars that are ten or more times the mass of the Sun can fuse elements heavier than carbon in their cores. The extra mass provides enough gravitational force needed to squeeze these heavier elements to undergo fusion, until elements about as heavy as iron on the periodic table are made. Iron is the boundary between fission and fusion; so fusing elements heavier than iron requires, rather than releases, energy. When the iron core builds up in these massive stars, they explode in a humongous explosion called a supernova.
A supernova releases as much energy in a year as the Sun does in its 10 billion-year lifetime. There is plenty of energy to make all the elements that will normally not fuse. The supernova also blasts these heavy elements out into space to be recycled into the next generation of stars.
The Crab Nebula is the remnant of a supernova that occurred on July 4, 1054. The material, enriched in heavy elements, will be recycled into nebulas such as the Orion Nebula which is in the process of forming new stars. Our solar system formed from a nebula that was also enriched in heavy elements by a prior generation of stars that exploded as supernovas.
The core that remains after the supernova explosion will collapse into a neutron star, which is a ball of neutrons with a mass comparable to the Sun but compressed to the size of a city.
If the core is more than about two to three times the mass of the Sun, it will collapse into a black hole. To become a black hole, the Sun would have to be compressed to a radius of fewer than three kilometers. A black hole is so highly compressed that its escape velocity exceeds the speed of light. Hence nothing can escape!
Because they manufacture and recycle heavy elements, supernovas play a crucial role in how you get here. The atoms in your body heavier than hydrogen were manufactured in the cores of stars and recycled by supernova explosions.
BACKGROUND RADIATION:
In 1965, American physicists Arno Penzias and Robert Wilson made a startling discovery. Disproving the expectations of most scientists of the day, they discovered that the universe is not entirely cold, but has an ambient temperature of about 3 Kelvin due to background radiation. Kelvin is the absolute temperature scale on which 0 K is absolute zero, the temperature marking the absence of all energy.
The recently developed Cosmic Background Explorer (COBE) detected, as it looked into deep space, a small amount of background radiation in all directions. The existence of background radiation agreed perfectly with predictions made by proponents of the Big Bang. Scientists interpret the energy observed by COBE as essentially leftover radiation from the Big Bang. Amazingly, an event that occurred so long ago has 'embers' still glowing throughout the known universe!
REDSHIFT - OUR EXPANDING UNIVERSE:
Additional evidence supporting the Big Bang theory is the observed expansion of the universe over time. This expansion is seen as a redshift in the light spectra emitted by stars and galaxies. To visualize the redshift, one needs to understand that stars are rich in the elements hydrogen and helium. Certain conditions in stars cause the atoms of all elements to emit energy. The energy released by each element emits a characteristic electromagnetic pattern that is analogous to the bar code found on the packaging of most products at the local supermarket.
