PART-3/8--The Universe: Big Bang to Now in 10 Easy Steps((The Origin, History, Evolution & Future of the Universe)

How the Universe Came to Be
INTRODUCTION

Credit: Subaru/ P. Capak (SSC/Caltech)

The broadly accepted theory for the origin and evolution of our universe is the Big Bang model, which states that the universe began as an incredibly hot, dense point roughly 13.7 billion years ago. So, how did the universe go from being fractions of an inch (a few millimeters) across to what it is today?

Here is a breakdown of the Big Bang to now in 10 easy-to-understand steps.



10.How It All Started

Credit: NASA/WMAP

The Big Bang was not an explosion in space, as the theory's name might suggest. Instead, it was the appearance of space everywhere in the universe, researchers have said. According to the Big Bang theory, the universe was born as a very hot, very dense, single point in space.
In 2001, NASA launched the Wilkinson Microwave Anisotropy Probe (WMAP) mission to study the conditions as they existed in the early universe by measuring radiation from the cosmic microwave background. Among other discoveries, WMAP was able to determine the age of the universe — about 13.7 billion years old.

9.The Universe's First Growth Spurt

Credit: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team

When the universe was very young — something like a hundredth of a billionth of a trillionth of a trillionth of a second (whew!) — it underwent an incredible growth spurt. During this burst of expansion, which is known as inflation, the universe grew exponentially and doubled in size at least 90 times.
After inflation, the universe continued to grow, but at a slower rate. As space expanded, the universe cooled and matter formed.
8.Too Hot to Shine

Credit: NASA/WMAP

Light chemical elements were created within the first three minutes of the universe's formation. As the universe expanded, temperatures cooled and protons and neutrons collided to make deuterium, which is an isotope of hydrogen. Much of this deuterium combined to make helium.

For the first 380,000 years after the Big Bang, however, the intense heat from the universe's creation made it essentially too hot for light to shine. Atoms crashed together with enough force to break up into a dense, opaque plasma of protons, neutrons and electrons that scattered light like fog.
7.Let There Be Light

Credit: ESA/ LFI & HFI Consortia

About 380,000 years after the Big Bang, matter cooled enough for electrons to combine with nuclei to form neutral atoms. This phase is known as "recombination," and the absorption of free electrons caused the universe to become transparent. The light that was unleashed at this time is detectable today in the form of radiation from the cosmic microwave background.

Yet, the era of recombination was followed by a period of darkness before stars and other bright objects were formed.
6.Emerging from the Cosmic Dark Ages

Credit: ESA XMM-Newton/EPIC, LBT/LBC, AIP (J. Kohnert)

Roughly 400 million years after the Big Bang, the universe began to come out of its dark ages. This period in the universe's evolution is called the age of re-ionization.
During this time, clumps of gas collapsed enough to form the very first stars and galaxies. The emitted ultraviolet light from these energetic events cleared out and destroyed most of the surrounding neutral hydrogen gas. The process of re-ionization, plus the clearing of foggy hydrogen gas, caused the universe to become transparent to ultraviolet light for the first time.
5.More Stars and More Galaxies

Credit: ESA, Hubble, NASA

Astronomers comb the universe looking for the most far-flung and oldest galaxies to help them understand the properties of the early universe. Similarly, by studying the cosmic microwave background, astronomers can work backwards to piece together the events that came before.
4.Birth of Our Solar System

Credit: NASA

Our solar system is estimated to have been born a little after 9 billion years after the Big Bang, making it about 4.6 billion years old. According to current estimates, the sun is one of more than 100 billion stars in our Milky Way galaxy alone, and orbits roughly 25,000 light-years from the galactic core.

Many scientists think the sun and the rest of our solar system was formed from a giant, rotating cloud of gas and dust known as the solar nebula. As gravity caused the nebula to collapse, it spun faster and flattened into a disk. During this phase, most of the material was pulled toward the center to form the sun.
3.The Invisible Stuff in the Universe

Credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

In the 1960s and 1970s, astronomers began thinking that there might be more mass in the universe than what is visible.
This mysterious and invisible mass became known as dark matter. Dark matter is inferred because of the gravitational pull it exerts on regular matter. One hypothesis states the mysterious stuff could be formed by exotic particles that don't interact with light or regular matter, which is why it has been so difficult to detect.

Dark matter is thought to make up 23 percent of the universe. In comparison, only 4 percent of the universe is composed of regular matter, which encompasses stars, planets and people.
2.The Expanding and Accelerating Universe

Credit: NASA, ESA, D. Coe (NASA Jet Propulsion Laboratory/California Institute of Technology, and Space Telescope Science Institute), N. Benitez (Institute of Astrophysics of Andalusia, Spain), T. Broadhurst (University of the Basque Country, Spain), and H. Ford

In the 1920s Hubble observed that the universe is not static, but rather is expanding.

Decades later, in 1998, the prolific space telescope named after the famous astronomer, the Hubble Space Telescope, studied very distant supernovas and found that, a long time ago, the universe was expanding more slowly than it is today. This discovery was surprising because it was long thought that the gravity of matter in the universe would slow its expansion, or even cause it to contract.

Dark energy is thought to be the strange force that is pulling the cosmos apart at ever-increasing speeds, but it remains undetected and shrouded in mystery. The existence of this elusive energy, which is thought to make up 73 percent of the universe, is one of the most hotly debated topics in cosmology.
1.Still a Lot to Learn

Credit: NASA

Dark matter and dark energy remain two of the biggest mysteries, but cosmologists continue to probe the universe in hopes of better understanding how it all began.




http://www.space.com/13320-big-bang-universe-10-steps-explainer.html