THEORIES ON THE ORIGIN OF UNIVERSE

The Big Bang Theory 

In cosmology, the Big Bang is the scientific theory that describes the early development and shape of the universe.

The Big Bang Theory is the most accepted theory for the origin and evolution of our universe. The big bang theory states that at some time in the distant past there was nothing. It suggests that around 10 to 14 billion years ago, the part of the universe we can see today was only a few millimetres across. According to this theory, at the beginning of time, all of the matter and energy in the universe was concentrated in a very dense state, from which it "exploded" and this is known as the Big Bang.

The Big Bang marks the instant at which the universe began. From a dense, hot ball of gas, radiation and subatomic particles. This exploded and began expanding rapidly outward. As it expanded it cooled and electrons, protons and neutrons formed. As the universe grew in size, the temperature dropped, which eventually formed huge numbers of Hydrogen, Helium and Lithium nuclei. After many millions of years the expanding universe, at first a very hot gas, thinned and cooled enough to condense into individual galaxies and then stars. Stars and galaxies began to form about one billion years following the Big Bang. It has since expanded from this hot dense state into the vast and much cooler cosmos we currently inhabit.

Evidence for the Big Bang Theory

American astronomer Edwin Hubble provided some of the greatest supporting evidence for the theory with his 1929 discovery that the light of distant galaxies was generally shifted toward the red end of the spectrum, this is called the Red Shift. This happens when stars are moving rapidly away from Earth. This evidence means that it is obvious that the universe is expanding.

The second evidence is that this theory predicts that 25 percent of the total mass of the universe should be the helium that formed during the first few minutes, an amount that agrees with observations.Thirdly, a cosmic background noise was the discovery in 1965, is received from every part of the sky. This background radiation has the same intensity and distribution of frequencies in all directions and is not linked with any individual celestial object. It has a black body temperature of -270 deg C and is interpreted as the electromagnetic remnant of the primordial fireball, stretched to long wavelengths by the expansion of the universe.

Other evidence that supports the big bang theory is the Isotropy of observable universe. Proponents of big bang also mention isotropy of the observable universe to one part in one hundred thousand as evidence that big bang is valid. They further state that what minute anisotropy does exist is consistent with big bang hypotheses which include the dark matter hypotheses.

Also Quasars are predicted to only be possible in the early stages of an active cosmos by the Big Bang theory, and observation evidence supports this, as quasar populations become denser the further away when you look at them.

Another piece of evidence for the Big Bang model is that it resolves Olbers' paradox of why the sky is black at night.

But the most convincing evidence is the presence of the cosmic background radiation, a theoretical prediction about photons left over from the big bang. The big-bang theory predicted this remnant radiation, which now glows at a temperature just 3 degrees above absolute zero. Cosmic Background Explorer (COBE) satellite, launched in 1989, showed that 99.97% of the radiant energy of the universe was released within the first year of the Big Bang event.

The Big Bounce Theory 

This is a theory that states there was actually something before the Big Bang. It suggests that another universe went through a Big Crunch and then 'bounced' back and gave birth to this universe, says Scientific American Science Editor Roger Highfield in his article "Before the Big Bang-the Big Bounce". The

Big Bounce seems to solve the problem of the unknown singularity factor of the Big Bang. It takes away the notion that the universe came to be from an infinite dense area with no mass, which goes against all mathematical notions.

Based on Loop Quantum Gravity, it combines Einstein's theory of gravity with that of quantum theory, which could provide light on the question of what was there before the Big Bang happened, says Dr. Martin Bojowald, Assistant Professor of Physics at Penn State University.

Cyclic Universe Theory

As the name implies, a cyclic universe explodes into existence in a Big Bang, and crunches out of existence over and over again in an endless cycle. This theory is an alternative to the Big Bang that has gotten much attention from scientists after Princeton physicist Paul Steinhardt and Neil Turok of Cambridge University published an article on it in the Science online edition.The Cyclic Universe Theory could explain the mystery of why the 'cosmological constant' is accelerating, which the Big Bang theory could not account for, says Ker Than in his article "Recycled Universe: Theory Could Solve Cosmic Mystery" on Space.com. It also answers the long-standing question of what was before the Big Bang.

Steady State Theory

Another alternative to the Big Bang theory is the Steady State theory. This theory was developed by Fred Hoyle and Thomas Gold in 1949. Ironically, Fred Hoyle was the person who coined the term 'Big Bang', sort of as a way to make fun of a theory he did not advocate. Steady State theory claims that the universe had no beginning, but it created new matter as older galaxies moved apart. However, discovery of the CMB (Cosmic Microwave Background radiation) became a big blow against Steady State, although Hoyle maintained that the background radiation could have originated without a Big Bang, states Chandra Wickramasinghe, of the Cardiff University Center for Astrobiology.

As cosmologists and astronomers keep researching, there will undoubtedly be many more theories to come. These new findings are what make the mysteries of the universe so exciting and what keep the search for knowledge an important issue for people who love learning about what lies beyond.

PLANET IN THE SOLAR SYSTEM

          

       Our solar system consists of an average star we call the Sun, the planets Mercury,Venus , Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes: the satellites of the planets; numerous comets, asteroids, and meteoroids; and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The Sun's nearest known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away. The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as massive and is 2 million light years away. Our galaxy, one of billions of galaxies known, is traveling through intergalactic space.

        The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits. When looking down from above the Sun's north pole, the planets orbit in a counter-clockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic. Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elliptical of all the planets. Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune. The axis of rotation for most of the planets is nearly perpendicular to the ecliptic. The exceptions are Uranus and Pluto, which are tipped on their sides.

        From our small world we have gazed upon the cosmic ocean for thousands of years. Ancient astronomers observed points of light that appeared to move among the stars. They called these objects "planets," meaning wanderers, and named them after Roman deities—Jupiter, king of the gods; Mars, the god of war; Mercury, messenger of the gods; Venus, the goddes of love and beauty, and Saturn, father of Jupiter and god of agriculture. The stargazers also observed comets with sparkling tails, and meteors or shooting stars apparently falling from the sky. Since the invention of the telescope, three more planets have been discovered in our solar system: Uranus (1781), Neptune (1846), and, now downgraded to a dwarf planet, Pluto (1930). 

          In addition, there are thousands of small bodies such as asteroids and comets. Most of the asteroids orbit in a region between the orbits of Mars and Jupiter, while the home of comets lies far beyond the orbit of Pluto, in the Oort Cloud. The four planets closest to the sun—Mercury, Venus, Earth, and Mars—are called the terrestrial planetsbecause they have solid rocky surfaces. The four large planets beyond the orbit of Mars—Jupiter, Saturn, Uranus, and Neptune—are called gas giants. Tiny, distant, Pluto has a solid but icier surface than the terrestrial planets. Nearly every planet—and some of the moons—has an atmosphere. Earth's atmosphere is primarily nitrogen and oxygen. Venus has a thick atmosphere of carbon dioxide, with traces of poisonous gases such as sulfur dioxide. Mars's carbon dioxide atmosphere is extremely thin. Jupiter, Saturn, Uranus, and Neptune are primarily hydrogen and helium. When Pluto is near the sun, it has a thin atmosphere, but when Pluto travels to the outer regions of its orbit, the atmosphere freezes and collapses to the planet's surface. In that way, Pluto acts like a comet. Moons, Rings, and Magnetospheres There are 140 known natural satellites, also called moons, in orbit around the various planets in our solar system, ranging from bodies larger than our own moon to small pieces of debris. From 1610 to 1977, Saturn was thought to be the only planet with rings. We now know that Jupiter, Uranus, and Neptune also have ring systems, although Saturn's is by far the largest. Particles in these ring systems range in size from dust to boulders to house-size, and may be rocky and/or icy. 

          Most of the planets also have magnetic fields, which extend into space and form a magnetosphere around each planet. These magnetospheres rotate with the planet, sweeping charged particles with them. The sun has a magnetic field, the heliosphere, which envelops our entire solar system. Ancient astronomers believed that the Earth was the center of the universe, and that the sun and all the other stars revolved around the Earth. Copernicus proved that Earth and the other planets in our solar system orbit our sun. Little by little, we are charting the universe, and an obvious question arises: Are there other planets where life might exist? Only recently have astronomers had the tools to indirectly detect large planets around other stars in nearby solar systems.