Theories of the Universe
BIG BANG THEORY
![Picture](/uploads/3/7/8/1/37819847/nearby-galaxy-l_orig.jpg)
Most astronomers believe the Universe began in a Big Bang about 14 billion years ago. At that time, the entire Universe was inside a bubble that was thousands of times smaller than a pinhead. It was hotter and denser than anything we can imagine.
Then it suddenly exploded. The Universe that we know was born. Time, space and matter all began with the Big Bang. In a fraction of a second, the Universe grew from smaller than a single atom to bigger than a galaxy. And it kept on growing at a fantastic rate. It is still expanding today.
As the Universe expanded and cooled, energy changed into particles of matter and antimatter. These two opposite types of particles largely destroyed each other. But some matter survived. More stable particles called protons and neutrons started to form when the Universe was one second old.
Over the next three minutes, the temperature dropped below 1 billion degrees Celsius. It was now cool enough for the protons and neutrons to come together, forming hydrogen and helium nuclei.
After 300 000 years, the Universe had cooled to about 3000 degrees. Atomic nuclei could finally capture electrons to form atoms. The Universe filled with clouds of hydrogen and helium gas.
Then it suddenly exploded. The Universe that we know was born. Time, space and matter all began with the Big Bang. In a fraction of a second, the Universe grew from smaller than a single atom to bigger than a galaxy. And it kept on growing at a fantastic rate. It is still expanding today.
As the Universe expanded and cooled, energy changed into particles of matter and antimatter. These two opposite types of particles largely destroyed each other. But some matter survived. More stable particles called protons and neutrons started to form when the Universe was one second old.
Over the next three minutes, the temperature dropped below 1 billion degrees Celsius. It was now cool enough for the protons and neutrons to come together, forming hydrogen and helium nuclei.
After 300 000 years, the Universe had cooled to about 3000 degrees. Atomic nuclei could finally capture electrons to form atoms. The Universe filled with clouds of hydrogen and helium gas.
Geocentric vs. Heliocentric
![Picture](/uploads/3/7/8/1/37819847/geocentric-vs-heliocentric-01_orig.jpg)
GEOCENTRIC MODEL(Ptolemic Thoery)
The geocentric model of the cosmos is a paradigm which places the Earth at the center of the universe. Common in ancient Greece, it was believed by both Aristotle and Ptolemy. Most Greeks assumed that the Sun, Moon, stars, and planets orbit Earth. Similar ideas were held in ancient China.The geocentric model was gradually replaced by the heliocentric model of Copernicus and Galileo due to the simplicity and predictive accuracy of that newer model.
HELIOCENTRIC MODEL(Copernican Theory)
Heliocentrism is the belief that the sun is the center of the universe; as opposed to the Ptolemaic system, according to which Earth is at the center of the universe. It recognizes that the planets are orbiting Sol, but later it was discovered that the sun is just a star in the Milky Way, and that the latter is just one of the galaxies in the universe.
Heliocentric comes from the Greek, "helios", for Sun. The heliocentric model of the solar system, in which it is argued that Terra orbits Sol, was first proposed by Aristarchus (c.270 BC). The theory is often credited to Copernicus. This theory solved the issue of planetary retrograde motion (with respect to the celestial sphere), by arguing that such motion was only perceived and apparent; rather than real. Heliocentrism was notably advanced by Kepler and Newton.
The geocentric model of the cosmos is a paradigm which places the Earth at the center of the universe. Common in ancient Greece, it was believed by both Aristotle and Ptolemy. Most Greeks assumed that the Sun, Moon, stars, and planets orbit Earth. Similar ideas were held in ancient China.The geocentric model was gradually replaced by the heliocentric model of Copernicus and Galileo due to the simplicity and predictive accuracy of that newer model.
HELIOCENTRIC MODEL(Copernican Theory)
Heliocentrism is the belief that the sun is the center of the universe; as opposed to the Ptolemaic system, according to which Earth is at the center of the universe. It recognizes that the planets are orbiting Sol, but later it was discovered that the sun is just a star in the Milky Way, and that the latter is just one of the galaxies in the universe.
Heliocentric comes from the Greek, "helios", for Sun. The heliocentric model of the solar system, in which it is argued that Terra orbits Sol, was first proposed by Aristarchus (c.270 BC). The theory is often credited to Copernicus. This theory solved the issue of planetary retrograde motion (with respect to the celestial sphere), by arguing that such motion was only perceived and apparent; rather than real. Heliocentrism was notably advanced by Kepler and Newton.