Physics and astronomy

Introduction

For thousands of years scientists from different countries have been contributing important discoveries and ideas that have shaped modern science. This chapter looks at some important discoveries in physics and astronomy.

Where did it all begin?

Aristotle

Aristotle was a scientist who lived in Ancient Greece. Based on observations of some natural events, mathematical calculations and logic, Aristotle proposed that the universe was a sphere with the Earth at the centre. He divided all natural substances into four main groups: earth, air, fire and water. Aristotle also proposed that the heavens moved naturally in a complex circular motion and were made of a fifth element called ether.

Ptolemy

Ptolemy lived in Alexandria, which is in the territory of modern-day Egypt. Ptolemy studied and further developed Aristotle's theory of the structure of the universe. Ptolemy proposed that the universe revolved around the Earth, which was stationary (not moving). According to Ptolemy, the universe was divided into a number of spheres: the moon sphere, the planets' spheres and the stars' spheres. Ptolemy also put together a catalogue of 48 constellations, the names of which are still used today. The model of the universe proposed by Ptolemy was accepted for about 1500 years and today is referred to as the Ptolemaic system.

Copernicus

A sixteenth century Polish scientist, Nicolaus Copernicus was the first scientist to propose the heliocentric (centred around the sun) model of the universe. He claimed that all the planets, including Earth, moved in orbits around the sun. He showed how this new system could be used to accurately calculate the positions of the planets. Copernicus is considered to be the founder of modern astronomy.

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Galileo Galilei

A seventeenth century Italian scientist, Galileo Galilei, was the first to use a telescope. He made many important astronomical discoveries, such as the natural satellites (sometimes referred to as moons) of the planet Jupiter and the phases of the planet Venus, which are similar to those of Earth's moon. As a result of his new, daring scientific statements, Galileo was accused by the Roman church of being a heretic (a Christian who disagrees with traditional church statements).

Isaac Newton

Mathematician and physicist Isaac Newton lived in England. Newton defined the laws of motion and universal gravitation which he used to predict precisely the motions of the stars and planets around the sun. Newton also calculated the relative masses of celestial bodies according to their gravitational forces. Newton constructed the first reflecting telescope (a telescope which uses a mirror to gather and focus light from a distant object.)

Wright

Thomas Wright was an eighteenth century English astronomer, mathematician, instrument-maker and architect. Wright is best known for his publication about the Milky Way in which he explained the appearance of the Milky Way as an optical effect. The Milky Way is a galaxy made up of millions of different stars. According to Wright, the brightest stars are those that are closest to Earth. The most distant stars appear as very faint spots of light.

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William Frederick Herschel

Sir William Frederick Herschel was an eighteenth century English scientist. He discovered the planet Uranus and explained nebulae. A nebula is a mass of clouds of gas or dust which reflects the light of nearby stars. Herschel also developed a theory of the evolution of stars. Herschel suggested that the whole universe is changing over time.

Edwin Hubble

American scientist Edwin Hubble was the first to classify galaxies. A galaxy is a large collection of stars, gas and dust held together by gravitation. He discovered that galaxies move away from each other. The further away they were, the faster they moved. He also came up with the idea that the universe began with a super-powerful explosion. This theory is now called the Big Bang theory.

Albert Einstein

German-born scientist Albert Einstein formulated the theory of relativity which is a theory of motion and energy. Einstein was also the first to discover the relationship between the mass of an object and the energy it can generate. Einstein is often called the greatest scientist of the twentieth century.

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Max Planck and Warner Karl Heisenberg

At the beginning of the 20th century, German scientists Max Planck and Werner Karl Heisenberg together with Danish physicist Niels Bohr made very important discoveries that led to the development of quantum physics. Quantum (a Latin word meaning how much) physics is a theory of the structure and behaviour of elementary particles of matter called atoms. Quantum physics explains the nature of light, chemical bonding forces and radioactivity. Radioactivity is a spontaneous flow of energy from atoms.

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Arno Penzias and Robert Wilson

In 1965 American scientists Arno Penzias and Robert Wilson detected a signal from space that they could not explain. Finally, they recognised it as what is now called the Cosmic Microwave Background (CMB), or radiation, left over from the initial explosion of the universe or the Big Bang.