4.2 Formation of the Universe

Introduction

How did the Earth come to be revolving around the Sun? How did the Milky Way Galaxy form? And while we're at it, where did the universe come from, and how long has it been around?

You are not the only one asking these questions. People have been coming up with theories to answer these questions for many years. In this lesson you will examine the current scientific theories that explain the formation of the universe.

The Big Bang Theory

The Big Bang theory was developed in the early 1900s. It states that about 15 billion years ago an explosion caused the expansion of matter and radiation into space. The explosion was the beginning of space and time as we know it. Seconds after the explosion, energy was converted into particles and anti-particles (i.e. electrons and positrons). Within minutes, traces of hydrogen and helium nuclei were created. Millions of years later, stars and galaxies began to form. The chemical reactions in stars created all the other elements found in the Universe today. 

Watch the video below to learn more about the Big Bang Theory to explain the formation of the Universe.

The Doppler Effect

 The Big Bang Theory suggests that the universe is continually expanding. Measurements of the Doppler Effect support this theory. The Doppler Effect is the change in frequency (and wavelength) of a source when it is moving relative to an observer. If the source is moving towards an observer, the wavelength squashes up and the frequency increases. When the object is moving away from the observer, the wavelength spreads out and the frequency decreases. This can be witnessed in everyday life when you hear the siren of an ambulance or police car moving towards you then away from you. The siren sounds higher in pitch (higher frequency) when the vehicle comes towards you and then seems lower in pitch (lower frequency) when it moves away from you.

The Expanding Universe and the Red Shift

In the 1920's, astronomer Edwin Hubble used the Doppler Effect to determine that the Universe is expanding. Hubble found that the light from distant galaxies was shifted towards lower frequencies, or the red end of the spectrum. This is known as a Red Doppler Shift, or a Red-shift. If the galaxies were moving towards Hubble, the light would have been blue-shifted. By analysing the spectra of distant galaxies, it has been discovered that, on average, galaxies are rushing away from our Milky Way Galaxy at thousands of kilometres per second. We know this because the spectra of these galaxies are red-shifted and the further out they are, the faster they are found to be moving. This at first seems to indicate that we may be at the centre of the Universe. However, it is thought that no matter where you are in the Universe, galaxies race away from you. Galaxies are not moving through space but space is thought to be expanding and the expansion is happening between all points in the Universe. 

Doppler Effect - Big Bang Theory Style

Sheldon from 'The Big Bang Theory' TV show dresses as 'The Doppler Effect' for Halloween...enjoy!

Cosmic Microwave Background Radiation

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Technology now exists to look at the sky by focussing on forms of radiation other than light. As a result we have gained a different perspective and have increased our knowledge of the Universe. Since the sky was first viewed using microwaves in 1965, it has been found that the Universe is filled with microwave radiation. This is now known to be traces of radiation coming from the remnants of the Big Bang. The energy of the Big Bang has been red shifted into microwaves because the Universe is expanding. This light is seen today as the Cosmic Microwave Background Radiation (CMBR) - the ‘afterglow’ of the Big Bang.

The Blue Shift

On a smaller scale though, some galaxies are colliding with others due to the large force of gravity between them. The Large and Small Magellanic Clouds are two dwarf galaxies gravitationally attracted to our own Milky Way Galaxy. (The spectra of these two galaxies are blue-shifted.) It is hypothesised that they will eventually collide with our galaxy, although this is billions of years away! Object stationary Spectral lines red-shifted – object moving away from us; Spectral lines blue-shifted – object moving towards us

Support for the Big Bang Theory Summarized

The Big Bang theory is based on the General Theory of Relativity, the theory developed in the 1900's by Albert Einstein. The major observations that support the Big Bang theory are the expansion of the Universe (first seen by Edwin Hubble in the 1920s), the abundance of the different chemical elements seen in the Universe and the detection of the CMBR (Cosmic Microwave Background Radiation). The name ‘Big Bang’ is a little misleading as it suggests that there was a huge explosion in space. Instead, it is better to think of the Big Bang as an expansion. The name ‘Big Bang’ was invented by astronomer Fred Hoyle who was trying to ridicule the theory, but it was so catchy that it stuck.