1. Science A Physics – P1 Science A Physics – P1 Topic 7d : The Solar System & its place in an evolving Universe Topic 7d : The Solar System & its place in an evolving Universe

2. Origin of the Universe The various ways of observing the universe have given us a good deal of information relating to its origin. Much of the relevant data requires an understanding of two related scientific principles:  Doppler effect (Doppler shift)  Red shift  Doppler effect (Doppler shift)  Red shift

3. When you stand on a station platform, high speed trains can pass straight through the station without stopping. If the train sounds its horn as it passes through the station, you may have noticed a change in the pitch of the sound as it passes. The Doppler Effect

4. Once the train has passed and is moving away from you, the pitch is lower. The waves are stretched further apart, so they have a longer wavelength. As the train approaches it has a constant high pitch. The waves are squashed together, so they have a relatively short wavelength. The Doppler Effect

5. Press ‘Start’ to simulate the sound of an approaching sports car... The Doppler Effect happens with all sources of moving sound. As the car approaches, the pitch gets higher. As the car moves further away, the pitch gets lower. This phenomenon is known as the Doppler Effect or Doppler Shift. It is a feature of all waves, not just sound.

6. Observing Starlight When electrons move from a high energy outer shell to a lower energy inner shell, light of a certain wavelength and colour is produced. Within a star, different chemical elements produce light of different wavelengths. The colour which an element produces depends on the difference in energy between its electron shells. The final colour produced is a result of many different wavelengths as the electrons move between different shells in the same atom. Each element has its own unique spectrum of wavelengths.

7. When a beam of white light is shone through a prism, the light disperses, forming a visible spectrum. Spectroscopy The resulting spectrum can be displayed as it would appear if it was projected onto a screen...

8. In 1929 the astronomer Edwin Hubble proposed a theory that light coming from distant galaxies appeared more red than expected due to the Doppler Effect. These lines are caused by the outer layers of the Sun absorbing some of the light. The black lines are called absorption lines. When a spectrometer is used to observe the spectrum produced by sunlight, black lines are seen across the spectrum. Red Shift Edwin Hubble with his telescope

9. However, when light from distant galaxies is assessed in the same way, the absorption lines are not located in the same places. This phenomenon is called red shift. The lines are moved nearer to the red end of the spectrum where the wavelengths are longer. Red Shift Movement of Black Absorption Lines Longer WavelengthShorter Wavelength

10. This tells us that more distant galaxies are moving away from us at a faster rate than closer ones. Red shift tells us that distant galaxies are moving away from us. This means that the Universe is expanding. Galaxies further away have more red shift than closer galaxies.

11. The Steady State Theory In this theory, the Universe has no beginning or end, and has always been in existence. The Steady State theory states that the Universe is the same now as it has always been, and will remain so forever. In 1948 three scientists, Fred Hoyle, Herman Bondi and Thomas Gold put forward a theory proposing that as the Universe expands, new matter is continuously being created in the gaps between existing matter. The theory does not suggest the source of this ‘new matter’. The Steady State theory was popular in the 1960’s, but has now become obsolete.