Expansion of the Universe
Earth and Space

Elastic band universe

Remote teaching support for 14-16 16-19 IOP RESOURCES

In this activity students build a model universe using washers and elastic bands. You can use it to introduce Hubble’s law.

Equipment

Each student will need:

  • 6 assorted washers (or paper clips)
  • 5 elastic bands of the same thickness (and ideally of different lengths)
  • Small sticker to indicate ‘home’
  • Ruler or tape measure
  • Graph paper (or laptop with Microsoft Excel or similar)
  • Sticky tape
  • A copy of the student instructions


Teaching notes

By following instructions on their activity sheet students should build a one-dimensional model of a universe. After expanding it to double its initial length they will need to stick the washers at the end of the chain to the table/floor to measure distances.

When they plot a change in distance against distance graph they should find that it is a straight line. Repeating with a different washer as the home galaxy reveals that the gradient of the graph is the same irrespective of which washer they consider to be ‘home’. Like real galaxies, the galaxies in the model seem to move away from home, but home is not the centre of the expansion. Observers in all galaxies will see the galaxies move away from them with a speed that is proportional to their distance from their galaxy. This is known as Hubble’s law.

ModelUniverse
The washers do not expandGalaxies do not expand (they are gravitationally bound)
The elastic bands expand, carrying washers with themSpace between the galaxies expands, carrying galaxies with it

Learning outcome

Students explain why observers in all galaxies see the galaxies move away from them with a speed that is proportional to their distance.

With thanks to the Perimeter Institute of Theoretical Physics for permission to adapt their activity

Expansion of the Universe
is formalised by Hubble's Law
is described by Dark Matter Dark Energy
can be analysed using the quantity Hubble's Constant
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