The Expanding Universe

This lesson explores the concept of the expanding universe in greater depth, including Hubble's observations, the implications of expansion, and the ultimate fate of the universe, as required by the AQA GCSE Physics specification (4.8.2). This is a Physics-only topic. You need to understand how the universe is expanding, what this means for the distances between galaxies, and the current scientific understanding of the future of the universe.

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Hubble's Observations

In the 1920s, the American astronomer Edwin Hubble made observations that fundamentally changed our understanding of the universe. By studying the light from distant galaxies, Hubble found two crucial things:

1. The universe contains many galaxies beyond our own Milky Way. Before Hubble, many astronomers thought the Milky Way was the entire universe. Hubble showed that "spiral nebulae" were actually separate galaxies, each containing billions of stars.

2. The light from nearly all distant galaxies is red-shifted. This meant that nearly all galaxies are moving away from us. Crucially, Hubble found that the speed at which a galaxy recedes is proportional to its distance from us.

This relationship — known as Hubble's Law — can be expressed as:

v = H x d