Red-Shift and the Big Bang

This lesson covers red-shift, the expanding universe, and the Big Bang theory, as required by the AQA GCSE Physics specification (4.8.2). This is a Physics-only topic. You need to understand how observations of red-shift provide evidence for the expansion of the universe and how this supports the Big Bang theory.

---

The Electromagnetic Spectrum and Light from Stars

Before understanding red-shift, you need to recall that light is part of the electromagnetic spectrum. White light from a star can be split into a spectrum of colours (red, orange, yellow, green, blue, indigo, violet) using a prism or a spectrometer.

Each chemical element in a star's atmosphere absorbs light at specific wavelengths, producing a pattern of dark lines called an absorption spectrum (or line spectrum). These dark lines act as a "fingerprint" for each element — by studying the pattern, scientists can identify which elements are present in a distant star.

Key points: