In this deck, we'll explore one of the biggest ideas in all of science: the origin of the universe. We'll look at the evidence that the universe is expanding, and how this leads to the currently accepted scientific model for how it all began, known as the Big Bang theory.

To understand the evidence, we first need to think about light from distant stars and galaxies. When light from a star is passed through a special instrument, it can be split into a spectrum of colours, like a rainbow. But within this spectrum, there are dark lines where specific wavelengths of light have been absorbed by elements in the star's atmosphere. Every element has a unique pattern of these lines, like a barcode.

Now, imagine an ambulance siren. As it moves towards you, the sound waves are squashed together, making the pitch higher. As it moves away, the waves are stretched out, making the pitch lower. This is called the Doppler effect. The same thing happens with light waves. If a galaxy is moving away from us, the light waves it emits are stretched out. This stretching shifts the light towards the longer-wavelength, red end of the spectrum.