Imagine you're standing on a street corner. An ambulance rushes towards you, sirens blaring, the pitch climbing ever higher. Then, in an instant, it flies past and the siren drops to a lower note, like an audio rollercoaster. Our intuition might tell us the siren changed, but that's not the case.

What we experience is the Doppler Effect, a phenomenon that defies common sense. The siren's sound waves are like ripples in a pond. As the ambulance speeds toward us, these waves compress, boosting the pitch. Once it passes, the waves stretch out, lowering the pitch. It's like squashing and pulling a slinky, but with sound.

This effect isn't limited to sound. It applies to light too, affecting how we perceive distant stars and galaxies. When they move towards us, their light shifts to blue; moving away, it shifts to red. The universe itself is a concert of compression and expansion.

Next time you hear an ambulance, ask yourself: How else does motion shape my perception?