The Big Bang theory is the most widely accepted scientific explanation of how the Universe came into being and how it came to exist as it does today.

According to the Big Bang theory, the Universe began as a tiny, hot, dense piece of matter billions of years ago, then cooled and expanded until it reached its current size. The Universe continues to expand.

The Doppler Effect

The Doppler Effect, named for Austrian physicist Christian Doppler, refers to the way in which waves produced by an object increase in frequency as that object moves closer to the observer.

For example, suppose someone drives and ambulance past you. As the ambulance approaches you, the pitch of the siren will sound higher. As the ambulance moves past you, the siren’s pitch will growlower.

The reason for this is that as the ambulance moves toward you, the sound waves that come between it and your ears are compressed. There are more sound waves in a smaller amount of space – the sound waves have a higher frequency. Your brain interprets this as the siren having a higher pitch.

The reverse happens when the ambulance moves away.

The Doppler effect works with light as …