Pitara Kids Network

What does a Train Whistle tell us about the Universe?

I remember my first visit to the railway station as a child of five. The excitement of the approaching train was an experience I have never quite forgotten. At first I heard a train whistle far away, low and distant. As the train got closer, the sound of the whistle not only increased, it became shriller, and difficult to bear. So much so that I covered my ears in alarm!

Once the excitement had passed, I discovered a secret – even with my eyes closed and by just hearing the whistle, I could tell whether a train was approaching or moving away.

Doppler discovered that if any object giving out sound, is moving toward you, the frequency of the sound increases. That is why as the train gets closer, the sound of the whistle increases, it also became shriller.

On a lazy day a couple of years later, as I threw a stone in a pond to see the ripples it created, an older cousin explained that voices or sounds of any kind, and even light, travelled in a similar manner – in waves.

She named a scientist called Doppler, who discovered that if any object giving out sound and light, is moving toward you, the frequency of the sound or light waves increases. If it is moving away, the frequency of waves and thus, sound or light, decreases. The discovery was called the Doppler effect.

Understanding the universe with Mr Doppler’s help

Doppler effect or Doppler shift is the change in frequency of a wave for an observer moving relative to its source.

Then scientists tried to apply this phenomenon to the galaxies around our Milky Way, where the solar system is situated. They carefully measured the frequency of light coming from these galaxies and found the frequency of light decreasing, in the same way that I found the sound of the train whistle decreasing as it moved out of the station.

This led the scientists to the thought that all the galaxies are speeding away from each other. So, if things are moving away from each other, they were surely together at one place at some point of time?

The Big Bang and the expanding universe

Scientists claim that the entire universe was a small point in the past. A huge explosion called the ‘Big Bang’ created every known (and unknown) substance in the universe. The explosion caused the universe to expand. As the universe expanded it cooled down and created galaxies and stars. Slowly, planets were formed and among them, our solar system as well.

So that was it! A simple phenomenon that we get to observe in our daily lives can actually hold the key to the biggest mysteries of the origin of the universe.