In 1965, a very important astronomical discovery was made, this was the detection of the background radiation which supported the Big Bang theory (For details of the Big Bang see image 10). But, the Big Bang theory, together with the detection of the red shift in the spectrum of far away galaxies, gave birth to yet a new discovery. This was the momentous discovery that the universe is expanding.
When you hear a police car, a train or an ambulance approaching you and then moving away, you will notice a change in the sound of its siren. As the vehicle approaches, the siren wails at a higher pitch than when it moves away. Yet, really, the siren is wailing at the same pitch all the time. To the driver of the vehicle the sound of the siren never changes. Why does this happen? The reason is that the waves of sound emitted by the siren change in frequency, which causes a change in pitch. This principle, which is called the Doppler effect after its discoverer, applies to any waves and not only that of sound. When applied to light waves it was found that if the source of light is approaching, its light would be shifted towards the blue end of the spectrum, while as light from a receding source would be shifted towards the red end of the spectrum. When analysing the light we receive from distant galaxies it was found that they all had a red shift meaning that they were flying away from us. This contribution of the red shift analysis meant that the universe is indeed expanding.
This conclusion is literally mentioned in the Quran in the above verse.
Note that the word "expanding" is used in the present tense and not in the past which once again is in agreement with the fact that the expansion of the universe is a continuous process.