Question

How does the universe expand?

Answer 1

Hint: The expansion of the universe can be observed in the form of red shift (explained by Doppler’s effect) and is theorized to have been caused by the Big bang that took place at the beginning of the formation of the observable universe.

Complete answer:
It has been theorized that about 13.9 billion years ago, all the mass of the universe was concentrated in a very small volume and an expansion occurred, called the big bang which then separated and spread that initial mass across the universe. This theory has been formulated because as we observed the stars and planets around us consistently, with the help of powerful telescopes, we came to observe that the stars were moving farther apart. This conclusion followed because we saw a red shift in the wavelength of the light that the distant stars emitted. By the virtue of Doppler’s shift, it has been known that when the emitter of the light moves farther away from the observer, the wavelength observed becomes longer or more than the original wavelength. As we know that the red light has longer wavelength (as compared to blue), the shift in wavelength observed is called red shift.
Therefore, as we observed the red shift, we came to the conclusion that the universe must be expanding, as the stars are moving farther from us. This led to the Big Bang theory which helped in explaining the observation as to why the universe is expanding. By the virtue of that theory, we can generalize that due to that initial bang (explosion), the universe is ever expanding.

Note:
One can also think about an explosion taking place here on earth. Now here, we have air resistance, so the explosion fades away. But if we had a place where there was no resistance, the components would fly away forever.