Question

What evidence shows that the universe is expanding?

Answer 1

We shall first understand what is meant by an expanding universe. The term universe is expanding means that it has been continuously growing ever since “The Big Bang”. That is, everything is moving away from everything. At the local level, this is not visible because gravity keeps everything intact. But the galaxies or star constellations that are very far away from us are moving farther away from us due to the expanding nature of the universe.

Complete step-by-step solution:
The universe is expanding, was first proven by an American Astronomer, Edwin Hubble. He used a very common and similar analogy that we use in Sound waves, “Doppler Effect”. But he used them for electromagnetic waves. This is known as the Red Shift of wavelengths.
When light waves coming from very distant stars or galaxies were studied, he saw the line spectrum of EM waves shifted towards the Red end of the electromagnetic spectrum. By measuring the level by which it has shifted, he saw that he can calculate the speed of the object and its relative distance.
He used this principle and various data sets to conclude that the relative distance of increase of these galaxies is directly proportional to their speeds. This was confirmed decades later by a number of experiments done by the Hubble’s telescope. All this data concluded that the universe is expanding at a rate comparable to the speed of light.

Note: In Hubble’s research paper, he concluded that the rate at which the universe is expanding is a constant value. But this wasn’t entirely found to be true. And, this was then explained by defining a new term, “Dark Energy” which is still one of the least known and researched topics in Physics.