Age of the Universe - Looking Back into the Past

 

Image of Distant Galaxies. Image Credit: Google

  

So when it comes to the age of the universe, it sounds quite scary to me. Scary maybe, because of the wild stretches of the universe, maybe because all we can imagine is how big the planet we are living on is. And then, we come to know that we are the part of solar system having 8 more planets, a giant star, the Sun at the centre and more than 200 moons. And then there are thousands of comets and millions of asteroids, both of which are heavenly bodies. Then the fact that our solar system is the part of Milky Way galaxy, which further has billions of stars, out of which our sun is one. And further to our astonishment, there are so far, 200 billion galaxies known in the universe. Just amazing!

Looking Back into the Past

You must be wondering, what do the stretches of the universe have to do with the age of the universe? If I say, when we look up to the sky, we are looking into the past, and as we start looking farther and farther beyond the sky, obviously by using telescopes, then we are looking further and further into the past. So, this is the point. The age of the universe can be determined if we can explore the stretches of the universe. This is a simple concept. Let us start, by escaping from the earth's surface and reaching out further into the universe. 

What is a Light-year?

As we already come to know, distances along the universe are enormous, so we use a unit called Light Year to measure these huge distances. A light year is defined as the distance that light travels in one year on earth. So, what is light year unit equivalent to? We know light travels at the speed of about 300, 000 km per second. This speed multiplied by 1 year (365 × 24 × 60 × 60 = 31,536,000 seconds) gives 9.46 trillion kilometres. Thus a light year equals 9.46 trillion kilometres. To further understand the concept of a light year, let us consider the simple experiment. 

If we place the mirror on the surface of the moon and send the light from the earth, we will come to know, that light after being reflected back from the mirror, reaches the earth in 2.6 seconds. That is, light reaches the moon in 1.3 seconds. Thus we can say the moon is 1.3 light seconds away from us. Which comes out to be 380,000 kilometres away. So this is how, by using the concept of a light year, we can measure distances into the universe precisely. 

How do we See Things?

Basic Vision Principal. Image Credit: Google

Now, before moving further let’s revise the basic concept of light and vision. We know, we can see objects, when the light after being reflected from them enters our eyes. Now, consider the moon that object. Since it takes 1.3 seconds for the light to reach us from the moon, thus we are actually looking at the moon how it was 1.3 seconds back in the past. This is how by measuring the distances into space we can actually look back into the past and thus can measure the age of the universe. 

Oldest Known Galaxy

By using the same technique, we had come to know that sun is further apart, about 8 light minutes away from us. And if we look even farther away outer planet, like Neptune, a light signal takes 4 hours to get there. Looking beyond our galaxy tells us that Andromeda, our neighbour and thus the nearest galaxy is about 2.5 million light years away from us. And if we manage to see further to the farthest and thus the oldest known galaxy so far, we would end up with GN-z11, a galaxy 13.4 billion light years away.

Oldest known galaxy, GN-z11. Credit: Google

What if we look, further deeper? There is nothing, no stars, no galaxies. And thus looking beyond GN-z11, say 13.6 billion light years back, the universe was too young, and no stars were born. That was just a couple of hundred million years after the beginning of the universe. There's nothing we can see out there, and the era is called the Dark Ages. This was the beginning of the universe. And we can conclude from precise studies and experimental results that the universe is somewhat 13.7 to 13.8 billion years old.