Observable universe vs entire universe: the big difference

With the help of powerful telescopes, humanity has gained access to the oldest light from the early days of the universe. Although this is an incredible discovery, we will never be able to see pass our observable universe. The true size of the universe is much, much larger than what we can see.


Observable universe vs entire universe is a mind-boggling comparison. Just because we can’t see past Earth’s horizon does not mean there is nothing out there. The same principle applies to the observable and the entire universe. The observable universe is roughly 46 billion light-years in diameter or 92 billion light-years across, however, the entire universe might be infinitely larger.

As our technology over the years improved, astronomers were able to look deeper and deeper into the violent past of our universe – up until just a few moments after the Big Bang. Looking back into the early days of the universe has given us a good understanding of just how big it is.


What is the observable universe?

From our point of view, Earth is located at the center of the universe, and to some degree, it is true. An observable universe is a spherical region of the entire universe that can be observed from Earth.

What this means is that you can’t see past the edge of the observable universe, although we know it is much larger. It has nothing to do with our current technology and rather refers to the physical limit created by the speed of light itself. Basically, nature itself has drawn the line and said: “Nope you won’t be able to look any further” xoxo Nature.

Everything you see with your own eyes or with the help of telescopes is part of the observable universe. And you can see it because light has had time to reach the observer – us. If you look at the Sun, you are looking into the past, because the light and information that it carries, traveled 8 minutes and 20 seconds to get here. If the Sun suddenly “turned off”, we would know about it only after the last rays of sunlight reached us – 8 minutes and 20 seconds later.


How big is the observable universe?

Now that we know how far a light year is, we can take a closer look at how big the observable universe is.

We know that universe is around 13,8 billion years old. The oldest light in the universe is the cosmic microwave background that dates back to just 380 000 years after the Big Bang. You with me? Good! Now comes the tricky part.

Like a ship in the middle of the ocean with the horizon at 5 kilometers (3,1 miles) in every direction, Earth’s observers can turn their telescopes in any direction to peer 13,8 billion light-years away.

Since light needs time to travel through the vacuum of space and reach us, you might think that radius of the observable universe is 13,8 billion light-years or 27,6 billion light-years across, but it is much more than that. In fact, it is roughly 92 billion light-years across, because our universe is constantly expanding, and we need to take this inflation into account.

Meaning that observers from Earth might see a galaxy that lies 13,8 billion light-years away at the time of the Big Bang, the universe has continued to expand throughout its lifetime. If inflation occurred at a constant rate, that same galaxy is now 46 billion light-years away, making the diameter of the observable universe a sphere around 92 billion light-years across.

How big is the entire universe?

This is one of the many mysteries of the universe. Since we are limited to our bubble of the observable universe there is no precise way of telling how big the entire universe is. You can’t put a number on infinity. Even between numbers “1” and “2” are an infinite amount of other numbers.

However, there are several interesting theories and calculations which speculate how big the entire universe is. If we assume that the universe is finite, then by some calculations it could be as large as seven trillion light-years or 250 times larger than the observable universe. That number was calculated by a team of researchers led by Mihran Vardanyan at the University of Oxford in 2011.

If we look at other theories proposed by scientists, then the universe is infinitely big with no end to it. In this infinite space, there is an infinite number of possibilities for atoms to arrange themselves. That means if the universe truly is infinite, then somewhere out there is another planet Earth where you are sitting at your computer, reading this exact blog post, and wondering the same questions. Let that sink in for you and an infinite number of other copies of you in different parts of infinite cosmos.


Our visible universe has a radius of about 46 billion light-years even though it is only about 13,8 billion years old. And to top it off we are looking into the past and see planets, stars, and very distant galaxies as they were a long time ago.

Next time you will look up to the skies know that the light from these distant stars traveled many years to reach your eyes and very well might not even be there any longer. Imagine a distant star going supernova right at this moment. The event happened, but our bubble of observable universe hasn’t expanded yet for us to see it. It will take years for our bubble to expand and light from that supernova to reach an observer on the Earth.

But probably the most mind blowing thing about the size of the universe is the fact that all of the matter and energy was condensed in the infinitely small point which exploded and gave birth to time itself. Just imagine – the foundations of atoms in your body were already laid some 13,8 billion years ago.


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