Everyone knows the universe is big, but just how big is it? The trouble is that it is so absurdly large that its size is exceptionally difficult to comprehend. I wanted to try and imagine the vastness of this great plain, and so I put together some analogies to help.
Firstly, let us comprehend just the size of our own solar system. When we are talking about galaxies and the edges of the observable universe itself, it can be easy to forget from the comparison just how big a single solar system is. A solar system is comprised of a central mass, usually a star, which is often orbited by planetary bodies. We live on the third planet from the Sun in our solar system, on average 300 times closer to the centre than Pluto, the outermost body, and you could fit well over one thousand Earths in between us and the Sun – the distance is phenomenal. If you were scaled down to the size of a microscopic E. Coli bacterium, the Sun would still be ten times the size of Mount Kilimanjaro by comparison. That’s just the central mass of a single solar system, most of it is empty space. There are an estimated 250 billion solar systems in our galaxy, and an estimated one trillion galaxies in the observable universe.
What do we mean when we say ‘observable’ universe?
As the name suggests, this refers to the known portion of the universe which we can actually see. The reason we can’t see beyond this portion is that the distance from here to the edges is so unbelievably huge that photons of light (travelling 186,000 miles every second!) have not had enough time in the history of the universe (nearly 14 billion years) to reach us. It is impossible to know what lies beyond the edges of the observable universe, because there is no way of seeing it. We can only wait millions and billions, perhaps even trillions of years for the light to reach us before it can be seen. There are some theoretical equations which calculate an estimated current size of the whole universe, but it is believed to be ever expanding, and at an exponential rate.
The grain of sand analogy
One very popular analogy to explain the scale of the universe is the grain of sand analogy, and it goes something like this: Imagine you are walking along a stretch of beach, and you kneel down to take up a handful of sand. Each grain is roughly half a millimetre wide, and in a single handful you are holding an estimated 2 million grains. Imagine how many millions there are in a bucket; imagine how many hundreds of billions there are on that one beach; imagine how many thousands of trillions there are in each small stretch of desert – imagine what incomprehensible number there are in the world, and then consider this:
There are more stars in the observable universe than grains of sand on Earth.
Following this analogy, if our sun was the size of one of these grains of sand then, by comparison, the Earth would be just half the size of a human red blood cell, and you would be less than a billionth of the size of a single neutron.
More impressive yet is the distance between two stars in the same galaxy. The size of this gap between stars which are “neighbours” is unfathomable. On average, the space between two stars is 5 lightyears – this can be hard to imagine, so let’s go back to our grain of sand analogy: if the first star was half a millimetre across, as a grain of sand is, the next star wouldn’t be for 15km – that’s more than twice the length of the Las Vegas strip.
One grain of sand representing a star, more than two Las Vegas strips, and then the next grain of sand. Those are the local stars. Imagine spacing out 250 billion grains of sand by 15 kilometres each, and you have a tiny, tiny, scale model of our galaxy, which would still be 3 times the width of the largest planet in our solar system.
A neutron – a single sub-atomic particle – is a billion times larger than you, and the observable universe is still 60,000 times the size of the Sun. If that wasn’t enough, you should also know that the most popularly accepted estimate is that the observable universe is just 0.000000000000000000000067% of the entire universe at present. Also, as it expands exponentially, it passes the speed of light, meaning that it is growing away from us faster than the light can travel towards us, and therefore, there will come a point where we will never ever, even in an infinite amount of time, be able to see what’s beyond this point.
So yeah, it’s big.