Everyone knows that the universe is big.
It’s the biggest thing there is.
But it can be quite difficult to appreciate just how big it is.
As big as most people imagine the universe to be, in reality, it is much, much bigger.
In order to get a sense of how big it is, it can be useful to start with a familiar
object, such as the Earth, and discuss its size in units that are familiar to us.
Then the next step involves scaling up from there, introducing new units as we go, but
making their definitions and relative sizes quite clear, so that we have some point of
reference at all times.
So let’s put this strategy to use and start with the Earth.
How big is the Earth?
Its diameter is just under eight thousand miles, or a bit less than thirteen thousand
kilometers.
To us puny little humans, the planet is very large indeed.
But it’s still just a speck of dust on a grain of sand on the tip of an iceberg as
far as the universe goes.
Even the distance to the nearest other object, our moon, is much greater than it appears
here, as it is not even remotely to scale.
The distance to the moon is about 384 thousand kilometers, making it a little more than thirty
earth diameters away.
So to make this earth-moon system to scale, we would need to put thirty earths edge to
edge, and then the moon.
Next, let’s zoom out to view the inner solar system, consisting of the sun and the four
rocky planets, those being Mercury, Venus, Earth, and Mars.
Though we can also see the asteroid belt, let’s keep things concrete, and take this
diameter as being twice the orbital radius of Mars, which brings us to 456 million kilometers.
This is more than a thousand times the distance between the earth and the moon.
Now let’s zoom out to encapsulate the outer solar system as well, which extends to the
outermost planet, Neptune, and some dwarf planets with irregular orbits.
Again, to keep things concrete, the average distance between Neptune and the sun is around
4.5 billion kilometers, so doubling that brings us to a diameter of around 9 billion kilometers.
This is around twenty times larger than when we capped it at Mars, which goes to show you
just how far the outer planets really are.
Now if we are to leave our solar system to view other nearby stars, it will become ridiculous
to continue to measure distances using kilometers.
We have to switch to the light year.
This is the distance that light travels in one year, which is equal to about 9.4 trillion
kilometers.
Looking at our local neighborhood of stars, the closest star to our own, Proxima Centauri,
is a little over four light years away, which means it would take several thousand copies
of our solar system lined up edge to edge to get there.
Interstellar space is quite an empty, lonely place, so don’t make the mistake of misinterpreting
out of scale images like these to think that stars are very close together.
Just this section visible here, with only a small handful of the closest stars, must
be around 30 to 40 light years across, acting as our little stellar neighborhood.
Next we can zoom out to see our entire Milky Way galaxy.
This has a diameter of a little over 100 thousand light years, which means that most of the
stars we can see in the night sky with the naked eye are relegated to a tiny little speck
in one of the arms of this galaxy, which is where we live.
Next let’s zoom out to view the local group, consisting of around 30 galaxies.
The Milky Way is the second largest of these galaxies after the Andromeda galaxy, which
we are on a collision course with.
This group has a diameter of around 10 million light years.
Next, we zoom out to view the Laniakea supercluster, home to around 100,000 galaxies.
Our galaxy sits in the Virgo supercluster, a smaller section of this larger structure,
which has an overall diameter of around 500 million light years.
Then we can zoom out even further, to see how the system of adjacent superclusters takes form.
We are now looking at millions of galaxies, covering a diameter of at least three billion
light years.
At this point we have lost all ability to see individual galaxies, which now just appear
like collections of dust.
And finally, we can zoom out to view the entire observable universe at once.
This structure has a diameter of around 93 billion light years, which is limited by the
age of the universe, since light can only have been traveling to get to us for almost
as long as the universe has existed.
Therefore, we don’t actually know how big the entire universe is.
There is data to suggest that the entire universe is approximately 250 times larger than the
observable universe, but we really can’t be sure, and it certainly could be much larger
than that.
Now even though we have traveled a vast distance, we have done so in a series of big jumps between
well-defined structures.
Let’s now take a more continuous journey from the surface of the earth all the way
to the edge of the observable universe and back.
This physics-defying odyssey will give us an even better appreciation for the immensity
of our universe, so let’s buckle up and blast off into space.