The word “vast” gets tossed around a lot to describe things like the backseat of an SUV, or a big lawn or the open ocean. These things can all be vast, depending on your frame of reference, but if there is anything that can truly be described as “vast” it is the universe.
The size of the universe defies any adequate description or human comprehension. Consider light. Light travels at the cosmic speed limit of 186,000 miles per second.
Satellite view of Chicago
I live in Chicago, and I am often amazed at how big this city is. I could spend my whole life exploring this city and not get to see everything. Google tells me that there are 4300 miles of road in Chicago — longer than the United States is wide — but light could travel every road in the entire city 43 times in one second. One second to travel the entire distance that my first car traveled in its entire lifetime. One second to travel around the Earth’s equator seven times.
Our sun is 93 million miles from where I am sitting. At a steady pace of 3 miles per hour, it would take 3500 years to walk to the sun without any breaks for eating or sleeping. The same light that can circle the whole earth seven times in one second takes 8 whole minutes to get from the sun to our planet. Along the way, there are two planets, one about the same size as earth, and one a bit smaller. Venus has a surface area of 177 million square miles — that’s over 750,000 Chicagos. There are six more planets in our solar system, a handful of dwarf planets, an asteroid belt, an Oort cloud, and more.
The nearest star to our own is Proxima Centauri. Light from our sun takes 4.3 years to get there. 4.3 years going as fast as it is possible for anything to travel.
Our planet is located in a backwater arm of the Milky Way Galaxy. Light takes 100,000 years to travel its diameter. The same light in the same time could circle the earth over 20,000,000,000,000 (20 trillion) times.
The nearest galaxy to the Milky Way is the Andromeda Galaxy. It is 220,000 light years across, and 2.5 million light years from Earth. Although it contains somewhere in the order of one trillion stars, the entire galaxy is only visible from Earth as a single point of light.
The observable universe is 93,000,000,000 (93 billion) light years across. Light would take 93 billion years to go from one end of the universe that we know to the other. There is more universe out there, but the light from those parts hasn’t reached us yet because the universe isn’t old enough. The universe is only 13 billion years old.
The observable universe is estimated to have around 100-200 billion galaxies. We don’t know exactly how many there are, because it would take too long for our instruments to count them all. And again, there is more to the universe than what we can see. We don’t know how much more because, well, we can’t see it.
The Hubble “Ultra Deep Field” is a view of part of the universe when it was less than a billion years old.
I hope I have given a glimpse of just how big the universe is. It is impossible for me to say exactly how big it is, not just because nobody knows, but because the size is completely incomprehensible. It defies language to describe it, and our brains to understand it. Even if the exact size were known, the number expressing it would be meaningless.
A lot of people hear how big the universe is and it makes them feel small. We are the center of our own lives, and what goes on in our lives is important to us. People used to believe that the Earth was the center of the universe because they couldn’t get their heads around the fact that we are unimportant. But to the universe, we are less than unimportant. For the sake of comparison, a speck of dust is in the order of 100µm (100 nanometers) wide. I am a little shy of 2 meters tall. I am therefore approximately 20 million times the size of a speck of dust (length, not volume).
The Earth has a diameter of about 12,000 miles. Our galaxy has a diameter of about 600,000,000,000,000,000 (600 quadrillion) miles. Our galaxy alone is 50 trillion times bigger than the Earth. People like to give “a speck of dust” as a measure of insignificance, but to our galaxy alone, the earth is far, far less significant than a speck of dust is to a human. And to the universe, our entire galaxy is insignificant. It is perfectly understandable that the universe makes some people feel small.
The size of the universe bothers me, too, but not because it makes me feel small. It has never been a problem for me to reconcile my own insignificance in the scheme of things.
I am troubled by the fact that I will spend my life exploring Chicago. I will spend my life getting to know one or two dozen people really well, a have a passing familiarity with maybe one or two hundred more. If I were still a researcher, I would spend my life trying to discover as much about the world as I could. As a non-researcher, I will spend my life learning as much of what others have discovered as I can. But there is so much that I will never know.
For all of the things we know about earth, there is so much more that we don’t know. We are just now starting to discover how common other planets are in our galaxy.
We know that the universe is believed to be about one quarter dark matter, but we don’t even know what dark matter is.
When I look up in the sky and see all that I can see, and understand what I can’t see, it makes me sad that I will never get to know so much of what is out there. So many galaxies. So many stars. So many planets. And I have to spend my life on just this one, with only my short life to see what I can see. There is so much to see on Earth, but the universe holds sights that we cannot possibly fathom.
The “Pillars of Creation”
I am troubled because I am a scientist, and I am greedy. Scientists are driven by the knowledge of the things we do not yet know. We see a hole in our knowledge and we want to fill it in. We are humbled by the knowledge of what we do not yet know, and seeing the vastness of the universe can be crushing.
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