It is difficult for the human mind to grasp the scales of the universe, from the tiniest details of the atom, as small as 0.1 nanometers (a ten-billionth of a meter), to the vastness of the Universe, spanning 93 billion light-years. These extremes challenge the limits of our understanding.
To illustrate this, let’s start with a quick example: what comes to mind when you think about the scales described in the quote below?
If you spread the atoms in a human body to match the density of intergalactic space, they would form a sphere roughly 200 times Earth’s diameter – twice the size of the Sun – and large enough to contain seven million Earths or the equivalent volume of six Suns.
Sounds crazy, right? Let’s explore how to make sense of these concepts together.
Why We Struggle With the Scales of the Universe
The human mind wasn’t built to understand extremes. Our difficulty in understanding vast scales comes from how humans evolved to perceive and interact with the world. For most of human history, survival meant focusing on immediate concerns like avoiding predators, finding food, and navigating landscapes. Evolution shaped us to develop skills and knowledge that helped us survive and reproduce, ignoring aspects of reality that didn’t directly affect our survival.
While understanding millimeters to kilometers (or dozens to thousands) was useful for our ancestors, scales like nanometers, light years, or billions were irrelevant to understanding our direct environment and left out of our intuitive grasp. The same concept applies to how we perceive time.
For instance, our eyes have evolved to detect only a very narrow band of the electromagnetic spectrum, less than a trillionth of the full range. To put it in perspective, if we stretch the electromagnetic spectrum from Los Angeles to New York, the light we perceive is a strip narrower than a human hair. Similarly, our hearing spans only 20 Hz to 20,000 Hz, a small fraction of the full range of sound frequencies. Below or above those frequencies, the world is silent to us.
A quick note. This article is not meant to be a scientific paper but just a fun and engaging exploration. To make it as simple as possible, I will round up large numbers when it doesn’t change the core message; thus, 94 million becomes 100 million, and 24.8 becomes 25. Also, I will do my best to show dimensions in both metric and imperial systems.
Let’s go. We’ll start with the vastness of the universe, continue with how human size compares to the scale of the universe, and end with the atomic and subatomic scales.
The Scales of the Universe: Understanding the Solar System
We’ve all seen those images of our solar system, where the sun sits somewhere in the middle, and the planets go in perfect circles around it, right? The sun is big and bright, and the planets are a bit smaller and nearby. It creates the feeling that everything is neat and compact – something like this:
Our solar system, however, is far more vast, complex, and empty than it might appear in simplified illustrations like this. Let’s dive deeper into how its scale compares to our everyday experiences.
Scaling Down the Solar System: A Basketball Sun and a Peppercorn Earth
To better understand our solar system, let’s bring everything down to a dimension more relatable to our everyday objects. Let’s condense everything until the Sun becomes the size of a basketball. That is 1,7 X 1010, or 17 trillion times smaller. On this scale:
- The Sun becomes about the size of a basketball (~24 cm), while the Earth is a 2 mm peppercorn, orbiting 25 meters (85 feet) away.
- Neptune, the size of a pea (~1 cm), would be more than 2,500 feet away (~800 meters).
- Jupiter would be the size of a golf ball, rotating at 441 feet away.
- Mercury, the closest planet to the Sun, would be less than 1 mm (a poppy seed) rotating at about 10 feet away.
- Proxima Centauri, the closest star, would be about 6,700 km away (~4,200 miles), or the distance between New York and London.
One surprising fact is just how empty the space is. On Earth, we are used to seeing trees, rocks, and many other objects all around us. But in our solar system, the Sun represents 99.8% of all matter, with the planets making up most of the rest. Between them, there are barely any atoms – more on that later. So, the “basketball” you hold is pretty much everything there is.
Our solar system is a mile-wide disk with a basketball-sized Sun in the middle and a few specks of dust circling it.
Quiz Time: The Emptiness of Space
How big would the Earth be if you removed all the empty space from the atoms that comprise it, compressing it to its core material? The entire planet would be about the size of a sugar cube. And how heavy would it be? Well, it would still weigh just as much as it does now!
Let’s continue our analogy and look beyond our solar system. The Milky Way galaxy spans 100,000 light years in diameter. If we shrink it by 17 trillion times, its diameter ends up around 50 million kilometers, roughly a third of the distance between Earth and the Sun. This is so big that it breaks our intuitive understanding that we’ve built up to this point.
How about our neighbor, Andromeda galaxy? it is about twice as large as the Milky Way galaxy (~200,000 light-years across) and sits about 2.5 million light years away. Think about the Milky Way as a 15 cm small plate and Andromeda as a 30 cm dinner plate sitting about 4 meters away. A bit easier to visualize galaxy scales.
Key Takeaways: Scaling the Solar System
Let’s recap: if we shrink our solar system by a factor of about 17 trillion, we end up with a disk nearly one mile across. At its center is a basketball-sized Sun with some stardust circling it in mostly empty space – that is our solar system!
- Sun: The size of a basketball, holding 99.8% of the solar system’s mass.
- Earth: A peppercorn orbiting 25 meters (85 feet) away.
- Jupiter: A golf ball at 134 meters (441 feet).
- Neptune: A pea 780 meters (2,560 feet) away.
- Proxima Centauri: 6,700 km away (4,200 miles), or the distance from New York to London.
- Milky Way Galaxy: Around 50 million miles in diameter, or about half the distance from the Earth to the Sun.
If you want to know the true relationship between the Sun and Earth, visualize this: you’re holding a basketball in your hand, representing the Sun, while the Earth is a peppercorn going in circles 25 meters away.
The Atomic World
Now that we’ve explored the vastness of outer space let’s look inward. From the vast cosmos to the atomic level, the scales of the universe reveal a strong contrast.
The human body has roughly 37 trillion cells. If each cell were a grain of sand, we could build more than 10 Great Pyramids of Giza! Each cell contains about 200 trillion atoms. So, how many atoms does your body have? No need to do the math: ~7 octillion atoms (7 X 1027 atoms). That’s a lot!
Human Cells: The Building Blocks of Life
This content isn’t part of the main story but I found some of these facts too fascinating to leave out:
- Red Blood Cells: They make up roughly 70–80% of all the cells in your body. They live an average of 120 days
- Gut Bacteria: About 30–50 trillion bacteria live in your digestive system – though not actually “yours,” they help break down food and weigh around 4 kg (9 lb). Your gut’s surface area spans 300–400 m², roughly the size of a tennis court.
- Think about how incredible this is: these cells aren’t even yours – they’re bacteria living inside you, working alongside your body, and they outnumber your own cells.
- Neurons: You have around 86 billion of these nerve cells, transmitting signals at speeds up to 270 mph. Most are in your brain, though some, like those in the sciatic nerve, can be a meter long.
- Fat Cells: They can expand to 50 times their original size to store energy.
- DNA: Each cell’s DNA, if uncoiled, would stretch to 2 meters. Multiplied by your 37 trillion cells, that’s enough length to go to the Sun and back 250 times.
The atoms themselves are about 0.1 nanometers (10-10 meters) – extremely small and mostly empty. Although our world seems solid (we are aware of chairs and tables), atoms are held in place by relatively strong forces that create this stability.
If we increase a hydrogen nucleus to the size of a tennis ball, its electron will orbit 1.2 kilometers (0.75 miles) away, making the whole atom 2.4 kilometers wide (1.5 miles). – similar to a marble sitting in the middle of a stadium with its electron spinning out in the stand.
Atoms, Density, and Intergalactic Space
Let’s revisit the opening quote and make sense of it.
In interstellar space (within the Milky Way), the matter density is 1 million atoms per cubic meter. In the intergalactic space (between the Milky Way and Andromeda), that concentration drops to 1 atom per cubic meter. With a simple calculation, if we spread out the 7 octillion atoms in the human body into a sphere of intergalactic density, you would get a diameter about 200 times Earth’s, large enough to hold seven million Earths inside.
Atomic Structures and the Scales of the Universe
These are some staggering small dimensions already, but the universe goes even lower, all the way down to the Planck length, 1.6×10-35 meters, the smallest distance we can meaningfully measure according to the current physics. The Planck length would be the size of the “strings” from the string theory. Think of this as the building block of the universe, where space itself is “grainy,” like a grid, made up of these stings that vibrate at this tiny scale.
To visualize how small that is, imagine expanding an atom to the size of the observable universe (93 billion light years). On that scale, the Planck length would be the size of a large tree.
Quiz Time: What is a Quinvigintillion?
Here’s a question for you: What is a quinvigintillion? If your guess is “a very large number,” you are correct. A quinvigintillion is 1078. Why do I mention this? One last number for you: the amount of atoms in the observable universe is 100 quinvigintillions, or 1080.
Number of atoms in the universe = 100000000000000000000000000000000000000000000000000000000000000000000000000000000
Conclusion
I hope this exploration through the scales of the universe has provided some clarity on the vastness of our reality beyond everyday perception. From the smallest measurable distances to the largest cosmic structures, there are over 60 orders of magnitude, with our world sitting in a narrow range somewhere in the middle. It is a miracle that our minds are capable of probing these extremes and making sense of them. By exploring these scales, we gain a clearer sense of our place in the universe and the limits of our current knowledge.