Most of us think we get it. We’ve seen the posters of the solar system in elementary school where the planets are lined up like marbles on a desk. It looks manageable. It looks like a neighborhood. But honestly, those posters are a total lie. If you actually drew the solar system to scale on a piece of paper, the planets would be so small you couldn't even see them without a microscope. Space is empty. Like, really empty. When you ask how big is space, you aren't just asking about distance. You're asking about a scale of existence that our monkey brains aren't actually wired to process.
It’s huge.
Even the "close" stuff is ridiculously far away. Take the Moon. It looks like it’s right there, hanging in the sky. You could fit every single planet in our solar system—Jupiter, Saturn, all of them—in the gap between the Earth and the Moon. And you’d still have about 5,000 miles to spare. That’s just our front porch. Beyond that, the numbers start to get so large they basically become meaningless. We use terms like "light-years" because if we used miles or kilometers, we’d be writing down zeros until our pens ran out of ink.
The Local Neighborhood Is a Ghost Town
Let’s talk about the Sun for a second. It’s the center of our world, right? It takes light—the fastest thing in the universe—eight minutes and twenty seconds to get from the Sun to your face. If the Sun vanished right now, you’d still be enjoying the sunshine for nearly nine minutes before the lights went out. That's 93 million miles. But that’s nothing. If you wanted to drive to the Sun at 65 miles per hour, it would take you 163 years. You'd need a lot of snacks.
Voyager 1 is the furthest man-made object. It’s been hauling tail away from us since 1977. It’s currently traveling at about 38,000 miles per hour. Even at that blistering speed, it hasn't even left the "neighborhood." It’s currently in interstellar space, sure, but it won’t even reach the Oort Cloud—the theoretical shell of icy debris surrounding our system—for another 300 years. To get through it? Another 30,000 years. Voyager is basically a snail on a salt flat.
Space isn't just big; it's expanding. This is the part that trips people up. In 1929, Edwin Hubble noticed that galaxies aren't just sitting there. They’re moving away from us. And the further they are, the faster they’re moving. It’s not that they’re flying through space like bullets; it’s that the space between them is stretching. Think of it like raisins in a loaf of bread dough. As the bread bakes and expands, the raisins get further apart. The raisins aren't "walking" away; the dough is just getting bigger.
Why Light-Years Are a Time Machine
When we look at the stars, we aren't seeing them as they are. We’re seeing them as they were. The nearest star system to us is Proxima Centauri. It’s 4.2 light-years away. If that star exploded today, we wouldn't know about it until the year 2030.
Distance in space is time.
If you look at the Andromeda Galaxy—the closest major galaxy to the Milky Way—you’re looking at light that left its source 2.5 million years ago. Back then, humans didn't even exist in our current form. We’re basically looking at ghosts. The scale is so massive that by the time the information reaches us, the source might already be gone. It’s a bit haunting if you think about it too long.
How Big Is Space Beyond the Milky Way?
Our galaxy, the Milky Way, is about 100,000 light-years across. It contains somewhere between 100 billion and 400 billion stars. That's a lot of fireballs. But the Milky Way is just one galaxy in a "Local Group" of about 54 galaxies. And the Local Group is just a tiny corner of the Laniakea Supercluster, which contains 100,000 galaxies.
It gets worse.
The Observable Universe is a sphere about 93 billion light-years in diameter. Wait, you might ask, how can it be 93 billion light-years wide if the universe is only 13.8 billion years old? Nothing travels faster than light, right? True. But remember the expanding bread dough. While the light has been traveling toward us for 13.8 billion years, the space it traveled through has been stretching. The "stuff" that emitted that light is now much further away than it was when the light started its journey.
- The Solar System: 0.002 light-years wide.
- The Milky Way: 100,000 light-years wide.
- The Observable Universe: 93,000,000,000 light-years wide.
And that’s just what we can see. Because the universe is expanding, there are parts of space that are moving away from us faster than the speed of light. Their light will never reach us. Ever. We are effectively trapped in a bubble of visibility. What’s outside that bubble? We don’t know. It could be infinite. Some theories, like those discussed by physicists like Alan Guth, suggest the "entire" universe could be $10^{23}$ times larger than the observable part. That number is so big it’s basically just a placeholder for "we have no idea."
The Great Nothingness
One of the biggest misconceptions about space is that it’s full of stuff. It’s not. It’s almost entirely empty. If you took all the matter in the universe and spread it out evenly, you’d have about six protons per cubic meter. That’s a vacuum better than anything we can create in a lab on Earth.
Even within galaxies, stars are incredibly lonely. If the Sun were a grain of sand, the next closest grain of sand (Proxima Centauri) would be 20 miles away. There is a lot of "nothing" in between the "something." This is why when galaxies "collide"—which the Milky Way and Andromeda will do in about 4 billion years—the individual stars almost never actually hit each other. They just dance around in the void.
Dark Matter and the Invisible Bulk
To make matters even weirder, most of the "stuff" in space isn't even the stuff we can see. Regular matter—the atoms that make up you, me, the Earth, and the stars—only accounts for about 5% of the universe. The rest is Dark Matter (27%) and Dark Energy (68%).
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We can't see Dark Matter. We only know it’s there because its gravity keeps galaxies from flying apart. Without it, the Milky Way would have shredded itself ages ago. Then there's Dark Energy, the mysterious force that’s actually accelerating the expansion of the universe. It’s pushing everything away from everything else. Essentially, space isn't just big; it's getting bigger, faster, every single second.
Why This Matters for Us
It’s easy to feel small when you realize the Earth is a "pale blue dot" (as Carl Sagan famously put it) in a massive, dark ocean. But there’s a practical side to this scale. Understanding how big is space dictates everything we do in terms of technology and exploration.
We can't use traditional rockets to go to other stars. It’s just not physically possible with our current lifespan. If we want to reach the stars, we have to rethink physics—warp drives, solar sails, or generational ships. The scale of the universe is the ultimate engineering challenge.
Real-World Perspectives on the Void
Astronomers like Katie Mack have pointed out that the sheer size of the universe also determines its fate. If the expansion continues to accelerate because of Dark Energy, we eventually hit a "Heat Death." Galaxies will move so far apart they disappear from each other's view. Eventually, even atoms might get ripped apart. It’s a long way off—trillions of years—but the size of the vacuum is the very thing that might eventually end everything.
There’s also the "Boötes Void." This is a region of space about 330 million light-years in diameter that contains almost no galaxies. It’s just... a hole. By all rights, it should have thousands of galaxies in it. It has maybe 60. It’s a reminder that space isn't just big and empty—it’s also weirdly inconsistent.
Perspective Is Everything
So, how do you wrap your head around this? You don't. Not really. But you can try to visualize it. If the Earth were the size of a cherry tomato, the Sun would be about 500 feet away. Pluto would be nearly four miles away. The nearest star? That would be 30,000 miles away.
That’s for a tomato-sized Earth.
The scale is humbling. It’s also a bit of a relief. All our problems, our politics, our stresses—they all happen on this one tiny rock in an incomprehensibly large vacuum. It makes our world feel incredibly fragile and incredibly special at the same time.
Actionable Insights for the Aspiring Stargazer
If this existential dread hasn't completely overwhelmed you, there are ways to experience this scale for yourself. You don't need a PhD or a multi-billion dollar telescope to get a sense of the void.
- Download a Scale App: Use something like "The Scale of the Universe 2" or "Universe Sandbox." They let you zoom from the plank length all the way to the observable universe. It's the best way to see how we fit into the hierarchy.
- Find a Dark Sky Park: Most people have never seen the Milky Way because of light pollution. Go to a designated International Dark Sky Park. Seeing the "smudge" of our own galaxy with your naked eye changes how you feel about the night sky.
- Track the ISS: The International Space Station orbits only about 250 miles up. Seeing it streak across the sky reminds you how close we are to the "edge," yet how far we have to go.
- Study the James Webb Space Telescope (JWST) Images: Look at the "Deep Field" images. Every tiny speck of light in those photos isn't a star—it's an entire galaxy with billions of its own stars.
- Calculate Your Light-Travel Time: Next time you look at Jupiter, remember the light you're seeing is about 40 minutes old. You're looking at the past.
The universe is under no obligation to be small enough for us to understand. But the fact that we can even measure its vastness is pretty impressive for a bunch of mammals on a wet rock. We might be tiny, but our ability to look up and ask the right questions is what makes the vastness feel a little less lonely. Space is big, sure, but our curiosity is trying its best to keep up.