Ever looked up at the night sky and thought, “Okay, but… how big is all this, really?” what exists beyond the edges of what we can see? The cosmos, the part we can see, is called the observable universe, so we try to understand how big is the observable universe. The distance is far beyond what we can comprehend from our brains here on Earth. Sure, in numbers, we can say how big it is. But the reality is that it’s just incomprehensible. The observable universe is a bubble centered around Earth, defined by the reach of light over billions of years.
Check this article out, too: What is Antimatter Used For? Life Changing Use Cases
What is the difference between the observable and normal universe? Well, that’s a topic for another day. But in essence, light takes time to travel, and the universe has only been around for about 13.8 billion years. So, we can only see stuff whose light has had time to reach us. It’s not that the rest doesn’t exist—we’re just waiting for its signal. Like when you text your friend and they ghost you for a week. Same energy. Even though the universe is 13.8 billion years old, the observable universe is way bigger than 13.8 billion light-years across Because space itself is expanding. The stuff we see now was much closer when it sent its light, but it’s been stretching away from us ever since. As a result, the observable universe is about 93 billion light-years across. Do you realize how big of a number that is?
Let’s check out how big is the observable universe in more detail, what that means for our research, and many more details.
Introduction to the Observable Universe
Before we can answer the big question—how big is the observable universe—we need to understand what we’re discussing. The term “observable universe” is a specific region of the universe that we can see based on one simple limitation: the speed of light.
I have a much more detailed article on what is the observable universe – check it out at the hyperlink above in the first paragraph of the article.
That speed limit means there’s a cosmic bubble around us, a kind of sphere of visibility defined by how far light has traveled since the beginning of time (or at least, since the Big Bang). It’s not the whole universe—just the part that’s been polite enough to send its light our way in time for us to catch it. Anything beyond that? It’s there (probably), but we’re stuck in the dark until the light finally shows up.
What Defines the Observable Universe?
The speed of light limits the observable universe. Since light takes time to travel, we can only see objects whose light has reached us over billions of years. This creates a confined bubble around Earth, where distant galaxies appear as they were in the past. Cosmic expansion plays a crucial role in this phenomenon. As space stretches, galaxies move farther apart, increasing the distances we measure. What was once a mere billion light-years away is now much farther due to this ongoing expansion.
Think of it like this: when you flip on a flashlight in a pitch-dark room, the light travels outward in all directions. The longer it stays on, the farther it goes. Our universe is like that flashlight, but it’s been on for 13.8 billion years. And space hasn’t just been sitting still. It’s been expanding. A lot. This means the objects we can see today have moved far beyond the original distance their light had to travel to reach us.
The Role of Light and Time in Cosmic Measurements
Light and time are intertwined in our understanding of the cosmos. Light is our cosmic messenger. It’s the reason we know anything about space. And it always travels at the same speed: 299,792 kilometers per second. But not instant. The finite speed of light means we observe distant objects as they were billions of years ago. That means when we look at distant galaxies, we’re actually looking back in time. A galaxy that’s 1 billion light-years away? We’re seeing it as it looked 1 billion years ago.
Space itself expands, stretching the distances between galaxies. This expansion transforms what we perceive as the universe’s size, making it far larger than the light-years light has traveled. That’s why, when we talk about how big the observable universe is, we end up with numbers that feel like they were made up by someone who failed math.
Determining the Size of the Observable Universe
We know all this information, but how do we actually measure the size of the observable universe? How do we know how big is the observable universe? It’s a tough question. Determining the size of the observable universe isn’t guesswork or pulling numbers out of a starry hat. It’s built on a stack of observations, physics, and a whole lot of math.
First, we use the cosmic microwave background (CMB), basically the afterglow of the Big Bang. It’s the oldest light we can detect and our most reliable time capsule. Scientists measure tiny variations in this microwave radiation to map out distances and expansion rates across the universe.
Next up is redshift. When galaxies move away from us, the light they emit stretches out like a siren that drops in pitch as an ambulance zooms by. The more stretched the light, the farther away the galaxy is and the faster it’s moving. By looking at redshift, we can trace how fast the universe has been expanding over time.
Calculating Distance and Diameter
Astronomers use astronomical objects like Cepheid variable stars and Type 1A supernovae as benchmarks. These things can give us reliable measurements for distances up to billions of light years. Scientists can calculate how far they are from Earth by observing their brightness and redshift. The observable universe is a sphere with us at the center—not because we’re special, but because that’s the point from which we’re observing. It stretches out in all directions about 46.5 billion light-years. So if it’s 46.5 billion light-years in one direction, you double it to get the full diameter: 93 billion light-years. That’s the total span of the observable universe.
But how do we calculate that? We start with how long the universe has existed—13.8 billion years. Multiply that by the speed of light, and you get 13.8 billion light-years… if the universe wasn’t expanding. But it is. So, instead, we use our knowledge of the expansion rate (aka the Hubble constant) to account for how much the universe has stretched.
Exploring Cosmic Expansion and Hubble’s Law
Now we’re diving into one of the biggest reasons our observable universe is as big as it is: cosmic expansion. The universe isn’t just sitting there like a cosmic snow globe. It’s actively stretching out, and it has been since the Big Bang. This isn’t expansion like a balloon getting bigger—it’s space itself growing. The galaxies aren’t flying through space. Space is doing the moving.
As space expands, distant galaxies move away from us at speeds proportional to their distance. This means the farther a galaxy is, the faster it appears to recede. The speed at which light has traveled over 13.8 billion years defines the observable limit, but expansion stretches these distances even further. For human observers, this creates a unique challenge. Light from distant galaxies takes billions of years to reach us, showing us the universe as it was in the past. Meanwhile, the ongoing expansion rate means those galaxies are now much farther away than when their light began its journey.
Understanding Hubble’s Law and Its Implications
Hubble’s Law is the main framework we use to understand the expansion. The law says that a galaxy’s recession speed is directly proportional to its distance from us. This relationship reinforces the idea of an ever-expanding universe, where space itself is stretching over time.
It goes like this: velocity = Hubble constant × distance. This means, the farther away something is in space, the faster it moves away from us. When Edwin Hubble discovered this back in the 1920s, it turned the entire idea of a static universe into its head. Suddenly, the universe was dynamic. Alive. Stretching. And we had a way to measure it.
The Hubble constant (which is basically the expansion rate of the universe) helps us figure out how fast things are moving and how far away they are. The higher the constant, the faster the expansion.
Key Factors in Understanding How Big is the Observable Universe
Okay, so we understand how big the observable universe is and have a way to calculate that. But how exactly do we do that? Is it just simple math, or do we account for stuff in space, like dark matter? There are two critical elements: dark energy and the cosmic microwave background.
The Impact of Dark Energy and Expansion Rate
Dark energy makes up about 68% of the universe – that’s a lot. This energy is the main force that drives the expansion I mentioned above. It is the cause of the universe being in an accelerated expansion state. It pushes galaxies apart and stretches the fabric of space itself. As a result, the universe grows larger over time, challenging our ability to measure its true size.
Hubble’s Law says that the galaxies move away faster at an increased expansion rate. This and dark energy’s influence shape the observable universe’s boundaries.
Insights from Cosmic Microwave Background Observations
The cosmic microwave background (CMB) is a relic from the universe’s first moments. It’s the oldest light in the universe we can see. It’s a really faint glow that we detected by advanced instruments. Since it’s the oldest light, we can see a small snapshot of the universe about 380,000 years after the Big Bang. It’s like a treasure of data to study the first moments of the universe and understand the limits of the universe.
Scientists can map the early universe’s structure and composition by studying the CMB. These observations refine our understanding of the expansion of the universe and the role of dark energy. The CMB also confirms the universe’s flat geometry, supporting the idea of an infinite cosmos.
Comparing the Observable Universe to the Entire Universe
There is the observable universe, but what is beyond that? The entire universe is potentially way bigger than what we can see. Maybe even infinite. Yep, you read that right: infinite. And our tools and brains are only scratching the surface. But this is basically impossible to know unless we can somehow travel faster than light and travel to the edge of the observable universe.
The observable universe is like standing on a foggy mountaintop. You can see in all directions until the fog blocks your view—but that doesn’t mean the mountain ends there. It just means you can’t see past the fog. Likewise, we don’t know exactly how much more is out there beyond our observational reach, but odds are, it’s a whole lot.
Observable Limits Versus Theoretical Extents
The observable universe has a hard limit set by light and time. But the entire universe? Theoretically, it could go on forever. The cosmic microwave background sets our observations’ limits. The oldest light that exists. This boundary marks the edge of what we can see, about 46 billion light-years away. Beyond this, the universe could extend infinitely, as suggested by theories like general relativity.
Finite Measurement and the Concept of an Infinite Universe
So, I say that there is a limit to what we can see, and beyond the observable universe, there may be an infinite universe. But does that mean that there is a wall that disconnects the rest of the universe between us and there? Well, no.
If you could travel to the edge of the observable universe, you’d probably only see pitch-dark or more space. The light would have time to reach there, but not us. In theory, you may not even be able to find that line between the observable universe and the rest.
There is an episode of Doctor Who released sometime in 2023 (special episode released on December 2, 2023, Wild Blue Yonder) where the Doctor goes to the edge of the universe. They encounter species that don’t know light or the universe as we know it – they don’t even know shapes. It was a cool concept when I watched it. I definitely recommend it.
Conclusion
The short answer to how big is the observable universe is that it’s 93 billion light years. It’s easy to write and read this number, but the actual reality of how big this is is incomprehensible. For reference, one light year takes 1 year to travel at light speed (we can’t do that now). To go to the edge of the observable universe, it’d take 93 billion years.
There are also theories about what lies beyond the observable universe. Nothing? Infinite universe? Something we can’t comprehend? We don’t know. It’s like we are stuck in a massive library with a flashlight—you can only see the shelves around you, but the building might stretch on forever into the dark. Maybe the universe is finite, maybe it’s infinite, maybe it’s shaped like a giant donut, and we’re all living on the glaze.
What we do know is that thanks to light, time, cosmic expansion, and a whole lot of brilliant humans arguing over telescope data, we’ve got a pretty amazing glimpse into the grandest show in existence. And the best part? We’re still just getting started. Every new observation pushes our understanding—and our imaginations—even farther.
FAQ
What defines the observable universe?
The observable universe is the portion of the cosmos we can see from Earth, limited by the distance light has traveled since the Big Bang, approximately 13.8 billion years ago.
How does light help us measure cosmic distances?
Light travels at a constant speed, allowing us to calculate distances by measuring how long it takes to reach us.
What is Hubble’s Law, and why is it important?
Hubble’s Law describes how galaxies move away from us at speeds proportional to their distance. It’s crucial for understanding the expansion rate and scale of the cosmos.
Can we ever observe the edge of the universe?
Due to the universe’s expansion and the finite speed of light, there’s a limit to how far we can see. The “edge” remains beyond our observational reach.