• Like what you see?

    Discover the wonders of the universe! Join the Hamilton RASC community today — visit our membership page to get started!

94% of the Universe is Out of Reach: The Mind-Blowing Reality of Cosmic Expansion

Looking Out Into the Vastness of the Universe

The universe is unimaginably vast. When we look up at the night sky, we see only a tiny fraction of what’s out there—a mere handful of galaxies out of the trillions that populate the cosmos. But here’s the mind-boggling part: most of those galaxies—about 94%—are permanently beyond our reach. Even with the fastest spaceship imaginable, we could never reach them. Why? It all comes down to how space itself expands and stretches the distances between galaxies faster than the speed of light.

Let’s break this down step by step, from the size of the universe to why it’s slipping out of our grasp.

The Observable Universe vs. The Whole Universe

First, let’s talk about what we mean by “observable universe.” The universe is about 13.8 billion years old, so you might think the farthest we can see is 13.8 billion light-years away—right? Wrong! The observable universe is much larger, with a radius of 46 billion light-years. This means its diameter is a whopping 93 billion light-years across.

Why the discrepancy? It’s because the universe has been expanding ever since the Big Bang. Light from distant galaxies has traveled billions of years to reach us, but during that time, space itself has been stretching. The galaxies that emitted that light are now much farther away than when their light first began its journey.

However, the observable universe is just the part of the universe we can see. The entire universe is likely much larger—possibly infinite. If it’s finite, some estimates suggest it could be at least 250 times larger than the observable universe. And beyond what we can see, galaxies and regions of space exist that are forever hidden from us.

The Cosmic Expansion Line: 18 Billion Light-Years Away

Here’s where it gets even wilder: there’s a line in the universe, known as the cosmic event horizon, that marks the limit of what we can ever reach. This line lies about 18 billion light-years away. Any galaxy beyond that distance is moving away from us faster than the speed of light—not because the galaxy itself is speeding through space, but because space itself is expanding.

Let’s be clear: this doesn’t violate Einstein’s rules about the speed of light. Galaxies aren’t zooming through space like race cars; it’s the fabric of space itself that’s stretching, dragging the galaxies along. This means galaxies beyond 18 billion light-years are permanently out of reach. Even if we could travel at the speed of light, we’d never catch up to them because space keeps stretching faster than we could ever move.

Why 94% of the Universe is Beyond Our Reach

The universe’s expansion isn’t slowing down—it’s speeding up, thanks to an invisible force called dark energy. This mysterious force acts like an anti-gravity effect, pushing space apart faster and faster over time. Because of this acceleration, galaxies that are currently within our observable universe are crossing the cosmic event horizon all the time.

Every year, about 160 billion stars (spread across countless galaxies) slip beyond the event horizon, joining the 94% of the universe we can never reach. In the distant future, only galaxies within our Local Group (a small cluster of about 50 galaxies) will remain gravitationally bound to us. The rest of the universe will drift away, leaving us in a cosmic bubble of isolation.

A Universe That’s Always Changing

It’s hard to imagine, but the universe we see today won’t look the same billions of years from now. As time goes on:

The observable universe will shrink: While we’ll still be able to see galaxies that emitted light billions of years ago, the galaxies themselves will be farther away than ever—and eventually, new galaxies will stop appearing in our observable horizon.

Galaxies will “disappear” from reach: They won’t vanish, but their light will get stretched so much by the expansion of space that it will become undetectable.

The Local Group will dominate: In a trillion years, the Milky Way and Andromeda (which are on a collision course) will form a massive galaxy, and all that remains of the universe we know will be within our small galactic neighborhood.

Why Does This Matter?

This cosmic reality might feel a little isolating, but it also highlights the dynamic, ever-changing nature of the universe. Understanding these concepts helps us appreciate:

The role of dark energy: Whatever this mysterious force is, it’s shaping the fate of the cosmos.

Our place in time: We live in a golden age of the universe where we can observe galaxies before they disappear forever.

The fragility of knowledge: The universe we see today is only a snapshot of a much larger, incomprehensible whole.

Questions to Test Your Cosmic Curiosity

1. Why is the observable universe 46 billion light-years in radius, not 13.8 billion light-years?

Answer: Because the universe has been expanding since the Big Bang. Light has been traveling toward us for 13.8 billion years, but the space it traveled through has been stretching, making the distance much larger.

2. What is the cosmic event horizon?

Answer: It’s the distance (currently about 18 billion light-years) beyond which galaxies recede faster than the speed of light due to the expansion of space.

3. What happens to galaxies beyond the event horizon?

Answer: They continue moving away from us, and even their light will eventually become undetectable as it gets stretched by the expansion of space.

4. What percentage of the universe is already unreachable?

Answer: About 94%. These regions are too far away and are receding faster than the speed of light.

5. What will the universe look like in the far future?

Answer: Only the galaxies in our Local Group will remain gravitationally bound to us. The rest of the universe will be so far away that it will effectively disappear from view.

The Final Frontier

The vastness of the universe is awe-inspiring and humbling. While 94% of it may be forever beyond our reach, the fact that we can study and understand these cosmic truths is a testament to human curiosity and ingenuity. So, the next time you look up at the stars, remember: you’re peering into the past of a universe that’s far larger, and stranger, than we can ever imagine.

Comments are closed.