Are There Limits to Our Universe Reach?
Ever wonder if there’s a border we’ll never cross, places we can never reach, no matter how hard we try? Turns out, even with the coolest sci-fi tech, we’re kinda stuck in a limited little corner of the universe, just with the stuff inside it. So, how much universe is actually out there for us, and how far can we really go?
The Universe Around Us: Not Forever, and Slowing Down
When you gaze up at the night sky, you might think it’ll just stay there forever. Stars pop into existence and then fade away in a cycle that feels endless, but it’s not, really.
Take our own home galaxy, the Milky Way. It’s huge, up to 200,000 light years across, packed with maybe 100 to 400 billion stars. You’d guess tons of new stars are being born here every year, right? Thousands, maybe millions? Nope, the answer is only around three new stars each year.
Get this: 95% of all the stars that will ever exist in the universe have already been born. We’re living at the very tail end of the age when stars form. It’s like being at the start of the end of the universe as we know it. New star formation is just going to keep slowing down.
The Expanding Universe: Everything’s Rushing Away!
But there’s more to the story. It turns out the whole universe is actively rushing away from us. Our Milky Way isn’t flying solo. It hangs out with the Andromeda galaxy and over 50 smaller dwarf galaxies. Together, they form what we call the Local Group. This is our galactic neighborhood, a patch of space about 10 million light years wide.
Our Local Group is just one of hundreds like it that make up a larger structure called the Laniakea Supercluster. And even that is just one among countless superclusters floating around. In total, scientists figure there are about 2 trillion galaxies in the part of the universe we can currently see (the observable universe).
Here’s the kicker, and let this sink in: even if we could zip around at the speed of light, about 94% of the galaxies we can see right now are already completely unreachable for us. Forever. The simple fact that there’s a hard limit for us, and so much universe a human will never, ever touch, can feel a bit scary.
Why Are Most Galaxies Out of Reach? It Starts with the Big Bang
So, why are almost all those galaxies already beyond our grasp? It all comes back to how galaxies got there in the first place: the Big Bang.
Think of it simply: roughly 10 to the power of -36 seconds after the Big Bang, the baby universe was a tiny, tiny bubble of energy. It wasn’t perfectly smooth, though. Some spots were just a little, tiny bit denser than others. And this had massive consequences!
A process called Cosmic Inflation kicked in. The observable universe blew up super fast, from the size of something like a marble to trillions of kilometers across, all in just a trillionth of a second. That speed was so intense that those tiny density differences got stretched from subatomic distances (smaller than an atom!) all the way into distances as big as the gaps between galaxies. This is why the universe isn’t uniform; it has denser regions (pockets with more stuff) and less dense regions.
After that short, powerful burst of inflation stopped, gravity started trying to pull everything back together. Inside those denser pockets, gravity won. Over long stretches of time, these pockets grew into the groups of galaxies we see today, like our Local Group.
Our Local Group is our dense pocket of the universe. But on larger scales, outside these denser pockets, the expansion of space never stopped. This means our Local Group is surrounded by lots of other structures and galaxies, but none of them are held together by gravity with us.
The Expanding Universe Accelerates!
And it gets worse for us: the universe’s expansion is actually speeding up! We don’t fully know why this is happening, so we invented a concept called dark energy to try and explain it. You can picture it as an invisible force that’s pushing space to expand faster and faster. (We’ll dive deeper into dark energy another time, though!)
For now, just know that the universe is expanding quicker and quicker.
This faster expansion creates something called a cosmological horizon around us. Everything beyond this horizon is moving away from us faster than the speed of light relative to us. So, anything that crosses this horizon is lost to us forever – we can never interact with it again. It’s kind of like the event horizon of a black hole, but it’s surrounding us.
As mentioned before, 94% of the galaxies we see today have already passed this horizon. They’re gone forever.
Seeing the Unreachable: Looking into the Ancient Past
Wait a minute – if we can’t interact with them, how can we still see them?
Good question! We see things because light reaches us. And while the speed of light is the absolute fastest thing there is, it still takes time to travel across the universe.
Every second, light reaches us from galaxies that have already passed the horizon. This is because when that light started its journey, those galaxies were much, much closer to us. We aren’t seeing them as they are now; we’re looking at their incredibly ancient past and seeing where they were billions of years ago.
So, the observable universe (the bit we can see) is much, much bigger than the universe we can actually do anything with. In a way, the universe is putting on a fantastic show for us, letting us see things that are forever out of reach. We have zero idea what these galaxies look like today, and we never will. But hey, we’ll keep seeing their old light hitting our telescopes for a long, long time.
Interestingly, this means the observable universe actually appears to be getting bigger right now, just because more and more light that was released billions of years ago from super-distant galaxies is finally arriving here.
Still, all those other galaxy pockets outside our Local Group will one day cross our cosmological horizon. When they do, their light simply won’t be able to reach us anymore. From our perspective, they’ll just fade away into the darkness.
Every second of your life, roughly 60,000 stars cross this horizon. Since you started watching the video this text comes from, about 22 million stars have moved permanently out of our reach.
The Reachable Bit: A Small but Still Huge Playground
Okay, so 94% of the observable universe is beyond the cosmic horizon and unreachable. That still leaves us with 6% that is technically within reach! That’s still a mind-boggling amount of stuff.
This reachable part includes all the galaxy pockets that are less than about 18 billion light years away. They are still moving away from us, but slowly enough that, in theory, we could physically get to them. Though, honestly, the chances of that happening are shrinking with every second that passes.
Everything more than about 5 million light years away is already moving away from us. But the galaxy groups closest to us outside the Local Group are receding the slowest. This means there is a potential, though rapidly closing, time window to jump between galaxy groups.
The challenge, though? It’s extreme. We’re talking difficulty levels even for mythical Type III civilizations (the kind that could harness a whole galaxy’s energy). Even traveling at the speed of light, a trip to the Mafii group, the closest pocket of galaxies outside the Local Group, would take 11 million years.
If some super-motivated, super-advanced civilization somehow took on this challenge, their potential sphere of influence could expand to hundreds or maybe thousands of galaxies. But as time marched on and the universe kept expanding, they would eventually become forever separated from everything else.
It’s pretty safe to say that humans, as we are or even with foreseeable tech, won’t be making that journey. For us, the Local Group is almost certainly the biggest structure we will ever be a part of.
Just traveling between the stars within our own galaxy would be an epic, monumental achievement. We’d be incredibly successful if we managed to colonize just our own little cosmic backyard (our galaxy), which, get this, accounts for only about 0.000000000000001% of the entire observable universe.
The Future: An Island in the Dark
As dark energy keeps pushing the rest of the universe away, our Local Group will actually become even more tightly bound together. All its galaxies, big and small, will eventually merge into one massive elliptical galaxy. It’ll probably get the very creative name Milkdromeda (Milky Way + Andromeda).
This merging process, billions of years from now, might even smash huge gas clouds together, kicking off a new wave of star formation for a while. This fresh light will be much appreciated, because eventually, all those galaxies outside Milkdromeda will be so far away that their light becomes too faint to see.
Once that happens, no information from outside the Local Group will ever reach us again. The universe outside Milkdromeda will simply vanish from view.
Imagine a being born in the far, far future in Milkdromeda. When they look far out into what seems like empty space, all they’ll see is… more emptiness and darkness. They won’t see the cosmic background radiation (the afterglow of the Big Bang). They won’t have a way to learn about the Big Bang itself. They might have no clue about what we know today: the nature of the expanding universe, how it began, or how it will end. They might simply think their galaxy is the entire universe, static and eternal. Milkdromeda will be an isolated island, slowly getting darker and darker.
Still, with its trillions of stars, the Local Group is certainly a big enough playground to keep humanity busy for a very, very long time. After all, we still haven’t even figured out how to leave our own solar system! We have dozens of billions of years, at the very least, just to explore our galaxy.
And we are incredibly lucky to exist right at this perfect moment in time, when we can look into the night sky and see not only glimpses of our far future (galaxies merging) but also our most distant past (the Big Bang’s afterglow, the light from early galaxies).
As isolated as our Local Group might seem in the grand scheme of things, it’s our home. And it really is a spectacular place.
Behind the Scenes: A Correction
Just a quick note on how this came about. You might have noticed we actually made a video like this a few years ago. But, unfortunately, it had a mistake we really regretted. We said it would be physically impossible to ever leave the Local Group to reach other galaxy groups. As we’ve shown in this text, that’s not quite right. It’s not physically impossible to go further, it’s just extremely, extremely unlikely it will ever happen for humans.
So why did we leave the old video up? Well, we talked to astrophysicists about the mistake, and they felt it didn’t really affect the core message. The parts they considered important were correct, and they suggested we just leave it and move on. Based on that feedback, we decided to spare the old video.
But since 2016 (and honestly, thanks to you wonderful folks!), we’ve been able to grow K**_ and add fact-checkers to our team. We’ve developed a much more in-depth process involving experts and detailed source documents to avoid these kinds of mistakes and to be more transparent about our work. We know we can’t avoid all mistakes forever, but we can definitely work hard to get better.
This video correction kept bothering us, so we finally decided to replace it. Not just re-upload the old one, but completely remake it – better, longer, and with more fun universe facts to make it worth your while. Sorry it took us so long! We’ll keep the old video up but add a comment and change the title to clear things up.
If you’d like to support us and our sometimes exhausting (but hopefully worthwhile!) methods, you can watch, share, and click the bell button. Or, you could grab something from our shop! Inspired by this topic, we created a Milky Way poster and a Local Group poster. We’re even working on a series all about the entire universe. Check out our shop for more sciencey and K**_ galaxy products designed with love and produced with care.
Anyway, thank you for reading!