In the last post about the Observable Universe, I discussed the sheer scale of the cosmos and that mind-bending 46.5 billion light-year edge. But as I kept digging into how we actually measure that expansion, I stumbled into a conflicting opinion among the astronomers. This made me further explore the Hubble Tension, and now I finally understand why astronomers might be freaking out.

The universe is currently presenting us with two different answers to the same basic question: “How fast are we growing?” During my school days, I studied Hubble’s Law, which states that “galaxies are moving away from Earth at speeds proportional to their distance, providing key evidence for the expansion of the universe.” In 1929, Edwin Hubble proposed the Hubble constant, which quantifies the rate of the universe’s expansion. This constant can be measured by observing the distances of celestial objects and the speeds at which they are moving away from us.

We have two primary methods for measuring the Hubble Constant. Currently, these two methods are at a standoff. To keep things simple while I was wrapping my head around this, I started calling them the “Baby Picture” team and the “Local” team“.

On one side, we have the “Baby Picture” Team (which scientists formally call the Early Universe or CMB measurements). They look at the Cosmic Microwave Background, the afterglow of the Big Bang, to calculate how fast the universe should be expanding based on its initial conditions. Their math gives us a speed of 67.4 km/s/Mpc.

On the other side, there’s the “Local” Team (officially known as the Late Universe or Distance Ladder measurements). Instead of looking at the beginning of time, they look at what’s happening right now, measuring actual stars and galaxies in our neck of the woods. Their measurement comes in much higher, at roughly 73 km/s/Mpc.

A gap of five or six units might not seem like a big deal, but in the world of physics, it’s a total disaster. It’s like two people measuring your height: one insists you’re 5’8″ and the other is positive you’re 6’1″, and both are certain their tape measures are perfect.

This disagreement is what scientists call the Hubble Tension. It’s the ultimate “it doesn’t add up” moment, creating a massive conflict between the “blueprints” we see in the early universe and the “finished house” we see in our local neighborhood today.

I found a paper published in January 2025 titled “The Hubble Tension in Our Own Backyard: DESI and the Nearness of the Coma Cluster, ” which addresses the ongoing debate about the expansion rate of the universe. The research team, led by Dan Scolnic, used the Dark Energy Spectroscopic Instrument (DESI) to obtain the most precise measurement to date, 76.5 km/s/Mpc. This measurement is even faster than previously anticipated. As a result, it effectively rules out the possibility of measurement error. This indicates that the universe around us is definitely expanding faster than expected.

Are We Currently in a Bubble?

So, if the measurements aren’t wrong, what is?

To answer this, when I further searched on the net, I came across a groundbreaking new study from the Royal Astronomical Society titled, “Earth Inside Huge Void May Explain Big Bang Expansion Rate Puzzle“, which suggested that the problem is not the math, it’s our own address, where we live.

To understand this better, let us think of it as a giant game of cosmic tug-of-war. Usually, matter is spread out evenly, so everyone is pulling on each other with equal strength. But because we live in a ‘void’ (an empty pocket), there are way fewer people on our side of the rope. Meanwhile, the rest of the universe outside our bubble is packed with matter. Because they have more ‘players’ (more gravity), they are pulling galaxies away from us much harder and faster than they normally would. From our perspective in the middle, it looks like everything is rushing away, but really, they’re just being winched out by the heavy-hitters outside our neighborhood.

The study suggests Earth and the Milky Way are drifting through a massive cosmic void spanning 2 billion light-years. This region contains significantly less matter than the rest of the universe. Because we are in this “empty” pocket, gravity from the denser universe outside the bubble is pulling galaxies away from us faster than normal.

If this theory is right, then we can say for sure that the universe isn’t breaking the laws of physics; we just happen to live in a weird, lonely neighborhood. In fact, the researchers calculate it is 100 times more likely that we reside in such a void than in a normal region.

It’s a humbling thought: We might be looking out at the universe from the inside of a giant cosmic ghost town, wondering why everything is running away from us so fast.

When I was reading about the universe’s age the other night, I stumbled onto a Wikipedia page about the “observable universe,” and it honestly blew my mind. It’s one of those things that sounds like science fiction, the idea that there’s a hard limit to what we can see, and it’s way further away than you’d think.

If the universe is roughly 13.8 billion years old, you’d assume the furthest thing we can see is 13.8 billion light-years away. But the actual number is about 46.5 billion light-years in every direction. That makes the whole observable universe a giant sphere about 93 billion light-years across. Here is what I discovered about the boundaries of our cosmic neighborhood.

Observable Edge

The observable edge, or cosmic horizon, can be thought of as a time-delay boundary rather than a physical wall. It represents the furthest limit from which light has had enough time to travel and reach our eyes since the Big Bang. Everything within this boundary forms a perfect sphere with us at the center. This isn’t because we are in the middle of the universe, but because we are the center of our own perspective. The scale of this sphere is difficult to visualize, but the data gives us a framework for just how much “room” we have to explore.

So, how is the radius 46.5 billion light-years if the light has only been traveling for 13.8 billion years? While light travels toward us, the space through which it travels is actually expanding. It’s like a runner trying to finish a marathon while the road itself is being stretched behind and in front of them. The light eventually reaches us, but the source of that light has since moved much further away.

Why the math doesn’t seem to add up

The reason the edge is so much further away than the age of the universe is because of the way space stretches. A lot of people use the “expanding balloon” analogy to explain this, and it’s probably the best way to visualize it.

Imagine you have a balloon that hasn’t been blown up yet. You draw two dots on it with a Sharpie to represent galaxies. If you start blowing air into that balloon, the rubber stretches and the dots move away from each other. Now, imagine a tiny ant crawling from one dot to the other. While the ant is walking, the balloon is growing. By the time the ant reaches the second dot, the actual distance it covered is much longer than the distance between the dots when it first started its journey.

In this scenario, light is the ant. While light is traveling toward us, the space through which it’s traveling is expanding. So, by the time the light from a distant galaxy finally hits our telescopes, that galaxy has been pushed much further away than it was when it first emitted that light.

The trippy part is that because this expansion is actually speeding up, there are parts of the universe that are basically “dropping off” our map. These regions are moving away from us faster than the speed of light. That doesn’t mean the galaxies themselves are breaking physics; it just means the space between us is growing so fast that light can never bridge the gap. It’s like trying to run up a down-escalator that’s moving way faster than you can sprint. You’ll just never reach the top.

The first snapshot of the universe

If we look as far back as possible, to the very edge of that 46.5 billion light-year radius, we find the Cosmic Microwave Background (CMB). This is essentially the afterglow of the Big Bang.

For the first 380,000 years, the universe was so hot and crowded that light couldn’t even move; it was like a thick, glowing fog. Eventually, things cooled down enough for light to break free, and that light has been traveling through space for billions of years. Because the universe has stretched so much since then (an expanding balloon analogy), those light waves have been stretched until they became microwaves.

New problems in 2025

Scientists are actually in a bit of a crisis over this right now. As of early 2025, data from the James Webb Space Telescope and recent studies from the Atacama Cosmology Telescope have confirmed something called the “Hubble Tension.”

Basically, when we look at the CMB to see how fast the universe should be expanding, we get one answer. But when we look at actual stars and galaxies today, they seem to be moving much faster than the early data predicted. Research published throughout 2024 and into 2025 suggests we might need “New Physics” to explain the gap, maybe a weird version of dark energy that only existed for a little while right after the universe began.

It’s a bit humbling to realize that even with our best tech, we’re essentially sitting inside a bubble, looking at a “baby picture” of the cosmos that we’re still trying to fully understand.

Where does this leave us?

Realizing that our maps of the universe are still being redrawn is actually pretty exciting. We often think of science as a finished book, but the “Hubble Tension” reminds us that we’re still very much in the middle of the story. The fact that the universe we see today doesn’t quite match the “baby picture” from the CMB doesn’t mean we’re wrong, it just means there’s something massive and invisible still waiting to be discovered.

At the end of the day, the 46.5 billion light-year edge isn’t a wall, it’s just the limit of our current perspective. We are small observers in a vast, stretching fabric, trying to decode a message that has been traveling for billions of years. It’s a reminder that no matter how much we think we’ve figured out, the cosmos still has plenty of ways to surprise us. Whether the answer lies in new physics or a deeper understanding of dark energy, the search itself is what keeps us looking up.