Residing in a cosmic void: What It Means for Our Universe

Our Milky Way galaxy could be located in a space void, where there is relatively little matter compared to other areas of the universe. This would mean that we are even more isolated than we thought. Scientists are also grappling with the Hubble tension, a cosmic mystery challenging our understanding of the universe's expansion.

Scientists used to consider the Hubble constant a reliable guide, but our recent observations question this reliability. The speeds we see in real life don't match up with the distances we calculated and expected. They aren't sure why these measurements don't add up.

Researchers followed the moves of supernovas and saw that the universe seems to expand faster around us than it does overall as if it's actively avoiding us specifically. After considering this, they began to assume that we might all live in a cosmic void.

Cosmic voids are vast empty spaces between galaxies, kind of like between my ears. They make our entire world look like a big sponge.

Now, let's go back to the beginning. Just a fraction of a second after the Big Bang, right after the beginning of everything, the universe was a hot compressed plasma. It only had very tiny variations in density called quantum fluctuations.

After the Big Bang, the universe began to expand. Those quantum fluctuations grew together with it, creating regions of varying matter density. Because of that, the universe didn't expand everywhere uniformly. Instead, little clumps of matter began to gather together over a long period, creating massive structures called galaxies.

Galaxies are arranged in huge walls and filaments with enormous gaps in between, and these gaps are voids, also known as dark space. Now, these voids aren't truly empty. They hold more than 15% of the amount of matter found on average throughout the entire universe.

They still contain gas, dust, dark matter, and even stars and galaxies. However, they have less density than regions with galaxies, about a tenth of the average matter density, which is why we consider them nearly empty. Usually, they'll have a diameter ranging from about 30 to 300 million light-years. That is an enormous distance even on a space scale.

For comparison, most planets and nebulas we found so far have a distance of hundreds and rarely thousands of light-years away from us. In the case of voids, if you were in the middle of one, it would just look like seemingly eternal darkness. The closest stars would be so far away that they would be almost invisible to you.

Some of them are especially large. They're known as Super voids. The largest known one was creatively named Giant Void. It's so big it's impossible for us to even imagine, 1.5 billion light-years away, with a diameter of 1 to 1.3 billion light-years. Yeah, it's a big dark vacuum.

But even this giant vacuum isn't empty. The Giant Void houses 17 separate galaxy clusters within its expanse. However, it might not be the biggest emptiness in our universe.

There's this thing called the CMB Cold Spot. It's this unusually large and chilly area of our universe that we saw through the microwaves. It stood out on the map of our universe with its unexpectedly low temperatures, and scientists have spent many years trying to figure out what the thing is.

Scientists proposed in 2015 that a place called might be the largest supervoid ever, called the Great Void. It's about 1.8 billion light-years in diameter, a thousand times larger than typical voids. There's no consensus on whether it's possible, but some speculate that it might be a trace of our collision with a parallel world. However, it's impossible to confirm or deny this hypothesis with our current technology.

In any case, as the universe expands, these voids will grow, and the walls connecting galaxy clusters will stretch and break. Eventually, the voids will merge, leaving gravitationally bound galaxy clusters as islands in the expanding emptiness. In other words, the great emptiness will consume everything in our world sooner or later.

So it turns out we might be a rare occasion in a supervoid. When of the 15% of matter, this would explain why relatively few galaxies surround us. This discovery, if true, challenges the standard model of cosmology, which we created with Albert Einstein's help. It would mean that gravity, in general, behaves differently than what we expected. According to the standard model, such a significant under-density shouldn't exist."