NASA’s Estimate of All Galaxies Explained

追加: 2026-06-03

[00:00:04]Look up at the night sky. You see a few thousand stars, maybe a smear of light if you're far from the city. But what if I told you that every single point of darkness between those stars, every tiny black [music] patch of nothing is hiding entire galaxies. Not just one, not just a hundred, thousands of them hiding in plain sight. And we've only just started to [music] understand how deep this rabbit hole actually goes. The number we're going to land on by the end of this [music] video is so large, it will make the word billion feel embarrassingly small.

[00:00:42]This is the story of galaxies. Not just how many there are, but how we [music] figured it out, how many we've actually seen, and the number that will genuinely make your brain short circuit. This is also the story of how science keeps humbling itself. Every time we think we have the answer, the universe quietly reveals that we were thinking too small.

[00:01:06]Now, I've spent a lot of time digging into astrophysics research, translating the kind of science that lives in journals into something that actually [music] makes sense to real people. And this topic, it's one of the most mind-melting things I've ever come across. Not just because the numbers are big, but because of what those numbers [music] say about our place in all of this. So stick with me. Here's what we're going to cover. First, we'll start with what people used to believe because the history here is wild. Then we'll get into what telescopes actually showed us, including that one famous image that changed [music] everything.

[00:01:47]After that, we'll talk about the number scientists thought they knew, and the new number that blew that wide open. And finally, we'll zoom out to something even bigger that most people never even think about. Each step is going to make the last one feel like a warm-up.

[00:02:07]Let's start at the beginning. For most of human history, people thought the Milky Way was the whole universe, everything there was. The stars above you, that was it. The idea that those faint, fuzzy patches [music] of light, what astronomers called nebulae, could actually be entire galaxies on their own. That wasn't even on the table.

[00:02:31]Scientists debated it for decades. They called it the Great Debate. On one side, Harlow Shapley argued those fuzzy smudges [music] were just clouds of gas and dust inside our own galaxy. On the other side, Heber Curtis argued they were island universes, entire systems of stars unimaginably far away. Both sides had evidence. Both sides had smart people. And for years, nobody could prove who was right.

[00:03:03]It wasn't until the 1920s that an astronomer named Edwin Hubble finally settled it. Using the 100-in Hooker telescope at Mount Wilson Observatory, he identified a specific type of pulsing star called a Cepheid variable inside the Andromeda Nebula. Cepheid variables are incredibly useful because their brightness tells you exactly how far away they are. And the distance Hubble calculated was staggering. Andromeda wasn't inside our galaxy. It was nearly a million light-years [music] away.

[00:03:38]Those fuzzy patches weren't clouds of gas inside our galaxy. They were entire [music] galaxies, billions of stars so far away they looked like smudges.

[00:03:49]That single discovery didn't just expand [music] the universe, it exploded it.

[00:03:55]Overnight, the cosmos went from one galaxy to potentially millions, and we had barely scratched the surface.

[00:04:05]Now, here's where things get really interesting. Jump forward to 1995.

[00:04:11]Scientists pointed the Hubble Space Telescope at a tiny patch of sky, a piece of space no bigger than a grain of sand held at arm's length. An area so dark, so empty-looking, that many astronomers thought there would be nothing there. They let it stare at that spot for 10 consecutive days, >> [music] >> no interruptions, just staring into the void.

[00:04:38]What came back changed everything. In that tiny sliver of darkness, that grain of [music] sand, Hubble captured around 3,000 galaxies. Each one a city of stars. Each one containing hundreds of billions of suns. Spiral galaxies, elliptical galaxies, galaxies colliding, galaxies in various stages [music] of formation. All of them ancient, all of them real. And that was just one grain of sand out of the entire sky. They called it the Hubble Deep Field.

[00:05:14]And it told us something [music] staggering.

[00:05:16]The universe wasn't just big, it was incomprehensibly, almost offensively, enormous. Scientists later repeated [music] the experiment in other patches of sky. The Hubble Deep Field South, the Hubble Ultra Deep Field.

[00:05:32]And each time, >> [music] >> the result was the same. Galaxies everywhere, in every direction, in every dark corner. The universe is not mostly empty. It is mostly full of things we hadn't been able to see.

[00:05:47]From that image, scientists started doing the math.

[00:05:51]>> [music] >> They extrapolated. They counted. They calculated. And they landed on a number that became the standard answer for [music] decades. About 200 billion galaxies in the observable universe. 200 billion. It sounds enormous. [music] And it is. But here's the thing.

[00:06:10]That number was wrong. Or at least, it was way too small.

[00:06:17]In 2016, a team of astronomers led by Christopher Conselice at the University of Nottingham took a fresh look at all the data. They used new 3D models of the universe combined with images from telescopes across decades of observation. And they realized something that nobody had fully accounted for before.

[00:06:38]Most galaxies are too small and too faint for our telescopes to see.

[00:06:44]Think about that for a moment. All our observations, every deep field image, every galaxy survey ever conducted was only showing us the bright ones. The big ones. The ones loud enough to shout across the cosmos. But there's a whole population of smaller, dimmer, younger galaxies that are essentially invisible to us with current technology. We were counting the loudest voices in a crowd and calling it the whole population. It wasn't even close.

[00:07:16]When Conselice's team factored those in, the number didn't double. It didn't triple. The new estimate came in at 2 trillion galaxies. 2 trillion. That's 10 times more than what we thought. Two followed by 12 zeros. If you counted one galaxy per second, non-stop, no breaks, no sleep, you'd be counting for 63,000 years before you finished.

[00:07:42]Let that sit for a second.

[00:07:43]Two trillion galaxies, and each galaxy has, on average, hundreds of billions of stars. Some have more. Our own Milky Way has somewhere between 100 and 400 billion stars. The Andromeda galaxy next door has about a trillion. The giant elliptical galaxy IC 1101 has an estimated [music] 100 trillion. And there are two trillion of these things scattered across space. Each one a universe in its own right. Each one containing more stars than there are grains [music] of sand on every beach on Earth.

[00:08:21]Now, pause. Because here's the part most people miss. And it's the part that, for me, is the most profound of all.

[00:08:32]Everything we've been talking about, every galaxy, every number, every deep field image, is the observable universe.

[00:08:40][music] That's the part of the universe we can actually see. Light has had 13.8 billion years to travel toward [music] us since the Big Bang.

[00:08:50]So, we can only see as far as light has had time to reach us. That's a sphere about 93 billion light [music] years across.

[00:08:58]But the universe doesn't stop there.

[00:09:01]Space is expanding, and it's [music] expanding faster than light can travel in some places. Which means there are regions of the universe, entire portions of existence, from which light will never, ever reach us. We can't see them.

[00:09:18]We can't measure them. We can't observe them in any way. They are beyond the cosmic horizon, permanently and forever.

[00:09:27]How big is the total universe beyond that horizon? We genuinely don't know.

[00:09:33]Some models suggest it could [music] be hundreds of times larger than the observable part. Others suggest it could be thousands of times larger. And some of the most serious models in theoretical cosmology suggest it could be infinite, truly infinite. No edges, no boundary, no wall at the end. Just more space and more galaxies stretching on in every direction without limit.

[00:10:01]And here's the thing that hits hardest when you really sit with it.

[00:10:06]Two trillion galaxies is just what we can see. It's just the tip. Everything we've ever observed, every photograph [music] ever taken through every telescope ever built across the entire history of human science.

[00:10:21]It's a thin sliver of a much larger [music] reality that we may never fully understand. We are looking at the universe through a keyhole.

[00:10:30]>> [music] >> And what we can see through that keyhole alone contains two trillion galaxies.

[00:10:36]We are not the center of the universe.

[00:10:39]We're not even close. We're on one [music] planet orbiting one star inside one galaxy among two trillion others.

[00:10:48]>> [music] >> Inside an observable bubble that may itself be a tiny fraction [music] of something incomprehensibly larger. If that doesn't shift something in you, I don't know what will.

[00:11:00]That is the honest, staggering answer to how many galaxies [music] exist. So, let's bring it back down to Earth for a second.

[00:11:10]We started with the Milky Way.

[00:11:13]The whole universe, people thought. Then Hubble proved the existence of other galaxies, shattering that assumption permanently. Then the deep field revealed the true density of the cosmos.

[00:11:26]Thousands [music] of galaxies in a grain of sand. Then two trillion became the new number, replacing the old estimate of 200 billion. And then, we remembered that we can only see a fraction of what's out there.

[00:11:39]That the observable universe is just [music] a window, not the full picture.

[00:11:45]The universe keeps getting bigger every [music] time we look. Not because it's growing, though it is, but because our tools get better, our models get sharper, and our understanding peels [music] back another layer of something that seems to have no bottom. Every generation [music] of scientists has thought they were close to understanding the full scale. Every generation has been wrong.

[00:12:10]If you found this as mind-blowing as I did, drop a comment below and tell me what part hit you hardest. Was it the 2 trillion? The grain of sand with 3,000 [music] galaxies hiding inside it? Or the idea that most of the universe is completely [music] invisible to us, forever? Beyond a horizon we can never cross. [music] I genuinely want to know which one stopped you cold. Until next time, keep looking up. The darkness between the stars is not empty. It never was.