Is the Big Bang Wrong? The Universe's Expansion Doesn't Add Up（原声文稿）

Transcript of 宇宙膨胀对不上数：大爆炸理论要塌了吗 （中文完整文稿）。

There is a crisis unfolding in cosmology, and the answer could decide how we understand the entire universe.

For almost a century, we've known that we live in an expanding universe.

In 1929, Edwin Hubble showed that galaxies are drifting apart, and the farther away they are, the faster they seem to go.

That single discovery became the backbone of modern cosmology, shaping everything from the Big Bang to the birth of galaxies.

At the center of it all sits one number, the rate at which the universe is expanding. We call it the Hubble constant.

For decades, we believed we were closing in on its true value. Now, astronomers are not so sure.

So are we standing on the edge of a scientific revolution, or is something about our entire model of the universe simply wrong?

I'm Alex Mercer, and this is Astros.

Today, we're going to explore the crisis gripping cosmology and see how Hubble's greatest discovery turned into one of the biggest headaches in modern science.

For most of human history, the universe was small, or at least we thought it was.

Many ancient cultures pictured a flat earth sitting beneath a dome of stars.

The sun and moon rose and set, the constellations wheeled overhead, and that was the cosmos.

By the second century, astronomers like Claudius Ptolemy had built a more refined picture with Earth fixed at the center and the sun, moon, planets, and stars all circling around us.

That geocentric model ruled for more than a thousand years.

Then in the 1500s, Nicholas Copernicus placed the sun in the center instead, with Earth just as one of several planets in orbit around it.

It was a radical idea, and it opened the door to a much bigger universe.

In the 1700s, William Herschel began mapping the stars of our own galaxy, the Milky Way, and revealed it to be a huge, flattened disk.

But even then, astronomers argued over a bigger question. Was the Milky Way the entire universe?

Or was it just one island among many in a far larger ocean of space?

That argument lasted until 1923, when Edwin Hubble settled it.

Working at Mount Wilson Observatory in California, Hubble pointed the 100 -inch Hooker telescope at Andromeda.

At the time, it was the largest telescope on Earth, and with it, he did something nobody had done before.

He picked out individual stars inside Andromeda, and among them he found a special kind of pulsating star called a Cepheid variable.

These stars are incredibly useful thanks to the work of Henrietta Leavitt.

Leavitt catalogued more than 2 ,400 variable stars, and she discovered that the time a cepheid takes to pulse is tied directly to how bright it truly is.

That means if you measure how long it takes to pulse and compare its real brightness to how bright it looks from Earth, you can calculate how far away it is.

Astronomers call this Leavitt's Law.

Hubble applied it to Andromeda, and the result was staggering.

He calculated that Andromeda sat around 900 ,000 light -years away. That's far too distant to be part of the Milky Way.

Andromeda was a galaxy in its own right, with its own stars sitting completely outside hours.

Overnight, the known universe became immeasurably larger.

And Hubble wasn't finished.

He went on to use Levitt's law on 23 more galaxies, some as far as 20 million light -years' ray. The conclusion was unavoidable.

Our galaxy was one of millions, and astronomy would never be the same.

But his next great discovery relied on the work of another astronomer, a man named Vesto Slipher. Slifer.

Slifer was born on a farm in Indiana in 1875, and he joined the Lowell Observatory in Flagstaff, Arizona in 1901.

Between 1912 and 1925, he carefully studied the light from more than 40 spiral galaxies. Here's why that mattered.

Light can be split into its component colors, and different elements leave behind different patterns in that spectrum. spectrum.

If the object producing that light is moving away from you, those same patterns appear, but they're shifted toward the red end of the spectrum.

We call that effect redshift.

Schleifer noticed that almost every galaxy he looked at showed this redshift, meaning they were nearly all moving away from us.

But there was a catch.

He had no way to measure how far away those galaxies were, so he couldn't work out how fast they were really moving.

In 1927, a Belgian scientist named Georges Lemait proposed something bold.

If the universe looks the same in every direction, and if Einstein's theory of relativity is correct, then the universe has to be expanding.

It was an elegant idea, but Lemait had no observational evidence to back it up, and so most people ignored it.

A Soviet scientist named Alexander Friedman had explored a similar idea a few years earlier, and it too had gone largely unnoticed.

So which brings us back to Hubble.

Like most scientists at the time, Hubble hadn't heard of either theory.

He was just looking at galaxies from Mount Wilson, and he saw the same thing Sluyfer had seen, galaxies moving away from us. But Hubble had something Sluyfer didn't. He had distances.

And that let him spot a pattern that nobody had noticed before. War.

The farther away a galaxy was, the greater its redshift, which meant the faster it was racing away, and this was happening in every direction. More observations confirmed it.

Nearly every galaxy was receding, and the redshift of each one was directly proportional to its distance from Earth.

This was a huge breakthrough, because it meant one thing.

the universe is expanding.

Hubble published his findings in 1929, and they became the first observational support for Lemaites' expanding universe, the idea that would grow into what we now call the Big Bang.

That relationship between distance and speed is where the Hubble constant comes from. It tells us how quickly space is stretching.

Hubble's own first estimate was roughly 500 km per second for every megaparsec of distance.

A megaparsec is about 3 .26 million light -years.

So, according to that early number, a galaxy one megaparsec away would be receding at around 500 km every second.

That figure turned out to be far too high, and Hubble spent much of his career trying to refine it, but the idea behind it became one of the most important in in all of science.

The Hubble constant helps us work out the age of the universe and its size, and those numbers feed into almost every other calculation cosmologists make.

So you'd think that by now we'd have this number nailed. Instead, we found something that doesn't add up.

Astronomers have two main ways to measure the Hubble constant, and they disagree with each other.

The first method looks at the universe as it is now, billions of years after the Big Bang.

It's often called the Cosmic Distance Ladder, or the Late Universe method, and it works much the way Hubble's original work did.

You measure how far away galaxies are, you measure how much their light is redshifted, and from that you calculate how fast space is expanding.

The more distant galaxies we can measure, and the more carefully we can calibrate those distances, the more precise the result becomes. systems.

Over the years, this approach has settled on a value of about 73 .5 kilometers per second per megaparsec.

That's much lower than Hubble's first guess, but it's been measured with real precision. The second method works in a completely different way.

Instead of looking at the present, it looks back at the very beginning and then rewinds and fast -forwards the clock using our best physics.

It's known as the early universe method. It relies on the Cosmic Microwave Background, or CMB.

This is ancient light, a faint glow of microwave radiation that fills the entire sky, and it's essentially a snapshot of the universe about 380 ,000 years after the Big Bang.

Its existence was predicted in 1948 by Ralph Alfer and Robert Herman.

In the 1960s, Arno Penzius and Robert Wilson detected it by accident, and they won a Nobel Prize for the discovery.

But it took until the early 2000s to get an image sharp enough to be truly useful.

In 2003, the Wilkinson Microwave Anisaltropy probe, known as WMAP, released a full map of the sky, showing the universe at a time before any stars had even formed. Here's one way to picture how this works.

Imagine you arrive at the site of an explosion that's already happened.

Debris is scattered everywhere and you can't tell what the original object looks like.

But then, someone hands you a photograph, taking just moments after the blast began.

Suddenly, you can trace each fragment back to where it came from. That's what cosmologists do with the CMB.

They take that early snapshot, apply the laws of physics, and press play, running the universe forward to see what it should look like today.

The European Space Agency's Planck satellite took this even further.

It captured an incredibly detailed map of the background radiation, revealing tiny temperature fluctuations.

Those small ripples are the seeds of everything.

They grew into the vast cosmic web of dark matter, with its galaxy clusters and enormous empty voids.

When astronomers feed the Planck data into our standard model and run it forward, they get a predicted Hubble constant of about 67 .4 kilometers per second per megaparsec. And now you can see the problem.

That's noticeably lower than the roughly 73 we measure from Redshift.

moved. Two methods, two answers, and a gap that just won't close.

To understand why that matters so much, we need to talk about the model they're both built on.

The Hubble constant isn't just a number sitting in a textbook, it's woven into our deepest ideas about physics, from Einstein's general relativity to the picture of a universe that began hot and dense and has been expanding ever since.

The framework that holds all of this together is called the Lambda Cold -Dark Matter Model, or Lambda CDM.

It took shape in the late 1990s, and for a long time it has worked beautifully.

One surprising feature of that model is that the expansion of the universe is speeding up.

Scientists had assumed gravity would slow it down over time.

Instead, in the late 90s, they discovered the opposite. it.

Something is pushing space apart faster and faster, and we call that something dark energy.

Thankfully, that discovery didn't break the model. It became a part of it.

The more the universe grows, the more dark energy matters, and the faster the expansion becomes.

Now, you might wonder whether that acceleration explains our two different numbers. numbers.

Both methods are meant to give us the expansion rate as it is today, so the acceleration isn't the cause of the disagreement. That leaves us with a real puzzle.

How can one cosmological model produce two different values for something so fundamental?

This disagreement is known as the Hubble Tension.

It isn't called that because of some physical tension in space itself.

More likely it's named for the mood it creates at cosmology conferences.

And honestly, I understand why.

Because if it's real, it could mean our whole picture of the cosmos is incomplete.

For a long time, many scientists hoped this was just a measurement problem.

The thinking went, as our instruments improve and data piles up, the two values should slowly move toward each other and meet somewhere in the middle.

But that isn't what's happening.

As new independent measurements arrive, the gap isn't closing, it's getting harder to ignore. Take one recent example. Some galaxies host what are called megamasers.

These are regions where molecules like water vapor amplify microwave radiation near a supermassive black hole at the heart of a galaxy.

It's similar to a laser, but it produces microwaves instead of visible light.

Megamasers are extremely powerful, and astronomers can map their emissions with great precision.

That lets them measure the mass of the black hole and, importantly, work out the geometric distance to the host galaxy without relying on the usual distance ladder.

In 2020, a team led by Dom Pesci used this method and found a Hubble constant of 73 .9, with very high confidence.

Then, in late 2024, a team that included Daniel Skolnick and Nobel laureate Adam Race used data from the dark energy spectroscopic instrument.

They studied 12 Type Ia supernovae spread across the coma galaxy cluster, about 320 million light -years away.

Their result was 76 .5.

And then in 2025, researchers at the Inter -University Center for Astrophysics and Astronomy in India took another approach.

They used mirror variable stars in our own galaxy as reference points, then measured mirror variables in distant galaxies, a technique similar to the original Cepheid method. Their answer was 73.

Three very different methods and three very similar answers.

Each one lands close to 73 or higher, and each one sits well outside the margin of error for the Planck result based on the CMB.

Something doesn't fit.

Several astronomers have started to sound the alarm.

Daniel Skolnick, a physics professor at Duke University and the lead author of that supernova study, has said that our model of cosmology might be broken and that the Hubble tension is starting to feel more like a Hubble crisis.

And it's easy to see why this matters.

If the model we use to interpret the universe is on shaky ground then so are the answers it gives us.

When galaxies formed, how clusters evolved, even our predictions for the far future of the cosmos, all of it hangs in the balance.

Consider the two possible outcomes.

If the true Hubble constant is the lower value, the one from the background radiation, then we live in a universe about 13 .8 billion years old and it will most likely keep expanding forever—a steady, predictable future with dark energy staying constant.

But if the true value is the higher one, the one we see from Redshift, then the universe is expanding faster than our model allows.

In that case, the universe might be younger, perhaps 12 to 13 billion years old, and it could mean we're missing something fundamental about the early universe, about dark energy, or even about relativity itself.

So, how might scientists resolve this?

Some have suggested radical changes to the standard model.

Ideas include dark matter that decays over time, or dark energy that isn't constant but changes as the universe ages.

Some researchers have even explored altering the equation of state for dark energy, which might point to changes in general relativity itself.

That's the kind of shift that would force us to rethink not only the cosmos, but physics as a whole.

But there's another idea that's been gaining attention, and it could rescue our model without rewriting the laws of nature. All it needs is a little spin.

And no, I'm not joking.

A 2025 paper by Belaj Andrei Sagetti, Istvan Sapudi, Imre Farinkparna, and Gargeli Gabor Barnafoldi, proposes that we may have overlooked a very slow rotation of the entire universe.

universe. The idea is that the universe turns once every 500 billion years.

That's so slow that we'd never notice it directly, but it could be enough to influence how space has expanded over cosmic history.

And here's the exciting part.

Their early calculations suggest that this tiny spin could explain both values at once.

When rotation is added to the model, it predicts an early universe with a lower expansion rate, just like the CMB tells us, and it also predicts a present -day universe with a higher expansion rate, matching what we see in redshift measurements.

In other words, both camps could be right, because they're measuring the expansion at different times in a universe that's been slowly turning.

István Sápudi, one of the authors from the University of Hawaii, explained the concept by quoting the ancient Greek philosopher Heraclitus.

He said, panta rei, which means everything flows or everything moves, and given how promising those early results look, that might be true on the grandest scale of all.

Now I do want to be careful here.

The authors themselves are clear that this is a preliminary calculation and it focuses only on the Hubble constant.

The next step is to build more complex models and run detailed simulations to see whether the idea holds up against other observations, like the distribution of galaxies and the patterns in the CMB.

A hypothesis is only as good as its ability to survive those tests. So, where does that leave us?

I think it's a reminder of how much there still is to learn about the universe, but it's also far too early to throw out our entire model of cosmic evolution, especially when we might be on the verge of discovering the one missing piece that makes everything fit.

And even if the spinning universe turns out to be right, it wouldn't mean abandoning everything we know.

It would mean a new, rotating version of our model, with some of the cosmic parameters adjusted to reflect a slightly different reality.

It's also worth noting that the idea has one major advantage. It doesn't break any known laws of physics.

Whatever the answer turns out to be, this is a remarkable time to be watching cosmology.

A century after Hubble first showed us that space is stretching, we're still discovering that the universe has more to teach us.

And personally, I find something wonderful about the thought that our planet spins, our solar system turns, the Milky Way rotates, and perhaps, on the greatest scale of all, the entire universe is turning along with them.

If you enjoyed this journey through the Hubble Tension, make sure to subscribe to asterisk so you don't miss the next one.

And let me know in the comments, do you think the universe is spinning, or is the real answer something even stranger?

I'm Alex Mercer, thanks for watching, and I'll see you out there among the stars.