Using innovative strategies that astronomers use to identify the shape of distant, dim galaxies, Adejumoke Owolabi, a master’s student at the University of Hull, and her mentor Kevin Pimbblet, a professor of astrophysics and director of the Centre of Excellence for Data Science, Artificial Intelligence and Modelling at the University of Hull, have described a groundbreaking technique to spot deepfakes created by machine-learning artificial intelligence (AI) from genuine photographs.

Their research findings were presented at the U.K. Royal Astronomical Society’s National Astronomy Meeting on 15 July this year.

Deepfake concern

In what The New York Times described as the “First A.I. Election”, Argentina witnessed two rival candidates, Sergio Massa and Javier Milei, using artificial deepfake technology based on AI to create hyper-realistic video, audio, and pictures during their recent election campaigns.

Not too long ago, Russian cyber agents hacked into a Ukrainian television channel and created a deepfaked video of Ukraine’s President Volodymyr Zelenskyy. In the video, he was shown asking his compatriots to lay down their weapons, and it quickly went viral.

Why, during the recent general elections in India, unscrupulous actors used AI tools to create avatars of Indian politicians. Alarmingly, these avatars were manipulated to spread audio and video messages to undermine political rivals.

Others have used deepfake tools to defame actresses by creating pornography involving their images. Such manipulation can make it difficult for the people at large to distinguish real from counterfeit, trap them in insidious narratives and beliefs, and ultimately undermine trust in democratic institutions.

The shapes of galaxies

A counterpunch to this problem may just lie in the stars.

Galaxies are vast cosmic islands of gas clouds, dust, and billions of stars held together by gravity. They come in various shapes and sizes and their appearance can give us clues about how they formed and evolved. For instance, if one galaxy formed after two older galaxies collided, it will contain some distinct signs of that collision. If a galaxy is pulled and consumed by a nearby massive galaxy, it will show signs of this interaction as well.

In the 1930s, the American astronomer Edwin Hubble classified thousands of known galaxies based on their appearance into four groups: elliptical, spiral, barred spiral, and irregular, plus various subclasses. Today, thanks to astronomical telescopes, we have data about millions of galaxies in the universe. And thanks to the efforts of half a million volunteers who participated in a crowdsourcing citizen-science programme called Galaxy Zoo, it has been possible to organise these galaxies using Hubble’s rubric.

Multiple large-scale astronomy projects, including the ground-based Vera C. Rubin Telescope and space-based observatories such as the Wide Field Infrared Survey Telescope and the James Webb Space Telescope, are also currently in progress. The Vera C. Rubin Observatory (previously known as the Large Synoptic Survey Telescope) is projected to produce 36 TB of data after scanning the skies every night. Even a dedicated citizen-science effort would struggle to manage such a large output.

AI in astronomy

While a visual approach to classification is the ideal way to determine a galaxy’s shape and structure — its morphology, i.e. — astronomers are resorting to AI-based solutions to manage the Big Data level of data many new astronomy projects have been generating. These data pertain to the billions, even trillions, of galaxies across the observable universe, most of which are too dim to classify using just one’s eyes.

Specifically, astronomers have been using machine learning and computer vision techniques to characterise galaxies’ morphologies. One popular set of parameters used in this exercise is called CAS, which stands for ‘concentration, asymmetry, and smoothness’. Computers evaluate these three parameters by analysing the level of light in each pixel of a digital image of a galaxy.

The concentration parameter quantifies the amount of light in the centre of a galaxy compared to its outer parts. The asymmetry index indicates the fraction of the light in a galaxy that is non-symmetric while the smoothness index indicates the fraction of light contained in clumps.

Another method, called the Gini index, is used to measure the relative distribution of light among pixels, which is also useful to identify different morphologies but especially those of galaxies that are merging with each other.

Into the eye of a deepfake

Typically, in a photograph of a person’s face, the eyes reflect ambient light, including the images of people and objects nearby. Adejumoke Owolabi noted that the reflections on the left and the right eyes could be analysed using the CAS parameters and the Gini index to check if they matched. If the reflections did match, the photograph is likely to be the actual thing, a legitimate photograph. If they didn’t match, it is likely to be a deepfake.

Dr. Owolabi analysed reflections of light in the eyes of several authentic and AI-generated images in this way and found that the parameters were consistent in genuine photos, as one would expect from the laws of physics. But she also noticed a small but detectable — by computers, at least — mismatch in deepfakes generated using AI-based tools.

Further, she found that the Gini index could predict whether an image had been deepfaked more efficiently than the CAS parameters could. Using the Gini index, she and Dr. Pimbblet, her mentor, detected digitally manipulated facial images accurately 70% of the time.

“It’s important to note that this is not a silver bullet for detecting fake images,” Dr. Pimbblet said in a press release issued by the Royal Astronomical Society. “There are false positives and false negatives; it’s not going to get everything. But this method provides us with a basis, a plan of attack, in the arms race to detect deepfakes.”

T.V. Venkateswaran is a science communicator and visiting faculty member at the Indian Institute of Science Education and Research, Mohali.

A view of Ariel composed by NASA/JPL-Caltech, December 12, 2016.
| Photo Credit: Kevin M. Gill

The Solar System has many mysteries. We don’t know why the Sun’s corona is so hot. We don’t know why Saturn’s moon Titan has such a significant atmosphere. We don’t know why Triton rotates in the direction opposite to its host planet, Neptune, although a recent study found an answer: Triton and Pluto had a common origin before Neptune pulled Triton to itself.

Another mystery in the Solar System may be coming to a similar close. Astronomers have been curious why the surface of Uranus’s moon Ariel has frozen carbon dioxide (CO₂). At that distance from the Sun, the CO₂ should have already vaporised into space — yet the ice covers the moon’s surface. On July 24, NASA’s James Webb Space Telescope (JWST) reported evidence of a liquid ocean buried under Ariel’s surface, supplying CO₂ to the world above.

The people behind the finding came to this conclusion when they found carbon monoxide. If Ariel has to have this compound, it has to have a surface temperature around 18 degrees C less than what it is or it could have a subsurface water ocean producing carbon oxides. One side of Ariel has cracks and grooves through which icy slop and these compounds could be gushing out to the surface. JWST also found signs of carbonite minerals, which could be formed when water interacts with rocks.

More studies and space missions will be needed to confirm these details. If they are, we’ll have yet another water-bearing moon out there.

Washington:

NASA released on Friday a pair of images taken by the James Webb Space Telescope showing two galaxies – one nicknamed the Penguin and the other the Egg – in the process of merging in sort of a cosmic ballet as the U.S. space agency marked two years since it unveiled the orbiting observatory’s first scientific results.

Webb, which was launched in 2021 and began collecting data the following year, has reshaped the understanding of the early universe while taking stunning pictures of the cosmos. The two galaxies in the images are situated 326 million light-years from Earth in the constellation Hydra. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

“We see two galaxies, each a collection of billions of stars. The galaxies are in the process of merging. That’s a common way that galaxies like our own build up over time, to grow from small galaxies – like those that Webb has found shortly after the Big Bang – into mature galaxies like our own Milky Way,” said Jane Rigby, NASA Webb senior project scientist.

Since becoming operational, Webb has observed galaxies teeming with stars that formed within a few hundred million years of the Big Bang event that marked the beginning of the universe about 13.8 billion years ago.

The mingling Penguin and Egg galaxies are collectively known as Arp 142. They are shown in the imagery joined by a haze that is a mix of stars and gas amid their slow-motion merger.

The Penguin galaxy, so dubbed because its shape from the perspective of the telescope resembles that flightless bird, including a beak-like region, is formally called NGC 2936. It is a spiral-shaped galaxy, now a bit distorted. The Egg galaxy, also named for its shape, is formally called NGC 2937. It is a compact elliptical-shaped galaxy. Together, their appearance is suggestive of a penguin guarding its egg.

Their interaction, according to NASA, was set in motion between 25 and 75 million years ago, and they are expected to become a single galaxy hundreds of millions of years from now.

Webb has detected the earliest-known galaxies and has provided insight into areas such as the composition of planets beyond our solar system, known as exoplanets, and the nature of star-forming regions in the cosmos.

“This mission has allowed us to look back to the most distant galaxies ever observed and understand the very early universe in a new way,” said Mark Clampin, astrophysics division director at NASA headquarters. “For example, with Webb, we’ve found that these very early galaxies are more massive and brighter than we expected, posing the question: How did they get so big so quickly?”

Webb was designed to be more sensitive than its Hubble Space Telescope predecessor, which also is continuing its work. Webb looks at the universe mainly in the infrared, while Hubble has examined it primarily at optical and ultraviolet wavelengths.

“Webb is the largest, most powerful telescope ever put in space. It specializes in capturing infrared light – wavelengths of light longer than our eyes can see. With its incredible sensitivity to those wavelengths, we’ve been able to look back into the early universe in a way previous missions couldn’t, see through dust and gas into the heart of star formation, and examine the composition of exoplanet atmospheres like never before,” Clampin said.

Looking ahead, Clampin added, “Some of Webb’s most exciting investigations will be the things we haven’t even thought of yet.”

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)

A new study has revealed more spiral galaxies in the universe’s youth than astronomers had expected.

The universe is about 13.8 billion years old and is home to different kinds of galaxies, from spiral to elliptical and those with or without bulges. Astronomers previously believed spiral galaxies formed about 6 billion years ago, but a new study by a group of astronomers from the University of Missouri in the U.S. has called this belief into question. It was published on June 11 in the Astrophysical Journal Letters.

While the universe’s younger galaxies have tended to be spiral, the older ones have a variety of shapes. Astronomers study them to understand how they formed and evolved. But studying the older galaxies is more difficult because the light from them is fainter.

Not just hot air

An important idea in astronomy is that as the universe cooled down from a dense plasma state, it contained more and more hot gas. They formed clumps of matter that eventually gravitated to become galaxies. These early galaxies had irregular shapes and lacked disks. But as they cooled as well, they formed hot, thick disks that later became thinner and finally spiral ‘arms’ — a process that took billions of years.

This theory is now suspect. “Our work shows that this cooling down and spiral formation occur around the same cosmic time,” said Vicki Kuhn, a graduate student at the University of Missouri and a member of the study.

Astronomers routinely see stars forming in real-time but since all the galaxies have already formed, they use a sort of astronomical archaeology to study them. “We don’t see proto-galaxies,” said Girish Kulkarni of the Tata Institute of Fundamental Research, Mumbai, who was not involved in the study. “What we do then is study how the galaxies evolve. The spiral galaxy fraction is one way to do this biography.”

Seeing further into the past

The first step is to use light of the infrared and optical wavelengths to detect galaxies in the early universe. Since older galaxies are harder to detect, we need powerful telescopes. Ideally, astronomers would like to observe light emitted when the universe was around 500 million years old, when the galaxies were thought to be forming.

NASA’s James Webb Space Telescope, launched in 2021, has helped astronomers gaze much deeper into the universe’s past than before. The University of Missouri team used the telescope to study a cohort of 873 galaxies individually and identified at least 216 spiral galaxies. Some of them dated to 1.5 billion years after the universe’s birth.

For the study, all six authors went through each image to classify it as spiral or non-spiral. Prerana Biswas, a postdoctoral researcher at the Indian Institute of Astrophysics, Bengaluru, who wasn’t involved in the study, said the method is crude but shows the result is free of human bias. Abhijeet Borkar, a research scientist at the Astronomical Institute of the Czech Academy of Sciences in Prague, agreed. He wasn’t involved in the study either.

But while Dr. Biswas said future studies should use automatic algorithms to spot spiral galaxies, Dr. Borkar said there are few alternatives to this sort of verification. “Even for invoking machine learning or neural networks, this is the first step. The only way to improve is to have a larger number of astronomers” going through the data.

An underestimate comes to light

The researchers then compared the number of spiral galaxies to the total number of galaxies. They found that between 3 billion and 7 billion years after the Big Bang, the fraction of galaxies with spiral shapes increased from about 8% to 48%. Previous observations had indicated an increase from 5% to 30% instead. “It’s much greater than what was known before,” Dr. Kulkarni said.

Dr. Borkar was in fact taken aback by the fact that spiral-armed galaxies were fully formed so early.

The new observation shows the number of spiral galaxies is high as well as that they increased in number as the universe evolved.

Dr. Kulkarni explained how astronomers study the formation of galaxies. They develop mathematical models on powerful computers and let them evolve with time. While dark matter and gravity exert dominant influences on the universe’s evolution, they aren’t enough to produce galaxies. So astrophysicists include hot, dense gases in the simulation. These simulations have thus far matched what astronomers have observed.

As the universe ages, the gases cool and clump together, and stars form. As the stars evolve, they give rise to supernovae, which create most of the elements we have on the earth today. Some black holes are formed, too, and a few of them sit at the centres of galaxies and exert their own influences.

From simplistic to complicated

Given the uncertainty in many of these models’ parameters, astrophysicists also use observations to refine them — and such refinements are often crucial.

The Hubble Space Telescope is famed for its clear images of distant celestial objects and astrophysicists have used it to refine many models. But then some studies found signs that the early universe had many galaxies with disks. Astronomers think such galaxies were actively forming new stars.

The authors of the present study didn’t compare their observations with the simulations, however, which has puzzled Dr. Kulkarni.

He also said the link between these sophisticated simulations and the present-data may not be easy to decipher. All experts agreed astronomers must carefully reexamine the existing framework of observational data and theoretical studies.

“The earlier scenario was more simple,” Dr. Borkar said. Now “the theories need to be made more complicated.” He added that it’s possible that while stars are formed in some regions of galaxies, hot gases could be present simultaneously in other regions.

‘No one knows’

The new findings could also affect what astronomers understand about the rate of the formation of stars in the universe. For earth-like planets to form around stars, spiral galaxies should host a sufficient amount of elements heavier than iron in their spiral arms. When heavier stars die and blow up as supernovae, they throw out these elements into the arms. But if something else gets in the way of star formation — such as the influence of black holes — then not enough stars will form in the first place.

As the universe aged, spiral galaxies became more populous even around the time star formation peaked. Over time, spiral gases have less and less gas in their spiral arms, slowing the formation of more stars. But collisions between galaxies, like the one predicted to occur between our Milky Way and its neighbouring Andromeda in about 5 billion years, could restart this process into a second life while also creating an elliptical galaxy.

Overall, our view of the universe’s cycle of forming galaxies, stars, and earth-like planets seems to be getting more complicated. What does it imply for our understanding of galaxy formation? Dr. Biswas said, “I can safely say that no one knows.”

Debdutta Paul is a science writer at the International Centre for Theoretical Sciences, Bengaluru, and a freelance science journalist.

This handout image obtained on May 30, 2024 courtesy of NASA/ESA/CSA STScI shows an infrared image from NASA’s James Webb Space Telescope. A galaxy, JADES-GS-z14-0 (shown in the pullout), was determined to be at a redshift of 14.32 (+0.08/-0.20), making it the current record-holder for the earliest known galaxy.
| Photo Credit: AFP

NASA’s James Webb Space Telescope has spotted the earliest-known galaxy, one that is surprisingly bright and big considering it formed during the universe’s infancy— at only 2% its current age.

Webb, which by peering across vast cosmic distances is looking way back in time, observed the galaxy as it existed about 290 million years after the Big Bang event that initiated the universe roughly 13.8 billion years ago, the researchers said. This period spanning the universe’s first few hundred million years is called cosmic dawn.

The telescope, also called JWST, has revolutionized the understanding of the early universe since becoming operational in 2022. The new discovery was made by the JWST Advanced Deep Extragalactic Survey (JADES) research team.

This galaxy, called JADES-GS-z14-0, measures about 1,700-light years across. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). It has a mass equivalent to 500 million stars the size of our sun and was rapidly forming new stars, about 20 every year.

Before Webb’s observations, scientists did not know galaxies could exist so early, and certainly not luminous ones like this.

“The early universe has surprise after surprise for us,” said astrophysicist Kevin Hainline of Steward Observatory at the University of Arizona, one of the leaders of the study published online this week ahead of formal peer review.

“I think everyone’s jaws dropped,” added astrophysicist and study co-author Francesco D’Eugenio of the Kavli Institute for Cosmology at the University of Cambridge. “Webb is showing that galaxies in the early universe were much more luminous than we had anticipated.”

Until now, the earliest-known galaxy dated to about 320 million years after the Big Bang, as announced by the JADES team last year.

“It makes sense to call the galaxy big, because it’s significantly larger than other galaxies that the JADES team has measured at these distances, and it’s going to be challenging to understand just how something this large could form in only a few hundred million years,” Mr. Hainline said.

“The fact that it’s so bright is also fascinating, given that galaxies tend to grow larger as the universe evolves, implying that it would potentially get significantly brighter in the next many hundred million years,” Mr. Hainline said.

While it is quite big for such an early galaxy, it is dwarfed by some present-day galaxies. Our Milky Way is about 100,000 light years across, with the mass equivalent to about 10 billion sun-sized star.

The JADES team in the same study disclosed the discovery of the second oldest-known galaxy, from about 303 million years post-Big Bang. That one, JADES-GS-z14-1, is smaller – with a mass equal to about 100 million sun-sized stars, measuring roughly 1,000 light years across and forming about two new stars per year.

“These galaxies formed in an environment that was much more dense and gas-rich than today. In addition, the chemical composition of the gas was very different, much closer to the pristine composition inherited from the Big Bang – hydrogen, helium and traces of lithium,” Mr. D’Eugenio said.

Star formation in the early universe was much more violent than today, with massive hot stars forming and dying quickly, and releasing tremendous amount of energy through ultraviolet light, stellar winds and supernova explosions, Mr. D’Eugenio said.

Three main hypotheses have been advanced to explain the luminosity of early galaxies. The first attributed it to supermassive black holes in these galaxies gobbling up material. That appears to have been ruled out by the new findings because the light observed is spread over an area wider than would be expected from black hole gluttony.

It remains to be seen whether the other hypotheses – that these galaxies are populated by more stars than expected or by stars that are brighter than those around today – will hold up, Mr. D’Eugenio said.

A false-color image obtained by the James Webb Space Telescope (JWST) shows the galaxy JADES-GS-z7-01-QU, the universeÕs earliest-known “dead” galaxy, a galaxy that has stopped star formation, in this undated handout picture obtained by Reuters.
| Photo Credit: Reuters

The James Webb Space Telescope, or JWST for short, is one of the most advanced telescopes ever built. Planning for JWST began over 25 years ago, and construction efforts spanned over a decade. It was launched into space on Dec. 25, 2021, and within a month arrived at its final destination: 930,000 miles away from Earth. Its location in space allows it a relatively unobstructed view of the universe.

The telescope design was a global effort, led by NASA, and intended to push the boundaries of astronomical observation with revolutionary engineering. Its mirror is massive – about 21 feet (6.5 meters) in diameter. That’s nearly three times the size of the Hubble Space Telescope, which launched in 1990 and is still working today.

It’s a telescope’s mirror that allows it to collect light. JWST’s is so big that it can “see” the faintest and farthest galaxies and stars in the universe. Its state-of-the-art instruments can reveal information about the composition, temperature and motion of these distant cosmic objects.

As an astrophysicist, I’m continually looking back in time to see what stars, galaxies and supermassive black holes looked like when their light began its journey toward Earth, and I’m using that information to better understand their growth and evolution. For me, and for thousands of space scientists, the James Webb Space Telescope is a window to that unknown universe.

Just how far back can JWST peer into the cosmos and into the past? About 13.5 billion years.

Time travel

A telescope does not show stars, galaxies and exoplanets as they are right now. Instead, astronomers are catching a glimpse of how they were in the past. It takes time for light to travel across space and reach our telescopes. In essence, that means a look into space is also a trip back in time.

This is even true for objects that are quite close to us. The light you see from the Sun left it about 8 minutes, 20 seconds earlier. That’s how long it takes for the Sun’s light to travel to Earth.

You can easily do the math on this. All light – whether sunlight, a flashlight or a light bulb in your house – travels at 186,000 miles (almost 300,000 kilometers) per second. That’s just over 11 million miles (about 18 million kilometers) per minute. The Sun is about 93 million miles (150 million kilometers) from Earth. That comes out to about 8 minutes, 20 seconds.

But the farther away something is, the longer its light takes to reach us. That’s why the light we see from Proxima Centauri, the closest star to us aside from our Sun, is 4 years old; that is, it’s about 25 trillion miles (approximately 40 trillion kilometers) away from Earth, so that light takes just over four years to reach us. Or, as scientists like to say, four light years.

Most recently, JWST observed Earendel, one of the farthest stars ever detected. The light that JWST sees from Earendel is about 12.9 billion years old.

The James Webb Space Telescope is looking much farther back in time than previously possible with other telescopes, such as the Hubble Space Telescope. For example, although Hubble can see objects 60,000 times fainter than the human eye is able, the JWST can see objects almost nine times fainter than even Hubble can.

The Big Bang

But is it possible to see back to the beginning of time?

The Big Bang is a term used to define the beginning of our universe as we know it. Scientists believe it occurred about 13.8 billion years ago. It is the most widely accepted theory among physicists to explain the history of our universe.

The name is a bit misleading, however, because it suggests that some sort of explosion, like fireworks, created the universe. The Big Bang more closely represents the appearance of rapidly expanding space everywhere in the universe. The environment immediately after the Big Bang was similar to a cosmic fog that covered the universe, making it hard for light to travel beyond it. Eventually, galaxies, stars and planets started to grow.

That’s why this era in the universe is called the “cosmic dark ages.” As the universe continued to expand, the cosmic fog began to rise, and light was eventually able to travel freely through space. In fact, a few satellites have observed the light left by the Big Bang, about 380,000 years after it occurred. These telescopes were built to detect the splotchy leftover glow from the Big Bang, whose light can be tracked in the microwave band.

However, even 380,000 years after the Big Bang, there were no stars and galaxies. The universe was still a very dark place. The cosmic dark ages wouldn’t end until a few hundred million years later, when the first stars and galaxies began to form.

The James Webb Space Telescope was not designed to observe as far back as the Big Bang, but instead to see the period when the first objects in the universe began to form and emit light. Before this time period, there is little light for the James Webb Space Telescope to observe, given the conditions of the early universe and the lack of galaxies and stars.

Peering back to the time period close to the Big Bang is not simply a matter of having a larger mirror – astronomers have already done it using other satellites that observe microwave emission from very soon after the Big Bang. So, the James Webb Space Telescope observing the universe a few hundred million years after the Big Bang isn’t a limitation of the telescope. Rather, that’s actually the telescope’s mission. It’s a reflection of where in the universe we expect the first light from stars and galaxies to emerge.

By studying ancient galaxies, scientists hope to understand the unique conditions of the early universe and gain insight into the processes that helped them flourish. That includes the evolution of supermassive black holes, the life cycle of stars, and what exoplanets – worlds beyond our solar system – are made of.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

A big open problem in cosmology is the Hubble tension. There are two equally valid ways to measure how fast the universe is expanding, but they have yielded two very different estimates. No amount of rechecking and refining calculations has made this tension go away.

In a study published recently in Monthly Notices of The Royal Astronomical Society (MNRAS), scientists from Germany and the U.K. led with a radical explanation for the tension: our model used to understand the universe is wrong.

This model is called Λ cold dark matter, or “lambda CDM”. It’s currently the simplest model that explains various features of the universe, including radiation leftover from the Big Bang, the arrangement of galaxies in the universe, and the fact that the universe is expanding.

But cosmologists are also looking for a new, better model that can explain some things the Λ CDM model can’t, such as the Hubble tension. Repeated measurements and computations have ascertained the Hubble tension exists and that it’s not some aberration in the data.

In a paper published after the MNRAS one in The Astrophysical Journal Letters, a different group disproved a flaw some scientists had suspected in one of the two ways to measure the universe’s expansion – meaning the tension is real.

For now, the model does seem to be the problem.

These results also come against the backdrop of a meeting this week in London, where cosmologists will gather to discuss whether this model has become outdated for other reasons as well.

Is our universe open, closed or flat?

Our universe started to expand after the Big Bang event around 14 billion years ago. It may continue to expand unabated forever. If it does, it will be an open universe. But if at some point the expansion stops, because of the gravitational forces exerted by the galaxies, say, the universe could collapse and become closed.

A closed universe is said to have a positive curvature of space – like a sphere. Such a universe will be finite even if it has no bounds. That is, in this universe, we can travel forever without falling off an ‘edge’.

In an open universe, space will warp in the opposite direction. That is, it will have a negative curvature, resembling a saddle.

There is another possibility between these assumptions: that the universe will continue to expand forever, but the rate of expansion, which is currently increasing, will eventually start decreasing thanks to the gravitational forces. The rate will take an infinite amount of time to drop to zero, so the universe will keep expanding, just slower and slower.

This special approximation leads to a flat universe. And according to many cosmologists, this is the state of our universe at this time.

That the universe is flat doesn’t mean it’s like a 2D sheet of paper. Instead, flatness means if you start to draw two parallel lines in space and you keep drawing them, they will remain parallel no matter how far you go. (In a spherical or a saddle-like space, the lines will intersect somewhere.)

The Big Bang’s afterglow

Cosmologists deduced this based on studying the cosmic microwave background (CMB). This is a sea of photons, the particles of light, present throughout the universe. They are leftover from the Big Bang, its afterglow. Scientists have measured temperature changes in the CMB and studied its large-scale properties using complicated trigonometry. And they found that it has nearly zero curvature.

The Wilkinson Microwave Anisotropy Probe (WMAP), BOOMERanG, and ’Planck’ are three telescopes in space. They study the CMB and their data is clear: the observable universe is flat with a 0.4% margin of error. In 2021, researchers with the Atacama Cosmology Telescope reported based on astronomical data that they could find no evidence that the space of our universe is non-flat.

Based on these studies, cosmologists have estimated space to be expanding at around 68 kilometres per second per megaparsec ((km/s)/Mpc). That is, an object one megaparsec (3.26 million lightyears) away is moving away at 68 km/s.

The cosmic distance ladder

The CMB is one way to study the universe’s expansion. The other is called the cosmic distance ladder – a set of techniques used to measure the distance to objects that are close, further away, and very far away from the earth. One object in particular is the Cepheid variable star.

The Cepheid variables have a unique feature: their brightness varies in a predictable way over time. Based on how bright a Cepheid variable is, scientists can estimate how far away it is. Using this, cosmologists have estimated based on various Cepheid variables (and other such objects) is 73 (km/s)/Mpc.

Hubble versus JWST

The best way to follow these stars is using the near-infrared radiation they emit. Unlike visible light, such radiation can pass through intervening dust clouds and reach us. Cepheid variable stars may also be crowded in some places.

Fortunately, NASA’s James Webb Space Telescope (JWST) can track both near-infrared radiation and has instruments good enough to distinguish between radiation from two Cepheid variable stars close to each other in the sky.

In the study published in The Astrophysical Journal Letters, researchers checked a concern that the data collected by NASA’s previously best space telescope, the Hubble, had some flaws in its readings that gave rise to the Hubble tension.

They analysed more than a thousand sharp observations of Cepheid variables recorded by JWST. “The superior resolution of JWST negates crowding noise, the largest source of variance in the near-infrared [brightness] relations measured with the Hubble space telescope,” they wrote.

In the end, they found “no significant difference” in estimates of the stars’ distance based on Hubble telescope and JWST data, even after correcting for “local crowding” and “choice of filters”.

In sum, the Hubble tension is real and its origins remain a mystery.

Qudsia Gani is an assistant professor in the Department of Physics, Government Degree College Pattan, Baramulla.