Tag Archives: universe

Physicists Say We Were Completely Wrong About How Gravity Works

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A new theoretical proposal suggests scrapping nearly everything we think we know about gravity in order to understand the universe.

A theoretical proposal published in the journal Reports on Progress in Physics is making some bold claims about our previous understanding of quantum physics. Mainly, that we were wrong.

The proposed theory grapples with the fact that quantum mechanics (basically modern physics) and general relativity (Einstein's theory of gravity) both describe the universe perfectly, but are mathematically incompatible with each other.

To make them work, the proposal suggests scrapping almost everything we think we know about gravity, as Live Science explains. Instead, the authors touch up the theory to match known and observable physics, something they call unified gravity.

Although quantum field theory — the framework explaining how subatomic particles behave — is one of the most accurate theoretical concepts of all time according to theoretical physicist David Tong, it still leaves out classical gravity, which we know as the bending of space-time.

Instead, unified gravity assumes gravity is managed by four connected components that perfectly interact with one another, a tweak that allows general relativity to respectfully play ball with quantum mechanics without sneaking off into other dimensions. In short, a model that physicists could actually test in real life.

"The main advantages or differences in comparison with many other quantum gravity theories are that our theory does not need extra dimensions that do not yet have direct experimental support," co-author Jukka Tulkki told Live Science.

The discrepancy between the theories of physics and gravity has a long history. To get around it, some have proposed that the universe may be made of tiny chunks. Others, like the string theorists of the late 1960s and 70s, argued for a one-dimensional framework of particle physics.

String theory ballooned into five separate theories back in the 80s, and has since come under increasing scrutiny as its proponents struggle to make any predictions we can actually prove.

"Are you chasing a ghost or is the collection of you just too stupid to figure this out?" as Neil deGrasse Tyson quipped back in 2011. This new model is an attempt to skip all that.

Going forward, there's a lot of work to be done before we know if the budding theory bears fruit.

"Given the current pace of theoretical and observational advancements, it could take a few decades to make the first experimental breakthroughs that give us direct evidence of quantum gravity effects," Mikko Partanen, the study's other author told Live Science. "Indirect evidence through advanced observations could be obtained earlier."

Still, it offers physicists a bold new trail to blaze in the long-running search to unite quantum physics with the theory of gravity — the possibility of unraveling the tangled secrets of the known universe.

More on Physics: Physicist Says He's Identified a Clue That We're Living in a Computer Simulation

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Scientists Intrigued by Bridge of Dark Matter Inside Huge Galaxy Cluster

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The mysterious dark matter

The Perseus cluster is a vast swirl of thousands of galaxies, all bound together by gravity. Famed for its unbelievable size — containing the mass of some 600 trillion suns — it also has a reputation for being one of the few "relaxed" galaxy clusters out there: it shows no signs of having undergone a powerful but disruptive merger with another galaxy, which is how these clusters typically grow. In a word, Perseus looks settled down and pretty stable.

But that may not be the case, according to an international team of astronomers. As detailed in a new study published in the journal Nature Astronomy, the astronomers have found a "bridge" of dark matter that leads to the center of the cluster, which they believe is the remnant of a massive object slamming into the galactic swirl billions of years ago. If this is evidence of a major merger, it'd mean that Perseus isn't so "relaxed" after all.

"This is the missing piece we've been looking for," said study coauthor James Jee, a physicist at University of California, Davis, in a statement about the work. "All the odd shapes and swirling gas observed in the Perseus cluster now make sense within the context of a major merger."

Dark matter is the invisible substance believed to account for around 80 percent of all mass in the universe. While we can't interact with dark matter, its gravity appears to be responsible for governing the shapes of the cosmos's largest structures, pulling "normal" matter together around "clumps" of itself to form the galaxies that we see.

To make the discovery, the astronomers sifted through data collected by the Subaru Telescope in Japan to look for signs of what's known as gravitational lensing. This occurs when the gravity of a massive object bends the light of more distant sources like a lens, magnifying our view of what lies behind it. 

By measuring how the light is being distorted, astronomers can infer traits about the object that's causing the lensing. This technique is known as weak gravitational lensing, and can only be used when there's a large number of galaxies that the distortion's incredibly subtle effects can be observed on. It's one of the primary ways that astronomers map the distribution of dark matter throughout the cosmos.

Using this technique, the astronomers found a dark matter clump located inside the Perseus cluster around 1.4 million light years away from its center, weighing a colossal 200 trillion solar masses (the entire Milky Way, for reference, weighs about 1.5 trillion solar masses). But the clump clearly was a highly disruptive intruder, because it left behind an enormous dark matter "bridge" linking it to the center of the cluster. According to the astronomers, it's as good as a sign of a collision between the clump and the cluster as it gets. And from simulations they performed, this epic merger occurred some five billion years ago — the echoes of which still affect Perseus' structure to this day.

"It took courage to challenge the prevailing consensus, but the simulation results from our collaborators and recent observations from the Euclid and XRISM space telescopes strongly support our findings," lead author HyeongHan Kim, an astronomer at Yonsei University in South Korea, said in the statement.

More on dark matter: Scientists Say Dark Matter May Be Giving Off a Signal

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There’s Something Very Strange About Our Galaxy

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Researchers have found that there's something highly unusual about the Milky Way, setting it apart from other galaxies.

Galactic Outlier

Researchers have found that there's something highly unusual about the Milky Way that sets it apart from galaxies which, on a surface level, appear similar.

As detailed in three recent papers published in The Astrophysical Journal, a team of researchers examined a mountain of data as part of the Satellites Around Galactic Analogs (SAGA) survey, which was dedicated to comparing the Milky Way to 101 other galaxies that are similar in mass.

The distinction is technical but significant, the researchers say: they found that the Milky Way has surprisingly few smaller satellite galaxies compared to its peers — and some of them have mysteriously stopped forming new stars.

"Now we have a puzzle," said Stanford astrophysics professor Risa Wechsler, who cofounded SAGA and coauthored all three papers, in a statement. "What in the Milky Way caused these small, lower-mass satellites to have their star formation quenched?"

Satellite Activity

The findings suggest our galaxy's evolutionary history is strikingly different, setting it apart from all the others — research that could also force scientists to reexamine how we understand the formation of galaxies.

"Our results show that we cannot constrain models of galaxy formation just to the Milky Way," said Wechsler. "We have to look at that full distribution of similar galaxies across the universe."

At the core of the researchers' findings is dark matter, the mysterious substance that scientists believe makes up 85 percent of the matter in the universe, but has yet to be directly observed. Researchers have previously found that massive halos of dark matter allow galaxies to form within them, creating gravitational forces strong enough for ordinary matter to clump together.

"Perhaps, unlike a typical host galaxy, the Milky Way has a unique combination of older satellites that have ceased star formation and newer, active ones... that only recently fell into the Milky Way's dark matter halo," Wechsler suggested.

When Wechsler and her colleagues examined 378 small satellite galaxies that orbit the 101 much larger galaxies like the Milky Way, they found that half the Milky Way's satellites were no longer forming stars, unlike most other galaxies, whose satellites were still active stellar factories.

It all raises an intriguing question: why is our galactic home different?

"To me, the frontier is figuring out what dark matter is doing on scales smaller than the Milky Way, like with the smaller dark matter halos that surround these little satellites," Wechsler said.

More on galaxy formation: This Ancient "Rebel" Galaxy Closely Mirroring the Milky Way Has Astronomers Freaked Out

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There's Something Very Strange About Our Galaxy