Latest news with #generalrelativity
Yahoo
14 hours ago
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Experts ask where the center of the universe is
When you buy through links on our articles, Future and its syndication partners may earn a commission. This article was originally published at The Conversation. The publication contributed the article to Expert Voices: Op-Ed & Insights. About a century ago, scientists were struggling to reconcile what seemed a contradiction in Albert Einstein's theory of general relativity. Published in 1915, and already widely accepted worldwide by physicists and mathematicians, the theory assumed the universe was static – unchanging, unmoving and immutable. In short, Einstein believed the size and shape of the universe today was, more or less, the same size and shape it had always been. But when astronomers looked into the night sky at faraway galaxies with powerful telescopes, they saw hints the universe was anything but that. These new observations suggested the opposite – that it was, instead, expanding. Scientists soon realized Einstein's theory didn't actually say the universe had to be static; the theory could support an expanding universe as well. Indeed, by using the same mathematical tools provided by Einstein's theory, scientists created new models that showed the universe was, in fact, dynamic and evolving. I've spent decades trying to understand general relativity, including in my current job as a physics professor teaching courses on the subject. I know wrapping your head around the idea of an ever-expanding universe can feel daunting – and part of the challenge is overriding your natural intuition about how things work. For instance, it's hard to imagine something as big as the universe not having a center at all, but physics says that's the reality. First, let's define what's meant by "expansion." On Earth, "expanding" means something is getting bigger. And in regard to the universe, that's true, sort of. Expansion might also mean "everything is getting farther from us," which is also true with regard to the universe. Point a telescope at distant galaxies and they all do appear to be moving away from us. What's more, the farther away they are, the faster they appear to be moving. Those galaxies also seem to be moving away from each other. So it's more accurate to say that everything in the universe is getting farther away from everything else, all at once. This idea is subtle but critical. It's easy to think about the creation of the universe like exploding fireworks: Start with a big bang, and then all the galaxies in the universe fly out in all directions from some central point. But that analogy isn't correct. Not only does it falsely imply that the expansion of the universe started from a single spot, which it didn't, but it also suggests that the galaxies are the things that are moving, which isn't entirely accurate. It's not so much the galaxies that are moving away from each other – it's the space between galaxies, the fabric of the universe itself, that's ever-expanding as time goes on. In other words, it's not really the galaxies themselves that are moving through the universe; it's more that the universe itself is carrying them farther away as it expands. A common analogy is to imagine sticking some dots on the surface of a balloon. As you blow air into the balloon, it expands. Because the dots are stuck on the surface of the balloon, they get farther apart. Though they may appear to move, the dots actually stay exactly where you put them, and the distance between them gets bigger simply by virtue of the balloon's expansion. Now think of the dots as galaxies and the balloon as the fabric of the universe, and you begin to get the picture. Unfortunately, while this analogy is a good start, it doesn't get the details quite right either. Important to any analogy is an understanding of its limitations. Some flaws are obvious: A balloon is small enough to fit in your hand – not so the universe. Another flaw is more subtle. The balloon has two parts: its latex surface and its air-filled interior. These two parts of the balloon are described differently in the language of mathematics. The balloon's surface is two-dimensional. If you were walking around on it, you could move forward, backward, left, or right, but you couldn't move up or down without leaving the surface. Now it might sound like we're naming four directions here – forward, backward, left and right – but those are just movements along two basic paths: side to side and front to back. That's what makes the surface two-dimensional – length and width. The inside of the balloon, on the other hand, is three-dimensional, so you'd be able to move freely in any direction, including up or down – length, width and height. This is where the confusion lies. The thing we think of as the "center" of the balloon is a point somewhere in its interior, in the air-filled space beneath the surface. But in this analogy, the universe is more like the latex surface of the balloon. The balloon's air-filled interior has no counterpart in our universe, so we can't use that part of the analogy – only the surface matters. So asking, "Where's the center of the universe?" is somewhat like asking, "Where's the center of the balloon's surface?' There simply isn't one. You could travel along the surface of the balloon in any direction, for as long as you like, and you'd never once reach a place you could call its center because you'd never actually leave the surface. In the same way, you could travel in any direction in the universe and would never find its center because, much like the surface of the balloon, it simply doesn't have one. Part of the reason this can be so challenging to comprehend is because of the way the universe is described in the language of mathematics. The surface of the balloon has two dimensions, and the balloon's interior has three, but the universe exists in four dimensions. Because it's not just about how things move in space, but how they move in time. Our brains are wired to think about space and time separately. But in the universe, they're interwoven into a single fabric, called 'space-time.' That unification changes the way the universe works relative to what our intuition expects. And this explanation doesn't even begin to answer the question of how something can be expanding indefinitely – scientists are still trying to puzzle out what powers this expansion. So in asking about the center of the universe, we're confronting the limits of our intuition. The answer we find – everything, expanding everywhere, all at once – is a glimpse of just how strange and beautiful our universe is. This article is republished from The Conversation under a Creative Commons license. Read the original article.
Yahoo
16 hours ago
- Science
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Scientists Detect Sign of Something Impossible Out in Deep Space
The very concept of black holes seems improbable. Albert Einstein infamously refused to believe they could exist, even though his theory of general relativity was instrumental in predicting them. Now, scientists have witnessed evidence of something about these baffling cosmic monstrosities that further stretches the boundaries of both physics and credulity: a titanic collision of two already enormous black holes so utterly extreme that it has scientists wondering if the event they seem to have detected is even possible. As detailed in a new yet-to-be-peer-reviewed paper by a consortium of physicists, the resulting black hole, whose signal has been designated GW231123, boasts an astonishing mass about 225 times that of our Sun — easily making it the largest black hole merger ever detected. Previously, the record was held by a merger that formed a black hole of about 140 solar masses. "Black holes this massive are forbidden through standard stellar evolution models," Mark Hannam at the Laser Interferometer Gravitational-Wave Observatory (LIGO), which made the detection, said in a statement about the work. "This is the most massive black hole binary we've observed through gravitational waves, and it presents a real challenge to our understanding of black hole formation." Black holes can produce huge, propagating ripples in spacetime called gravitational waves, which were predicted by Einstein back in 1916. Nearly 100 years later, LIGO — which consists of two observatories on opposite corners of the US — made history by making the first ever detection of these cosmic shudders. The merger was first spotted in November 2023 in a gravitational wave, GW231123, that lasted just a fraction of a second. Even so, it was enough to infer the properties of the original black holes. One had a mass roughly 137 times the mass of the Sun, and the other was around 103 solar masses. During the lead up to the merger, the pair circled around each other like fighters in a ring, before finally colliding to form one. These black holes are physically problematic because it's likely that one, if not both of them, fall into an "upper mass gap" of stellar evolution. At such a size, it's predicted that the stars that formed them should have perished in an especially vicious type of explosion called a pair-instability supernova, which results in the star being completely blown apart, leaving behind no remnant — not even a black hole. Some astronomers argue that the "mass gap" is really a gap in our observations and not the cause of curious physics. Nonetheless, the idea is "a hill at least some people were willing to get wounded on, if not necessarily die on," Cole Miller of the University of Maryland, who was not involved in the research, told ScienceNews. But perhaps the black holes weren't born from a single star. "One possibility is that the two black holes in this binary formed through earlier mergers of smaller black holes," Hannam said in the statement. Equally extreme as their weight classes are their ludicrously fast spins, with the larger spinning at 90 percent of its maximum possible speed and the other at 80 percent, both of which are equal to very significant fractions of the speed of light. In earthly terms, it's somewhere around 400,000 times our planet's rotation speed, according to the scientists. "The black holes appear to be spinning very rapidly — near the limit allowed by Einstein's theory of general relativity," Charlie Hoy, a member of the LIGO Scientific Collaboration at the University of Portsmouth, said in the statement. "That makes the signal difficult to model and interpret. It's an excellent case study for pushing forward the development of our theoretical tools." The researchers will present their findings at the GR-Amaldi meeting in Glasgow, which takes place this week. "It will take years for the community to fully unravel this intricate signal pattern and all its implications," according to LIGO member Gregorio Carullo at the University of Birmingham — so, tantalizingly, we're likely only scratching the surface of this mystery. More on space: James Webb Space Telescope Spots Stellar Death Shrouds
Yahoo
16-05-2025
- Science
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New theory could finally make quantum gravity a reality
When you buy through links on our articles, Future and its syndication partners may earn a commission. Physicists have developed a novel approach to solving one of the most persistent problems in theoretical physics: uniting gravity with the quantum world. In a recent paper published in the journal Reports on Progress in Physics, the scientists outline a reformulation of gravity that could lead to a fully quantum-compatible description — without invoking the extra dimensions or exotic features required by more speculative models, like string theory. At the heart of the proposal is a rethinking of how gravity behaves at a fundamental level. While the electromagnetic, weak and strong forces are all described using quantum field theory — a mathematical framework that incorporates uncertainty and wave-particle duality — gravity remains the outlier. General relativity, Einstein's theory of gravity, is a purely classical theory that describes gravity as the warping of space-time geometry by mass and energy. But attempts to blend quantum theory with general relativity often run into fatal mathematical inconsistencies, such as infinite probabilities. The new approach reinterprets the gravitational field in a way that mirrors the structure of known quantum field theories. "The key finding is that our theory provides a new approach to quantum gravity in a way that resembles the formulation of the other fundamental interactions of the Standard Model," study co-author Mikko Partanen, a physicist at Aalto University in Finland, told Live Science in an email. Instead of curving space-time, gravity in their model is mediated by four interrelated fields, with each one similar to the field that governs electromagnetism. These fields respond to mass in much the same way that electric and magnetic fields respond to charge and current. They also interact with each other and with the fields of the Standard Model in a way that reproduces general relativity at the classical level while also allowing quantum effects to be consistently incorporated. Related: 'Einstein's equations need to be refined': Tweaks to general relativity could finally explain what lies at the heart of a black hole Because the new model mirrors the structure of well-established quantum theories, it sidesteps the mathematical problems that have historically hindered efforts to quantize general relativity. According to the authors, their framework produces a well-defined quantum theory that avoids common problems — such as unphysical infinities in observable quantities and negative probabilities for physical processes — that typically arise when general relativity is quantized using conventional, straightforward methods. A key advantage of the approach is its simplicity. Unlike many models of quantum gravity that require undetected particles and additional forces, this theory sticks to familiar terrain. "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," Jukka Tulkki, a professor at Aalto University and co-author of the paper, told Live Science in an email. "Furthermore, the theory does not need any free parameters beyond the known physical constants." This means the theory can be tested without waiting for the discovery of new particles or revising existing physical laws. "Any future quantum gravity experiments can be directly used to test any (forthcoming) predictions of the theory," Tulkki added. Despite the promising features, the model is still in its early stages. Although preliminary calculations indicate that the theory behaves well under the usual consistency checks, a complete proof of its consistency remains to be worked out. Moreover, the framework has yet to be applied to some of the deepest questions in gravitational physics, such as the true nature of black hole singularities or the physics of the Big Bang. "The theory is not yet capable of addressing those major challenges, but it has potential to do so in the future," Partanen said. Experimental verification may prove even more elusive. Gravity is the weakest of the known forces, and its quantum aspects are incredibly subtle. Direct tests of quantum gravity effects are beyond the reach of current instruments. RELATED STORIES —In a first, physicists spot elusive 'free-range' atoms — confirming a century-old theory about quantum mechanics —Physicists create hottest Schrödinger's cat ever in quantum technology breakthrough —Scientists claim to find 'first observational evidence supporting string theory,' which could finally reveal the nature of dark energy "Testing quantum gravity effects is challenging due to the weakness of gravitational interaction," Tulkki said. Still, because the theory includes no adjustable parameters, any future experiment that probes quantum gravitational behavior could potentially confirm — or rule out — the new proposal. "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," Partanen said. "Indirect evidence through advanced observations could be obtained earlier." For now, Partanen and Tulkki's work opens up a fresh direction for theorists searching for a quantum theory of gravity — one that stays grounded in the successful frameworks of particle physics while potentially unlocking some of the most profound mysteries of the universe.
Yahoo
14-02-2025
- Science
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Fastest exoplanet ever is dragged through space at 1.2 million mph by hypervelocity star
When you buy through links on our articles, Future and its syndication partners may earn a commission. Is it a bird? Is it a plane? No, it's super Neptune! But this Superman-mimicking planet is not blasting through space on its own. It is being dragged along by its parent star. NASA scientists have discovered what they suspect is the hypervelocity star racing through space with a Neptune-like planet in tow. The system appears to be moving at an incredible speed of 1.2 million miles per hour (1.9 million kilometers per hour). If the discovery is confirmed, this will be the fastest extrasolar planet, "exoplanet," system ever seen. "We think this is a so-called super-Neptune world orbiting a low-mass star at a distance that would lie between the orbits of Venus and Earth if it were in our solar system," said team leader Sean Terry, a researcher at NASA's Goddard Space Flight Center. "If so, it will be the first planet ever found orbiting a hypervelocity star." The star and the planet it drags along with it were first hinted at in data collected way back in 2011 thanks to a chance alignment and a phenomenon first predicted by Albert Einstein in 1915 in his magnum opus theory, general relativity. Gravitational lensing becomes useful to planet-hunters when planets pass background stars not associated with them. The way these planets warp space causes a tiny shift in the stars' position when seen from Earth. This effect, called "microlensing," can therefore be used to detect otherwise dark planets way beyond the limits of the solar system that are effectively invisible using traditional light-based astronomy. In this case, the team detected a microlensing signal that indicated two cosmic objects. They determined one of these lensing bodies has a mass around 2,300 times greater than its companion, but weren't able to determine the exact masses of the objects because they were simply too far away."Determining the mass ratio is easy," team member David Bennett, a senior research scientist at the University of Maryland, College Park and NASA Goddard, said. "It's much more difficult to calculate their actual masses."Bennett was part of the team behind the 2011 discovery that suspected that the lensing bodies were a star with a mass around one-fifth of the sun's mass and a planet 29 times as massive as Earth. Alternatively, the first object could be a closer "rogue planet" with no parent star and a mass around 4 times that of Jupiter. That would have made the second lensing body a moon associated with this planet. To end this confusion, Bennett joined this new team, and they began scouring data collected by the Keck Observatory in Hawaii and the star-tracking spacecraft Gaia. The team reasoned that if this pair of lensing bodies were indeed a rogue planet and its trailing moon, then without the aid of lensed background starlight, they would be invisible. However, if this is a star dragging along a super Neptune, then, though the planet would be too faint to see, the light from the star should make it identifiable. This search seems to have been successful. The researchers spotted a strong suspect star located around 24,000 light-years from Earth. That places the star right by the central bulge of the Milky Way, where stellar bodies are densely packed. The team then looked at the star's position in 2011 and compared it to its location in 2021. The change in location over 10 years revealed the system's high speed. Though the scientists have estimated this star is dragging its exoplanet along at 1.2 million mph, what they have examined thus far represents its motions in just two star system could also be moving towards or away from Earth. If it is, this could push its speed up to over 1.3 million mph (600 kilometers per second).This is significant because that speed exceeds the escape velocity of the Milky Way. That means this hypervelocity star and its planet could be destined to escape the Milky Way and go intergalactic, though this process would take millions of years. Related Stories: — Hubble telescope sees an angry star and an evaporating planet — James Webb Space Telescope suggests this exoplanet is our 'best bet' at finding an alien ocean — 12 out-of-this-world exoplanet discoveries in 2023 The team will now attempt to conclusively determine if the lensing body spotted in 2011 is indeed this suspect star. "If high-resolution observations show that the star just stays in the same position, then we can tell for sure that it is not part of the system that caused the signal," team member and University of Maryland researcher Aparna Bhattacharya said. "That would mean the rogue planet and exomoon model is favored." Moving beyond this system, this team and other scientists will now attempt to discover more planets associated with hypervelocity stars. This search will get a major boost when the Nancy Grace Roman Space Telescope launches in May 2027. Roman could also help get to the bottom of what launches some stars with such incredible speeds. "In this case, we used MOA for its broad field of view and then followed up with Keck and Gaia for their sharper resolution, but thanks to Roman's powerful view and planned survey strategy, we won't need to rely on additional telescopes," Terry said. "Roman will do it all." The team's research was published on Tuesday (Feb. 10) in The Astronomical Journal.
