Latest news with #PhysicalReviewD
Yahoo
23-05-2025
- Science
- Yahoo
Aliens Might Be Talking, but Our Ears Aren't Quantum Enough to Hear Them, a Scientist Says
Here's what you'll learn when you read this story: For 75 years, scientists have consistently pondered the Fermi Paradox, which asks why we don't hear from other civilizations when there are so many Earth-like worlds in the galaxy. A recent study analyzes whether these civilizations might be using quantum communication technologies beyond our own, which could explain why we don't 'hear' them. Although interstellar quantum communication is possible, the technology to detect such communications is still far from our reach. In 1950, Enrico Fermi asked the question that all of us have likely pondered at some point in our lives: Where are all of the aliens? He wasn't the first to consider this question—Soviet sci-fi legend Konstantin Tsiolkovsky, for one, asked a similar query in some of his unpublished manuscripts—and he certainly wouldn't be the last. If anything, the question has accumulated ever greater urgency as astronomers have slowly realized that there are likely billions of Earth-like planets in our galaxy alone, and we're discovering more tantalizing, potentially-life-supporting planetary candidates all the time. This 'Fermi Paradox' has spawned dozens of theories, ideas, and hypotheses in the 75 years since. Maybe a 'Great Filter' lies in our distant past—the unlikely development of eukaryotic cells is a compelling candidate—or maybe (and this is the real bummer) it still lies ahead in our future. Are the aliens just not interested? A galaxy-spanning intelligence scoring a solid 'III' on the Kardashev Scale would likely be indifferent about a sub-I species intent on poisoning its own atmosphere. In other words, maybe we're an ant among giants. Or, maybe more simply, aliens are reaching out to us, but we're just not listening—not in the right way, at least. In a study published back in 2020 in the journal Physical Review D, University of Edinburgh physicist Arjun Berera determined that quantum communication—that is, communication that leverages photon qubits rather than the more classical radio waves we use today—could maintain what's known as coherence over interstellar distances. This idea got Berera's colleague Lantham Boyle, a fellow theoretical physicist at the University of Edinburgh, to start pondering if aliens throughout our galaxy (and beyond) could be using communication technologies outside of the classical realm (specifically quantum communication) that we simply can't hear. 'It's interesting that our galaxy (and the sea of cosmic background radiation in which it's embedded) 'does' permit interstellar quantum communication in certain frequency bands,' Boyle told back in September. This curiosity eventually led to the writing of a paper, which has been uploaded to the pre-print server arXiv, titled 'On Interstellar Quantum Communication and the Fermi Paradox.' In the paper, Boyle sets out to determine if an institute like the Search for Extraterrestrial Intelligence (SETI) could somehow incorporate quantum communication detection as part of their never-ending search for interstellar beings. While the answer to that question is technically yes, it's practically a very strong, no-bones-about-it 'no.' The problem is the size of the dish we'd need to construct in order to hear this quantum convo. For example, Boyle calculated that interstellar quantum communication would need to use wavelengths of at least 26.5 centimeters in order to avoid quantum depolarization due to the cosmic microwave background (CMB). That's all well and good, but that means that to communicate quantumly with Alpha Centauri—the nearest star to our own—we'd need a diffraction-limited telescope with a diameter of roughly 100 kilometers (60 miles), which is an area larger than the city of London. To put it mildly, SETI doesn't have that kind of budget. 'We have seen that the sender must place nearly all of their photons into our receiving telescope, which implies that the signal must be so highly directed that only the intended receiving telescope can hope to detect any sign of the communication,' Boyle wrote. 'This is in sharp contrast to classical communication, where one can broadcast photons indiscriminately into space, and an observer in any direction who detects a small fraction of those photons can still receive the message.' Of course, if such an advanced civilization is capable of overcoming these engineering challenges, it's also likely that they could just glimpse our little corner of the cosmos and know we're not technologically equipped to hear what they're sending. So, who knows? Maybe some silicon-based lifeforms orbiting a M-type star in the Large Magellanic Cloud have a regular quantum correspondence with the reigning Kardashev III civilization in Andromeda all about the peculiar apes on one particular spiral arm of the Milky Way that won't return their calls. You Might Also Like The Do's and Don'ts of Using Painter's Tape The Best Portable BBQ Grills for Cooking Anywhere Can a Smart Watch Prolong Your Life?
New York Times
19-03-2025
- Science
- New York Times
‘More Than a Hint' That Dark Energy Isn't What Astronomers Thought
An international team of astronomers on Wednesday unveiled the most compelling evidence to date that dark energy — a mysterious phenomenon pushing our universe to expand ever faster — is not a constant force of nature but one that ebbs and flows through cosmic time. Dark energy, the new measurement suggests, may not resign our universe to a fate of being ripped apart across every scale, from galaxy clusters down to atomic nuclei. Instead, its expansion could wane, eventually leaving the universe stable. Or the cosmos could even reverse course, eventually doomed to a collapse that astronomers refer to as the Big Crunch. The latest results bolster a tantalizing hint from last April that something was awry with the standard model of cosmology, scientists' best theory of the history and the structure of the universe. The measurements, from last year and this month, come from a collaboration running the Dark Energy Spectroscopic Instrument, or DESI, on a telescope at Kitt Peak National Observatory in Arizona. 'It's a bit more than a hint now,' said Michael Levi, a cosmologist at Lawrence Berkeley National Laboratory and the director of DESI. 'It puts us in conflict with other measurements,' Dr. Levi added. 'Unless dark energy evolves — then, boy, all the ducks line up in a row.' The announcement was made at a meeting of the American Physical Society in Anaheim, Calif., and accompanied by a set of papers describing the results, which are being submitted for peer review and publication in the journal Physical Review D. 'It's fair to say that this result, taken at face value, appears to be the biggest hint we have about the nature of dark energy in the ~25 years since we discovered it,' Adam Riess, an astrophysicist at Johns Hopkins University and the Space Telescope Science Institute in Baltimore who was not involved in the work but shared the 2011 Nobel Prize in Physics for discovering dark energy, wrote in an email. But even as the DESI observations challenged the standard model of cosmology, a separate result has reinforced it. On Tuesday, the multinational team that ran the Atacama Cosmology Telescope in Chile released the most detailed images ever taken of the infant universe, when it was a mere 380,000 years old. (That telescope was decommissioned in 2022.) Their report, not yet peer-reviewed, seems to confirm that the standard model was operating as expected in the early universe. One element in that model, the Hubble constant, describes how fast the universe is expanding, but over the last half-century measurements of the constant have starkly disagreed, an inconsistency known as the Hubble tension. Theorists have mused that perhaps an additional spurt of dark energy in the very early universe, when conditions were too hot for atoms to form, could resolve this tension. The latest Atacama results seem to rule out this idea. But they say nothing about whether the nature of dark energy might have evolved later in time. Both reports evoked effusive praise from other cosmologists, who simultaneously confessed to a cosmic confusion about what it all meant. 'I don't think much is left standing as far as good ideas for what might explain the Hubble tension at this point,' said Wendy Freedman, a cosmologist at the University of Chicago who has spent her life measuring the universe and was not involved in either study. Michael Turner, a theorist at the University of Chicago, who was also not involved in the studies, said: 'The good news is, no cracks in the cosmic egg. The bad news is, no cracks in the cosmic egg.' Dr. Turner, who coined the term 'dark energy,' added that if there was a crack, 'it has not opened wide enough — yet — for us to clearly see the next big thing in cosmology.' Dark expectations Astronomers often compare galaxies in an expanding universe to raisins in a baking cake. As the dough rises, the raisins are carried farther apart. The farther they are from each other, the faster they separate. In 1998, two groups of astronomers measured the expansion of the universe by studying the brightness of a certain type of supernova, or exploding star. Such supernovas generate the same amount of light, so they appear predictably fainter at farther distances. If the expansion of the universe were slowing, as scientists believed at the time, light from faraway explosions should have appeared slightly brighter than foreseen. To their surprise, the two groups found that the supernovas were fainter than expected. Instead of slowing down, the expansion of the universe was actually speeding up. No energy known to physicists can drive an accelerating expansion; its strength should abate as it spreads ever more thinly across a ballooning universe. Unless that energy comes from space itself. This dark energy bore all the earmarks of a fudge factor that Albert Einstein inserted into his theory of gravity back in 1917 to explain why the universe was not collapsing under its own weight. The fudge factor, known as the cosmological constant, represented a kind of cosmic repulsion that would balance gravity and stabilize the universe — or so he thought. In 1929, when it became clear that the universe was expanding, Einstein abandoned the cosmological constant, reportedly calling it his biggest blunder. But it was too late. One feature of quantum theory devised in 1955 predicts that empty space is foaming with energy that would produce a repulsive force just like Einstein's fudge factor. For the last quarter-century, this constant has been part of the standard model of cosmology. The model describes a universe born 13.8 billion years ago, in a colossal spark known as the Big Bang, and composed of 5 percent atomic matter, 25 percent dark matter and 70 percent dark energy. But the model fails to say what dark matter or dark energy actually are. If dark energy really is Einstein's constant, the standard model portends a bleak future: The universe will keep speeding up, forever, becoming darker and lonelier. Distant galaxies will eventually be too far away to see. All energy, life and thought will be sucked from the cosmos. 'Something to go after' Astronomers on the DESI team are trying to characterize dark energy by surveying galaxies in different eras of cosmic time. Tiny irregularities in the spread of matter across the primordial universe have influenced the distances between galaxies today — distances that have expanded, in a measurable way, along with the universe. Data used for the latest DESI measurement consisted of a catalog of nearly 15 million galaxies and other celestial objects. Alone, the data set does not suggest that anything is awry with the theoretical understanding of dark energy. But combined with other strategies for measuring the expansion of the universe — for instance, studying exploding stars and the oldest light in the universe, emitted some hundred thousand years after the Big Bang — the data no longer lines up with what the standard model predicts. The discrepancy between data and theory is at most 4.2 sigma (in the units of uncertainty preferred by physicists), representing one in 50,000 chances that the results are a fluke. But the mismatch is not yet at five sigma (equal to one in 3.5 million chances), the stringent standard set by physicists to claim a discovery. Still, the disconnect is enticingly suggestive that something in the cosmological model is not well understood. Scientists might need to revise how they interpret gravity or make sense of the ancient light from the Big Bang. DESI astronomers think the problem could be the nature of dark energy. 'If we introduce a dynamical dark energy, then the pieces of the puzzle fit together better,' said Mustapha Ishak-Boushaki, a cosmologist at the University of Texas at Dallas who helped lead the latest DESI analysis. Will Percival, a cosmologist at the University of Waterloo in Ontario and a spokesperson for the DESI collaboration, expressed excitement about what lies on the horizon. 'This is actually a little bit of a shot in the arm for the field,' he said. 'Now we've got something to go after.' In the 1950s, astronomers claimed that only two numbers were needed to explain cosmology: one related to how fast the universe was expanding and another describing its deceleration, or how much that expansion was slowing down. Things changed in the 1960s, with the discovery that the universe was bathed in light from the Big Bang, known as the cosmic microwave background. Measuring this background radiation allowed scientists to investigate the physics of the early universe and the way that galaxies subsequently formed and evolved. As a result, the standard model of cosmology now requires six parameters, including the density of both ordinary and dark matter in the universe. As cosmology has become more precise, additional tensions have arisen between predicted and measured values of these parameters, leading to a profusion of theoretical extensions to the standard model. But the latest results from the Atacama Cosmology Telescope — the clearest maps to date of the cosmic microwave background — seem to slam the door on many of these extensions. DESI will continue collecting data for at least another year. Other telescopes, on the ground and in space, are charting their own views of the cosmos; among them are the Zwicky Transient Facility in San Diego, the European Euclid space telescope and NASA's recently launched SPHEREx mission. In the future, the Vera C. Rubin Observatory will begin recording a motion picture of the night sky from Chile this summer, and NASA's Roman Space Telescope is set to launch in 2027. Each will soak up the light from the sky, measuring pieces of the cosmos from different perspectives and contributing to a broader understanding of the universe as a whole. All serve as ongoing reminders of just what a tough egg the universe is to crack. 'Each of these data sets comes with its own strengths,' said Alexie Leauthaud, a cosmologist at the University of California, Santa Cruz, and a spokesperson for the DESI collaboration. 'The universe is complicated. And we're trying to disentangle a lot of different things.'
Yahoo
07-03-2025
- Science
- Yahoo
A New Theory Says Gravity May Come From Entropy—Which Could Lead to a Unified Theory of Physics
A new theory suggests that gravity could possibly be the result of entropy. If true, this would mean that everything in the universe would fall apart if it all remained unchanged. This theory tries to reconcile Einstein's theory of general relativity (which sees gravity as a warping of spacetime) with quantum theory (which views the universe as being made of extremely small objects that can exist in particle or wave form). It is possible that the theory could also allow for gravitational fields to be made of dark matter, which continues to elude us. Entropy. The word itself should cause insomnia. It means that matter and energy will degrade—ultimately leading to chaos in the universe—if things are left alone. So why is a new theory suggesting that gravity could possibly emerge from entropy? Yup, you read that right: quantum relative entropy may determine the action of gravity. This is what physicist and mathematician Ginestra Bianconi from Queen Mary University of London proposes in a new theory. There's just one issue—for this to work, two theories that have forever been at odds with each other need to harmonize. The idea of quantum relative entropy mashes up the clashing concepts of general relativity and quantum theory. Einstein's theory of general relativity sees gravity as the curvature or warping of spacetime by an object, with more massive objects having a greater effect on the spacetime surrounding them. For example, the Sun is 330,000 times the mass of the Earth. As a result, our planet is orbiting within the huge distortion in spacetime that the Sun's enormous presence has caused, like a quarter rolling around one of those oversized funnels. Quantum theory, on the other hand, views the universe as being made of extremely small objects (think subatomic particles) that act as both particles and waves. Particles are minuscule pieces of matter, while waves are disturbances that transfer energy. According to quantum mechanics, the universe is described on micro and nano scales. Relativity is the opposite, in the sense that it describes matter on cosmic scales. Finding a way to connect general relativity and quantum mechanics has proved to be an enduring headache for scientists. To that end, enter Bianconi's theory. She posits that spacetime is actually a quantum operator, meaning that it acts on quantum states to turn them into different types of quantum states. Quantum entropy quantifies (no pun intended) how much disorder or unpredictability is in the state of something, which helps distinguish between two quantum states. Bianconi, in her work, found that she could use it to describe how spacetime and matter interact. 'Gravity is derived from an entropic action coupling matter fields with geometry [of spacetime],' she said in a study recently published in Physical Review D. By allowing quantum entropy to describe differences between matter and spacetime, Bianconi's theory modifies general relativity by first giving the fabric of spacetime low energy and a small curvature, and then by predicting a small cosmological constant (which explains how much and how fast the universe is expanding). The new theory also incorporates a G-field, or gravitational field. G-fields are vector fields—which means they have both magnitude and direction—that explain how space is influenced by an object. Bianconi uses the G-field as what is known as a Lagrangian multiplier, which finds the maximum and minimum of a function. Waves, which are one of the two quantum states, are described by a wave function. Finding the maximum and minimum of a wave function with a G-field could reconcile quantum theory with general relativity. If the clash between the theories is finally resolved, you end up with quantum gravity, which would exist in particle and wave form. That said, gravity existing in particle form raises another question. Dark matter is made of particles, but the nature of those particles remains an enigma, since they have never been directly observed. Bianconi thinks that, if gravity can exist as particles, the G-field might offer an explanation for dark matter. 'This work proposes that quantum gravity has an entropic origin and suggests that the G-field might be a candidate for dark matter,' she said in a press release. There's still a lot of work that needs to be done before this idea is anywhere near confirmed. But, there's a chance that chaos brings about gravity, which in turn might, in one form, possibly be dark matter. Mind blown. You Might Also Like The Do's and Don'ts of Using Painter's Tape The Best Portable BBQ Grills for Cooking Anywhere Can a Smart Watch Prolong Your Life?
