Latest news with #KittPeakNationalObservatory
National Geographic
23-04-2025
- Science
- National Geographic
How will the universe end? The question just got an unexpected twist.
Dark Energy Spectroscopic Instrument (DESI) collects data at the Kitt Peak National Observatory (KPNO) in Arizona. Recent results from the survey suggest that dark energy is even weirder than expected. If you had asked me a year ago about the most likely ultimate fate of the universe, I would have been able to answer immediately. As a cosmologist, I've spent a lot of time thinking about the end of the universe—I even wrote a book on the topic. We know the universe is expanding, and that expansion is speeding up. In the far distant future, this accelerating expansion will empty out the cosmos until there's essentially nothing left. Stars burn out, matter decays, black holes evaporate, and eventually nothing is left but a few stray particles of light diffusing away the waste heat of all creation. This scenario is sometimes called the 'heat death' or the 'big freeze', and it's a straightforward consequence of our best working theory for how the universe behaves. But if you asked me today, I would hesitate. The results announced in late March by the Dark Energy Spectroscopic Instrument (DESI), building on a previous data release last year, paint a very different picture of our universe by challenging our best guess as to the nature of its most important—and most mysterious—component: dark energy. DESI has created the largest 3D map of our universe to date, tracking millions of galaxies. By examining the underlying structure of matter in the universe, the project aims to learn more about the nature of dark energy. In the animation above, Earth is at the center and bluer points indicate more distant objects. DESI Collaboration/DOE/KPNO/NOIRLab/NSF/AURA/R. Proctor The origins of dark energy When dark energy was first discovered, it was, to put it mildly, a surprise. In the late 1990s, astronomers discovered that the expansion of the universe, initially set off by the big bang, has been subtly speeding up over the last few billion years. The acceleration was clear in the data, and confirmed by multiple groups, but it didn't seem to make any sense. Researchers expected expansion to decelerate, not accelerate. Everything in the cosmos—galaxies, stars, gas, dust, even pure energy—has a gravitational effect on everything else. And gravity pulls objects together, never to pushes them apart. So while astronomers have known for more than a hundred years that distant galaxies are moving away from each other, and moving away from us, with the expansion of the cosmos, the only sensible expectation was that the gravity of all that stuff should resist the expansion and, gradually, slow it down. If the expansion of the universe was accelerating, though, it was as though something was actively stretching space out from within, over and above the residual expansion from the big bang. Nothing known to exist in the universe should be able to do that. Fortunately for astronomers, Albert Einstein's theory of gravity—general relativity—offered a potential loophole. While it was still true that no known substance could make the universe accelerate in its expansion, Einstein did leave open the possibility that space itself could do the job. In his equations for the evolution of the cosmos, he added a term called a 'cosmological constant' —depicted as the Greek letter Λ or 'lambda'—that essentially gave space itself the ability to swell from within and push back against gravitational collapse. When Einstein first proposed it, astronomers didn't know the universe was expanding. Once observations pointed to an expanding universe, he took the term out of his equations, wrote it off as a mistake, and moved on to more sensible things. When faced with their unexpected observations of acceleration, modern astronomers thought that perhaps the cosmological constant could explain the unexpected stretching of space. Bizarre as it was, it did. The cosmological constant also presented a compelling timeline. Back when the universe was smaller and denser, gravity was gradually slowing the expansion, and the cosmological constant didn't have much effect. But as soon as the universe became big and diffuse enough, about six billion years ago, all that extra empty space meant that the tiny bit of stretching tendency could take over, causing the expansion to speed back up. For the last few decades, every observation seemed to be in reasonable agreement with this narrative, so physicists integrated a cosmological constant into their model of how the universe works. The cosmological constant falls under the umbrella of the more generic term dark energy, which refers to anything that causes cosmic acceleration and encompasses the possibility of a cosmological constant or something even weirder. A cosmological constant—or something weirder? By keeping the definition of dark energy broad, we've also kept an open mind for other explanations. Maybe dark energy isn't an inherent property of space, but actually some kind of as-yet unknown energy field (sometimes called 'quintessence' or 'dynamical dark energy'). This field could be acting like a cosmological constant now—stretching space in just the same way—but instead of being a constant property of space, it might be something that changes with time, either growing weaker or stronger as the universe evolves. Figuring out what exactly is happening with dark energy, and whether it really is a cosmological constant, has been the driving motivation for several major observational projects in recent years, including DESI. Whatever dark energy is, by our best astrophysical accounting, it makes up something like 70 percent of the energy density of the universe. It's the most important thing in the cosmos, both in terms of its amount and in terms of its influence on cosmic evolution. If dark energy is a cosmological constant, the heat death scenario where the universe ends dark and cold and empty is virtually assured. We can calculate how long it will be before distant galaxies are pulled away from us so fast we can no longer see them (about 100 billion years), and we can determine how long it will be before the cosmos fully succumbs to its own inevitable decay (the number is too big to easily express in words). Since DESI's results have come out, though, people have been asking how that picture might change. Constants aren't supposed to change The DESI results appear to agree better with a kind of dark energy that gets weaker over time than with a cosmological constant. The results are pretty compelling but not yet what we in physics would call a 'discovery'. If the finding is correct, the expansion is still accelerating, but not as much as it was when dark energy first began to dominate. That's definitely not how a cosmological constant works. Some news stories about the results have suggested that this is reason for a certain kind of optimism. Maybe the heat death isn't our fate after all. Perhaps the weakening of dark energy means that the expansion will enter a coasting phase, or eventually stop altogether. Some have even floated the idea that this evolving dark energy could weaken so much that it becomes an attractive force, reversing expansion completely and leading to a 'big crunch'. Personally, I would advocate quite a bit more caution in these interpretations. Even if DESI's results completely hold up to scrutiny and are confirmed by other surveys, they give us essentially no information about the future. The only reason we can make inferences about our fate with a cosmological constant is that we know exactly how it behaves: It's constant. With dynamical dark energy, though, until we know what drives its evolution, we have no handle on what will happen next. Maybe we'll get something else entirely. Taken at face value, the DESI results suggest that in an earlier epoch, dark energy was in what physicists call the 'phantom' regime. Phantom dark energy is dark energy that gets more powerful over time in a way that can literally rip the universe apart. If it really was phantom in the past, there's nothing to say it can't shift that direction again, potentially leading to a rather ghastly fate called the 'big rip.' On the theory side, there are reasons to doubt that phantom dark energy can happen at all, but if it can, it doesn't exactly inspire optimism. What happens if dark energy disappears? I should say that even if dark energy weakens so much that it disappears entirely, and even if expansion completely stops, that's also not necessarily a reprieve. Stars will still explode or fade away as the hydrogen they contain is converted into helium in their cores. Black holes will grow and eventually evaporate. And one way or another the cosmos will tend toward disorder and decay, as some of our most reliable physical laws require. It's also possible that an entirely different fate could befall us, driven by a quantum shift in the laws of physics: a weird and decidedly un-survivable phenomenon known as vacuum decay. If dark energy really does go away, and if vacuum decay doesn't happen, some slim prospects for keeping anything like life going in an expanding universe might theoretically exist, but I'd say they're more technical than practical. There just isn't a lot of room in our current understanding of cosmology for a happily-ever-after. Personally, I'm excited to see how this debate develops, despite the bleak prognosis. DESI's results could lead to the first major cosmological paradigm shift since dark energy was discovered, and a complete rewriting of our model of the universe. Dark energy will probably destroy everything, eventually. But in the meantime, the quest to understand it has driven some incredible discoveries. And there's no telling what the universe has in store for us next.
Boston Globe
17-04-2025
- Science
- Boston Globe
The Town and The City Festival in Lowell, Tucson's new Astro Trail, and a watch geared to runners
Get Starting Point A guide through the most important stories of the morning, delivered Monday through Friday. Enter Email Sign Up Sign up for Tucson's new (and free) Astro Trail guide and use it to explore the area's stunning night sky preserves and other astronomical attractions, including the newly reopened Kitt Peak National Observatory (pictured here). Handout Advertisement THERE Explore Tucson's new Astro Trail Visit observatories, dark sky preserves, science centers, a planetarium, and numerous other space-related sites along greater Tucson's new Astro Trail. The Tucson area, which has the headquarters for Dark Sky International (formerly the International Dark Sky Association), has been known as a stargazer's haven ever since regional officials enacted light pollution ordinances in the 1970s. Sign up for the new free Astro Trail guide and use it to explore the area's stunning night sky views and astronomical attractions. Highlights include the Pima Air and Space Museum, which is one of the largest non-government-funded aviation and space museums in the world; the newly reopened Kitt Peak National Observatory, which is home to one of the largest arrays of optical and radio telescopes in the world; the Flandrau Science Center and Planetarium, which recently opened its new Universe of Science exhibit, focusing on the human brain, a monsoon storm, and deep space; and Saguaro National Park, one of only two national parks to receive an Urban Night Sky Place designation. Also see a sample of the Bennu asteroid at the Gem and Mineral Museum (one of only three public places where a piece of this asteroid can be viewed), visit the newly reopened and renovated Fred Lawrence Whipple Observatory Visitor and Science Center, and enjoy immersive stargazing programs and astronomy camps through the Mount Lemmon Skycenter, which offers access to two of the largest public telescopes in the southwest. Sign up for the guide online and then receive a mobile passport (through a text link) that lists all exhibits, attractions, and astronomical-related destinations, and discounts to local restaurants and sites. Advertisement Amazfit's Cheetah Pro GPS watch is made for runners. Handout EVERYWHERE A watch geared to runners Whether you're running on routes near home or exploring a new destination — for fun or training — check out Amazfit's Cheetah Pro watch, which is made for runners. The lightweight watch has exceptional GPS technology that helps track your movements when running through forests or cities with tall buildings. Download color maps and routes from the Zepp app so you can accurately navigate new runs even in offline mode. Also store your favorite route and then track your improvement on that route over time. The watch tracks heart rate, stress, sleep, and oxygen saturation so you can train better and run smarter. It also offers AI-powered coaching that provides personalized training input to help you improve over time, and adjusts your workout schedule each week based on your progress (so you don't overtrain and to help you reach your race or training goals). Create templates on the watch for interval training and use those to easily guide you through workouts. Store songs on the Cheetah Pro so you can run with music. The Cheetah Pro has an ultra-bright, easy-to-read, and durable (Gorilla Glass 3) screen, a nylon strap, and a battery that lasts up to 14 days (but requires a proprietary plug to recharge). Choose from a selection of watch face themes and opt for a daily morning update that provides the current weather, your sleep data, and the watch's battery power. Currently $159.99. Advertisement KARI BODNARCHUK Kari Bodnarchuk can be reached at
