Quanta Magazine

Last spring, a team of nearly 1,000 cosmologists announced that dark energy — the enigmatic agent propelling the universe to swell in size at an ever-increasing rate — might be slackening. The bombshell result, based on the team’s observations of the motions of millions of galaxies combined with other data, was tentative and preliminary. Today, the scientists report that they have analyzed more than twice as much data as before and that it points more strongly to the same conclusion: Dark energy is losing steam.? ? “We are much more certain than last year that this is definitely a thing,” said Seshadri Nadathur, a member of the Dark Energy Spectroscopic Instrument (DESI) collaboration, the group behind the new result.? ? Their finding, presented today at the Global Physics Summit in Anaheim, California, aligns with that of a second group of cosmologists, the 400-strong Dark Energy Survey (DES). Having also observed a huge swath of the cosmos, DES reported evidence of varying dark energy in a paper earlier this month and in a talk today at the Anaheim meeting.?? ? “It’s interesting that things are pushing in this direction and that multiple experiments are seeing some tension” with the idea that dark energy is constant, said Michael Troxel, a member of the DES team based at Duke University.? ? If the evidence of evolving dark energy holds up as more data accrues — and this is not guaranteed — it would upend cosmologists’ understanding of our ultimate destiny. Dark energy that has a constant density and pressure would doom our cosmos to expand for all time until unbridgeable gulfs separate every particle from all the others, snuffing out all activity. But dark energy that evolves makes alternative futures possible. “It challenges the fate of the universe,” said Mustapha Ishak-Boushaki, a cosmologist at the University of Texas at Dallas and DESI team member. “It’s game-changing.” ? ?? Keep reading: https://lnkd.in/eVDp_CVD

In 1917, mathematician Sōichi Kakeya posed a deceptively simple question. Over a century later, the answer has come to light. https://lnkd.in/eQq-uUmb

The story usually goes a little something like this: Quantum researchers create an algorithm that they believe solves a problem better than anything else. Shortly thereafter, classical researchers come up with one that equals it. But recently, a speedy new quantum algorithm cropped up — and classical computers are still catching up. https://lnkd.in/gxzwwQCE

For computer scientists, solving problems is a bit like mountaineering. First they must choose a problem to solve — akin to identifying a peak to climb — and then they must develop a strategy to solve it. Classical and quantum researchers compete using different strategies, with a healthy rivalry between the two. Quantum researchers report a fast way to solve a problem — often by scaling a peak that no one thought worth climbing — then classical teams race to see if they can find a better way.? ? This contest almost always ends as a virtual tie: When researchers think they’ve devised a quantum algorithm that works faster or better than anything else, classical researchers usually come up with one that equals it. Just last week, a purported quantum speedup, published in the journal Science, was met with immediate skepticism from two separate groups who showed how to perform similar calculations on classical machines. ? But in a paper posted on the scientific preprint site arxiv.org last year, researchers described what looks like a quantum speedup that is both convincing and useful. The researchers described a new quantum algorithm that works faster than all known classical ones at finding good solutions to a wide class of optimization problems (which look for the best possible solution among an enormous number of choices).? ? So far, no classical algorithm has dethroned the new algorithm, known as decoded quantum interferometry (DQI). It’s “a breakthrough in quantum algorithms,” said Gil Kalai, a mathematician at Reichman University and a prominent skeptic of quantum computing. Reports of quantum algorithms get researchers excited, partly because they often illuminate new ideas about difficult problems, and partly because, for all the buzz around quantum machines, it’s not clear which problems will actually benefit from them. A quantum algorithm that outperforms all known classical ones on optimization tasks would represent a major step forward in harnessing the potential of quantum computers. ?? Keep reading: https://lnkd.in/gxzwwQCE ?? Daniel Garcia for Quanta Magazine

A new proof is cracking open previously sealed mathematical realms. “All these problems that [mathematicians] dreamed about someday solving, they all look approachable now,” said mathematician Larry Guth. https://lnkd.in/eQq-uUmb

Mathematics, unfettered by the typical constraints of reality, is all about possibility. In this week's Fundamentals newsletter, staff writer Joseph Howlett explains how classification gives mathematicians a way to start exploring that limitless potential.

Micrometeorites, a type of space dust, escaped notice until the 1870s, when the HMS Challenger expedition dredged some up from the bottom of the Pacific Ocean. (On land, the accumulation of terrestrial dust tends to overwhelm and conceal the cosmic kind.) For a century, scientists thought that the strange spherules found on the seafloor had dripped off the molten surfaces of larger meteors as they crashed through the atmosphere. In fact, cosmic dust flecks off asteroids and floats to Earth. They are tiny messengers from hundreds of millions of miles away. Antarctica is the most bountiful site of micrometeorites on the planet. Strong southerly winds help sweep away earthly debris, so that as much as 10% of the dust lodged in the ice comes from space. These grains carry with them distinctive messages. From each speck of space dust, we can glean information not only about its cosmic origins, but also about its destination: Earth at different points in the planet’s history. ?? Dust off some of our archival content on micrometeorites: https://lnkd.in/gR8UJ6F

In the ’90s, Cris Moore (left) crafted a Turing machine out of a simple apparatus you could imagine sitting in a lab. It was a vivid demonstration that a system obeying nothing more than high school physics could have an unpredictable nature. “It’s a bit shocking that it’s undecidable,” said physicist Toby Cubitt (right), who lectured about Moore’s machine after it captured his imagination as a graduate student. “It’s literally a single particle bouncing around a box.” https://lnkd.in/e4_dwpQR

Two key factors influence whether a planet has an atmosphere: Is the planet’s gravity strong enough to keep air molecules from escaping to space? And how much air has been stripped away by radiation? Those factors stay in balance around a dividing line known as the cosmic shoreline. https://lnkd.in/enzQ7yT3

Consider a pencil lying on your desk. Try to spin it around so that it points once in every direction, but make sure it sweeps over as little of the desk’s surface as possible. You might twirl the pencil about its middle, tracing out a circle. But if you slide it in clever ways, you can do much better. “It’s just a problem about how straight lines can intersect one another,” said Jonathan Hickman, a mathematician at the University of Edinburgh. “But there’s such an incredible richness encoded in it — an incredible array of connections to other problems.” For five decades, mathematicians have sought the best possible solution to the three-dimensional version of this challenge: Hold a pencil in midair, then point it in every direction while minimizing the volume of space it moves through. This straightforward problem has eluded some of the greatest living mathematicians, and it lurks beneath a host of open problems. Now, the hunt for a solution appears to be over. In a paper recently posted on the scientific preprint site arxiv.org, Hong Wang of New York University’s Courant Institute and Joshua Zahl of the University of British Columbia have proved the three-dimensional Kakeya conjecture — they’ve established an absolute limit to how small such a pattern of movements can be. “This thing doesn’t need hyping up,” said Nets Katz, a mathematician at Rice University. “It’s a once-in-a-century kind of result.” Keep reading: https://lnkd.in/eQq-uUmb ?? DVDP for Quanta Magazine