Ars Technica glimpsed a possible future at the Johns Hopkins University Applied Physics Laboratory: a solar simulator "that can shine with the intensity of 20 Suns..." "They think it could be the key to interstellar exploration." "It's really easy for someone to dismiss the idea and say, 'On the back of an envelope, it looks great, but if you actually build it, you're never going to get those theoretical numbers,'" says Benkoski, a materials scientist at the Applied Physics Laboratory and the leader of the team working on a solar thermal propulsion system. "What this is showing is that solar thermal propulsion is not just a fantasy. It could actually work." In 2019, NASA tapped the Applied Physics Laboratory to study concepts for a dedicated interstellar mission. At the end of next year, the team will submit its research to the National Academies of Sciences, Engineering, and Medicine's Heliophysics decadal survey, which determines Sun-related science priorities for the next 10 years... In mid-November, [APL's] Interstellar Probe researchers met online for a weeklong conference to share updates as the study enters its final year. At the conference, teams from APL and NASA shared the results of their work on solar thermal propulsion, which they believe is the fastest way to get a probe into interstellar space. The idea is to power a rocket engine with heat from the Sun, rather than combustion. According to Benkoski's calculations, this engine would be around three times more efficient than the best conventional chemical engines available today. "From a physics standpoint, it's hard for me to imagine anything that's going to beat solar thermal propulsion in terms of efficiency," says Benkoski. "But can you keep it from exploding...?" If the interstellar probe makes a close pass by the Sun and pushes hydrogen into its shield's vasculature, the hydrogen will expand and explode from a nozzle at the end of the pipe. The heat shield will generate thrust. It's simple in theory but incredibly hard in practice. A solar thermal rocket is only effective if it can pull off an Oberth maneuver, an orbital-mechanics hack that turns the Sun into a giant slingshot. The Sun's gravity acts like a force multiplier that dramatically increases the craft's speed if a spacecraft fires its engines as it loops around the star... The big takeaway from his research, says Dean Cheikh, a materials technologist at NASAâ(TM)s Jet Propulsion Laboratory, is there's a lot of testing that needs to be done on heat shield materials before a solar thermal rocket is sent around the Sun. But it's not a deal-breaker. "Additive manufacturing is a key component of this, and we couldn't do that 20 years ago. Now I can 3D-print metal in the lab."

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Long-time Slashdot reader 00_NOP is a software engineer (with a PhD in real-time computing) re-visits a historic research paper on the financial trade-offs between disk space (then costing about $20,000 per kilobyte) and (volatile) memory (costing about $5 per kilobyte): Thirty-five years ago that report for Tandem computers concluded that the cost balance between memory, disk and CPU on big iron favoured holding items in memory if they were needed every five minutes and using five bytes to save one instruction. Update the analysis for today and what do you see? Well my estimate is that we should aim to hold items that we have to access 10 times a second. And needless to say, some techniques for saving data space are more efficient than they were 35 years ago, their article points out. "The cost of an instruction per second and the cost of a byte of memory are approximately equivalent — that's tipped the balance somewhat towards data compression (eg., perhaps through using bit flags in a byte instead of a number of booleans for instance), though not by a huge amount."

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To discard the theory of dark matter, "you'll need to replace it with something even more bizarre: a force of gravity that, at some distances, pulls massive objects together and, at other distances, pushes them apart." That's how Science magazine describes a new study, adding that "The analysis underscores how hard it is to explain away dark matter" — even though "after decades of trying, physicists haven't spotted particles of dark matter floating around." [T]o do away with dark matter, theorists would also need explain away its effects on much larger, cosmological scales. And that is much harder, argues Kris Pardo, a cosmologist at NASA's Jet Propulsion Laboratory, and David Spergel, a cosmologist at Princeton University. To make their case, they compare the distribution of ordinary matter in the early universe as revealed by measurements of the afterglow of the big bang — the cosmic microwave background (CMB) — with the distribution of the galaxies today.... Pardo and Spergel derived a mathematical function that describes how gravity would have had to work to get from the distribution of ordinary matter revealed by the CMB to the current distribution of the galaxies. They found something striking: That function must swing between positive and negative values, meaning gravity would be attractive at some length scales and repulsive at others, Pardo and Spergel report this week in Physical Review Letters. "And that's superweird," Pardo says... In a paper posted in June to the preprint server arXiv, theoretical cosmologists Constantinos Skordis and Tom Zlosnik of the Czech Academy of Sciences present a dark matter-less theory of modified gravity they say jibes with CMB data. To do that, researchers add to a theory like general relativity an additional, tunable field called a scalar field. It has energy, and through Einstein's equivalence of mass and energy, it can behave like a form of mass. Set things up just right and at large spatial scales, the scalar field interacts only with itself and acts like dark matter... Skordis's and Zlosnik's paper is "very exciting," Pardo says. But he notes that in some sense it merely replaces one mysterious thing — dark matter — with another — a carefully tuned scalar field. Given the complications, Pardo says, "dark matter is kind of the easier explanation."

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To discard the theory of dark matter, "you'll need to replace it with something even more bizarre: a force of gravity that, at some distances, pulls massive objects together and, at other distances, pushes them apart." That's how Science magazine describes a new study, adding that "The analysis underscores how hard it is to explain away dark matter" — even though "after decades of trying, physicists haven't spotted particles of dark matter floating around." [T]o do away with dark matter, theorists would also need explain away its effects on much larger, cosmological scales. And that is much harder, argues Kris Pardo, a cosmologist at NASA's Jet Propulsion Laboratory, and David Spergel, a cosmologist at Princeton University. To make their case, they compare the distribution of ordinary matter in the early universe as revealed by measurements of the afterglow of the big bang — the cosmic microwave background (CMB) — with the distribution of the galaxies today.... Pardo and Spergel derived a mathematical function that describes how gravity would have had to work to get from the distribution of ordinary matter revealed by the CMB to the current distribution of the galaxies. They found something striking: That function must swing between positive and negative values, meaning gravity would be attractive at some length scales and repulsive at others, Pardo and Spergel report this week in Physical Review Letters. "And that's superweird," Pardo says... In a paper posted in June to the preprint server arXiv, theoretical cosmologists Constantinos Skordis and Tom Zlosnik of the Czech Academy of Sciences present a dark matter-less theory of modified gravity they say jibes with CMB data. To do that, researchers add to a theory like general relativity an additional, tunable field called a scalar field. It has energy, and through Einstein's equivalence of mass and energy, it can behave like a form of mass. Set things up just right and at large spatial scales, the scalar field interacts only with itself and acts like dark matter... Skordis's and Zlosnik's paper is "very exciting," Pardo says. But he notes that in some sense it merely replaces one mysterious thing — dark matter — with another — a carefully tuned scalar field. Given the complications, Pardo says, "dark matter is kind of the easier explanation."

Read more of this story at Slashdot.

I saw an ad on YouTube for a product I'm interested in, but didn't catch its name before they started showing me another ad.

"Bitcoin is now trading near $18,000, up almost 100% in six months," notes Bloomberg columnist Lionel Laurent, "and it's flirting with an all-time high reached in 2017 (which, given it was followed by an ugly crash, faithful Bitcoiners would rather forget)..." . But what exacty does that mean? He challenges the notion that Bitcoin is the new wealth-protecting investment like gold, asking "is this really being driven by people seeking protection from a more uncertain world...?" If anything, Bitcoin looks much more like the stock market on steroids than it does a digital version of gold, which has barely budged since the end of October as confidence about a Covid cure has gradually improved. You can see why hedge fund skeptics like Ray Dalio are dubious of Bitcoin's charms. The cryptocurrency's recent above-average correlation with equities is fine when everything's going up, but not in times of stress: In mid-March, for example, a flight to safety triggered by Covid cut Bitcoin's price in half. A recent Kansas City Fed study comparing bonds, gold and Bitcoin between 1995 and Feb. 2020 found Treasuries behaved "consistently" as a safe haven, gold "occasionally" and Bitcoin "never." Behind the talk of digital gold is the reality of an erratic, still-speculative asset with the potential for big price swings... While digital payment firms such as PayPal Holdings Inc. and Square Inc. have launched Bitcoin applications, this price jump is not about people buying cappuccinos. Data from Chainalysis estimates merchants made up only about 1% of crypto activity in North America between mid-2019 and mid-2020, while exchanges accounted for almost 90%... Crypto is still a heady bet on life-changing wealth, not a disruptor of how normal people use money.

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Today's song: Ironic.

I would say I know five people, all good writers, who put-together would have as many original ideas as the columnists on the NYT op-ed page. And they'd be more timely, because the people at the NYT are risk-averse, usually expressing ideas that there's already a consensus for. In other words, there isn't much new on the op-ed page. I always try to figure out how we can put our heads together and make a product that people will listen to, because the insiders in journalism almost never venture outside their circle. And like it or not they have huge power in forming our futures, for better or worse, and imho mostly worse.

For 108 years Americans have helped their postal service perform "Operation Santa." But this year's program will be fully digital and nationwide, reports CNN: The program allows children and families to write letters to Santa, which will then be processed and shared online beginning on December 4 at USPSOperationSanta.com. Once the letters are live, anyone in the U.S. can go online and adopt a letter, and help make a child or family's holiday wishes come true. Companies also can help adopt letters as teams. While anyone and everyone can write a letter, the program was started to help families and kids in need, said Kim Frum, a spokeswoman for the U.S. Postal Service (USPS). "The program has always been about providing holiday gifts for families who may not have the means to provide for anything more than basic everyday needs," Frum told CNN in email. Over the last 108 years, the USPS has received hundreds of thousands of letters as part of the "Operation Santa" program, Frum said. Last year alone, more than 11,000 packages were sent to people who wrote to Santa and had their letters adopted. USPS first launched an online pilot of USPS Operation Santa in 2017 in New York City, Frum said. It expanded to seven cities online in 2018, and 17 cities in 2019. The success of the digitization of the program helped pave the way for this year's expansion. The decision to go fully digital comes as coronavirus cases continue to surge nationwide, leaving the nation to grapple with the consequences, including the economic impact.

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Sidney Powell is Trolling 2.0.

InfoWorld reports: Firefox users can expect improved JavaScript performance in the Firefox 83 browser, with the Warp update to the SpiderMonkey JavaScript engine enabled by default. Also called WarpBuilder, Warp improves responsiveness and memory usage and speeds up page loads by making changes to JiT (just-in-time) compilers... Warp has been shown to be faster than Ion, SpiderMonkey's previous optimizing JiT, including a 20 percent improvement on Google Docs load time. Other JavaScript-intensive websites such as Netflix and Reddit also have shown improvement... Warp has replaced the front end — the MIR building phase — of the IonMonkey JiT... Mozilla also will continue to incrementally optimize the back end of the IonMonkey JiT, as Mozilla believes there is still room for improvement for JavaScript-intensive workloads.

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Jonah Peretti of Buzzfeed says that because the NYT is behind a paywall and therefore only accessible to rich people, it can no longer be considered The Paper of Record.

A graph I'd like to see. 1. Make a list of all the most influential journalists. 2. Put their names on a map. 3. If journo A reads journo B, then draw an arc with a pointer going from A to B. That's it. I'd just like to see who influences who.

As Thanksgiving is almost here, this is what I'm most thankful for. The functional parts of the American government held back the corrupt parts. We had a perfect national election. Squeaky clean. The Trumps are proving that. The courts, even judges appointed by Trump, are sticking to and enforcing the rule of law. Is that enough to keep the system going for a while longer? We don't know for sure, but right now, it looks like it is. And think of all the things that didn't hold. And the corruption that made that possible

I once had a script that gave me a breakdown of pubs I cite in my linkblog. I wonder what happened to it? Hmmm.