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How to Solve a Rubik's Cube in Only 23 Moves

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I've never solved a Rubik's Cube. I'm that guy who takes the stickers off puts them where I want them in order to get it over with. (Much to the consternation of any legitimate puzzle-solver who might try to use my cube in the future.) So it was with some amazement that I learned that Rubik's Cube solutions are an area of active mathematical research. There are scholars out there working on ideal cube-solving algorithms, and major progress is being made towards "God's algorithm" -- more on that in a moment.

Math god Tom Rokicki recently proved that all possible Rubik's Cube configurations can be solved in 23 turns or fewer. In order to arrive at this conclusion he needed massive computing power -- the research was done on supercomputers at Sony Pictures Imageworks (in the idle time between rendering special effects for Hollywood movies). Rokicki's conclusion states that for any legal Rubik's Cube configuration, a solution exists in 21, 22, or 23 moves. (And a few special-case cube configurations may be solvable in 20 or fewer.) Now the trick is...what are those moves?

Rokicki's research is interesting in that it doesn't actually tell you specifically how to solve a given cube (contrary to my catchy blog title above) -- it just proves that a solution exists for all possible legal cube configurations, and that solution is guaranteed to be achievable in 23 moves or fewer.

This research is one step in a process that may arrive at "God's algorithm," a theoretically ideal solution to a puzzle. From Wikipedia's page on the algorithm to end all algorithms:

God's algorithm is a notion originating in discussions of ways to solve the Rubik's Cube puzzle, but which can also be applied to other combinatorial puzzles and mathematical games. It stands for any practical algorithm that produces a solution having the least possible number of moves, the idea being that an omniscient being would know an optimal step from any given configuration.

...It is unknown whether a practical God's algorithm exists for Rubik's Cube.

Further reading: Rokicki's paper on 25-move solutions, a nice Slashdot explanation of the implications of the research, more on God's algorithm, and a highly math-intensive page on Optimal solutions for Rubik's Cube.

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science
Why a Howling Wind Sounds So Spooky, According to Science
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Halloween is swiftly approaching, meaning you'll likely soon hear creepy soundtracks—replete with screams, clanking chains, and howling winds—blaring from haunted houses and home displays. While the sound of human suffering is frightful for obvious reasons, what is it, exactly, about a brisk fall gust that sends shivers up our spines? In horror movie scenes and ghost stories, these spooky gales are always presented as blowing through dead trees. Do bare branches actually make the natural wailing noises louder, or is this detail added simply for atmospheric purposes?

As the SciShow's Hank Green explains in the video below, wind howls because it curves around obstacles like trees or buildings. When fast-moving air goes around, say, a tree, it splits up as it whips past, before coming back together on the other side. Due to factors such as natural randomness, air speed, and the tree's surface, one side's wind is going to be slightly stronger when the two currents rejoin, pushing the other side's gust out of the way. The two continue to interact back-and-forth in what could be likened to an invisible wrestling match, as high-pressure airwaves and whirlpools mix together and vibrate the air. If the wind is fast enough, this phenomenon will produce the eerie noise we've all come to recognize in horror films.

Leafy trees "will absorb some of the vibrations in the air and dull the sound, but without leaves—like if it's the middle of the winter or the entire forest is dead—the howling will travel a lot farther," Green explains. That's why a dead forest on a windy night sounds so much like the undead.

Learn more by watching SciShow's video below.

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Space
SpaceX's Landing Blooper Reel Shows That Even Rocket Scientists Make Mistakes
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SpaceX's Falcon 9 rocket launches.
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On March 30, 2017, SpaceX did something no space program had done before: They relaunched an orbital class rocket from Earth that had successfully achieved lift-off just a year earlier. It wasn't the first time Elon Musk's company broke new ground: In December 2015, it nailed the landing on a reusable rocket—the first time that had been done—and five months later landed a rocket on a droneship in the middle of the ocean, which was also unprecedented. These feats marked significant moments in the history of space travel, but they were just a few of the steps in the long, messy journey to achieve them. In SpaceX's new blooper reel, spotted by Ars Technica, you can see just some of the many failures the company has had along the way.

The video demonstrates that failure is an important part of the scientific process. Of course when the science you're working in deals with launching and landing rockets, failure can be a lot more dramatic than it is in a lab. SpaceX has filmed their rockets blowing up in the air, disintegrating in the ocean, and smashing against landing pads, often because of something small like a radar glitch or lack of propellant.

While explosions—or "rapid unscheduled disassemblies," as the video calls them—are never ideal, some are preferable to others. The Falcon 9 explosion that shook buildings for miles last year, for instance, ended up destroying the $200 million Facebook satellite onboard. But even costly hiccups such as that one are important to future successes. As Musk once said, "If things are not failing, you are not innovating enough."

You can watch the fiery compilation below.

[h/t Ars Technica]

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