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In the absence of gravity, electrostatic forces can induce semi-stable orbital motion between charged bodies. Using a homemade Van Der Graff generator to charge droplets with opposite polarity to a statically charged rod create these crazy orbits!

60,915 views • 5 months ago •via X (Twitter)

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There's a bacteriophage that turns bacteria into “liquid crystals.” Specifically, Pseudomonas aeruginosa bacteria make Pf phages, which are rod-shaped, negatively-charged, and measure about 2 micrometers in length (roughly the length of an E. coli cell). These phages leave the cells and enter their surroundings. There, they mix with polymers, also secreted by the cells, to form a crystalline matrix. Surprisingly, this is good for the cells. Although the phages kill some of them, it also makes their biofilms stickier and able to withstand certain antibiotics. These bacteria + phages are prevalent in cystic fibrosis patients; they've formed a sort of symbiotic relationship. The Pf phages are made from thousands of repeating copies of a coat protein, called CoaB, which wraps around a single-stranded, circular DNA genome. These genes are integrated directly on the bacterial chromosome. The bacteria “turn on” these phage genes when placed in a viscous environment with low oxygen levels. This is like a trigger to start forming a biofilm. And the cells make a lot of phages; about 100 billion per milliliter. These liquid crystals form because of a physics principle called “depletion attraction.” If you just mix a bunch of loose or flexible polymers together (such as long carbon chains) they will not form a liquid crystal. But if you mix stiff rods (the phages) with loose polymers at a high enough concentration, the polymers will force the phages close together to create a material that flows like a liquid despite being ordered like a crystal. See the video below. These liquid crystal biofilms are hard to get rid of. The negatively-charged phages block many antibiotics (like aminoglycosides, which are positively-charged) from entering cells. Liquid crystals also retain water, so these biofilms can survive on drier surfaces. I first heard about this from Malmesbury’s excellent newsletter, called “Telescopic Turnip.”

Niko McCarty.

50,077 views • 7 months ago

The three-body problem is a classic and notoriously difficult question in physics and mathematics. It asks: How do three objects, such as stars, planets, or moons, move under the influence of each other’s gravity? Unlike the simpler two-body problem, which has precise and predictable analytical solutions (like the Earth orbiting the Sun in an ellipse), the three-body problem quickly becomes chaotic and unpredictable. This complexity arises because each object's motion constantly affects, and is affected by, the other two. These gravitational interactions form a tangled and unstable system. In fact, there's no general formula that can solve all three-body scenarios exactly. This was first demonstrated in the 19th century by Henri Poincaré, whose work laid the foundations for chaos theory. While exact solutions remain elusive, scientists have discovered certain special cases where the motion is stable or periodic. One well-known example is the Lagrange points, where three bodies can maintain a stable triangular configuration. However, such neat solutions are rare. Today, thanks to powerful computers, researchers can simulate three-body systems with remarkable accuracy, helping us study triple-star systems, exoplanets, and asteroid dynamics. Yet even small changes in the starting conditions can lead to dramatically different outcomes, highlighting the sensitive dependence on initial conditions that defines chaotic systems. The three-body problem is actually a specific case of the broader n-body problem, where n can be any number of interacting bodies. As n increases, the complexity and unpredictability rise even further. The three-body problem serves as a vivid example of how simple laws of nature, like Newton’s law of gravity, can produce behavior that is intricate, unexpected, and profoundly difficult to predict.

Erika 

215,120 views • 1 year ago