Sean Carroll is a physicist at JPL and the author of many popular, smart books about physics for a lay audience; his weekly Mindscape podcast is a treasure-trove of incredibly smart, fascinating discussions with people from a wide variety of backgrounds. Read the rest

Caltech theoretical physicist Sean Carroll, author of Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime, explains the concept of a "dimensions" at five different levels of complexity. Dr. Carroll sure has a big brane. Read the rest

Don't think his manager won't raise hell over their client working under these unsafe conditions. Read the rest

A favorite kitchen chemistry (and physics) experiment of kids (and adults), Ooblek is the weird result of mixing cornstarch with water. Now, MIT engineers have developed a mathematical model that can predict and simulate how the non-Newtonian fluid switches between liquid and solid depending on the pressure applied to it. From MIT News:

Aside from predicting what the stuff might do in the hands of toddlers, the new model can be useful in predicting how oobleck and other solutions of ultrafine particles might behave for military and industrial applications. Could an oobleck-like substance fill highway potholes and temporarily harden as a car drives over it? Or perhaps the slurry could pad the lining of bulletproof vests, morphing briefly into an added shield against sudden impacts. With the team’s new oobleck model, designers and engineers can start to explore such possibilities.

“It’s a simple material to make — you go to the grocery store, buy cornstarch, then turn on your faucet,” says Ken Kamrin, associate professor of mechanical engineering at MIT. “But it turns out the rules that govern how this material flows are very nuanced...”

Kamrin’s primary work focuses on characterizing the flow of granular material such as sand. Over the years, he’s developed a mathematical model that accurately predicts the flow of dry grains under a number of different conditions and environments. When (grad student Aaron) Baumgarten joined the group, the researchers started work on a model to describe how saturated wet sand moves. It was around this time that Kamrin and Baumgarten saw a scientific talk on oobleck.

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Making a solar hot-dog oven is a science fair standby, but JohnW539's CNC-milled Sundogger Instructable really digs into the classroom portion, drawing on the creator's experience as a physics/astronomy/computer science prof at Middle Tennessee State University. Read the rest

Three basement levels of the Louvre are given over to the Centre de recherche et de restauration des musées de France (C2RMF), which provides research and restoration services to France's 1,200+ art museums and galleries. Read the rest

When I was very little, my big brother brought me in to school for show-and-tell. In the lunchroom, a kid fired a rubber band that hit me right in the face. I still remember the welt. This fascinating video uses high-speed footage to explain the physics behind this age-old form of weaponry. It also reminded me of the traumatic experience that forever made me a conscientious objector to the rubber band wars.

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In 1977, just a few months after Voyager 1 and 2 began their grand tour of the solar system, Carl Sagan gave the esteemed Christmas Lectures at the Royal Institution of Great Britain. You can watch them below via YouTube or at the Read the rest

Vantablack is a pigment made from carbon that is so black that anything painted with it looks like a hole in reality. It absorbs 99.965% of visible light. The Action Lab Man made something even blacker than Vantablack, then shines lights and lasers onto it to see if it visibly reflects the light. He uses marks made with a black Sharpie and a paint called Black 2 (which absorbs 95% of visible light) to compare how well his black square absorbs light. There's a surprising reveal at the end. Read the rest

The Action Lab Man demonstrates the physics of flowing air in several fun ways to explore Richard Feynman's "reverse sprinkler problem." A hypothetical reverse sprinkler (the sort that spins) is one that sucks in the fluid that surrounds it. Which direction does it turn? This question has led to lively debate among physics enthusiasts.

This question is also posed in a great physics puzzle book, called Thinking Physics. Read the rest

Stephen Hawking's final book, Brief Answers to the Big Questions, was released posthumously Tuesday by his children. Read the rest

Stephen Hawking's final paper that he and his colleagues completed just days before his death has now been published. It's titled "Black Hole Entropy and Soft Hair," co-authored with Sasha Haco, Malcolm J. Perry, and Andrew Strominger, about the black hole information paradox. Here is the abstract:

A set of infinitesimal VirasoroL⊗VirasoroR diffeomorphisms are presented which act non-trivially on the horizon of a generic Kerr black hole with spin J. The covariant phase space formalism provides a formula for the Virasoro charges as surface integrals on the horizon. Integrability and associativity of the charge algebra are shown to require the inclusion of `Wald-Zoupas' counterterms. A counterterm satisfying the known consistency requirement is constructed and yields central charges cL=cR=12J. Assuming the existence of a quantum Hilbert space on which these charges generate the symmetries, as well as the applicability of the Cardy formula, the central charges reproduce the macroscopic area-entropy law for generic Kerr black holes.

The Guardian has a translation:

In the latest paper, Hawking and his colleagues show how some information (contained in an object that falls into a black hole) at least may be preserved. Toss an object into a black hole and the black hole’s temperature ought to change. So too will a property called entropy, a measure of an object’s internal disorder, which rises the hotter it gets.

The physicists, including Sasha Haco at Cambridge and Andrew Strominger at Harvard, show that a black hole’s entropy may be recorded by photons that surround the black hole’s event horizon, the point at which light cannot escape the intense gravitational pull.

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A metaphor for social media, courtesy of /u/imjustkidding on Reddit: "My breakfast sausages begged for their lives this morning. Listen to their cries for mercy." Read the rest

In normal life, you open the car door before getting into the car. Operation A happens before operation B. That's the causal order of things. But a new quantum switch weirdly enables two operations to happen simultaneously. From Science News:

The device, known as a quantum switch, works by putting particles of light through a series of two operations — labeled A and B — that alter the shape of the light. These photons can travel along two separate paths to A and B. Along one path, A happens before B, and on the other, B happens before A.

Which path the photon takes is determined by its polarization, the direction in which its electromagnetic waves wiggle — up and down or side to side. Photons that have horizontal polarization experience operation A first, and those with vertical polarization experience B first.

But, thanks to the counterintuitive quantum property of superposition, the photon can be both horizontally and vertically polarized at once. In that case, the light experiences both A before B, and B before A, Romero and colleagues report.

While this is deeply weird and amazing, it unfortunately doesn't occur at the human scale but rather in the quantum realm where measurements are in the nanometers. Still, quantum switches do have clear applications in future communications and computation systems.

"Indefinite Causal Order in a Quantum Switch" (Physical Review Letters)

image: detail from Salvador Dali's "Persistence of Memory" Read the rest

When you snap dry spaghetti before dropping it into the pot, it sometimes results in an explosion of shards. To understand the physics of the phenomenon, MIT mathematicians used computer simulation and a custom machine to break lots of sticks of spaghetti. It turned out that spaghetti that's twisted first reduces the strength of vibrations that cause more cracks. From Science News:

This strategy may not be much practical help in the kitchen; Patil and colleagues aren’t selling their spaghetti snapper for $19.95 — and even if they were, meticulously twisting and bending pieces of pasta one-by-one is hardly efficient meal prep. Still, the discovery of the bend-and-twist technique may lend new insight into controlling the breakage of all kinds of brittle rods, from pole vault sticks to nanotubes.

And from their scientific paper in PNAS:

Fracture processes are ubiquitous in nature, from earthquakes to broken trees and bones. Understanding and controlling fracture dynamics remain one of the foremost theoretical and practical challenges in material science and physics. A well-known problem with direct implications for the fracture behavior of elongated brittle objects, such as vaulting poles or long fibers, goes back to the famous physicist Richard Feynman who observed that dry spaghetti almost always breaks into three or more pieces when exposed to large bending stresses. While bending-induced fracture is fairly well understood nowadays, much less is known about the effects of twist. Our experimental and theoretical results demonstrate that twisting enables remarkable fracture control by using the different propagation speeds of twist and bending waves.

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"Are wormholes real or are they just magic disguised as physics and maths?" (Kurzgesagt – In a Nutshell)

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Before he demonstrates an elaborate example of using a laser to push an object, The Action Lab gives an accessible overview of light physics and relativistic mass. Read the rest