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

In 1992, University of Melbourne researchers TT Lim and TB Nickels wrote a scientific paper titled "Instability and reconnection in the head-on collision of two vortex rings." The research so inspired Smarter Every Day's Destin Sandlin that he launched his own research effort to study the phenomenon and capture it using high-speed video. Four years later, he's shared this magnificent video above. You can also watch all 12 hours of the 1x speed video below.

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Quantum physics gets real weird real fast, and one idea gaining more currency of late is the concept of quantum retrocausality, where a decision made in our experience of the present may influence what we experience as the past.

These aren't a bunch of Time Cube type cranks, either. From a helpful overview by Lisa Zyga:

First, to clarify what retrocausality is and isn't: It does not mean that signals can be communicated from the future to the past—such signaling would be forbidden even in a retrocausal theory due to thermodynamic reasons. Instead, retrocausality means that, when an experimenter chooses the measurement setting with which to measure a particle, that decision can influence the properties of that particle (or another particle) in the past, even before the experimenter made their choice. In other words, a decision made in the present can influence something in the past.

Huw Price has done some great introductory lectures like this on the concept:

• WTF is Quantum Retrocausality? (YouTube / Seeker) Read the rest

I promise you, the payoff from this video is worth two minutes of your time. Read the rest

Dianna Cowern, aka YouTube's Physics Girl, recruited skateboarding legend Rodney Mullen and a couple of friends with a high-speed camera for this look at the physics of skateboarding. Read the rest

Pecos Hank has seen his share of storms, as evidenced by his cool footage of ominous green-hued clouds. He explains the science behind why massive thunderstorms can "go green," as they say in stormchaser parlance. Read the rest

As advanced atom smashers like the Large Hadron Collider come online, older ones are sometimes abandoned or, better, used for unexpected science experiments. Examples range from recording high-speed X-rays of the biological "motor" that flaps a fly's wings to finding an easter egg in a Degas painting. In the video above, Science Hack Day "global instigator" Ariel Waldman reveals how researchers hack particle accelerators for new uses.

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Fidget spinners are wonderful. Read the rest

To show off the Magnus effect, again, 5 balls of varying size are thrown off a 200m cliff. Fun ensues. Read the rest