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

“It just seemed that cosmology was more exciting, because it really did seem to involve the big question: Where did the universe come from?” — Stephen Hawking, 8 January 1942 - 14 March 2018

British physicist Stephen Hawking has died at the age of 76. He was known for his groundbreaking work with black holes and relativity. Read the rest

Southern California might seem like a strange place to study snowflakes, but that's where Ken Libbrecht perfected his technique for making identical snowflakes. Read the rest

So, what exactly is going to happen to that Tesla that Elon Musk shot into space?

It's going to wander around the solar system, sure. But there are planets and gravity and stuff, so what are the odds of it eventually slamming into something?

Small, but not zero -- according to this fun analysis by a group of astrophysicists! They modeled the Telsa's current trajectory and estimated that there's a mid-to-low-single-digit chance that it hits Earth or Venus over the next million years:

The orbital evolution is initially dominated by close encounters with the Earth. The first close encounter with the Earth will occur in 2091. The repeated encounters lead to a random walk that eventually causes close encounters with other terrestrial planets and the Sun. Long-term integrations become highly sensitive to the initial conditions after several such close encounters. By running a large ensemble of simulations with slightly perturbed initial conditions, we estimate the probability of a collision with Earth and Venus over the next one million years to be 6% and 2.5%, respectively. We estimate the dynamical lifetime of the Tesla to be a few tens of millions of years.

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See the tiny dot in the center of the photo above? That's a single strontium atom, visible to the naked eye. University of Oxford quantum physicist David Nadlinger's photo (full image below) won this year's Engineering and Physical Sciences Research Council's scientific photography competition.

“The idea of being able to see a single atom with the naked eye had struck me as a wonderfully direct and visceral bridge between the miniscule quantum world and our macroscopic reality," Nadlinger says. "A back-of-the-envelope calculation showed the numbers to be on my side, and when I set off to the lab with camera and tripods one quiet Sunday afternoon, I was rewarded with this particular picture of a small, pale blue dot.”

From the EPSRC:

'Single Atom in an Ion Trap’, by David Nadlinger, from the University of Oxford, shows the atom held by the fields emanating from the metal electrodes surrounding it. The distance between the small needle tips is about two millimetres.

When illuminated by a laser of the right blue-violet colour the atom absorbs and re-emits light particles sufficiently quickly for an ordinary camera to capture it in a long exposure photograph. The winning picture was taken through a window of the ultra-high vacuum chamber that houses the ion trap.

Laser-cooled atomic ions provide a pristine platform for exploring and harnessing the unique properties of quantum physics. They can serve as extremely accurate clocks and sensors or, as explored by the UK Networked Quantum Information Technologies Hub, as building blocks for future quantum computers, which could tackle problems that stymie even today’s largest supercomputers.

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Anil Dash's third law holds that "Three things never work: Voice chat, printers and projectors." But Joshua Rothman's long, fascinating, even poetic profile of the Xerox engineers who work on paper-path process improvements is such a bit of hard-science whimsy that it almost makes me forgive every hour I've spent swearing over jammed paper. Read the rest