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.

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.

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

Time crystals, a theoretical phase of matter proposed in 2012, can now be reliably created and measured, thanks to researchers at UC Berkeley. Above: a great primer on time crystals.

The discovery built on the work of several teams of researchers:

Time crystals repeat in time because they are kicked periodically, sort of like tapping Jell-O repeatedly to get it to jiggle, Yao said. The big breakthrough, he argues, is less that these particular crystals repeat in time than that they are the first of a large class of new materials that are intrinsically out of equilibrium, unable to settle down to the motionless equilibrium of, for example, a diamond or ruby.

“This is a new phase of matter, period, but it is also really cool because it is one of the first examples of non-equilibrium matter,” Yao said. “For the last half-century, we have been exploring equilibrium matter, like metals and insulators. We are just now starting to explore a whole new landscape of non-equilibrium matter.”

Maybe the next step is the development of these time crystals:

• Scientists unveil new form of matter: time crystals (UC Berkeley via EurekAlert) Read the rest

Don Komarechka captures astonishing photographs of snowflakes. His book Sky Crystals is a survey of snowflake science, a monograph of his macrophotography masterpieces, and a tutorial on the techniques. At Petapixel, Komarechka explains the surprising pop of color sometimes seen through the lens when he's shooting a snowflake:

As a snowflake grows it often creates a cavity or bubble inside of it where the inner side of the crystal grows slower than the top and bottom edge. This forces the layers of ice on either side of the bubble to be incredibly thin, so much so that light will interfere with itself.

Some light will reflect off the surface of the snowflake, but some will also enter the ice (slowing down due to the density of ice compared to air) and reflect off the inner ice/air boundary back towards the camera. If the ice is thin enough, the distance between the two rays of light is close enough to force them to interfere with each-other now that they are out of sync. Some wavelengths get amplified and others get reduced, resulting in a distinctive color emerging based on the thickness of the ice.

"How I Capture Vibrant Colors Inside Snowflakes" (PetaPixel)

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Filipino student Hillary Diane Andales won a $250,000 scholarship from the Breakthrough Junior Challenge for this entertaining and easy-to-understand explainer on relativity and the equivalence of reference frames. Read the rest

If you've ever observed "wine legs," the rivulets that form when you swirl wine in a glass, you've seen the Marangoni effect. Watch how scientists are using this effect to create tiny motors that emit no pollutants. Read the rest

Laser Maze is a super-fun electronic board game that challenges players to arrange angled mirrors to route a laser beam from an emitter to a sensor, avoiding obstacles; in The Quantum Game, you undertake the same fundamental task, but with a virtual laser that only emits one photon, and virtual beam-splitters, absorbtive polarizers, quarter-wave plates, polarizing beam splitters, Faraday rotators, and other exotic apparatus. Read the rest