How do these little beasties detect light anyway?
When it comes to senses like ours, tiny single-celled organisms floating in the ocean don't have much going on. And yet, as Sacha Coesel, the lead author of a new study from University of Washington researchers, puts it: "If you look in the ocean environment, all these different organisms have this day-night cycle. They are very in tune with each other, even as they get moved around. How do they know when it's day? How do they know when it's night?"
The answer, according to Coesel and her colleagues, is four previously unknown groups of photoreceptors that may help these organisms detect day, night, and each other.
Light and dark are vital to these organisms. When the sun is up, they become energized and grow. Cell division occurs at night when the darkness' ultraviolet wavelengths are less damaging to their DNA.
"Daylight is important for ocean organisms," says senior author Virginia Armbrust, "we know that, we take it for granted. But to see the rhythm of genetic activity during these four days, and the beautiful synchronicity, you realize just how powerful light is."
Photoreceptors and optogenetics
Credit: ktsdesign/Adobe Stock
This combination of optical technologies and genetics is giving researchers new insights into the workings of the brain, allowing them to, for example, turn on and off single neurons as they explore the brain's myriad pathways and interactions. Optogenetics also holds promise for better management of pain, and has cast new light on brain motor decision-making.
These new-found, naturally occurring photoreceptors may substitute for, or complement, human-made photoreceptors currently used in optogenetics. It's hoped that these newcomers will prove more sensitive and better equipped to respond to particular light wavelengths. Possibly because water filters out red light—the reason the ocean looks blue—the new photoreceptors are sensitive to blue and green wavelengths of light.
"This work dramatically expanded the number of photoreceptors — the different kinds of those on-off switches — that we know of," offers Armbrust.
Finding the new photoreceptors
Credit: Dror Shitrit/Simons Collaboration on Ocean Processes and Ecology/University of Washington
The researchers identified the previously undiscovered groups of photoreceptors by analyzing RNA they'd filtered from seawater samples taken far from shore. The samples were collected every four hours over the course of four days from the Northern Pacific Ocean near Hawaii. One set of samples was collected from currents running about 15 meters beneath the surface. A second set sampled deeper down, gathering water from between 120 and 150 meters, in the "twilight zone" where organisms get by with little sunlight.
Filtering the samples produced protists—single-celled organisms with a nucleus—measuring from 200 nanometers to one tenth of a millimeter across. Among these were light-activated algae as well as simple plankton that derive their energy from the organisms they consume.
Under-appreciated, tiny drivers of sea health
The new photoreceptors help fill in at least one of the blanks in our knowledge of the countless floating communities of microscopic creatures in our seas, communities that have a far greater impact on our planet than many people realize.
Says Coesel, "Just like rainforests generate oxygen and take up carbon dioxide, ocean organisms do the same thing in the world's oceans. People probably don't realize this, but these unicellular organisms are about as important as rainforests for our planet's functioning."
Using modern tools, a team of astronomers uses celestial sleuthing to figure out when Vermeer painted his masterpiece "View of Delft."
- The origin of Vermeer's acclaimed landscape has long puzzled historians.
- The painting is of the artist's home town, but exactly when it was made is a mystery.
- A team of astronomers have uncovered clues hidden in the artwork.
Just 35 paintings done by Johannes Vermeer survive.
The best-known among these is his captivating "Girl with a Pearl Earring." Part of what makes it so arresting is Vermeer's masterful use of light — his model's eyes practically glow with life and intelligence, staring straight back into your own. You may not be as familiar with "View of Delft," a landscape that writer Marcel Proust declared "the most beautiful painting in the world." Vermeer's genius here makes viewing this masterpiece feel as if you're actually there, warmed by the morning sun that illuminates the scene across the water.
Or is it the afternoon sun? Not much is known about Vermeer's life, and people have puzzled over this landscape for years, trying to identify exactly the view it depicts and when Vermeer could have painted it. Some experts had tagged its source of light as coming from the west, while others felt that it must've been directly overhead.
Now a team of researchers from Texas State University led by astronomer Donald Olsen have solved the riddle, thanks in part to the uncanny manner in which Vermeer was able to capture the play of light and shadow. When was it painted? According to the study, it was September 3 or 4, 1659 at 8 a.m. from a second-story inn window.
The research is published in the March 2020 issue of astronomy magazine Sky & Telescope.
What did Vermeer paint?
Delft today, a bit to the right of the painter's view and closer-in
Image source: Hit1912/Shutterstock
Olson, along with fellow astronomer Russell Doescher and three students — Charles Condos, Michael Sánchez, and Tim Jenison — took a multidisciplinary approach to their sleuthing.
The first question to be resolved was the location from which Vermeer painted the picture, and what he was painting.
Says Olson, "The students and I worked for about a year on this project. We spent a lot of time studying the topography of the town, using maps from the 17th and 19th centuries and Google Earth."
They concluded that Vermeer was looking northward from the second story of an inn across the triangular Kolk harbor, located at the southern end of his hometown. The students mapped out the painting's landmarks with Google Earth and calculated the angles and distances to reveal that it represented a 42-degree-wide view of the harbor from Vermeer's vantage point. "Google Earth is spectacularly accurate when it comes to distances and angles, so we used it as our measuring stick," Sánchez says.
The online research was followed up with a physical visit to Delph by Olson and Droescher, during which the retired professors took their own measurements and an array of photographs to confirm and expand on the students' conclusions.
When did Vermeer paint it?
Image source: Mauritshuis, The Hague/Big Think
Important clues can be found in the Nieuwe Kerk tower, located to the right of landscape's center. Some experts concluded, for example, that the painting had been done in 1660, but the tower rules out that possibility. While Vermeer's rendering shows the openings in the belfry as being empty, carillon bells — still present today — were installed there starting in April 1660. This would still leave the early months of 1660, except that in Delft there would be no leaves on the painting's trees before late April or early May. So much for 1660.
As for the time, look at the clock in the picture. To many, the clock has two hands that show a time just after 7 a.m. The authors of the new research noticed in other paintings from the period that the two hands of a clock were always lined up. Further research revealed, however, that clocks of this period didn't actually have two hands — they had just one, an hour hand. With this in mind, Vermeer's clock looks a lot more like 8 a.m.
Finding the date was a bit trickier, but again the octagonal Nieuwe Kerk tower provided an answer. Each of the tower's eight corners has its own stone column. The right side of the center-most column is lit, while its left is in shadow. On the next column to the left, however, is a thin sliver of light not blocked by the center column. Trusting Vermeer's careful depiction of light and shadow, the team was able to use this subtle detail to deduce the precise angle of sunlight shown in the painting. "That's our key," says Olson. "That's the sensitive indicator of where the sun has to be to do that, to just skim the one projection and illuminate the other. The pattern of light and shadows was a sensitive indicator of the position of the sun."
The team used astronomical software to identify any days on which the sun was at precisely that angle around 8 in the morning. The software returned two periods, one in April 1660, which was discarded for the reasons noted above, and the other around September 3-4, 1659.
Art takes time
The days identified by the Texas State researchers are most likely those on which Vermeer made the preliminary observations from which he executed the painting. Says Olson, "Vermeer is known to have worked slowly. Completing all the details on the large canvas of his masterpiece may have taken weeks, months or even years."
Still, "His remarkably accurate depiction of the distinctive and fleeting pattern of light and shadows on the Nieuwe Kerk suggests that at least this detail was inspired by direct observation of the sunlit tower rising above the wall and roofs of Delft."
And now we know when.
Olive oil leads to the discovery of a law that applies to atoms, superconductors, and even high energy physics.
- Physicists at the Dutch research institute AMOLF used olive oil in an experiment on light phase transitions.
- The scientists found that light would behave the same way in atoms, superconductors, and high energy physics.
- The discovery can lead to applications in new computing and sensing systems.
The dressing in your salad might redefine science if you look carefully enough. Researchers in the Netherlands used a drop of olive oil to discover a new universal law of phase transitions.
The research was carried out by the Interacting Photons group of the AMOLF institute, which focuses on fundamental physics. The experiment involved dropping olive oil into an optical cavity system of photons bouncing back and forth between two mirrors. It was set up to explore how light goes through phase transitions the way it would in boiling water, for example.
What's fascinating, this system had "memory" in how the oil made photons interact with themselves, as the group leader Said Rodriguez explained. "We created a system with memory by placing a drop of olive oil inside the cavity", said Rodriguez. "The oil mediates effective photon-photon interactions, which we can see by measuring the transmission of laser light through this cavity."
The research team, which also included Rodriguez's PhD students Zou Geng and Kevin Peters, increased and decreased the distances between the mirrors at different speeds and noted how light transmitted through the cavity was affected. They saw that the direction in which the mirrors moved influenced how much light got through the cavity, finding that "the transmission of light through the cavity is non-linear." This behavior of light, called hysteresis, is present in the phase transitions of boiling water or magnetic materials.
The scientists also increased the speed with which the oil-filled cavity opened and closed, observing that under such conditions the hysteresis was not always present. This allowed them to extrapolate a universal law. "The equations that describe how light behaves in our oil-filled cavity are similar to those describing collections of atoms, superconductors and even high energy physics," elaborated Rodriguez, adding: "Therefore, the universal behavior we discovered is likely to be observed in such systems as well."
An optical cavity formed by two mirrors used in the experiment. Light going through the cavity bounces between the mirrors until leaving to where the transmission is measured. The scientists filled this cavity with olive oil and moved the mirrors at varying speeds.
Credit: Henk-Jan Boluijt (AMOLF)
The researchers think their discovery may have potential applications in computing or sensing systems.
Check out their new study in Physical Review Letters.
A mind-blowing explanation of the speed of light
We have arrived: Big Think's most popular video of 2019 tells us light exists outside of time.
- Taking the #1 spot on Big Think's 2019 top 10 countdown, NASA's Michelle Thaller reminds us the only things that travel at the speed of light are photons.
- Nothing with any mass at all can travel at the speed of light because as it gets closer and closer to the speed of light, its mass increases. And if it were actually traveling at the speed of light, it would have an infinite mass.
- Light does not experience space or time. It's not just a speed going through something. All of the universe shifts around this constant, the speed of light. Time and space itself stop when you go that speed.
It turns out light can not only be twisted, but at different speeds.
- An unsuspected property of light, called "self-torque," had just been discovered.
- The discovery will allow scientists to control the behavior of light in a new way.
- The potential applications are still being worked out, but look very exciting.
It's not often that scientists discover an entirely new property of light. The last time was in 1992, when researchers figured out how to twist light. Now, however, scientists at Spain's Universidad de Salamanca and the University of Colorado in the U.S. have uncovered a new thing light can do — they describe it as "self-torque."
The newly discovered property may one day provide scientists a way of manipulating very tiny objects and improve light-based communication devices, along with myriad other uses similar to those already being explored for twisted light.
First, the history of orbital angular momentum
Orbital angular momentum in a light beam and a particle within it. Image source: E-karimi / Wikimedia Commons
Twisted light beams have to do with a property called "orbital angular momentum" (OAM). It's a subset of angular momentum. Imagine an object attached to a string swinging round and around a pole to which the string is connected — the force with which it goes around the pole is its angular momentum. Technically, it's calculated in the other direction, if you will: It's the measurement of the amount of force it would take to stop the object from circling the pole.
In 1932, scientists realized that a perpendicular cross-section of a light wave revealed oscillating mini-waves within it. While typically these mini-waves oscillate together, that's not always the case. In some light beams, researchers found mini-waves out of phase with each other and rotating around the larger beam's center. A particle hit by such a beam of light will orbit that center like a planet orbiting a star. Hence "orbital angle momentum." At the time, these weird light waves were considered to be organically produced by oddly behaving electrons spinning around nuclei.
In the 1970s, lasers allowed the creation of "vortex beams," with "vortex" here meaning a hole in the middle of a light beam. Now we know that it's not really a hole, but rather an area where out-of-phase mini-waves overlap and cancel each other out as they spin around the center of a beam. Though it wasn't realized at the time, what the scientists were seeing was a manifestation of OAM.
In 1991, physicist Robert Spreeuw in Han Woerdman's lab at Leiden University in the Netherlands began dreaming up ways to deliberately create light beams with OAM. He presented his ideas to his team during a coffee break. "The first reactions were a bit skeptical," Spreeuw says. "But we kept thinking about it and, bit by bit, it started to look more realistic."
In 1992, Woerdman, working with colleague Les Allen, successfully twisted light and demonstrated how a photon within it would share the beam's OAM. In 1993, they published their technique of sending a light beam through a lens shaped like a seashell to produce twisted light.
In such a beam, mini-waves rotate around the center of the beam as a helix. If you shine the beam onto a table, or make a perpendicular cross-section, it looks like a donut: Light around a seemingly empty center.
Since then, twisted light beams have proven extremely useful as optical tweezers with which microscopic particles can be captured and manipulated. In the area of communications, they've enabled higher data rates by allowing the manipulation of light characteristics such as color, intensity, and polarization. They also may make possible finer-grained medical diagnostic tools, the stimulation of atoms and molecules into exotic states, and controllers for micro- and non-scale machinery.
The researchers behind the new discovery had been combining pairs of waves with the same OAM by firing them into a cloud of argon gas, from whence they emerged as a single twisted beam, having overlapped and merged within the cloud. The scientists started wondering what would happen if they tried the same thing with two donut beams that had different OAMs and that were out of sync with each other by a few quadrillionths of a second.
The resulting beam was something surprising and unpredicted. It corkscrewed around its center, more tightly — and so, faster — at one end than the other. A photon at the front of the beam would actually be traveling slower than one at the back. The conclusion was that not only did the light beams have OAM that allowed them to twist, but that the application of one to another in the right way produced a force that could affect the speed of the waves' twisting — they named that force "self-torque," as a previously unsuspected type of push that can alter the speed at which light waves twist.
Cross-sectioned or shined on a flat surface, a beam with self-torque looks like a French croissant instead of a donut. One of the scientists, Kevin Dorney, muses to National Geographic, "You wouldn't expect from adding donuts that you would get a croissant."
Twisted light, already so useful in so many ways, just gained a new level of malleability.