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Researchers find that laser light has the ability to cast shadows

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A blue laser was used to illuminate the ruby cube from the side while a high-power green laser was focused through it for the experiment. In order to produce a matched region in the illuminating light and a darker area that looks as a shadow of the green laser beam, the green laser increases the optical absorption of the blue illuminating laser beam.

Is it possible for light to cast a shadow? Researchers have discovered that, in some circumstances, a laser beam can behave like an opaque object and cast a shadow, which may sound like a philosophical conundrum. The finding casts doubt on the conventional wisdom regarding shadows and creates new opportunities for devices that could manipulate another laser beam with a laser beam.

“Laser light casting a shadow was previously thought impossible since light usually passes through other light without interacting,” said Raphael A. Abrahao, the leader of the study team from Brookhaven National Laboratory, formerly at the University of Ottawa. “Our demonstration of a very counter-intuitive optical effect invites us to reconsider our notion of shadow.”

In Optica, scientists explain how they demonstrated that a laser beam could block light and produce a visible shadow because of a nonlinear optical process using a ruby crystal and particular laser wavelengths. Light can affect another optical field when it interacts with a material in an intensity-dependent manner.

“Our understanding of shadows has developed hand-in-hand with our understanding of light and optics,” Abrahao stated. “This new finding could prove useful in various applications such as optical switching, devices in which light controls the presence of another light, or technologies that require precise control of light transmission, like high-power lasers.”

The new study is a part of a broader investigation of nonlinear optical processes and the interaction of two light beams under specific conditions.

Some experimental drawings created with 3D visualization software portray the shadow of a laser beam because they interpret it as a cylinder without taking into account the physics of a laser beam. This idea was first raised during a lunch chat. Could this be done in a lab? asked some of the scientists.

“What started as a funny discussion over lunch led to a conversation on the physics of lasers and the nonlinear optical response of materials,” Abrahao remarked. “From there, we decided to conduct an experiment to demonstrate the shadow of a laser beam.”

The researchers accomplished this by shining a blue laser sideways on a cube of regular ruby crystal and passing a high-power green laser through it. The material’s reaction to the blue wavelength is locally altered when the green laser enters the ruby. Whereas the blue laser behaves like illumination, the green laser behaves like a regular object.

On a screen, the interaction of the two light sources produced a shadow that could be seen as a dark spot where the blue light was blocked by the green laser. Because it was visible to the unaided eye, followed the outlines of the surface it fell on, and followed the location and form of the laser beam, which functioned as an object, it satisfied all the requirements for a shadow.

The ruby’s optical nonlinear absorption is what causes the laser shadow effect. The green laser produces a corresponding region in the illuminating light with reduced optical intensity by increasing the blue illuminating laser beam’s optical absorption. As a result, the green laser beam appears as a shadow in a darker area.

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Boeing Starliner crews will have an extended stay on the ISS due to SpaceX’s delay

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NASA said on Tuesday that it has decided to postpone the launch until at least late March because SpaceX’s upcoming crew rotation mission to the ISS would utilize a new Dragon spacecraft that won’t be ready by the initial February launch date.

For the two NASA astronauts who traveled to the ISS last June on Boeing’s troubled Starliner spacecraft, that means an even longer stay. On June 5, they took off from Cape Canaveral, Florida, aboard a United Launch Alliance Atlas V on the first crewed mission of Starliner. They arrived at the ISS one day later for a stay that was only expected to last eight days.

NASA decided to be cautious and maintain Butch Wilmore and Suni Williams aboard the ISS while sending Starliner home without a crew due to issues with the spacecraft’s thrusters and helium leaks on its propulsion module.

In order for Williams and Wilmore to have a trip home, they will now be traveling on the SpaceX Crew Dragon Freedom, which traveled up to the ISS and docked in September, although with only two crew members on board rather than the customary four.

When Crew-10 arrived in late February, the mission’s goal was to take a trip home.

However, NASA confirmed that Crew-10 will not fly with its replacement crew until late March. This allows NASA and SpaceX time to prepare the new Dragon spacecraft, which has not yet been given a name, for the voyage. Early January is when it is anticipated to reach Florida.

“Fabrication, assembly, testing, and final integration of a new spacecraft is a painstaking endeavor that requires great attention to detail,” stated Steve Stich, the program manager for NASA’s Commercial Crew. “We appreciate the hard work by the SpaceX team to expand the Dragon fleet in support of our missions and the flexibility of the station program and expedition crews as we work together to complete the new capsule’s readiness for flight.”

It would be the fifth Dragon spacecraft with a crew. Its fleet of four current Dragon spacecraft has flown 15 times, sending 56 passengers to space, including two who were two-time fliers. The first crewed trip took place in May 2020. Each spacecraft’s name is chosen by the crew on its first flight.

According to NASA, teams considered using the other crew Dragon spacecraft that were available but decided that rescheduling Crew-10’s launch date was the best course of action.

JAXA (Japan Aerospace Exploration Agency) astronaut and mission specialist Takuya Onishi will undertake his second spaceflight, Roscosmos cosmonaut and mission specialist Kirill Peskov will make his first spaceflight, NASA astronaut and commander Anne McClain will make her second spaceflight, and NASA astronaut and pilot Nichole Ayers will become the first member of the 2021 astronaut candidate class to reach space.

Given that Crew-9 won’t be able to return home until a handover period following Crew-10’s arrival, Wilmore and Williams may have to spend nearly nine months aboard as a result of the delay.

Rotations aboard the ISS typically last six months.

It is unclear when and how Starliner will receive its final certification so that it can start trading off the regular ferry service with SpaceX, as NASA’s Commercial Crew Program aims to have two providers for U.S.-based rotation missions with SpaceX and Boeing. This is due to the Crew Flight Test mission’s incomplete launch.

According to the terms of its contract, Boeing must deliver six missions to the ISS before the space station’s service ends, which is presently scheduled for 2030.

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Ancient DNA Reveals When Humans and Neanderthals Interbred

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Neanderthals and humans likely mixed and mingled during a narrow time frame 45,000 years ago, scientists reported Thursday.

Researchers analyzed ancient genes to pinpoint the time period, which is slightly more recent than previous estimates for the mating.

Modern humans emerged in Africa hundreds of thousands of years ago and eventually spread to Europe, Asia, and beyond. Somewhere along the way, they met and mated with Neanderthals, leaving a lasting fingerprint on our genetic code.

Scientists don’t know exactly when or how the two groups entangled. But ancient bone fragments and genes are helping scientists figure that out.

“Genetic data from these samples really helps us paint a picture in more and more detail,” said study co-author Priya Moorjani at the University of California, Berkeley.

The research was published Thursday in the journals Science and Nature.

To pin down the timeline, researchers peeked at some of the oldest human genes from the skull of a woman, called Zlatý kůň or Golden Horse, named after a hill in the Czech Republic where it was found. They also examined bone fragments from an early human population in Ranis, Germany, about 140 miles (230 kilometers) away. They found snippets of Neanderthal DNA that placed the mating at around 45,000 years ago.

In a separate study, researchers tracked signs of Neanderthal DNA in our genetic code over 50,000 years. They found Neanderthal genes related to immunity and metabolism that may have helped early humans survive and thrive outside of Africa.

We still carry Neanderthals’ legacy in our DNA. Modern-day genetic quirks linked to skin color, hair color, and even nose shape can be traced back to our extinct former neighbors. And our genetic code also contains echoes from another group of extinct human cousins called Denisovans.

Future genetic studies can help scientists detangle exactly what—and who—we’re made of, said Rick Potts, director of the Smithsonian’s Human Origins program, who was not involved with the new research.

“Out of many really compelling areas of scientific investigation, one of them is: well, who are we?” Potts said.

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NASA postpones the next Artemis flights much more

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NASA has postponed the first crewed landing of the program until mid-2027, delaying the following two Artemis trips to the moon.

After identifying the primary cause of Orion heat shield erosion on the Artemis 1 mission two years ago, NASA leadership announced at a news conference on December 5 that they were postponing the Artemis 2 and 3 flights.

Artemis 2, which was originally planned to launch in September 2025, would now debut in April 2026 under the updated schedule. It will be the first crewed voyage of Orion to take four astronauts from the United States and Canada around the moon.

As a result, Artemis 3, which will use SpaceX’s Starship vehicle for the first crewed landing of the entire exploration effort, will be delayed. Originally scheduled for September 2026, that mission is now anticipated to occur in mid-2027.

Following an examination of Artemis 1’s heat shield deterioration, NASA changed that timeline. In October, agency representatives claimed to have identified the cause of the heat shield material’s release, but they did not elaborate on the cause or NASA’s plans to fix it.

NASA Deputy Administrator Pam Melroy said the issue was related to Orion’s “skip” reentry, in which the capsule enters and exits the atmosphere to release energy. In the outer layers of the heat shield, more heat was retained than anticipated, resulting in trapped gases. “This caused internal pressure to build up and led to cracking and uneven shedding of that outer layer,”  she said.

This judgment was confirmed by an independent review panel after a thorough study. “There were a lot of links in the error chain that accumulated over time that led to our inability to predict this in ground tests,” stated Amit Kshatriya, deputy assistant administrator of NASA’s Moon to Mars Program Office. This included modifications to the shape of the material blocks and modifications to the manufacturing process of the heat shield material, known as Avcoat.

He said that in areas of the Avcoat material with the required greater permeability to let the gasses out, that was verified. “In those places, we did not witness in-flight cracking, and that was the key clue for us.”

NASA will alter the reentry profile, including shortening the skip phase of the reentry, rather than replacing the entire heat shield for the Artemis 2 mission. According to ground tests, those adjustments should be enough to prevent material from breaking off as a result of cracking.

The agency has been working on a number of other Orion issues while looking into the heat shield issue, such as a battery issue that was reported in January but was reportedly fixed, according to Kshatriya.

Despite an upcoming presidential transition that would probably rethink the entire Artemis design, agency chiefs said they made the decision immediately to prevent future delays. “We’re on a day-for-day slip. We had to make this decision,” Melroy stated. “If you’re waiting for a new admininstrator to be confirmed and a team to come up to speed on all this technical work we’ve all been tracking very closely, I think that would be actually far worse.”

Shortly after President-elect Donald Trump stated on December 4 that he would select Jared Isaacman to oversee the agency, NASA Administrator Bill Nelson claimed he spoke with Isaacman. He did, however, add that he and other authorities had a discussion prior to the meetings in which they confirmed the revised plan for Artemis 2 and 3. Melroy went on to say that NASA could have been consulted on the decision, but the incoming administration has not dispatched a transition team there.

Nelson, however, maintained that the present architecture was still the most effective way to send humans back to the moon in spite of the problems and delays, pointing out that even with the most recent postponement, NASA would still make a lunar landing before China’s projected 2030 lunar mission.

“Are they going to axe Artemis and insert Starship?” In reference to the impending Trump administration, Nelson stated. Only Orion is rated for human spaceflight outside of Earth’s orbit, he said. “I expect that this is going to continue.”

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