What is an attosecond? A physical chemist explains the tiny time scale behind Nobel Prize-winning research

Aaron W. Harrison, Austin College

A group of three researchers earned the 2023 Nobel Prize in physics for work that has revolutionized how scientists study the electron – by illuminating molecules with attosecond-long flashes of light. But how long is an attosecond, and what can these infinitesimally short pulses tell researchers about the nature of matter?

I first learned of this area of research as a graduate student in physical chemistry. My doctoral adviser's group had a project dedicated to studying chemical reactions with attosecond pulses. Before understanding why attosecond research resulted in the most prestigious award in the sciences, it helps to understand what an attosecond pulse of light is.

How long is an attosecond?

“Atto” is the scientific notation prefix that represents 10⁻¹⁸, which is a decimal point followed by 17 zeroes and a 1. So a flash of light lasting an attosecond, or 0.000000000000000001 of a second, is an extremely short pulse of light.

In fact, there are approximately as many attoseconds in one second as there are seconds in the age of the universe.

Previously, scientists could study the motion of heavier and slower-moving atomic nuclei with femtosecond (10⁻¹⁵) light pulses. One thousand attoseconds are in 1 femtosecond. But researchers couldn't see movement on the electron scale until they could generate attosecond light pulses – electrons move too fast for scientists to parse exactly what they are up to at the femtosecond level.

Attosecond pulses

The rearrangement of electrons in atoms and molecules guides a lot of processes in physics, and it underlies practically every part of chemistry. Therefore, researchers have put a lot of effort into figuring out how electrons are moving and rearranging.

However, electrons move around very rapidly in physical and chemical processes, making them difficult to study. To investigate these processes, scientists use spectroscopy, a method of examining how matter absorbs or emits light. In order to follow the electrons in real time, researchers need a pulse of light that is shorter than the time it takes for electrons to rearrange.

As an analogy, imagine a camera that could only take longer exposures, around 1 second long. Things in motion, like a person running toward the camera or a bird flying across the sky, would appear blurry in the photos taken, and it would be difficult to see exactly what was going on.

Then, imagine you use a camera with a 1 millisecond exposure. Now, motions that were previously smeared out would be nicely resolved into clear and precise snapshots. That's how using the attosecond scale, rather than the femtosecond scale, can illuminate electron behavior.

Attosecond research

So what kind of research questions can attosecond pulses help answer?

For one, breaking a chemical bond is a fundamental process in nature where electrons that are shared between two atoms separate out into unbound atoms. The previously shared electrons undergo ultrafast changes during this process, and attosecond pulses made it possible for researchers to follow the real-time breaking of a chemical bond.

The ability to generate attosecond pulses – the research for which three researchers earned the 2023 Nobel Prize in physics – first became possible in the early 2000s, and the field has continued to grow rapidly since. By providing shorter snapshots of atoms and molecules, attosecond spectroscopy has helped researchers understand electron behavior in single molecules, such as how electron charge migrates and how chemical bonds between atoms break.

On a larger scale, attosecond technology has also been applied to studying how electrons behave in liquid water as well as electron transfer in solid-state semiconductors. As researchers continue to improve their ability to produce attosecond light pulses, they'll gain a deeper understanding of the basic particles that make up matter.

Aaron W. Harrison, Assistant Professor of Chemistry, Austin College

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Nationwide test of Wireless Emergency Alert system could test people's patience – or help rebuild public trust in the system

Elizabeth Ellcessor, University of Virginia and Hamilton Bean, University of Colorado Denver

The Wireless Emergency Alert system is scheduled to have its third nationwide test on Oct. 4, 2023. The Wireless Emergency Alert system is a public safety system that allows authorities to alert people via their mobile devices of dangerous weather, missing children and other situations requiring public attention.

Similar tests in 2018 and 2021 caused a degree of public confusion and resistance. In addition, there was confusion around the first test of the U.K. system in April 2023, and an outcry surrounding accidental alert messages such as those sent in Hawaii in January 2018 and in Florida in April 2023.

The federal government lists five types of emergency alerts: National (formerly labeled Presidential), Imminent Threat, Public Safety, America's Missing: Broadcast Emergency Response (Amber), and Opt-in Test Messages. You can opt out of any except National Alerts, which are reserved for national emergencies. The Oct. 4 test is a National Alert.

We are a media studies researcher and a communications researcher who study emergency alert systems. We believe that concerns about previous tests raise two questions: Is public trust in emergency alerting eroding? And how might the upcoming test rebuild it?

Confusion and resistance

In an ever-updating digital media environment, emergency alerts appear as part of a constant stream of updates, buzzes, reminders and notifications on people's smartphones. Over-alerting is a common fear in emergency management circles because it can lead people to ignore alerts and not take needed action. The sheer volume of different updates can be similarly overwhelming, burying emergency alerts in countless other messages. Many people have even opted out of alerts when possible, rummaging through settings and toggling off every alert they can find.

Even when people receive alerts, however, there is potential for confusion and rejection. All forms of emergency alerts rely on the recipients' trust in the people or organization responsible for the alert. But it's not always clear who the sender is. As one emergency manager explained to one of us regarding alerts used during COVID-19: “People were more confused because they got so many different notifications, especially when they don't say who they're from.”

When the origin of an alert is unclear, or the recipient perceives it to have a political bias counter to their own views, people may become confused or resistant to the message. Prior tests and use of the Wireless Emergency Alert system have indicated strong anti-authority attitudes, particularly following the much-derided 2018 test of what was then called the Presidential Alert message class. There are already conspiracy theories online about the upcoming test.

Trust in alerts is further reduced by the overall lack of testing and public awareness work done on behalf of the Wireless Emergency Alert system since its launch in June 2012. As warning expert Dennis Mileti explained in his 2018 Federal Emergency Management Agency PrepTalk, routine public tests are essential for warning systems' effectiveness. However, the Wireless Emergency Alert system has been tested at the national level only twice, and there has been little public outreach to explain the system by either the government or technology companies.

More exposure and info leads to more trust

The upcoming nationwide test may offer a moment that could rebuild trust in the system. A survey administered in the days immediately following the 2021 national test found that more respondents believed that the National Alert message class label would signal more trustworthy information than the Presidential Alert message class label.

Similarly, in contrast to the 2021 test, which targeted only select users, the Oct. 4 test is slated to reach all compatible devices in the U.S. Since users cannot opt out of the National Alert message class, this week's test is a powerful opportunity to build awareness about the potential benefits of a functional federal emergency alert system.

The Oct. 4 test message is expected to state, “THIS IS A TEST of the National Wireless Emergency Alert system. No action is needed.” We instead suggest that action is, in fact, urgently needed to help people better understand the rapidly changing mobile alert and warning ecosystem that confronts them. Familiarity with this system is what will allow it to support public health and safety, and address the crises of the 21st century.

Here are steps that you can take now to help make the Wireless Emergency Alert system more effective:

• The Wireless Emergency Alert system is only one form of emergency alert. Identify which mobile notification systems are used by your local emergency management organizations: police, fire and emergency services. Know which systems are opt-in and opt-out, and opt in to those needed. Ensure access to other sources of information during an emergency, such as local radio and television, or National Oceanic and Atmospheric Administration weather radio.

• Understand the meaning of mobile device notification settings. Just because you are opted in to “Emergency Alerts” on your cellphone does not necessarily mean you are signed up to receive notifications from local authorities. Check the FEMA website for information about the Wireless Emergency Alert system and your local emergency management organizations' websites about opt-in systems.

• Have a plan for contacting family, friends and neighbors during an emergency. Decide in advance who will help the vulnerable members of your community.

• Find out if your local emergency management organizations test their alert systems, and make sure to receive those local tests.

• Anticipate the possibility that mobile systems will be damaged or unavailable during a crisis and prepare essentials for sheltering in place or quick evacuation.

Finally, push back on the lack of information and rise of misinformation about alerts by sharing reliable information about emergency alerts with your family and friends.

Elizabeth Ellcessor, Associate Professor of Media Studies, University of Virginia and Hamilton Bean, Associate Professor of Communication, University of Colorado Denver

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Superconductivity at room temperature remains elusive a century after a Nobel went to the scientist who demonstrated it below -450 degrees Fahrenheit

David D. Nolte, Purdue University

On April 8, 1911, Dutch physicist Heike Kamerlingh Onnes scribbled in pencil an almost unintelligible note into a kitchen notebook: “near enough null.”

The note referred to the electrical resistance he'd measured during a landmark experiment that would later be credited as the discovery of superconductivity. But first, he and his team would need many more trials to confirm the measurement.

Their discovery opened up a world of potential scientific applications. The century since has seen many advances, but superconductivity researchers today can take lessons from Onnes' original, Nobel Prize-winning work.

I have always been interested in origin stories. As a physics professor and the author of books on the history of physics, I look for the interesting backstory – the twists, turns and serendipities that lie behind great discoveries.

The true stories behind these discoveries are usually more chaotic than the rehearsed narratives crafted after the fact, and some of the lessons learned from Onnes' experiments remain relevant today as researchers search for new superconductors that might, one day, operate near room temperature.

Superconductivity

A rare quantum effect that allows electrical currents to flow without resistance in superconducting wires, superconductivity allows for a myriad of scientific applications. These include MRI machines and powerful particle accelerators.

Imagine giving a single push to a row of glass beads strung on a frictionless wire. Once the beads start moving down the wire, they never stop, like a perpetual motion machine. That's the idea behind superconductivity – particles flowing without resistance.

For superconductors to work, they need to be cooled to ultra-low temperatures colder than any Arctic blast. That's how Onnes' original work cooling helium to near absolute zero temperature set the stage for his unexpected discovery of superconductivity.

The discovery

Onnes, a physics professor at the University of Leiden in the Netherlands, built the leading low-temperature physics laboratory in the world in the first decade of the 20th century.

His lab was the first to turn helium from a gas to a liquid by making the gas expand and cool. His lab managed to cool helium this way to a temperature of -452 degrees Farenheit (-269 degrees Celsius).

Onnes then began studying the electrical conductivity of metals at these cold temperatures. He started with mercury because mercury in liquid form can conduct electricity, making it easy to fill into glass tubes. At low temperatures, the mercury would freeze solid, creating metallic wires that Onnes could use in his conductivity experiments.

On April 8, 1911, his lab technicians transferred liquid helium into a measurement cryostat – a glass container with a vacuum jacket to insulate it from the room's heat. They cooled the helium to -454 F (-270 C) and then measured the electrical resistance of the mercury wire by sending a small current through it and measuring the voltage.

It was then that Onnes wrote the cryptic “near enough null” measurement into his kitchen notebook, meaning that the wire was conducting electricity without any measurable resistance.

That date of April 8 is often quoted as the discovery of superconductivity, but the full story isn't so simple, because scientists can't accept a scribbled “near-enough null” as sufficient proof of a new discovery.

In pursuit of proof

Onnes' team performed its next experiment more than six weeks later, on May 23. On this day, they cooled the cryostat again to -454 F (-270 C) and then let the temperature slowly rise.

At first they barely measured any electrical resistance, indicating superconductivity. The resistance stayed small up to -452 F, when it suddenly rose by over a factor of 400 as the temperature inched up just a fraction of a degree.

The rise was so rapid and so unexpected that they started searching for some form of electrical fault or open circuit that might have been caused by the temperature shifts. But they couldn't find anything wrong. They spent five more months improving their system before trying again. On Oct. 26 they repeated the experiment, capturing the earlier sudden rise in resistance.

One week later, Onnes presented these results to the first Solvay Conference, and two years later he received his Nobel Prize in physics, recognizing his low-temperature work generally but not superconductivity specifically.

It took another three years of diligent work before Onnes had his irrefutable evidence: He measured persistent currents that did not decay, demonstrating truly zero resistance and superconductivity on April 24, 1914.

New frontiers for critical temperatures

In the decades following Onnes' discovery, many researchers have explored how metals act at supercooled temperatures and have learned more about superconductivity.

But if researchers can observe superconductivity only at super low temperatures, it's hard to make anything useful. It is too expensive to operate a machine practically if it works only at -400 F (-240 C).

So, scientists began searching for superconductors that can work at practical temperatures. For instance, K. Alex Müller and J. Georg Bednorz at the IBM research laboratory in Switzerland figured out that metal oxides like lanthanum-barium-copper oxide, known as LBCO, could be good candidates.

It took the IBM team about three years to find superconductivity in LBCO. But when they did, their work set a new record, with superconductivity observed at -397 F (-238 C) in 1986.

A year later, in 1987, a lab in Houston replaced lanthanum in LBCO with the element yttrium to create YBCO. They demonstrated superconductivity at -292 F. This discovery made YBCO the first practical superconductor, because it could work while immersed in inexpensive liquid nitrogen.

Since then, researchers have observed superconductivity at temperatures as high as -164 F (-109 C), but achieving a room-temperature superconductor has remained elusive.

In 2023, two groups claimed they had evidence for room-temperature superconductivity, though both reports have been met with sharp skepticism, and both are now in limbo following further scrutiny.

Superconductivity has always been tricky to prove because some metals can masquerade as superconductors. The lessons learned by Onnes a century ago – that these discoveries require time, patience and, most importantly, proof of currents that never stop – are still relevant today.

David D. Nolte, Distinguished Professor of Physics and Astronomy, Purdue University

This article is republished from The Conversation under a Creative Commons license. Read the original article.