One of the proton’s biggest mysteries isn’t a mystery after all
A question that's baffled physicists for nine years has been resolved by the simplest possible answer.
- A startling result nine years ago sent physicists scrambling.
- Protons, muons, and hydrogen might have been caught doing something unexpected.
- Incredibly accurate new research definitively solves the riddle.
When Randolf Pohl of the Max Planck Institute of Quantum Optics set about in 2010 to measure the radius of a proton, he knew pretty much what to expect. Dozens of earlier measurements had arrived at 0.8751 fentometers, or fm (a quadrillionth of a meter). Imagine his surprise when his measurement was 4 percent smaller: 0.84087 fm. Pohl had replaced the electron used in previous research with a muon, so the inference was that the presence of a muon was somehow shrinking the proton. This would be a very big deal, a new and unexpected interaction mandating a rethink of particle physics. Indeed, physicists have been trying to crack the so-called "proton radius puzzle" now for nearly 10 years, in hundreds of papers. Now a study by Eric Hessels of York University in Toronto reveals that earlier measurements were simply wrong, according to a paper published this month in Science. Never, as they say, mind.
Image source: Harper 3D/Shutterstock
The process of measuring protons is extremely complicated and the technology involved has become far more sensitive over time, so it's not that much of a shock to learn that the earlier value for a proton's radius turned out to be off — that 0.8751 figure having been an average derived from dozens of measurements.
In measuring the proton, the key factor is the proton's interaction with the electron that orbits it. The orbit isn't the same simple circling path we see in our solar system. There are times when an electron's path overlaps the proton, and so the electron spends time partially inside it, bound to it, and riding the vacuum between the quarks and gluons of which the proton is comprised.
When the electron is partially inside the proton, it's referred to as the electron's 2S state. At this time, the proton's own charge drops as kinetic energy and potential energy battle each other for control of the electron, pulling it back and forth and weakening its bond with the proton. As the bond decreases, the electron's own energy increases, since less of it is spent in its bond with the proton.
Eventually, the bond between proton and electron is weak enough that the electron hops back outside of the proton, entering its 2P state. The electron's energy drops slightly in the 2P state as it has to spend more of it to remain bound to its now-separate proton.
The difference between the 2S and 2P charges is called the "Lamb shift," after Willis Lamb, who attempted to measure it in 1947. It represents the amount of energy the electron spends escaping the proton, revealing the strength of the proton's bond during the electron's 2S state. The proton's size accounts for less than 0.01% of the Lamb shift, so extremely fine measurements are required, but the larger the proton, the stronger its influence.
To create a Lamb shift to measure, physicists fire lasers into hydrogen gas to cause its atoms' electrons to jump from 2S to P states. They usuallly use hydrogen due to the simple architecture of its atoms: a proton and just one electron. This (somewhat) simplifies measurements, as other elements' multiple electrons would allow for potentially complex interactions that would also have to be measured and factored in.
Muons and electrons finally agree
Eric Hessels and measuring apparatus
Image source: York University
When Pohl got his surprising result in 2010, he was using custom hydrogen atoms in which the electron was replaced with a muon. Muons are particles created by the decay of pions in the atmosphere and are very similar to electrons, with some key differences. First, they last only a vanishingly quick 10-6 seconds before they decay into, typically, an electron, an electron-antineutrino, and a muon neutrino. Most significantly for proton measurement, however, is that they're some 200 times the mass of an electron.
This is why Pohl used them in his measurements. Since muons are so much heavier than electrons and orbit their protons more tightly, they'd remain in their 2S state longer, and the Lamb shift would be more significantly influenced by the proton's size than it would be with normal, or "electronic," hydrogen.
The new measurements by Hessels and his colleagues used electronic hydrogen instead of muon hydrogen to derive their new radius: 0.833 fm, essentially the same as Pohl's 0.834 within an acceptable margin of error. The technique they developed allowed them to measure the Lamb shift in parts-per-million. "After eight years of working on this experiment, we are pleased to record such a high-precision measurement that helps to solve the elusive proton-radius puzzle," Hessels tells York's yFile.
Pohl, who must have wondered at times over the last decade if he had been mistaken, lauded Hessels' new measurement, reportedly calling it "a fantastic result." Scoring one for Occam's razor, he appreciates that the new research "points to the most mundane explanation."
So the baffling mystery turns out to have been a non-issue all along. This is good news for those seeking confirmation that physicists do know what they think they know about particle interactions, and bad news for those hoping for a reason to blow up the often mind-bending theories of particle physics. Hessels' own take on resolving such a tantalizing discrepancy lies somewhere in the middle: "We know that we don't understand all the laws of physics yet, so we have to chase down all of these things that might give us hints."
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Scientists discover the inner workings of an effect that will lead to a new generation of devices.
- Researchers discover a method of extracting previously unavailable information from superconductors.
- The study builds on a 19th-century discovery by physicist Edward Hall.
- The research promises to lead to a new generation of semiconductor materials and devices.
Credit: Gunawan/Nature magazine
Students who think the world is just cheat less, but they need to experience justice to feel that way.
- Students in German and Turkish universities who believed the world is just cheated less than their pessimistic peers.
- The tendency to think the world is just is related to the occurence of experiences of justice.
- The findings may prove useful in helping students adjust to college life.
The world is just? That’s news to a lot of people.<p>The study is the most recent addition to a long line of work focusing on the belief in justice, our behavior, and our reactions to evidence that might suggest injustice occasionally occurs. This study focuses on a personal belief in a just world, (PBJW) rather than a general belief in a just world (GBJW). The difference between them must be highlighted.</p><p>GBJW is the stance that justice prevails all over the world and that people tend to get what they deserve. PBJW is more focused on the individual's social environment and their belief that they tend to be treated justly. While several studies show PBJW correlates with a higher sense of well-being and a variety of other positive effects, a high GBJW is associated with less life satisfaction, negative behavior, and callousness towards the suffering of <a href="https://link.springer.com/book/10.1007%2F978-1-4939-3216-0" target="_blank">others</a>. This study controlled for GBJW, and focused on PBJW as much as possible. </p><p>To assure that culture was not a factor, the study included students at universities in both Germany and Turkey. </p><p>The researchers gave students at the four participating universities a series of questionnaires that asked if they ever cheated in class, if they perceived the world to be just, if they though that justice always prevailed everywhere, their tendencies towards socially appropriate behavior, their life satisfaction, and if they felt like they were treated justly by their teachers and fellow students. </p><p>The answers were statistically analyzed for relationships. While some of the connections seem trivially true, others were surprising. <strong></strong></p><p>PBJW turned out to only be an indirect predictor of if a student was likely to cheat. Both a belief in a just world and a lower likelihood of cheating were mediated by the justice experiences of the students, with more of these positive experiences lowering the rate of cheating and improving their belief in justice. This was also associated with higher levels of life satisfaction. </p><p>These effects existed across all demographics in both countries. </p>
What does this mean? Is a belief in justice a self-fulfilling prophecy?<iframe width="730" height="430" src="https://www.youtube.com/embed/6oMv-azHNCA" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><p>In a way, it seems to be. People who have reason to think the world is just to them tend to interpret events in a way to sustain that belief and behave in a just manner. In a larger sense, the take away from this study is that experiences of justice, both from peers and instructors, is vital to student's wellbeing and understanding that the rules that exist about cheating are part of a larger, legitimate, system. </p><p>The researchers, citing previous studies on the perception of justice, note that "justice experiences (1) signal that university students are esteemed members of their social group, which in turn conveys feelings of belonging and social inclusion and (2) motivate them to accept and observe university rules and norms. These cognitive processes may thus strengthen their well-being and decrease the likelihood that they cheat."</p><p>The authors also suggest that if you want people (not only students) to act justly; consider treating them with "civility, respect, and dignity."</p><p>Sometimes, all it can take to help somebody act virtuously is to treat them well. Likewise, people treated harshly can rarely find reason to play by rules that don't protect them. The findings of this study will certainly add to the literature on how we perceive justice in the world around us, but might also help us remember that there are real consequences to our actions which can be much larger than we imagine. <strong></strong></p>
This could change how researchers approach vaccine development.
- The reason children suffer less from the novel coronavirus has remained mysterious.
- Researchers identified a cytokine, IL-17A, which appears to protect children from the ravages of COVID-19.
- This cytokine response could change how researchers approach vaccine development.
A member of staff wearing personal protective equipment (PPE) takes a child's temperature at the Harris Academy's Shortland's school on June 04, 2020 in London, England.
Photo by Dan Kitwood/Getty Images<p>Experts don't want to place kids at the back of the line, regardless of how strong their immune systems appear. At least one company, Moderna, <a href="https://www.businessinsider.com/coronavirus-vaccine-for-kids-moderna-plans-pediatric-trial-2020-9" target="_blank">hopes to begin testing</a> vaccines in pediatric volunteers by year's end.</p><p>Innate immune response is especially high during childhood (compared to adaptive immunity). This makes evolutionary sense: nature wants an animal to survive until its ready to procreate. Turns out the children in the study possessed high levels of cytokines that boost their immune response. The biggest impact is made by IL-17A, which appears to protect the youngest cohort from the ravages of the coronavirus. </p><p>While both age groups produced antibodies to fight off the infamous spike protein, adults that produce neutralizing antibodies actually suffer a <em>worse</em> fate. Herold says this "over-vigorous adaptive immune response" might promote inflammation, triggering acute respiratory distress syndrome (ARDS). </p><p>This matters for vaccine development. As Herold says, </p><p style="margin-left: 20px;">"Our adult COVID-19 patients who fared poorly had high levels of neutralizing antibodies, suggesting that convalescent plasma—which is rich in neutralizing antibodies—may not help adults who have already developed signs of ARDS. By contrast, therapies that boost innate immune responses early in the course of the disease may be especially beneficial."</p><p>Herold says current vaccine trials are focused on boosting neutralizing-antibody levels. With this new information, researchers may want to work on vaccines that boost the innate immune response instead. </p><p>With <a href="https://www.nytimes.com/interactive/2020/science/coronavirus-vaccine-tracker.html" target="_blank">at least 55 vaccine trials</a> underway, every piece of data matters. </p><p>--</p><p><em>Stay in touch with Derek on <a href="http://www.twitter.com/derekberes" target="_blank">Twitter</a>, <a href="https://www.facebook.com/DerekBeresdotcom" target="_blank">Facebook</a> and <a href="https://derekberes.substack.com/" target="_blank" rel="noopener noreferrer">Substack</a>. His next book is</em> "<em>Hero's Dose: The Case For Psychedelics in Ritual and Therapy."</em></p>
Researchers from the University of Toronto published a new map of cancer cells' genetic defenses against treatment.