Why on Earth is the planet’s day getting shorter?

Source: The Conversation – UK – By James O’Donoghue, Research Associate Professor in Planetary Astronomy, Meteorology, University of Reading

Quality Stock Arts/Shutterstock

Earth will complete a rotation 1.33 milliseconds earlier than usual on Tuesday, August 5. That makes it one of the shortest days of 2025 at 86,399.99867 seconds long. How that happens, and how we can even measure it with such precision, might make your head spin faster too.

On average, Earth physically rotates in 23 hours, 56 minutes, 4 seconds and 90.5 milliseconds – this is called a sidereal day. It is Earth’s “true” rotation relative to distant objects in deep space, like stars.

However, the kind of day most people go by is 24 hours long and that is called a solar day – it’s the time between two sunrises, or consecutive noons. The extra 4 minutes comes from the fact that Earth has to rotate 1 more degree, to 361 degrees, for the Sun to appear in the same place again.

Both kinds of day are slightly shorter on August 5 2025, largely due to what is happening with winds in Earth’s atmosphere, fluid circulation in the ocean and magma – and even the Moon’s gravitational pull.

Deviations from 24 hours have been accurately measured since the 1970s using atomic clocks and astronomy. Over the course of a year, these changes build up: in 1973, for example, the sum of deviations added up to +1,106 milliseconds, meaning that the Earth lagged behind in its rotation by just over a second. Leap seconds were introduced in the same year to correct for this, with one second added to the clock at the end of the day – 23:59:60.

Absurd levels of accuracy are needed in time-keeping. Global positioning systems (more commonly called GPS) can pinpoint where you are in space, that’s no problem. But if the planetary surface you are on has physically spun slightly faster or slower than expected that day, an uncorrected GPS won’t know that, and your position won’t match with your map.

A 1.33 millisecond deviation translates to a position error of about 62 cm at the equator, so 1973’s cumulative drift would have caused GPS errors of around half a kilometre if left uncorrected over the year.

Why doesn’t the Earth stay still?

To find out how fast the Earth is spinning at all, you need to find a reference frame in which, ideally, nothing is moving. Everything in space moves relative to everything else, but the farther we look, the more still things seem; just as distant hills appear to move slower while you’re on a train, and nearby farms rush by.

Luckily, there are objects so magnificently bright that they outshine entire galaxies. These are quasars, and they are visible across the universe from billions of light years away.

Quasars are supermassive blackholes up to billions of times the mass of our Sun, which emit between 100 and 10,000 times more light than our entire galaxy, the Milky Way. Quasars are detectable from billions of light years across the universe, where things are essentially stationary, so they act as cosmic beacons.

Radio telescopes measure our position relative to these, yielding values of Earth’s true rotation period to sub-millisecond accuracy.

Those ultra‑precise observations are also the starting point for computer models which include movements of the atmosphere, oceans, celestial motions and more to predict the length of day. This is how we know, in advance, when a day is shorter, and how to correct GPS as a result.

Winds in Earth’s atmosphere are the biggest influence on the length of each day as a result of their collisions with the land surface, particularly when they hit mountain ranges. Incredible as it may sound, wind actually slows the spin of the Earth this way.

Earth’s prevailing winds are fastest in the northern hemisphere winter, but slowest from June to August, so the summer months always bring the shortest days of the year (even though we tend to say these are the “longest” days in the northern hemisphere, because of their greater daylight duration).

These daily and seasonal changes are just short‑lived blips atop broader slowdowns. Over decades, the melting of the polar ice caps has been slowing the Earth’s rotation. To understand why, consider a spinning ballerina retracting their outstretched arms – they begin to spin much faster. A spinning ball, like Earth, is no different.

Earth is oblate, meaning the surface at the equator is 21.5 km farther from the centre of the planet than the surface at the poles. As climate change melts the polar ice caps, meltwater moves from the poles to the equator via the ocean. Rising sea levels mean water is farther from the surface, and just like the ballerina moving their arms back out, it aids Earth’s slowdown. Redistribution of Earth’s mass changes our rotation in similar ways, including by earthquakes.

A graph showing how day length has changed.
Historical deviation of day length from the 24-hour day (86,400 seconds).
Ⅱ Ⅶ Ⅻ/International Earth Rotation and Reference Systems Service

The Moon, while beautiful, can be a huge drag over billions of years. Earth’s oceans are raised by the Moon’s gravity, but as the Earth rotates, the raised oceans are carried slightly ahead of the Moon in its orbit. But the Moon continues pulling on those oceans, dragging them backwards against the Earth’s anticlockwise rotation, which slows us down.

Earth’s rotational energy isn’t lost, it’s transferred to the Moon, which gains orbital speed and causes it to escape Earth’s gravity a little better – this is why it’s moving away from us at 3.8 cm a year. Our length of day has increased from 17 hours 2.5 billion years ago largely due to the Moon sapping Earth’s angular momentum over the eons.

Earth’s rotation has slowed every year from 1973 to 2020 (where precise measurements exist), with each year accumulating hundreds of milliseconds of lag, which has already been accounted for by adding 27 leap seconds. Things changed from 2020 – the Earth started spinning faster instead of slower every year, probably the result of angular momentum exchange between the Earth’s core and mantle, but modulated by the numerous other motions we’ve explored.

July 5, July 22 and August 5 were singled out as some of this year’s fastest days far in advance, because on top of the Earth’s internal motions and seasonal quirks in atmospheric winds, the Moon’s position in orbit also slows the Earth twice per orbit (every two weeks). This is because when the Moon is directly above the equator, all of its tidal drag acts east to west, but on these dates, it is positioned farthest north and south, weakening that effect.

You won’t notice the sunrise arrive 1.33 milliseconds sooner, but to precision atomic clocks, quasar‐referenced astronomical measurements, it will be obvious.

The Conversation

James O’Donoghue receives funding from the UK Science and Technology Facilities Council (STFC).

ref. Why on Earth is the planet’s day getting shorter? – https://theconversation.com/why-on-earth-is-the-planets-day-getting-shorter-260946

How much protein do you really need? Too much or too little can be harmful

Source: The Conversation – UK – By Dan Baumgardt, Senior Lecturer, School of Physiology, Pharmacology and Neuroscience, University of Bristol

Prostock-studio/Shutterstock

Does anyone else think we’ve all become a bit too protein-obsessed? Once upon a time, we got our protein from meat, fish, dairy and pulses. Now it seems like every consumable product comes loaded with it — from energy bars to protein-packed cereals and baked goods.

I’m surprised no one’s thought of stirring it into their tea for a boost. Oh wait, they have.

That’s not to say I’m anti-protein. Far from it. Protein plays an essential role in body functions such as growth, immunity and digestion. It’s important that we get enough of it each day.

But the million-dollar questions we should be asking are: how much do we actually need? When is it too much, or too little? And where should we be getting it from?

Protein is one of the three macronutrients we need in the largest amounts – the others being carbohydrates and fats. Micronutrients such as vitamins and minerals are important too, but they’re needed in much smaller quantities — typically milligrams, or even micrograms.

Protein is involved in a huge range of physiological processes. It’s of course crucial for muscle growth and repair. Bodybuilders looking for an Adonis (or Amazonian) physique often consume large amounts alongside strength training. But protein isn’t just about muscles – it’s a core structural material for bone, skin, hair and nails too.

It also plays vital roles inside the body. It allows muscles to contract, makes up digestive and metabolic enzymes, and is a key component of haemoglobin (which carries oxygen), ferritin (which stores iron) and antibodies (which fight infection).

But remember: protein doesn’t work in isolation. Our bodies also rely on carbohydrates and fats — providing short and long-term energy sources that are just as important.

Carbohydrates provide four calories of energy per gram, and fats proide nine calories per gram. While protein can also be used as an energy source – also producing four calories per gram – carbs are more accessible for tissues to use rapidly. And crucially, building muscle also requires fuel. So, if your diet is too low in carbohydrates, your muscle gains may stall and you may find yourself depleted of energy.

In general, protein is filling and can help reduce snacking. And too little protein can be harmful. Protein deficiency can occur due to inadequate diet, eating disorders, or conditions such as cancer, Crohn’s, or liver disease. Symptoms include fatigue, muscle wasting and a weakened immune system.

Because protein also helps regulate fluid balance in the body, a deficiency can lead to swelling or oedema. In severe cases, as seen in some developing countries, the condition kwashiorkor — marked by a swollen belly — can result from inadequate protein intake.

How much?

It can sometimes be difficult to work out how much protein you should be eating each day, especially when different sources give variable advice.

A good starting point is to consider your overall energy requirements. Government recommendations suggest that up to 35% of your daily calories should come from fat, and up to 50% from carbohydrates. That leaves a minimum of 15% for protein — which for someone on a 2,500-calorie diet works out to about 95g of protein per day.

Another calculation accounts for your body size too, giving a value more specific to the individual. Around 0.8g protein per kilogram of body weight for a sedentary adult is advised.

For athletes and bodybuilders – who often aim for around 2g per kilogram — this can mean as much as 200g of protein a day. And that’s hard to achieve through regular food alone. For context, 30 eggs contain 200g of protein, as does 2.5kg of cooked beans. Certain foods have more protein (like the go-to chicken breast), though the overall volume of food required can still be high.

That’s where protein powder often comes in — usually offering 20g–30g of protein per scoop – as supplementation. It’s absolutely fine to incorporate some powder or shakes into a healthy diet alongside wholefoods, which are the best protein sources. But it’s important to set limits – and avoid the temptation to go overboard.

Too much

Is it possible to be taking on too much protein? The answer is yes, if you’re regularly consuming more than your body needs.

Excess protein is broken down and excreted through the kidneys, which may cause dehydration and place additional strain on renal function. Unused protein can also be converted into fat, potentially leading to weight gain. High-protein diets are sometimes associated with gastrointestinal side effects such as bloating, diarrhoea and bad breath.

And while many high-protein foods are healthier, others (such as red or processed meats) may also be high in saturated fat, which can increase the risk of serious conditions like heart disease.

So yes — protein is essential, but balance is key. Your daily needs depend on your body size, activity levels and general health. Consider your goals: are you aiming to maintain a certain weight, or looking to lose fat or gain muscle? Some starting points are:

  • aim for at least 0.8g protein per kilogram of body mass daily
  • balance it with adequate carbs and fats
  • prioritise wholefood sources over protein supplements where possible
  • increase your intake responsibly if you’re training hard or trying to gain muscle
  • but be cautious with too high, sustained intakes — these may do more harm than good.

As someone who could do with a wee bit more in his own diet, I’m off to try that protein-in-my-tea trick. Wish me luck.


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The Conversation

Dan Baumgardt does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. How much protein do you really need? Too much or too little can be harmful – https://theconversation.com/how-much-protein-do-you-really-need-too-much-or-too-little-can-be-harmful-261211

A red meat allergy from tick bites is spreading – and the lone star tick isn’t the only alpha-gal carrier to worry about

Source: The Conversation – USA (3) – By Lee Rafuse Haines, Associate Research Professor of Molecular Parasitology and Medical Entomology, University of Notre Dame

Steak and other red meats can trigger an allergic reaction in people with alpha-gal syndrome. Vicushka/Moment via Getty Images

Hours after savoring that perfectly grilled steak on a beautiful summer evening, your body turns traitor, declaring war on the very meal you just enjoyed. You begin to feel excruciating itchiness, pain or even swelling that can escalate to the point of requiring emergency care.

The culprit isn’t food poisoning – it’s the fallout from a tick bite you may have gotten months earlier and didn’t even notice.

This delayed allergic reaction is called alpha-gal syndrome. While it’s commonly called the “red meat allergy,” that nickname is misleading, because alpha-gal syndrome can cause strong reactions to many products, beyond just red meat.

The syndrome is also rapidly spreading in the U.S. and around the globe. The Centers for Disease Control and Prevention estimates as many as 450,000 people in the U.S. may have it. And it’s carried by many more tick species than most people realize.

A map shows the numbers of confirmed alpha-gal syndrome cases in a band from Oklahoma and Nebraska to Virginia and the Carolinas. There is also a collection in northern Minnesota and Wisconsin, and another in Florida.
Cases of suspected alpha-gal syndrome based on confirmed laboratory evidence.
CDC

What is alpha-gal syndrome?

Alpha-gal syndrome is actually an allergy to a sugar molecule with a tongue-twisting name: galactose-alpha-1,3-galactose, shortened to alpha-gal.

The alpha-gal sugar molecule exists in the tissues of most mammals, including cows, pigs, deer and rabbits. But it’s absent in humans. When a big dose of alpha-gal gets into your bloodstream through a tick bite, it can send your immune system into overdrive to generate antibodies against alpha-gal. In later exposure to foods containing alpha-gal, your immune system might then launch an inappropriate allergic response.

A reddish-brown tick with a large yellow spot on its back sits on a leaf.
A lone star tick (Amblyomma americanum) found near Aden, Va. The tick can cause alpha-gal syndrome as well as carry other diseases, including ehrlichiosis, tularemia and Southern tick-associated rash illness.
Judy Gallagher via Wikimedia, CC BY

Often this allergy is triggered by eating red meat. But the allergy also can be set off by exposure to a range of other animal-based products, including dairy products, gelatin (think Jell-O or gummy bears), medications and even some personal care items. The drug heparin, used to prevent blood clotting during surgery, is extracted from pig intestines, and its use has triggered a dangerous reaction in some people with alpha-gal syndrome.

Once you have alpha-gal syndrome, it’s possible to get over the allergy if you can modify your diet enough to avoid triggering another reaction for a few years and also avoid more tick bites. But that takes time and careful attention to the less obvious triggers that you might be exposed to.

Why more people are being diagnosed

As an entomologist who studies bugs and the diseases they transmit, what I find alarming is how rapidly this allergy is spreading around the globe.

Several years ago, experts thought alpha-gal syndrome was primarily limited to the southeastern U.S. because it was largely associated with the geographical range of the lone star tick.

A Maryland woman finds a lone star tick on her skin in 2017.
How a tick feeds.
National Institute of Allergy and Infectious Diseases via Wikimedia Commons, CC BY

However, both local and global reports have now identified many different tick species across six continents that are capable of causing alpha-gal syndrome, including the prolific black-legged tick, or deer tick, which also transmits Lyme disease.

These ticks lurk in yards and urban parks, as well as forests where they can stealthily grab onto hikers when they touch tick-infested vegetation. As tick populations boom with growing deer and human populations, the number of people with alpha-gal syndrome is escalating.

Why ticks are blamed for alpha-gal syndrome

There are a few theories on how a tick bite triggers alpha-gal syndrome and why only a small proportion of people bitten develop the allergy. To understand the theories, it helps to understand what happens as a tick starts feeding on you.

When a tick finds you, it typically looks for a warm, dark area to hide and attach itself to your body. Then its serrated teeth chew through your skin with rapid sawing motions.

As it excavates deeper into your skin, the tick deploys a barbed feeding tube, like a miniature drilling rig, and it secretes a biological cement that anchors its head into its new tunnel.

A magnified view of a tick's mouth.
A tick’s mouth is barbed so it can stay embedded in your skin as it draws blood over hours and sometimes days.
National Institute of Allergy and Infectious Diseases

Once secure, the tick activates its pumping station, injecting copious amounts of saliva containing anesthetics, blood thinners and, sometimes, alpha-gal sugars into the wound so it can feed undetected, sometimes for days.

One theory about how a tick bite causes alpha-gal syndrome is linked to the enormous quantity of tick saliva released during feeding, which activates the body’s strong immune response. Another suggests how the skin is damaged as the tick feeds and the possible effect of the tick’s regurgitated stomach contents into the bite site are to blame. Or it may be a combination of these and other triggers. Scientists are still investigating the causes.

What an allergic reaction feels like

The allergy doesn’t begin right away. Typically, one to three months after the sensitizing tick bite, a person with alpha-gal syndrome has their first, disturbing reaction.

Alpha-gal syndrome produces symptoms that range from hives or swelling to crushing abdominal pain, violent nausea or even life-threatening anaphylactic shock. The symptoms usually start two to six hours after a person has ingested a meat product containing alpha-gal.

Due to a general lack of awareness about the allergy, however, doctors can easily miss the diagnosis. A study in 2022 found that 42% of U.S. health care practitioners had never heard of alpha-gal syndrome. A decade ago, people with alpha-gal syndrome might go years before the cause of their symptoms was accurately diagnosed. Today, the diagnosis is faster in areas where doctors are familiar with the syndrome, but in many parts of the country it can still take time and multiple doctor visits.

Unfortunately, with every additional tick bite or exposure to food or products containing alpha-gal, the allergy can increase in severity.

Ticks at different ages and sexes compared to a dime (which is quite a bit larger).
The lone star tick isn’t the only one that can cause alpha-gal syndrome. Black-legged ticks have also been connected to cases.
U.S. Army

If you think you have alpha-gal syndrome

If you suspect you may have alpha-gal syndrome, the first step is to discuss the possibility with your doctor and ask them to order a simple blood test to measure whether your immune system is reacting to alpha-gal.

If you test positive, the main strategy for managing the allergy is to avoid eating any food product from a mammal, including milk and cheese, as well as other potential triggers, such as more tick bites.

Read labels carefully. Some products contain additives such as carrageenan, which is derived from red algae and contains alpha-gal.

In extreme cases, people with alpha-gal syndrome may need to carry an EpiPen to prevent anaphylactic shock. Reputable websites, such as the CDC and alphagalinformation.org, can provide more information and advice.

Mysteries remain as alpha-gal syndrome spreads

Since alpha-gal syndrome was first formally documented in the early 2000s, scientists have made progress in understanding this puzzling condition. Researchers have connected the allergy to specific tick bites and found that people with the allergy can have a higher risk of heart disease, even without allergy symptoms.

But important mysteries remain.

Scientists are still figuring out exactly how the tick bite tricks the human immune system and why tick saliva is a trigger for only some people. With growing public interest in alpha-gal syndrome, the next decade could bring breakthroughs in preventing, diagnosing and treating this condition.

For now, the next time you are strolling in the woods or in long grasses, remember to check for ticks on your body, wear long sleeves, long pants and tick repellent to protect yourself from these bloodthirsty hitchhikers. If you do get bitten by a tick, watch out for odd allergic symptoms to appear a few hours after your next steak or handful of gummy bears.

The Conversation

Lee Rafuse Haines is affiliated with the Liverpool School of Tropical Medicine as an Honorary Fellow.

ref. A red meat allergy from tick bites is spreading – and the lone star tick isn’t the only alpha-gal carrier to worry about – https://theconversation.com/a-red-meat-allergy-from-tick-bites-is-spreading-and-the-lone-star-tick-isnt-the-only-alpha-gal-carrier-to-worry-about-262428

« Comment ne pas être tué par une bombe atomique ? » En 1950, les curieux conseils de « Paris Match »

Source: The Conversation – France (in French) – By Anne Wattel, Professeure agrégée, Université de Lille

Il y a 80 ans, le 6 août 1945, se déroulait une tragédie nommée Hiroshima. Les mots de la bombe se sont alors imposés dans l’espace médiatique : « E = mc2 », « Little Boy et Fat Man », « radiations », « bikini », « gerboise », « globocide »…

Dans le Souffle d’Hiroshima, publié en 2024 aux éditions Epistémé (librement accessible en format numérique), la chercheuse Anne Wattel (Université de Lille) revient, à travers une étude culturelle qui s’étende de 1945 à 1960, sur la construction du mythe de l’atome bienfaisant.

Ci-dessous, nous reproduisons un extrait du chapitre 3, consacré à l’histoire du mot « bikini » ainsi qu’à un étonnant article publié par Paris Match en 1950.


« Il y a eu Hiroshima […] ; il y a eu Bikini avec sa parade de cochons déguisés en officiers supérieurs, ce qui ne manquerait pas de drôlerie si l’habilleuse n’était la mort. » (André Breton, 1949

Juillet 1946 : Bikini, c’est la bombe

Lorsqu’en 1946, le Français Louis Réard commercialise son minimaliste maillot de bain deux pièces, il l’accompagne du slogan : « Le bikini, première bombe anatomique. »

On appréciera – ou pas – l’humour et le coup de com’, toujours est-il que cette « bombe », présentée pour la première fois à la piscine Molitor, le 5 juillet 1946, est passée à la postérité, que le bikini s’est répandu sur les plages et a occulté l’atoll des îles Marshall qui lui conféra son nom, atoll où, dans le cadre de l’opération Crossroads, les Américains, après avoir convaincu à grand renfort de propagande la population locale de s’exiler (pour le bien de l’humanité), multiplièrent les essais atomiques entre 1946 et 1958.

La première bombe explose le 1er juillet 1946 ; l’opération est grandement médiatisée et suscite un intérêt mondial, décelable dans France-soir qui, un mois et demi avant « l’expérience », en mai 1946, renoue avec cet art subtil de la titraille qui fit tout son succès :

« Dans 40 jours, tonnerre sur le Pacifique ! Bikini, c’est la bombe » (France-soir, 19-20 mai 1946)

Mais la bombe dévie, ne touche pas l’objectif et la flotte cobaye est quasiment intacte. C’est un grand flop mondial, une déception comme le révèlent ces titres glanés dans la presse française :

  • « Deux navires coulés sur soixante-treize. “C’est tout ?” » (Ce soir, 2 juillet 1946) ;

  • « Bikini ? Ce ne fut pas le knockout attendu » (Paris-presse, 2 juillet 1946) ;

  • « À Bikini, la flotte cobaye a résisté » (France-soir, 2 juillet 1946).

C’est un « demi-ratage », un possible « truquage » pour l’Aurore (2 juillet 1946) ; et le journal Combat se demande si l’expérience de Bikini n’a pas été volontairement restreinte (Combat, 2 juillet 1946).

Les essais vont se poursuivre, mais le battage médiatique va s’apaiser. Le 26 juillet, Raymond Aron, dans Combat, évoque, effaré, la déception générale occasionnée par la première bombe et se désespère alors qu’on récidive :

« Les hommes seuls, maîtres de leur vie et de leur mort, la conquête de la nature, consacrée par la possession d’un pouvoir que les sages, dans leurs rêves, réservaient aux dieux : rien ni personne ne parviendra à voiler la grandeur tragique de ce moment historique. »

Et il conclut :

« […] Aujourd’hui, rien ne protège l’humanité d’elle-même et de sa toute-puissance mortelle. »




À lire aussi :
Bonnes feuilles : « Des bombes en Polynésie »


Premier-Avril 1950 : « Comment ne pas être tué par une bombe atomique »

L’hebdomadaire français Paris Match, qui a « le plus gros tirage dans les années 1950 avec près de 2 millions d’exemplaires chaque semaine », dont « l ‘impact est considérable » et qui « contribue à structurer les représentations », propose dans son numéro du 1er avril 1950 une couverture consacrée, comme c’est fréquemment le cas, à l’aristocratie (ici la famille royale de Belgique) mais, dans un unique encadré, bien visible en haut de page, le titre, « Comment ne pas être tué par une bombe atomique », se présente comme un véritable produit d’appel d’autant plus retentissant qu’on sait officiellement, depuis septembre 1949, que l’URSS possède la bombe atomique.

Paris Match, 54, 1er avril 1950, première de couverture et titres des pages 11 et 12.
© Paris Match/Scoop

L’article, qui nous intéresse et qui se déploie sur deux pleines pages, est écrit par Richard Gerstell qu’un encadré présente comme « un officier de la marine américaine », « un savant », « docteur en philosophie », « conseiller à la défense radiologique à l’Office de la défense civile des États-Unis ». L’auteur est chargé par le ministère de la défense d’étudier les effets de la radioactivité des essais atomiques de Bikini et d’élaborer des « plans pour la protection de la population civile contre une éventuelle attaque atomique ».

L’encadré inséré par la rédaction de Paris Match vise donc à garantir la crédibilité du rédacteur de l’article, un homme de terrain, un scientifique, dont on précise qu’il « a été exposé plusieurs fois aux radiations atomiques et n’en a d’ailleurs pas souffert physiquement (il n’a même pas perdu un cheveu) », qui rend compte de sa frayeur lorsque le compteur Geiger révéla que ses cheveux étaient « plus radioactifs que la limite ». Il s’agit donc, du moins est-ce vendu ainsi, du témoignage, de l’analyse d’un témoin de choix ; il s’agit d’une information de première main.




À lire aussi :
Bombe atomique et accident nucléaire : voici leurs effets biologiques respectifs


Dans les premiers paragraphes de l’article de Match, Gerstell explique avoir eu, dans les premiers temps, « la conviction que la destruction atomique menaçait inévitablement une grande partie de l’humanité ». C’est pourquoi il accueillit favorablement la parution de l’ouvrage de David Bradley, No Place to Hide (1948), qui alertait sur les dangers de la radioactivité. Mais il ne s’appuyait alors, confie-t-il, que sur une « impression » ; il manquait de recul. En possession désormais des « rapports complets des expériences de Bikini et des rapports préliminaires des nouvelles expériences atomiques d’Eniwetok », il a désormais « franchement changé d’avis ».

L’article publié dans Match vise un objectif : convaincre que la radioactivité, sur laquelle on en sait plus que sur « la poliomyélite ou le rhume », « n’est, au fond, pas plus dangereuse que la fièvre typhoïde ou d’autres maladies qui suivent d’habitude les ravages d’un bombardement ».

Fort de son « expérience “Bikini” », durant laquelle, dit-il, « aucun des 40 000 hommes » qui y participèrent « ne fut atteint par la radioactivité », Gerstell entend mettre un terme aux « légendes » sur les effets de cette dernière (elle entraînerait la stérilité, rendrait des régions « inhabitables à jamais »). « Tout cela est faux », clame-t-il ; la radioactivité est « une menace beaucoup moins grande que la majorité des gens le croient ».

Un certain nombre de précautions, de conseils à suivre pour se protéger de la radioactivité en cas d’explosion nucléaire sont livrés aux lecteurs de Paris Match : fermer portes et fenêtres, baisser les persiennes, tirer les rideaux ; ôter ses souliers, ses vêtements avant de rentrer chez soi, les laver et frotter ; prendre des douches « copieuses » pour se débarrasser des matières radioactives ; éviter les flaques d’eau, marcher contre le vent ; s’abriter dans une cave, « protection la plus adéquate contre les radiations »…

On laisse le lecteur apprécier l’efficacité de ces mesures…

Pour se protéger de la bombe elle-même dont « la plupart des dégâts sont causés par les effets indirects de l’explosion », se coucher à plat ventre, yeux fermés ; pour éviter les brûlures, trouver une barrière efficace (mur, égout, fossé) ; porter des « vêtements en coton clair », des pantalons longs, des blouses larges, « un chapeau aux bords rabattus »…

Ainsi, ce témoin, ce « savant », qui étudia l’impact de la radioactivité, rassure-t-il le lectorat français de Match : on peut se protéger de la bombe atomique, des radiations ; il suffit d’être précautionneux.

Foin des légendes ! Ce regard éclairé, scientifiquement éclairé, s’appuie sur l’expérience, sur Bikini, sur Hiroshima et Nagasaki pour minorer (et c’est peu dire) le danger des radiations, car, c’est bien connu, « les nuages radioactifs à caractère persistant sont vite dissipés dans le ciel » (cela n’est pas sans nous rappeler l’incroyable mythe du nuage qui, à la suite de la catastrophe de Tchernobyl, le 26 avril 1986, se serait arrêté aux frontières de la France) ; « la poussière radio-active persistante qui se dépose sur la peau ne paraît pas dangereuse » ; « au voisinage immédiat du point d’explosion, une pleine sécurité peut être assurée par 30 centimètres d’acier, 1 mètre de béton ou 1 m 60 de terre. À un kilomètre et demi, la protection nécessaire tombe à moins d’un centimètre d’acier et quelques centimètres de béton ».

En avril 1950, l’Américain Richard Gerstell, dont les propos sont relayés en France par l’hebdomadaire Paris Match, niait encore l’impact de la radioactivité.

The Conversation

Anne Wattel ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d’une organisation qui pourrait tirer profit de cet article, et n’a déclaré aucune autre affiliation que son organisme de recherche.

ref. « Comment ne pas être tué par une bombe atomique ? » En 1950, les curieux conseils de « Paris Match » – https://theconversation.com/comment-ne-pas-etre-tue-par-une-bombe-atomique-en-1950-les-curieux-conseils-de-paris-match-259333

Le « fibremaxxing » est à la mode. Voici pourquoi cela pourrait poser problème

Source: The Conversation – in French – By Lewis Mattin, Senior Lecturer, Life Sciences, University of Westminster

Les fibres sont essentielles, c’est incontestable. Mais dans le monde des tendances santé en ligne, ce qui était au départ un conseil alimentaire judicieux s’est transformé en « fibremaxxing », une tendance qui consiste à consommer des quantités astronomiques de fibres au nom du bien-être.

Au Canada, les recommandations suggèrent que les femmes ont besoin de 25 grammes de fibres par jour et les hommes 38 grammes de fibres par jour. Les enfants et les adolescents ont généralement besoin de beaucoup moins.

Pourtant, malgré des recommandations claires, la plupart des Canadiennes et Canadiens n’atteignent pas leur objectif quotidien en matière de fibres. L’un des principaux responsables ? L’essor des aliments ultra-transformés. Pas moins de 46 % de l’apport énergétique quotidien consommé au pays en 2015 provenait d’aliments ultratransformés. Les enfants étaient d’ailleurs les plus grands consommateurs.

Quand les bons aliments disparaissent de nos assiettes

Les aliments ultra-transformés sont généralement pauvres en fibres et en micronutriments, tout en étant riches en sucre, en sel et en graisses malsaines. Lorsque ces aliments dominent notre assiette, les aliments complets naturellement riches en fibres sont évincés.

Des études montrent que plus la consommation d’aliments ultra-transformés augmente, plus la consommation de fibres diminue, ainsi que celle d’autres nutriments essentiels. Il en résulte une population qui est loin d’atteindre son objectif quotidien en matière de fibres.

Les fibres alimentaires sont essentielles à une bonne santé dans le cadre d’une alimentation équilibrée. On les trouve principalement dans les aliments d’origine végétale.

Ajouter des aliments riches en fibres à vos repas et collations tout au long d’une journée type, par exemple en optant pour du pain complet au petit-déjeuner, en conservant la peau des fruits comme les pommes, en ajoutant des lentilles et des oignons à un chili pour le dîner et en mangeant une poignée de graines de citrouille ou de noix du Brésil entre les repas, aiderait une personne moyenne à atteindre ses besoins quotidiens de 30 g.

Consommer trop de fibres

Avec le fibremaxxing, ce qui pourrait rendre cette tendance quelque peu dangereuse, c’est le fait de supprimer d’autres groupes d’aliments tels que les protéines, les glucides et les lipides et de les remplacer par des aliments riches en fibres, des compléments alimentaires ou des poudres.

C’est là que le risque potentiel pourrait atténuer les avantages d’une augmentation de la consommation de fibres, car, à ma connaissance, aucune étude solide n’a été menée chez l’homme sur la consommation à long terme de plus de 40 g de fibres par jour. (Certains partisans du « fibremaxxing » recommandent de consommer entre 50 et 100 g par jour.)


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Consommer trop de fibres trop rapidement, surtout sans boire suffisamment d’eau, peut entraîner des ballonnements, des crampes et de la constipation. Cela peut également provoquer une accumulation de gaz qui peut aussi entraîner des flatulences au mauvais moment, comme pendant les trajets quotidiens.

Des passagers regardent avec suspicion quelqu’un hors champ
Quelqu’un a fait du fibremaxxing.
William Perugini/Shutterstock

Une augmentation rapide de la consommation de fibres ou une consommation excessive peut interférer avec l’absorption de micronutriments essentiels tels que le fer, qui soutient le fonctionnement normal de l’organisme, ainsi que des macronutriments, qui fournissent l’énergie nécessaire au mouvement, à la réparation et à l’adaptation.

Pas que des inconvénients

Cependant, il est important de se rappeler que l’augmentation de la quantité de fibres dans votre alimentation offre de nombreux avantages pour la santé. Elles favorisent un système digestif sain en stimulant le transit intestinal et en réduisant l’apparition de maladies inflammatoires de l’intestin.

Les fibres solubles aident à réguler la glycémie en ralentissant l’absorption du glucose, ce qui les rend particulièrement utiles pour les personnes à risque de diabète de type 2. Elles réduisent également le taux de cholestérol LDL (mauvais cholestérol), ce qui diminue le risque de maladies cardiaques. Les fibres procurent une sensation de satiété plus longue, ce qui favorise une gestion saine du poids et la régulation de l’appétit. Ces résultats sont tous bien documentés.

De plus, une alimentation riche en fibres a été associée à un risque moindre de certains cancers, en particulier le cancer du côlon, car elle aide à éliminer efficacement les toxines de l’organisme. Augmenter progressivement votre consommation de fibres jusqu’à atteindre les niveaux recommandés, grâce à une alimentation équilibrée et variée, peut avoir de réels bienfaits pour la santé.

Au vu des preuves, il est clair que beaucoup d’entre nous pourraient tirer profit d’une consommation plus importante de fibres, mais dans la limite du raisonnable.

En attendant d’en savoir plus, il est plus prudent de respecter les recommandations actuelles en matière de consommation de fibres et de les consommer sous forme naturelle plutôt que sous forme de poudres ou de compléments alimentaires. Les fibres sont essentielles, mais il ne faut pas nécessairement en consommer davantage.

Ignorez les modes sur les réseaux sociaux et privilégiez l’équilibre : céréales complètes, légumes, noix et graines. Votre intestin – et vos compagnons de trajet – vous en remercieront.

La Conversation Canada

Lewis Mattin est affilié à la Physiological Society, à la Society for Endocrinology, à In2Science et au réseau Ageing and Nutrient Sensing Network financé par l’UKRI.

ref. Le « fibremaxxing » est à la mode. Voici pourquoi cela pourrait poser problème – https://theconversation.com/le-fibremaxxing-est-a-la-mode-voici-pourquoi-cela-pourrait-poser-probleme-262282

EPA removal of vehicle emissions limits won’t stop the shift to electric vehicles, but will make it harder, slower and more expensive

Source: The Conversation – USA (2) – By Alan Jenn, Associate Professor of Civil and Environmental Engineering, University of California, Davis

Customers have embraced electric vehicles; policy changes may decrease that interest but will not eliminate it. Carlin Stiehl/Los Angeles Times via Getty Images

The U.S. government is in full retreat from its efforts to make vehicles more fuel-efficient, which it has been waging, along with state governments, since the 1970s.

The latest move came on July 29, 2025, when the Environmental Protection Agency said it planned to rescind its landmark 2009 decision, known as the “endangerment finding,” that greenhouse gases pose a threat to public health and welfare. If that stands up in court and is not overruled by Congress, it would undo a key part of the long-standing effort to limit greenhouse gas emissions from vehicles.

As a scholar of how vehicle emissions contribute to climate change, I know that the science behind the endangerment finding hasn’t changed. If anything, the evidence has grown that greenhouse gas emissions are warming the planet and threatening people’s health and safety. Heat waves, flooding, sea-level rise and wildfires have only worsened in the decade and a half since the EPA’s ruling.

Regulations over the years have cut emissions from power generation, leaving transportation as the largest source of greenhouse gas emissions in the U.S.

The scientific community agrees that vehicle emissions are harmful and should be regulated. The public also agrees, and has indicated strong preferences for cars that pollute less, including both more efficient gas-burning vehicles and electric-powered ones. Consumers have also been drawn to electric vehicles thanks to other benefits such as performance, operation cost and innovative technologies.

That is why I believe the EPA’s move will not stop the public and commercial transition to electric vehicles, but it will make that shift harder, slower and more expensive for everyone.

A multilane highway is packed with cars and trucks.
Transportation is the largest source of greenhouse gas emissions in the U.S.
Brandon Bell/Getty Images

Putting carmakers in a bind

The most recent EPA rule about vehicle emissions was finalized in 2024. It set emissions limits that can realistically only be met by a large-scale shift to electric vehicles.

Over the past decade and a half, automakers have been building up their capability to produce electric vehicles to meet these fleet requirements, and a combination of regulations such as California’s zero-emission-vehicle requirements have worked together to ensure customers can get their hands on EVs. The zero-emission-vehicle rules require automakers to produce EVs for the California market, which in turn make it easier for the companies to meet their efficiency and emissions targets from the federal government. These collectively pressure automakers to provide a steady supply of electric vehicles to consumers.

The new EPA move would undo the 2024 EPA vehicle-emissions rule and other federal regulations that also limit emissions from vehicles, such as the heavy-duty vehicle emissions rule.

The possibility of a regulatory reversal puts automakers into a state of uncertainty. Legal challenges to the EPA’s shift are all but guaranteed, and the court process could take years.

For companies making decade-long investment decisions, regulatory stability matters more than short-term politics. Disrupting that stability undermines business planning, erodes investor confidence and sends conflicting signals to consumers and suppliers alike.

An aerial view shows a very large building with an even larger parking lot outside, filled with cars.
Car manufacturers in the U.S. have invested large sums of money to produce electric vehicles.
Elijah Nouvelage/Getty Images

A slower roll

The Trump administration has taken other steps to make electric vehicles less attractive to carmakers and consumers.

The White House has already suspended key provisions of the Inflation Reduction Act that provided tax credits for purchasing EVs and halted a US$5 billion investment in a nationwide network of charging stations. And Congress has retracted the federal waiver that allowed California to set its own, stricter emissions limits. In combination, these policies make it hard to buy and drive electric vehicles: Fewer, or no, financial incentives for consumers make the purchases more expensive, and fewer charging stations make travel planning more challenging.

Overturning the EPA’s 2009 endangerment finding would remove the legal basis for regulating climate pollution from vehicles altogether.

But U.S. consumer interest in electric vehicles has been growing, and automakers have already made massive investments to produce electric vehicles and their associated components in the U.S. – such as Hyundai’s EV factory in Georgia and Volkswagen’s Battery Engineering Lab in Tennessee.

Global markets, especially in Europe and China, are also moving decisively toward electrifying large proportions of the vehicles on the road. This move is helped in no small part due to aggressive regulation by their respective governments. The results speak for themselves: Sales of EVs in both the European Union and China have been growing rapidly.

But the pace of change matters. A slower rollout of clean vehicles means more cumulative emissions, more climate damage and more harm to public health.

The EPA’s proposal seeks to slow the shift to electric vehicles, removing incentives and raising costs – even though the market has shown that cleaner vehicles are viable, the public has shown interest, and the science has never been clearer. But even such a major policy change can’t stop the momentum of those trends.

The Conversation

Alan Jenn does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. EPA removal of vehicle emissions limits won’t stop the shift to electric vehicles, but will make it harder, slower and more expensive – https://theconversation.com/epa-removal-of-vehicle-emissions-limits-wont-stop-the-shift-to-electric-vehicles-but-will-make-it-harder-slower-and-more-expensive-262384

When it comes to finance, ‘normal’ data is actually pretty weird

Source: The Conversation – USA (2) – By D. Brian Blank, Associate Professor of Finance, Mississippi State University

When business researchers analyze data, they often rely on assumptions to help make sense of what they find. But like anyone else, they can run into a whole lot of trouble if those assumptions turn out to be wrong – which may happen more often than they realize. That’s what we found in a recent study looking at financial data from about a thousand major U.S. companies.

One of the most common assumptions in data analysis is that the numbers will follow a normal distribution – a central concept in statistics often known as the bell curve. If you’ve ever looked at a chart of people’s heights, you’ve seen this curve: Most people cluster near the middle, with fewer at the extremes. It’s symmetrical and predictable, and it’s often taken for granted in research.

A one-minute introduction to the concept of the bell curve.

But what happens when real-world data doesn’t follow that neat curve?

We are professors who study business, and in our new study we looked at financial data from public U.S. companies – things like firm market value, market share, total assets and similar financial measures and ratios. Researchers often analyze this kind of data to understand how companies work and make decisions.

We found that these numbers often don’t follow the bell curve. In some cases, we found extreme outliers, such as a few large firms being thousands of times the size of other smaller firms. We also observe distributions that are “right-skewed,” which means that the data is bunched up on the left side of the chart. In other words, the values are on the lower end, but there are a few really high numbers that stretch the average upward. This makes sense, because in many cases financial metrics can only be positive – you won’t find a company with a negative number of employees, for example.

Why it matters

If business researchers rely on flawed assumptions, their conclusions – about what drives company value, for example – could be wrong. These mistakes can ripple outward, influencing business decisions, investor strategies or even public policy.

Take stock returns, for example. If a study assumes those returns are normally distributed, but they’re actually skewed or full of outliers, the results might be distorted. Investors hoping to use that research might be misled.

Researchers know their work has real-life consequences, which is why they often spend years refining a study, gathering feedback and revising the article before it’s peer-reviewed and prepared for publication. But if they fail to check whether data is normally distributed, they may miss a serious flaw. This can undermine even otherwise well-designed studies.

In light of this, we’d encourage researchers to ask themselves: Do I understand the statistical methods I’m using? Am I checking my assumptions – or just assuming they’re fine?

What still isn’t known

Despite the importance of data assumptions, many studies fail to report tests for normality. As a result, it’s unclear how many findings in finance and accounting research rest on shaky statistical grounds. We need more work to understand how common these problems are, and to encourage best practices in testing and correcting for them.

While not every researcher needs to be a statistician, everyone using data would be wise to ask: How normal is it, anyway?

The Conversation

The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.

ref. When it comes to finance, ‘normal’ data is actually pretty weird – https://theconversation.com/when-it-comes-to-finance-normal-data-is-actually-pretty-weird-259365

Why leisure matters for a good life, according to Aristotle

Source: The Conversation – USA (3) – By Ross Channing Reed, Lecturer in Philosophy, Missouri University of Science and Technology

What we do in our free time says a lot about what makes us happy. Halfpoint Images/Moment via Getty Images

In his powerful book “The Burnout Society,” South Korean philosopher Byung-Chul Han argues that in modern society, individuals have an imperative to achieve. Han calls this an “achievement society” in which we must become “entrepreneurs” – branding and selling ourselves; there is no time off the clock.

In such a society, even leisure risks becoming another kind of work. Rather than providing rest and meaning, leisure is often competitive, performative and exhausting.

People feeling pressure to self-promote, for example, might spend their free time posting photos of an athletic race or an elaborate vacation on social media
to be viewed by family, friends and potential employers, adding to exhaustion and burnout.

As a philosopher and philosophical counselor, I study connections between unhealthy forms of leisure and burnout. I have found that philosophy can help us navigate some of the pitfalls of leisure in an achievement society. The celebrated Greek philosopher Aristotle, who lived from 384 to 322 B.C.E., in particular, can offer important insights.

Aristotle on self-development

Aristotle begins the famous “Nicomachean Ethics” by pointing out that we are all searching for happiness. But, he says, we are often confused about how to get there.

A man running outdoors on a paved pathway surrounded by palm trees and buildings.
Exercise needs to be done in moderation to achieve health goals.
AzmanL/E+ via Getty images

Aristotle believed that pleasure, wealth, honor and power will not ultimately make us happy. True happiness, he said, required ethical self-development: “Human good turns out to be activity of soul in accordance with virtue.”

In other words, if we want to be happy, Aristotle contended, we must make reasoned choices to develop habits that, over time, become character traits such as courage, temperance, generosity and truthfulness.

Aristotle is explicitly linking the good life to becoming a certain kind of person. There is no shortcut to ethical self-development. It takes time – time off the clock, time not engaged in some kind of entrepreneurial self-promotion.

Aristotle is also telling us about the power of our choices. Habits, he argues, are not just about action, but also motives and character. Our actions, he says, actually change our desires. Aristotle says: “By abstaining from pleasures we become temperate, and it is when we have become so that we are most able to abstain from them.”

In other words, good habits are the result of moving incrementally in the right direction through practice.

For Aristotle, good habits lead to ethical self-development. The converse is also true. To this end, for Aristotle, having good friends and mentors who guide and support moral development are essential.

How Aristotle helps us understand leisure

In an achievement society, we are often conditioned to respond to external pressures to self-promote. We may instead look to pleasure, wealth, honor and power for happiness. This can sidetrack the ethical development required for true happiness.

True leisure – leisure that is not bound to the imperative to achieve – is time we can reflect on our real priorities, cultivate friendships, think for ourselves, and step back and decide what kind of life we want to live.

The Greek word “eudaimonia,” often translated simply as happiness, is the term Aristotle uses to describe human thriving and flourishing. According to philosopher Jane Hurly, Aristotle views “leisure as essential for human thriving.” Indeed, “for both Plato and Aristotle leisure … is a prerequisite for the achievement of the highest form of human flourishing, eudaimonia,” as philosopher Thanassis Samaras argues.

While we may have limited means to acquire pleasure, wealth, honor and power, Aristotle tells us that we have control over the most important variable in the good life: what kind of person we will become. Leisure is crucial because it is time in which we get to decide what kind of habits we will develop and what kind of person we will become. Will we capitulate to achievement society? Or utilize our free time to develop ourselves as individuals?

When leisure is preoccupied with entrepreneurial self-promotion, it is difficult for moral development to take place. Free time that is not hijacked by the imperative to achieve is required for the development of a consistent relationship to oneself – what I call a relationship of self-solidarity – a kind of reflective self-awareness necessary to aim at the right target and make moral choices. Without such a relationship, the good life will remain elusive.

Leisure reimagined

Rather than adopting the achievement society’s formulation of the good life, we may be able to formulate our own vision. Without one’s own vision, we risk becoming mired in bad habits, leading us away from the moral development through which the good life becomes possible.

Aristotle makes it clear that we have the power to change not only our behaviors but our desires and character. This self-development, as Aristotle writes, is a necessary part of the good life – a life of eudaimonia.

The choices we make in our free time can move us closer to eudaimonia. Or they could move us in the direction of burnout.

The Conversation

Ross Channing Reed does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. Why leisure matters for a good life, according to Aristotle – https://theconversation.com/why-leisure-matters-for-a-good-life-according-to-aristotle-260392

Football and faith could return to the Supreme Court – this time, over loudspeakers

Source: The Conversation – USA (3) – By Charles J. Russo, Joseph Panzer Chair in Education and Research Professor of Law, University of Dayton

Private schools want to pray over the loudspeaker – at a public facility, during games run by a state association. John Coletti/Photodisc via Getty Images

With the start of another high school football season around the corner, a long-simmering dispute has heated up: prayers at games.

Kennedy v. Bremerton, the case of a high school football coach praying on the field after games, has been in the spotlight since the Supreme Court’s 2022 ruling. But another football controversy first emerged in 2015, when two Christian schools in Florida made it to the state championships. The games were run by the state’s high school athletic association, a government body.

Association officials barred the teams from conducting a joint prayer over the loudspeaker at the public stadium before kickoff. Allowing a prayer, they said, would violate federal and constitutional law. The First Amendment’s establishment clause forbids the government from establishing an official religion, from giving preference to a specific religion and from giving favor to or disfavoring religion in general.

Officials at one of the schools, Cambridge Christian, filed suit, arguing that banning the prayer violated its right to free speech and to the free exercise of religion. Lower courts entered orders in the association’s favor, but attorneys for the school petitioned the Supreme Court to hear the case.

As a faculty member who teaches and researches law relating to religion and education, I believe the justices are likely to take the case – and that its outcome could be consequential. I say this because the Supreme Court’s recent record in First Amendment cases has been more friendly to religious plaintiffs than ever in its history.

A police officer with his back to the camera stands outside the Supreme Court.
The Supreme Court is expected to announce this fall whether it will hear Cambridge Christian’s case.
AP Photo/Mariam Zuhaib

Government speech

Following multiple rounds of litigation, Cambridge Christian School v. Florida High School Athletic Association reached a federal appeals court in September 2024. The 11th Circuit unanimously affirmed an order upholding the association’s policy not to allow prayer over the public address system.

The 11th Circuit based its findings in its view that prayer would be a form of “government speech”: that it would be perceived as representing the state association, not just the Christian schools. While the First Amendment limits the government’s ability to regulate private speech, the government is free to regulate its own speech.

Therefore, the court held that association officials did not violate the school’s right to free speech or free exercise of religion.

In part, the 11th Circuit relied on a similar Supreme Court case from 2000, which also examined prayer at a high school football game: Santa Fe Independent School District v. Doe.

In the Santa Fe ruling, the justices invalidated a board’s policy of allowing prayer over the public-address system “by a speaker representing the student body, under the supervision of school faculty.” Such a policy violated the First Amendment’s establishment clause, they determined, because “an objective Santa Fe High School student will unquestionably perceive the inevitable pregame prayer as stamped with her school’s seal of approval.”

Endorsement test

According to reasoning known as the “endorsement test,” a message violates the establishment clause if someone listening would reasonably assume that the government is endorsing religion. This test originated in Lynch v. Donnelly, a 1984 dispute over a public Christmas display in a Rhode Island park owned by a nonprofit.

Recently, however, the Supreme Court explicitly rejected the endorsement test – potentially strengthening Cambridge Christian’s case. The court rejected it and a similar set of criteria, called the “Lemon test,” in another football-related case, 2022’s Kennedy v. Bremerton School District.

The majority opinion upheld the right of a football coach in a public high school, Joseph Kennedy, to pray silently on the field at the end of games. The justices explained that the establishment clause does not “require the government to single out private religious speech for special disfavor,” adding that the court “long ago abandoned Lemon and its endorsement test offshoot.”

A man with silver hair who is wearing a short-sleeved blue polo stands before microphones, as a half-dozen people stand around him.
Former assistant football coach Joseph Kennedy after his case, Kennedy vs. Bremerton School District, was argued before the Supreme Court on April 25, 2022.
Win McNamee/Getty Images

The Lemon test“ was the standard the Supreme Court had used since 1971 to evaluate interactions between the government and religion. Under Lemon, there were three key criteria for whether a law or government speech violated the establishment clause. To be permitted, a governmental action must have a secular purpose, and its main effect cannot either advance or inhibit religion. Lastly, the action “must not foster ‘an excessive government entanglement with religion.‘”

In Bremerton, repudiating Lemon, the justices declared that courts should instead assess establishment clause claims based on “historical practices and understandings.”

If the Supreme Court agrees to hear Cambridge Christian’s appeal, the justices will face two issues. The first is whether communal prayer over a loudspeaker before a state athletic association game is indeed government speech – especially because officials permitted a wide array of nonreligious private speech over the loudspeaker. The second issue is whether the endorsement factor of the government-speech doctrine revives the endorsement test.

Recent record

If the justices agree to hear Cambridge Christian, it must be viewed against the court’s recent history in disputes over religion. The majority has often been friendly toward religious plaintiffs in cases under both religion clauses of the Constitution: establishment and free exercise.

In recent years, for example, the justices allowed aid to faith-based school students, found that a board could not prevent Kennedy from praying silently on the field after games, and granted employees time off to worship.

Two important issues remain to be seen: first, whether the justices will continue expanding the boundaries of religious freedom; and second, whether Cambridge Christian will generate such a result.

Regardless of how the Supreme Court rules – and whether it does rule – Florida has already adopted a law requiring athletic associations to allow participating high schools “to make brief opening remarks, if requested … using the public address system at the event.”

Come fall 2025, the Supreme Court will decide whether to hear the case. If so, its judgment may clarify whether private speech using public PA systems becomes governmental speech. Because the 11th Circuit relied on the endorsement test that the Supreme Court expressly repudiated, it seems likely that the justices will hear the appeal and rule in Cambridge Christian’s favor.

If the court does agree to review Cambridge Christian, it may well expand the parameters of religious expression in public – not just at football games.

The Conversation

Charles J. Russo does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. Football and faith could return to the Supreme Court – this time, over loudspeakers – https://theconversation.com/football-and-faith-could-return-to-the-supreme-court-this-time-over-loudspeakers-262104

Des primes d’assurance personnalisées moins chères grâce à l’IA ? Voici pourquoi il s’agit d’une pente glissante

Source: The Conversation – in French – By Arthur Charpentier, Professeur, Université de Rennes 1 – Université de Rennes

L’assurance repose sur un principe de solidarité que mettent à mal les algorithmes chargés de constituer nos profils. À mesure en effet que les algorithmes se précisent, la facture se personnalise. Divers profils « à risque » peuvent ainsi se retrouver exclus des régimes d’assurance, tant les coûts sont élevés. La personnalisation a une légitimité évidente. On doit toutefois lui concilier un accès équitable à l’assurance.

Il faut d’abord savoir que l’assurance est traversée par un paradoxe fondamental. D’un côté, ses principes mêmes supposent un mécanisme collectif où chacun contribue selon sa capacité, et tire profit de la solidarité en cas de sinistre. De l’autre, les avancées technologiques, les données de plus en plus massives et les méthodes actuarielles de plus en plus précises poussent à individualiser toujours davantage les tarifs.

À cette tension s’ajoute un cadre légal de plus en plus exigeant, qui interdit toute forme de discrimination fondée sur des données sensibles, parfois corrélées à des facteurs de risque pourtant pertinents.

Professeur de mathématiques à l’Université du Québec à Montréal (UQAM), je suis co-auteur du Manuel d’Assurance et auteur récent de l’ouvrage Insurance, Biases, Discrimination and Fairness. Cet article revient sur la difficulté de concilier la mutualisation solidaire, qui fonde l’assurance, avec l’hypersegmentation tarifaire rendue possible par les mégadonnées, sans exclure ni discriminer les assurés.


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La segmentation tarifaire

Les compagnies d’assurance utilisent depuis longtemps la classification comme pilier de leur modèle économique : âge, sexe, profession, zone géographique, historique de sinistralité…

En 1662, le statisticien anglais John Graunt publie les Bills of Mortality, une première analyse statistique des registres de décès de Londres. En 1693, l’astronome anglais Edmund Halley élabore la première table de mortalité chiffrée, qui permet de calculer l’espérance de vie à chaque âge. Ces travaux posent les bases d’une tarification différenciée selon l’âge et le sexe, longtemps restés les deux grands critères de segmentation en vie-décès.

À la même époque, après le Grand Incendie de Londres en 1666, les premiers contrats d’assurance incendie apparaissent : les compagnies collectent des données sur la nature des matériaux de construction et la densité urbaine. Aux XVIIIe–XIXe siècles, on segmente les tarifs selon la proximité des bâtiments voisins et la présence de services de lutte contre l’incendie, donnant naissance aux premières « zones à haut risque » et « zones à faible risque ».

Avec l’essor de l’automobile dans les années 1910–1920, les assureurs américains commencent à relever systématiquement le nombre de sinistres, l’âge et le sexe des conducteurs. Dès les années 1920, on distingue plusieurs « classes » tarifaires : jeunes conducteurs, conductrices, conducteurs expérimentés, permettant de fixer des primes variables en fonction du profil.

Aujourd’hui, les actuaires disposent d’algorithmes sophistiqués, d’outils de machine learning et d’une avalanche de données : télématique embarquée, objets connectés, géolocalisation, comportement de conduite ou de vie… Pour l’assureur, affiner la segmentation lui permet de facturer chaque assuré « à son vrai niveau de risque », en réduisant les effets de subvention croisée des bons risques vers les mauvais, tout en améliorant la rentabilité globale.

Mais une tarification trop fine réduit la mutualisation ; elle peut rendre l’assurance très coûteuse, voire inaccessible pour certains segments à haut risque. Aussi, aujourd’hui, l’actuaire cherche un équilibre subtil, visant à capter les bonnes informations pour différencier les profils, tout en préservant la viabilité de la communauté assurée.

Les assurés et l’illusion de la personnalisation gagnante

En Europe, la proposition législative FIDA (Financial Data Access Framework) ouvrirait aux assureurs un accès encadré aux données financières des particuliers. Son but est d’affiner la connaissance des comportements de dépense et de remboursement. Dans ce contexte, la promesse d’une tarification ultra-personnalisée suscite autant d’espoirs de baisse de primes que de craintes de profilage excessif, et d’exclusions importantes.

Face à ce nouvel afflux de données, de nombreux clients perçoivent la personnalisation comme une approche gagnant‑gagnant : si je gère mieux mon budget, je bénéficierai d’une ristourne ; si mes habitudes d’épargne et de remboursement sont jugées vertueuses, ma prime santé diminuera ; si mon profil financier se bonifie, mon assurance habitation se fera plus légère.

Cette logique de « pay‑as‑you‑live » ou « pay‑how‑you‑drive » séduit : l’individu se pense maître de son coût d’assurance par ses choix de vie.

Pourtant, plusieurs points méritent d’être soulignés.

  • Le principe de mutualisation n’est pas neutralisé : ceux qui ne peuvent pas adopter les comportements les plus vertueux restent dépendants de la solidarité des autres. En effet, même si les personnes les plus à risque paient davantage à titre individuel, celles qui sont moins à risque continuent néanmoins de supporter une part des coûts grâce au principe de mutualisation.

  • L’asymétrie d’information se renforce, l’assureur connaissant mieux les statistiques que le client. L’offre de personnalisation s’appuie en effet souvent sur des corrélations, parfois ténues, dont le client ignore la portée.

  • Une personnalisation très fine peut contraindre les plus à risque à se surassurer, ou au contraire à renoncer à s’assurer, fragilisant la mutualité.

Ainsi, même renforcée par l’accès aux données financières, la « personnalisation » n’est pas nécessairement synonyme d’ « empowerment » pour le consommateur.

Le cadre légal : quand la lutte contre la discrimination s’impose

Le développement des données massives en assurance soulève d’importantes questions éthiques et juridiques : jusqu’où peut‑on exploiter des variables sensibles pour prédire le risque ?




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En France et dans l’Union européenne, la législation interdit explicitement la discrimination fondée sur des critères protégés : origine ethnique, genre, orientation sexuelle, handicap, convictions religieuses, etc. La Directive Solvabilité II (UE) impose aux assureurs d’utiliser des modèles de risque « transparents » et non discriminatoires.

Contrairement à l’Union européenne – qui bannit la tarification différenciée selon des critères protégés (genre, origine, handicap) –, le modèle québécois offre un cadre encore permissif. Si la Charte des droits et libertés de la personne du Québec interdit également la discrimination, elle prévoit des exemptions propres aux assureurs : ceux-ci peuvent, lorsqu’un facteur est statistiquement pertinent, fonder la tarification sur l’âge, le sexe ou l’état civil.

Cet usage, autorisé sur la seule base d’une corrélation, soulève des questions.

Éthique et responsabilité sociale des assureurs

Au‑delà de la seule conformité juridique, les assureurs sont de plus en plus jugés sur leurs pratiques éthiques et leur responsabilité sociale par des associations de consommateurs et les médias, qui relaient les incidents de discrimination algorithmique et exercent une pression de réputation.

Depuis quelques années, les assureurs doivent donc se demander, collectivement, comment garantir un accès équitable à leurs produits pour les populations vulnérables, sans sacrifier la viabilité financière de leurs portefeuilles. Certains modèles novateurs proposent des formules « solidaires » ou des tarifs plafonnés pour éviter l’exclusion.

Les assureurs se voient imposer sans cesse plus de transparence. Ils doivent expliquer de façon claire les critères tarifaires, rendre accessibles les clefs de calcul pour éviter le sentiment d’arbitraire. Enfin, ils doivent intégrer la protection des données et la vie privée dès la conception des offres ( « privacy by design »), préserver la confiance.

Les assureurs qui sauront concilier personnalisation, équité et inclusion deviendront les acteurs de référence pour les clients soucieux d’éthique.

Réconcilier solidarité et données : un défi crucial

Le défi, on le voit, est de taille.

Il s’agit ni plus ni moins de réconcilier la finesse actuarielle avec les valeurs de redistribution et de solidarité qui ont fondé le métier d’assureur.

C’est dans cette tension résolue que se jouera l’avenir de l’assurance : ni pure discrimination tarifaire ni simple personnalisation illusoire, elle les conjuguera plutôt en un équilibre permettant à chacun de contribuer selon son risque et de bénéficier à sa juste mesure de la mutualisation des aléas de la vie.

La Conversation Canada

Arthur Charpentier est membre (fellow) de l’Institut Louis Bachelier. Il a reçu des financements du CRSNG (NSERC) de 2019 à 2025, du Fond AXA Pour la Recherche de 2020 à 2022, puis de la Fondation SCOR pour la Science de 2023 à 2026.

ref. Des primes d’assurance personnalisées moins chères grâce à l’IA ? Voici pourquoi il s’agit d’une pente glissante – https://theconversation.com/des-primes-dassurance-personnalisees-moins-cheres-grace-a-lia-voici-pourquoi-il-sagit-dune-pente-glissante-259861