The neutrino is a notorious troublemaker in the world of particle physics. This tiny, elusive particle with no electric charge likely permeates every corner of the universe, but you’d be hard-pressed to know that without extremely specialized instruments. Trillions pass through you every second, in fact, all without interacting with a single atom of your body. That is but one of the reasons why, for something so supposedly abundant and fundamental, we know painfully little about the neutrino—not even something so basic as its mass.

But neutrino physics might be on the verge of an experimental breakthrough: physicists with the Karlsruhe Tritium Neutrino (KATRIN) experiment in Germany have succeeded in measuring the upper limit of the neutrino’s mass to a mere 0.45 electron volts (eV), which is less than one millionth of the mass of an electron. These results, published last week in Science, represent just a fraction of KATRIN’s investigations; about three quarters of the detector’s planned data haul from its ongoing 1,000-day campaign remains to be analyzed and revealed.

Another reason for excitement is that KATRIN has achieved a twofold increase in sensitivity from just last year, when some researchers raised questions as to whether the experiment would even be able to make progress on physicists’ decades-long quest to gauge the neutrino’s mass. And the KATRIN team intends to push the detector even further, says Alexey Lokhov, a co-author of the new study and an experimental physicist at Karlsruhe Institute of Technology in Germany. By the conclusion…

Get the Popular Science daily newsletter

Last week, I got my belt loop hooked on a cabinet handle and accidentally yanked the door clean off the hinges. While mishaps like that can be annoying, they can also be an opportunity to get a new power tool to facilitate your home improvement project. Right now, Home Depot is throwing its Spring Black Friday sale, and just about every Ryobi power tool in existence is on sale. To sweeten the deal, Ryobi batteries are discounted to a ridiculous extent, so now is the time to stock up your garage with a whole new rack of power tools and all the batteries you need to keep them running. Here are some of our favorite tool deals from the sale.

ONE+ HP 18V 20 in. Self-Propelled Lawn Mower w/ (2) 6.0 Ah Batteries — $399 WITH FREE TOOL (was $429)

See it

That discount may not look steep, but in addition to the $30 off the regular price, this mower also comes with a free tool worth between $69 and $79. You can choose the ONE+ 18V 90 MPH 250 CFM Cordless Battery Leaf Blower, 150-Watt Push Start Power Source and Charger for ONE+ 18-Volt Battery, ONE+ 18V 13 in. Cordless Battery String Trimmer, or ONE+ 18V 18 in. Cordless Battery Hedge Trimmer (Tool Only). Just make sure to add the free item to your cart in addition to the mower before checkout.

The mower itself is a 20-inch wide self-propelled model that includes a pair of burly 6 Ah batteries as well as a charger. It’s ideal for roughly a half-acre of land. It offers seven different heights for optimal mowing on your grass, and it’s very easy to store.

ONE+ 18V Lithium-Ion Kit with 2.0 Ah and…

biology: The study of living things. The scientists who study them are known as biologists. 

biomedical: Having to do with medicine and how it interacts with cells or tissues. 

biomedical engineer: An expert who uses science and math to find solutions to problems in biology and medicine; for example, they might create medical devices such as artificial knees. 

biomedical engineering: Combining engineering and biology to aid human health. Professions in this field develop artificial limbs, use biotechnology to produce new drugs and develop models to understand how diseases work. 

blood vessel: A tubular structure that carries blood through the tissues and organs. 

cell: (in biology) The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.  

code: (in computing) To use special language to write or revise a program that makes a computer do something. (n.) Code also refers to each of the particular parts of that programming that instructs a computer’s operations. 

coding: (in computing) A slang term for developing computer programming — or software — that performs a particular, desired computational task. 

cyst: A group of cells that form a type of bubble-like shell or sac. Some cysts develop as a result of disease or tissue damage. Others may develop as a​​ normal, protective feature during certain phases of a parasite’s maturation. 

electronics: Devices that are powered by electricity but whose properties are controlled by the semiconductors or other circuitry that channel or gate the movement of electric charges. 

engineering: The field of research that uses math and science to solve practical problems. Someone…

The artificial intelligence (AI) race is heating up: the number and quality of high-performing Chinese AI models is rising to challenge the US lead, and the performance edge between top models is shrinking, according to an annual state of the industry report.

The report highlights that as AI continues to improve quickly, no one firm is pulling ahead. On the Chatbot Arena Leaderboard, which asks users to vote on the performance of various bots, the top-ranked model scored about 12% higher than the tenth-ranked model in early 2024, but only 5% higher in early 2025 (see ‘All together now’). “The frontier is increasingly competitive — and increasingly crowded,” the report says.

The Artificial Intelligence Index Report 2025 was released today by the Institute for Human Centered AI at Stanford University in California.

---

On supporting science journalism

If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

---

The index shows that notable generative AI models are, on average, still getting bigger, by using more decision-making variables, more computing power and bigger training data sets. But developers are also proving that smaller, sleeker models are capable of great things. Thanks to better algorithms, a modern model can now match the performance that could be achieved by a model 100 times larger two years ago. “2024 was a breakthrough year for smaller AI models,” the index says.

Bart Selman, a computer scientist at Cornell University in…

Science is helping researchers judge books by their covers — and revealing surprising beneficiaries of medieval trading routes in the process.

Dozens of rare, fur-covered volumes from 12th and 13th century French monasteries are wrapped with seal skins that may have come from as far away as Greenland, researchers report April 9 in Royal Society Open Science. The findings challenge the assumption that the books’ makers used only locally sourced materials and suggest that they were part of an extensive trade network.

adolescent: Someone in that transitional stage of physical and psychological development that begins at the onset of puberty, typically between the ages of 11 and 13, and ends with adulthood.

anxiety: A nervous reaction to events causing excessive uneasiness and apprehension. People with anxiety may even develop panic attacks.

brain scan: A technique to view structures inside the brain, typically with X-rays or a magnetic resonance imaging (or MRI) machine. With MRI technology — especially the type known as functional MRI (or fMRI) — the activity of different brain regions can be viewed during an event, such as viewing pictures, computing sums or listening to music.

cisgender: Someone whose gender identity matches that of the sex they were assigned at birth. (The Latin prefix cis- means “on the same side.”)

data: Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.

data processing: Putting data into a computer and having the computer store, organize or change it with the aim or extracting useful information from those data.

depression: (in medicine) A mental illness characterized by persistent sadness and apathy. Although these feelings can be triggered by events, such as the death of a loved one or the move to a new city, that isn’t typically considered an “illness” — unless the symptoms are prolonged and harm an individual’s ability to perform normal daily tasks (such as working, sleeping or interacting with others). People suffering from depression often feel they lack the energy needed to get anything done. They may have difficulty concentrating on things or showing an interest in normal events. Many times, these feelings seem to be triggered by nothing; they can appear out of…