Sub-part-per-trillion test of the Standard Model with atomic hydrogen
TL;DR
Scientists made an incredibly precise measurement of light emitted by hydrogen atoms that tested one of physics' most fundamental theories - the Standard Model - to an accuracy of 0.7 parts per trillion. This measurement also resolved a long-standing disagreement about the size of protons by confirming the smaller value found in previous experiments with exotic atoms.
Quantum electrodynamics (QED), the first relativistic quantum field theory, describes light-matter interactions at a fundamental level and is one of the pillars of the Standard Model (SM). Through the extraordinary precision of QED, the SM predicts the energy levels of simple systems such as the hydrogen atom with up to 13 significant digits1, making hydrogen spectroscopy an ideal test bed. The consistency of physical constants extracted from different transitions in hydrogen using QED, such as the proton charge radius rp, constitutes a test of the theory. However, values of rp from recent measurements2-7 of atomic hydrogen are partly discrepant with each other and with a more precise value from spectroscopy of muonic hydrogen8,9. This prevents a test of QED at the level of experimental uncertainties. Here we present a measurement of the 2S-6P transition in atomic hydrogen with sufficient precision to distinguish between the discrepant values of rp and enable rigorous testing of QED and the SM overall. Our result ν2S-6P = 730,690,248,610.79(48) kHz gives a value of rp = 0.8406(15) fm at least 2.5-fold more precise than from other atomic hydrogen determinations and in excellent agreement with the muonic value. The SM prediction of the transition frequency (730,690,248,610.79(23) kHz) is in excellent agreement with our result, testing the SM to 0.7 parts per trillion (ppt) and, specifically, bound-state QED corrections to 0.5 parts per million (ppm), their most precise test so far.
- 1Measured the 2S-6P transition frequency in hydrogen to be 730,690,248,610.79(48) kHz, achieving unprecedented precision
- 2Determined the proton charge radius to be 0.8406(15) fm, which is 2.5 times more precise than previous atomic hydrogen measurements
- 3Confirmed the smaller proton radius value from muonic hydrogen experiments, resolving the 'proton radius puzzle'
- 4Tested the Standard Model to 0.7 parts per trillion accuracy - the most stringent test ever achieved
- 5Validated quantum electrodynamics bound-state corrections to 0.5 parts per million precision
Baby chicks pass the bouba-kiki test challenging a theory of language
Imagine you hear the made-up words "bouba" and "kiki" - which one sounds round and soft, and which sounds sharp and spiky? Most people say "bouba" sounds round and "kiki" sounds sharp. This is called the bouba-kiki effect, and scientists thought it might be special to humans and related to how we developed language. But this study found that baby chickens, just hours after hatching, make the same connections! When they heard "bouba-like" sounds, 80% of the chicks walked toward round, curved shapes rather than spiky ones. This suggests that connecting sounds with shapes isn't learned or uniquely human - it might be a basic way that many animals' brains work, going back hundreds of millions of years in evolution.
Single-minus gluon tree amplitudes are nonzero
Imagine tiny particles called gluons are like spinning tops. Their spin can be in one of two directions, which physicists call 'plus' or 'minus'. For decades, the rulebook seemed to say that you could never have a situation where just one gluon was spinning 'minus' and all the others were spinning 'plus' — that outcome was thought to be zero. This paper found a loophole. Under very specific, purely mathematical conditions that don't exist in our physical reality but are useful for calculations, this interaction can happen. The researchers wrote down the exact recipe for it, fixing a small but important detail in our fundamental rulebook for how the universe works.
Liver exerkine reverses aging- and Alzheimer’s-related memory loss via vasculature
This discovery could lead to new treatments for age-related memory loss and Alzheimer's disease that don't require physical exercise. Instead of just telling people to exercise more, doctors might eventually be able to give patients the specific liver protein (GPLD1) or drugs that block TNAP to achieve the brain benefits of exercise. This is especially important for elderly or disabled people who cannot exercise regularly but still want to protect their memory and cognitive function.
Rock art from at least 67,800 years ago in Sulawesi
Imagine finding a spray-painted handprint on a cave wall. Over thousands of years, a thin, glassy layer of minerals, like limescale in a kettle, grew on top of it. Scientists used a high-tech laser to analyze that mineral layer. By measuring the natural radioactive decay of elements within it, they figured out the layer is about 71,600 years old. Since the handprint is underneath that layer, it must be at least that old, with the most conservative estimate being 67,800 years. This makes it one of the oldest pieces of art ever found and proves that the early humans who lived on this Indonesian island, who had to cross the ocean to get there, were creating symbolic art.