Weaker Gravity, Thorium Traps and a Black Hole in a Fibre

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Cold open

0:24Host 1Welcome to the Hastrup Review of Science — where artificial intelligence reads real science, so you don't have to pretend you understood the paper.

0:34Host 1This week's lead: the dark energy signal from the DESI survey may be explained just as well by gravity being eight tenths of a percent weaker on cosmic scales.

0:45Host 2If that holds, the question shifts from what dark energy is doing to whether Newton's constant is the same everywhere. And the next data releases can test it.

A glitch in gravity

0:56Host 1Alicia, what exactly did they fit?

0:59Host 2Wen, Hergt, Afshordi and Scott combined the newest microwave background data from Planck, the Atacama Cosmology Telescope and the South Pole Telescope with DESI's second release of baryon acoustic oscillation distances. Instead of the usual two-parameter evolving dark energy, they added one parameter: the ratio of the gravitational constant that drives cosmic expansion to the one we measure locally. A mismatch like that is a generic low-energy signature of Horava-type gravity theories.

1:29Host 1And the number?

1:30Host 2The ratio comes out at zero point nine nine two, plus or minus zero point zero zero two five. That is cosmological gravity about eight tenths of a percent weaker, a three point three sigma preference, and it holds at three point three sigma when lensing and supernovae are added.

1:48Host 2The sharper test is predictive. Fitted to the microwave background alone, the glitch model predicts the one to two percent downward shift in distances that DESI then measured, while the dark energy model fitted the same way predicts almost nothing.

2:03Host 1Caveats?

2:04Host 2It is an arXiv preprint, and the Bayesian evidence favours the glitch and evolving dark energy equally over the standard model, which the authors say is not a verdict. Adding supernovae weakens the glitch's evidence advantage, and the result depends somewhat on how perturbations are modelled, though it stays at or above two point eight sigma in their tests.

2:26Host 2Why it matters: one parameter that makes two data sets agree is a more falsifiable reading of the DESI anomaly than two parameters that absorb it.

2:36Host 1The full story is in this paper's deep dive, out this week in the feed.

Thorium clock crystals

2:41Host 1From the largest scales to a single nucleus. Thorium two twenty-nine.

2:46Host 2Thorium two twenty-nine has a nuclear excited state at only eight point three six electron volts, low enough to drive with an ultraviolet laser, which makes it the leading candidate for a nuclear clock. Thorium-doped calcium fluoride clocks now run in three laboratories. But the crystal is not a passive holder: radiation frees electrons and holes that can knock the nucleus out of its excited state.

3:11Host 1What did this team measure?

3:13Host 2At a Japanese synchrotron, they recorded how the crystal glows under X-rays, after the beam stops, and while it is heated, from minus one hundred ninety to plus one hundred fifty degrees Celsius. They identified eleven charge traps with depths between zero point one one five and zero point five three five electron volts. One trap, which releases its charge near minus fifty-six degrees, lines up with a previously reported peak in isomer yield near minus sixty degrees.

3:43Host 1So trapped charges shield the nucleus?

3:45Host 2That is the picture: a carrier stuck in a lattice trap is not available to quench the thorium. The caveat is that this matches temperature features rather than measuring trap occupancy directly, the traps are not yet assigned to specific defects, and it is a preprint.

4:03Host 2Why it matters: it gives clock builders operating rules, such as running near one hundred degrees to cut the background glow more than a hundredfold, and annealing the crystal every one to two weeks.

4:15Host 1The deep dive on this one is out this week in the feed.

A black hole in a fibre

4:20Host 1Third physics story: a black hole analogue inside an optical fibre.

4:24Host 2Terrier, Fatome, Kibler and Torres send a sub-picosecond light pulse, a soliton, down five kilometres of fibre. To a weaker probe wave travelling alongside, the soliton behaves like the potential around a black hole, including an analogue of the light ring, the unstable orbit where light can circle the hole.

4:45Host 1What is the signature?

4:47Host 2A light ring rings with a complex frequency: the real part sets the tone, the imaginary part sets how fast it decays. In the probe's spectrum, that appears as a flat plateau whose edges are fixed by the real part, and a fall-off beyond it set by the imaginary part. They saw both, at two pump wavelengths, in agreement with simulations.

5:09Host 1Has this not been done before?

5:11Host 2Earlier work measured only the oscillation, so this is the first observation of both halves of an analogue light-ring resonance. The caveat is that this is classical wave optics with matching mathematics, so it says nothing directly about real black holes. The elegant part: largely off-the-shelf telecom hardware.

5:32Host 2Why it matters: these are the same quasinormal modes that gravitational-wave detectors hear in a merger's ringdown, now measurable on a lab bench.

5:42Host 1The full deep dive is out this week in the feed. First, a word from this week's sponsor.

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Diet and the ageing brain

6:32Host 1Singapore, and thirty years of diet records.

6:36Host 2The Singapore Chinese Health Study recruited sixty-three thousand adults in the nineteen nineties. This analysis follows eight hundred ninety-two of them, with diet scored against the blood-pressure-lowering DASH pattern at ages forty-four to fifty-five and again at sixty-one to seventy-three, then brain scans and cognitive testing at sixty-eight to eighty-two.

6:58Host 1What tracked with what?

7:00Host 2Better diet in midlife and in early old age were each linked to better late-life verbal memory, even with both modelled together. Midlife diet went with more white matter volume, later diet with fewer white matter lesions and less free water in grey matter, a marker of inflammation. Each of those brain measures accounted for about twelve percent of the diet and memory link.

7:24Host 1And people who started badly?

7:26Host 2Those who improved from a low midlife score had better verbal memory than those who stayed low, though still below the consistently high group. Late improvement was not wasted.

7:37Host 1Caveats?

7:38Host 2It is observational and a bioRxiv preprint, so confounding by health, wealth and education remains possible despite adjustment. Only survivors who returned were scanned, the later diet measure was a twenty-one item screener rather than the full questionnaire, and the salt component of DASH was dropped.

7:57Host 2Why it matters: thirty-year diet data paired with brain imaging is rare, and it points to two windows for diet, not one.

8:05Host 1The deep dive is out this week in the feed.

Heat and muscle

8:09Host 1Next, saunas and hot baths.

8:11Host 2Rodrigues and Minett, in the journal Temperature, review forty studies of passive heating: thirty on acute effects and ten on repeated exposure. The core finding is a split. Warming the muscle improves contractile function and rapid force, while raising core temperature can lower maximal voluntary force by reducing drive from the nervous system.

8:32Host 1So for a sprinter: warm muscles, cool core?

8:35Host 2That is a reasonable reading for a warm-up, though the review says the minimum or optimal heat dose is not established. The authors argue cumulative heat load, rather than peak temperature, is the better way to frame it.

8:49Host 1And with repeated exposure?

8:51Host 2Repeated sessions with enough muscle and core heating improved maximal strength, rate of force development and walking performance, mainly in sedentary people, older adults and patients. The evidence is dominated by healthy young men and isometric lab tests, so transfer to trained sprinting is unproven.

9:09Host 2Why it matters: heat is a cheap, drug-free stimulus with a plausible mechanism, and this review maps where the evidence stops.

9:17Host 1The deep dive is out this week in the feed.

Kidneys and energy balance

9:21Host 1Last paper: resisting obesity through the kidneys.

9:24Host 2Cutler and colleagues screened eleven genetically divergent mouse strains on an obesity-inducing diet. One strain stayed lean and insulin sensitive, with little fat building up in liver and muscle, despite eating more calories.

9:39Host 1Where did the energy go?

9:40Host 2Into the urine. These kidneys broadly suppressed the transporters that reclaim filtered nutrients, a natural version of what the gliflozin class of diabetes drugs does for glucose.

9:52Host 1And the cost?

9:53Host 2Caveats: this is one mouse strain, a peer‑reviewed journal article, and we did not have the full text, so we are working from the abstract and will not quote effect sizes.

10:04Host 2Why it matters: it treats nutrient loss through the kidney as a third term in energy balance, alongside intake and expenditure, and shows it carries a trade-off.

10:14Host 1The deep dive is out this week in the feed.

Sign-off

10:18Host 1That was the Hastrup Review of Science.

10:20Host 2Deep dives all week in the feed. Thank you for listening.