Readers weigh in on the Brazil nut effect, clock entropy and more

Cover of June 5, 2021 issue

How ’bout them nuts?

X-ray CT scans reveal that jostling a box of mixed nuts nudges oblong Brazil nuts to point more vertically, allowing the bulky nuts to rest on top as smaller ones sink to the bottom, Maria Temming reported in “How physics helps Brazil nuts come out on top” (SN: 6/5/21, p. 4).

Reader Charvak Kant asked if this phenomenon, called the Brazil nut effect, applies to objects of all shapes — including spheres whose orientations wouldn’t change.

Shape affects the Brazil nut effect, but exactly how is still unclear, says imaging scientist Parmesh Gajjar of the University of Manchester in England. It is very difficult to experimentally examine mixtures of objects, Gajjar says, but size does strongly influence how particles segregate. Even spheres of different sizes in a mixture will separate. In fact, the very first study to use the phrase “Brazil nut effect,” published in Physical Review Letters in 1987, was done on spherical objects, he says.

Chaotic clocks

As a clock becomes more accurate, it generates more disorder, Emily Conover reported in “Strict timekeeping creates entropy” (SN: 6/5/21, p. 13).

Reader Steve Comins wondered why an accurate clock would emit more disorder than an inaccurate clock that ticks too fast.

In short, consistency is key, Conover says. In the context of the story, an inaccurate clock refers to one whose ticks are unevenly spaced, she says. Some ticks may come faster and some slower than they should, so you can’t predictably tell time. But a clock that ticks consistently faster or consistently slower than normal could still be accurate, as long as you figure out the rate at which it’s ticking.

For example, a clock that consistently ticks twice in one second could still accurately tell time; you’d just have to count each tick as a half-second. Such a fast-ticking clock would likely emit more entropy than a normal clock, but it would also be more precise, in accordance with the researchers’ results, Conover says.

Fluid definitions

A wave in one of Saturn’s rings shows that the planet’s core is spread out and bloated with hydrogen and helium, Ken Croswell reported in “Saturn’s heart is fuzzy and diffuse” (SN: 6/5/21, p. 9).

Saturn’s immense gravity squeezes most of the planet’s hydrogen and helium, which exist as gases on Earth, into a fluid, Croswell reported. Reader Ken Koutz questioned the use of the term “fluid,” given that gases are already considered fluids.

While a fluid can be a gas or a liquid, physicists often use the term to refer to supercritical states, in which distinct gas and liquid phases are blurred, story editor Chris Crockett says. “That is exactly what is thought to happen deep inside giant planets such as Saturn,” he says. “The fluid there is neither gas nor liquid, strictly speaking, but it still has fluid properties.”

Putting the squeeze on dead stars

The most massive neutron star known has a surprisingly large diameter, suggesting that the matter within it is less squeezable than expected, Emily Conover reported in “Neutron stars may not be so squishy” (SN: 6/5/21, p. 8).

Reader Jim Barr wanted to know what “squeezable” means in the context of neutron stars.

This term refers to how much a material compresses under pressure, Conover says. For example, if you squeeze a steel ball in your hand, it won’t get significantly smaller. But if you do the same with a foam ball, it will. And the harder you squeeze the foam ball, the smaller it will get.

For neutron stars, the question is whether the core gets smaller when squeezed by gravity. The more massive a star, the greater the gravitational pressure. So whether a more massive star is bigger, smaller or the same size as a less massive one depends on whether the star’s core compresses or not.