Readers discuss quantum gravity and more

Words matter

An ancient grave with a sword, shield and mirror belonged to a woman who about 2,000 years ago may have fought in raids and helped fend off enemy attacks in what’s now southwestern England, Bruce Bower reported in “Iron Age warrior grave belonged to a woman” (SN: 1/13/24, p. 5).

Reader Cathryn Brenner expressed disappointment in a phrase in the story. “The woman warrior was described as potentially having a ‘violent streak.’ The connotation of violent streak, if not the actual meaning, is negative and used to describe a personality trait that is evidenced in the frequent use of violence or physical harm to others across many contexts,” Brenner wrote. “I see no evidence in this article that, if she was a warrior, she acted in any way other than a male warrior — raiding and defending. And I have never ever ever seen a male warrior described with this term! I am shocked that at this time, this phrase got past everyone involved with the article.”

Shifting spins

Enormous polygonal rock patterns lie near Mars’ equator deep below the surface, radar data suggest. The finding hints that the Red Planet’s equator was once much icier than it is now, perhaps because of differences in the tilt of the planet’s axis, Elise Cutts reported in “Buried polygons hint at Mars’ tipsy past” (SN: 1/13/24, p. 12).

Reader Robert Walty wondered if some sort of cosmic collision could have caused the tilt of Mars’ axis to change. “It has often been suggested that the reason Uranus’ spin axis is on its side could be due to a collision with another large body in the past. This collision hypothesis was not mentioned in the article,” Walty wrote.

It likely was not an event, such as an asteroid impact, that caused a change in Mars’ tilt, but rather the natural evolution of the planet’s spin over time, says geoscientist Ross Mitchell, who along with colleagues discovered the patterns.

Earth’s axis is tilted at an average of 23.3 degrees. Stabilized by our moon, the planet’s tilt wobbles by a little more than a degree from that average, says Mitchell, of the Chinese Academy of Sciences’ Institute of Geology and Geophysics in Beijing. But Mars’ two small moons provide no such stabilizing effect. So even though the Red Planet’s tilt is currently quite similar to Earth’s at an average of 25 degrees, it might have varied drastically in the past — between around 15 and 40 degrees, he says.

What’s more, simulations of the solar system’s history suggest that the Red Planet’s average tilt may have been greater than 40 degrees for most of its existence, Mitchell adds. If true, that “would mean that most of the climate history recorded in the Martian geologic record might be very different from the current cold, dry climate we know today.”

The new finding supports such a prediction, Mitchell says. The radar images of the ancient polygonal rock patterns buried under Mars’ surface suggest that the planet’s equator, which currently is “dry as a bone,” experienced freeze-thaw cycles of water a few billion years ago.

Questioning quantum gravity

Random fluctuations in gravitational fields might allow physicists to seal the rift between the general theory of relativity, which describes gravity, and quantum physics, without the need for a theory of quantum gravity, Emily Conover reported in “What if gravity isn’t quantum?” (SN: 1/13/24, p. 15).

Reader John Rippingale wondered what could cause random fluctuations in a gravitational field.

In this theory of gravity that some researchers propose, there is intrinsic randomness in the way that spacetime bends in response to a massive quantum particle, Conover says. As a result, the gravitational field of an object would appear to fluctuate slightly. “So if this theory is correct, there’s no need for a cause for that randomness — it’s just a fact of nature,” she says.