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PERCOLATION INSPIRATION

It was an absolute delight to read about percolation theory in “The Math of Making Connections,” by Kelsey Houston-Edwards. Please feature more articles by this author and about mathematics as applied to science. I’m not a mathematician, yet I enjoy learning about theory and application. I love the expanse of disciplines you cover.

I am an African-American woman with a biology degree. I used to work as a research assistant in cancer research. That was until the racism that I consistently encountered wore me down, and I just didn’t want to ever work with scientists again. Although I am in another line of work, I haven’t lost my love of the sciences and mathematics. Your magazine provides me with the joy I used to feel but without the heartache.

TRACIE S. JOHNSON via e-mail

One approach to developing a theory of quantum gravity is called loop quantum gravity (LQG). It treats space as a discrete substance composed of individual spatial atoms, or nodes, at the Planck distance scale of 10⁻³⁵ meter. They are connected to one another in a way that would seem to lend itself very well to percolation theory, which is precisely geared toward modeling the connections among discrete nodes. Has percolation been applied to advancing LQG and quantum gravity?

EDWARD ROSENBLATT via e-mail

HOUSTON-EDWARDS REPLIES: In response to Rosenblatt: In percolation theory, a “dial” controls the local connectivity of a network. When its needle lands on a critical point, a phase transition occurs, and the global connectivity of the network changes dramatically. To apply the theory to LQG, one needs to describe how and why this dial moves to the critical point. But as theoretical physicist Lee Smolin explained in an e-mail to Scientific American, nature exhibits several instances of “self-organized critical phenomena,” in which the dial tunes itself toward the critical threshold. Smolin hypothesizes that such a self-organized phase transition might explain “the emergence of classical spacetime in a quantum theory of gravity,” including loop quantum gravity. He and physicist Mohammad Ansari explored these ideas in the 2008 paper “Self-Organized Criticality in Quantum Gravity.” It is unclear how extensively a “self-tuning” version of percolation could be used for understanding a self-organized phase transition in the case of LQG.

CLIMATE PRIORITY

I was troubled by “What to Do about Natural Gas,” Michael E. Webber’s article about ways to decarbonize the natural gas system. Pointing out that the primary alternative, electrification, will be challenging is fair enough. But electrification does not have barriers that are greater than, or even equal to, a zero-carbon gas system, which faces structural limitations. To his credit, Webber names some of these limitations. But his presentation of them as solvable with some tweaks is disingenuous. Even by the gas industry’s own estimates, two decades of scaling up all low-carbon gases would displace only about 13 percent of the U.S.’s existing gas demand. Also, it would squander any genuinely sustainable gases that could be used where we might actually need them, such as chemical feedstocks, shipping and aviation.

Keeping warming within the 1.5 degrees Celsius limit necessary to avoid catastrophic climate destabilization requires us to reach net-zero emissions, meaning we must leave the majority of the world’s existing gas reserves unburned. And whether methane is synthetic, biogenic or fracked, if it’s pumped through the existing distribution network, it will face leakage, adding to atmospheric warming.

Perhaps the most important omission is that decarbonizing gas does not solve the health impacts of combustion. With low-carbon gases, we only get more expensive ways of polluting our homes.

SASAN SAADAT Research and policy analyst, Earthjustice

WEBBER REPLIES: It seems that we agree that addressing climate change is the most urgent and important challenge of the 21st century. That realization led me to the conclusion that we need every solution possible to get us to carbon neutrality (and carbon negativity!) as quickly, safely and affordably as possible. As I write in the article, I think the first two priorities for decarbonizing the economy are (1) conservation and efficiency and (2) electrification. Because low-carbon fuels play an important role for sectors that are difficult to electrify, we need to make progress on decarbonizing gases as the third step.

As someone who invented sensors to measure the emissions from combustion, I’m well aware of its pollution. And as someone who quantitatively analyzes different forms of energy, I’m also aware of the significant ecosystem impacts of some utility-scale renewables. The energy system is all about trade-offs, and there is no one fuel or technology option that is purely villainous or virtuous. Rather we must design a suite of solutions that meets society’s complex needs.

PREDICTIONS AND MEMORY LOSS

In “Prediction Predicament” [Advances], Hannah Seo notes that making predictions impairs people’s ability to remember predictive events. I see this a lot in the martial arts. Often when an instructor demonstrates a technique, the students will be busy imagining what comes next and how they think the technique should be performed while failing to see the variation that the instructor is demonstrating. It’s like the students are watching to confirm their predictions instead of observing to learn something new.

IAN MCINTYRE via e-mail

RECOVERING FROM ADDICTION

“Hope for Meth Addiction,” by Claudia Wallis [Science of Health], encouragingly describes the growing evidence base for contingency management as an effective treatment for stimulant use disorder, particularly in conjunction with bupropion and naltrexone. It notes that one trial of the two drugs found that they helped a significant number of treated users test methamphetamine-free “at least three quarters of the time.”

Wallis’s piece is to be applauded for its apparent recognition that complete abstinence is not the only recovery pathway. Harm reduction is effective, and reoccurrence of substance use is not unusual for most people as they seek recovery. While abstinence-based approaches may be ideal for some, they don’t work for everyone. Contingency management and harm reduction are both important strategies that can lead to improved health and wellness for those who are still struggling with harmful substance use.

Ann Herbst Interim CEO, Young People in Recovery

ERRATA

In “The Math of Making Connections,” by Kelsey Houston-Edwards, the bottom illustration in the box “Square Lattice” should have depicted the white pipe at the top left of the lattice filling with water.

In “Scientists: Admit You Have Values,” by Naomi Oreskes [Observatory], the end of the quote attributed to Francis Bacon should have read: “… man prefers to believe what he wants to be true.”

Edited by Dava Sobel

It is perhaps not strange that the Radiates, a type of animals

whose home is in the sea, many of whom are so diminutive

in size, and so light and evanescent in substance, that they

are hardly to be distinguished from the element in which

they live, should have been among the last to attract the

attention of naturalists.

They say I came to science

through marriage. As though

I wouldn’t have, otherwise.

 

As though I was dragged, by accident,

like a jellyfish caught in a net.

 

The truth is I married for science.

It was a way in. Like

a radiate, I got what I wanted

without attracting undue attention.

Nothing can be more unprepossessing than a sea-anemone

when contracted. A mere lump of brown or whitish jelly, it

lies like a lifeless thing on the rock to which it clings, and it is

difficult to believe that it has an elaborate and exceedingly

delicate internal organization, or will ever expand into such

grace and beauty as really to deserve the name of the flower

after which it has been called … the whole summit of the

body seems crowned with soft, plumy fringes.

We are all lumps, aren’t we, before we find

the thing we love? The things?

My husband and I, lumped together,

blossomed into beauty. I know

that sounds maudlin. Let me try again.

 

These animals … thrive well in confinement.

For some women, marriage is a prison.

They enter it willingly. It keeps them

safe from the world. Our marriage

was more like a boat.

 

They may also multiply by a process of self-division.

We had no children. I took notes.

Another way of saying it is I wrote books.

At every point in our studies

of sea creatures and each other,

I was in charge of the words.

 

The name Jelly-fish is an inappropriate one, though the

gelatinous consistency of these animals is accurately enough

expressed by it; but they have no more structural relation

to a fish than to a bird or an insect.

Jellyfish are neither jelly nor fish,

as I was not truly wife nor scientist.

Have you seen them move?

It looks as if they move by breathing.

 

Encountering one of those huge Jelly-fishes, when out

in a row-boat one day, we attempted to make a rough

measurement of his dimensions upon the spot. He was

lying quietly near the surface, and did not seem in the

least disturbed by the proceeding, but allowed the oar,

eight feet in length, to be laid across the disk, which

proved to be about seven feet in diameter. Backing the

boat slowly along the line of the tentacles, which were

floating at their utmost extension behind him, we then

measured these in the same manner, and found them to

be rather more than fourteen times the length of the oar…

As I write these lines I remember

that day in the boat and how happy

we were. A person could measure

our happiness in oars. A person could

lay down oar after oar and still need

more oars.

 

Our laughter echoing over the waves.

No one to hear it besides each other—

and the biggest jellyfish we ever saw.

Author’s Note: All italic quotations are from Agassiz’s Seaside Studies in Natural History (1865). In addition to her scientific research, Agassiz collaborated with her husband, natural historian Louis Agassiz, on marine expeditions. She was a co-founder and the first president of Radcliffe College.

If you had 1,000 butts, what would you do with them? The marine worm Ramisyllis multicaudata is one of only two known animals to find itself in this rather awkward situation (shopping for pants must be a nightmare)—and it isn’t yet telling. But given that that many booties doesn’t “just happen” to a worm, there must be a pretty good reason, and a new anatomical study has offered up some tasty clues.

The story starts off normally enough. Ramisyllis is a bristle worm that lives inside the water passages of a sponge called Petrosia in a shallow reef off the coast of northern Australia. Its lone, unremarkable and rather lethargic head is buried deep in the sponge. Shortly after that things get weird.

Its body begins to branch repeatedly and without pattern. The legion resulting posteriors may protrude into the seawater through natural holes in the sponge and amble along its surface. One “small” sponge observed by scientists was festooned with more than 100 crawling worm fannies, sometimes more than 10 to a single opening. Although sponges are many remarkable things, sentient is not one of them, and that must surely be counted as a win here.

Further, each branch contains its own set of internal organs. According to the first detailed anatomical study of these worms, published this year in the Journal of Morphology by a team from Spain, Australia and Germany, these organs are in no way different from that of the unbranched juvenile. They further found that the worm’s gut is continuous throughout the entire labyrinthine animal—but conspicuously empty. No sponge tissue has ever been found inside, nor food particles of any kind.

Yet they also found the worm’s hind gut is covered in cilia and microvilli, little fingerlike extensions that maximize the surface area available for nutrient absorption (your own gut is covered in a similar velvety lining of villi and microvilli). That implies their gut could still function, although how the sprawling animals could survive on invisible food that enters only through their woefully inadequate regulation-sized mouth remains a mystery.

What makes these worms particularly interesting to me is that they appear to be an animal that has adopted a fungal lifestyle. Look at a fungus under a microscope, and you will see a system of branching tubes with a strong resemblance to Ramisyllis. And this similarity suggests what these worms might be up to in their sponges.

Fungi are absorptive feeders. They tunnel into their food, secrete digestive enzymes and then resorb the resulting goo. The reason their highly branched, filamentous bodies put the emphasis on surface area is that rather than having a long intestine crammed into a small body as we do, their entire body is an intestine, inside out. In this setup, the more body you have, the more food you can eat.

It’s been known for a while that soft-bodied marine invertebrates can absorb dissolved organic matter (a.k.a. liquid food) directly from seawater through their “skin.” But Ramisyllis may have taken this to the next level: the anatomy team discovered the worm’s body is also suspiciously covered in long microvilli. Given the strong emphasis on square footage in the Ramisyllis body plan—and the lack of emphasis on producing heads or mouths commensurate with the situation—one must strongly suspect that, like fungi, they have converted their outsides into insides.

If their highly branched bodies aren’t suggestive enough of fungi, allow me to present Exhibit B: their bonkers reproductive system.

The first clue that to their extremely alternative lifestyle is the fact that Ramisyllis is never going to go on a date. Once you’ve crammed your thousands of tentaclelike branches into the water passages of a Petrosia sponge, you’ve made a commitment to a house, not a relationship (or even a hookup). The usual solution is to simply boot your millions of cheap gametes directly into the water, wave bye-bye, and turn on some must-see TV. Corals and sea anemones are notable practitioners of this enviable reproductive art.

But this is not the route Ramisyllis and many other syllid polychaete worms took. At the back of their bodies sits a little tail called a pygidium (trilobites also had this cute butt flap). Just in front of it lies the polychate worm version of the apical meristem in plants: a place where stem cells continuously generate new body parts called the posterior growth zone. Polychaete worms have these in order to make new segments. But it is an unusual situation for animals, and it has led to some unusual results.

Sometimes, instead of making a new standard segment, these regions start building a head containing a rudimentary brain and four eyes. After the head come more body segments stuffed with gametes, and before you know it there’s a sexy little hot rod attached to the mother ship, to be jettisoned when the time is ripe. These stripped-down clones (botanically termed “stolons”; strawberry runners and other horizontal plant stems are also called stolons) are armed with paddles, driving directions, a libido and little else.

In short, Ramisyllis makes autonomous gonads that lie in that hazy middle ground between detachable penis and college freshman. The group to which these worms belong—the syllids—are perhaps unique among bilaterally symmetrical animals in this bizarre reproductive strategy, termed “gemmiparous schizogamy.” Certain insects, of course, do something similar in that they produce ephemeral adults whose sole aim is to knock extremely tiny, extremely urgent boots, but they generally live as larvae for a much longer period. And they do not bud from existing insects. That’s a very mycological way of doing things.

Indeed, the image of a Ramisyllis stolon amidst the branches of its generative worm is strikingly similar to photographs of the fungus Fusarium bearing its distinctive boat-shaped spores. Stolons of other nonbranching syllid species can also be made in bunches or chains, just like fungal spores.

It may be this very reproductive habit is what allowed syllid worms to grow multiple-choice bodies. The ability to make a branch bearing a sex-seeking clone may only be a few mutations away from substituting the regular bits instead.

Still, something about this story bugs me. If their whole bodies can absorb dissolved food, why is there such an emphasis on all the myriad backsides reaching the surface of the sponge? In one specimen dissected by scientists, bunches of worm butts were found stuffed into sponge cul-de-sacs. The scientists interpreted this as the thwarted attempt of said backsides to reach the surface. The tails also contain a bright white pigment of unknown function that they make whether or not they reach topside.

Why is it so vital the tails find an exit? Is the dissolved organic matter really that much tastier outside the sponge? And why are they wearing the equivalent of reflective highway paint? Is it just for sunscreen? Or is there some other use?

Even though Ramisyllis is apparently doing what I would do with a thousand booties—shake them—exactly what that it is really doing with them remains a mystery.

This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.