Granular convection

In a serving of mixed nuts, the larger Brazil nuts will often end up on the surface

A demonstration of the Brazil nut effect using a glass jar, a cup of rice, and a stack of coins serving as the intruder initially located at the bottom.


A video demonstrating how shaking a bag of muesli causes the larger ingredients to rise to the surface

It may be counterintuitive to find that the largest and (presumably) heaviest particles rise to the top, but several explanations are possible:

  • When the objects are irregularly shaped, random motion causes some oblong items to occasionally turn in a vertical orientation. The vertical orientation allows smaller items to fall beneath the larger item.[3] If subsequent motion causes the larger item to re-orient horizontally, then it will remain at the top of the mixture.[3]
  • The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimally low; it has the tendency to be higher due to there being more empty space around the larger Brazil nuts than around smaller nuts.[] When the nuts are shaken, the system has the tendency to move to a lower energy state, which means moving the center of mass down by moving the smaller nuts down and thereby the Brazil nuts up.[]
  • Including the effects of air in spaces between particles, larger particles may become buoyant or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture. (According to Heinrich Jaeger, “[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.”[7])
  • The same explanation without buoyancy or center of mass arguments: As a larger particle moves upward, any motion of smaller particles into the spaces underneath blocks the larger particle from settling back in its previous position. Repetitive motion results in more smaller particles slipping beneath larger particles. A greater density of the larger particles has no effect on this process. Shaking is not necessary; any process which raises particles and then lets them settle would have this effect. The process of raising the particles imparts potential energy into the system. The result of all the particles settling in a different order may be an increase in the potential energy—a raising of the center of mass.
  • When shaken, the particles move in vibration-induced convection flow; individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall.
  • The pore size distribution of a random packing of hard spheres with various sizes makes that smaller spheres have larger probability to move downwards by gravitation than larger spheres.[8]

Study techniquesEdit


This phenomenon results in raisins tending to rise to the top of a box of breakfast cereal, so that the first servings of the cereal contain more raisins than usual, and only flakes are left at the bottom of the box.

This phenomenon is one of the causes of inverse grading which can be observed in many situations including soil liquefaction during earthquakes or mudslides. Granular convection is also exemplified by debris flow, which is a fast moving, liquefied landslide of unconsolidated, saturated debris that looks like flowing concrete. These flows can carry material ranging in size from clay to boulders, including woody debris such as logs and tree stumps. Flows can be triggered by intense rainfall, glacial melt, or a combination of the two.

See alsoEdit


  1. Granular Convection and Size Separation. The University of Chicago
  2. Rosato, A.; Strandburg, K.J.; Prinz, F.; Swendsen, R.H. (1987). “Why the Brazil Nuts are on Top”. Physical Review Letters. 58 (10): 1038–41. doi:10.1103/physrevlett.58.1038. PMID 10034316.
  3. ^ a b c d e f Gajjar, Parmesh; Johnson, Chris G.; Carr, James; Chrispeels, Kevin; Gray, J. M. N. T.; Withers, Philip J. (2021-04-19). “Size segregation of irregular granular materials captured by time-resolved 3D imaging”. Scientific Reports. 11 (1): 8352. doi:10.1038/s41598-021-87280-1. ISSN 2045-2322. PMC . PMID 33875682.
  4. Rietz, Frank; Stannarius, Ralf (2008). “On the brink of jamming: Granular convection in densely filled containers”. Physical Review Letters. 100 (7): 078002. arXiv:. Bibcode:2008PhRvL.100g8002R. doi:10.1103/PhysRevLett.100.078002. PMID 18352597. S2CID 28054132.
  5. Baffling Patterns Form in Scientific Sandbox, Wired, Brandon Keim, October 28, 2009
  6. Grains of Sand Reveal Possible Fifth State of Matter, Wired, Brandon Keim, June 24, 2009
  7. “Sidney Nagel and Heinrich Jaeger Q&A”. Retrieved .
  8. W.Soppe, Computer simulation of random packings of hard spheres, Powder Technology, Volume 62, Issue 2, August 1990, Pages 189-197,
  9. Abbott, Derek (2009). “Developments in Parrondo’s Paradox”. Applications of Nonlinear Dynamics. Springer. pp. 307–321. ISBN 978-3-540-85631-3.
  10. Knight, James B.; Jaeger, H. M.; Nagel, Sidney R. (1993-06-14). “Vibration-induced size separation in granular media: The convection connection”. Physical Review Letters. 70 (24): 3728–3731. Bibcode:1993PhRvL..70.3728K. doi:10.1103/PhysRevLett.70.3728. ISSN 0031-9007. PMID 10053947.
  11. Nemiroff, R.; Bonnell, J., eds. (22 April 2007). “Smooth Sections of Asteroid Itokawa”. Astronomy Picture of the Day. NASA.
  12. Wright, Esteban; Quillen, Alice C.; South, Juliana; Nelson, Randal C.; Sánchez, Paul; Siu, John; Askari, Hesam; Nakajima, Miki; Schwartz, Stephen R. (2020). “Ricochets on asteroids: Experimental study of low velocity grazing impacts into granular media”. Icarus. 351: 113963. arXiv:. Bibcode:2020Icar..35113963W. doi:10.1016/j.icarus.2020.113963. PMC . PMID 33087944. S2CID 219965690.
  13. excerpt from Recollections of a Busy Life Archived 2012-09-10 at, by Horace Greeley 1869

External linksEdit

  • Beads in a Box on YouTube
  • The Brazil Nut Effect on PhysicsWeb
  • Yan, X.; Q. Shi; M. Hou; K. Lu; C. K. Chan (2003-07-03). “Effects of Air on the Segregation of Particles in a Shaken Granular Bed”. Physical Review Letters. 91 (1): 014302. Bibcode:2003PhRvL..91a4302Y. doi:10.1103/PhysRevLett.91.014302. PMID 12906541.
  • The Brazil Nut Effect: Numerical Simulation Example of a numerical simulation of the Brazil Nut Effect.
  • “Why brazils always end up on top”, BBC News, 15 November 2001
  • “Why does shaking a can of coffee cause the larger grains to move to the surface?”, Scientific American, 9 May 2005
  • “Of airbags, Avalungs and avalanche safety”, Toronto Star, 13 January 2008
  • Bowley, Roger (2009). “Γ – Ratio of Acceleration to Gravity (and the Brazil Nut effect)”. Sixty Symbols. Brady Haran for the University of Nottingham.

Be it ever so humble, there's no ingredient like raisins.

The first thing that comes to mind when I think of raisins is small sticky fingers — my now-grown children’s, I suppose, though they might as well have been my own — prying one dark, shriveled nugget of sweet, gummy goodness after another from a tiny, bright-red Sun-Maid box into an equally sticky mouth. Those miniature cartons contained the perfect portable snack, offering cranky kids everywhere a boost of sugar-fueled energy as well as a conveniently distracting activity. 

As a child and later a parent, I embraced raisins wholeheartedly. Like so many Jews of Central and Eastern European descent, I’ve enjoyed them in rice pudding, rugelach, noodle kugel and challah. If I could have done without them in my grandmother’s stuffed cabbage, I now know that sweet-and-sour is often an acquired taste.

It is also a common pairing in Jewish cuisines, particularly at Shabbat, having originated in the days before refrigeration when a sweet element would be added to foods preserved with vinegar to balance out the sharp acidity. 

Once raisins made their way to Europe from the Levant in the 14th century, they became an integral part of Ashkenazi cooking. 

“They were called in Western Yiddish and in Eastern Yiddish,” according to food historian Gil Marks in his Encyclopedia of Jewish Food. “If someone was disrespected,” he writes, “the typical response was ‘Iz mayn neshome den a rozshinke,’” meaning, “Is my soul a raisin?”

If the question alluded to the dark, shriveled nature of the fruit, it ignores the fact that raisins held a place of high honor in many Jewish celebrations. (They were often reserved for special occasions, because as an imported product they were relatively expensive.) 

Sprinkling raisins and nuts over the groom during Shabbat services before an Ashkenazi wedding became a custom meant to encourage fertility and sweetness in the marriage.

Raisins are as prevalent in Sephardic and Mizrahi kitchens as they are in the Ashkenazic ones I grew up in and around. From Persian jeweled rice to North African stews to Venetian pastas and Levantine stuffed vegetables, raisins appear — often paired with walnuts or pine nuts — in countless dishes.    

There are 32 recipes listed under “raisins” in The Jewish Cookbook, by Leah Koenig — including Ashkenazic favorites like baked apples and babka as well as dishes from the far reaches of the Diaspora such as , a sweetened porridge made by the Bene Israel Jews in India. The dish — “decorated with fresh and dried fruit, flowers, nuts, and coconut — is at the center of a ceremony originally created to honor the prophet Elijah. “The ceremony,” Koenig writes, “is held at births, engagements, graduations, or any other auspicious occasion.” 

Claudia Roden’s classic The Book of Jewish Food also includes over 30 raisin dishes.

Referring to the culinary legacy of Jews forced to convert or leave Spain during the Inquisition, Marks writes: “Raisins, along with nuts and oil, remain the signature ingredients of baking of the secret Jews, descendants of Conversos, most of whom do not know of their Jewish roots, of the American Southwest.”

Raisins even made it into wine. In places where Jews didn’t have access to fresh grapes — or when, as happened with the Conversos, the only wine available might be the sacramental wine of the Catholics — they created raisin wine from the dried fruit that was available to them. 

According to Nathan, we can thank raisin-wine-and mead-making Eastern European Jews, apparently, for bringing the idea of sweet kosher wine to these shores.

In Hebrew, the word for raisin is — from the root “to shrivel.” But whether the stuff of nursery snacks, everyday dishes, or celebratory feasts — and shrivel though it surely does —it is most assuredly an ingredient that shines within the pantheon of iconic Jewish ingredients. 

Tagliatelle with chicken, raisins, and pignoli

This dish offers a wonderful example of the prolific use of raisins paired with pine nuts in Sephardic kitchens.

This recipe, inspired by Tagliatelle Frisinal from Claudia Roden’s The Book of Jewish Food, is a great way to use up leftover chicken — particularly from a store-bought rotisserie bird. It’s also a wonderful example of the prolific use of raisins paired with pine nuts in Sephardic kitchens.  The sauce isn’t “saucy,” in that there’s hardly any liquid, especially once the pasta absorbs what little there is. This is the way the dish is intended, and it won’t be dry if you give it a quick  toss with a splash of hot pasta water and some good extra-virgin olive oil at the end. 

½ cup golden raisins 

½ cup pignoli (pine) nuts

2 tablespoons olive oil

2 cloves garlic, minced

2 teaspoons chopped fresh rosemary or ½ teaspoon dried rosemary crushed between your palms to release the flavor

2 cups (about ½ pound) cooked shredded chicken (rotisserie works great here)

1 cup dry white wine, vermouth or chicken broth

¼–½  teaspoon salt, or to taste

Freshly grated black pepper to taste

½ cup fresh Italian (flat-leaf) parsley, roughly chopped, plus more for garnish

Extra-virgin olive oil for drizzling

1 pound tagliatelle or fettuccine, preferably fresh

  1. Bring a large pot of water to a boil and add at least a tablespoon of salt. If using dried pasta, add it now. If using fresh pasta, you will add it after Step 6.
  2. In a small bowl or a cup, soak raisins in warm water.
  3. Heat a large skillet over medium-low heat. Add the pignoli nuts and cook, shaking the pan periodically, until nuts are fragrant and lightly golden, about 2 minutes. Set nuts aside.
  4. Add olive oil to the pan and add garlic. Cook, stirring with a wooden spoon, for a minute or two, until garlic softens. (If it becomes pale golden that’s fine, but make sure not to let it get dark or it will be bitter. Move off the heat if necessary.)
  5. Drain and add raisins, along with the rosemary, and cook, continuing to stir, for 1–2 minutes. 
  6. Raise heat to medium-high. Add chicken, then wine or other liquid, and simmer gently, scraping up anything that’s stuck to the bottom of the pan so it becomes part of the sauce.
  7. If using fresh pasta, add it to the salted boiling water now, and cook according to package directions. Set a timer, and drain when pasta is ready — reserving about a quarter cup of the water in a bowl or cup — and transfer to a large serving bowl. (Cover it loosely if sauce isn’t ready.)
  8. When liquid has reduced slightly, turn off the heat. Add salt, pepper, parsley, and reserved pignolis and toss to combine. 
  9. Pour chicken-raisin sauce over the pasta and drizzle with a bit of the reserved pasta water to loosen things up, along with a little extra-virgin olive oil, and toss. Taste for seasoning, adding more salt, pepper, water and olive oil if desired. Serve immediately.

As Good Friday draws closer, there is one debate that always seems to rear its head.

The discussion surrounds a local delicacy that will be on almost every dinner table this weekend-Ducana.

But there seems to be no consensus on the right way to make the Easter staple.

So, every year around this time, Antiguans begin debating amongst themselves on whether the traditional dish should contain raisins.

Let’s settle this once and for all:

In a recent poll in which 346 persons voted within three hours, majority of residents (53 per cent) voted for Ducana without raisins.

“Why would you dare ruin a wonderful thing with fly looking things like raisins?” one woman remarked.

Ducana served with saltfish and salad.

Meanwhile, 20 per cent like it with raisins and 27 per cent did not have a preference.

“It doesn’t matter, as long as they are edible and taste good, I will eat them,” one avid Ducana lover said.

One man however said that he will never eat a Ducana meal unless it contains raisins or even cherries.

“You guys have no idea what you are missing,” he said.
Ducana consists of grated sweet potatoes, mixed together with coconut, sugar, spices, and flour, folded in banana leaves or foil, and boiled until firm.

Ducana in foil paper and fig leaves.

It is much like Jamaica’s ‘Blue draws’ and somewhat similar to Barbados’ Conkie.

Antiguan’s pair it with saltfish for the perfect sweet and salty combination.

On Easter Friday locals will be challenging themselves to see how many of these palm sized treats they can eat in the first ever Ducana eating competition.

The raisin meditation focuses all your senses to calm anxious thoughts.

Fear, anxiety, worry, and dread are all shiny objects to a frenetic mind. And sometimes the mind latches on to an anxiety and won’t let go, leaving us with repetitive thoughts and outsized worries about things far outside of our control.

One of the best ways to break a cycle of anxious thinking is to give the mind something to focus on instead. We can then step back and interrogate our thoughts, recognizing that the threat we perceive is not so near or dire. This kind of focus can be achieved by bringing our whole body into the task through the use of all of our senses. We can do this with a very simple mindfulness practice called the raisin meditation.

What Is the Raisin Meditation?

More specifically you may be asking, “Why a raisin?” You could really use any small treat, but there’s something poetic about using this small, common piece of dried fruit to completely transform one’s state of mind.

The goal is to redirect the spotlight of your attention onto something mundane and present. Take your mind out of the anxiety-filled future and into this moment by bringing to bear all of your senses. You can’t smell or hear the future; your senses are always in the moment. And that’s the beauty and simplicity of the raisin meditation.

How to Practice the Raisin Meditation

  • First, get a raisin and find a quiet place to do your meditation.
  • Sit in a relaxed position that you know you can hold for several minutes without readjusting, on a cushion on the floor or in a chair. If in a chair, try to sit upright with shoulders over your hips so you can get a deep breath. Keep feet flat on the floor so you can feel the earth beneath you. You can close your eyes or pick a spot in front of you to gently fix your gaze upon.
  • Take a few deep breaths and try to bring your attention to this moment. Hold the raisin in an open palm in front of you. Lay your gaze on the raisin, looking at it with curiosity. Inspect each wrinkle slowly, tracing its outline with your eyes. Notice its rich color—the longer you look at it the more shades of purple you might discover. Enjoy the shape of it—does it remind you of anything? Take a couple minutes to completely take it in.
  • Then, notice how the raisin feels in your hand. What is the relationship between its size and its weight? Can you feel its weight? Roll it around in your palm, feeling it tumble. Place it between two fingers and feel its ridges, some places smooth, others rough or sticky. Squeeze the raisin gently—is it squishier or firmer than you thought?
  • Although it is tiny and dehydrated, your raisin may still have a scent to it. Bring it to your face and breathe deeply. Smell its sweetness. Notice how faint or how strong it is. Locate the tingle in your nose. Summon the memory of the smell of the whole box or bag of raisins, perhaps a familiar scent going back to your childhood. Be with this scent in the moment.
  • Your mind may still wander. Anxious thoughts or sensations may intrude, and that’s ok. As it happens, just bring your attention back to the raisin and your senses.
  • Once you’ve spent some time seeing, feeling, and smelling the raisin, now is the time to taste it. Place it in your mouth but don’t chew it yet. Just feel it on your tongue, combining taste with touch. Push it around your mouth, feel it behind your lips and on the roof of your mouth. Focus on its unique taste. Eventually, bring it between your teeth and clamp down slowly. Hold it there.
  • Bring your ears into the mix, listen to the sound of your teeth and jaw at work as you begin to chew. In this moment, we combine touch, taste, smell, and hearing to captivate our attention. The mind may still try to take you to an anxious place, but now you’ve got all your senses working together to offer something else to focus on.
  • Swallow the raisin and feel it travel to your stomach. Consider all the places this raisin has been: the hands that tended to the grape; the sun that nurtured its growth, caused the water to evaporate; and caramelized its sugars; the dust that settled on it; and vehicles and people who transported the raisin to your local store—all for it to be used as a tool for relaxation and focus in this moment.

The Gift of the Raisin Meditation

The raisin meditation is a great reminder that we are more than our thoughts. By activating all our bodily senses we gently coerce our mind to stay in the present, allowing our body to calm and our mind to slow. For at least a few moments we’ve slowed the cycle of anxious thoughts and reminded ourselves of the gift of this moment.

Senses not in sync? Discover how to balance your five senses for best health results.

Harvard law professor Adrian Vermeule is capo di tutti capi of the mob calling themselves Integralists. The Integralists argue that of the two powers that rule man—the temporal and the spiritual—the temporal must be subordinate to the spiritual because political rule must be ordered to man’s final end. Therefore, according to Vermeule, man’s final end must somehow be connected to the deep state. 

They met recently at a conference organized by my friend Anne Hendershott of Franciscan University of Steubenville, and intellectual pilgrim Sohrab Ahmari. 

Orthodox. Faithful. Free.

Sign up to get Crisis articles delivered to your inbox daily

This comment puts me in mind of raisins. 

Farmers rediscovered they did not own their own crop. Hanson explains that the federal government owns the nation’s annual raisin crop even before it is harvested. 

Here’s at least one of the problems. If this had been decided by the legislative process, it would have been possible to throw the rascals out at election time and change the law. But this was decided by a low-level bureaucrat in a federal agency. Put aside that this was merely “guidance” and could have been ignored; but it was received by ideologues on the ground as a royal degree that they had to accept. And how does one begin to find and then change the mind of a low-level bureaucrat. This is a profound democratic deficit. 

Vermeule is alarmed the deep state is being unspooled. A federal court just determined that a meddlesome agency called the Consumer Financial Protection Bureau no longer gets automatic funding free from meddlesome politicians. Funding for the bureau had been severed from Congressional approval. If this sounds vaguely unconstitutional, I agree. We shall see if this holds up in the Supreme Court. 

Also at issue is whether the deep state gets to set its own rules without Congressional approval. The Chevron case is the one to watch. In 1984, the Supreme Court decided that federal courts had to defer to any federal agency’s “reasonable interpretation” of an ambiguous statute. What this means is that the deep state gets to set its own rules and then interpret them on its own. The taxpayer and his political representative be damned. Professor Hamburger sees Chevron on its last legs. Integralist Vermeule would see this as the end of the republic. 

If all of this is integralism, most of us would say—paraphrasing Flannery O’Connor on if the Eucharist were merely a symbol—“to hell with it.” 

Jump to recipe if you like, but be sure to read the whole post for instructional photos & other tips.

Rum Raisin Ice Cream. If you are a fan of rum raisin ice cream, this homemade version may well be the best you will ever try. A few simple ingredients truly create something exceptionally delicious.

Rum Raisin Ice Cream

Rum Raisin Ice Cream

Spouse’s favourite ice cream is Häagen-Dazs Rum Raisin. However, for some unknown reason it has not been available here for some years. 

Because she craved it so much, I set out to make my own rum raisin ice cream version.

This recipe is in my humble opinion, even better than the Häagen-Dazs version. Soaking the raisins in the rum for a day or two is essential.

Raisins for Hot Cross Buns shown in a white bowl.

Sultana Raisins are what I used in this recipe but you can use any kind you like.

Leaving the ice cream in the freezer a day before serving makes it even better. This is often the case inn such recipes where the flavours have been allowed to blend.

This is now my new recipe for getting myself out of trouble with the better half. 😉

For those reading from outside Newfoundland, we sometimes call this ‘Ragged Rock Rum Raisin Ice Cream’. Ragged Rock is a brand of amber rum sold in this province.

You can, of course, substitute your favourite brand but the name won’t roll off the tongue quite as well for fans of alliteration. 😉

Rum Raisin Ice Cream

Rum Raisin Ice Cream

You may also want to try another favourite Locally inspired ice cream. Newfoundland blueberries are just exceptional in this Blueberry Ripple Ice Cream.

For the folks who have been asking if you can make this without an ice cream maker, I’m afraid not. To get the proper fine crystal structure and creamy texture you will need one.

I have found the ice cream maker that I use to be well worth the small investment.

Cuisinart Ice cream maker

The Cuisinart Ice Cream Maker that I use.

Need more culinary inspiration?

Rock Recipes most popular posts of the last decade image with title text for Pinterest

Like this Rum Raisin Ice Cream recipe?

Rum Raisin Ice Cream

Rum Raisin Ice Cream

You can also sign up for our FREE newsletter to know immediately when we add new recipes. You’ll also get weekly suggestions for great family friendly  meals and desserts too!

Rock Recipes a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites. Our product recommendations are almost exclusively for those we currently use or have used in the past.

Prep Time:

Cook Time:

Total Time:

Rum Raisin Ice Cream – if you are a fan of rum raisin ice cream, this homemade version may well be the best you will ever try. A few simple ingredients truly create something exceptionally delicious.


  • 1 cup raisins
  • 4 ounces dark or amber rum, I like dark for this recipe because it has deeper flavour and also adds some colour.
  • 1 cup sugar
  • 6 egg yolks
  • 2 cups whipping cream, 35% milk fat or higher
  • 2 cups whole milk
  • 1 tbsp pure vanilla extract


  1. Soak raisins in the rum overnight in an airtight container. I like to use a mason jar so that I can shake it every now and then to ensure the raisins are evenly soaked.
  2. Combine the milk and cream and heat in the microwave (or on top of the stove over medium heato scalding but not boiling.
  3. In a medium sized saucepan whisk together the egg yolks and sugar very well for about 3 minutes until the mixture is pale and fluffy.
  4. Whisking constantly, add about a cup of the scaled milk to the egg yolk mixture. This tempers the egg yolks so that they do not cook and scramble. Whisk in about another cup and make sure it is well blended with the egg yolk mixture. Finally add the remaining scaled milk and cream and make sure it is well blended in.
  5. Place the saucepan over medium heat and stir constantly but slowly for about 5 minutes until the mixture slightly thickens. At this point you should be able to dip the wooden spoon in the custard and draw a distinct line with your finger on the back of the wooden spoon. Do not boil or mixture may curdle.
  6. Remove from heat and stir in the vanilla extract. Chill the custard very well for several hours or overnight. I chill it overnight while the raisins soak in the rum.
  7. When completely chilled, stir the custard well and pour into your ice cream maker. Process for 20- 30 minutes until the ice cream becomes as thick as possible.
  8. Transfer the ice cream quickly to a chilled metal or glass bowl and very quickly fold in the soaked raisins and any rum that has not been absorbed by them.
  9. Place in an airtight container and freeze in the coldest part of your refrigerator freezer or deep freezer. for several hours or preferably overnight before serving.
  10. I like to fold the ice cream at least a couple of times every couple of hours to make sure all of the raisins do not settle to the bottom of the container and to make sure they get evenly distributed throughout the ice cream.



Serving Size


Amount Per Serving

The nutritional information provided is automatically calculated by third party software and is meant as a guideline only. Exact accuracy is not guaranteed. For recipes where all ingredients may not be used entirely, such as those with coatings on meats, or with sauces or dressings for example, calorie & nutritional values per serving will likely be somewhat lower than indicated.

Researchers use a version of the Doppler effect to gauge the distances of objects. This is similar to figuring out the location of an ambulance based on its siren: The siren sounds higher in pitch as it approaches and then lower as it recedes. The farther away a galaxy is, the faster it moves away from us, and so its light stretches to longer wavelengths and appears redder. The magnitude of this “redshift” is expressed as z, where a given value for z tells you how long an object’s light must have traveled to reach us.

One of the first papers on JWST data came from Naidu, the MIT astronomer, and his colleagues, whose search algorithm flagged a galaxy that seemed inexplicably bright and unaccountably distant. Naidu dubbed it GLASS-z13, indicating its apparent distance at a redshift of 13 — further away than anything seen before. (The galaxy’s redshift was later revised down to 12.4, and it was renamed GLASS-z12.) Other astronomers working on the various sets of JWST observations were reporting redshift values from 11 to 20, including one galaxy called CEERS-1749 or CR2-z17-1, whose light appears to have left it 13.7 billion years ago, just 220 million years after the Big Bang — barely an eyeblink after the beginning of cosmic time.

Some astronomers and media outlets claimed that JWST was breaking cosmology, but not everyone was convinced. One problem is that ΛCDM’s predictions aren’t always clear-cut. While dark matter and dark energy are simple, visible matter has complex interactions and behaviors, and nobody knows exactly what went down in the first years after the Big Bang; those frenetic early times must be approximated in computer simulations. The other problem is that it’s hard to tell exactly how far away galaxies are.

In the months since the first papers, the ages of some of the alleged high-redshift galaxies have been reconsidered. Some were demoted to later stages of cosmic evolution because of updated telescope calibrations. CEERS-1749 is found in a region of the sky containing a cluster of galaxies whose light was emitted 12.4 billion years ago, and Naidu says it’s possible the galaxy is actually part of this cluster — a nearer interloper that might be filled with dust that makes it appear more redshifted than it is. According to Naidu, CEERS-1749 is weird no matter how far away it is. “It would be a new type of galaxy that we did not know of: a very low-mass, tiny galaxy that has somehow built up a lot of dust in it, which is something we traditionally do not expect,” he said. “There might just be these new types of objects that are confounding our searches for the very distant galaxies.”

The Lyman Break

Everyone knew that the most definitive distance estimates would require JWST’s most powerful capability.

JWST not only observes starlight through photometry, or measuring brightness, but also through spectroscopy, or measuring the light’s wavelengths. If a photometric observation is like a picture of a face in a crowd, then a spectroscopic observation is like a DNA test that can tell an individual’s family history. Naidu and others who found large early galaxies measured redshift using brightness-derived measurements — essentially looking at faces in the crowd using a really good camera. That method is far from airtight. (At a January meeting of the American Astronomical Society, astronomers quipped that maybe half of the early galaxies observed with photometry alone will turn out to be accurately measured.)

But in early December, cosmologists announced that they had combined both methods for four galaxies. The JWST Advanced Deep Extragalactic Survey (JADES) team searched for galaxies whose infrared light spectrum abruptly cuts off at a critical wavelength known as the Lyman break. This break occurs because hydrogen floating in the space between galaxies absorbs light. Because of the continuing expansion of the universe — the ever-rising raisin loaf — the light of distant galaxies is shifted, so the wavelength of that abrupt break shifts too. When a galaxy’s light appears to drop off at longer wavelengths, it is more distant. JADES identified spectra with redshifts up to 13.2, meaning the galaxy’s light was emitted 13.4 billion years ago.

Brant Robertson, a JADES astronomer at the University of California, Santa Cruz, says the findings show that the early universe changed rapidly in its first billion years, with galaxies evolving 10 times quicker than they do today. It’s similar to how “a hummingbird is a small creature,” he said, “but its heart beats so quickly that it is living kind of a different life than other creatures. The heartbeat of these galaxies is happening on a much more rapid timescale than something the size of the Milky Way.”

But were their hearts beating too fast for ΛCDM to explain?

Theoretical Possibilities

As astronomers and the public gaped at JWST images, researchers started working behind the scenes to determine whether the galaxies blinking into our view really upend ΛCDM or just help nail down the numbers we should plug into its equations.

One important yet poorly understood number concerns the masses of the earliest galaxies. Cosmologists try to determine their masses in order to tell whether they match ΛCDM’s predicted timeline of galaxy growth.

A galaxy’s mass is derived from its brightness. But Megan Donahue, an astrophysicist at Michigan State University, says that at best, the relationship between mass and brightness is an educated guess, based on assumptions gleaned from known stars and well-studied galaxies.

One key assumption is that stars always form within a certain statistical range of masses, called the initial mass function (IMF). This IMF parameter is crucial for gleaning a galaxy’s mass from measurements of its brightness, because hot, blue, heavy stars produce more light, while the majority of a galaxy’s mass is typically locked up in cool, red, small stars.

But it’s possible that the IMF was different in the early universe. If so, JWST’s early galaxies might not be as heavy as their brightness suggests; they might be bright but light. This possibility causes headaches, because changing this basic input to the ΛCDM model could give you almost any answer you want. Lovell says some astronomers consider fiddling with the IMF “the domain of the wicked.”

Leave a Reply

Your email address will not be published. Required fields are marked *