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Galaxies Like Grains of Salt

I’m riffing on a Brian Aldiss title this morning, the reference being the author’s 1959 collection Galaxies Like Grians of Sand, which is a sequence of short stories spanning millions of years of Earth’s future (originally published as The Canopy of Time). But sand is appropriate for the exercise before us today, one suggested by memories of the day my youngest son told me he had to construct a model of an atom and we went hunting all over town for styrofoam balls. It turns out atoms are easy.

Suppose your child comes home with a project involving the creation of a scale model of the galaxy. Pondering the matter, you announce that grains of salt can stand in for stars. Sand might work as well, but salt is easier because you can buy boxes of salt at the grocery. So while your child goes outside to do other things, you and your calculator get caught up in the question of modeling the Milky Way. Just how much salt will you need?

Most models of the galaxy these days come in at a higher number than the once canonical 100 billion stars. In fact, 200 billion may be too low. But let’s economize by sticking with the lower number. So you need 100 billion grains of salt to make your scale model accurate. A little research reveals that the average box of Morton salt weighs in with about five million grains. Back to the calculator. You will need 20,000 boxes of salt to make this work. The local grocery doesn’t keep this much in stock, so you turn to good old Amazon, and pretty soon a semi has pulled up in front of your house with 20,000 blue boxes of salt.

But how to model this thing? I wouldn’t know where to begin, but fortunately JPL’s Rich Terrile thought the matter through some time back and he knows the answer. If we want to reflect the actual separation of stars just in the part of the galaxy we live in, we have to separate each grain of salt by eleven kilometers from any of its neighbors. Things get closer as we move in toward the bulge. Maybe your child has lots of friends to help spread the salt? Let’s hope so. And plenty of room to work with for the model.

I mention all this because I was talking recently with Nate Simpson, lead developer of Kerbal Space Program 2, and colleague Jon Cioletti. This is the next iteration of the remarkable spaceflight simulation game that offers highly realistic launch and orbital physics capabilities. We were talking deep space, and the salt box comparison came naturally, because these guys are also in the business of reaching a broader audience with extraordinary scales of time and space.

I strongly recommend Kerbal, by the way, because I suspect Kerbal Space Program has already turned the future career path of more than a few young players in the direction of aerospace, just as, say, science fiction novels or Star Trek inspired an earlier generation in that direction. Watching what develops as Kerbal goes into version 2 will be fascinating.

Unexpected Interstellar Targets

But I was also thinking about the salt box analogy because it can be so difficult to get interstellar distances across to the average person, who may know on some level that a galaxy is a very big place, but probably doesn’t have that deep awe that a real acquaintance with the numbers delivers. I think about craft trying to navigate these immensities, and also about objects like ‘Oumuamua and 2I/Borisov, the first two known interstellar objects we have detected. What vast oceans of interstellar space such tiny objects have drifted through! Clearly, as our ability to observe them grows, we’ll find many more such objects, and one of these days we’ll get a mission off to study one up close (probably designed by Andreas Hein and team).

Image: This Hubble Space Telescope image of 2I/Borisov shows the first observed rogue comet, a comet from interstellar space that is not gravitationally bound to a star. It was discovered in 2019 and is the second identified interstellar interloper, after ‘Oumuamua. 2I/Borisov looks a lot like the traditional comets found inside our solar system, which sublimate ices, and cast off dust as they are warmed by the Sun. The wandering comet provided invaluable clues to the chemical composition, structure, and dust characteristics of planetary building blocks presumably forged in an alien star system. It’s rapidly moving away from our Sun and will eventually head back into interstellar space, never to return. Credit: NASA, ESA, and D. Jewitt (UCLA).

I was heartened to learn over the weekend that the James Webb Space Telescope will likely have a role to play in further detection efforts. Indeed, there is now a Webb Target of Opportunity program that homes in on just such discoveries. Here is how a Target of Opportunity is defined on the JWST website:

A target for JWST observation is deemed a Target of Opportunity (ToO) if it is associated with an event that may occur at an unknown time, and in this way ToOs are distinct from time constrained observations.

Sounds made to order for interstellar interlopers. But we can add this:

ToO targets include objects that can be identified in advance, but which undergo unpredictable changes (e.g., some dwarf novae), as well as objects that can only be identified in advance by class (e.g., novae, supernovae, gamma ray bursts, newly discovered comets, etc.). ToOs are generally not suitable for observations of periodic phenomena (e.g., eclipsing binary stars, transiting planets, etc.). ToO proposals must provide a clear definition of the trigger criteria and present a detailed plan for the observations to be performed in the technical justification of the PDF submission if the triggering event occurs. A ToO activation may consist of a single observation or of a set of observations executed with a pre-specified cadence.

Martin Cordiner (NASA GSFC/Catholic University of America) is principal investigator of the Webb Target of Opportunity program to study the composition of an interstellar object:

“The supreme sensitivity and power of Webb now present us with an unprecedented opportunity to investigate the chemical composition of these interstellar objects and find out so much more about their nature: where they come from, how they were made, and what they can tell us about the conditions present in their home systems, The ability to study one of these and find out its composition — to really see material from around another planetary system close up — is truly an amazing thing.”

Image: This artist’s illustration shows one take on the first identified interstellar visitor, 1I/’Oumuamua, discovered in 2017. The wayward object swung within 38 million kilometers of the Sun before racing out of the solar system. 1I/’Oumuamua still defies any simple categorization. It did not behave like a comet, and it had a variety of unusual characteristics. As the complex rotation of the object made it difficult to determine the exact shape, there are many models of what it could look like. Credit: NASA, ESA, and J. Olmsted and F. Summers (STScI).

When astronomers detect another interstellar interloper, they’ll first need to confirm that it’s on a hyperbolic orbit, and if JWST is to come into play, that its trajectory intersects with the telescope’s viewing field. If that’s the case, Cordiner’s team will use JWST’s Near-Infrared Spectrograph (NIRSpec) to examine gasses released by the object due to the Sun’s heat. The spectral resolution available here should allow the detection of molecules ranging from water, methanol, formaldehyde and carbon dioxide to carbon monoxide and methane. The Mid-infrared instrument (MIRI) will track any dust or solid particles produced by the object.

The near- and mid-infrared wavelength ranges will be used to examine interstellar interlopers for the first time with this program, making this fertile ground for new discoveries. The assumption being that such objects exist in vast numbers, the Webb Target of Opportunity program should find material to work with, and likely soon, especially given JWST’s ability to detect incoming objects at extremely faint magnitudes. Are most such discoveries likely to be comet-like, or do we have the possibility of finding other objects as apparently anomalous as ‘Oumuamua?


{ 29 comments… add one }
  • Ronald February 22, 2022, 16:58

    Hothouse by Aldiss was always one of my favorites, and of course the Helliconia trilogy.

  • Geoffrey Hillend February 22, 2022, 17:04

    Wow! If the salt grains are eleven kilometers apart, then ten of them would be one hundred and ten kilometers apart, so increase 100 billion suns by a factor of ten and we get a model roughly one trillion kilometers wide or on fifth of a light year or at least a lot larger than our solar system considering the closer packed stars in the center.

    We found ‘Oumuanua’ without the JWST, so I don’t know how often they come but if would certainly be nice to look at one with the JWST when it is closet to us or the Sun.

    • Geoffrey Hillend February 27, 2022, 16:49

      Maybe it’s more like a tenth of a light year since one trillion kilometers is 621 billion miles which is still a large area.

  • Simon February 22, 2022, 17:11

    This is highly interesting! Reminds me to read the one novel of Brian Aldiss which I own, bought it used for dirt cheap a couple years ago…

  • Alex Tolley February 22, 2022, 19:16

    I read Aldiss’ short story collection with the Bruce Pennington cover for the NEL edition: “The Canopy of Time”.

    A great British writer with some very memorable and creative stories (although I was never able to manage to get far into “Barefoot in the Head”).

    [BTW – the book link has a spelling error: ‘grains” not “grians”]

    If we want to reflect the actual separation of stars just in the part of the galaxy we live in, we have to separate each grain of salt by eleven kilometers from any of its neighbors.

    On that scale, what is the distance from the center of the galaxy (Trantor) to its edge (Terminus)?

  • gbaikie February 22, 2022, 20:11

    “A little research reveals that the average box of Morton salt weighs in with about five million grains. Back to the calculator. You will need 20,000 boxes of salt to make this work. ”

    Why not count a star for how volume of space it illuminates by some amount.
    Or our sun’s sunlight make Mars look like dim star.
    Whereas if our star was Proxima Centauri, at Mars distance, Mars would be too dim to see.
    Or the size of star is amount volume of space it lights up [by some amount].
    So, something as dim and small as Proxima Centauri could equal one grain of salt, and stars like our Sun could equal many grain of salt, and some others like golf balls.
    Anyhow one made the star bigger, by the amount volume they illuminate [by some amount- like say 500 watts per square meter] rather the radius of their light producing atmospheres.
    Though if one could decide how much sunlight needed for it to within a habitable zone- the size of star could be the size of it’s habitable zone and that could equal to a grain of salt. Though still huge area- could be tiny lights in a golf course.

  • kzb February 22, 2022, 22:21

    I like the grains of salt model idea, in fact it interested me so much I checked it !
    Unfortunately I can’t replicate the result. If a grain of salt is 0.1mm diameter and an average star is say 200,000km in diameter, the scale factor is 5E-16.
    One light-year on this scale is about 5 metres, so in our galactic neighbourhood the grains of salt would be about 20-25 metres apart.
    Taking the classical diameter of our galaxy as 100,000LY, it is about 500km in diameter when made of salt-grain stars.
    Am I doing something wrong?

  • Brian Altmeyer February 22, 2022, 22:51

    Bit of a tangent thought inspired by the “grains of salt” description: The enormity of such scales makes some people despair of humanity playing any role in truly deep time, but I think it just means our strategies will be subtle.

    No magic physics needed; just more details. E.g., someone from the 18th century or earlier who was told to conceptualize the workings of a modern processor would imagine an impossible number and scale of metallic gears, and just throw their hands up. They would likewise despair of the energy requirements of a jet aircraft, realizing them to be effectively infinite if they had to generate the energy with onboard steam boilers as they understood them.

    But the subtleties realized since then have brought such outputs into the realm of physical possibility, then technological possibility, and finally practicality.

    I am probably just an incurable optimist, but I fully expect a Deep Time humanity to do the same with galactic scales of distance; accumulating little details and tricks in the nuances of otherwise known principals until they add up to a sudden expansion of horizons. Probably repeatedly, as this has been the case repeatedly so far.

    Since infinities are not physically real quantities, if they show up in physical calculations, that’s just a pointer at where theory needs to evolve in reference to the empirical universe. The idea of unconditional limits presupposes that we are even capable of framing unconditional questions about the universe we inhabit; something we can safely declare false.

    More than once, we have found what was assumed absolute to be only circumstantial.

    Look deep enough at the texture of a wall, and you find where it stops being a wall.

  • Henry Cordova February 23, 2022, 1:09

    The universe is extravagantly large. All you really need is one Milky Way, all those other galaxies are superfluous, especially since we’ll never really get a good look at any of them. And we have only known that for about a century. Even our own home galaxy has places we’ll never see up close unless we can find a way to travel there. Not only are we insignificant, but everything we can ever hope to see or know is insignificant.

    As for the ability to visualize the times and distances involved, forget it. Even training in the sciences and math cannot give you a real appreciation of the numbers involved. Sure, you can write down the zeroes, even do meaningful calculations, but you never really get an emotional grasp of it all.

    And it works going the other way, too. When I was kid, I used to own one of those old fashioned radium-dial alarm clocks, you know, the ones which poisoned the factory workers who painted the numbers on the dials. I took it into a dark closet, let my eyes fully adapt to the darkness, and looked at the glowing numbers with a jeweler’s loupe. (about 10x magnification).

    A little bit of radium was mixed in with a phosphorescent paint which flashed when a radium atom disintegrated. An alpha particle emitted during the disintegration interacts with the electron cloud of a nearby phosphorus atom. The flash is just visible to the human eye, under the right conditions, as I discovered. What is actually experienced in this experiment is an infinity of flashes, each barely resolved at the limit of human vision, reminiscent of raindrops falling and splashing unto a flat sea during a furious rainstorm, or the drumming of a cloudburst onto a tin roof. The individual events can actually be perceived!

    Every one of those flashes is one radium atom decaying, and the half-life of radium is 1600 years, which gives you some idea of how many atoms are there, ready for their turn to die. ” Infinity in a grain of send, eternity in an hour.”

    For obvious reasons, this sort of clock is difficult to find these days, but if you ever get a chance to try this experiment yourself, don’t hesitate. Its the only way you can emotionally grasp what you think you know intellectually.

    There must be some kind of metaphysical significance to all this…Or maybe we just think there is.

  • kzb February 23, 2022, 7:51

    Oops I made 3 orders of magnitude mistake in my post above !
    Sorry about that, I had microns in my brain or something.
    The scale factor is actually 5 E-13 and not 5 E-16 as I stated above.
    On this scale, 1 light-year is 4.73km.
    Salt-grain stars in our neighbourhood would be roughly 20km apart.
    I guess the difference from 11km as stated in the article is down to what sizes you ascribe to salt grains and the average star.
    The galaxy would be about 500,000km across on this scale.

    • Alex Tolley February 23, 2022, 14:55

      IOW is larger than the distance from the Earth to the Moon. What an art project that would make, if every grain was illuminated by laser light so that the whole galaxy of grains was brightly shining on that scale. Placed in space beyond the Moon, it might last for a short while before it dissipated. But what a sight!

      Seems like a Jon Lomberg sort of project.

  • Scott Guerin February 23, 2022, 10:40

    Preview paragraph of an article I’m writing for CD…check my math!

    “Imagine if the 2.5 million light-year separation between M31 and the Milky Way were scaled down to 100 meters. At that scale, (.04mm = 1LY) the Milky Way galaxy would be about 4 meters in diameter, M31 almost twice that. A message, inscribed in the shell of a highly trained mail snail, would move from the model Milky Way to the model M31 at almost 7 times the speed of light, that’s warp factor 1.7 in terms of Star Trek’s Enterprise performance.”

  • ljk February 23, 2022, 12:23

    Here is some scale for you: If the entire Sol system were the size of a cup of coffee, the Milky Way galaxy would be the size of North America!

  • Ron S. February 23, 2022, 13:58

    If we use salt grains for stars, what do we use for the greater quantity of dark matter in the galaxy?


    • Paul Gilster February 23, 2022, 20:31

      Will have to give that one some serious thought!

    • Alex Tolley February 23, 2022, 22:00

      Lots of black pepper? Molasses?

      • Paul Gilster February 24, 2022, 7:14

        OK Alex, your job is to calculate the amount of molasses needed to accurately model the Milky Way’s dark matter.

        • Alex Tolley February 24, 2022, 11:14

          Using this as a reference Scientists weighed all the mass in the Milky Way galaxy. It’s mind-boggling, the mass of the galaxy is 4% stars and 84% dark matter. So dark matter (molasses) is 22x the stars (salt).

          Assuming your Morton’s salt boxes are the 737g (1 lb) size, we need 324,289,000 g of molasses. The popular Grandma’s brand of molasses comes in a 12 fl oz jar. (using the density of molasses as 1.6x water, that is 568 g). So you need 570,915 jars of molasses for your model.

          Now, how you apply that is another problem…

  • Robin Datta February 24, 2022, 2:17

    Maybe – just mybe – JWST could crack the Fermi Paradox with incontrovertible evidence: from afar with an exoplanet/exomooxn or perhaps nearer to home with an interstellar intruder?

  • Robin Datta February 24, 2022, 2:31

    Almost a bit dated now, and seen by many, but still one of the better realistic visual projections of our universe:

    A Flight Through the Universe, by the Sloan Digital Sky Survey
    YouTube · Berkeley Lab Aug 8, 2012

  • William February 25, 2022, 3:30

    This exercise reminds me of the Galaxy Garden

  • wdk March 1, 2022, 0:01

    Maybe you could get another galaxy to substitute for the Milky one.
    How about the Lesser Magellanic Cloud. It will save on delivery fees.

    Brian Aldiss stories were a little disturbing when I read them as a grammar schooler when they came out in paperback. “Starship” did not prepare me for “Galaxies Like Grains of Sand”, about midway between the former and Lovecraft stories. This left me with the question: “Are we sure we want to go out and do this?”

    Since I later became fascinated by planets in binary star systems, however, was rather fascinated by the trilogy Aldiss wrote circa 1980 about Helliconia.

    The underlying idea was that a planet with humanoid life in a couple of species experienced prolonged seasons, durations of millenia, resulting in cyclic advances and declines of civilization. It was a little easier reading than the aforementioned stories, especially when you are down with the flu and have intermittent fever.

    From my own experience with 3 body systems, I think that similar climate effects could have been brought on by precession of apsides and ccentricity variations. Or else it would have been more plausible than the assumption of two different main sequence stars in such an eccentric and long duration orbit. There also seemed to be suggestions in the first volume that someone else beside the spacecraft from Earth was watching Helliconia. But this and other creatures were introduced and then forgotten. Or so it seemed.

    Shortly after reading this series, perhaps it was on Discovery cable, I saw animated excerpts of what looked like a screen adaptation of the story. Was it just a brief illustration or actually a feature film?

    • Paul Gilster March 1, 2022, 5:57

      Good to have you back, my friend.

  • James M. Essig March 2, 2022, 13:34

    Given the huge amount of hydrogen in our cosmic light-cone which for practical purposes I assume is of about 13.75 billion light-years in radius, some fascinating prospects emerge for consideration. What I have to say is related to applications of using a large fraction of the energy available in a given cosmic light-cone to power mass-drivers capable of accelerating craft to kinetic energies in principle beyond that contained in a present era cosmic light-cone in our universe. These ideas are currently science fiction for sure. However, perhaps they are not as absurd as proposals of super-luminal travel that would violate chronological protection conjectures.

    Here is my latest writing this morning in my book, “Breaching The Light Barrier. Volume 8.”. The book is still very much in the writing stage.

    Here, we consider a solenoidal electromagnet that spans the diameter of a cosmic light-cone yet produces a magnetic field having more total energy than otherwise in the cosmic light-cone of location.

    Accordingly, the electromagnet and its magnetic field may have somewhat greater to much greater mass-energy than would a black hole in ordinary 4-D space-time of radius equal to that of a cosmic light-cone.

    Accordingly, the kinetic energy of a craft accelerated down such a huge electromagnet may obtain somewhat greater to many times greater kinetic energy than is contained within a cosmic light-cone of the same cosmic era.

    The general idea is that magnetic field would extend over one cosmic light-cone diameter.

    Ideally, a solenoidal electromagnet would grow in a self-assembling manner facilitated by advanced computer nanotechnology methods.

    For example, the solenoid may be produced of background hydrogen which is nanotechnologically converted into solenoidal extensions. The hydrogen would be converted to a superconductive metallic phase. Accordingly, nano-molecular machines would be beamed at near light-speed in mass beams, or even effectively the speed of light in cases where the molecular machines are quantum-mechanically teleported. This way, the length of the tube may progress through space at velocities of construction as great as the velocity of light.

    As another example, chaotic processes might be harnessed for which the wavefront of a hydrogen gas cloud compression mechanism proceeds at substantially the speed of light. The gas clouds would be perturbed in just the proper manners so that nano-technology equipment would condense out of the cloud to enable the construction of the solenoid to proceed at the speed of light.

    As yet another example, astronauts and mechanized systems may be accelerated to velocities close to that of light whereby these combinations would perturb hydrogen gas clouds as said combinations traveled. The perturbation may be either chaotic and dependent on initial conditions, mediated by drop-away molecular and macroscopic machines, or due to a series of astronaut and machinery drop away processes for which the drop-away assets slow relative to the background to extents conducive to controlled assembly of the solenoid segments.

    As yet another example, portions of the solenoid may be locally or dispersively fabricated and then sent on itineraries to be joined to the growing end of the solenoid. Thus, the segments of the solenoid may be sent at near the velocity of light upon which the segments would slow to a virtual stand-still at the leading edges of the solenoid where they would then self-graft onto the primary solenoid. The segments directed to the leading edges of the solenoid can have any useful angle of incidence of travel relative to the leading edges of the solenoid thus opening up the entire volumes of light-cones for mediating the construction and transit of the segments.

    Since solenoids can grow along both directions along their lengths, the recessional velocity of the ends of the solenoids with respect to each other upon the solenoid attaining length of one cosmic light-cone diameter unit would then be equal to at least twice the velocity of light. For cases where the solenoid end extends just outside of a cosmic light-cone radius unit centered on the mid-point of the solenoids for which the construction wavefront of the solenoids progresses at substantially the speed of light relative to the local background, the recessional velocity of the construction wavefronts from each other grows to at least four times the speed of light.

    Refer to the subject portions of this book that cover spacecraft recessional velocities from the point of origin for expanding universes as functions of relativistic velocities or light-speed velocity with respect to the background and cosmic light-cone radius units of separation of the spacecraft with respect to its point of origin.

    Thus, in a way, super-luminal classical systems are possible.
    Electromagnets of extra-cosmic-light-cone extension may in principle be collapsed in destructive or non-destructive manners. Destructive collapse may be mediated by chemical or nuclear explosives and non-destructive collapse can be mediated by mechanical or electromechanical aspects that constrict the solenoidal cross-section.

    The solenoid may be made of elastic superconductors to facilitate non-destructive compression.

  • Mike Serfas March 4, 2022, 9:31

    Grains of salt seem a little large for this. According to http://www.vendian.org/envelope/dir0/grain_feel.html the grains of salt are 0.5 mm, which would make your box about 5 cups. So let’s replace these with “PM 2.5 particles” ( https://en.wikipedia.org/wiki/PM-2.5 ) commonly spoken of regulators. Fortunately, we don’t have to figure out what these are, because part’s is part’s, and they can regulate your barbecue grill instead of a chemical plant to get the count down. Now 2.5 is 2.5 microns, so these are 2000 times smaller in every direction than salt grains. Instead of 20000 boxes of PM 2.5s you only need 2E4/8E9 = 1/400000 of a box. Well shaken and mixed, of course. Using a density roughly like salt (they could be salt after all), I’ll suppose a liter or so of irregular salt grains might weigh around 2 kg, and then we have 5 milligrams of PM2.5 particles in that box. According to Wikipedia and/or some European regulatory agency, that’s enough to raise your lung cancer risk by 18000%, if we don’t care the particles are salt; but that’s in a meter cube. Disseminated 11 km/2000 = 5.5 meters away from each other to form a galaxy model, the risk would be lower; multiply that by I dunno, 150000/4?, we can fit the whole model in a 200-km metropolitan region.

    The good news is that someone has probably set up a very good model of the Milky Way that you’re standing somewhere inside right now. The bad news is they have many (all?) of the other galaxies modelled in the same space, reportedly causing 4 million deaths a year, and you have to go through the air particle by particle to figure out which star is in the galaxy you’re interested in.

    • Alex Tolley March 4, 2022, 11:50

      At 2.5um, the modeled stars are invisible w/o a microscope. It would be hard enough to see salt grains so thinly dispersed, but micron-sized particles would really be hard to detect. ;)

      Bacteria would be good “particles” to meet the 2.5um diameter. Unfortunately, they might replicate and increase the density of the galaxy quite quickly. To keep that in check. we have to add “dark matter” phage viruses. Now we have an evolving galaxy, where the bacteria stars emerge, grow and then die, in a cycle of rebirth, but with the available energy slowly being lost to entropy. The galaxy eventually dies, just being composed of dormant bacterial spores as “black holes” and cooling “white dwarfs”, and phage viruses with no more like bacteria to infect and replicate from.

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