Tag: Jeremy

It’s in The Book

On By rolcottIn Chemistry, Physics: Entropy and Thermodynamics, Physics: Quantum Mechanics, UncategorizedLeave a comment

A young man’s knock, eager yet a bit hesitant. “Door’s open, Jeremy, c’mon in.”

“Hi, Mr Moire, I’ve got something to show you. It’s from my acheii, my grandfather. He said he didn’t need it any more now he’s retired so he gave it to me. What do you think?”

“Wow, the CRC Handbook of Chemistry And Physics, in the old format, not the 8½×11″ monster. An achievement award, too — my congratulations to your grandfather. Let’s see … over 3000 pages, and that real thin paper you can read through. It’s still got the math tables in front — they moved those to an Appendix by the time I bought my copy. Oooh yeah, lots of data in here, probably represents millions of grad student lab hours. Tech staff, too. And then their bosses spent time checking the work before publishing.”

“Acheii said I’d have to learn a lot before I could use it properly. I see lots of words in there I don’t recognize.” <opens book to a random page> “See, five- and six‑figure values for, what’re Specific Heat and Enthalpy?”

“Your grandfather’s absolutely correct. Much of the data’s extremely specialized. Most techs, including me, have a few personal‑favorite sections they use a lot, never touch the rest of the book. These particular pages, for instance, would be gold for a someone who designs or operates steam‑driven equipment.”

“But what do these numbers mean?”

“Specific Heat is the amount of heat energy you need to put into a certain mass of something in order to raise its temperature by a certain amount. In the early days the Brits, the Scots really, defined the British Thermal Unit as the amount of energy it took to raise the temperature of one pound of liquid water by one degree Fahrenheit. You’d calculate a fuel purchase according to how many BTUs you’d need. Science work these days is metric so these pages tabulate Specific Heat for a substance in joules per gram per °C. Tech in the field moves slow so BTUs are still popular inside the USA and outside the lab.”

“But these tables show different numbers for different temperatures and they’re all for water. Why water? Why isn’t the Specific Heat the same number for every temperature?”

“Water’s important because most power systems use steam or liquid water as the working fluid or coolant. Explaining why heat capacity varies with temperature was one of the triumphs of 19th‑century science. Turns out it’s all about how atomic motion but atoms were a controversial topic at the time. Ostwald, for instance—”

“Who?”

“Wilhelm Ostwald, one of science’s Big Names in the late 1800s. Chemistry back then was mostly about natural product analysis and seeing what reacted with what. Ostwald put his resources into studying chemical processes themselves, things like crystallization and catalysis. He’s regarded as the founder of Physical Chemistry. Even though he invented the mole he steadfastly maintained that atoms and molecules were nothing more than diffraction‑generated illusions. He liked a different theory but that one didn’t work out.”

“Too bad for him.”

“Oh, he won the first Nobel Prize in Chemistry so no problem. Anyway, back to Specific Heat. In terms of its molecules, how do you raise something’s temperature?”

“Um, temperature’s average kinetic energy, so I’d just make the molecules move faster.”

“Well said, except in the quantum world there’s another option. The molecules can’t just waggle any which way. There are rules. Different molecules do different waggles. Some kinds of motion take more energy to excite than others do. Rule 1 is that the high‑energy waggles don’t get to play until the low‑energy ones are engaged. Raising the temperature is a matter of activating more of the high‑energy waggles. Make sense?”

“Like electron shells in an atom, right? Filling the lowest‑energy shells first unless a photon supplies more energy?”

“Exactly, except we’re talking atoms moving within a molecule. Smaller energies, by a factor of 100 or more. My point is, the heat capacity of a substance depends on which waggles activate as the temperature rises. We didn’t understand heat capacity until we applied quantum thinking to the waggles.”

“What about ‘Enthalpy’ then?”

Crystal photo by JJ Harrison

~ Rich Olcott

Mushy stuff

On By rolcottIn Crazy Theories, Physics: Black Holes and Relativity, UncategorizedLeave a comment

“Amanda! Amanda! Amanda!”

“All right, everyone, settle down for our final Crazy Theorist. Jim, you’re up.”

“Thanks, Cathleen. To be honest I’m a little uncomfortable because what I’ve prepared looks like a follow-on to Newt’s idea but we didn’t plan it that way. This is about something I’ve been puzzling over. Like Newt said, black holes have mass, which is what everyone pays attention to, and charge, which is mostly unimportant, and spin. Spin’s what I’ve been pondering. We’ve all got this picture of a perfect black sphere, so how do we know it’s spinning?”

Voice from the back of the room — “Maybe it’s got lumps or something on it.”

“Nope. The No-hair Theorem says the event horizon is mathematically smooth, no distinguishing marks or tattoos. Question, Jeremy?”

“Yessir. Suppose an asteroid or something falls in. Time dilation makes it look like it’s going slower and slower as it gets close to the event horizon, right? Wouldn’t the stuck asteroid be a marker to track the black hole’s rotation?”

“Excellent question.” <Several of Jeremy’s groupies go, “Oooh.”> “Two things to pay attention to here. First, if we can see the asteroid, it’s not yet inside the horizon so it wouldn’t be a direct marker. Beyond that, the hole’s rotation drags nearby spacetime around with it in the ergosphere, that pumpkin‑shaped region surrounding the event horizon except at the rotational poles. As soon as the asteroid penetrates the ergosphere it gets dragged along. From our perspective the asteroid spirals in instead of dropping straight. What with time dilation, if the hole’s spinning fast enough we could even see multiple images of the same asteroid at different levels approaching the horizon.”

Jeremy and all his groupies go, “Oooh.”

“Anyhow, astronomical observation has given us lots of evidence that black holes do spin. I’ve been pondering what’s spinning in there. Most people seem to think that once an object crosses the event horizon it becomes quantum mush. There’d be this great mass of mush spinning like a ball. In fact, that was Schwarzchild’s model for his non-rotating black hole — a simple sphere of incompressible fluid that has the same density throughout, even at the central singularity.”

VBOR — “Boring!”

“Well yeah, but it might be correct, especially if spaghettification and the Firewall act to grind everything down to subatomic particles on the way in. But I got a different idea when I started thinking about what happened to those two black holes that LIGO heard collide in 2015. It just didn’t seem reasonable that both of those objects, each dozens of solar masses in size, would get mushed in the few seconds it took to collide. Question, Vinnie?”

“Yeah, nice talk so far. Hey, Sy and me, we talked a while ago about you can’t have a black hole inside another black hole, right, Sy?”

“That’s not quite what I said, Vinnie. What I proved was that after two black holes collide they can’t both still be black holes inside the big one. That’s different and I don’t think that’s where Jim’s going with this.”

“Right, Mr Moire. I’m not claiming that our two colliders retain their black hole identities. My crazy theory is that each one persists as a high‑density nubbin in an ocean of mush and the nubbins continue to orbit in there as gravity propels them towards the singularity.”

VBOR —”Orbit? Like they just keep that dance going after the collision?”

“Sure. What we can see of their collision is an interaction between the two event horizons and all the external structures. From the outside, we’d see a large part of each object’s mass eternally inbound, locked into the time dilation just above the joined horizon. From the infalling mass perspective, though, the nubbins are still far apart. They collide farther in and farther into the future. The event horizon collision is in their past, and each nubbin still has a lot of angular momentum to stir into the mush. Spin is stirred-up mush.”

Cathleen’s back at the mic. “Well, there you have it. Amanda’s male-pattern baldness theory, Newt’s hyper‑planetary gear, Kareem’s purple snowball or Jim’s mush. Who wins the Ceremonial Broom?”

The claque responds — “Amanda! Amanda! Amanda!”

~ Rich Olcott

Virial Yang And Yin

On By rolcottIn Physics: Entropy and Thermodynamics, UncategorizedLeave a comment

“But Mr Moire, how does the Virial Equation even work?”

“Sometimes it doesn’t, Jeremy. There’s an ‘if’ buried deep in the derivation. It only works for a system in equilibrium. Sometimes people use the equation as a test for equilibrium.”

“Sorry, what does that mean?”

“Let’s take your problem galaxy cluster as an example. Suppose the galaxies are all alone in the Universe and far apart even by astronomical standards. Gravity’s going to pull them together. Galaxy i and galaxy j are separated by distance Rij. The potential energy in that interaction is Vij = G·mi·mj / Rij. The R‘s are very large numbers in this picture so the V attractions are very small. The Virial is the average of all the V’s so our starting Virial is nearly zero.”

“Nearly but not quite zero, I get that. Wait, if the potential energy starts near zero when things are far apart, and a falling‑in object gives up potential energy, then whatever potential energy it still has must go negative.”

“It does. The total energy doesn’t change when potential energy converts to kinetic energy so yes, we say potential energy decreases even though the negative number’s magnitude gets larger. It’d be less confusing if we measured potential energy going positive from an everything-all-together situation. However, it makes other things in Physics much simpler if we simply write (change in potential energy)+(change in kinetic energy)=0 so that’s the convention.”

“The distances do eventually get smaller, though.”

“Sure, and as the objects move closer they gain momentum and kinetic energy. Gaining momentum is gaining kinetic energy. You’re used to writing kinetic energy as T=m·v²/2, but momentum is p=m·v so it’s just as correct to write T=p²/2m. The two are different ways of expressing the same quantity. When a system is in equilibrium, individual objects may be gaining or losing potential energy, but the total potential energy across the system has reached its minimum. For a system held together by gravity or electrostatic forces, that’s when the Virial is twice the average kinetic energy. As an equation, V+2T=0.”

“So what you’re saying is, one galaxy might fall so far into the gravity well that its potential energy goes more negative than –2T. But if the cluster’s in equilibrium, galaxy‑galaxy interactions during the fall‑in process speed up other galaxies just enough to make up the difference. On the flip side, if a galaxy’s already in deep, other galaxies will give up a little T to pull it outward to a less negative V.”

“Well stated.”

“But why 2? Why not 3½ or some other number?”

“The 2 comes from the kinetic energy expression’s ½. The multiplier could change depending on how the potential energy varies with distance. For both gravity and electrostatic interactions the potential energy varies the same way and 2 is fine the way it is. In a system with a different rule, say Hooke’s Law for springs and rubber bands, the 2 gets multiplied by something other than unity.”

“All that’s nice and I see how the Virial Equation lets astronomers calculate cluster‑average masses or distances from velocity measurements. I suppose if you also have the masses and distances you can test whether or not a collection of galaxies is in equilibrium. What else can we do with it?”

“People analyze collections of stars the same way, but Professor Hanneken’s a physicist, not an astronomer. He wouldn’t have used class time on the Virial if it weren’t good for a broad list of phenomena in and outside of astronomy. Quantum mechanics, for instance. I’ll give you an important example — the Sun.”

“One star, all by itself? Pretty trivial to take its average.”

“Not averaging the Sun as an object, averaging its plasma contents — hydrogen nuclei and their electrons, buffeted by intense heat all the way down to the nuclear reactions that run near the Sun’s core. It’s gravitational potential energy versus kinetic energy all over again, but at the atomic level this time. The Virial Theorem still holds, even though turbulence and electromagnetic effects generate a complicated situation.”

“I’m glad he didn’t assign that as a homework problem.”

“The semester’s not over yet.”

~~ Rich Olcott

A Virial Homework Problem

On By rolcottIn Astronomy: Techniques, Physics: Entropy and Thermodynamics, Uncategorized1 Comment

“Uh, Mr Moire? Would you mind if we used Old Reliable to do the calculations on this problem about the galaxy cluster’s Virial?”

Data extracted and re-scaled from Fig 2 of Smith (1936), The Mass of the Virgo Cluster

“Mm, only if you direct the computation, Jeremy. I want to be able to face Professor Hanneken with a clear conscience if your name ever comes up in the conversation. Where do we start?”

“With the data he printed here on the other side of the problem sheet. Old Reliable can scan it in, right?”

“Certainly. What are the columns?”

“The first one’s clear. The second column is the distance between the galaxy and the center of the cluster. Professor Hanneken said the published data was in degrees but he converted that to kiloparsecs to get past a complication of some sort. The third column is, umm, ‘the relative line‑of‑sight velocity.’ I understand the line‑of‑sight part, but the numbers don’t look relativistic.”

“You’re right, they’re much smaller than lightspeed’s 300,000 km/s. I’m sure the author was referring to each galaxy’s motion relative to the other ones. That’s what the Virial’s about, after all. I’ll bet John also subtracted the cluster’s average velocity from each of the measured values because we don’t care about how the galaxies move relative to us. Okay, we’ve scanned your data. What do we do next?”

“Chart it, please, in a scatter plot. That’s always the first thing I do.”

“Wise choice. Here you go. What do we learn from this?”

“On the whole it looks pretty flat. Both fast and slow speeds are spread across the whole cluster. If the whole cluster’s rotating we’d see faster galaxies near the center but we don’t. They’re all moving randomly so the Virial idea should apply, right?”

“Mm-hm. Does it bother you that we’re only looking at motion towards or away from us?”

“Uhh, I hadn’t thought about that. You’re right, galaxy movements across the sky would be way too slow for us to detect. I guess the slowest ones here could actually be moving as fast as the others but they’re going crosswise. How do we correct for that?”

“Won’t need much adjustment. The measured numbers probably skew low but the average should be correct within a factor of 2. What’s next?”

“Let’s do the kinetic energy piece T. That’d be the average of galaxy mass m times v²/2 for each galaxy. But we don’t know the masses. For that matter, the potential energy piece, V=G·M·m/R, also needs galaxy mass.”

“If you divide each piece by m you get specific energy, joules/kilogram of galaxy. That’s the same as (km/s)². Does that help?”

“Cool. So have Old Reliable calculate v²/2 for each galaxy, then take the average.”

“We get 208,448 J/kg, which is too many significant figures but never mind. Now what?”

“Twice T would be 416,896 which the Virial Theorem says equals the specific potential energy. That’d be Newton’s G times the cluster mass M divided by the average distance R. Wait, we don’t know M but we do know everything else so we can find M. And dividing that by the galaxy count would be average mass per galaxy. So take the average of all the R distances, times the 416,896 number, and divide that by G.”

“What units do you want G in?”

“Mmm… To cancel the units right we need J/kg times parsecs over … can we do solar masses? That’d be easier to think about than kilograms.”

“Old Reliable says G = 4.3×10-3 (J/kg)·pc/Mʘ. Also, the average R is … 890,751 parsecs. Calculating M=v²·R/G … says M is about 90 trillion solar masses. With 29 galaxies the average is around 3 trillion solar masses give or take a couple of factors of 2 or so.”

“But that’s a crazy number, Mr Moire. The Milky Way only has 100 billion stars.”

“Sometimes when the numbers are crazy, we’ve done something wrong. Sometimes the numbers tell us something. These numbers mutter ‘dark matter‘ but in the 1930s only Fritz Zwicky was listening.”

~~ Rich Olcott

  • Thanks again to Dr KaChun Yu for pointing out Sinclair Smith’s 1936 paper. Naturally, any errors in this post are my own.

Viral, Virial, What’s The Difference?

On By rolcottIn Physics: Entropy and Thermodynamics, UncategorizedLeave a comment

A young man’s knock at my office door, eager yet a bit hesitant. “C’mon in, Jeremy, the door’s open.”

“Hi, Mr Moire. Got a minute?”

“It’s slow season, Jeremy. What can I do for you?”

“It’s my physics homework, sir. Professor Hanneken asked a question that I don’t understand.”

“John’s a bit of a joker but asking unsolvable questions isn’t usually one of his things. Well, except for that one about how long it would take to play Mahler’s Piano Quartet if you had only two musicians because of budget restrictions. What’s the question?”

“He wants us to use something called ‘the viral theorem‘ to deduce things about a certain galaxy cluster. I know what viral memes are but I don’t think I’ve ever heard of a theorem that spreads like a virus. I’ve done searches on my class notes and online textbook — nothing. So what is it and how am I supposed to use it?”

“Do you have the question with you?”

“Yessir, it’s #4 on this sheet.”

“Ah, just as I thought. Read it again. The word is ‘virial,’ not ‘viral.’ Big difference.”

“I suppose, but what’s a virial then?”

“We need some context. Imagine a cluster of free‑floating objects bound together by mutual forces of attraction. No central attractor, just lots of pairwise pulling, okay?”

“What kind of forces?”

“That’s the thing, it doesn’t matter. Gravitational, electrostatic, rubber bands even. The only restriction is that the force between each pair of objects follows the same force‑distance rule. For rubber bands it’s mostly just 1/distance until you get near the elastic limit. For gravity and electrostatics the rule is that force runs as 1/distance2. Got that picture?”

<grin> “It’d be tricky rigging up those rubber bands to not get tangled. Anyhow, instead of planets around the Sun you want me to think of stars held in a cluster by each other’s gravity. Do they all have to be the same size or the same distance apart?”

“No, because of what happens next. You’re thinking right — a heavier star pulls harder than a lighter one, and two stars close together feel more mutual force than stars far apart. We account for that variation by taking an average. Multiply force times distance for every possible pairing, then divide the total by the number of objects. The averaged number is the Virial, symbol V.”

“Wait, force times distance. That’s the Physics definition of work, like pulling something up against gravity.”

“Exactly. Work is directed energy. What we’re talking about here is the amount of energy required to pull all those objects away from the center of mass or charge or whatever, out to their current positions. The Virial is the average energy per object. It’s average potential energy because it depends on position, not motion.”

“They’d release all that energy if they just fell together so why don’t … wait, they’re going all different directions so momentum won’t let them, right?”

“You’re on your way. Motion’s involved.”

“Umm … Kepler’s Law — the closer any two of them get, the faster they orbit each other … OH! Kinetic energy! When things fall, potential energy’s converted to kinetic energy. Is there an average kinetic energy that goes up to compensate for the Virial getting smaller?”

“Bingo. When you say ‘average kinetic energy‘ what quantity springs to mind?”

“Temperature. But that’s only for molecules.”

“No reason we can’t define a galactic analog. In fact, Eddington did that back in 1916 when he brought the notion from gas theory over to astrophysics. He even used ‘T‘ for the kinetic average, but remember, this T refers to kinetic energy of stars moving relative to each other, not the temperatures of the stars themselves. Anyhow, the Virial Theorem says that a system of objects is in gravitational or electrostatic equilibrium when the Virial is T/2. Clausius’ ground‑breaking 1870 proof for gases was so general that the theorem’s been used to study everything from sub‑atomic particles to galaxies and dark matter.”

<bigger grin> “With coverage like that, the Virial’s viral after all. Thanks, Mr Moire.”

~~ Rich Olcott

  • Thanks to Dr KaChun Yu for helpful pointers to the literature. Naturally, any errors in this post are my own.

No Symphony on Mars

On By rolcottIn Astronomy: Planetary Science, Physics: Waves, Uncategorized2 Comments

“Evening, Jeremy, a scoop of your pistachio gelato, please. What’re you reading there?”

“Hi, Mr Moire. It’s ‘A City on Mars‘ by Kelly and Zach Weinersmith. One of my girlfriends read it and passed it along to me. She said it’s been nominated for a Hugo even though it’s non‑fiction and it argues against the kind of go‑to‑Mars‑soon planning that Mr Musk is pushing.”

“Is she right about the argument?”

“Pretty much, so far, but I’m not quite done. You get a clue, though, from the book’s subtitle — ‘Can we settle space, should we settle space, and have we really thought this through?‘ Here’s your gelato.”

“Thanks. Not just Mars, space also?”

“That’s right. It’s about the requirements and implications for people living in space and on the Moon and on Mars. The discussion starts with making and raising babies.”

“That first part sounds like fun.”

“Well, you’d think so, but apparently you need special equipment. Hard to stay in contact if there’s no gravity to key on. But that’s only the start of a problem cascade. Suppose the lady gets pregnant. The good news is in zero gravity it’s easy for her to move around. The bad news is we don’t know whether Earth gravity’s important for making babies develop the way they’re supposed to. Also, delivering a baby isn’t the only medical procedure that’d be a real challenge in zero‑g where you need to keep fluid droplets from bouncing around the cabin and into the air system.”

“Whoa. Hmm, never thought about it in this context before, but babies leak. Diapers can help, but babies burp up stuff along with the air. Yuck! Tears they cry in space would just stay on their eyes instead of rolling down cheeks. So … we’d need OB/GYN clinics and nurseries somewhere down a gravity well.”

“For sure, although no‑one knows whether even the Moon’s 1/6‑g is strong enough for good development. I know my little cousins burn up a lot of energy just running around. Can’t give a toddler resistance bands or trust it on a treadmill.”

“So we need an all‑ages gym down there, too, with enough room for locals and visiting spacers.”

“You’re coming round to the Weinersmiths’ major recommendation — don’t go until you can go big! Don’t plan on growing from a small colony, plan on starting with a whole city that can support everything you need to be mostly self‑sufficient.”

“So you’re young, Jeremy. Are you looking forward to being a Mars explorer?”

“I’ll admit all that rusty landscape reminds me of Navajoland, but I think I’d rather stay here. On Mars I’d be trapped in tunnels and domes and respirators and protective coveralls. I wouldn’t be able to just go out and run under the sky the way I was brought up to do.”

“Wouldn’t be able to do a lot of things. Concerts would sound weird, according to a paper I just read.”

“Sure, wind instruments wouldn’t work with bubble helmets. We could still have strings, percussion and electronics, though, right?”

“Sure you could have them. But it’s worse than that. Mars atmosphere is very different from Earth’s. Its temperature measured in kelvins is 25% colder. The pressure’s 99% lower. Most important, molecule for molecule Mars’ mostly‑CO2 atmosphere’s is 50% heavier than Earth’s N2‑O2 mixture. Those differences combine to muffle sounds so they don’t carry near as far as they would on Earth. Most sounds travel about 30% more slowly, too, but that’s where a CO2 molecule’s internal operation makes things weird.”

“Internal? I thought molecules in sound waves just bounced off each other like little billiard balls.”

“That’s usually the case unless you’re at such high pressures that molecules can start sticking to each other. CO2 under Mars conditions is different. If there’s enough time between bounces, CO2 can convert some of its forward kinetic energy into random heat. The threshold is about 4 milliseconds. A sound wave frequency longer than that travels noticeably slower.”

“Four milliseconds is 250 Hertz — that’s a middle B.”

“Mm-hm. Hit a cymbal and base drum simultaneously, your audience hears the cymbal first. Terrible acoustics for a band.”

~~ Rich Olcott

Sounds, Harsh And Informative

On By rolcottIn Astronomy: Techniques, Chemistry, Physics: Waves, UncategorizedLeave a comment

Vinnie’s frowning. “Wait, Sy. I get how molecules bumping into each other can carry a sound wave across space if the frequency’s low enough and that can maybe account for galaxies having spiral arms. So what’s that got to do with the Sonication Project?”

Now Jeremy’s frowning. “What’s sonication got to do with Astronomy? One of my girl friends uses sonication in Biology lab when she’s studying metabolism in plant cells.”

“Whoa! Sonification, not sonication — they could have called it soundify‑cation but sonification‘s classier. ‘Sonication‘ uses high‑intensity ultrasound to jiggle a sample so roughly that cell walls can’t take the stress. They break open and spill the cell’s internal soup out where your friend’s probes can get to it. Tammy, the chemist down the hall from my lab, uses sonication, too.”

“Whoa, Susan, wouldn’t sonication break up molecules?”

“Depends on the frequency and intensity, Vinnie. Sonication can mess up big floppy proteins and DNA, but chemists who play with little peptides and such don’t care. Tammy does solid‑state chemistry. She’s looking for superconductors and she actually does want to break things. The field’s hot category these days is complex copper oxides doped with other metals. You synthesize those compositions by sintering a mix of oxide powders. To maximize contact for a good reaction you need really fine‑grained powders. Sonication does a great job of shattering brittle oxide grains down to bits just a few‑score atoms wide. But Tammy’s technique is even more elegant than that.”

“Elegant sneezes from the powder?”

Susan wallops my shoulder. “No, Sy, the powders are so small they’d be a lung hazard and some of them are toxic. Everything’s done behind respiratory protection.” <Susan doesn’t joke about lab safety.> “There’s evidence that some of these materials are only superconductive if they have the right kind of layered structure. Turns out that if Tammy has her sonicator setup just right when she preps a sample for sintering, the sound wave peaks and valleys inside the machine make the shattered particles settle out in interesting layers.”

“Like Chladni figures.”

“Oh, you know about them.”

“Yeah, I wrote about them a few years ago. Waves do surprising things.”

The Bullet Cluster (1E 0657-56)
Sonification Credit: NASA/CXC/SAO/K.Arcand,
SYSTEM Sounds (M. Russo, A. Santaguida), based on X-Ray image by NASA/CXC/CfA/M.Markevitch,
Optical and lensing map: NASA/STScI, Magellan/U.Arizona/D.Clowe,
Lensing map: ESO WFI

Vinnie’s getting impatient. “So what’s sonification then?”

Tinkly music bursts from Cathleen’s tablet. “This one’s listenable, Susan, and it’s a nice demonstration of what sonification’s about and how arbitrary it can be. You start with complicated multi‑dimensional data and use some process to turn it into audible signals. The process algorithm can use any sound characteristics you like — loudness, pitch, timbre, whatever. This example started with the famous Bullet Cluster image that most people accept as the first direct confirmation of dark matter. All the white‑ish thingies are galaxies except for the ones with pointy artifacts — those are stars. The pink haze is X‑ray light from the same region. The blue haze comes from a point‑by‑point assessment of how badly the galaxy images have been distorted by gravitational lensing — that’s an estimate of the dark matter mass between us and that region of sky. Got all that?”

“And that vertical line is like a scan going across the picture?”

“It’s not like a scan, it is a scan. Imagine a collection of tiny multi‑spectral cameras arranged along a carrier bar. As the bar travels across the picture, each camera emits three signals proportional to the amount of white, pink and blue light it sees. If you look close, just to the right of the line, you’ll see moving white, red and blue line‑charts of the respective signals.”

“That’s fine, but what’s with the sound effects?”

“The Project’s sonification processing generated hiss and rumble sounds whose loudness is proportional to the red and blue signals. Each white‑ish peak became a ping whose pitch indicates position along that bar.”

“Why go to all that trouble?”

“The sounds encode the picture for vision‑challenged people. Beyond that, the Project participants hope that with the right algorithms, their music will reveal things the pictures don’t.”

“They should avoid screamy sounds.”

~~ Rich Olcott

Galaxies Sing In A Low Register

On By rolcottIn Astronomy, Physics: Waves, UncategorizedLeave a comment

Jeremy gets a far‑away look. ”It’s gotta be freakin’ noisy inside the Sun.” just as our resident astronomer steps into Cal’s Coffee.

“Wouldn’t bet that, Jeremy. Depends on where you are in the Sun and on how you define noise.”

Vinnie booms, quietly. ”We just defined it, Cathleen. Atoms or molecules bumping each other in compression waves. Oh, wait, that’s ‘sound,’ you said ‘noise.’ Is that different?”

Susan slurps the last of her chocolate latte. ”Depends on your mood, I guess. All noise is sound, but some sound can be signal. Some people don’t like my slurping so for them it’s noise but Cal hears it as an order for another which makes him happy.”

“Comin’ up, Susan. Hey, Cathleen, maybe you can slap down Sy. He said spiral galaxies have something to do with sound which don’t make sense. Set him straight, okay?”

“Sy, have you all settled that sound isn’t limited to what humans hear?”

“Sure. Everybody’s agreed that infrasound and ultrasound are sound, and that Bishop Berkeley’s fallen tree made a sound even though nobody heard it. That’s probably what got Jeremy thinking about sound inside the Sun.” Jeremy nods.

“Then Vinnie’s definition is too limited and Sy’s statement is correct. Probably.”

That gets a reaction from everyone, though mine is a smile. ”Let ’em have it, Cathleen.”

“Okay. Let’s take Jeremy’s idea first and then we’ll get to galaxies.” <fetches her tablet from her purse and a display on her tablet> “Here’s a diagram of the Sun I did for class. If you restrict ‘sound‘ to mean only coherent waves borne by atoms and molecules, there’s no sound in the innermost three zones. The only motion, if Sy grants I can call it that, is photons and subnuclear particles randomly swapping between adjacent nuclei that are basically locked into position by the pressure. Not much actual atomic motion until you’re up in the Convection Zone where rising turbulence is the whole game. Even there most of the particles are ions and electrons rather than neutral atoms. Loud? You might say so but it’d be a continuous random crackle‑buzz, not anything your ears would recognize. Sound waves as such don’t happen until you reach the atmospheric layers. Up there, oh yes, Jeremy, it’s loud.”

Geologist Kareem is a quiet guy, normally just sits and listens to our chatter, but Cathleen’s edging onto his turf. ”How about seismic waves? If there’s a big flare or CME up top, won’t that send vibrations all the way through?”

“Good point, Kareem. Yes, the Sun has p and s waves just like Earth does, but they travel no deeper than the Convection Zone. A different variety we may not have, g waves, would involve the core. Unfortunately, theory says g waves are so weak that the Convection Zone’s chaos swamps them. Anyway, the Sun’s s, p and g waves wouldn’t contribute to what Jeremy would hear because their frequencies are measured in hours or days. Can I get to galaxies now?”

“Please do.”

A Hubble view of NGC 5457, the Pinwheel Galaxy. Credit: NASA, ESA.

“Thanks.” <another display on her tablet> “Here’s a classic spiral galaxy. Gorgeous, huh? The obvious question is, is it winding in or spraying out? The evidence says ‘No‘ to both. The stars are neither pulled into a whirlpool nor flung out from a central star‑spawner. By and large, the stars or clusters of them are in perfectly good Newtonian orbits around the galactic center of gravity. So why are they collected into those arms? Here’s a clue — most of the blue stars are in the arms.”

“What’s special about blue stars?”

“In general, blue stars are large, hot and young. Our Sun is yellow, about halfway through a 10‑million‑year lifetime. The blue guys burn through their fuel and go nova in a tenth of that time. Blue stars out there tell us that the arms serve as stellar nurseries. It’s not stars gathering into arms, it’s galaxy‑wide rotating waves of gas birthing stars there. There’s argument about whether the wave rotation is intrinsic or whether there’s feedback as each wave is pulled along by star formation at the leading edge and pushed by novae at the trailing edge. Sy’s point, though, is that an arm‑dwelling old red star would experience the spinning gas density pattern as a basso profundo sound wave with a frequency even lower than the million‑year range. Right, Sy?”

“As always, Cathleen.”

~~ Rich Olcott

  • More thanks to Alex.

Screams And Thunders

On By rolcottIn Astronomy: Techniques, Physics: Waves, UncategorizedLeave a comment

Coffee time. I step into Cal’s shop and he’s all over me. ”Sy, have you heard about the the NASA sonification project?”

Susan puts down her mocha latte. “I didn’t like some of what they’ve released. Sounds too much like people screaming.”

Jeremy looks up from the textbook he’s reading. ”In space, no-one can hear you scream.”

Vinnie rumbles from his usual table by the door. “Any of these got anything to do with the Cosmic Hum?”

“They have nothing to do with each other, except they do. Spiral galaxies, too.”

“Huh?”
 ”Huh?”
  ”Huh?”
   ”Huh?”

“A mug of my usual, Cal, please, and a strawberry scone.”

“Sure, Sy, here ya go, but you can’t say something like that around here without you tellin’ us how come.”

“Does the name Bishop Berkeley ring a bell with anyone?”

Vinnie’s on it. ”That the ‘If a tree falls in the forest…‘ guy, right? Claimed there’s no sound unless somebody’s there to hear it?”

“And by extension, no sound outside human hearing range.”

“But bats and them use sound we can’t hear.”
 ”So do elephants and whales.”

“Well there you go. So are we agreed that he was wrong?”

“Not quite, Mr Moire. His definition of ‘sound‘ was different from one you’d like. He was a philosopher theorizing about perception, but you’re a physicist. You two don’t even define reality the same way.”

Vinnie’s rumble. ”Good shot, Jeremy. Sound is waves. Sy and me, we talked about them a lot. One molecule bangs into the next one and so on. The molecules don’t move forward, mostly, but the banging does. Sy showed me a video once. So yeah, people listening or not, that tree made a sound. There’s molecules up in space, so there’s sound up there, too, right, Sy?”

“Mmm, depends on where you are. And what sounds you’re equipped to listen for. The mechanism still works, things advancing a wave by bouncing off each other, but the wave’s length has to be longer than the average distance between the things.” <drawing Old Reliable, pulling up display> “Here’s that video Vinnie saw. I’ve marked two of the particles. You see them moving back and forth over about a wavelength. Suppose a much shorter wave comes along.”

“Umm… Each one would get a forward kick before they got back into position. They wouldn’t oscillate, they’d just keep moving in that direction. No sound wave, just a whoosh.”

“Right, Jeremy. Each out‑of‑sync interaction converts some of the wave’s oscillating energy into one‑way motion. The wave doesn’t get energy back. A dozen wavelengths along, no more wave. So the average distance between particles, we call it the mean free path, sets limits to the length and frequency of a viable wave. Our ears would say it filters out the treble.”

“Space ain’t quite empty so it still has a few atoms to bump together. What kinds of limits do we get out there?”

“Well, there’s degrees of empty. Interplanetary space has more atoms per cubic meter than interstellar which is more crowded than intergalactic. Nebulae and molecular clouds can be even less empty. Huge range, but in general we’re talking wavelengths longer than a million kilometers. Frequencies measured in months or years — low even for your voice, Vinnie.”

Jeremy gets a look on his face. ”One of my girlfriends is a soprano. We tested her in the audio lab and she could hit a note just under two kilohertz, that’s two thousand cycles per second. My top screech was below half that. I could scream in space, but I guess not low enough to be heard.”

“Yeah, keep that spacesuit helmet closed and be sure your radio intercom’s working.”

“Wait, what about screaming over the radio?”

“Radio operates with electromagnetic waves, not bumping atoms. Mean free path limits don’t apply. Radio’s frequency range is around a hundred megahertz, screeching’s no problem. Your broadcast equipment’s response range would set your limits.”

“Sy, those screamy sounds I objected to — you say they can’t have traveled across space as sound waves. Was that a radio transmission?”

“Maybe, Susan. From what I’ve read, we’ve picked up beaucoodles of radio sources, all different types and all over the sky. Each broadcasts a spectrum of different radio frequencies. Some of them are constant radiators, some vary at different rates. You may have heard a recording of a kilohertz variable source.”

<shudder> “All nasty treble, no bass or harmony.”

~~ Rich Olcott

  • Thanks to Alex, who raised several questions.

Map-ematics

On By rolcottIn Astronomy: Planetary Science, General: Fun Stuff, Uncategorized1 Comment

Big Vinnie lumbers into my office, a grin on his face and a sheaf of papers in his hand. “Sy, you gotta see these, you’ll love ’em.”

Vinnie and I go way back, so I string him along a little. “New clients, I suppose? Wealthy ones, with interesting problems?”

“Nah, just goofiness. Me and Larry, don’t think you’ve met him yet, were having pizza in Eddie’s place. Larry’d brought his laptop and we got to playing with some map software he just bought. You ever hear of a GIS?”

“Geographic Information Systems? Sure, they go back a century and a half to the guy who mapped cholera cases in London and traced the source back to a contaminated water pump. You use a GIS to produce mapped visualizations of useful geographically‑distributed statistics.”

“Yeah, that, except we weren’t going for anything useful. Here’s the first one we did. We had a list of states alphabetical‑like. There’s whole blocks that start with the same letter, like eight that start with ‘M.’ We told the mapper to put a different color on any three or more that share a letter. Silly, huh?”

“Mm-hm. I don’t see any pattern to it.”

“Right. We didn’t, either, so we went on to build a second map where each state’s colored by the date it entered the Union. We tried a bunch of different color schemes, finally settled on this one.”

“Nice. You can almost see the country growing year‑to‑year. … Ah, Hawai’i’s in there, too, tucked away in the southwest corner. It’s color’s so pale you have to look for it. West Virginia — let me guess, right around 1860 or so, right?”

“1863. Those folks rebelled against the Southern rebellion. Anyway, Jeremy was kinda looking over our shoulder and this map lit a fire for him. You know he’s doing an Indigenous History project with Professor Begaye. He ran off and brought back a list of where each state’s name came from. We coded that up, fed it to the program and this came out.”

“Wow. The Europeans pretty much claimed the coasts but look at all the green. It’s like the states acknowledged they were built on Native land. Indiana comes right out and admits it.”

“Yup. Jeremy said it was pretty poor compensation. I understand how he feels.”

“So, did you map anything more than the USA?”

“Of course. Larry wanted more silly so we went with the number of letters in each country’s name.”

“I don’t understand this one. Peru’s green for its short name, naturally, and so are Chad and Cuba, but why are Iran and Iraq different colors? Russia’s name isn’t longer than Saudi Arabia and Madagascar. How can five‑letter Congo be purple for a really long name? Doesn’t make sense.”

“Our name list came from the International Standards Organization. Larry and me, we’re both international charter pilots. We’re often checking ISO files for radio frequencies, airport codes and the like. According to ISO, Iraq is ‘IRAQ‘, but Iran is ‘IRAN (ISLAMIC REPUBLIC OF).’ Russia is ‘RUSSIAN FEDERATION‘ which is longer than the other two. The USA would be redder if it was ‘UNITED STATES OF AMERICA,’ but it’s ‘UNITED STATES‘ and tied with ‘LIECHTENSTEIN‘ and ‘GUINEA‑BISSAU‘ at 13 characters so it’s brown.”

“And Congo?”

“The ISO name is ‘CONGO, THE DEMOCRATIC REPUBLIC OF THE.’ That’s not even the longest. It’s beat by ‘KOREA, DEMOCRATIC PEOPLE’S REPUBLIC OF‘ and ‘MACEDONIA, THE FORMER YUGOSLAV REPUBLIC OF.’ Politics, I suppose, and maybe ego. But I ain’t showed you the coolest map.”

“I’m all eyes.”

“You’ve read Andy Weir’s book, ‘The Martian‘?”

“Of course. Saw the movie, too. It was a nice change watching a drama that didn’t involve people battling each other physically or emotionally.”

“Uh. Yeah. I just saw it as an adventure story. Whatever. You remember Watney’s epic drive across that red desert to recover parts from the Pathfinder lander and then get to the launch vehicle?”

“Mm‑hm, though I don’t remember the geography.”

“Well, here’s his road map — Aries Base in Acidalia Planitia to Pathfinder in Chryse Planitia to take‑off from Schiaparelli Crater. Cool, huh?”

“Quite cool.”

Mars image credit: EMM/EXI/Dimitra Atri/NYU Abu Dhabi Center for Space Science

~~ Rich Olcott