Teena And The Quantum Birds

“Hey, Uncle Sy, what’s quantum?”

“That’s a big question for a small person, Teena.  Where’d you hear that word?”

“You and Mommy were talking and you said that something had to do with quantum mechanics.  I know car mechanics work on cars so I want to know what the quantum mechanics work on.”

“That’s a fun question, Sweetie, because there actually is a kind of car called a Quantum.  Not very many of them and they’re made in England so you don’t often see one here.  But the quantum mechanics we were talking about is completely different.  I’ll take it one word at a time, OK?”

<sigh> “OK, but let’s sit on the porch swing, I can tell this will take a while.”

“Oh, it’s not going to be that bad.  You know what mechanisms are, right?”

“Um.. they’re not like people or animals and they’re not like my tablet thingie…. They’ve got gears and things.”

“Good enough.  A big part of physics is thinking about how mechanisms work and that’s called ‘mechanics.’  There’s lots of different kinds of mechanisms.  Each kind has a different kind of mechanics, like ‘celestial mechanics’ which is thinking about how stars and planets move, and ‘fluid mechanics’ which is thinking about how liquids and gases move.  With me so far?”

“So quantum mechanics is thinking about how quantums move.  But what’s a quantum?”

“Quantum isn’t a thing, it’s a set of rules that add up to be a theory.  The first rule is, it only applies to things that are very, very small.  That’s what the word ‘quantum’ has come to mean — the smallest possible amount of something.  So quantum rules apply to quantum-sized things.”

“As small as my water bears?”

“Much smaller.  Things that are as small compared to a water bear as a water bear egg is small compared to you.  Things like molecules and atoms, and those are made of lots of parts that are even way smaller.”

“Ooo, that’s teeny.  How do you even see them?”

“Well, you don’t.  They’re far too small to see even with a microscope.  It’s worse — if you did try to see an atom’s parts, any light you could shine on them would move them around so they’re not where they were when you started to look.”

“Then how do the quantum mechanics people learn about them?”

“Umm…  Ah! See that flock of birds flying past?”

“Mommy says they’re starlings but I think they’re blackbirds.”

“Could be either or both, it’s hard to tell when they’re in the air like that.  Sometimes the two kinds flock together.  If it’s a flock of starlings, the flock is called a murmuration, which is one of my favorite words.”

“Oh, that’ll be one of my favorites now, too.  Murmuration, mmmurmuration, mmmm.  I love  ‘M‘ words.”

“Anyway, can you see what direction any one bird is flying?”

“No, there’s too many and they go back and forth and it’s too confusing and I like the shapes the whole murmuration makes.”

“But can you point to the middle of it and see how the pattern moves?”

“It’s right the— ooo, look, it did a spiral!”

“Murmurations are sorta like the kind of thing the quantum mechanics people work with.  They look at lots and lots of quantum-size things to see how the typical ones and the special ones behave.  Then they try to work out what the behavior rules are.  Sometimes the rules are really simple, like the rules the birds use.”

“Birds use rules?  I thought they could fly wherever they wanted to.”

“Sometimes they do, but if they’re flying in a murmuration they definitely follow rules.  Most of them.  Most of the time.  If I were one of those birds, I’d stay about the same distance from each of my neighbor birds, I’d usually fly in about the same direction as my neighbors are flying, and I’d also aim at about the middle of the flo— murmuration.  Scientists have found that just those three rules account for most of how a murmuration behaves.  Cool, huh?”

“Simple rules for bird brains, that’s funny!”

“But look at the beautiful shapes those simple rules make.”Murmuration 1

~~ Rich Olcott


A Three-dog Night Would Be So Cool

“So we’ve got three fundamentally different messengers from the stars, Mr Feder.  The past couple of years have given us several encouraging instances of receiving two messengers from the same event.  If we ever receive all three messengers from the same event, that might give us what we need to solve the biggest problem in modern physics.”

“That’s a pretty deep statement, Moire.  Care to unpack it?  The geese here would love to hear about it.”

“Lakeside is a good place for thoughts like this.  The first messenger was photons.  We’ve been observing starlight photons for tens of thousand of years.  Tycho Brahe and Galileo took it to a new level a few centuries ago with their careful observation, precision measurements and Galileo’s telescope.”

“That’s done us pretty good, huh?”

“Oh sure, we’ve charted the heavens and how things move, what we can see of them.  But our charts imply there’s much we can’t see.  Photons only interact with electric charge.  Except for flat-out getting absorbed if the wavelength is right, photons don’t care about electrically neutral material and especially they don’t care about dark matter.”

“So that’s why we’re interested in the other messengers.”

“Exactly.  Even electrically neutral things have mass and interact with the gravitational field.  You remember the big news a few years ago, when our brand-new LIGO instruments caught a gravitational wave signal from a couple of black holes in collision.  Black holes don’t give off photons, so the gravitational wave messenger was our only way of learning about that event.”

“No lightwave signal at all?”

“Well, there was a report of a possible gamma-ray flare in that patch of sky, but it was borderline-detectable.  No observatory using lower-energy light saw anything there.  So, no.”

“You’re gonna tell me and the geese about some two-messenger event now, right?”

“That’s where I’m going, Mr Feder.  Photons first.  Astronomers have been wondering for decades about where short, high-energy gamma-ray bursts come from.  They seem to happen randomly in time and space.  About a year ago the Fermi satellite’s gamma-ray telescope detected one of those bursts and sent out an automated ‘Look HERE’ alert to other observatories.  Unfortunately, Fermi‘s resolution isn’t wonderful so its email pointed to a pretty large patch of sky.  Meanwhile back on Earth and within a couple of seconds of Fermi‘s moment, the LIGO instruments caught an unusual gravitational wave signal that ran about a hundred times slower than the black-hole signals they’d seen.  Another automated ‘Look HERE’ alert went out.  This one pointed to a small portion of that same patch of sky.  Two messengers.”

“Did anyone find anything?”

“Seventy other observatories scrutinized the overlap region at every wavelength known to Man.  They found a kilonova, an explosion of light and matter a thousand times brighter than typical novae.  The gravitational wave evidence indicated a collision between two neutron stars, something that had never before been recorded.  Photon evidence from the spewed-out cloud identified a dozen heavy elements theoreticians hadn’t been able to track to an origin.  Timing details in the signals gave cosmologists an independent path to resolving a problem with the Hubble Constant.  And now we know where those short gamma-ray bursts come from.”

“Pretty good for a two-messenger event.  Got another story like that?”

“A good one.  This one’s neutrinos and photons, and the neutrinos came in first.  One neutrino.”

One neutrino?”

“Yup, but it was a special one, a super-high-powered neutrino whose incoming path our IceCube observatory could get a good fix on.  IceCube sent out its own automated ‘Look HERE’ alert.  The Fermi team picked up the alert and got real excited because the alert’s coordinates matched the location of a known and studied gamma-ray source.  Not a short-burster, but a flaring blazar.  That neutrino’s extreme energy is evidence for blazars being one of the long-sought sources of cosmic rays.”

“Puzzle solved, maybe.  Now what you said about a three-messenger signal?”grebe messenger pairs“Gravitational waves are relativity effects and neutrinos are quantum mechanical.  Physicists have been struggling for a century to bridge those two domains.  Evidence from a three-messenger event could provide the final clues.”

“I’ll bet the geese enjoyed hearing all that.”

“They’re grebes, Mr Feder.”

~~ Rich Olcott

Heavenly Messengers

A gorgeous Fall day, a little bit cool-ish, perfect for a brisk walk in the park.  I’m striding along the lake-bound path when there’s a breathless shout behind me.  “Hey, Moire, wait up!  I got questions!”

“Hello, Mr Feder.  What’s the topic this time?  And keep up, please, I’ve got geese to watch.”

“I been reading in the business pages <puff, puff> about all the money different countries are putting into ‘multi-messenger astronomy.’  <puff>  What’s that about, anyway?  Who’s sending messages and ain’t the Internet good enough?”

“It’s not who, Mr Feder, it’s what — stars, galaxies, black holes, the Universe.  And the messages are generally either ‘Here I am‘ or ‘Something interesting just happened‘.  The Internet just doesn’t reach that far and besides, no kitten pictures.”

“Pretty simple-sounding messages, so why the big bucks for extra message-catchers?”

“Fair question.  It has to do with what kind of information each messenger carries.  Photons, for instance.”

“Yeah, light-waves, the rainbow.”

“Way more than the rainbow.  Equating light-waves to just the colors we see is like equating sound-waves to just the range from A4 through F4# on a piano.”

“Hey, that’s less than an octave.”

“Yup, and electromagnetism’s scale is hugely broader than that.  Most of the notes, or colors, are way out of our range.  A big tuba makes a deep, low-frequency note but a tiny piccolo makes a high note.  Photon characteristics also scale with the size of where they came from.  Roughly speaking, the shorter the light’s wave-length, the smaller the process it came out of and the smaller its target will be.  Visible light, for instance, is sent and received by loosely-held charge sloshing inside an atom or molecule.  Charge held tight to a nucleus gives rise to higher-energy photons, in the ultra-violet range or beyond.”

“Like how beyond?”

“X-rays can rip electrons right out of a molecule.  Gamma rays are even nastier and involve charge activity inside a nucleus, like during a nuclear reaction.”

“How about in the other direction?  Nothing?”

“Hardly.  Going that way is going to bigger scales.  Infra-red is about parts of molecules vibrating against each other, microwave is about whole molecules rotating.  When your size range gets out to feet-to-miles you’re looking at radio waves that probably originated from free electrons or ions slammed back and forth by electric or magnetic fields.”

“So these light ranges are like messengers that clue us in on what’s going on out there?  Different messengers, different kindsa clues?”

“You got the idea.  Add in that what happens to the light on the way here is also important.  Radio and microwave photons with their long wavelengths swerve around dust particles that block out shorter-wavelength ones.  Light that traversed Einstein-bent space lets us measure the masses of galaxies.  Absorption and polarization at specific wavelengths tell us what species are out there and what they’re doing.  Blue-shifts and red-shifts tell us how fast things are moving towards and away from us.  And of course, atmospheric distortions tell us we’ve got to put satellite observatories above the atmosphere to see better.”

“One messenger, lots of effects.”

“Indeed, but in the past few years we’ve added two more, really important messengers.  Photons are good, but they’re limited to just one of the four fundamental forces.”

“Hey, there’s gotta be more than that.  This is a complicated world.”

“True, but physicists can account for pretty much everything at the physical and chemical level with only four — electromagnetism, gravity, the strong force that holds nuclei together and the weak force that’s active in nuclear transformation processes.  Photons do electromagnetism and that’s all.”

“So you’re saying we’ve got a line on two of the others?”

“Exactly.  IceCube and its kin record the arrival of high-energy neutrinos.  In a sense they are to the weak force what photons are to electromagnetism.  We don’t know whether gravitation works through particles, but LIGO and company are sensitive to changes in the gravitational field that’s always with us.  Each gives us a new perspective on what’s happening out there.”

“So if you get a signal from one of the new messengers at the same time you get a photon signal…”

“Oh, look, the geese are coming in.”

Heavenly messengers

~~ Rich Olcott

“Hot Jets, Captain Neutrino!”

“Hey, Cathleen, while we’re talking IceCube, could you ‘splain one other thing from that TV program?”

“Depends on the program, Al.”

“Oh, yeah, you weren’t here when we started on this.  So I was watching this program and they were talking about neutrinos and how there’s trillions of them going through like my thumbnail every second and then IceCube saw this one neutrino that they’re real excited about so what I’m wondering is, what’s so special about just that neutrino? How do they even tell it apart from all the others?”

“How about the direction it came from, Cathleen?  We get lotsa neutrinos from the Sun and this one shot in from somewhere else?”

SMBH jet and IceCube
Images from NASA and JPL-Caltech

“An interesting question, Vinnie.  The publicity did concern its direction, but the neutrino was already special.  It registered 290 tera-electron-volts.”


“Sorry, scientific shorthand — tera is ten-to-the-twelfth.  A million electrons poised on a million-volt gap would constitute a Tera-eV of potential energy.  Our Big Guy had 290 times that much kinetic energy all by himself.”

“How’s that stack up against other neutrinos?”

“Depends on where they came from.  Neutrinos from a nuclear reactor’s uranium or plutonium fission carry only about 10 Mega-eV, wimpier by a factor of 30 million.  The Sun’s primary fusion process generates neutrinos peaking out at 0.4 MeV, 25 times weaker still.”

“How about from super-accelerators like the LHC?”

“Mmm, the LHC makes TeV-range protons but it’s not designed for neutrino production.  We’ve got others that have been pressed into service as neutrino-beamers. It’s a complicated process — you send protons crashing into a target.  It spews a splatter of pions and K-ons.  Those guys decay to produce neutrinos that mostly go in the direction you want.  You lose a lot of energy.  Last I looked the zippiest neutrinos we’ve gotten from accelerators are still a thousand times weaker than the Big Guy.”

I can see the question in Vinnie’s eyes so I fire up Old Reliable again.  Here it comes… “What’s the most eV’s it can possibly be?”  Good ol’ Vinnie, always goes for the extremes.

“You remember the equation for kinetic energy?”

“Sure, it’s E=½ m·v², learned that in high school.”

“And it stayed with you.  OK, and what’s the highest possible speed?”

“Speed o’ light, 186,000 miles per second.”

“Or 300 million meters per second, ’cause that’s Old Reliable’s default setting.  Suppose we’ve got a neutrino that’s going a gnat’s whisker slower than light.  Let’s apply that formula to the neutrino’s rest mass which is something less than 1.67×10-36 kilograms…”Speedy neutrino simple calculation“Half an eV?  That’s all?  So how come the Big Guy’s got gazillions of eV’s?”

“But the Big Guy’s not resting.  It’s going near lightspeed so we need to apply that relativistic correction to its mass…Speedy neutrino relativistic calculation“That infinity sign at the bottom means ‘as big as you want.’  So to answer your first question, there isn’t a maximum neutrino energy.  To make a more energetic neutrino, just goose it to go even closer to the speed of light.”

“Musta been one huge accelerator that spewed the Big Guy.”

“One of the biggest, Al.”  Cathleen again.  “That’s the exciting thing about what direction the particle came from.”

“Like the North Pole or something?”

“Much further away, much bigger and way more interesting.  As soon as IceCube caught that neutrino signal, it automatically sent out a “Look in THIS direction!” alert to conventional observatories all over the world.  And there it was — a blazar, 5.7 billion lightyears away!”

“Wait, Cathleen, what’s a blazar?”

“An incredibly brilliant but highly variable photon source, from radio frequencies all the way up to gamma rays and maybe cosmic rays.  We think the thousands we’ve catalogued are just a fraction of the ones within range.  We’re pretty sure that each of them depends on a super-massive black hole in the center of a galaxy.  The current theory is that those photons come from an astronomy-sized accelerator, a massive swirling jet that shoots out from the central source.  When the jet happens to point straight at us, flash-o!”


“I wouldn’t worry about a neutrino flood.  The good news is IceCube’s signal alerted astronomers to check TXS 0506+056, a known blazar, early in a new flare cycle.”

“An astrophysical fire alarm!”

~~ Rich Olcott

Cube Roots

Cathleen steps into at Al’s for her morning coffee-and-scone.  “Heard you guys talking neutrinos so I’ll bet Al got you started with something about IceCube.  Isn’t it an awesome project?  Imagine instrumenting a cubic kilometer of ice, and at the South Pole!”

“Ya got me, Cathleen.  It knocked me out that anyone would even think of building it.  Where did the idea come from, anyhow?”

“I don’t know specifically, but it’s got a lot of ancestors, going back to the Wilson Cloud Chamber in the 1920s.”

“Oh, the cloud chamber!  Me and my brother did one for the Science Fair — used dry ice and some kind of alcohol in a plastic-covered lab dish if I remember right, and we set it next to one of my Mom’s orange dinner plates.  Spooky little ghost trails all over the place.”

“That’s basically what the first ones were.  An incoming particle knocks electrons out of vapor molecules all along its path.  The path is visible because the whole thing is so cold that other vapor molecules condense to form micro-droplets around the ions.  Anderson’s cloud chambers were good enough to get him a Nobel Prize for discovering the positron and muon.  But table-top devices only let you study low-energy particles — high-energy ones just shoot through the chamber and exit before they do anything interesting.”

“So the experimenters went big?”

“Indeed, Sy, massive new technologies, like bubble chambers holding thousands of gallons of liquid hydrogen or something else that reacts with neutrinos.  But even those experiments had a problem.”

“And that was…?”

FirstNeutrinoEventAnnotated 2
Adapted from public domain image
courtesy of Argonne National Laboratory

“They all depended on photography to record the traces.  Neutrino-hunting grad students had to measure everything in the photos, because neutrinos don’t make traces — you only find them by finding bigger particles that were disturbed just so.  The work got really intense when the astrophysicists got into the act, trying to understand why the Sun seemed to be giving off only a third of the neutrinos it’s supposed to.  Was the Sun going out?”

“Wait, Cathleen, how’d they know how many neutrinos it’s supposed to make?”

“Wow, Vinnie, you sure know how to break up a narrative, but it’s a fair question.  OK, quick answer.  We know the Sun’s mostly made of hydrogen and we know how much energy it gives off per second.  We’ve figured out the nuclear reactions it must be using to generate that energy.  The primary process combines four hydrogen nuclei  to make a helium nucleus.  Each time that happens you get a certain amount of energy, which we know, plus two neutrinos.  Do the energy arithmetic, multiply the number of heliums per second by two and you’ve got the expected neutrino output.”

“So is the Sun going out?”

“As usual, Al cuts to the chase.  No, Al, it’s still got 5 billion years of middle age ahead of it.  The flaw in the argument was that we assumed that our detectors were picking up all the neutrinos.”

“My mutations!”

“Yes, Vinnie.  Our detector technology at the time only saw electron neutrinos.  The Sun’s reactions emit electron neutrinos.  But the 93-million mile trip to Earth gave those guys plenty of time to oscillate through muon neutrino to tau neutrino and back again.  All we picked up were the ones that had gone through an integer number of cycles.”

“We changed technology, I take it?”

“Right again, Sy.  Instead of relying on nuclear reactions initiated by electron neutrinos, we went so spark chambers — crossed grids of very fine electrified wire in a box of argon gas.  Wherever a passing neutrino initiated an ionization, zap! between the two wires closest to that point.  Researchers could computerize the data reduction.  Turns out that all three neutrino flavors are pretty good at causing ionizations so the new tech cleared up the Solar Paradox, but only after we solved a different problem — the new data was point-by-point.  Working back from those points to the traces took some clever computer programming.”

“Ah, I see the connection with IceCube.  It doesn’t register traces, either, just the points where those sensors see the Cherenkov flashes.  It’s like a spark chamber grown big.”

“Cubic-kilometer big.”

~~ Rich Olcott

Einstein’s Revenge

Vinnie’s always been a sucker for weird-mutant sci-fi films so what Jennie says gets him going.  “So you got these teeny-tiny neutrinos and they mutate?  What do they do, get huge and eat things?”

“Nothing that interesting, Vinnie — or uninteresting, depending on what you’re keen on.  No, what happens is that each flavor neutrino periodically switches to another flavor.”

“Like an electron becomes a muon or whatever?”

“Hardly.  The electron and muon and tau particles themselves don’t swap.  Their properties differ too much —  the muon’s 200 times heaver than the electron and the tau’s sixteen times more massive than that.  It’s their associated neutrinos that mutate, or rather, oscillate.  What’s really weird, though, is how they do that.”

“How’s that?”

“As I said, they cycle through the three flavors.  And they cycle through three different masses.”

“OK, that’s odd but how is it weird?”

“Their flavor doesn’t change at the same time and place as their mass does.”Neutrino braid with sines

“Wait, what?”

“Each kind of neutrino, flavor-wise, is distinct — it reacts with a unique set of particles and yields different reaction products to what the other kinds do.  But experiments show that the mass of each kind of neutrino can vary from moment to moment.  At some point, the mass changes enough that suddenly the neutrino’s flavor oscillates.”

“That makes me think each mass could be a mix of three different flavors, too.”

“Capital, Vinnie!  That’s what the math shows.  It’s two different ways of looking at the same coin.”

“The masses oscillate, too?”

“Oh, indeed.  But no-one knows exactly what the mass values are nor even how the mass variation controls the flavors.  Or the other way to.  We know two of the masses are closer together than to the third but that’s about it.  On the experimental side there’s loads of physicists and research money devoted to different ways of measuring how neutrino oscillation rates depend on neutrino energy content.”

“And on the theory side?”

“Tons of theories, of course.  Whenever we don’t know much about something there’s always room for more theories.  The whole object of experiments like IceCube is to constrain the theories.  I’ve even got one I may present at Al’s Crazy Theory Night some time.”

“Oh, yeah?  Let’s hear it.”

“It’s early days, Al, so no flogging it about, mm?  Do you know about beat frequencies?”

“Yeah, the piano tuner ‘splained it to me.  You got two strings that make almost the same pitch, you get this wah-wah-wah effect called a beat.  You get rid of it when the strings match up exact.”  He grabs a few glasses from the counter and taps them with a spoon until he finds a pair that’s close.  “Like this.”

“Mm-hmm, and when the wah-wahs are close enough together they merge to become a note on their own.  You can just imagine how much more complicated it gets when there are three tones close together.”

I see where she’s going and bring up a display on Old Reliable —an overlay of three sine waves.   “Here you go, Jennie.  The red line is the average of the three regular waves.”Three sines on Old Reliable“Thanks, Sy.  Look, we’ve got three intervals where everything syncs up.  See the new satellite peaks half-way in between?  There’s more hidden pattern where things look chaotic in the rest of the space.”

“Yeah, so?”

“So, Vinnie, my crazy theory is that like a photon’s energy depends on its wave frequency in the electromagnetic field, a neutrino is a combination of three weak-field waves of slightly different frequency, one for each mass.  When they sync up one way you’ve got an electron neutrino, when they sync up a different way you’ve got a muon neutrino, and a third way for a tau neutrino.”

I’ve got to chuckle.  “Nothing against your theory, Jennie, though you’ve got some work ahead of you to flesh it out and test it.  I just can’t help thinking of Einstein and his debates with Bohr.  Bohr maintained that all we can know about the quantum realm are the averages we calculate.  Einstein held that there must be understandable mechanisms underlying the statistics.  Field-based theories like yours are just what Einstein ordered.”

“I could do worse.”Neutrino swirl around Einstein

~~ Rich Olcott

The Neapolitan Particle

“Welcome back, Jennie.  Why would anyone want to steer an ice cube?

“Thanks, Jeremy, it’s nice to be back..  And the subject’s not an ice cube, it’s IceCube, the big neutrino observatory in the Antarctic.”

“Then I’m with Al’s question.  Observatories have this big dome that rotates and inside there’s a lens or mirror or whatever that goes up and down to sight on the night’s target.  OK, the Hubble doesn’t have a dome and it uses gyros but even there you’ve got to point it.  How does IceCube point?”

“It doesn’t.  The targets point themselves.”


“Ever relayed a Web-page?”


“Guess what?  You don’t know where the page came from, you don’t know where it’s going to end up.  But it could carry a tracking bug to tell someone at some call-home server when and where the page had been opened.  IceCube works the same way, sort of.  It has a huge 3D array of detectors to record particles coming in from any direction.  A neutrino can come from above, below, any side, no problem — the detectors it touches will signal its path.”

IceCube architecture
Adapted from a work by Francis Halzen, Department of Physics, University of Wisconsin

“How huge?”

“Vastly huge.  The instrument is basically a cubic kilometer of ultra-clear Antarctic ice that’s ages old.  The equivalent of the tracking bugs is 5000 sensors in a honeycomb array more than a kilometer wide.  Every hexagon vertex marks a vertical string of sensors going down 2½ kilometers into the ice.  Each string has a couple of sensors near the surface but the rest of them are deeper than 1½ kilometers.  The sensors are looking for flashes of light.  Keep track of which sensor registered a flash when and you know the path a particle took through the array.”

icecube event 3“Why should there be flashes? I thought neutrinos didn’t interact with matter.”

“Make that, they rarely interact with matter.  Even that depends on what particle the neutrino encounters and what flavor neutrino it happens to be at the moment.”

That gets both Al and me interested.  His “Neutrinos come in flavors?” overlaps my “At the moment?”

“I thought that would get you into this, Sy.  Early experiments detected only 1/3 of the neutrinos we expected to come from the Sun.  Unwinding all that was worth four Nobel prizes and counting.  The upshot’s that there are three different neutrino flavors and they mutate.  The experiments caught only one.”

Vinnie’s standing behind us.  “You’re going to tell us the flavors, right?”

“Hoy, Vinnie, Jeremy’s question was first, and it bears on the others.  Jeremy, you know that blue glow you see around water-cooled nuclear fuel rods?”

“Yeah, looks spooky.  That’s neutrinos?”

“No, that’s mostly electrons, but it could be other charged particles.  It has to do with exceeding the speed of light in the medium.”

“Hey, me and Sy talked about that.  A lightwave makes local electrons wiggle, and how fast the wiggles move forward can be different from how fast the wave group moves.  Einstein’s speed-of-light thing was about the wave group’s speed, right, Sy?”

“That’s right, Vinnie.”

“So anyhow, Jeremy, a moving charged particle affects the local electromagnetic field.  If the particle moves faster than the surrounding atoms can adjust, that generates light, a conical electromagnetic wave with a continuous spectrum.  The light’s called Cherenkov radiation and it’s mostly in the ultra-violet, but enough leaks down to the visible range that we see it as blue.”

“But you said it takes a charged particle.  Neutrinos aren’t charged.  So how do the flashes happen in IceCube?”

“Suppose an incoming high-energy neutrino transfers some of its momentum to a charged particle in the ice — flash!  Even better, the flash pattern provides information for distinguishing between the neutrino flavors.  Muon neutrinos generate a more sharp-edged Cherenkov cone than electron neutrinos do.  Taus are so short-lived that IceCube doesn’t even see them.”Leptons

“I suppose muon and tau are flavors?”

“Indeed, Vinnie.  Any subatomic reaction that releases an electron also emits an electron-flavored neutrino.  If the reaction releases the electron’s heavier cousin, a muon, then you get a muon-flavored neutrino.  Taus are even heavier  and they’ve got their own associated neutrino.”

“And they mutate?”

“In a particularly weird way.”

~~ Rich Olcott

Bigger than you’d think

Al’s coffee shop, the usual mid-afternoon crowd of chatterers and laptop-tappers.  Al’s walking his refill rounds, but I notice he’s carrying a pitcher rather than his usual coffee pot.  “Hey, Al, what’s with the hardware?”

“Got iced coffee here, Sy.  It’s hot out, people want to cool down.  Besides, this is in honor of IceCube.”

“Didn’t realize you’re gangsta fan.”

“Nah, not the rapper, the cool experiment down in the Antarctic.  It was just in the news.”

“Oh?  What did they say about it?”

“It’s the biggest observatory in the world, set up to look for the tiniest particles we know of, and it uses a cubic mile of ice which I can’t think how you’d steer it.”

A new voice, or rather, a familiar one. “One doesn’t, Al.”
Neutrino swirl 1“Hello, Jennie.  Haven’t seen you for a while.”

“I flew home to England to see my folks.  Now I’m back here for the start of the Fall term.  I’ve already picked a research topic — neutrinos.  They’re weird.”

“Hey, Jennie, why are they so tiny?”

“It’s the other way to, Al.  They’re neutrinos because they’re so tiny.  Sy would say that for a long time they were simply an accounting gimmick to preserve the conservation laws.”

“I would?”

“Indeed.  People had noticed that when uranium atoms give off alpha particles to become thorium, the alpha particles always have about the same amount of energy.  The researchers accounted for that by supposing that each kind of nucleus has some certain quantized amount of internal energy.  When one kind downsizes to another, the alpha particle carries off the difference.”

“That worked well, did it?”

“Oh, yes, there are whole tables of nuclear binding energy for alpha radiation.  But when a carbon-14 atom emits a beta particle to become nitrogen-14, the particle can have pretty much any amount of energy up to a maximum.  It’s as though the nuclear quantum levels don’t exist for beta decay.  Physicists called it the continuous beta-spectrum problem and people brought out all sorts of bizarre theories to try to explain it.  Finally Pauli suggested maybe something we can’t see carries off energy and leaves less for the beta.  Something with no charge and undetectable mass and the opposite spin from what the beta has.”

“Yeah, that’d be an accounting gimmick, alright.  The mass disappears into the rounding error.”

“It might have done, but twenty years later they found a real particle.  Oh, I should mention that after Pauli made the suggestion Fermi came up with a serious theory to support it.  Being Italian, he gave the particle its neutrino name because it was neutral and small.”

“But how small?”

“We don’t really know, Al.  We know the neutrino’s mass has to be greater than zero because it doesn’t travel quite as fast as light does.  On the topside, though, it has to be lighter than than a hydrogen atom by at least a factor of a milliard.”


“Oh, sorry, I’m stateside, aren’t I?  I should have said a billion.  Ten-to-the-ninth, anyway.”

“That’s small.  I guess that’s why they can sneak past all the matter in Earth like the TV program said and never even notice.”

This gives me an idea.  I unholster Old Reliable and start to work.

“Be right with you… <pause> … Jennie, I noticed that you were being careful to say that neutrinos are light, rather than small.  Good careful, ’cause ‘size’ can get tricky at this scale.  In the early 1920s de Broglie wrote that every particle is associated with a wave whose wavelength depends on the particle’s momentum.  I used his formula, together with Jennie’s upper bound for the neutrino’s mass, to calculate a few wavelength lower bounds.Neutrino wavelength calcMomentum is velocity times mass.  These guys fly so close to lightspeed that for a long time scientists thought that neutrinos are massless like photons.  They’re not, so I used several different v/c ratios to see what the relativistic correction does.  Slow neutrinos are huge, by atom standards.  Even the fastest ones are hundreds of times wider than a nucleus.”

“With its neutrino-ness spread so thin, no wonder it’s so sneaky.”

“That may be part of it, Al.”

“But how do you steer IceCube?”

~~ Rich Olcott

Naming the place and placing the name

“By the way, Cathleen, is there any rhyme or reason to that three-object object‘s funky name?  I’ve still got it on Old Reliable here.”

PSR J0337+1715

“It’s nothing like funky, Sy, it’s perfectly reasonable and in fact it’s far more informative than a name like ‘Barnard’s Star.’  The ‘PSR‘ part says that the active object, the reason anyone even looked in that system’s direction, is a pulsar.”

“And the numbers?”

“Its location in two parts.  Imagine a 24-hour clockface in the Solar Plane.  The zero hour points to where the Sun is at the Spring equinox.  One o’clock is fifteen degrees east of that, two o’clock is another fifteen degrees eastward and so on until 24 o’clock is back pointing at the Springtime Sun.  Got that?”

“Mm, … yeah.  It’d be like longitudes around the Earth, except the Earth goes around in a day and this clock looks like it measures a year.”

“Careful there, it has nothing to do with time.  It’s just a measure of angle around the celestial equator.  It’s called right ascension.

“How about intermediate angles, like between two and three o’clock?”

“Sixty arc-minutes between hours, sixty arc-seconds between arc-minutes, just like with time.  If you need to you can even go to tenths or hundredths of an arc-second, which divide the circle into … 8,640,000 segments.”

“OK, so if that’s like longitudes, I suppose there’s something like latitudes to go with it?”

“Mm-hm, it’s called declination.  It runs perpendicular to ascension, from plus-90° up top down to 0° at the clockface to minus-90° at the bottom.  Vivian, show Sy Figure 3 from your paper.”Right ascension and declination“Wait, right ascension in hours-minute-seconds but declination in degrees?”

“Mm-hm.  Blame history.  People have been studying the stars and writing down their locations for a long time.  Some conventions were convenient back in the day and we’re not going to give them up.  So anyway, an object’s J designation with 4-digit numbers tells you which of 13 million directions to look to find it.  Roughly.”


“That’s what the ‘J‘ is about.  If the Earth’s rotation were absolutely steady and if the Sun weren’t careening about a moving galaxy, future astronomers could just look at an object’s angular designation and know exactly where to look to find it again.  But it’s not and it does and they won’t.  The Earth’s axis of rotation wobbles in at least three different ways, the Sun’s orbit around the galaxy is anything but regular and so on.  Specialists in astrometry, who measure things to fractions of an arc-second, keep track of time in more ways than you can imagine so we can calculate future positions.  The J-names at least refer back to a specific point in time.  Mostly.  You want your mind bent, look up epoch some day.”

“Plane and ship navigators care, too, right?”

“Not so much.  Earth’s major wobble, for instance, shifts our polar positions only about 40 parts per million per year.  A course you plotted last week from here to Easter Island will get you there next month no problem.”

Old Reliable judders in my hand.  Old Reliable isn’t supposed to have a vibration function, either.  Ask her about interstellar navigation.  “Um, how about interstellar navigation?”Skewed Big Dipper

“Oh, that’d be a challenge.  Once you get away from the Solar System you can’t use the Big Dipper to find the North Star, any of that stuff, because the constellations look different from a different angle.  Get a couple dozen lightyears out, you’ve got a whole different sky.”

“So what do you use instead?”

“I suppose you could use pulsars.  Each one pings at a unique repetition interval and duty cycle so you could recognize it from any angle.  The set of known pulsars would be like landmarks in the galaxy.  If you sent out survey ships, like the old-time navigators who mapped the New World, they could add new pulsars to the database.  When you go someplace, you just triangulate against the pulsars you see and you know where you are.”

If they happen to point towards you! You only ever see 20% of them.  Starquakes and glitches and relativistic distortions mess up the timings.  Poor Xian-sheng goes nuts each time we drop out of warp.

~~ Rich Olcott

Rhythm Method

A warm Summer day.  I’m under a shady tree by the lake, watching the geese and doing some math on Old Reliable.  Suddenly a text-message window opens up on its screen.  The header bar says 710-555-1701.  Old Reliable has never held a messaging app, that’s not what I use it for.  The whole thing doesn’t add up.  I type in, Hello?

Hello, Mr Moire.  Remember me?

Suddenly I do.  That sultry knowing stare, those pointed ears.  It’s been a yearHello, Ms Baird.  What can I do for you?

Another tip for you, Mr Moire.  One of my favorite star systems — the view as you approach it at near-lightspeed is so ... meaningful.  Your astronomers call it PSR J0337+1715.

So of course I head over to Al’s coffee shop after erasing everything but that astronomical designation.  As I hoped, Cathleen and a few of her astronomy students are on their mid-morning break.  Cathleen winces a little when she sees me coming.  “Now what, Sy?  You’re going to ask about blazars and neutrinos?”

I show her Old Reliable’s screen.  “Afraid not, Cathleen, I’ll have to save that for later.  I just got a message about this star system.  Recognize it?”

“Why, Sy, is that a clue or something?  And why is the lettering in orange?”

“Long story.  But what can you tell me about this star system?”

“Well, it’s probably one of the most compact multi-component systems we’re ever going to run across.  You know what compact objects are?”

“Sure.  When a star the size of our Sun exhausts most of its hydrogen fuel, gravity wins its battle against heat.  The star collapses down to a white dwarf, a Sun-full of mass packed into a planet-size body.  If the star’s a bit bigger it collapses even further, down to a neutron star just a few miles across.  The next step would be a black hole, but that’s not really a star, is it?”

“No, it’s not.  Jim, why not?”

“Because by definition a black hole doesn’t emit light.  A black hole’s accretion disk or polar jets might, but not the object itself.”

“Mm-hm.  Sy, your ‘object’ is actually three compact objects orbiting  around each other.  There’s a neutron star with a white dwarf going around it, and another white dwarf swinging around the pair of them.  Vivian, does that sound familiar?”

“That’s a three-body system, like the Moon going around the Earth and both going around the Sun.  Mmm, except really both white dwarfs would go around the neutron star because it’s heaviest and we can calculate the motion like we do the Solar System.”

“Not quite.  We can treat the Sun as motionless because it has 99% of the mass.  J0337+1715’s neutron star doesn’t dominate its system as much as the Sun does ours.  That outermost dwarf has 20% of its system’s mass.  Phil, what does that suggest to you?”

“It’d be like Pluto and Charon.  Charon’s got 10% of their combined mass and so Pluto and Charon both orbit a point 10% of the way out from Pluto.  From Earth we see Pluto wobbling side to side around that point.  So the neutron star must wobble around the point 20% outward towards the heavy dwarf.  Hey, star-wobble is how we find exoplanets.  Is that what this is about, Mr Moire?  Did someone measure its red-shift behavior?”PSR J0337+1715Cathleen saves me from answering.  “Not quite.  The study Sy’s chasing is actually a cute variation on red-shift measurements.  That ‘PSR‘ designation means the neutron star is a pulsar.  Those things emit electromagnetic radiation pulses with astounding precision, generally regular within a few dozen nanoseconds.  If we receive slowed-down pulses then the object’s going away; sped-up and it’s approaching, just like with red-shifting.  The researchers  derived orbital parameters for all three bodies from the between-pulse durations.  The heavy dwarf is 200 times further out than the light one, for instance.  Not an easy experiment, but it yielded an important result.”

My ears perk up.  “Which was…?”

“The gravitational force between the pulsar and each dwarf was within six parts per million of what Newton’s Laws prescribe.  That observation rules out whole classes of theories that tried to explain galaxies and galaxy clusters without invoking dark matter.”

Cool, huh?


~~ Rich Olcott