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.”
~~ Rich Olcott
“Half an eV? That’s all? So how come the Big Guy’s got gazillions of eV’s?”
“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.”
“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.”
“Why should there be flashes? I thought neutrinos didn’t interact with matter.”
“Hello, Jennie. Haven’t seen you for a while.”
Momentum 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.”
“Wait, right ascension in hours-minute-seconds but declination in degrees?”
Cathleen 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.”
With my finger I draw in the frost on his gelato cabinet. “Imagine this is a brass ball, except I’ve pulled one side of it out to a cone. Someone’s loaded it up with extra electrons so it’s carrying a high negative charge.”
“They’re certainly eye-catching, but I thought Jupiter’s all baby-blue and salmon-colored.”
Hard Science Ain't Hard 
