Conjunction Function

Author’s note — This was supposed to have been posted on 13 December, a week before the conjunction, but then Arecibo happened. That topic took precedence and two parts. Please pretend you’re reading this before 21 December.

hi, Sy. taking orders for tonite’s delivery. u want pizza? calzone?

Hi, Eddie. How about a veggie stromboli?

sure, no problem. @ your office about 6:45, OK?

That’ll be good. See you then.

btw, question for you about the jupiter-saturn thing coming up

The conjunction? Sure. We can talk when you get here.

<bah-dap-dap> “C’mon in, Eddie, the door’s open.”

“Hiya, Sy. Here’s your stromboli. Sorry I’m a little late. I figured we’d be talking so I took care of my other customers first. I wrapped it real good, is it still hot enough?”

<tasting pause> “Perfect, Eddie. So what’s your question?”

“OK, I been reading on the internet about how Jupiter and Saturn are gonna collide on December 21 and we’re all gonna die so don’t bother about Christmas. But I also read that this happened before like 800 years ago and we’re still here so the ‘all gonna die‘ part don’t sound right.”

“Good thinking. We’re not going to die, they’re not going to collide, and Great Conjunctions happen way more often than every 800 years. You said you’d be asking about that so I built a couple of diagrams using planet positions I pulled from NASA’s slick Eyes on The Solar System app. OK, let’s start with this south‑facing view of the system as it was a year ago.”

Planetary positions, 15 Dec 2019

“Pretty, kinda, but what’s it mean?”

“That orange dot in the center is the Sun. The circles are planet orbits, and the colored dots show the position of each planet. All the planets and most of their moons go counterclockwise when viewed from Solar north — that’s what the little arrows show.”

“I thought Jupiter was way bigger than Earth.”

“It is. There’s no way you can get planet distances and planet sizes to scale in the same diagram. Distances are too big and even Jupiter’s too small. These distances are about right, but all the dots are just markers.”

“Funny, Sy — you dropped Jupiter half-way between Earth and Saturn.”

“That’s where it is. The distance between each pair of orbits is almost exactly 4½ times the distance between Earth and the Sun. Of course, the distance between the planets themselves depends on where each one is in its orbit and that changes all the time. Earth flies along its path three times faster than Saturn goes. Last December, Earth was 186 million miles further away from Saturn than it was in July.”

“Those dotted lines are sight-lines? That picture says that last December we had a clear view of Saturn but Earth and Jupiter were playing peek-a-boo around the Sun.”

“Exactly, and what a great lead‑in to my second diagram, calculated for next Monday.”

Planetary positions, 21 Dec 2020

“The two sight-lines overlap. They’ll look like just one planet, sorta. So that’s what all the fuss is about? They’re still that huge distance away from each other, not close to us at all.”

“Overlap’s a good word, though the official term is conjunction. The only things close together are images as seen from Earth. That last qualifier is important. What you see depends on where you stand. Our Curiosity rover on Mars won’t see a Great Conjunction like this for another month, on 31 Jan 2021.”

“What makes it a Great Conjunction? Is it brighter or something?”

“In a way. In principle you can have a conjunction of any two visible astronomical bodies. The phrase Great Conjunction only applies to Jupiter‑Saturn events. Of the classical planets Jupiter and Saturn are the slowest‑moving so their conjunction happens least often. They’re also the biggest and reflect more sunlight than Mercury or Mars so, yeah, their conjunctions tend to be especially bright.”

“But you said it happens a lot.”

“About every 20 years. You’re thinking about that 800‑year‑old event. That was the last time the two images were so close, less than a tenth of a degree apart.”

“So anyhow, we’re not all gonna die. Guess I’ll go Christmas shopping after all.”

“You do that, but shop local, OK?”

“That’s my motto now.”

~~ Rich Olcott

Earth’s Closed Eye

Question in the chat box, Maria, and I paraphrase to preserve anonymity — ‘So the Arecibo telescope won’t work any more. Why should we care? There’s lots of other telescopes that could so the same job.‘”

“But profesora, there aren’t. Arecibo is special in many ways. First, it is a very good telescope. That means it has high sensitivity and high resolution. Compare two radio telescopes with different‑size dishes and the same kinds of antennas and everything else. The one with the bigger dish is more sensitive because it can capture more photons. Arecibo’s 300‑meter dish used to be the largest in the world. China activated their FAST instrument five years ago. Its 500‑meter dish should make it more than 200 times as sensitive as Arecibo, but it doesn’t because neither telescope is designed to use the entire dish surface at once except for looking straight up. Their active areas are about the same.”

Is FAST another one of those goofy acronyms?

“Of course. It stands for ‘Five‑hundred‑meter Aperture Spherical radio Telescope‘ but in Chinese its name is Tianyan, which means ‘Heaven Eye.’ I think that is more pretty. FAST and Arecibo overlap their wavelength ranges, although FAST can receive some longer wavelengths and Arecibo can receive some shorter ones. Oh, there is also a big Russian radio telescope, RATAN‑600, with an even bigger diameter. But it is a ring, not a disk, so not as sensitive as Arecibo or FAST.”

A ring? Why did they build it that way?

“Because of the other thing you need in a good telescope, resolution. If you have good resolution in an image, you can see points that are very close together. The how‑close limit angle comes from dividing the light wavelength by the dish diameter. The diameter of RATAN’s ring is 600 meters, so RATAN’s resolving power is twice as good as Arecibo’s 300‑meter disk. RATAN doesn’t need to be sensitive, though, because it is used mostly for looking close at the Sun, not at stars and galaxies. That is OK because RATAN is so far north.”

What difference does that make?

“No telescope can see what is below its horizon. RATAN is at 43° north, almost 1400 miles north of Arecibo. It has a good view of the northern sky but cannot see down to the Equator where many asteroids and all the planets are.”

Sorry, Maria, that’s not quite correct. Earth is tilted relative to the orbital plane by 23° so even Arecibo only sees the northern portion of planetary orbits. While I’ve got the mic I’ll add some background on RATAN‑600. RATAN is the acronym for ‘Academy of Sciences Radio Telescope’ in Russian. It was built in the Cold War era when that part of the world was the USSR. Although I don’t believe it’s ever been publicly confirmed, many people think that RATAN‑600‘s original purpose was detection of ICBMs coming in over the North Pole. However, over the decades it has been a productive source of information for the solar physics community. Back to you, Maria.

“That is good to know, profesora. Thank you. So, Arecibo is — was —special because of its sensitivity and its resolution. It is also about 500 miles further south than FAST. But Arecibo has one additional feature that FAST cannot have — radar. Arecibo has high-powered transmitters that can send out terawatt pulses to things in the Solar System that are closer than Saturn. The dish gathers echoes that give us detailed knowledge of those objects. For instance, Arecibo’s radar echoes from Mercury showed us that the planet is not tidally locked to the Sun. We used to think Mercury’s day was 88 days long, like its year, but now we know it rotates in only 59 days.”

Why can’t the Chinese just add transmitters to FAST?

“The Chinese designers gave FAST a light‑weight antenna carriage to hang over its dish. Arecibo’s 900‑ton carriage can handle massive transmitters, but FAST’s cannot. There is one other radio telescope with radar, at Goldstone, California, but it has less than one‑millionth the power of Arecibo’s transmitters. Without Arecibo’s sensitivity, resolution, location and high-powered radar capability we cannot find near‑Earth asteroids on track to hit us.”

~~ Rich Olcott

Author’s note — Early in the morning of 1 December, after I completed last week’s and this post, the National Science Foundation reported that Arecibo’s central instrument platform has fallen onto the dish as a result of further cable failures.
“Vale, nostri servi boni et fidelis”
Farewell, our good and faithful servant.

Arecibo ¡que lástima!

Hello, Astronomy video class. I’ve made room in the syllabus schedule for a quick talk from someone with a personal connection to a timely topic. You may know we’ve lost one of Astronomy’s premier radio telescopes, Puerto Rico’s Arecibo Observatory. I’ve asked Maria to fill us in on the what and the why. If you have a question, type it into your chat window and I’ll relay it to her. Maria, you’re on.”

“Thank you, profesora. Yes, I do know Arecibo because I have worked there. I grew up in Hatillo, a small city on the north coast about half an hour away from the Observatory. My teacher of science in high school, somehow he got me a summer job there. Sometimes I worked in the gift shop, sometimes I helped the guided tours, but my best thing was running errands because then I could visit the science offices and chat with people about what they were doing. There I fell in love with Astronomy and that is why I came here to study.

“When people think of Arecibo they think of the big 300 meter dish, about 1000 feet across. Sharing my screen for you… there. This picture I got from Wikipedia:

The Arecibo Observatory
photo by JidoBG, licensed under the Creative Commons Attribution-Share Alike 4.0 International

“The installation sits in very rough mountains. They are so rough because they are mostly limestone that slowly dissolves in water. The water seeps in through cracks to attack the rock and make cliffs and holes and caves. The Arecibo observatory is where it is because water eroded a cavern close to the surface. The topmost material fell into the empty space to make a huge round sinkhole like very few other places in the world.”

Question from the chat, Maria. Did the rock actually dissolve into that convenient smooth reflector shape?

“¡Por Dios no! The circular shape, yes, but the sinkhole floor is nearly flat. The dish itself is many aluminum panels fixed to a floating steel grid. Here is a picture Mr Phil Perillat took from beneath the dish. I don’t know Mr Perillat’s title but he is always very busy keeping things running.

“Above you see the grid, five meters or more above the ground. The grid is supported by concrete all around the edges. Coming down from the grid you see cables leading to those round concrete piers. These cables pull the grid down into its curved shape which is actually a piece of a sphere.”

A sphere, not a parabola?

“No, profesora, and that is important. A fixed dish with a parabola shape like most telescope mirrors always would aim straight up. It would see targets at the top of the sky but for only a few minutes as the Earth turns through the day. With a sphere‑shaped dish and the antennas mounted where the center of the sphere would be, then the whole sky is in focus. The scientists aim the telescope by moving the antennas to point at different parts of the dish like you look at different parts of one of those funny mirrors in, sorry I don’t know the word, una casa de la diversión.”

A funhouse.”

“Thank you. The antenna carriage is so complicated because it must look at different parts of the dish. Here you see the carriage:

The Arecibo receiver mounting and dome
Photo by Phil Perillat, National Astronomy and Ionosphere Center

“The antennas point downward from inside that dome. When motors swing the dome along that crescent‑shaped arc, the antennas scan along an arc of the dish. More motors can rotate the arc around that circular track. By swinging and rotating together, the antennas can follow the reflection of any object that moves through the sky.”

All those motors and tracks and antennas must be heavy.”

“Yes, 900 tons hanging 500 feet above the grid. Eighteen cables hold it up. Each is many strands of steel braided together. Compressed air blows through the braids to prevent corrosion, but the storms won out in the end. Three cables have failed and it is too dangerous for repair. So sad.”

~~ Rich Olcott

Author’s note — Early in the morning of 1 December, after I completed this and next week’s posts, the National Science Foundation reported that Arecibo’s central instrument platform had fallen onto the dish as a result of further cable failures.
“Vale, nostri servi boni et fidelis”
Farewell, our good and faithful servant.

Only a H2 in A Gilded Cage

“OK, Susan, you’ve led us through doing high-pressure experiments with the Diamond Anvil Cell and you’ve talked about superconductivity and supermagnetism. How do they play together?”

“It’s early days yet, Sy, but Dias and a couple of other research groups may have brought us a new kind of superconductivity.”

“Another? You talked like there’s only one.”

“It’s one of those ‘depends on how you look at it‘ things, Al. We’ve got ‘conventional‘ superconductors and then there are the others. The conventional ones — elements like mercury or lead, alloys like vanadium‑silicon — are the model we’ve had for a century. Their critical temperatures are generally below 30 kelvins, really cold. We have a 60‑year‑old Nobel‑winning theory called ‘BCS‘ that’s so good it essentially defines conventional superconductivity. BCS theory is based on quantum‑entangled valence electrons.”

“So I guess the unconventional ones aren’t like that, huh?”

“Actually, there seem to be several groups of unconventionals, none of which quite fit the BCS theory. Most of the groups have critical temperatures way above what BCS says should be the upper limit. There are iron‑based and heavy‑metals‑based groups that use non‑valence electrons. There are a couple of different carbon‑based preparations that are just mystical. There’s a crazy collection of copper oxide ceramics that can contain five or more elements. Researchers have come up with theories for each of them, but the theories aren’t predictive — they don’t give dependable optimization guidelines.”

“Then how do they know how to make one of these?”

“Old motto — ‘Intuition guided by experience.’ There are so many variables in these complex systems — add how much of each ingredient, cook for how long at what temperature and pressure, chill the mix quickly or anneal it slowly, bathe it in an electrical or magnetic field and if so, how strong and at what point in the process… Other chemists refer to the whole enterprise as witch’s‑brew chemistry. But the researchers do find the occasional acorn in the grass.”

“I guess the high‑pressure ploy is just another variable then?”

“It’s a little less random than that, Sy. If you make two samples of a conventional superconductor, using different isotopes of the same element, the sample with the lighter isotope has the higher critical temperature. That’s part of the evidence for BCS theory, which says that electrons get entangled when they interact with vibrations in a superconductor. At a given temperature light atoms vibrate at higher frequency than heavy ones so there’s more opportunity for entanglement to get started . That set some researchers thinking, ‘We’d get the highest‑frequency vibrations from the lightest atom, hydrogen. Let’s pack hydrogens to high density and see what happens.'”

“Sounds like a great idea, Susan.”

“Indeed, Al, but not an easy one to achieve. Solid metallic hydrogen should be the perfect case. Dias and his group reported on a sample of metallic hydrogen a couple of years ago but they couldn’t tell if it was solid or liquid. This was at 5 megabars pressure and their diamonds broke before they could finish working up the sample. Recent work has aimed at using other elements to produce a ‘hydrogen‑rich’ environment. When Dias tested H2S at 1.5 megabar pressure, they found superconductivity at 203 kelvins. Knocked everyone’s socks off.”

“Gold rush! Just squeeze and chill every hydrogen‑rich compound you can get hold of.”

“It’s a little more complicated than that, Sy. Extreme pressures can force weird chemistry. Dias reported that shining a green laser on a pressurized mix of hydrogen gas with powdered sulfur and carbon gave them a clear crystalline material whose critical temperature was 287 kelvins. Wow! A winner, for sure, but who knows what the stuff is? Another example — the H2S that Dias loaded into the DAC became H3S under pressure.”

“Wait, three hydrogens per sulfur? But the valency rules—”

“I know, Sy, the rules say two per sulfur. Under pressure, though, you get one unattached molecule of H2 crammed into the space inside a cage of H2S molecules. It’s called a clathrate or guest‑host structure. The final formula is H2(H2S)2 or H3S. Weird, huh? Really loads in the hydrogen, though.”

“Jupiter has a humungous magnetic field and deep‑down it’s got high‑density hydrogen, probably metallic. Hmmm….”

~~ Rich Olcott

Zeroing In on Water

<chirp, chirp> “Moire here.”

“Hi, Sy, it’s me, Vinnie. I just heard this news story about finding water on the Moon. I thought we did that ten years ago. You even wrote about it.”

“The internet never forgets, does it? That post wasn’t quite right but it wasn’t wrong, either.”

“How can it be both?”

“There’s an old line in Science — ‘Your data’s fine but your conclusions are … nuts.’ They use a different word in private. Suppose you land on a desert island and find a pirate’s treasure chest. Should the headlines say you’d found a treasure?”

“Naw, the chest might be empty or full of rocks or something.”

“Mm-hm. So, going back to that post… I was working from some reports on NASA’s Lunar Reconnaissance Orbiter. Its LAMP instrument mapped how strongly different Moon features reflected a particular frequency of ultraviolet light. That frequency’s called ‘Lyman‑alpha.’ Astronomers care about it because it’s part of starlight, it’s reflected by rock, and it’s specifically absorbed by hydrogen atoms. Sure enough, LAMP found some places, typically in deepshadow craters, that absorbed a lot more Lymanalpha than other places.”

“And you wrote about how hydrogen atoms are in water molecules and the Moon’s deep crater floors near the poles are sheltered from sunlight that’d break up water molecules so LAMP’s dark spots are where there’s water. And you liked how using starlight to find water on the Moon was poetical.”

“Uhh… right. All that made a lot of sense at the time and it still might be true. Scientists leapt to the same hopeful conclusion when interpreting data from the MESSENGER mission to Mercury. That one used a neutron spectrometer to map emissions from hydrogen atoms interacting with incoming cosmic rays. There again, the instrument identified hydrogen collected in shaded craters at the planet’s poles. Two different detection methods giving the same positive indication at the same type of sheltered location. The agreement seemed to settle the matter. The problem is that water isn’t geology’s only way or even its primary way to accumulate hydrogen atoms.”

“What else could it be? Hydrogen ions in the solar wind grab oxide ions from Moon rock and you’ve got water, right?”

“But the hydrogens arrive one at a time, not in pairs. Any conversion would have to be at least a two‑step process. The Moon’s surface rocks are mostly silicate minerals. They’re a lattice of negative oxide ions that’s decorated inside with an assortment of positive metal ions. The first step in the conversion would be for one hydrogen ion to link up with a surface oxide to make a hydroxide ion. That species has a minus‑one charge instead of oxide’s minus‑two so it’s a bit less tightly bound to its neighboring metal ions. Got that?”

“Gimme a sec … OK, keep going.”

“Some time later, maybe a century maybe an eon, another hydrogen ion comes close enough to attack our surface hydroxide if it hasn’t been blasted apart by solar UV light. Then you get a water molecule. On balance and looking back, we’d expect most of the surface hydrogen to be hydroxide ions, not water, but both kinds would persist better in shadowed areas.”

“OK, two kinds of hydrogen. But how do we tell the difference?”

“We evaluate processes at lower‑energies. Lyman‑alpha photons pack over 10 electronvolts of energy, enough to seriously disturb an atom and blow a molecule apart. O‑H and H‑O‑H interact differently with light in the infra‑red range that just jiggles molecules instead of bopping them. For instance, atom pairs can stretch in‑out. Different kinds of atom bind together more‑or‑less tightly. That means each kind of atom pair resonates at its own stretch energy, generally around 6 microns or 0.41 electronvolts. NASA’s Cassini mission had a mapping spectrometer that could see down into that range. It found O‑H stretching activity all over the Moon’s surface.”

“But that could be either hydroxyls or water.”

“Exactly. The new news is that sensors aboard NASA’s airborne SOFIA mission map light even deeper into the infra‑red. It found the 3‑micron, 0.21‑electronvolt signal for water’s V‑shape scissors motion. That’s the water that everybody’s excited about.”

“Lots of it?”

“Thinly spread, probably, but stay tuned.”

~~ Rich Olcott

A Star’s Tale

It’s getting nippy outside so Al’s moved his out‑front coffee cart into his shop. Jeremy’s manning the curbside take‑out window but I’m walking so I step inside. Limited seating, of course. “Morning, Al. Here’s my hiking mug, fill ‘er up with high‑test and I’ll take a couple of those scones — one orange, one blueberry. Good news that the Governor let you open up.”

“You know it, Sy. Me and my suppliers have been on the phone every day. Good thing we’ve got long‑term relationships and they’ve been willing to carry me but it gets on my conscience ’cause they’re in a crack, too, ya know?”

“Low velocity of money hurts everybody, Al. Those DC doofuses and their political kabuki … but don’t get me started. Hey, you’ve got a new poster over the cash register.”

“You noticed. Yeah, it’s a beaut. Some artist’s idea of what it’d look like when a star gets spaghettified and eaten by a black hole. See, it’s got jets and a dust dusk and everything.”

“Very nice, except for a few small problems. That’s not spaghettification, the scale is all wrong and that tail-looking thing … no.”

Artist’s impression of AT2019qiz. Credit: ESO/M. Kornmesser
Under Creative Commons Attribution 4.0 International License

“Not spaghettification? That’s what was in the headline.”

“Sloppy word choice. True spaghettification acts on solid objects. Gravity’s force increases rapidly as you approach the gravitational center. Suppose you’re in a kilometer-long star cruiser that’s pointing toward a black hole from three kilometers away. The cruiser’s tail is four kilometers out. Newton’s Law of Gravity says the black hole pulls almost twice as hard on the nose as on the tail. If the overall field is strong enough it’d stretch the cruiser like taffy. Larry Niven wrote about the effect in his short story, Neutron Star.”

“The black hole’s stretching the star, right?”

“Nup, because a star isn’t solid. It’s fluid, basically a gas held together by its own gravity. You can’t pull on a piece of gas to stretch the whole mass. Your news story should have said ‘tidal disruption event‘ but I guess that wouldn’t have fit the headline space. Anyhow, an atom in the star’s atmosphere is subject to three forces — thermal expansion away from any gravitational center, gravitational attraction toward its home star and gravitational attraction toward the black hole. The star breaks up atom by atom when the two bodies get close enough that the black hole’s attraction matches the star’s surface gravity. That’s where the scale problem comes in.”

Al looks around — no waiting customers so he strings me along. “How?”

“The supermassive black hole in the picture, AT2019qiz, masses about a million Suns‑worth. The Sun‑size star can barely hold onto a gas atom at one star‑radius from the star’s center. The black hole can grab that atom from a thousand star‑radii away, about where Saturn is in our Solar System. The artist apparently imagined himself to be past the star and about where Earth is to the Sun, 100 star‑radii further out. Perspective will make the black hole pretty small.”

“But that’s a HUGE black hole!”

“True, mass‑wise, not so much diameter‑wise. Our Sun’s about 864,000 miles wide. If it were to just collapse to a black hole, which it couldn’t, its Event Horizon would be about 4 miles wide. The Event Horizon of a black hole a million times as massive as the Sun would be less than 5 times as wide as the Sun. Throw in the perspective factor and that black circle should be less than half as wide as the star’s circle.”

“What about the comet‑tail?”

“The picture makes you think of a comet escaping outward but really the star’s material is headed inward and it wouldn’t be that pretty. The disruption process is chaotic and exponential. The star’s gravity weakens as it loses mass but the loss is lop‑sided. Down at the star’s core where the nuclear reactions happen the steady burn becomes an irregular pulse. The tail should flare out near the star. The rest should be jagged and lumpy.”

“And when enough gets ripped away…”

“BLOOEY!”

~~ Rich Olcott

  • Thanks to T K Anderson for suggesting this topic.
  • Link to Technical PS — Where Do Those Numbers Come From?.

The Edges of The Universe

<chirp, chirp> “Moire here.”

“Um, Uncle Sy?”

“Hi, Teena! I didn’t know you knew my phone number. It’s past your bedtime. How are you? Is everything OK?”

“I’m fine. Mommie dialed you for me. I had a question she said you could answer better than her and that would be my bedtime story.”

“Your Mommie’s a very smart person in several ways. What’s your question?”

“Where’s the edge of the Universe?”

“Whoa! Where’d that question come from?”

“Well, I was lying on my bed and I thought, the edge of me is my skin and the edge of my room is the walls and the edge of our block is the street but I don’t know what any of the bigger edges are so I asked Mommie and she said to ask you. She’s writing something.”

“Of course she is. One answer is you’re smack on an edge, but some people think that’s a wrong answer so let’s talk about all the edges, OK?”

“On an edge??!? I’m in the middle of my bed.”

“Hey, I heard you sit up. Lie back down, this is supposed to be a bedtime story so we’re supposed to be calm, OK? All right, now. Once upon a time —”

“Really?”

“Yes, really. Now hush and let me start. Once upon a time, people thought that the sky was a solid bowl or maybe a curtain that came down all the way to meet the Earth just over the horizon, and that was the edge of the Universe. But then people started traveling and they realized that the horizon moved when they did.”

“Like rainbows.”

“Exactly like rainbows. Eventually they’d traveled everywhere they could walk. As they went they made maps. According to the maps, the world they knew about was surrounded by ocean so the edge of the Universe was the ocean.”

“Except for Moana’s people that crossed the ocean.”

“Right, but even they only went from island to island. Their version of a map was as flat as the paper maps the European and Chinese explorers used.”

“But the world is really round like my world ball.”

“Yes, it is. It took humans a long time to accept that, because it meant their world couldn’t be all there is. A round world would have to float in space. Think about this — what’s the edge of our world?”

“Umm … the air?”

“Very good, sweetie. Way up, 60 miles high, the air gets so thin that we call that height the Edge of Space.”

“That’s the inside edge of space. Where’s the outside edge of space?”

“It’s moved outward as our astronomers have gotten better at looking far away. For a long time they thought that the outermost stars in our Milky Way galaxy marked the edge of the Universe. Then an astronomer named Edwin Hubble—”

“Oh, like the Hubble Space Telescope that made the pretty pictures in my ‘Stronomy book!”

“Mm-hm, the Hubble was named for him because he did such important work. Anyway, he showed that what people thought were stardust clouds inside the Milky Way were actually other galaxies like ours but far, far away. With the Hubble and other telescopes we’ve pushed out our known Universe to … I don’t even know the name of such a big number.”

“So that’s the edge?”

“We don’t think so, but we don’t know. Maybe space and galaxies go on forever, maybe galaxies peter out but space goes on, maybe something weird. But there’s a special ‘direction’ that we think does have an edge, maybe two.”

<yawn> “What’s that?”

“Time. One edge was the Big Bang, fourteen billion years ago. We’re pretty sure of that one. The scientists and philosophers argue about whether there’s another edge.”

“Wouldn’t jus’ be f’rever?”

“Mr Einstein thought it would. In fact, he thought that the future is as solidly real as the past is and we’re just watching from the windows of a train rolling along the time tracks.”

“Don’ like that, wanna do diffren’ things.”

“Me, too, sweetie. I prefer the idea that the future doesn’t exist yet; we’re on the front edge of time, building as we go. Dream about that, OK?”

“Okayyyyyy

~~ Rich Olcott

To Swerve And Project

A crisp Fall dawn, crisp fallen leaves under my feet as I jog the path by the park’s lake.

“Hey! Moire! How about these red sunrises and sunsets? Remind you of Mars?”

“Morning, Mr Feder. Not much, and definitely not dawn or dusk. Those tend more to blue, as a matter of fact.”

“Waitaminnit, Moire. I seen that Brad Pitt Martian movie, him driving hisself all alone across that big plain — the place is blood‑red.”

“Think a minute, Mr Feder. If he was all alone, who was running the cameras?”

“Uhhh, right. Movie. Yeah, they were really on Earth so they could director the lighting and all. But they said they’d scienced the … heck out of it.”

“Oh they did, better than most movies, but artistic license took over in a couple of places. People expect Mars to be red, not mostly clay colored like it really is, so the producers served up red.”

“Wait, I remember the conversation about Earth is blue because of the oceans and Mars is red because of its rusty atmosphere. So what’s with the sky colors?”

“Looking up at sunlight through an atmosphere is very different from looking down at the surface. It all has to do with how what’s in the atmosphere interacts with sunlight. Take Earth’s blue sky, for instance.”

“My favorite color.”

“Sure it is. OK, the Sun’s disk takes up much less than 1% of the sky but that’s enough to give us all our sunlight photons. A fraction of them run into something on the way down to Earth’s surface. What happens depends on how big the something is compared to the photon wavelength. Much larger things, maybe an airplane, completely block the photons and we get a shadow.”

“Obviously.”

“Yeah, but life’s more interesting for smaller somethings. For things like air molecules and dust particles that are much smaller than the the wavelength of visible light, the waves generally swerve around the particle. How much they swerve depends on the wavelength — extreme blue light bends about ten times more than extreme red light for the same scattering particle. So suppose there’s a kid a few miles away from us looking at the sky while we’re looking at it here. There’s a sunbeam with a rainbow‑load of photons headed for the kid, but there are dust particles in the way. Get the picture?”

“Sure, sure, get on with it.”

“So some of the light swerves. The red swerves a little but the blue light swerves ten times as much, enough that it heads straight for us. What color do we see when we look in that direction?”

“Blue, of course.”

“Blue everywhere in the lit‑up sky except when we look straight at the Sun.”

“What about these pretty red sunsets and the red skies over the wildfires?”

“Two different but related phenomena. Sunsets first. An incoming photon with just the right wavelength may simply be absorbed by a molecule. Doesn’t happen often, but there’s lots of molecules. Turns out that oxygen and ozone absorb blue light more strongly than red light. When we’re looking horizontally towards a sunset we’re looking through many more oxygen molecules than when we look vertically. We see the red part of a blue‑filtered version of that swerve rainbow.”

“And the fire skies?”

“The fires released huge amounts of fine smoke particles, just the right size for color‑scattering. Blue light swerves again and again until it’s either absorbed or shot out to space. Red light survives.”

Upper image – Golden Gate Bay under fiery skies, Sept 2020
Lower image – Sunset from Gusev Crater, Mars
Credit: NASA/JPL/Texas A&M/Cornell

“So what’s different about Mars?”

“Three things — Mars dust is different from Earth’s, its atmosphere is a lot thinner, and there’s practically no atmospheric water or oxygen. Rusty Mars dust is the size of smoke particles. With no rain or snow to settle out the dust, it stays aloft all the time. Rust is red because it absorbs blue light and reflects only the red part. With less diffused sunlight, Mars’ sky is basically the black of space overlaid with a red tint. Sunsets are blue‑ish because what blue light there is can travel further.”

“Earth skies are better.”

~~ Rich Olcott

Question Time

Cathleen unmutes her mic. “Before we wrap up this online Crazy Theories contest with voting for the virtual Ceremonial Broom, I’ve got a few questions here in the chat box. The first question is for Kareem. ‘How about negative evidence for a pre-mammal civilization? Played-out mines, things like that.‘ Kareem, over to you.”

“Thanks. Good question but you’re thinking way too short a time period. Sixty‑six million years is plenty of time to erode the mountain a mine was burrowing into and take the mining apparatus with it.

“Here’s a different kind of negative evidence I did consider. We’re extracting coal now that had been laid down in the Carboniferous Era 300 million years ago. At first, I thought I’d proved no dinosaurs were smart enough to dig up coal because it’s still around where we can mine it. But on second thought I realized that sixty-six million years is enough time for geological upthrust and folding to expose coal seams that would have been too deeply buried for mining dinosaurs to get at. So like the Silurian Hypothesis authors said, no conclusions can be drawn.”

“Nice response, Kareem. Jim, this one’s for you. ‘You said our observable universe is 93 billion lightyears across, but I’ve heard over and over that the Universe is 14 billion years old. Did our observable universe expand faster than the speed of light?‘”

“That’s a deep space question, pun intended. The answer goes to what we mean when we say that the Hubble Flow expands the Universe. Like good Newtonian physicists, we’re used to thinking of space as an enormous sheet of graph paper. We visualize statements like, ‘distant galaxies are fleeing away from us‘ as us sitting at one spot on the graph paper and those other galaxies moving like fireworks across an unchanging grid.

“But that’s not the proper post-Einstein way to look at the situation. What’s going on is that we’re at our spot on the graph paper and each distant galaxy is at its spot, but the Hubble Flow stretches the graph paper. Suppose some star at the edge of our observable universe sent out a photon 13.7 billion years ago. That photon has been headed towards us at a steady 300000 kilometers per second ever since and it finally reached an Earth telescope last night. But in the meantime, the graph paper stretched underneath the photon until space between us and its home galaxy widened by a factor of 3.4.

“By the way, it’s a factor of 3.4 instead of 6.8 because the 93 billion lightyear distance is the diameter of our observable universe sphere, and the photon’s 13.7 billion lightyear trip is that sphere’s radius.

“Mmm, one more point — The Hubble Flow rate depends on distance and it’s really slow on the human‑life timescale. The current value of the Hubble Constant says that a point that’s 3×1019 kilometers away from us is receding at about 70 kilometers per second. To put that in perspective, Hubble Flow is stretching the Moon away from us by 3000 atom‑widths per year, or about 1/1300 the rate at which the Moon is receding because of tidal friction.”

“Nice calculation, Jim. Our final question is for Amanda. ‘Could I get to one of the other quantum tracks if I dove into a black hole and went through the singularity?‘”

“I wouldn’t want to try that but let’s think about it. Near the structure’s center gravitational intensity compresses mass-energy beyond the point that the words ‘particle’ and ‘quantum’ have meaning. All you’ve got is fields fluctuating wildly in every direction of spacetime. No sign posts, no way to navigate, you wouldn’t be able to choose an exit quantum track. But you wouldn’t be able to exit anyway because in that region the arrow of time points inward. Not a sci‑fi story with a happy ending.”

“<whew> Alright, folks, time to vote. Who presented the craziest theory? All those in favor of Kareem, click on your ‘hand’ icon. … OK. Now those voting for Jim? … OK. Now those voting for Amanda? … How ’bout that, it’s a tie. I guess for each of you there’s a parallel universe where you won the virtual Ceremonial Broom. Congratulations to all and thanks for such an interesting evening. Good night, everyone.”

~~ Rich Olcott

Smart Dinosaurs?

<chirp, chirp> “Moire here, what can I do for you while staying six feet away?”

“Hi, Sy, this is Cathleen. you’re invited to to an experiment.”

“What sort of experiment?”

“You’ve been to a few of our ‘Crazy Theory’ events. We can’t do those now, of course, but we’re trying it online. Interested?”

“Sounds like fun. Email me the details and I’ll dial in.”


“Hi, everyone, welcome to our first-ever online ‘Crazy Theories’ seminar. I’m afraid it’ll be a bit different from our traditional affairs. Everyone but the presenter’s on mute so don’t bother shouting encouragement or booing. Any spitballs or wadded-up paper napkins you throw you get to clean up. As always at the end we’ll take a vote to award the Ceremonial Broom for the craziest theory. Type your questions and comments in the chat box; we’ll get to them after the presenter finishes. Everybody got all that? OK, our first presenter is from my Planetology class. Go ahead, Kareem.”

“Hey, everybody. I’m Kareem and my Crazy Theory isn’t mine, personally, but it’s the one that got me into Planetology class. Its was in this science fiction novel I read a couple of years ago. The story’s complicated and has a lot of science that I didn’t understand, but the part that caught my imagination was his idea that what killed off the dinosaurs was smart dinosaurs.”

<consults notes>

“A little history first. In the late 1970s two scientists named Alvarez discovered that all around the Earth there’s a thin layer of soil with more than ten times the normal amount of an element called iridium. They found that the layer was 66 million years old, which just matched the end of the Cretaceous Era when the last of the dinosaurs died off. They knew that some meteorites have a lot of iridium so in 1980 they suggested that a meteor strike must have done the deed.

“That idea was so controversial that John McLoughlin came up with his own explanation and based his book on it. He supposed that about 66 million years ago evolution produced intelligent dinosaurs that took over the planet the way that we humans have in our time. They weren’t huge like T‑rex but they were big enough to use Triceratops as draft and meat animals and smart enough to develop lots of iridium‑based technology like we use copper. Anyway, they got into a world war and that was what wiped everything out and left behind the traces of iridium.”

<gulps down soda>

“McLaughlin’s book came out in 1988. Since than we’ve learned that the Alvarez guys were basically right although there was some other stuff going on, too. But the book got me thinking that maybe there could have been a world‑wide civilization and the only things left after 66 million years were bones and this trace of a metal they used. Humans have only been around for like a hundred thousand years and we’ve only been doing metals big‑time for a few hundred which is teeny compared to a million years. A paleontologist wouldn’t even be able to detect a time period that small. So my Crazy Theory is, maybe there were smart dinosaurs or something and we just haven’t found evidence for them.”

<burp>

“Ever since then I’ve kept an eye out for publications about what a vanished civilization might leave behind for us to discover. In this book Weisman lays out survival times for our civilization’s stuff — plastic, houses, roads and so on. Pretty much everything but Mount Rushmore and the Chunnel will have dissolved or eroded away much sooner than a million years. Really readable if you want more details.”

<more soda>

“I also found a paper, ‘The Silurian Hypothesis,’ that took a more technical approach. Their big library research project pulled results from scores of geologic isotope analysis and fossil survey reports looking for ancient times that resemble Earth’s sudden change since the start of the Industrial Age — climate, species declines, whatever. They found about a dozen, but as they said, ‘the known unique markers might not be indicative, while the (perhaps) more expected markers are not sufficient.’ In other words, my Crazy Theory might be crazy. Or maybe not.”

~~ Rich Olcott