astronomy, physics, science, Space, thought experiment

If the Sun went Supernova

I have to preface this article by saying that yes, I know I’m hardly the first person to consider this question.

I also have to add that, according to current physics (as of this writing in December 2017), the Sun won’t ever go supernova. It’s not massive enough to produce supernova conditions. But hey, I’ll gladly take any excuse to talk about supernovae, because supernovae are the kind of brain-bending, scary-as-hell, can’t-wrap-your-feeble-meat-computer-around-it events that make astronomy so creepy and amazing.

So, for the purposes of this thought experiment, let’s say that, at time T + 0.000 seconds, all the ingredients of a core-collapse supernova magically appear at the center of the Sun. What would that look like, from our point of view here on Earth? Well, that’s what I’m here to find out!

From T + 0.000 seconds to 499.000 seconds

This is the boring period where nothing happens. Well, actually, this is the nice period where life on Earth can continue to exist, but astrophysically, that’s pretty boring. Here’s what the Sun looks like during this period:

Normal Sun.png

Pretty much normal. Then, around 8 minutes and 19 seconds (499 seconds) after the supernova, the Earth is hit by a blast of radiation unlike anything ever witnessed by humans.

Neutrinos are very weird, troublesome particles. As of this writing, their precise mass isn’t known, but it’s believed that they do have mass. And that mass is tiny. To get an idea of just how tiny: a bacterium is about 45 million times less massive than a grain of salt. A bacterium is 783 billion times as massive as a proton. Protons are pretty tiny, ghostly particles. Electrons are even ghostlier: 1836 times less massive than a proton. (In a five-gallon / 19 liter bucket of water, the total mass of all the electrons is about the mass of a smallish sugar cube; smaller than an average low-value coin.)

As of this writing (December 2017, once again), the upper bound on the mass of a neutrino is 4.26 million times smaller than the mass of an electron. On top of that, they have no electric charge, so the only way they can interact with ordinary matter is by the mysterious weak nuclear force. They interact so weakly that (very approximately), out of all the neutrinos that pass through the widest part of the Earth, only one in 6.393 billion will collide with an atom.

But, as XKCD eloquently pointed out, supernovae are so enormous and produce so many neutrinos that their ghostliness is canceled out. According to XKCD’s math, 8 minutes after the Sun went supernova, every living creature on Earth would absorb something like 21 Sieverts of neutrino radiation. Radiation doses that high have an almost 100% mortality rate. You know in Hollywood how they talk about the “walking ghost” phase of radiation poisoning? Where you get sick for a day or two, and then you’re apparently fine until the effects of the radiation catch up with you and you die horribly? At 21 Sieverts, that doesn’t happen. You get very sick within seconds, and you get increasingly sick for the next one to ten days or so, and then you die horribly. You suffer from severe vomiting, diarrhea, fatigue, confusion, fluid loss, fever, cardiac complications, neurological complications, and worsening infections as your immune system dies. (If you’re brave and have a strong stomach, you can read about what 15-20 Sieverts/Gray did to a poor fellow who was involved in a radiation accident in Japan. It’s NSFW. It’s pretty grisly.)

But the point is that we’d all die when the neutrinos hit. I’m no religious scholar, but I think it’d be appropriate to call the scene Biblical. It’d be no less scary than the scary-ass shit that happens in in Revelation 16. (In the King James Bible, angels pour out vials of death that poison the water, the earth, and the Sun, and people either drop dead or start swearing and screaming.) In our supernova Armageddon, the air flares an eerie electric blue from Cherenkov radiation, like this…

685px-Advanced_Test_Reactor

(Source.)

…and a few seconds later, every creature with a central nervous system starts convulsing. Every human being on the planet starts explosively evacuating out both ends. If you had a Jupiter-sized bunker made of lead, you’d die just as fast as someone on the surface. In the realm of materials humans can actually make, there’s no such thing as neutrino shielding.

But let’s pretend we can ignore the neutrinos. We can’t. They contain 99% of a supernova’s energy output (which is why they can kill planets despite barely interacting with matter). But let’s pretend we can, because otherwise, the only spectators will be red, swollen, feverish, and vomiting, and frankly, I don’t need any new nightmares.

T + 499.000 seconds to 568.570 seconds (8m13s to 9m28.570s)

If we could ignore the neutrino radiation (we really, really can’t), this would be another quiet period. That’s kinda weird, considering how much energy was just released. A typical supernova releases somewhere in the neighborhood of 1 × 10^44 Joules, give or take an order of magnitude. The task of conveying just how much energy that is might be beyond my skills, so I’m just going to throw a bunch of metaphors at you in a panic.

According to the infamous equation E = m c^2, 10^44 Joules would mass 190 times as much as Earth. The energy alone would have half the mass of Jupiter. 10^44 Joules is (roughly) ten times as much energy as the Sun will radiate in its remaining 5 billion years. If you represented the yield of the Tsar Bomba, the largest nuclear device ever set off, by the diameter of a human hair, then the dinosaur-killing (probably) Chicxulub impact would stretch halfway across a football field, Earth’s gravitational binding energy (which is more or less the energy needed to blow up the planet) would reach a third of the way to the Sun, and the energy of a supernova would reach well past the Andromeda galaxy. 1 Joule is about as much energy as it takes to pick up an egg, a golf ball, a small apple, or a tennis ball (assuming “pick up” means “raise to 150 cm against Earth gravity.”) A supernova releases 10^44 of those Joules. If you gathered together 10^44 water molecules, they’d form a cube 90 kilometers on an edge. It would reach almost to the edge of space. (And it would very rapidly stop being a cube and start being an apocalyptic flood.)

Screw it. I think XKCD put it best: however big you think a supernova is, it’s bigger than that. Probably by a factor of at least a million.

And yet, ignoring neutrino radiation (we really can’t do that), we wouldn’t know anything about the supernova until nine and a half minutes after it happened. Most of that is because it takes light almost eight and a quarter minutes to travel from Sun to Earth. But ionized gas is also remarkably opaque to radiation, so when a star goes supernova, the shockwave that carries the non-neutrino part of its energy to the surface only travels at about 10,000 kilometers per second. That’s slow by astronomical standards, but not by human ones. To get an idea of how fast 10,000 kilometers per second is, let’s run a marathon.

At the same moment, the following things leave the start line: Usain Bolt at full sprint (10 m/s), me in my car (magically accelerating from 0 MPH to 100 MPH in zero seconds), a rifle bullet traveling at 1 kilometer per second (a .50-caliber BMG, if you want to be specific), the New Horizons probe traveling at 14 km/s (about as fast as it was going when it passed Pluto), and a supernova shockwave traveling at 10,000 km/s.

Naturally enough, the shockwave wins. It finishes the marathon (which is roughly 42.195 kilometers) in 4.220 milliseconds. In that time, New Horizons makes it 60 meters. The bullet has traveled just under 14 feet (422 cm). My car and I have traveled just over six inches (19 cm). Poor Usain Bolt probably isn’t feeling as speedy as he used to, since he’s only traveled an inch and a half (4.22 cm). That’s okay, though: he’d probably die of exhaustion if he ran a full marathon at maximum sprint. And besides, he’s about to be killed by a supernova anyway.

T + 569 seconds

If you’re at a safe distance from a supernova (which is the preferred location), the neutrinos won’t kill you. If you don’t have a neutrino detector (Ha ha!), when a supernova goes off, the first detectable sign is the shock breakout: when the shockwave reaches the star’s surface. Normally, it takes in the neighborhood of 20 hours before the shock reaches the surface of its parent star. That’s because supernovas (at least the core-collapse type we’re talking about) usually happen inside enormous, bloated supergiants. If you put a red supergiant where the Sun is, then Jupiter would be hovering just above its surface. They’re that big.

The Sun is much smaller, and so it only takes a couple minutes for the shock to reach the surface. And when it does, Hell breaks loose. There’s a horrific wave of radiation trapped behind the opaque shock. When it breaks out, it heats it to somewhere between 100,000 and 1,000,000 Kelvin. Let’s split the difference and say 500,000 Kelvin. A star’s luminosity is determined by two things: its temperature and its surface area. At the moment of shock breakout, the Sun has yet to actually start expanding, so its surface area remains the same. Its temperature, though, increases by a factor of almost 100. Brightness scales in proportion to the fourth power of temperature, so when the shock breaks out, the Sun is going to shine something like 56 million times brighter. Shock breakout looks something like this:

Sun Shock Breakout.png

But pretty soon, it looks like this:

Sun Supernova.blend

Unsurprisingly, this ends very badly for everybody on the day side. Pre-supernova, the Earth receives about 1,300 watts per square meter. Post-supernova, that jumps up to 767 million watts per square meter. To give you some perspective: that’s roughly 700 times more light than you’d be getting if you were currently being hit in the face by a one-megaton nuclear fireball. Once again: However big you think a supernova is, it’s bigger than that.

All the solids, liquids, and gases on the day side very rapidly start turning into plasma and shock waves. But things go no better for people on the night side. Let’s say the atmosphere scatters or absorbs 10% of light after passing through its 100 km depth. That means that, after passing through one atmosphere-depth, 90% of the light remains. Since the distance, across the Earth’s surface, to the point opposite the sun is about 200 atmosphere-depths, that gives us an easy equation for the light on the night side: [light on the day side] * (0.9)^200. (10% is approximate. After searching for over an hour, I couldn’t find out exactly how much light the air scatters, and although there are equations for it, I was getting a headache. Rayleigh scattering is the relevant phenomenon, if you’re looking for the equations to do the math yourself).

On the night side, even after all that atmospheric scattering, you’re still going to burn to death. You’ll burn to death even faster if the moon’s up that night, but even if it’s not, enough light will reach you through the atmosphere alone that you’ll burn either way. If you’re only getting light via Rayleigh scattering, you’re going to get something like 540,000 watts per square meter. That’s enough to set absolutely everything on fire. It’s enough to heat everything around you to blowtorch temperatures. According to this jolly document, that’s enough radiant flux to give you a second-degree burn in a tenth of a second.

T + 5 minutes to 20 minutes

We live in a pretty cool time, space-wise. We know what the surfaces of Pluto, Vesta, and Ceres look like. We’ve landed a probe on a comet. Those glorious lunatics at SpaceX just landed a booster that had already been launched, landed, and refurbished once. And we’ve caught supernovae in the act of erupting from their parent stars. Here’s a graph, for proof:

breakout_sim-ws_v6.png

(Source. Funnily enough, the data comes from the awesome Kepler planet-hunting telescope.)

The shock-breakout flash doesn’t last very long. That’s because radiant flux scales with the fourth power of temperature, so if something gets ten times hotter, it’s going to radiate ten thousand times as fast, which means, in a vacuum, it’s going to cool ten thousand times faster (without an energy source). So, that first bright pulse is probably going to last less than an hour. But during that hour, the Earth’s going to absorb somewhere in the neighborhood of 3×10^28 Joules of energy, which is enough to accelerate a mass of 4.959×10^20 kg. to escape velocity. In other words: that sixty-minute flash is going to blow off the atmosphere and peel off the first 300 meters of the Earth’s crust. Still better than a grisly death by neutrino poisoning.

T + 20 minutes to 4 hours

This is another period during which things get better for a little while. Except for the fact that pretty much everything on the Earth’s surface is either red-hot or is now part of Earth’s incandescent comet’s-tail atmosphere, which contains, the plants, the animals, most of the surface, and you and me. “Better” is relative.

It doesn’t take long for the shock-heated sun to cool down. The physics behind this is complicated, and I don’t entirely understand it, if I’m honest. But after it cools, we’re faced with a brand-new problem: the entire mass of the sun is now expanding at between 5,000 and 10,000 kilometers per second. And its temperature only cools to something like 6,000 Kelvin. So now, the sun is growing larger and larger and larger, and it’s not getting any cooler. We’re in deep dookie.

Assuming the exploding sun is expanding at 5,000 km/s, it only takes two and a quarter minutes to double in size. If it’s fallen back to its pre-supernova temperature (which, according to my research, is roughly accurate), that means it’s now four times brighter. Or, if you like, it’s as though Earth were twice as close. Earth is experiencing the same kind of irradiance that Mercury once saw. (Mercury is thoroughly vaporized by now.)

In 6 minutes, the Sun has expanded to four times its original size. It’s now 16 times brighter. Earth is receiving 21.8 kilowatts per square meter, which is enough to set wood on fire. Except that there’s no such thing as wood anymore, because all of it just evaporated in the shock-breakout flash.

At sixteen and a quarter minutes, the sun has grown so large that, even if you ignored the earlier disasters, the Earth’s surface is hot enough to melt aluminum.

The sun swells and swells in the sky. Creepy mushroom-shaped plumes of radioactive nickel plasma erupt from the surface. The Earth’s crust, already baked to blackened glass, glows red, then orange, then yellow. The scorched rocks melt and drip downslope like candle wax. And then, at four hours, the blast wave hits. If you thought things couldn’t get any worse, you haven’t been paying attention.

T + 4 hours

At four hours, the rapidly-expanding Sun hits the Earth. After so much expansion, its density has decreased by a factor of a thousand, or thereabouts. Its density corresponds to about the mass of a grain of sand spread over a cubic meter. By comparison, a cubic meter of sea-level air contains about one and a quarter kilograms.

But that whisper of hydrogen and heavy elements is traveling at 5,000 kilometers per second, and so the pressure it exerts on the Earth is shocking: 257,000 PSI, which is five times the pressure it takes to make a jet of abrasive-laden water cut through pretty much anything (there’s a YouTube channel for that). The Earth’s surface is blasted by winds at Mach 600 (and that’s relative to the speed of sound in hot, thin hydrogen; relative to the speed of sound in ordinary air, it’s Mach 14,700). One-meter boulders are accelerated as fast as a bullet in the barrel of a gun (according to the formulae, at least; what probably happens is that they shatter into tiny shrapnel like they’ve been hit by a gigantic sledgehammer). Whole hills are blown off the surface. The Earth turns into a splintering comet. The hydrogen atoms penetrate a full micron into the surface and heat the rock well past its boiling point. The kinetic energy of all that fast-moving gas delivers 10^30 watts per second, which is enough to sand-blast the Earth to nothing in about three minutes, give or take.

T + 4 hours to 13h51m

And the supernova has one last really mean trick up its sleeve. If a portion of the Earth survives the blast (I’m not optimistic), then suddenly, that fragment’s going to find itself surrounded on all sides by hot supernova plasma. That’s bad news. There’s worse news, though: that plasma is shockingly radioactive. It’s absolutely loaded with nickel-56, which is produced in huge quantities in supernovae (we’re talking up to 5% of the Sun’s mass, for core-collapse supernovae). Nickel-56 is unstable. It decays first to radioactive cobalt-56 and then to stable iron-56. The radioactivity alone is enough to keep the supernova glowing well over a million times as bright as the sun for six months, and over a thousand times as bright as the sun for over two years.

A radiation dose of 50 Gray will kill a human being. The mortality rate is 100% with top-grade medical care. The body just disintegrates. The bone marrow, which produces the cells we need to clot our blood and fight infections, turns to sterile red soup. 50 Gray is equivalent to the deposition of 50 joules of radiation energy per kilogram. That’s enough to raise the temperature of a kilo of flesh by 0.01 Kelvin, which you’d need an expensive thermometer to measure. Meanwhile, everything caught in the supernova fallout is absorbing enough radiation to heat it to its melting point, to its boiling point, and then to ionize it to plasma. A supernova remnant is insanely hostile to ordinary matter, and doubly so to biology. If the Earth hadn’t been vaporized by the blast-wave, it would be vaporized by the gamma rays.

And that’s the end of the line. There’s a reason astronomers were so shocked to discover planets orbiting pulsars: pulsars are born in supernovae, and how the hell can a planet survive one of those?

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art, silly

Morbid Curiosity: “The Garden of Earthly Delights” (probably NSFW)

This blog’s gettin’ fancy now! Because today, my curiosity isn’t focusing on fever-dream hypotheticals. Today, I’m expanding my curiosity into classic Medieval art!

Unfortunately, that art is Hieronymous Bosch’s The Garden of Earthly Delights, which is an even worse fever-dream. I should warn you, this post is probably not safe for work, for children, or for those who dislike nudity and (very mild) gore. It’s also not suitable for anyone who can’t pass a DC 25 sanity check. Just so you know.

Here’s the painting in its entirety. It’s a classic, probably painted sometime around 1500:

GOED Full

It’s pretty typical of the symbolic religious art of the time. It’s also stuffed full of fucking nightmare fuel. I know it’s kinda hard to see from that image above, but fret not! I found a high-resolution scan of the painting so that I could carve up the nightmare fuel into little morsels and present them to you, the dear reader, one-by-one.

I’m not exactly a talented art-appreciator. I’m the kinda guy who looks at a Jackson Pollock painting and thinks “Nope. Don’t get it. Looks like an accident. Maybe spaghetti.” So I haven’t divided the little fragments of The Garden by theme or symbolism. I’ve divided them into four broad categories: The Bestiary, for horrible creatures; Architecture, for horrible buildings; People Doing Weird Things, which explains itself; and Nightmare Fuel, for horrible things which defy categorization. Let’s get started! But before we do, let me show you what Jesus Christ thinks about this whole situation.

Christ is Worried.png

It’s okay, Jesus. I’m worried, too…

Continue reading

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Uncategorized

Ooh! An update!

Can you tell I’ve had too much coffee today? Either way, I just wanted to tell you guys why I’ve been so quiet lately: I’ve just started a proper full-time grown-up job. It’s weird. I don’t feel like I belong. I imagine this is what an actual hobo would feel like if he got booked into a permanent room at the Ritz-Carlton.

But don’t worry, I’m not abandoning this blog. Things just might be slow for a while.

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math, science

Life in Hyperbolic Space 1: Primer

It’s rare that weird, brain-bending ideas and video games meet, but in my experience, when they do, it’s pretty glorious. Portal, Prey, Antichamber, The Stanley Parable, and SUPERHOT are examples I’ve played personally. Also Miegakure (if it ever comes out, grumble grumble) will probably land instantly in that category, being a 4D puzzle game. But my most recent weird-game obsession has been HyperRogue. HyperRogue is awesome. Like Dwarf Fortress, it’s got a bit of a retro look with clean, minimalist graphics. And like Dwarf Fortress, it’s pretty obvious that a lot of love has gone into it. Here’s what the game looks like:

HyperRogue.png

Like many roguelikes (modeled after the ancient ASCII game Rogue), it’s played on a sort of chessboard. It looks at first glance like one of those board wargame or D&D-type hexagonal chessboards, but instead of being just hexagons, it’s got heptagons (7-sided polygons) too. You know what? That reminds me of the description of another geometric object:

Truncated Icosahedron

(Screenshot from the awesome polyhedron program polyHédronisme)

That is a truncated icosahedron, but I’d wager that most people know it better as either A) a soccer ball/football, or B) a molecule of C60: a fullerene, a buckyball.

Don’t worry. It’ll be clear in a moment what the hell I’m going on about. You see, HyperRogue takes place in the hyperbolic plane. A flat piece of paper is a Euclidean plane. The surface of a globe (or the Earth, or a buckyball) is a sphere. The hyperbolic plane is the third brother in the trio, so to speak, and it’s the weird brother. Their relationship makes more sense to me if I think in terms of polygons. Here’s another picture:

1000px-hexagonal_tiling-svg

(From the Wikimedia commons.)

The Euclidean plane (the hexagonal tiling above) consists of hexagons, each of which is bordered by six hexagons. The buckyball (football/soccer ball) farther above, representing spherical geometry, consists of pentagons, each of which is bordered by five hexagons. And at the very top of the page, the world of HyperRogue, representing the hyperbolic plane, consists of heptagons (7-sided polygons), each of which is bordered by seven hexagons. The hyperbolic plane is what would happen if you tried to sew up a soccer ball using heptagonal and hexagonal pieces of leather, rather than the usual pentagonal and hexagonal ones. Here’s what that looks like:

convoluted

(From the page of Frank Sotille, who has awesome templates so you can make your own hyperbolic football. I would’ve done it myself, but all of my Scotch tape has vanished.)

The only buckyball-type tiling that lays flat is the one with hexagons surrounded by hexagons. Pentagons surrounded by hexagons curves into a sphere, and heptagons surrounded by hexagons curls up into what HyperRogue’s creator calls a hypersian rug.

But here’s a more intuitive (though less precise) way to understand the hyperbolic plane. Consider the flat Euclidean plane. Pick a point. Draw a circle centered on that point. Measure the circumference of that circle. Draw another circle with the same center, but twice the radius. Measure the circumference of that circle. The farther you get from your starting point, the larger the circumference, but the increase is very predictable and linear. As a matter of fact, the circumference (the “amount of space”) you cover as you increase the radius of your circle increases exactly like this:

save (1)(1)

(Graphed with FooPlot.com)

Now do the same thing on a sphere: centered on the north pole, draw a very small circle with a given radius (with the radius measured across the curved surface of the sphere, not straight from point to point). Draw another circle with twice the radius. Up until you hit the equator, the circumference will increase, but eventually it maxes out and goes back down:

save (3)

(Circumference in the Euclidean plane in black, circumference on the sphere in red)

There’s another important effect to consider here: the sphere’s radius matters. That plot assumed a sphere of radius 1. Here’s what it would look like with a sphere of radius 2:

save (2)

It doesn’t make much sense to ask for the “scale” or “radius” of the Euclidean plane, because the answer is “infinity.” Any Euclidean plane is indistinguishable from any other, no matter how you swell or shrink it. Spheres, though, are distinguished by their radii: each has an inherent positive curvature.

Of course, on a sphere, the largest circle you can draw has a radius (measured across the surface of the sphere) of ½πR. the circumference of that circle lies right on the sphere’s equator. After that, the circumference decreases as the radius increases, because your circle’s shrinking as it approaches the opposite pole. It reaches zero when the radius is πR, and your radius-line stretches from one pole to the other.

The Euclidean plane has zero curvature. The sphere has positive curvature. The hyperbolic plane has negative curvature. The “radius” of a hyperbolic plane is defined as 1 / sqrt(-K), where K is a measurement called “Gaussian curvature.” (For comparison, the Gaussian curvature of a sphere is 1/(R²) ). K is the thing that’s zero for the plane, positive for the sphere, and negative for the hyperbolic plane. For a hyperbolic plane of K = -1, with a “radius” of 1, the circumference increases like this:

save (1)

(Hyperbolic circumference is the green line. The red line for a sphere with R = 1 (K=1) is included for comparison.)

That’s the weird thing about hyperbolic geometry: a sphere of infinite radius behaves exactly like the Euclidean plane (it is the Euclidean plane). But as the radius shrinks, the sphere contains less and less space (so to speak). To put it another way: if you were knitting a Euclidean plane (which people do, because mathematical knitting is a thing, which is awesome), then you’d need to knit in twice as much thread at radius 2 than you’d needed at radius 1. To knit a sphere, you’d need to knit less than twice as much thread in at twice the radius. And to knit a hyperbolic plane, you’d need to knit in more than twice as much yarn at twice the radius (according to the formula 2 * pi * R * sinh(r/R), where R = 1/sqrt(-K), and r is the radius measured through the plane; the equivalent relation for the sphere is 2 * pi * R * sin(r/R)). Where the Euclidean knit would give you a flat circular rug, and the spherical knit would give you a hacky-sack ball, the hyperbolic knit would give you something like this:

crochet_02

(Knitted by Daina Taimina, exhibited on the website of the Institute for Figuring.)

But the weird thing is that you can still do almost exactly the same geometry on the hyperbolic plane that you can do in the Euclidean plane. In fact, that’s why hyperbolic geometry is interesting: apart from a couple of weird quirks, it behaves just like a plane. That means you can make rigorous, valid, geometric proofs in the hyperbolic plane.

The Euclidean plane gets its name from Euclid of Alexandria, who is responsible for the infinite misery of people (like me) who just couldn’t get along with high-school geometry. But he condensed many centuries of Greek (and other) geometry into a set of postulates (axioms) from which you can prove pretty much anything that’s true in geometry. Here they are:

  1. You can draw a straight line between any two points.
  2. You can extend an existing straight line as far as you like.
  3. Using a compass, you can draw a circle with any center and any radius you want.
  4. All right angles are the same.
  5. If you’ve got two lines running alongside each other and another line running through both of those, and the angles on the insides of the intersections add up to less than a right angle, then the lines will intersect if you extend them far enough, and they’ll intersect on the side where the angle-sum is less than two right angles.

That last one, called the parallel postulate was a thorn in geometry’s side for a long time, because it seems a lot less elegant than the others, and it seems like the kind of thing you might be able to prove from the other axioms, which would mean it’s not an axiom, since axioms are your starting rules and theorems are what you prove using them. A less messy way to write the parallel postulate is:

5. Given any straight line, and given a point which doesn’t lie on that line, there is exactly one straight line through that point which never intersects the first line (the second line being the parallel).

Spherical geometry and hyperbolic geometry are both based on changing the parallel postulate. In spherical geometry, it becomes:

5. Given any straight line, and given a point which doesn’t lie on that line, there are zero straight lines through that point which never intersect the first line.

Or, to put it in simpler terms: because you’re on a sphere, lines that should be parallel (that is, lines which form a total of two right angles when intersected by a third line), inevitably intersect. Think of the north and south poles as two points. Draw the prime meridian from North to South. Now draw another line passing through the equator at 1° East longitude, 0 ° North latitude. At that point, the two lines are as parallel as lines get: they form ninety-degree intersections with the equator, and therefore, the interior angles on either side form exactly two right angles. But keep drawing those lines, and they’re going to intersect at the south pole, even though they should, according to Euclidean intuition, have stayed parallel.

In hyperbolic geometry, the parallel postulate is modified to the other extreme:

5. Given any straight line L, and given a point P which doesn’t lie on that line, there are an infinite number of straight lines through P which do not intersect L.

Poincare Parallels

That’s the Poincaré disk model, which fits the infinite hyperbolic plane into a finite circle. It’s elegant and simple, and it’s the model HyperRogue uses, so I’m going to stick with it. The red lines are the boundaries of the infinite set of lines which pass through P but never intersect L. It looks like the red lines intersect L at one end each, but the Poincaré disk model distorts distances more and more the closer you get to the edge. A picture’s worth a thousand words, so here’s a series of circles of equal radius starting from the center of the disk and moving outward:

CircleChain

(Both images rendered with the awesome (and free) geometry software GeoGebra)

I know they don’t look like circles of equal radius, but that’s just an artifact of the projection. The same way a Mercator map distorts Greenland so that it looks like it’s bigger than North America (when in reality it’s not much bigger than Quebec or Mexico), the Poincaré disk model distorts distances the closer you get to the edge of the circle. As a matter of fact, that bounding circle, as measured within the hyperbolic plane, is infinitely far from the center. You can’t ever reach it: it’s infinitely far from everywhere. So those intersections that seem to exist in the picture with the red and blue lines, they don’t actually exist, because you’d have to go infinitely far to get there. And keep in mind that, from any given point, it feels like you’re at the center of a Poincaré disk, so those lines don’t actually get closer to the line L the way the projection makes it seem. The projection is a necessary evil. You can do spherical geometry on an ordinary globe and remove all distortion, but you saw how messy and rumpled the hyperbolic version of a globe became: just look at the red crochet thing above. That’s not gonna happen. You have to live with the distortion.

The cool thing about the Poincaré disk model, though, is that it preserves angles, which makes it easy to do the kind of straightedge-and-compass geometry that’s so handy for geometric proofs.

And guess what? Just like we experience the world an almost-flat Euclidean space (relativity says it’s not perfectly flat, but it’s very close in our neighborhood, which I have to say to stop the nitpickers from yelling at me), there are three-dimensional spaces with spherical curvature, and there are three-dimensional spaces with hyperbolic curvature. In the next part, I’m going to talk about life in a highly-curved hyperbolic space. But before I go, let me leave you with a picture of something. In the Euclidean plane, you can only pack six equilateral triangles (all angles and edge-lengths the same) around a single point. The result looks like this:

1-uniform_n11.svg.png

(Source.)

In the hyperbolic plane, though, you can fit seven equilateral triangles around a vertex, and it looks like this (and don’t forget, those triangle are just as perfect and equilateral as the ones above; it just doesn’t look like it, because of the projection):

1024px-H2_tiling_237-4.png

(Source.)

You can actually fit eight triangles around a vertex too, although the triangles have to be larger (largeness being a slightly complicated concept in hyperbolic geometry, but we’ll get to that next time):

1024px-H2_tiling_238-4.png

(Source.)

And actually, it’s perfectly allowable to fit an infinite number of equilateral triangles around every vertex. That looks like this:

H2_tiling_23i-4.png

(Source.)

And remember, those triangles are still perfect and equilateral and regular. Hyperbolic space is weird. Remember that thing Christopher Lloyd said in Back to the Future? Get ready: we’re gonna see some serious shit.

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engineering, math, physics, thought experiment

The Treachery of Plumb-Lines

I’m pretty sure that’s my most pretentious article title to date, but really, the only pretentious thing about it is that it’s a Rene Magritte reference, because if you read it literally, that’s exactly what this article is about.

Imagine two skyscrapers. Both start from ordinary concrete foundations 100 meters by 100 meters, and each will be 1,000 meters high, when finished. We’ll call the first skyscraper Ruler, and the second skyscraper Plumb, for reasons I’ll explain.

Ruler is built exactly according to architectural specifications. Every corner is measured with a high-grade engineer’s square and built at precisely 90 degrees. Importantly, Ruler is constructed so that every floor is precisely 10 meters above the previous one, and every floor is 100 meters by 100 meters. This is done, of course, using a ruler. Because it’s kept so straight and square at every stage, Ruler is a very straight, square building.

Plumb, on the other hand, is kept straight and square using one of the oldest tricks in the architect’s book: the plumb-bob. True story: plumb-bobs are called that because, back in the day, they were almost always made of lead, and the Latin for lead is plumbus (or something like that; I took Latin in high school, but the teacher got deathly ill like two weeks in, so I never learned much). A well-made and well-applied plumb-bob is an excellent way to make sure something is absolutely vertical.

The builders of Plumb do use a ruler, but only to mark off the 10-meter intervals for the floors. They mark them off at the corners of the building, and they make sure the floors are perfectly horizontal using either a modified plumb-bob or a spirit level (which is largely the same instrument).

One might assume that Plumb and Ruler would turn out to be the exact same building. But anybody who’s read this blog knows that that’s the kind of sentence I use to set up a twist. Because Plumb was kept straight using plumb-bobs, and because plumb-bobs point towards the center of the Earth, and because the 100-meter difference between the east and west (or north and south walls) gives the bobs an angle difference of 0.009 degrees, Plumb is actually 11 millimeters wider at the top than at the bottom. Probably not enough to matter in architectural terms, but the difference is there.

Not only that, but Plumb’s floors aren’t flat, either, at least not geometrically flat. The Earth is a sphere, and because Plumb’s architects made its floors level with a spirit level or a plumb-bob, those floors aren’t geometrically flat: they follow the spherical gravitational equi-potential contours. Over a distance of 100 meters, the midpoint of a line across the Earth’s surface sits 0.2 millimeters above where it would were the line perfectly, geometrically straight. This difference decreases by the time you reach the 100th floor (the top floor) because the sphere in question is larger and therefore less strongly curved. But the difference only decreases by around a micron, which is going to get swamped out by even really small bumps in the concrete.

“Okay,” you might say, “so if you blindly trust a plumb-bob, your building will end up a centimeter out-of-true. What does that matter?” Well, first of all, if you came here looking for that kind of practicality, then this blog is just gonna drive you insane. Second, it doesn’t matter so much for ordinary buildings. But let’s say you’re building a 2,737-meter-long bridge (by total coincidence, the length of the Golden Gate Bridge). If you build with geometric flatness in mind, your middle pier is going to have to be 14.7 centimeters shorter than the ones at the ends. That’s almost the length of my foot, and I’ve got big feet. It’s not a big enough difference that you couldn’t, say, fill it in with concrete or something, but it’d certainly be enough that you’d have to adjust where your bolt-holes were drilled.

What’s the moral of this story? It’s an old moral that probably seems fairly ridiculous, but is nonetheless true: we live on the surface of a sphere. And, when it comes down to it, that’s just kinda fun to think about.

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biology, science, silly, thought experiment

Life at 1:1000 Scale, Part 1

You can’t see it, but out in the real world, I look like a Scottish pub brawler. I’ve got the reddish beard and the roundish Scots-Irish face and the broad shoulders and the heavy build I inherited from my Scotch and Irish ancestors (the hairy arms come from my Italian ancestors).

What I’m saying is that I’m a bulky guy. I stand 6 feet, 3 inches tall. That’s 190.5 centimeters, or 1,905 millimeters. Keep that figure in mind.

When I was a kid, the motif of someone getting shrunk down to minuscule size was popular. It was the focus of a couple of books I read. There was that one episode of The Magic Schoolbus which was pretty much just The Fantastic Voyage in cartoon form. There was the insufferable cartoon of my late childhood, George Shrinks.

As a kid, I was very easily bored. When I got bored waiting in line for the bathroom, for instance, I would imagine what it would actually be like to be incredibly tiny. I imagined myself nestled among a forest of weird looping trees: the fibers in the weird multicolored-but-still-gray synthetic carpet my school had. I imagined what it would be like to stand right beneath my own shoe, shrunk down so small I could see atoms. I realized that the shoe would look nothing like a shoe. It would just be this vast plain of differently-colored spheres (that was how I envisioned atoms back then, because that’s how they looked in our science books).

Now, once again, I find myself wanting to re-do a childhood thought experiment. What if I were shrunk down to 1/1000th of my actual size? I’d be 1.905 millimeters tall (1,905 microns): about the size of those really tiny black ants with the big antennae that find their way into absolutely everything. About the size of a peppercorn.

Speaking of peppercorns, let’s start this bizarre odyssey in the kitchen. I measured the height of my kitchen counter as exactly three feet. But because I’m a thousand times smaller, the counter is a thousand times higher. In other words: two-thirds the height of the intimidating Mount Thor:

mount_thor

(Source.)

I remember this counter as being a lot smoother than it actually is. I mean, it always had that fine-textured grainy pattern, but now, those textural bumps, too small to measure when I was full-sized, are proper divots and hillocks.

I don’t care how small I am, though: I intend to have my coffee. Anybody who knows me personally will not be surprised by this. It’s going to be a bit trickier now, since the cup is effectively a mile away from the sugar and the jar of coffee crystals, but you’d better believe I’m determined when it comes to coffee.

Though, to be honest, I am a little worried about my safety during that crossing. There’s a lot more wildlife on this counter than I remember. There’s a sparse scattering of ordinary bacteria, but I don’t mind them: they’re no bigger than ants even at this scale, so I don’t have to confront their waxy, translucent grossness. There is what appears to be a piece of waxy brown drainage pipe lying in my path, though. It’s a nasty-looking thing with creepy lizard-skin scales up and down it. I think it’s one of my hairs.

I’m more concerned about the platter-sized waxy slab lying on the counter next to the hair. There are two reasons for this: First, I’m pretty sure the slab is a flake of sloughed human skin. Second, and most important, that slab is being gnawed on by a chihahua-sized, foot-long monstrosity:

8f87b071ca15a175804fa780020feade

I know it’s just a dust mite, but let me tell you, when you see those mandibles up close, and those mandibles are suddenly large enough to snip off a toe, they suddenly get a lot more intimidating. This one seems friendly enough, though. I petted it. I think I’m gonna call it Liam.

My odyssey to the coffee cup continues. It’s a mile away, at my current scale, but I know from experience I can walk that far in 20 minutes. But the coffee cup is sitting on a dishcloth, drying after I last rinsed it out, and that dishcloth is the unexpected hurdle that shows up in all the good adventure books.

The rumpled plateau that confronts me is 10 meters high (32 feet, as tall as a small house or a tree), and its surface looks like this:

cover-12-3_1

(Source.)

Those creepy frayed cables are woven from what looks like translucent silicone tubing. Each cable is about as wide as an adult man. If I’d known I was going to be exposed to this kind of weird-textured information overload, I never would’ve shrunk myself down. But I need my coffee, and I will have my coffee, so I’m pressing forward.

But, you know, now that I’m standing right next to the coffee cup, I’m starting to think I might have been a little over-ambitious. Because my coffee cup is a gigantic ceramic monolith. It’s just about a hundred meters high (333 feet): as tall as a football field (either kind) is long–as big as a 19-story office building. I know insects my size can lift some ridiculous fraction of their body weight, but I think this might be a bit beyond me.

All’s not lost, though! After another twenty-minute trek, I arrive back at the sugar bowl and the jar of coffee. Bit of a snag, though. It seems some idiot let a grain of sugar fall onto the counter (that grain is now the size of a nightstand, and is actually kinda pretty: like a huge crystal of brownish rock salt), which has attracted a small horde of HORRIFYING MONSTERS:

pharoh-ant4-x532-new

(Source.)

That is a pharaoh ant. Or, as we here in the Dirty South call them, “Oh goddammit! Not again!” In my ordinary life, I knew these as the tiny ants that managed to slip into containers I thought tightly closed, and which were just about impossible to get rid of, because it seemed like a small colony could thrive on a micron-thin skid of ketchup I’d missed when last Windexing the counter.

Trouble is that, now, they’re as long as I am tall, and they’re about half my height at the shoulder. And they’ve got mandibles that could clip right through my wrist…

Okay, once again, I shouldn’t have panicked. Turns out they’re actually not that hostile. Plus, if you climb on one’s back and tug at its antennae for steering, you can ride it like a horrifying (and very prickly-against-the-buttock-region) pony!

I’m naming my new steed Cactus, because those little hairs on her back are, at this scale, icepick-sized thorns of death. I’m glad Cactus is just a worker, because if she was a male or a queen, I’m pretty sure she would have tried to mate with me, and frankly, I don’t like my chances of coming out of that intact and sane. Workers, though, are sterile, and Cactus seems a lot more interested in cleaning herself than mounting me, for which my gratitude is boundless.

I’ve ridden her to my coffee spoon, because I’m thinking I can make myself a nice bowl of coffee in the spoon’s bowl.

I’ve clearly miscalculated, and quite horribly, too: the bowl of this spoon is the size of an Olympic swimming pool: 50 meters (160 feet) from end to end. Plus, now that I’m seeing it from this close, I’m realizing that I haven’t been doing a very good job of cleaning off my coffee spoon between uses. It’s crusted with a patchy skin of gunk, and that gunk is absolutely infested with little poppy-seed-sized spheres and sausages and furry sausages, all of which are squirming and writing a little too much like maggots for my taste. I’m pretty sure they’re just bacteria, but I’m not going to knowingly go out and touch germs. Especially not when they’re just about the right size to hitch a ride on my clothes and covertly crawl into an orifice when I’m sleeping.

You know what? If I can’t have my coffee, I think this whole adventure was probably a mistake. I think I’m going to return to my ordinary body. Conveniently (in more ways than one), I’ve left my real body comatose and staring mindlessly at the cabinets above the counter. He’s a big beast: a mile high, from my perspective. An actual man-mountain. I’ll spare you the details of climbing him, because he wears shorts and I spent far too long climbing through tree-trunk-sized leg hairs with creepy-crawly skin microflora dangerously close to my face.

Now, though, I’m back in my brain and back at my normal size. And now that my weird little dissociative fugue is over, I can tell you guys to look out for part two, when I’ll tell you all the reasons there’s no way to actually shrink yourself down like that and live to tell about it.

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update

Stair Power!

Let’s say I, a human male massing 132 kg and carrying a 9-kilogram box of dusty old knick-knacks and other junk, ascend a 10-meter-high flight of stairs in 15 seconds. During that time, I’m expending 922 Watts, which is over nine times a human’s resting metabolism, and about one and a quarter horsepower.

This isn’t the start of a thought experiment. This is just my silly way of letting you guys know why I’ve been silent lately: helping people move is kind of a pain. Good exercise, though, if they, say, live on the third floor.

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