All posts by Chris

Short Story: Like An Arrow

Sometimes I get the urge to write a short story. Usually the feeling passes, but this one stuck with me and kept nagging until I let it out. More story notes at the bottom.

A shaggy dog barred my path through the door. He was my sister’s dog, a long-suffering poodle lounging in the Louisiana heat. “I can’t believe you make him put up with this humidity,” I said as I stepped over him and into the tiny office.

My sister grunted but didn’t look up from her pile of papers. “He doesn’t mind. You’re projecting.” It was true; I didn’t like the heat any more than George seemed to. Boulder was much more my style, but Lalita preferred to live in places that felt like saunas to me. Mumbai, Austin, and now Baton Rouge.

It was like she picked the stickiest, dingiest places just to keep me away. I know, projecting again. At least I visited her wherever her research funding happened to take her; she hadn’t been to see me in Boulder once in the decade I’d lived there.

“You could at least put a fan in here or something.” I looked around at the office, packed full of textbooks, reference books, papers, ebook readers, tablets, and more than one empty soda can. “Or do something about the flies. It’s—”

“—a pit, I know,” she said and swiveled around on her chair, finally looking me in the eye. “It’s a steaming mess of shocking proportions, and my clothes aren’t any better, and I’m wasting my life without a good solid job.” She tossed her hair back defiantly and stared directly at me. “Should I conference Mother in too, or have we covered it all ourselves?”

I held out my hands, warding off the tongue-lashing. “OK, OK. Truce.”

My sister relaxed and looked at the floor again. “You’ve only been here a day. Our half-life is usually at least three.”

“Half-life?”

She got a mischievous look in her eye, the way she used to look when we shared a secret as girls. “It usually takes three days before half our conversations are about each other’s failings.” She grabbed an end of chalk and drew a swooping line graph on the board nearest us, starting high and dropping off quickly. The scrawled legend read “substance”, and a dot marked a point half-way down. “We’re only a day in, though, so…” she trailed off while figuring out the current value. “…we should still be saying meaningful things about 85% of the time.”

I barely suppressed a smile. “Then let’s. Are you ready for lunch?” I didn’t mention how anxious I was to get away from the buzz of insects and into the air-conditioned restaurant.

“Ready,” she said, and grabbed a tablet from the desk. We stepped over the still-sleeping George, and Lalita reached down to give him a quick pat. “Watch over my work. Good dog.”

The restaurant was a blessed relief for me, but Lalita looked uncomfortable as soon as we sat down. “We could have eaten on campus,” she said and scowled at the menu.

“Don’t worry. I’ll cover it.” As soon as I said it, I knew it was the wrong thing to say. She frowned at me and closed the menu. “What? You know why I’m here. There’s no use pretending this is a sisterly visit.”

“OK, then. Let’s be plain,” she said. She picked up the tablet and turned it so I could see. “I’ve been thinking about what you said yesterday, and there’s something I want to show you.”

“About the teleportation project?” Again, I knew it was the wrong thing to say. I’d been saying the wrong things to her for decades, so why should it stop now? “What?”

“Stop calling it that,” she said. “When you call it teleportation people start thinking of transporters and time machines, and that’s what I’m trying to warn you about.”

I couldn’t help it. “Time machines?” I practically barked it, then realized where we were. I leaned in closer and whispered conspiratorially. “Who calls it a time machine?”

“NOT time machines!” she yelled. I reeled back and almost knocked over my water.

“All right, not time machines. Forget I said it. Show me what you were going to show me.” I leaned in again and focused on the tablet.

The graphic on the tablet was a sophisticated version of the ones I’d seen on Lalita’s chalkboards many times before. Lines split, joined, and crossed each other in intricate patterns. It looked like something out of a how-to book of sailor’s knots than anything I knew of physics, but I knew better than to make the analogy.

“What is it?” I asked.

“It’s a simulation of the kind of particle interactions we’ve been working with in the lab.” She started poking at the visualization, and dots raced from one side to the other, following the intertwined paths. Now it looked more like a hospital chart, except those usually didn’t backtrack and spin around each other.

“Back up,” I said. “What am I looking at here?”

“This is the simplified world lines of the particles as they interact. This axis is time–”

“No it isn’t. If it was, those particles shouldn’t be going the wrong way.” I pointed to places where some of the bright dots turned around and moved backwards relative to others.

She looked flustered. “Not if you give each particle it’s own arrow of time. You know that from relativity; there’s no preferred direction for them to point.”

Now it was my turn to frown. “Yes, I know what a space-time vector is. I also know that no matter which vector you choose, none of the others will point the other way entirely.”

“They do if you follow the quantum signatures in a continuous path instead of treating them as annihilations. That’s what we’ve been doing in the lab; verifying that certain antiparticles really are their counterparts traveling backwards in time.”

This was news to me, but not what I came here for. “If this is what you mean by not a time machine, please do tell me about your not-a-teleporter.”

She groaned and threw the tablet down on the table with a clatter. “You don’t listen!”

Luckily, our food was served at that moment. We sat in stony silence, and I noticed a speck of something move around in my water glass. A fly, apparently doing its impression of a crazed particle’s world-line. I asked for another glass of water.

“Look,” she said, “I know you can understand this. You’re an engineer, for God’s sake. Just listen.” She picked up the tablet again and started the dots on their travels. “By tracing the signatures, we showed that quantum teleportation–” –a warning look– “–listen! Quantum teleportation does truly impose the state of a particle, its identity you could call it, on a distant particle. More importantly, though, we showed *how*. Look at the green one here, and watch it teleport.”

She held her finger over one of the racing dots, and suddenly I saw what she meant. It traveled up and down along its path, but then turned around in a shower of sparks to zip back along a trail that I had assumed was another particle. That flew off—in the wrong direction, the negative-time direction—until it joined another group of swirling particles and made its way forward again. Finally it got back to its “original” time and met up with the sparks it had given up.

“It didn’t teleport at all, did it?” I couldn’t hide the disappointment in my voice. “It traveled back in time to make its way to where the duplicate was.”

Lalita beamed. “She can be taught! That’s exactly right. The laser doesn’t create a duplicate of the particle, it forces it to zigzag in time until it ends up in the right place.”

My head was swimming, and it was hard to make the leaps she expected of me. “OK, I get this part. Isn’t the end result the same?”

She scowled again. “Do you still get to send your spy-beams, you mean?”

“They aren’t spy beams.”

Her eyebrows shot up. “Oh really? You want to point a beam and send a camera to spy on someone.” She mimed the process with her hands, and I had to laugh.

“OK, OK. If they’re spy beams, why can’t it be a teleporter?”

Lalita looked serious again. “In a word: histories.”

“Histories.”

“Yes, histories.”

I waited for her to go on, but she must have been waiting for me to catch up. I stared at my water glass and noticed another fly had fallen in it, before I’d even taken a sip. I knew how it felt.

I finally gave up. “Which means?”

She leaned forward with the mischevious look again. “See? Physics is good for something. Each particle doesn’t have just one path it takes through space-time. Quantum physics shows us it takes all the paths it can, and the combined histories of all those paths are what we perceive.”

She paused again, but I still wasn’t getting it. “And?”

“And all those histories are important. They interact in ways that are more complex than a single world-line would. If you cause the particle’s path to be too restricted, too deterministic, a lot of the physics we rely on stops working.”

“Such as?”

“If we try to pin down the exact moment an atom changes state, it stops having the chance to do so. Its histories get so pinched that it can’t do its job.”

It finally dawned on me. “The teleported particle. It’s pinched?”

“Exactly.”

“What’s wrong with it?”

“Nothing much, if you’re working with one particle. The more complex you get, the more histories you’re pinching and the harder it is to hold everything together.”

I sagged in my seat. “So it’s impossible?”

“Well,” she said. “Nothing’s impossible. But we’re not going to be beaming any spies for you anytime soon.”

That night we managed to get through dinner without talking about spy beams or time machines. Lalita was much more comfortable in her own kitchen than the hotel restaurant, though I probably cooked there more than she did. She asked me about my work, and I told her as much as I could, minus the classified details. We talked about the lack of funding for pure physics research, and I gently offered for the thousandth time to get her an applied research position at my company. She gently ignored the offer for the thousandth time.

It was over the second bottle of wine that she dropped the bomb. I’ll always remember the scene exactly: the two of us sitting around her tiny kitchen table, her leaning down to feed George the remains of our meal with one hand while cradling a wine glass with the other. Me stacking dishes off to one side because I was avoiding any work in the humid evening. A moth hovering near the lamp above the table, bouncing annoyingly between the lampshade and the bulb cover without settling down.

“I worry about time travel.” She said it matter-of-factly, like she was talking about our mother’s new boyfriend or the rent.

“Do you, now?” I wasn’t sure how seriously to take her.

“I do. The results we’re getting in the lab are very troubling. I wish we had enough theory to know whether they’re as bad as I think or if they’re self-correcting.”

“Troubling? In what way?” I’m not sure why, but I’ve always felt a special dread when my sister’s work troubles her. The problems physicists worry about tend to be either trivial or world-ending, and it’s hard to tell which are which.

“Remember those pinched histories? They can be… bad.” Her voice trailed off.

“Bad? How bad?”

“Just as bad as I showed you. When we tried to affect quantum state over distances, it reached back into the past to make that possible and pinched all the histories involved. I wanted to see if we could use that effect to change quantum states in the past.” She frowned.

“And? Could you?”

“Yes, but…” She took a minute to scratch George behind the ears. “The pinching effect was a lot worse. The remaining histories deviated so far from the norm that we had trouble recording what actually happened. It was like every roll of the quantum dice came up sixes. Some of the most fundamental processes in the universe just… stopped.”

She drained her glass of wine and poured another. I noticed her hands shake a little.

“Is this why you don’t like time machines?” It was the wrong thing to say again, but this time she just deflated. For the first time, I felt bad about riling my sister. “I’m sorry. I’m just trying to understand.”

She gulped another glass and grabbed a tablet. “Do you ever wonder about aliens?” She poked violently at the tablet’s screen.

“What? Aliens?”

“Aliens. Specifically, where are they?” She showed me the tablet’s screen, now covered with a map of the sky, filled with stars and their myriad names. “A third of these stars have planets like Earth. Some of them have life like ours, and some of that life might evolve into beings capable of space travel or interstellar communication.” She paused, staring at the map.

“And?”

“And so where are they? According to the best odds we know, there should be civilizations spanning the entire galaxy, including here. Where is everyone?”

I still didn’t see where this was going. “If the theory doesn’t fit the data, don’t blame the data.”

“Oh, I don’t.” She had fire in her eyes now. “The best guess is that civilizations all reach some world-ending event before they get off their own planet.”

“Right, like nuclear weapons.”

“Yes, but we dodged that bullet. Someone else must have as well, but they’re still missing in action. So what’s coming for us? What’s going to snuff us out before we get anywhere?”

“Who says anything will?”

She looked at me as though I was being willfully ignorant. “What about time travel?”

My head was spinning, and it wasn’t the wine. I was starting to think that my sister was putting me on. “Time travel? You think we’ll be killed off by pinched histories?”

“It could happen.”

“Really?”

“Well…” She looked doubtful for a second. “I’m not sure. The strange thing about time is that no matter how you change it, it always turns out to have been that way.”

I groaned. “You’ve stopped making sense. I should go.” I stood up, a little uncertainly.

“No, wait. What I mean is that if pinched histories were going to end us, they would have already done so in the past. Our past. We wouldn’t be here–”

“–having this completely ludicrous conversation.” I said. “Good night.” I patted George and left before the conversation could get worse.

The next day I awoke with a start, sitting bolt upright in the hotel bed, a little disoriented about where I was. Something in my dream had been very important, but it drifted away before I could remember.

Over breakfast in the hotel restaurant, it came back to me all at once. I watched a fly wind its way around the lazily-spinning ceiling fan, and it all became clear. I dashed out of the hotel and nearly ran to the university before realizing that it was miles away and I’d die from heat exhaustion after a few blocks.

The taxi couldn’t get me there fast enough. The whole way I worried that my epiphany was a hangover-induced delusion, something my sister would tear to shreds with a single comment. Still, I had to tell her. It might be right.

George was draped across the doorway to her office again, and Lalita looked at me sleepily over her breakfast pastry. “Mff?” she said, and her eyes opened wide as I leaped over the shaggy dog.

I was out of breath, but I had to tell her. “You don’t have to worry. The pinched histories won’t get us, and time travel will turn out just fine.” I stood up straighter as I regained my breath. “Those other civilizations didn’t survive discovering time travel, but that doesn’t mean no one will. We will. We did.”

She swallowed her bite of pastry and a swig of tea. “How can you know that?”

“Look, you said it yourself. History is the way it will be, and anything we do to change it will already have been done. You’ll figure out the upper limit to what we can teleport safely to the past, and we’ll find a good use for it.” I was practically dancing. “In fact, I want you to come work with me on a new kind of spy beam anyone will appreciate. We’ll rewrite history in a good way, by learning all its secrets.”

Lalita just stood there, open mouthed. “What on Earth are you talking about?”

I pointed up at the ceiling, and Lalita’s eyes opened wider as she looked at the hundreds and hundreds of insects milling around up there. I beamed at her and declared triumphantly, “Time flies!”

Author’s Note

Yeah, sorry about that. The puns are bad and physics is awful, but at least the story and characterization are terrible.

This story came out of three ideas that nagged me incessantly:

  • The “time flies” concept came first. Wouldn’t it be great to be a fly on the wall at the signing of the Declaration of Independence? We always say that, but who’s actually doing something about it? Surely we could come up with a way to send a tiny fly-cam back in time and bring it back, all without interrupting the “original” history. Who notices another fly?
  • The idea that time travel destroys advanced civilizations was inspired by a discussion on Twitter about Fermi’s Paradox, mixed with recent research on the nature of cause and effect in increasingly-weird quantum interactions. [citation needed]
  • Oh yes, the puns. Some of my favorite Asimov short stories are either shaggy-dog stories (like Shah Guido G.) or discussions between two people about some kind of world-changing idea (like Darwinian Pool Room). Poor George is a nod to the former, and the two sisters provide the latter while also satisfying the Bechdel Test.

Experiment Sunday update: Electric Circuits

[Note: Each week my geeklet and I have "experiment sunday", a brief and casual exploration of hands-on science and engineering.]

This week’s experiment was a great success. That isn’t to say that it went off without a hitch; the hitches made for more valuable learning than the experiment itself. We set out to make a simple electric circuit, but what we ended up doing was troubleshooting and learning about unstated constraints.

The experiment was a series of steps from The Science Book Of Electricity (Gulliver Books, 1991). The book has a few simple experiments like this one, described in general terms with lots of photos. There’s no theory and not much in the way of details, but the descriptions were enticing enough to catch my eight-year-old geeklet’s interest without any pushing from Dad.

The first step was to make a simple circuit using a light-bulb holder, bulb, two lengths of wire, and a battery. Trivial stuff, we lacked some of the necessary materials. The hardware store had everything we needed, but our parts were lost among all the variations of bulbs and wiring available. (Lesson: a simple parts list contains a lot of assumptions.) We eventually picked out a basic bulb holder, a set of 4W night light bulbs, and three feet of coated copper wire.

On returning home, we set to wiring up the circuit. Stripping the wire was easy with a pair of scissors, but the wire itself was so thick as to be unwieldy. (Lesson: there’s wire, and there’s wire.) With some work, we were able to screw two lengths of wire onto the bulb holder. The geeklet taped one wire end to the negative end of a battery, and I touched the other wire to the positive end. Let there be light? Well, no. (Lesson: it probably won’t work the first time.)

Now came the fun part: troubleshooting! How did our setup differ from the book’s description? The geeklet noticed a caveat in the book: “The battery must be the same voltage as the bulb.” What did that mean, though? The battery’s voltage was printed helpfully on the side: 1.5V. The bulbs, though, were listed as 4W. (Lesson: units are important.) I talked a little bit about the difference between current and voltage, and we looked more closely at the package of bulbs. No hint of voltage listed anywhere. Hmm. A quick check with Mama (who recently had to buy bulbs for one of her projects) yielded the clue we needed: a bulb’s voltage is often listed on its base.

120V. A bit of a difference, then. What to do? Improvise! (Lesson: improvise!)

We scrounged through the tool box to see if there were any other bulbs. We found a krypton bulb for a flashlight, which was listed (now that we knew what to look for) as 3.6V. Closer, but how to make up the difference between a 1.5V battery and a 3.6V light? This gave me a chance to talk about serial vs. parallel circuits, and how batteries in series will add their voltage together. 3 batteries at 1.5V made 4.5V, which should be close enough to make the bulb light up.

The geeklet found and taped together three D cells, which made an impressive battery of batteries. We dropped the krypton bulb into the bulb holder—a loose fit, but it closed the circuit if placed carefully—and wired up the rest again. Let there be light? Yes! (Lesson: persistence pays off.)

The next step was to wire in a pair of thumbtacks, spaced slightly apart on a bit of cardboard. These allowed us to bridge the gap with pins, coins, cloth, buttons, and other things that may or may not carry electric current. A tester! (Lesson: even our improvised monster circuit met the requirements of the experiment.) Once that principle was shown, we used one of the handy current-carriers (a paperclip) to fashion a contact switch. The geeklet showed off the completed circuit and switch to Mama, and we talked about applications like telegraphs and signal lights.

Writing this up, I just now realize that we re-invented the flashlight using (essentially) flashlight parts. Oh well, the process was the important thing.

a note about passwords

Passwords bug me. Specifically, password management on most websites is maddening. Here are a few things to keep in mind when designing yours:

List your password-format rules up front. All too often, sites ask for a password with no indication of their format rules, then scream “ERROR!” when you don’t guess correctly. Yell at your users less by telling them what you want first.

Don’t limit the size of a password unless you absolutely have to. Honestly, it’s 2012. Databases can store unlimited-length strings, and the security of a password is improved by length. If your user wants to use the Gettysburg Address as a password, let them go for it.

Ditto for the content. If the user wants ancient Greek poetry for their password, then don’t freak out about the character set or complain that it doesn’t contain any numbers. Honestly, I once had a health-care provider prevent me from using spaces and punctuation in a password. “Alphanumeric characters only”. Way to be secure, guys.

Don’t limit the password format at all unless a compromised account will damage your service as a whole. No minimum length, no “special characters” requirement, no “at least one number”. I know, this is a tough one to swallow. Take an honest look at the worst a malicious user could do; if the only harmful effects are to the user choosing the password, then let them choose whatever they want.

Rate the strength of a password as the user types, and give hints on how to improve it. If you do this, though, get it right. It’s annoying to type in “correct horse battery staple” and have some out-of-date algorithm tell me it’s “Weak“. It’s worse if the system rejects it outright, but even the knowledge that your algorithm sucks makes me doubt the overall security of your system.

Check that your login fields are friendly to automatic login. I’m more likely to choose a unique password for a site when I can hand off the job of remembering it to my browser or keychain. Each time I have to click “forgot password”, though, my choice is going to be easier to remember (and probably less secure).

watching space stations dance

If you’re in Southern California on January 5th, you might get a chance to see two space stations in the sky at the same time. (Pretty cool, right?)

If it’s clear enough, and if I’ve read the magnitudes and times and directions correctly on Heavens Above, here’s what I’ll be doing that night:

  1. At 5:00pm I’ll go outside and stand in a nice dark spot. (I live in the middle of San Diego, so that takes a few minutes to find.)
  2. At 5:05 I’ll look to the northwest for a bright object moving toward the northeast. If it’s moving slowly and not blinking, it’s the International Space Station. Population: 6. I’ll wave to Daniel, Anton, Anatoli, Oleg, Donald, and André.
  3. At 5:07, when the ISS is as far up as it’ll get in the northeastern sky, I’ll look to the southwest for a dimmer object moving toward the northeast. If it’s moving slowly and not blinking, it’s Tiangong 1, the first part of China’s space station. Population: 0 so far.
  4. Until about 5:10, when Tiangong 1 is right overhead and ISS drops below the eastern horizon, I’ll watch the two of them share the sky.

Thanks to Allan Manangan for passing along the news from David Dickinson on Twitter.

The Mpemba Effect: A Good Case For Citizen Science?

I just read an intriguing article on the Mpemba effect at Skulls in the Stars. Between the history of the effect and the continuing puzzle of what causes it, this is the best example of science-as-a-process I’ve ever seen:

Mpemba made his accidental discovery in Tanzania in 1963, when he was only 13 years old and in secondary school. In spite of widespread disdain from his classmates, he surreptitiously continued experiments on the phenomenon until he had the good fortune in high school to interact with Professor Denis Osborne of the University College Dar es Salaam. Osborne was intrigued, carried out his own experiments, and in 1969 the two published a paper in the journal Physics Education.

So what did Osborne’s research show? He placed a 100 cm³ beaker filled with 70 cm³ of water on a sheet of insulating foam in a freezer, and timed how long it took for the water to freeze. For temperatures up to 20 °C, the time was roughly proportional to the temperature above freezing, up to a maximum of 100 minutes at 20 °C. For higher temperatures, however, the time dropped dramatically, down to 40 minutes for 80 °C water!

Be sure to read the complete article for the whole story, including many attempts to characterize the Mpemba effect over the years. 50 years later there still isn’t a strong consensus about what causes the effect, and in many cases it’s supposed to be difficult to reproduce.

To me, this is crying out for a citizen-science experiment with lots of participants, similar to the way Biocurious works. The experiments themselves are dirt simple (and cheap) to implement; all they really require is water, a heater, and a freezer. The rest is a matter of documenting all the (potentially) relevant variables, including the heater and freezer used, the source of the water, the type of containers, and even the geocoordinates of the experimenter. (Hey, who knows, right?)

A second generation of citizen-science experiments could then be designed based on trends in the first-generation data. The fun thing about this step is that (as Galaxy Zoo has shown) the data often suggests results that weren’t expected before it was being collected. (That shouldn’t be surprising; this is science after all.)

The point of each subsequent generation would be to build more accurate predictions of which experimental setups would or would not produce the Mpemba effect. Eventually it should be possible to make a set of statements like, “Heating 50 ml of 20 °C tap water in a 100W microwave for 90 seconds is 90% likely to reduce the time required to freeze it in a 1 m³ freezer by 35%.”

Why the citizen-science approach? I suspect that rather than trying to control all the known factors to produce the desired result, we instead want to track as many factors as possible to characterize the space of results. This particular effect will probably require a “vast multidimensional array of experiments“* to characterize properly, so enlisting a large number of citizen scientists makes a lot of sense.

Besides, each and every one of the test participants can have fun guessing at the real causes involved. Who doesn’t love a little armchair theorizing?

* Yes, I’m ‘citing’ Wikipedia. The original article cited there is inaccessible, and the rest of the Wikipedia summary is informative stuff.