Misc: December 2007 Archives


December 30, 2007

The elevator in the International Terminal at SFO only goes to two floors. Internally, it has two buttons, for the top floor and the bottom floor. But of course, when you get in it's either at the top floor or at the bottom and the only place it could go is the other floor. So, at most, you only need one button: next floor. I guess this would need a different internal design for the elevator software/firmware/wiring, but the programmer in me does find the current arrangement a bit inelegant.

December 25, 2007

Mrs. Guesswork and I are in White Rock, BC visiting her parents for the holidays. White Rock is only a few miles from the US, and I needed to go for a run, so I figured two great tastes that taste great together and header and headed for the border. Anyway, I usually fly into Canada (passport required) but my understanding was that you just needed ID to travel between the US and Canada, so I shoved my driver's license in my pocket and headed out.

I ran out to the 175th street border crossing and after a little screwing around figured out which building to go into. I showed the DHS guy my license and he asked me where my passport was (in my room) and said that due to the WHTI I would soon need a passport to enter the US. He asked me a bunch of questions about where I was born, etc. and then said that while he would let me into the US, without proof of citizenship the Canadians might not let me back in. I asked if he thought that was likely and he sort of waffled, but finally said that they might make me sit around until someone brought me a passport but that it probably wouldn't be a problem, especially if I had recently used my passport to enter Canada so they had records (I flew in on Monday).

I entered the US and ran to the Peace Arch border crossing. I went into the office there and showed my license and explained that I didn't have a passport. The woman asked me a bunch of questions (where I was staying, who I was with, etc.), then called over another agent who asked me some more questions, and then filled out some form, gave it to me, admonished me to carry proper ID, and send me over to another window where the agent asked me some more questions and said I could go on through.

A few notes about this:

  • It's not clear to me that you're actually required to show proof of citizenship just yet. The WHTI proof of citizenship requirements don't come into effect till January 31, 2008, so it seems like a driver's license should be enough for now.
  • A few minutes looking around and it's not as easy as you'd think to find a concrete statement of what the current identification requirements are. For Canadian citizens entering the US, it appears you need to present ID but that there's no actual requirement that you show proof of citizenship. The officer can accept an oral declaration of citizenship. According to the US customs officer, Canadian policy tends to track the US.
  • The American CBP officer did some sort of computer lookup. The Canadians didn't, so they clearly didn't check that I had actually ever presented a passport.
  • Regardless of the policy, letting me through seems to me the right plan—though of course I would say that—it's not like it's that hard to forge the relevant documents, so who would bother to come up with a story like mine and memorize all the details?
  • In neither case did people really try to physically stop me. In both cases, I went into and came out of the same door, so there was no real mechanism to make sure that I actually talked to anyone. In the CA->US direction, the CBP officer just gave me a piece of paper with a note on it to show to some other officer. Pretty hard to believe I couldn't have forged that. In the other direction there wasn't even that. And of course there aren't fences across the entire border.

Next time I'll bring my passport, though.


December 20, 2007

Proaxiom writes:
I've been trying for some time to find a globe oriented with Antarctica at the top. I could do this with a regular globe, but the writing would be upside-down.

I presume demand isn't great enough for anyone to manufacture such a globe. You can find maps with south-at-top orientation, mostly from Australia, but no globes.

I want to have such a globe to put it in my office. For me it serves as a reminder that many things we naturally think of as immutable are in fact completely arbitrary.

Here's Iain Banks:

"Sma, believe me; it has not all been 'fun.'" He leaned against a cabinet full of ancient projectile weapons. "And worse than that," he insisted, is when you turn the godamn maps upside down."

"What?" Sma said, puzzled.

"Turning the maps upside down," he repeated. "Have you any idea how annoying and inconvenient it is when you get to a place and find they map the place the other way up compared to the maps you've got? Because of something stupid like some people think a magnetic needle is pointing up to heaven, when other people think it's heavier and pointing down? Or because it's done according to the galactic plane or something? I mean, this might sound trivial, but it's very upsetting."

Incidentally, a lot of GPS-based navigation systems seem to be configured by default to orient the map in the direction you're travelling. I suppose you could get used to this, but really I'd rather have it oriented North up.


December 18, 2007

The other day I was listening to one of Thomas Laqueur's History 5 lectures and he mentioned that many older maps were centered on Jerusalem [*]. Laqueur observes that the center of a map is arbitrary and that there's nothing wrong with using Jerusalem as the center. Well, sort of. It's true that the Earth is roughly a sphere, but remember that it spins on an axis going between the North and South poles which gives it a natural asymmetry. So, while the longitude of the center of a map is certainly arbitrary and there's nothing particularly special about Greenwich1, the Equator is special and it would be sort of weird to center the map vertically anywhere else—and at about 31 degrees North, Jerusalem is way off the Equator.

Note that this isn't purely a matter of latitude not having been discovered yet. The Greeks knew that the Earth was a sphere and already had the idea of latitude and longitude. Techniques for measuring latitude (and impractical techniques for measuring longitude) were known in Medieval Europe as well at the time such maps were produced. The choice of the center of the map was an issue of religious commitments, not simple ignorance.

1. See Einstein's Clocks, Poincare's Maps: Empires of Time for a lucid description of the political maneuvering around the selection of GMT as the zero reference for time.


December 8, 2007

The TV in the apartment I was staying at in Vancouver featured some unusual extra channels:
  • Surveillance cameras covering the parking garage and the street in front of the apartment.
  • An apparently permanent head-on shot of a wood-burning fireplace.
  • A (live) screenshot of an Agilent spectrum analyzer attached to something or other.

The first two are a little weird—though I imagine a video fireplace might be of some value to someone—but I have to admit I don't have a good explanation for the spectrum analyzer thing.


December 4, 2007

Yesterday Dan Harkins cornered me in the hall and asked me the following question:
Given a random 128-bit integer d and another random x-bit integer n where x >> 128, what is the probability that n is an even multiple of d.

My immediate answer was 2-128. My second was to retract this and suggest that Dan ask a mathematician. My third was to try to work the problem. My reasoning below.

  • The probability that a random number is divisible by 1 is 1, divisible by 2 is 1/2, divisible by 3 is 1/3, etc.
  • If we assume that d is randomly distributed over 1..2128-1, then each of these probabilities is equiprobably, so we can compute:
  • This series (1 + 1/2 + 1/3, ...), the harmonic series.
  • The Harmonic series diverges, but very slowly. As the Wikipedia page says, the first 1043 terms sum to less than 100.
  • Since we're interested in the mean probability, we divide the sum by the number of terms, d, and since 1043 isn't that far off 2128, this means that we're looking at something like 2-120.

Unless I've screwed something up (always possible), I guess my intuition isn't completely broken.

UPDATE: 2/3 -> 1/3. Thanks to Dan for the fix.