[harshpotatoes]

I don't like his method of measuring the curvature distance.

I think it will be very difficult to align a local to the local tangent of the earth's surface. Over a distance of 700m, the earth's surface deviates by about 4cm. This means we would have to align our laser to within 50 microradians in order to accurately measure the deviation of the earth's surface.

Further more, his two beam system is setup using two lasers spaced about 4m apart requires even greater accuracy. Let's imagine system 1 is aligned to the local tangent at one end of the terminal (x = 0m), system 2 is aligned to the local tangent 4 m away at x = 4m, and heights of the two beams are measured at the opposite end of the terminal (x = 700 m). The height difference between these two beams will be about 1 micron. If we assume that the beams are large enough that there is no spread in beam size, then each beam is about 3 cm in diameter. This means we need to measure the beam height to better 0.003% accuracy relative to the beam size. I think this will be a very difficult measurement.

I think there is a way you could very accurately measure the relative angle between two beams in a larger interferometer and two lasers, but I'll have to think about how it would look...

Regardless, it's always fun to think about this small corrections to our expectations. To be honest, I was a little surprised to think about it, 4cm of deviation over 700m is actually a bit larger than I expected.

[lutorm]

You don't need to align anything: Point a single laser down the hallway and measure the height of the beam above the floor at the ends and at the midpoint. If the hallway is straight, these will fit a line; if the hallway is level, they will not. You can surely measure the heights to an accuracy much better than 4cm, and that's all that matters.

[bmelton]

Your approach mirrors what mine would have been. If the curvature of the earth can be measured over 725 meters, then to me, it's inconsequential whether or not that is detectable within this man-made construct.

That isn't to impugn the question, or the method, but that I'm less interested in whether the architects adjusted each each to be 4cm higher than they would need to be or not. Even if the airport were built over the course of 5 meters, in which the curvature would be (effectively) undetectable, the airport itself, being man-made, may exhibit irregularities caused by human error, shifting ground, variable bedrock, etc.

Regardless, the article was fantastically fun to read, as was your post.