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Imagine looking into a room where everything looks completely ordinary. But when you look into the mirrors, then all sorts of spooky things appear about the room — images, faces, writing. This could be an interesting way to tell an immersive ghost story.

You could do such a thing using circularly polarized light. In ordinary linearly polarized light (as in many sunglasses and projectors), all the light waves vibrate at the same angle. But in circularly polarized light, the light waves spiral — either clockwise or counterclockwise.

Most 3D movies are shown with linearly polarized light. When you wear those funny glasses, the filter over your left eye shows only polarized light slanting diagonally one way, and the other shows only polarized light slanting diagonally the other way.

This works fine as long as you don’t tilt your head to one side or the other. If you do that, then the angles don’t line up anymore, and each eye ends up seeing both images, which ruins the effect.

Some more expensive 3D projection works with circularly polarized light. The left eye filter sees only light waves that spiral one way (say, counterclockwise), and the right eye filter see only light waves that spiral the other way (say, clockwise).

And the effect works just as well even if you tilt your head. In fact, you can rotate each filter all you want, and everything still works, because the light waves are still spiraling in the proper direction.

OK, here’s the really cool part: When you bounce linearly polarized light off a mirror, you just get the same linearly polarized light back. But if you bounce circularly polarized light off a mirror, the reflected light switches orientation — clockwise turns to counterclockwise, and vice versa.

You could make some really interesting installations with this. For example, imagine looking into a room, through a window that lets through only clockwise circularly polarized light. Counterclockwise circularly polarized light projected onto walls and statues in this room would be invisible. But if you looked into the mirrors in that room, then all of those projected images would become visible.

Imagine the artistic possibilities!

In a major technological breakthrough, Apple Computer has been awarded a prize of more than $1 billion for its invention and dramatic demonstration of a time machine.

The award was in the form of damages to be paid to Apple from Samsung, which had the affrontery to employ a “pinch to zoom” gesture, among other things, in its Android phones.

The genius of Apple (and really, let’s be honest, the genius of Steve Jobs) was that it managed to invent this groundbreaking technology literally decades after Myron Krueger first demonstrated the pinch-to-zoom gesture in 1983.

How many companies have the brilliance and the foresight to invent something long after it had already been publicly demonstrated and widely known within the field, and then the business savvy to extract a vast sum from others for the violation of its patents on that invention?

As Apple continues to develop and refine this ingenious time machine technology, it will be exciting to see what other bold and innovative technologies from the past this company will manage to invent and to take ownership of.

Thanks to Stephan Ahonen for suggesting the use of CDMA for sending homing info to a rossum of robots.

As an alternative, maybe we can very the well known technique of sending a “chirp” in radar or sonar. In the chirp approach, rather than just sending a really short sound (and then waiting to see how long it takes to travel), you send out a continuous tone that rises in pitch over time (which makes a sawtooth pattern, since when you get to the highest pitch, you go back down to the lowest pitch and start again). Since you are sending a signal continuously, rather than just at intervals, you can get a better result.

Unfortunately, as Stephan pointed out, when objects are moving toward or away from your beacon, then Doppler effects will raise or lower the perceived pitch of your tone, thereby introducing errors.

Maybe instead of sending just one tone that varies linearly over time in pitch, we can send two tones, each with a different base pitch. We make both tones wobble in pitch, varying one tone over time as a sine function and the other as a cosine function (rather than a sawtooth, our two pitches trace out a circle over time). This method will be impervious to Doppler shifts, since both tones will rise and fall together, and we only care about the difference between the two pitches.

So to broadcast homing signals out to our rossum of robots, we will end up generating a total of four undulating ultrasonic tones: two from the speaker on one end of our separating rod, and two from the speaker at the other end.

I’ve been searching over the internet, but so far I can’t find any examples of somebody having tried using this kind of cyclic chirp.

“It seems to be, first of all, from what I understand from doctors, it’s really rare. If it’s a legitimate rape, the female body has ways to try to shut the whole thing down.” — Representative Todd Akin, Republican of Missouri, asserting that raped women don’t get pregnant

Of all the ways one could imagine to help Barack Obama get re-elected, probably nothing could top the effectiveness of the recent remark by Representative Todd Akin. It constitutes a perfect nuclear strike against the Romney campaign.

If there is a winning strategy for Mitt Romney this fall, it certainly does not lie in a discussion of abortion — and that’s why Romney/Ryan have carefully steered clear of this topic. It kind of brings to the surface the fact that Ryan was a co-sponsor of a bill that distinguishes “rape” from “forcible rape” (I’m not making this up), and that he has asserted that abortion should only be legal when the mother’s life is in danger.

If not for Akin’s outburst, those inconvenient facts might have stayed buried. Now, of course, they have become common knowledge. It kind of makes you wonder whether Akin is secretly on the payroll of the Obama re-election campaign.

Continuing from yesterday’s post, let’s explore this idea of calculating one’s location by analyzing the time delay from two separately located sound sources.

It would be easy to apply this principle to a swarm of robot vehicles. In this scheme, a stationary transmitter containing two physically separated speakers sends out periodic ultrasonic pulses. Each robot vehicle contains a clock, so it knows what time each pulse was supposed to have originated. By measuring the delay in receiving each of the two sounds, the robot can calculate its own location.

We can also do this in 3D, with a swarm of flying robot vehicles. In that case we would need a transmitter containing three speakers, physically arranged into a triangle, but the principle would be the same.

In any case, we can broadcast digital instructions saying where we want each robot to be. When any given robot is told where it should be, it will know which way it needs to go. This allows us to centralize the planning for the swarm’s behavior into a single computer, rather than requiring each robot to be smart on its own.

It would be fun to think of uses for such a swarm of robots — whether for artistic or practical purposes. But what would you call such a flock? A flock of crows is called a “murder” (hence the title of that work at the Park Avenue Armory). Bowing to literary precedent, perhaps it should be called a rossum of robots.

I went this weekend to see the brilliant immersive soundscape installation The Murder of Crows by Janet Cardiff & George Bures Miller, currently showing at the Park Avenue Armory. If you will be in NYC between now and September 9, I highly recommend it!

Essentially a dreamscape audio movie realized by 98 speakers placed around the Armory’s immense Diff Hall, the experience reminded me of the huge emotional power that sound can convey. I could literally feel, in my bones, doors creaking open and closed, marching footsteps, howling winds and other powerful sonic “images”, with a visceral immediacy far beyond what could be conveyed by mere visual means.

And of course I immediately set about trying to figure out how I could make one. It could be done with a binaural headset, but I wouldn’t want to have to wear earphones all the time. With a stationary audience of just a few people, you can do it with four speakers, each positioned at the corners of a square around the listeners.

To capture the soundscape, you would use four microphones arranged into a square exactly the same size. If pairs of microphones are the wrong distances from each other, then phase information is destroyed, and the experience will lose realism and immediacy. And you probably want the square to be fairly large, so it captures the way things move between the speakers.

So a faithful audio “camera” partly comes down to placing each microphone the correct distance away from the other microphones as the crow flies (so to speak). If you are doing this in a secluded location (eg: a beach), then you can just use six strings of the proper lengths — one between every pair of your four mike stands — and separate the mike stands until the strings are taut.

But if you are doing it in a crowded place, such as a New York City street, then you need to use some other method of calibrating distance. You could use optical measuring devices, such as time-of-flight cameras, but to me that seems needlessly expensive.

Since we already have high quality microphones, perhaps we can generate a sound and measure when that sound arrives at each microphone (a simple form of sonar). As a calibration device, we can place two small speakers a small known distance apart from each other (say, on opposite ends of a separating rod). A computer sends two simultaneous pings, one to each of the two calibration speakers — with the two pings having different pitches. From the time each of the pings arrives at each of the four mikes, we can calculate the exact position of all four mikes, and how each mike needs to be moved to get into proper position.

I’m sure there are other ways to do this. The important thing is to be able to capture wondrous immersive soundscapes wherever they may be. If a library of such immersive soundscapes could be developed, then this would be an experience anyone could enjoy at home.

If each of us looked
Like our soul, and kindness were
Treasured as beauty,

Would that be a world
Where war could never exist?
Imagine that world.

I am circling back to the problem I described last October of tiling a sphere with identical puzzle pieces, because I’d like to be able to quickly put together things like portable planetarium domes and big acoustic focusing mirrors. Ideally I’d want to be able to carry something small and portable, and then put up or take down the resulting sphere very quickly.

If we go with the identical puzzle piece approach, then a sphere requires 60 slightly curved shapes (or 30 shapes for a hemisphere, if you want a planetarium dome). In its disassembled state, the sphere would consist of a stack of identically shaped pieces. I’m thinking that a nice way to make something both stackable and easy to assemble/disassemble would be to put tiny magnets along the edges.

You’d want to orient the magnets, as in the diagram below, so that the pieces stick together properly both when assembled and when disassembled / stacked. One way to do this would be to orient four magnets (shown as red dots) so that the north poles of two magnets point out of the sphere, and the south poles of the other two magnets point out of the sphere:

While this scheme works, it requires a lot of tiny magnets — four magnets per piece. That’s 120 magnets for a dome, and 240 for a full sphere. Fortunately we can replace half the magnets with small pieces of metal (shown as blue dots below), which are cheaper:

Now all that remains is to build the thing and see if it all works. 🙂

New York in summer
Becomes a perfect playground.
Too bad summer ends.

I was recently having a conversation with two very intelligent and politically well-informed people, both of whom were shocked when I said that I knew from first hand experience that parts of our federal government are not corrupt. My friends were shocked not because they believed me, but rather from astonishment that I could be so hopelessly naive as to not realize that our government is rotten to the core, a hopeless miasma of stinking corruption, with everyone on the take.

In a wish to help me through my unfortunate gaffe, one of my conversants helpfully pointed out that my experience was, by definition, merely anecdotal, and therefore could seem real to me while not actually bearing any relation to reality.

It took me quite a while to realize what was going on in the conversation, and then only a bit longer to take them through the nature of my experience. I explained that my experience has mainly been with the NSF. Over the course of many years, interacting with an extremely large number of program officers, I have found every one of them not only to be scrupulous in ethics, but to go quite a bit further.

For example, whenever a junior faculty member is naive or inexperienced enough to offer to pay for lunch, NSF program officers will invariably explain, in a patient yet respectful manner, that they must never take money from their academic colleagues for lunch, for travel, for housing, or for anything else. Sometimes the program officer will cite the exact governing statutes, just to clarify the point. More recently I have interacted with representatives of the Obama administration’s Department of Education, and have found them to be exactly the same in this regard.

After I explained all this, my acquaintances finally acknowledged that this constituted more than “anecdotal” evidence. But they still did not budge on my larger point, which was that such successful models of uncorrupt governance could, with diligence, find their way into other parts of the government.

On this last point, my friends simply looked at me with a combination of pity and fondness. I think their fondness was in remembrance of a time in their lives when they too had been so naive and innocent. Before they had come to view all government, with the exception perhaps of a few oddly incongruous pockets of integrity here and there, as a seething pit of putrescent rot, a thing of horror and pestilence, the work of the very devil.