Archive For November, 2009
It’s finally happened. I’m officially an iPhone widow! After 2 years of patiently waiting for Apple to release O2′s greedy claws from their exclusive contract, The Partner has finally got his hands on the sleek black accessory of his dreams. You’d thin…
It’s finally happened. I’m officially an iPhone widow! After 2 years of patiently waiting for Apple to release O2′s greedy claws from their exclusive contract, The Partner has finally got his hands on the sleek black accessory of his dreams. You’d thin…
This is a cut-down still of part of the Airbus A380 cockpit, taken from airbus.com. It’s from a panoramic viewer, on a page that uses Flash to let you pan and tilt and zoom in and out of a view in any direction, so that you can really explore the cabin in detail, in high-res. If you want to look out of the window, look backwards, or look up at the ceiling while it spins, you can do that. The mouse scrollwheel zooms you in and out. It’s nice. The 360-360 photography is by gillesvidal.com.
The A380 is a very nice plane, with a famously-great cockpit control surface layout. It has a comfortable, relaxing, reassuring look to it (as opposed to some of the more traditional layouts with lumpy panels and dials everywhere all screaming “Look at MEEE!“). It doesn’t look scary – as a newbie, you can look at this user-interface and half-kid yourself that you might actually be able to fly it.
My concern when I first heard about the Airbus’ screen-based system was: what happens if a screen develops a fault, and you lose a whole bank of virtual instrumentation? Well, the A380 panels tackle that problem brilliantly – you notice how the eight main portrait-format screens all seem to be the same size? Well, they’re completely interchangeable. You’re supposed to be able to pop out any of the main screens and swap them round, live. There’s a couple of little grey rectangles below the bottom two corners of each screen panel, presumably those are the finger-latches. And apparently you can completely change the layout, so if one panel’s connection points are messed up, you can watch its data somewhere else. I like this plane.
So let’s explore …
Twin side-joysticks and QWERTY keyboards. I don’t know what those two rounded plastic bulges are … perhaps they’re calming devices, for the pilots to put their hands on in moments of stress. Or maybe they’re there so that if you get thrown towards the panel, you have something to grab onto that doesn’t accidentally result in you pressing an Important Switch by accident.
Three spare seats at the back (for parties), and an overhead camera (so that you can remember what you did the next morning). Fun Wagon!
Note the video camera views, on the centre screen. Useful for parking, and also for reminding yourself which airport you’re at. Also for checking that you still have the right number of engines, that none of them are on fire, that all your control surfaces are present and correct, and that your wheels haven’t fallen off. Without cameras (or a periscope), it’s not always easy to know if your wheels are really down, because planes tend not to have glass bottoms. The central panel showing the video views is the obvious “spare” section of control surface to use in flight for additional functions if further equipment is retrofitted that needs its own display space (like customised additional avionics – rocket launchers, anyone?). There’s a pull-out shelf thing in front of each seat that gives the pilots additional keyboards and pop-up screens for general flight admin and map-browsing.
Very Importantly: what looks like three cup-holders per side, left and right, away from the important controls, plus another five at the back left. It’s deeply important to have enough cup-holders (one for fresh coffee, one for water, and one for soup, or perhaps noodles?). That’s assuming that the holes aren’t for something more boring. There’s a clunky laptop-py thing at the back, for system-level stuff.
I like the documentation holder on the back of the door, made out of two types of sticky tape. But what’s that panel in the door, with the nasty scratch gouged in it? Is it a “people” version of a cat-flap? I also like the design of the door-hinges, with the hinge protruding inside the cabin, and the screws accessible. That means that the cabin crew can remove the door from its hinges from the inside, if it jams (say, after a crash). Someone’s put a lot of thought into this.
Twin microphones (for karaoke duets? Pilot-copilot comedy banter?). Between the “emergency power” and “oxygen” switches overhead (up above the left windscreen variable-speed wiper knob), there’s also an intriguing switch marked “Entertainment”. Hmm.
Rear right, there’s what looks like a locked cabinet marked CDROM. Well, if the Batmobile has one, I suppose the 380 ought to have one, too.
“Escape rope” compartments on both sides. Down to the rear left, by the fire extinguisher (whose sign I initially misread as “portable fire eating”), there’s a hatch set into the floor. I’ve seen this hatch drawn on a schematic with a ladder poking through that exits through the front wheel port. I guess this means that if you’re a pilot and you have a panic attack before takeoff, you can pop down through the floor and run away across the airfield without the passengers realising that you’ve gone.
The seat covers have large tags facing each other saying “Pilot” and “Copilot”, which might be useful for resolving cabin arguments. Point at the tag. ‘Nuff said. Also handy for avoiding those embarrassing “But I thought YOU were supposed to be flying the plane!” moments.
So, a very nice vehicle.
The only design decision here that I’d query is the upholstery. Pinstripe? Hmmm. But perhaps there’s a reason for that, too … perhaps striped material doesn’t show sweat stains so easily. You don’t want to be settling down into your seat for a long-haul flight, and be too conscious of the big sweaty patch left by the previous pilot. Eurgh. I wonder how often they change the covers?
With the addition of deep-pile furry tiger-pattern seat covers, vibro-back-massagers built into the seats, a proper entertainment system with giant speakers, and a couple of foot spas, I’d give this cabin 10/10.
City smart, moody with a whiff of sulphur, Interpol snatched their influences from the new wave. The music of Joy Division, Bauhaus, Television, The Psychedelic Furs and Magazine was ingested and polished to a diamond hard intensity. Spaces were opened up in the arrangements, the lyrics of Paul Banks drew breath and the results, the [...]
When I was a child, and into my teenage years and early twenties, I absolutely devoured fiction. Some time around the age of 22 or 23, though, I veered away from it and begun a search for ‘The Truth’. In terms of my reading habits, this manifested as an almost exclusive concentration on non-fiction. Yoga [...]
I’d like to extend a massive thanks to everyone that voted, looked through the book, helped spread the word or even bought a copy. Without readers, books are little but the remains of what was once a tree. For visitors who’ve not seen this one, click on the image or link above to go through to the book’s web page.
Although it might be a little late now that the contest is over, I’ve taken some of the feedback and added it into a flyer for the book. The intention was to get it done whilst I was still marketing it, but sometimes there’s just not enough hours in the day to fit in everything you want to do. Marketing the book itself was an educational experience and it’s left me with a stack of ideas for getting the word out about future projects.
There’s plenty more writing stuff in the pipeline at the moment, but the next project is going to be a new Control K track. Yoko Ono‘s released the stems of a song from her latest album under a Creative Commons licence and is inviting remixes. Couldn’t resist this one – the question is whether I’ll be able to get something decent completed in time for the deadline!
One can only try. So here goes…
How many saxophonists does it take to burst an eardrum? Who knows but I can tell you that when there’s seven of them in an enclosed space and they’re jamming hard, doobie, doobie, do, and the spit’s flying, it’s not advisable to sit on the front row. The leader of the band had a gammy [...]
This is an especially cool diagram for relativity theory, but it’s rather hard to find in print. There’s a limited version of it in Moreau’s 1994 “Wave front relativity” paper, and I put it in the book (chapter 8), but I can’t think offhand of anywhere else you’re liable to find it.
It’s simply an ellipse with lines radiating from one focus and converging on the other.
Imagine that you have a point-source of light giving off pulses. Surrounding the point-source is a spherical mirror, which catches the outgoing spherical EM wavefront and bounces it directly back to the source. All parts of the reflected wavefront arrive back at the source at the exact same moment.
This tells us (a) that all parts of the surface are at 90 degrees to the source, and (b) that all parts of the surface are at the same distance from the source.
=Relativistic Aberration=
Now let’s replay the same situation, but imagine how it would have looked to us if we were whizzing past the experiment in a spaceship (but not so close that we actually disturbed the light in any significant way).
Now, the geometry seems to be different. We’re forced to agree that the reflected wavefront still converges on the emitter (because nothing within the experimental region has physically changed), but since the light takes a finite time to go out and come back again, as far as we’re concerned, the experimental hardware has been moving while the light was out doing its thing.
For us, the light was being emitted from one position and refocused at another.
And the shape that does that is an ellipse.
If we look at the shape of the relativistic ellipse, we find that the outgoing rays are angled forwards … they have to be in order for them to be able to keep up with the “moving” source. And if we measure the angles of these rays on the diagram, it gives us the textbook relativistic aberration formula used by special relativity (and also by Newtonian optics, old ballistic emission theory, and any other relativistic model).
=Velocity-rescaling, distance and time under Special Relativity=
The thing that’s slightly counter-intuitive about the diagram is that if the radius of the sphere is half a light-second, and if it’s supposed to take exactly one second for the light to return to its starting point (so that the bouncing light makes a clock that supposedly ticks every second), you might expect the distance “v” that the object moves in one second to simply be the distance between the two points. Slightly perversely, under SR, it isn’t. The relative proportional velocity v/c (velocity quoted as a fraction of the speed of light) has to be the ratio between the focal point distance and the stretched, longest dimension of the ellipse. So if the distance between the focii is half the length of the ellipse, we can say that the velocity is half lightspeed
(in the diagram above, it’s 0.8c).
But since the ellipse is stretched, the distance between the points (if v is defined as a particular fraction of the speed of light) is stretched, too. If we’re to follow SR and say that lightspeed is a fixed global reference, then the distance between bounce-points is somewhat more than v metres.
Under special relativity, the width of the ellipse is assumed to be constant regardless of velocity, the ellipse is stretched by the Lorentz factor (calculated from our proportional velocity), and the “point-to-point” distance ends up elongated by the Lorentz factor, too.
Under special relativity we explain the extra distance by invoking Lorentz time dilation. We suggest that the particle travels further than expected in our coordinate system in one of its own seconds, for a given nominal velocity, because its clock is running slow (so for us, it travels for more than a second,and crosses more than v metres). Or we can argue that if an observer moving with the experiment sees a piece of paper with the diagram drawn on it passing by with the same proportional velocity of v, that for them, the distance between the marks is v metres, because their measurements indicate that the moving paper is Lorentz length-contracted. The ellipse looks like a giveaway that lightspeed isn’t globally fixed, but if we assume that it is, and need to explain why the ellipse somehow doesn’t really count as an ellipse, we end up with the traditional SR length-contraction and time-dilation explanations.
Contract the elongated ellipsoid by the magical gamma factor, and its outline turns neatly back into the original sphere.
=Doppler shifts=
The next thing that we can do is to look at the length of the lines. Turns out that, if we’re doing the SR version of the exercise, each ray elongates or shrinks by precisely the right ratio for special relativity’s relativistic Doppler effect. The forward and rearward distances are stretched and squashed by the ratio SQRT[(c-v)/(c+v)], and the 90-degree-aimed ray is stretched in length by SQRT[1 - vv/cc].
That’s the Lorentz transverse redshift prediction of special relativity.
=Ellipses are Cool=
So this one little diagram tells you almost everything that you need to know about special relativity. Once you’ve drawn it with the appropriate proportions for a given velocity, all you have to do is read off the angles and distances with a protractor and ruler to find SR’s physical predictions about the appearance of a moving body, as seen from any angle.
If you’d prefer not to rely on any “odd” theory-specific definitons of velocity, distance or time whenbuildign the ellipse, all you have to do is draw in two rays from a focus, with lengths rescaled by the theory’s particular Doppler shift predictions, and the rest of the diagram constructs itself. Along with the Minkowski lightcone diagram, it’s probably one of the most powerful diagrams in special relativity.
So why isn’t it in the books?
We-ell, perhaps the problem with the diagram is that it makes people think. Which leads to troubling ponderings, because it turns out that the diagram doesn’t have to be used with special relativity. It’ll compute the SR relationships if we deliberately stretch the point-to-point distance by the Lorentz factor, or if we use the SR “relativistic Doppler” relationships to define the reference wavelength-distances, or if we decide that lightspeed has to be defined as globally constant for all participants … but if we’re only interested in the principle of relativity, and we’re not prepared to commit to these extra SR-specific things, the ellipse also lets us plug in other assumptions, and lets us see the their consequences.
For instance, we know that old Newtonian optics was technically a “relativistic” theory (although nobody could get NO to work properly with wave theory). We know the forward and rearward wavelength changes associated with that theory, so we can draw in these two wave-distances from one of the focal points, and construct the rest of the ellipse around these maximum and minimum radii. What we end up with is an exact duplicate of the SR ellipse, with the same proportions and aberration angles, but with an additional Lorentz magnification. All the NO wavelengths are longer than their SR counterparts by a Lorentz ratio. So transverse redshifts aren’t unique to special relativity.
And then you notice some other things. The SR ellipse can be compacted back into its original circular outline just by contracting it on one axis. This is analogous to tilting the diagram off the page to produce a contracted “shadow”, which gets us into the subject of Minkowski spacetime, tilted planes of simultaneity, and other cool things. The SR family of ellipses actually represents constant-width tilted cross-sections through a constant Minkowski lightcone and can be visualised as projected conic sections.
The SR version of the constructed ellipse is the only one that has this special property.
This tells us that if we require spacetime to be “flat” in moving-body problems, the SR relationships are the only ones that work. We’re still freetoargue argue about the correct philosophical interpretation and presentation of the theory, and about whether the interpreted contractions and clock-changes are physically real or not (and about what wemean by “physically real” in the context of SR), but the defining Doppler characteristics of the theory – the things that dictate the final physical predictions and equations ofmotion, regardless of interpretation – are set, locked and non-negotiable once we’ve decided that we won’t be implementing curvature as part of the model. According to the ellipse, Relativity (limited to simple inertial motion) plus flat spacetime gives SR. It’s airtight.
If we now go back to the enlarged Newtonian version of the ellipse, we find that the rules are different. The enlarged NO wavelengths can’t be fitted back into the original sphere without distorting the centre of the ellipse out of the page. Instead of a tilted-and-rescaled cross-section through a fixed geometry (Minkowski spacetime) we end up with a geometry whose shape dynamically changes when there’s relative motion between physical masses. Instead of a purely “projective” tilt, we have a real physical change of shape. The causal structure of the metric now depends on the presence and motion of physical bodies embedded with it. We end up with a gravitomagnetic theory, with a different form of lightspeed constancy to SR. And that’s why nobody, including Einstein, could put together a sane-looking reference model for Newtonian optics that didn’t go crazy when you tried to treat it as wave theory. Newtonian optics simply doesn’t work in flat spacetime. The wavelengths don’t fit.
I still think that it’s a shame that they don’t teach the relativistic ellipse in physics classes. It’s a powerful tool, and a really handy device for demystifying special relativity. But perhaps it’s too powerful, and perhaps if you’re trying to convince a class that SR is the only possible answer, a tool that suggests the existence of alternative approaches spoils the narrative.
WriteClub, the casual networking meet-up for writers, is visiting London!
We’re continuing our mission of bringing writers together to chat, mingle and inspire each other.
The first WriteClub London meet-up is Tuesday 1 December.
Location: Yorkshire Grey pub, 46 Langham Street, London, W1W 7AX
For more details check WriteClub
Lloyd Cole – Live!
A filthy night in Brighton is not for the fainthearted, but Lloyd Cole is a talent worth braving the elements for. For those not in the know, Cole’s star burned brightly in the eighties when he was lauded by the music press as one of the most distinctive and literate songwriters around. [...]
