I just finished reading Robert P. Crease’s The Prism and the Pendulum: The Ten Most Beautiful Experiments in Science. The image above comes from the experiment Crease describes in his chapter “The Quantum Interference of Single Electrons.” A related editorial from Physics World, the same publication for which Crease wrote his original articles about “beautiful experiments,” goes into greater detail about the double-slit experiment, and the Wikipedia article on the same topic does a better job explaining than I care to attempt.

Indeed, the story behind the images above (easily read as a sequential series by people familiar with comics) is long and complicated. It has to do with the so-called “wave-particle duality” of electrons, which basically means that, under certain circumstances, electrons’ behavior is described by the mathematics of waves, while under other circumstances, we can think of them as particles. (They’re neither: “wave” and ”particle” are simply two mental images that humans rely on to visualize such behaviors.)

At any rate, the sequential images reveal the build up, over time, of an interference pattern between individual electrons passing through a double slit of sorts. Our intuition of electrons as particles runs right up against their behavior as waves in this case, because the individual electrons that form the images above slowly build up into an interference pattern, the likes of which we expect from waves.

In case all this gives you a slight headache (as well it might), you can check out a couple of films that describe the phenomenon quite beautifully…

Crease references a 14-minute movie from 1974, available from the Italian Institute for Microelectronics and Microsystems, which tells the story carefully, beginning with ripples in a fountain and proceeding through light interference to electron interference. A word of warning, however: the movie files clock in around 150MB. (Nosing around the parent directory yields links to better-quality versions of the film, BTW, although the files sizes are even greater.) For those with a bit of physics background, the film succeeds in providing a good sense of what’s going on (with extensive use of animated diagrams), although the visualization of the actual data leaves a bit to be desired.

Fear not, however! A web page from the research and development group at Hitachi also describes the double-slit experiment, and it links to a page with movies, including a 10.4MB MPEG demonstrating the accumulation of electrons much more clearly than the 1974 film. But hey, they had 15 years to work out the kinks.

So where am I going with all this? Well, I found my response to the various media rather interesting. I majored in physics (well, astronomy, technically, but our slogan was, “more physics than physics majors”), so I knew the story the images were supposed to be telling. The sequential series above is certainly more than enough for me to get the gist. But actually watching the videos introduced some challenges: in particular, the limitation of the imaging capabilities in 1974 makes seeing the phenomenon tricky, but combined with the compression artifacts (e.g., the blockiness caused by the MPEG-4 compression), it starts to take some imagination to reconstruct the experiment in the mind’s eye. Thus, the images “say” only what we’re prepared to “hear.” The story I extract is the story I already know.

The Hitachi video pretty well circumvents the data problem with the 1974 film, however, so taken together, the narrative of the folder film plus the data representation of the latter tell a decent story. I think. But I’ve heard this one before.

Subjective Lakes

A Cassini press release describes the identification of lakes on the surface of Titan, the large moon of Saturn’s visited by the Huygens probe a couple years back.

The image above shows a false-color representation of radar data, with low backscatter color-coded black-to-blue. I recently blogged about so-so use of false color, but I think the above image does a pretty good job. N.B., however, what the choice of color stretch is doing here. The transition from the warmish colors to the cool blue and black guides one’s eye to “read” the transition as being from solid land to liquid lakes. But we’re trusting the visualizer of the data to have performed that stretch correctly (or I should say, honestly).

This is an excellent example of how images—even those based on data—incorporate subjective elements. The eye perceives the color difference as stark and distinct, but the actual difference in pixel values might be quite small, so the color choice communicates a lot of information in this case. I’m not saying the image is lying or anything; I’m just saying that the image does not give anything near an objective sense of the data.

(There is no such thing as an objective image!)

The results are also reported in the current issue of Nature.

Jamais deux fois—pas de tout!

For the second day in a row, I’m taking my cue from Astronomy Picture of the Day (APOD). What a way to start the new year. But instead of light from the early history of the Universe, in the above image we’re looking at light from about a second and a half ago.

APOD actually presents an image similar to the one above, which includes grid lines that make the changing size of the Moon easier to discern. What’s almost impossible to see, however, is the slight nodding of the Moon (its libration) over the period of a year. As I looked at the APOD image, I immediately thought, “This would be much better as an animation!” And indeed, the images above (and the ones featured on APOD) have been assembled into both an animated GIF and a Flash animation. Kewl! I’ve seen simulations of the Moon’s libration, but seeing actual photographs assembled in this way creates a stronger impression.

(I chose this sequence over the APOD version not just because I’m perverse but because it shows one full revolution of the Moon, rather than a revolution-and-a-half. I find it easier to watch when it baically goes through an approximate single cycle then repeats.)

All the images come from Photo Astronomique, a website that features a whole page of animations of celestial phenomena, in addition to other great astrophotography.

Cosmic Color Schemes

I was really asleep at the wheel for this one. A Spitzer Space Telescope press release from 18 December describes the detection of light from “the Universe’s First Objects”—a version of the above image appears as today’s Astronomy Picture of the Day (APOD), which is what tipped me off (sorry to say).

Anyway, the image in question shows light “from a period of time when the universe was less than one billion years old, and most likely originated from the universe’s very first groups of objects—either huge stars or voracious black holes.” In the research paper, this light is referred to as “cosmic infrared background (CIB)” radiation, as opposed to the more familiar cosmic microwave background (CMB)” radiation.

Verbiage aside, what I find odd about this image is the choice to color-code intensity as color. A perusal of the aforementioned research article indicates that color information (i.e., the color of the background signal in infrared light) is minimal, but the blobby fluctuations that range from black to purple to pinkish-red to yellowy-white. To my eye, the color range (I hesitate to use the word “spectrum”) seems forced and unnatural—at least as a way of representing intensity—but I dunno. Honestly, however, I admire the choice to show blocked-out regions, which correspond to areas obscured by nearby stars and galaxies—as grey zones. Truth in advertising, as it were.

An associated image related to the press release confuses me even more. For some reason, data from the Cosmic Background Explorer (COBE) is used instead of data from the much more recent Wilkinson Microwave Anisotropy Probe (WMAP). Why? Perhaps becuse WMAP has better resolution…? I can’t say for sure because there are no units presented with the press images, making comparison difficult—i.e., I’d need to go back to the research article and the WMAP and COBE data to compare the two, which is something I haven’t time to do for a blog that is, in fact, not my day job.

So… I have mixed feelings. It’s a complicated concept to introduce to a lay public, but the variety of false color schemes—from COBE to WMAP to the above—muddy the waters. And it’s garish muddying at that.

Race against Time

In honor of New Year’s Day, I’m posting a snapshot from the “1-D Space Rally” game from a collection of Java applets that illustrate relativity. Joel Primack created the applets based on a series of interactive programs originally created for the Apple II.

Y’see, I’ve been reading The View from the Center of the Universe, written by Primack and his wife. I quite like the book, which attempts to put cosmological concepts in a more accessible framework, drawing on historical imagery and metaphors to help readers understand, as the subtitle puts it, “our extraordinary place in the cosmos.” Because Primack has played an active role in developing the cosmological concepts that form the core of the narrative, the content is first-rate, and the richness of the analogies terribly impressive. (Plus, Primack and Abrams’s “Cosmic Spheres of Time” figure resembles the interactive Digital Universe model that I work and play with on a day-to-day basis.) The authors have a website that supports the book’s content as well.

Anyway, the image. As it says in the introduction the aforementioned applets, the interactive “helps demonstrate why the ‘twin paradox’ is, in fact, not a paradox.” The curving red line represents the trajectory of my rocket (seen at bottom), while the green lines show pulses emitted at regular intervals—intervals which differ for the rocket and the point of origin because of relativistic effects. I did my best to fly as far from the starting point as possible before reversing and returning to the starting point; as a result, only 360 units of time passed on the rocket compared to 582 at the origin.

I like the interactive well enough, but I have it could use a little more documentation, and I have one major nitpick, clearly visible in the above snapshot: label the axes! The vertical blue line represents time, while the horizontal line represents distance; they should be labeled as such.

I found a few problems with some of the other interactives as well (light pulses that don’t travel at a consistent speed and an apparent lack of gravitational influence from Jupiter, for example). I’d be interested to know whether or not those details cause misconceptions for people who use the interactives. Perhaps a generation of students (on Apple IIs, even) could provide feedback.

Sadly, no near-light-speed spacecraft exist to help us travel into the future, aging more slowly than our earthbound compatriots. So as we celebrate a new year, we all celebrate together, growing older at the same depressing rate. At least we can simulate an alternative…

Happy new year!