Archive for December, 2007

Sweeney Todd: The Demon Barber of Fleet Street

Wednesday, December 26th, 2007

I haven’t seen the stage musical this movie is based on, so I can imagine it has a lot more entertainment value. The movie is a nicely produced grim deathfest. Marked by Tim Burton’s characteristic goth sensibilities, it’s nearly continuously unpleasant. Johnny Depp’s demonic barber is hell bent on revenge, and I could imagine going along with him on that journey. But he starts slitting throats indiscriminately while his downstairs neighbor cheerfully recycles the bodies into Mrs. Lovett’s meat pies. There’s a love story on the side, but it’s not developed enough to be very engaging. Understandably, given the subject matter, the songs are not exactly the kind you hum along and tap your feet to. I felt tempted to rewrite the story with songs from “My Fair Lady”. It could start off with the following to the tune of “Wouldn’t it be loverly”:
Sweeney Todd’s coming back to see
Just how sweet revenge can be
He’s been away in jail
He’s Sweeney Todd the barber

Locked away for fifteen years
Parted from his beloved shears
He lost his wife and child
He’s Sweeney Todd the barber

Anyway, I had more fun coming up with those two verses than I did watching the movie.

The Golden Compass

Wednesday, December 26th, 2007

Lots of different concepts hastily introduced make it hard to adjust to the alien world presented in this movie for those who have not read the book it is based upon. The movie follows a twelve-year-old girl, Lyra (a very likable Dakota Blue Richards), who escapes from the cool and scary Mrs. Coulter (Nicole Kidman) and tries to find her friend Roger who has apparently been taken by the “Gobblers”. Along the way she discovers what the Gobblers are and what they and Mrs. Coulter and the ruling Magisterium are up to. The story is set in a parallel world where everyone has a soul existing as a talking animal that accompanies you, called a daemon. That creates some nice storytelling possibilities, and it also turns out to be central to the evil designs of the Magisterium who also appear to be very interested in “dust” which is not the same thing at all as dust in our world.

While I could get used to daemons and a race of talking ice bears, the whole context and feel of the world is not developed enough at the beginning of the movie. I felt disconnected from what was going on because I didn’t know enough about the rules of the game. The movie is relatively short for the first in what might be a fantasy trilogy, coming in under two hours. Some additional time was desperately needed up front to help establish what life is like in this world and who and what the Magisterium are and what dust is and why Lyra is safe in Jordan college and why everyone is so afraid of Lord Asriel’s photo of a man channeling dust near the north pole. At the end of the movie it can be pieced together, but while it’s unfolding there are too many unfamiliar elements happening all at once to make it possible to care as much about them as the characters in the movie do.

There was some fuss about a boycott of this movie for allegedly having anti-Christian themes. I haven’t read the book, but it never would have occurred to me that there were any religious aspects to this movie one way or the other had I not heard about the boycott effort.

Pictures of the Hill Sphere

Monday, December 10th, 2007

Why does Saturn have rings? Or to rephrase it to a question that is a little easier to answer: why are there moons and rings? Most moons, like our own Moon, are formed from accretion in a disk around a planet similar to how planets formed in a disk around the Sun. Small particles in a disk of material run into each other and stick, gradually forming an object large enough to be called a moon. I’ll get to how large that is in a minute. Since Saturn’s rings is a crowded disk of material, why aren’t the ring particles sticking together to form a moon? The answer has to do with how particles stick. Ultimately, when making a moon, our good friend gravity, the weakest force in the universe, is the chief sticking force. In Saturn’s rings, as in the rings of the other giant planets, the gravitational attraction between ring particles that would otherwise lead them to accrete into a moon, is thwarted by the tidal force from the planet they are orbiting. The tidal force is the differential force of gravity across an object that results from the dependence of the strength of gravity on the distance separating the two gravitating objects. Consider, for example, two particles in orbits around Saturn with the particles coming close enough to each other to touch, but one particle on an orbit slightly closer to Saturn than the other. When those two particles are in contact with each other, the gravitational attraction between them is strongest. But at the same time they are both experiencing slightly different gravitational accelerations from Saturn. The closer one feels a stronger pull from Saturn than the further one. This difference in the gravitational force between the particles and Saturn is strong enough to overcome the attraction between the two particles, so they don’t end up sticking.
cartoon of tidal force
So how do we ever get moons? That differential tidal force depends very strongly on how close the particles are to the planet. Far from the planet, the difference in the gravitational force between the two particles becomes negligible just as the separation between the two particles gets smaller in comparison to their distance from Saturn. The distance from a planet where two ring particles can stick together is called the Roche limit.

Originally the term “Roche limit” referred to the distance beyond which a strengthless, fluid object could stably exist near a planet without breaking apart due to the tidal force. However, since large strengthless fluid objects orbiting planets are not a common situation, the term has been colloquially co-opted to refer to the rather fuzzy boundary separating the region where particles can accrete and where they cannot. As it turns out there are a variety of Roche limits depending on the densities of the objects and their relative sizes, so frequently the term “Roche zone” is used. For example, it is easier for a grain of sand to stick to a boulder than for two boulders to stick together, because when you compare the distances of the two objects, the center of the grain of sand is closer to the boulder than the center of another boulder can get. We can say that the grain of sand fits inside the boulder’s own Roche zone. This region of space around a boulder or moonlet orbiting a planet where the boulder’s gravitational pull wins out over the competing pull of the planet is frequently called the Hill sphere (though it is not spherical), while the term Roche zone is usually used to specify the region of space around a planet where accretion is not possible.

Cassini’s cameras have captured pictures of small moons that orbit within Saturn’s rings near the outer edge of Saturn’s Roche zone. These moonlets have gravitationally accreted some nearby ring material, but they cannot grow without bound because of the strong tidal force from Saturn. In fact, particles can only stick to certain locations on these moons where Saturn’s gravitational pull on them is not as strong as that of the moonlets. Ring particles have, in essence, filled the Hill spheres of these moonlets. Two articles published in Science describe how small moons of Saturn graphically show the accretion of material within their limited Roche lobes (or “Hill sphere”). This NASA press release as well as the Cassini ISS web site have pictures and more information.
small moons of Saturn
Image credit: NASA/JPL/SSI
Click the image to go to the Cassini web site for higher resolution versions with more information.

So how large does something need to be in order for it to be called a moon? While the IAU hasn’t weighed in on this yet, a functional definition that is being used in the Cassini era is that it is a moon if it is big enough to create a gap in the rings and basically be alone in its orbit. This is analogous to the IAU definition of a planet. It’s a relevant issue at Saturn because there are images of objects within the rings that create large disturbances, but are not big enough to create a gap. These objects are large ring particles that probably have the same shape as the moons shown above, but are too small to dynamically open a gap in the rings. They go by the nickname “propeller objects” for the shape of the perturbation they create in the rings.

American Gangster

Sunday, December 9th, 2007

Starting as a somewhat scattered and murky movie tracking the rise of Harlem drug boss Frank Lucas, American Gangster hits its stride halfway through once cop Richie Roberts (Russell Crowe) is given a special task force to tackle the rampant New York drug problem. The story of Roberts’ difficulties in his private life, involving a lengthy divorce proceeding and his night law-school studies, is more distracting than anything else. It also makes Crowe’s decision to portray Roberts with an awkward duck-like stride and nervous habits jar with the depiction of his character as a rampant womanizer. Denzel Washington brings Lucas to life as a chilling but somehow like-able killer that you nevertheless really want to see brought down. Stephen Zaillian’s screenplay was inspired by this New York Magazine article about Lucas. I recommend seeing the movie before reading the article, as I did. The latter half of the movie, especially, is gripping story-telling. It is fascinating to see the scale of the dope operation that Lucas ran in Harlem and to learn that his was but one of many. I found myself simultaneously hoping desperately for him to be captured, but also for him to come out of it all okay somehow.

There is more interesting information on Lucas here that provides a bit more dose of reality to some of Lucas’s claims as well as the dramatic depictions of events in the movie.

Chimpanzee Memory Tests

Wednesday, December 5th, 2007

These amazing video tests of chimpanzee visual recall show to my amateur eye that chimps process and retain the visual field in a way that is different than humans. Some explanation and commentary on the significance of the results can be found in this New Scientist article. As Darth Vader said, “Impressive. Most Impressive.”

Vote for the Best Cassini Images

Wednesday, December 5th, 2007

Dr. Carolyn Porco, Team Leader of the Cassini Imaging Team, is having a contest this month for the best color and monochrome images taken beby Cassini in nearly four years of observations of Saturn, as well as the best movies her team has put together. This is a great way to check out some of the coolest pictures from Cassini. The contest runs through the end of December.

Science and Hot Tempers

Sunday, December 2nd, 2007

Apparently there’s nothing like a post on UFOs and conspiracies to boost the number of comments on my blog. In response to this post on the burden of proof, one commenter says:

If you actualy believe that there is life on other planets, get out of your dream world and stop being such an idiot!

and

To believe that there is life on other planets, you need to believe in evolution. By the way…… there is no proof for evolution!! All evolution is is another religion, because you have to believe it, without any physical evidence! so stop acting like it is science…because its not!!

Everything he says is incorrect, though the implication in the third sentence that religion is something one believes without physical evidence is reasonable. Of course, one does not need to accept the fact of evolution to believe that there is life on other planets. Presumably the idea is that life was created on Earth by a deity, but to believe that deity created life only on the Earth in a universe with over 100 billion galaxies containing roughly 100 billion stars each is to have a very restrictive view of that deity’s powers as well as presuming it to be something of a wasteful, or at least mischievous, creator. I am sure there are many people who believe that some god or other created life on many worlds. Whether or not they also understand evolution is irrelevant.

As for proof of evolution, I refer the reader to any biology textbook as well as many fine museums. There is so much physical evidence for evolution, that to deny the existence of the evidence reveals a willful determination to ignore reality. As for life elsewhere in the universe, my expectation that it exists is based on scientific speculation, but certainly not on physical evidence, and perhaps this is what irked the person quoted above. In fact, when I reread what I wrote I expected to find that I had written that I “believed” there was life elsewhere in the universe. Instead I wrote

I would be thrilled by the discovery of extraterrestrial intelligence, but so far there is no evidence…

In fact, I do believe that there is life elsewhere, but what I believe is irrelevant to scientific inquiry. That’s the whole point of science: to advance understanding through observation and experimentation, in short, through evidence. This is also why the word “belief” is irrelevant to the question of evolution. It is based on evidence, not belief. The evidence is also that the Earth is not unique and that life developed on it through natural processes and that the laws of physics are the same throughout the universe. It is therefore a reasonable hypothesis that life exists elsewhere, and that’s why we are looking for the physical evidence through SETI and exploration of our neighboring planets and their moons. The hypothesis will remain a hypothesis until we obtain evidence. A persistent absence of evidence would be reason to discard the hypothesis, but we are so far from being able to explore other Earthlike worlds that it will be a long time before we can reject the hypothesis that there is life elsewhere.