Wednesday, February 07, 2007


Tomorrow morning, I confidently expect to awake and find the elegant spires and haphazard Victorian rooftops of Dorchester, transformed by the silent fall of billions of snowflakes.

An individual snowflake is itself an agglomeration of up to several hundred ice crystals, and a cubic foot of snow can contain roughly one billion crystals of ice. Conventional wisdom suggests that no two snowflakes are alike, but in the case of the simplest type of snowflake, this isn't actually true. According to Dr Karl Kruszelnicki:

In 1988, the scientist Nancy Knight (at the National Center for Atmospheric Research in Boulder, Colorado) was studying wispy high altitude cirrus clouds. Her research plane was collecting snowflakes on a chilled glass slide that was coated with a sticky oil. She found two identical (under a microscope, at least) snowflakes in a Wisconsin snowstorm.

As Dr Karl points out, these snowflakes were simply hexagonal prisms, rather than the more complex type of snowflake-crystal, which exhibit the classic six-fold spoked structure, seen in the picture above. And, as both Dr Karl and Kenneth G.Libbrecht of Caltech point out, if two such snowflakes are deemed alike, then they are only alike at the level of resolution provided by a microscope.


Neil Forsyth said...

Does that go for everything in the universe, then? That is, objects can be alike, but never identical. Come to think of it, from moment to moment, everything is changing ever so slightly, so that in an odd kind of way no thing is even identical to itself (if examined twice, with a short interval in between, at a microscopic level). All is flux! Or am I losing the run of myself here? There was that pre-Socratic guy I quite liked, what's his name...Heraclitus. That was his big idea, wasn't it? Did he drown in the end?

Gordon McCabe said...

According to Dr Wiki Pedia, "There are several legendary stories about Heraclitus, especially concerning his eventual death from illness, including his supposed attempt to stave off death using dung and ignoring doctors. These mostly stem from mis-interpretations of the metaphors in his fragments and an attempt to construct a narrative based on these fragments." Perhaps you're thinking of Robert Maxwell?

Can numerically distinct objects be qualitatively identical? Can one and the same object be qualitatively identical at different times? Personally, I would say yes, but only in the case of the intrinsic properties of elementary particles, as opposed to their extrinsic properties.

Here, I'm taking an intrinsic property of an object to be a property which the object possesses independently of its relationships to other objects, and I'm taking an extrinsic property of an object to be a property which the object possesses depending upon its relationships with other objects.

Neil Forsyth said...

Yes, maybe it was Maxwell I was thinking of. Wasn't it his thesis that you can never read a tabloid story twice and get the same meaning. There's the confusion. Thankfully, Maxwell was a numerically distinct object the likes of which we will probably never see again.

Susan Balée said...

Love your snowflakes, Gordon.... Even if a few of 'em are the same, they still inspire wonder. And I wonder if we're *ever* gonna get any again where I live!

Gordon McCabe said...

Well, Susan, global warming works in strange ways, and according to the latest IPCC report, the Antarctic ice sheet is actually expected to gain in mass due to increased snowfall. You never know, you might get more in Philadelphia as well!

You'll have to let us know if those rubber pavements in Philadelphia help to reduce the run-off from snow-melt.