Take a ball of loosely aggregated rock and ice, the nucleus of a comet, fresh from the distant reaches of the solar system. Throw it past the sun, really fast, but so close that the sun takes up a large fraction of the sky. What’s going to happen? The answer: nobody knows for sure. Yesterday we actually got to see this experiment carried out by nature. And what happened? After all the photographs and other data, nobody knows for sure. Comet ISON dimmed sharply and virtually disappeared, then, in part, reappeared [see the SOHO satellite's latest photo below, showing a medium-bright comet-like smudge receding from the sun, which is blacked out to protect the camera.] What is its future, and how bright will it be in the sky when it starts to be potentially visible at dawn in a day or two? Nobody knows for sure.
[Note Added --- Now we know: the comet did not survive, and the bright spot that appeared shortly after closest approach to the sun appears to have been all debris, without a cometary "core", or nucleus, to produce the additional dust and gas to maintain the comet's appearance. Farewell, ISON! Click here to see the video of the comet's pass by the sun, its brief flare after passage, and the ensuing fade-out.]
I could not possibly express this better than was done last night in a terrific post by Karl Battams, who has been blogging for NASA’s Comet ISON Observing Campaign. He playfully calls ISON “Schroedinger’s Comet”, in honor of Schroedinger’s Cat, referring to a famous and conceptually puzzling thought-experiment of Erwin Schroedinger, in which a cat is (in a sense) put in a quantum state in which it is neither/both alive nor/and dead. Linking the comet and the cat is a matter of poetic metaphor, not scientific analogy, but the metaphor is a pretty one.
Battams’ post beautifully captures the slightly giddy mindset of a scientist in the midst of intellectual chaos, one whose ideas, expectations and understanding are currently strewn about the solar system. He brings to you the experience of being flooded with data and being humbled by it… a moment simultaneously exciting and frustrating, when scientists know they’re about to learn something important, but right now they haven’t the faintest idea what going on.