Hubble! Bubbles! Satellites! Stars!

April 27, 2007

I’ve come across a number of physics-related items this week, and thought I would share them.

First, I found galleries of photographs that have been taken by the Hubble telescope over the years. I’ve been aware, of course, that these images were being collected, and I’ve admired the rare photo when I’ve come across it, but I’ve never stopped to look through an entire collection. There are some spectacular, fascinating images there.

Second, a major announcement from a pair of physicists working at Princeton University. At long last, and after many other men had failed and fallen below the table, they have succeeded in providing a mathematical description of that most mercurial of substances: beer foam. This discovery will doubtless lead to the founding of many new research institutes, all strategically placed near the campus bar. More precisely, they have studied the time-evolution of packed n-dimensional bubbles; the special case of n=3 applies to beer foam, at least for the first few glasses. At the press conference, one of the pair praised the other’s contribution to the discovery, saying “I had always known he was bright, but until now had not fully appreciated his Guinness.” His colleague, meanwhile, asked pardon of the assembled reporters, remarking that his friend meant well, but was well past the point of hilarity.

Earlier in the week I attended a seminar surveying the history of attempts to measure time. The talk began with ancient sun-dials and ended with modern atomic clocks. Into a discussion of the latter, the speaker brought the GPS satellite technology. Each satellite, it turns out, is equipped with an atomic clock, and it transmits time signals to GPS receivers on the earth. It is by collecting these signals from a variety of different satellites that the GPS receiver is able to deduce its position on the earth. In order for the method to work, however, it is necessary that the satellites be synchronized with one another, and even a drift of a few microseconds would have a serious negative effect on the precision of geo-location here below.Now, this is the interesting part: the need for such great precision requires that the satellites take into account relativistic effects in their time-keeping. They must compensate both for special relativity (on account of their high orbital speeds) and general relativity (on account of their being in a weaker gravitational field than terrestrial clocks). This is the most down-to-earth (so to speak) example of the importance of relativistic effects of which I am aware.

Finally, I discovered a great software package this week called Stellarium. It is a star-gazing aid: tell it your position and it generates sky maps. It is easy to use, and looks beautiful. Best of all, it’s free.

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