Archive for September 27, 2012

Extremely Deep Space

Posted in The Universe and Stuff with tags , , , on September 27, 2012 by telescoper

There’s been a lot of media coverage of this image, taken using the Hubble Space Telescope using an exposure time of 2 million seconds (aproximately 23 days), including a nice feature article on the BBC Website to which I refer you for more explanation, so I’ll keep this post brief. Suffice to say that the Hubble eXtreme Deep Field (XDF) is the deepest image of the sky ever obtained and it reveals the faintest and most distant galaxies ever seen, showing some galaxies as they were over 13 billion years ago. It’s also very very pretty…

And if the overwhelming scale of the Universe revealed by this picture makes you feel worthless and insignificant, just remember that things could have been much worse. You might have been Nick Clegg.

The Cruel Sea

Posted in Film with tags , , , on September 27, 2012 by telescoper

Taking a break from lecture preparations last night I decided to have a look through my collection of DVDs and found a box of old films made by Ealing Studios, among which was The Cruel Sea . The central character in the film is Lieutenant Commander George Ericson (played by Jack Hawkins), officer in command of the corvette HMS Compass Rose as it carries out its duties as a convoy escort vessel during World War II. Made in 1953, this is a war film, of course, but it stands out from many films of that genre because it is not only utterly convincing in its stark depiction of life on the Atlantic (and, later, Arctic) convoys during World War II but also extremely bleak in what it says about the dehumanising effect of the psychological and moral stresses that arise in armed conflict.

The outstanding sequence in the film is the following, in which HMS Compass Rose is attempting to hunt down a suspected U-boat. There’s a strong signal on the ASDIC (sonar) which convinces Sub-lieutenant Lockhart (played by a young Donald Sinden) that they have made contact with a U-boat. Ericson guides his ship towards the target, only to find that there are men in the water – survivors of a merchant vessel previously sunk by a U-boat’s torpedo – precisely where he must drop his depth charges. Does he attack, and kill the men in the water? Or does he spare them, and risk the U-boat killing hundreds more if it escapes? Such are the horrible decisions that have to be made in wartime, and the burden of having to make them must be intolerable.

I think what I admire most about this sequence is that it avoids giving a clear resolution. Was there actually a U-boat? Lockhart was convinced the signal represented a submarine, but ASDIC was known to produce false detections from, e.g. shoals of fish or even interfaces between regions of cold and warmer water.

Early in the war, escort vessels only had depth charges with which to attack submarines. That meant that they had to be directly above the target in order to strike and that, in turn, meant losing the ASDIC contact during the attack. The limited capability of the escorts to actually destroy submarines did not render them useless, as they could keep an individual U-boat submerged and occupied for hours on end. However, when U-boats became more numerous they began to attack in packs, outnumbering the escorts and causing carnage among the merchant vessels. Allied shipping losses reached disastrous levels, especially in 1943 when Britain was close to losing the war by strangulation of supply across the Atlantic.

Later on, the Royal Navy developed a forward throwing weapon (“The Hedgehog”) which allowed ships to attack U-boats while maintaining sonar contact and thus drastically improved their effectiveness during a deliberate attack. This together, with improvements in radar and provision of long range aircraft gradually turned the tide and disaster was averted.

Hunting a U-boat involved a great deal of guesswork and anticipation, hugely helped by knowing something about submarine tactics gained through intelligence work; at one level it was a relentless game of cat-and-mouse – absorbingly depicted in the film – but also of course no kind of “game” at all.

If there was indeed a U-boat in the scene shown above, it might have been destroyed (although one might expect oil and debris to rise to the surface in that case) or it might have escaped. This uncertainty adds another dimension to the moral dilemma of whether or not to attack: if you’re certain it’s a U-boat then you might attack, but what if it’s a probability of 90%? 50%? 10%? What form of calculus can be used in the seconds you have to make your decision?