Archive for Angels and Demons

Cosmology, Escher and the Field of Screams

Posted in Art, Education, The Universe and Stuff with tags , , , , , on March 20, 2012 by telescoper

Up early this morning for yet another busy day I thought I’d post a quick follow-up to my recent item about analogies for teaching physics (especially cosmology).

Another concept related to the cosmic microwave background that people sometimes have problems understanding is that of last scattering surface.

Various analogies are useful for this. For example, when you find yourself in thick fog you may have the impression that you are surrounded by an impenetrable wall at some specific distance around you. It’s not a physical barrier, of course, it’s just the distance at which there sufficient water droplets in the air to prevent light from penetrating further. In more technical terms the optical depth of the fog exceeds unity at the distance at which this wall is seen.

Another more direct analogy is provided by the Sun. Here’s a picture of said object, taken through an H-α filter..

What’s surprising to the uninitiated about an image such as this is that the Sun appears to have a distinct edge, like a solid object. The Sun, however, is far from solid. It’s just a ball of hot gas whose density and temperature fall off with distance from its centre. In the inner parts the Sun is basically opaque, and photons of light diffuse outwards extremely slowly because they are efficiently scattered by the plasma. At a certain radius, however, the material becomes transparent and photons travel without hindrance. What you see is the photosphere which is a sharp edge defined by this transition from opaque to transparent.

The physics defining the Sun’s photosphere is much the same as in the Big Bang, except that in the case of the Sun we are outside looking in whereas we are inside the Universe trying to look out. Take a look at this image from M.C. Escher:

The universe isn’t actually made of Angels and Demons – at least not in the standard model – but if you imagine you are in the centre of the picture  it nicely represents what it is like looking out through an expanding cosmology. Since light travels with finite speed, the further you look out the further you look back into the past when things were denser (and hotter). Eventually you reach a point where the whole Universe was as hot as the surface of a star, this is the cosmic photosphere or the last scattering surface, which is a spherical surface centred on the observer. We can’t see any further than this because what’s beyond is hidden from us by an impenetrable curtain,  but if we could just a little bit further we’d see the Big Bang itself where the density is infinite, not as a point in space but all around us.

Although it looks like we’re in a special place (in the middle) of the image, in the Big Bang theory everywhere is equivalent; any observer would see a cosmic photosphere forming a sphere around them.

And while I’m on about last scattering, here’s another analogy which might be useful if the others aren’t. I call this one the Field of Screams.

Imagine you’re in the middle of a very large, perhaps infinite, field crammed full of people, furnished with synchronised watches, each of whom is screaming at the top of their voice. At a certain instant, say time T, everyone everywhere stops screaming.

What do you hear?

Well , you’ll obviously  notice that it gets quieter straight away as the people closest to you have stopped screaming.  But you will still hear a sound because some of the sound entering your ear set out at a time before t=T. The speed of sound is 300 m/s or so, so after 1 second you will still hear the sound arriving from people further than 300 metres away. It might be faint, but it would be there. After two seconds you’d still be hearing from people further than 600 metres away,. and so on. At any time there’ll be circle around you, defined by the distance sound can have travelled since the screaming stopped – the Circle of Last Screaming. It would appear that you are in the centre of this circle, but anyone anywhere in the field would form the same impression about what’s happening around them.

Change sound to light, and move from two dimensions to three, and you can see how last scattering produces a spherical surface around you. Simples.


Turkeys and Angels

Posted in Uncategorized with tags , , , , , , , on March 4, 2009 by telescoper

Travelling to London on Saturday to see Doctor Atomic, I read an interesting piece in the Guardian review by Salman Rushdie. The general theme was inspired by the fact that a film director once told him that all movies made from novels were “rubbish”.

I was reminded of that piece today when I had a quick look at cosmic variance and found a post about the forthcoming film Angels and Demons by Dan Brown, author of The Da Vinci Code.  The post is mainly about the fact that Angels and Demons is based in the world of particle physics so some educational materials have been generated to cash in on it, so to speak. Nothing wrong with that as an idea. Every little helps.

The problem for me is that the film is  directed by Ron Howard and stars Tom Hanks. This is the same combination that took Brown’s enjoyably preposterous page-turner and made it into one of the worst pieces of cobbled-together garbage that I’ve ever seen in a cinema. The novel isn’t so bad for what it is, a formulaic but fairly well crafted thriller. The film is excruciating. The book of Angels and Demons is not as good as the book of the Da Vinci Code, so I shan’t be rushing to see the film when it is released in the UK, particle physics content notwithstanding.

This is only one example of a book being turned into a terrible film, but I can think of many counter-examples to the assertion that they’re all rubbish. Of course it helps if the book you start with isn’t rubbish itself.  As a recent example I  think of Atonement by Ian McEwan, a great book  turned into a pretty good film.

But the example that for me really refutes the argument is Death in Venice, by Thomas Mann:  a brilliant and disturbing novella about  physical and spiritual decay turned into a stunning visual masterpiece of a film by Luchino Visconti. The story is about the growing obsession of ageing writer Gustav von Aschenbach with a young Polish boy, Tadzio, in a city beset by a cholera epidemic. It’s not a story about paedophilia (nor even, in fact, particularly about homosexuality) although it doesn’t shrink from either of those themes. As the critic Lawrence J.  Quirk put it

Some shots of Björn Andrésen, the Tadzio of the film, could be extracted from the frame and hung on the walls of the Louvre or the Vatican in Rome. For this is not a pretty youngster who is supposed to represent an object of perverted lust; that was neither novelist Mann’s nor director-screen writer Visconti’s intention. Rather, this is a symbol of a beauty allied to those which inspired Michelangelo‘s David and Da Vinci‘s Mona Lisa, and which moved Dante to seek ultimate aesthetic catharsis in the distant figure of Beatrice.

In other words Tadzio symbolises beauty in a primarily aesthetic sense rather than a sexual one. Or maybe I protest too much.

The film is beautiful to look at and is held together by a riveting central performance by the late Dirk Bogarde in probably his greatest acting role. Here is the closing scene of the film, La Morte del Professore sulla Spiaggia, languidly paced but emotionally and erotically charged. Aschenbach, wearing make-up and with the  hair dye used to disguise his age melting in the heat, suffers a heart attack and dies while Tadzio stands in the sea, like an angel beckoning him  to a better world.

The music is the 4th movement (Adagietto) from Mahler‘s 5th Symphony. If ever there was music to die for, this is it.

And if this is a bit morbid for your taste, maybe you can suggest other great novels made into great movies?