Tuesday, May 02, 2006

Where it all started

Actually, I can't remember where it all started—I was always interested in the sky and the stars. Even though stars were scarce in New York City, we went camping often enough so that I learned the major constellations. In high school I even took some classes as the Haydn Planetarium. In those days the classes were held in the basement and you had to walk through the dusty meteorite exhibit to get to them. Nothing like the the snazzy, multimedia Haydn Planetarium of today.

I have this defining intellectual memory, however, of reading a book I found on the shelf at home: Nigel Calder's Einstein's Universe. He has a chapter called "Directed Futures" in which he uses the concept of the "light bubble" to explain space-time. Imagine a spaceship with beacons on the outside. A flash of light will spread outwards from the spaceship at the speed of light, and since nothing can travel faster than that, that light bubble defines the spaceship's possible future:

Now, put our spaceship near a massive object. Gravity displaces the light-bubble off-centre and as a result the astronaut's future is somewhat biassed in a certain direction in space—towards the massive object. An interchange occurs between time and space. Its meaning assails our prejudices about time more fiercely than the slowing down of clocks. A black hole again clarifies the point. Imagine the spaceship just crossing the dire perimeter at the surface of a large black hole. The astronaut is trapped for ever. His future now lies inside the black hole, because the light constituting the light-bubble cannot, by definition, escape from the black hole.

That image has stayed with me ever since, which is probably a testament to Calder's engaging style, at least as much as the subject matter.


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