The Slow Mirror: The Central Image and its Ramifications
10 November 2010
One day, back in 1989, I was considering how the speed of light depends on the medium through which it is passing. For example, it is slightly slower when passing through air than when through a vacuum. And I thought, what if beam of light passed across a medium that slowed it down a lot? I imagined a sheet of special glass that slowed light down so much that it took several seconds to pass through. And if several seconds were theoretically possible, then why not a week, a month or a year? Since a mirror is little more than glass backed with a reflective material, I came upon the idea of a “slow mirror” that would receive the light but slow it down so much that the light would only be reflected after four years.
The image of a slow mirror fascinated me, and I wrote my short story to explore its possibilities. I had just been to Buenos Aires, and I’d really been impressed by the city, so I decided to have the narrator of the story find the mirror in an antique store there. To me, that seemed perfect.
Many years later – about a year ago, in fact – I met a physicist from Brussels who told me that she and her colleagues are indeed trying to develop materials that will slow down the speed of light. At the moment, they area only able to slow it down by a tiny fraction of a second, but, who knows, perhaps they will one day be able to slow it down for a week, a month or a year!
For me, the idea of this “time delay” has strong emotional ramifications, because we all know that we often understand our actions only years later. We notice this most often when we are forced to make an important decision, for instance, whether or not to get married, or move to a foreign country, or change jobs. We give reasons for our decision, but only years later do we realize that what motivated us was something else entirely. In general, it can take us many years to come to any understanding of our actions. We live in the present, but it takes a long time for us to understand our life.