# Justin Li

## Time and Space

2007-12-25

I noticed something while having a conversation with some friends about locations. In the US more so than other countries, people describe distances by how long it takes to drive there. For example, Devil's Lake in Wisconsin is 4 hours drive north from Evanston, and Sacramento a 3 hour drive from San Francisco.

In one way, this is a very practical way of giving locations, because although it doesn't tell you where the place is exactly, it tells you how to get there, and how long it will take. What I find curious is that the time is not an absolute measure, either; it depends on the speed of the traveler. By using driving time as a measurement of distance, we are in fact assuming one thing: constant speed not only for the trip, but for all drivers.

That in turn reminded me of a suggestion someone made a long time ago. Some physicists suggested that distances should be measured in time units, with the constant being 3*10\^8, or the speed of light in a vacuum. Going from Evanston to Devil's Lake would be 1.04 milliseconds, and from San Francisco to Sacramento 0.470 ms.

I find it ironic that the US, where science education standards are dropping, would have a colloquial convention that demonstrates relativity.