You may have heard physicists describe the
moon as being 1.3 light-seconds away, or the
sun as 8 light-minutes away, and thought "what
is this nonsense? measuring distances with
time?"
But actually, we measure distances using time
almost every day. How far is it from your
house to the store? About ten minutes. And
how far is it from New York to Boston? About
four hours. Los Angeles to Sydney? 14 hours.
But of course, what we really mean is that
the store is ten bike-minutes from your house,
New York is 4 car-hours from Boston, and Sydney
is 14 plane-hours from LA. In fact, using
time to measure distances is so useful that
I only know the distance from LA to Sydney
in plane-hours, not miles or kilometers…
though I suppose I could figure it out by
multiplying 14 plane-hours by the 550-miles-per-hour
speed of a plane to get roughly 7500 miles.
But Sydney is also 5 sailboat-weeks from LA,
7 humpback-whale months from LA, 5 message-in-a-bottle
years from LA, and 0.04 light-seconds from
LA. On the other hand, the moon is 18 airplane-days
away, 6 car-months away, and 15 whale-years
away. Which means, in fact, that a whale might
swim as far as the distance to the moon over
the course of its lifetime .
And if that's not crazy enough, sometimes
we even measure times in distance! How long
is a movie? 8,000 feet – of film! And MinutePhysics?
30 meters.