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#### 一秒有多远

How far is a second?

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?

And how far is it from New York to Boston?

Los Angeles to Sydney?
14个小时
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
14机时×550英里/时≈7500英里
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, amazingly, that a whale might swim as far as the distance to the moon

over the cost of its lifetime .

And if that’s not crazy enough, sometimes we even measure times in distance!

How long is a movie?30 meters.

8,000 feet – of film!

And MinutePhysics?30 meters.

Last video:E＝mc²

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