国家地理:送给外星人的地图(5)

Appropriately, Dad's pulsar map looks like a fancy asterisk, a radial explosion of hatched lines that intersect at our solar system's location. Briefly, here's how his map works:

父亲的脉冲星地图，看起来很像一个漂亮的星号，影线呈放射状散开，在我们太阳系的位置相交。简单地说，他的地图是这样用的：

Each of the lines connect Earth to a pulsar. The hatch marks are binary numbers that reveal the pulsar's rotation rate (at the time the map was designed), and line lengths are roughly proportional to distance. Some of the pulsars parked on Dad's map -- for example, the Crab and Vela -- sit in the centers of beautiful nebulae created during the pulsars' violent formations. Presumably, any civilizations sharp enough to detect and snare a quiet interstellar spacecraft would know about pulsars. And by matching the rotation periods on the map with stellar signposts in the sky, aliens could find their way to Earth relatively easily.

每条影线都将地球与一颗脉冲星连接起来。影线标记表示的是脉冲星自转速率的二进制数字（在地图绘制时），影线的长度大致与距离成比例。我父亲地图上的一些脉冲星，落位于脉冲星剧烈形成时所创造出的美丽星云中央。据推测，任何能够敏锐地侦测并拦截安静的星际飞船的文明，都应该对脉冲星有所了解。通过将地图上的自转周期与天空中的指路星体一比照，外星人就可以相对容易地找到通往地球的路。

In addition, because the energy we see from pulsars comes from their spin and they slow down over time, Dad's map also points to Earth in the fourth dimension. By calculating the difference between the observed and coded rotation periods -- a difference that will be apparent after thousands of years -- aliens could figure out how long ago the map was made.

此外，由于我们从脉冲星观测到的能量来自于它们的自转，而且随着时间的推移它们转速会变慢，因此父亲的地图也标记出了地球在第四维度。通过计算观测到的自转周期和地图标记的自转周期之间的差异--这种差异在几千年后才会显现出来，外星人就能知道这幅地图是在多久以前绘制的。