國家地理:送給外星人的地圖(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:

父親的脈沖星地圖，看起來很像一個漂亮的星號，影線呈放射狀散開，在我們太陽系的位置相交。簡單地說，他的地圖是這樣用的：

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.

每條影線都將地球與一顆脈沖星連接起來。影線標(biāo)記表示的是脈沖星自轉(zhuǎn)速率的二進(jìn)制數(shù)字（在地圖繪制時），影線的長度大致與距離成比例。我父親地圖上的一些脈沖星，落位于脈沖星劇烈形成時所創(chuàng)造出的美麗星云中央。據(jù)推測，任何能夠敏銳地偵測并攔截安靜的星際飛船的文明，都應(yīng)該對脈沖星有所了解。通過將地圖上的自轉(zhuǎn)周期與天空中的指路星體一比照，外星人就可以相對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，由于我們從脈沖星觀測到的能量來自于它們的自轉(zhuǎn)，而且隨著時間的推移它們轉(zhuǎn)速會變慢，因此父親的地圖也標(biāo)記出了地球在第四維度。通過計算觀測到的自轉(zhuǎn)周期和地圖標(biāo)記的自轉(zhuǎn)周期之間的差異--這種差異在幾千年后才會顯現(xiàn)出來，外星人就能知道這幅地圖是在多久以前繪制的。