萬物簡史 第50期:事物的測定(8)

　　At Principia's heart were Newton's three laws ofmotion (which state, very baldly, that a thing movesin the direction in which it is pushed; that it will keepmoving in a straight line until some other force actsto slow or deflect it; and that every action has anopposite and equal reaction) and his universal lawof gravitation. This states that every object in theuniverse exerts a tug on every other. It may notseem like it, but as you sit here now you are pullingeverything around you—walls, ceiling, lamp, pet cat—toward you with your own little (indeed, very little)gravitational field. And these things are also pulling on you.

　　《原理》的核心是牛頓的三大運動定律(定律非常明確地指出，物體朝著推力的方向運動;它始終做直線運動，直到某種別的力起了作用，使它慢下來或改變它的方向;每個作用都有相等的反作用)以及他的萬有引力定律。這說明，宇宙里的每個物體都吸引每個別的物體。這似乎不大可能，但當(dāng)你在這里坐著的時候，你在用你自己小小的(的確很小)引力場吸引你周圍的一切事物--墻壁、天花板、燈、寵物貓。而這些東西也在吸引你。

　　It was Newton who realized that the pull of any two objects is, to quote Feynman again, "proportional to the mass of each and varies inversely as the square of the distance betweenthem." Put another way, if you double the distance between two objects, the attraction betweenthem becomes four times weaker. This can be expressed with the formula F = Gmm/R^2

　　which is of course way beyond anything that most of us could make practical use of, but at leastwe can appreciate that it is elegantly compact. A couple of brief multiplications, a simpledivision, and, bingo, you know your gravitational position wherever you go. It was the firstreally universal law of nature ever propounded by a human mind, which is why Newton isregarded with such universal esteem.

　　是牛頓認(rèn)識到，任何兩個物體的引力，再用費曼的話來說，“與每個物體的質(zhì)量成正比，以兩者之間距離的平方反比來變化”。換一種說法，要是你將兩個物體之間的距離翻一番，兩者之間的引力就弱4倍。這可以用下面的公式來表示： F=Gmm/(R^2) 這個公式對我們大多數(shù)人來說當(dāng)然是根本沒有實際用途的，但至少我們欣賞它的優(yōu)美，它的簡潔。無論你走到哪里，只要做兩個快速的乘法，一個簡單的除法，嘿，你就知道你的引力狀況。這是人類提出的第一個真正有普遍意義的自然定律，也是牛頓到處深受人們尊敬的原因。