Each of the four fundamental forces (gravity, electromagnetism, and the strong and weak nuclear forces) has a kind of theoretical knob.

四种基本力（万有引力、电磁力、强核力和弱核力）中的每一种都有一个理论上的旋钮。

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It's the least understood of all the four fundamental forces, and the weakest.

它是在四个基本力中，我们所知最少，也是最弱的力。

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However, of the four fundamental forces, gravity is by far the weakest, and it took until 2002 before gravity's quantum nature was proven.

然而，四种基本力中，引力是至今发现最弱的一个。而且直到2002年，引力的量子特性才被证明。

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However, of the four fundamental forces, gravity is by far the weakest, and it took until 2002 before gravity's quantum nature was proven.

BBC: Neutrons could test Newton's gravity and string theory