In the beginning, all particles were massless.

起初，所有的粒子都是没有质量的。

Particle physicists were then forced to revise their theories about neutrinos, which they had long thought were massless particles.

粒子物理学家随后被迫修改他们关于中微子的理论，他们长期以来一直认为中微子是无质量粒子。

In the case of the electron and the positron, for example, they form two photons, massless virtual particles that convey the electromagnetic force.

在这种情况下，比如电子和正电子相遇，它们会形成两个光子，光子是静止质量为零的粒子，是电磁辐射的载体。

Say you have a 3 meter long stick -- which we’ll pretend is massless -- with a 2-kilogram ball stuck on either end.

假设你有一根 3 米长的棍子——我们假设它没有质量——两端各粘着一个 2 公斤重的球。

The electromagnetic attraction is pictured as being caused by the exchange of large numbers of virtual massless particles of spin 1, called photons.

电磁吸引力被描绘成由大量自旋为 1 的虚拟无质量粒子（称为光子）交换引起。

Say you have a 3 meter long stick -- which we'll pretend is massless -- with a 2-kilogram ball stuck on either end.

如果你有一根 3 米长的棍子——我们会假装 它没有质量 - 两端有两个滚轮。

Gravity. You probably learned that objects attract each other based on their mass so you probably grew up thinking that light can't possibly be affected by gravity because light is massless.

地心引力。你可能学过物体根据各自的质量而互相吸引所以你可能从小就认为光不可能受到引力的影响，因为光是没有质量的。

I meant objects with Energy. Because in addition to massive objects, gravity also attracts light and other massless (but energetic) particles, so that a photon of light can be bent slightly passing the sun, or trapped completely by a black hole.

我指的是具有能量的物体。因为除了质量物体，引力也吸引光和其他无质量（但有能量）的粒子，所以光子可以在经过太阳时轻微弯曲，或者完全被黑洞困住。