translation.en: You can't see light. When it's dark, in a vacuum, if a person shines a beam of light straight across your eyes, you won't see it. Slightly technical, some physicists will disagree with this.
translation.zh: 你不能看见光。当黑暗的情况下，在真空中， 如果有人在你的眼前正方发射出一道光， 你是不会看见的。有一点专业了，一些物理学家不会赞同这个观点。