but it's not invisible if we mean definition No. 2 can't be sensed. Can't be observed.

但如果取第二个定义它就不再无形2,无法感知，不能观察。

耶鲁公开课 - 死亡课程节选

for he meant actually that we will never observe gravitational waves.

他的意思其实是我们永远无法观察引力波。

以爱因斯坦为榜样 - SpeakingMax英语口语达人

And the question for the theorist is to show how this two can be combined should be combined and how with sensitivity to both You can perceive things that you don't otherwise.

理论家面临的问题,就是要展示这两者是能够相结合的,应该结合起来，结合时要考虑到二者的感受,你除此之外无法观察到事物。

麻省理工公开课 - 电影哲学课程节选

They are not observable.

是无法观察到的。

耶鲁公开课 - 死亡课程节选

So I haven't really imagined the world in which I no longer exist, a world in which I'm dead, a world in which I'm incapable of thought and observation.

所以我并没有真正,想想自己不存在的世界，自己死后的世界，一个我无法再思考和观察的世界。

耶鲁公开课 - 死亡课程节选

We don't directly observe souls with our five senses.

我们无法通过五感直接观察到灵魂

耶鲁公开课 - 死亡课程节选