[AndrewC]

A quanta can be measured "directly".

Sure, ever heard of the photoelectric effect? Einstein got a Nobel Prize for the discovery of the law.

[js1138]

If it were a direct measurement, it would not have taken Einstein to notice it. Einstein did not measyre anything. He constructed a theory to explain a measured phenomenon. It remains a construct.

[donh]

Sure, ever heard of the photoelectric effect? Einstein got a Nobel Prize for the discovery of the law.

You consider that a direct measurement? With which of your senses do you detect that light comes in individual quanta?