[Planck] said instead [of possibility that amount of radiation could have just any value] that radiation came… — Stephen W. Hawking

[Planck] said instead [of possibility that amount of radiation could have just any value] that radiation came only in packets or quanta of a certain size. It is a bit like saying that you can't buy sugar loose in the supermarket, it has to be in kilogram bags.

p. 92Source: Wikiquote · CC BY-SA 4.0