I have been reading this thread with interest and considered many things back and forth. In my experience there IS momentariness, and it is actually taught in the suttas (dhammas are said to arise, persist and fall
). Example: Look to the left, look to the right. You have just witnessed momentariness of seeing. It is empirically given to experience.
The only thing is that it should not be abstracted into zero-length or "trillions cittas per second
" which are not empirical truth, unless it is actually experienced. As you are reading, the consciousness state changes with every letter, word, sentence. Consciousness is always consciousness of something, and it changes with its object - in this case letters, words, sentences. We do not live in some frozen state where nothing changes. If nothing would change, then you would never finish this sentence after starting to read it. IMHO,
"Known to him they arose, known to him they remained, known to him they subsided. He discerned, 'So this is how these qualities, not having been, come into play. Having been, they vanish
.' " - http://www.accesstoinsight.org/tipitaka ... .than.html
Maybe the number 10^21 of cittas per second should be taken metaphorically just like number "500" is metaphoric meaning "a lot". Indians were not precise with numbers like us, and unintended literalism for people removed from that time and culture can lead to hair splitting discussions such as these.