Difference between 'now and then' and 'again and again'

Question

What is the difference between these phrases?

1. now and then
2. again and again

Can they be used interchangeably?

Answer 1

Now and then is used to describe something that happens sometimes.

With again and again, you emphasize that something happens repeatedly. An alternative would be over and over again.

They cannot be used interchangeably - in fact, they feel more like antonyms (opposites of each other).

Answer 2

'Now and then' implies that it happens occasionally and at irregular intervals. 'Again and again' implies that it's happening a lot.