What's the difference between 慢慢 and 渐渐？ what's the difference between 慢慢 and 渐渐？

For example why can you use 慢慢 here，but not 渐渐？
ex） 你慢慢吃吧，别着急！
慢慢means slowly, 渐渐 means gradually.

you said 你可以慢慢吃 = you can eat slowly.
but not 你可以渐渐吃 = you can eat gradually.