From Longman Dictionary of Contemporary Englishthe secrets of life/nature/the universe etcthe secrets of life/nature/the universe etcSECRETthe things no one yet knows about life, nature etc → secret
Examples from the Corpus
the secrets of life/nature/the universe etc• Nobody expects you to reveal the secrets of the universe, only produce a well-written story.• We cease trying vainly to understand the secrets of the Universe as we have hitherto tried to do. 