“复杂难懂的事物”可以用英语表达为 "complex and incomprehensible things" 或 "complicated and hard-to-understand matters"。以下为更自然的表达建议：
1、 "complex and abstruse matters"
"abstruse" 强调学术性或深奥难解，适合专业领域。
2、 "intricate and perplexing concepts"
"intricate" 指结构复杂，"perplexing" 强调令人困惑，适合抽象理论。
3、 "convoluted and bewildering phenomena"
"convoluted" 指逻辑或表达迂回，"bewildering" 突出迷惑感，适合科学或哲学现象。
使用场景示例：The mathematical theorem was so complex and abstruse that even experts struggled to grasp it.
（这个数学定理如此复杂深奥，连专家都难以理解。）
Quantum physics deals with intricate and perplexing concepts that challenge our intuition.
（量子物理学涉及复杂且令人困惑的概念，挑战着我们的直觉。）
根据语境选择词汇，可更精准地传达“复杂难懂”的层次感。