grammar - What are the differences between 広める and 広げる and between 広まる and 広がる?

I find the difference between 「広める (他動詞) 広げる (他動詞)」 and between 「広まる (自動詞) 広がる (自動詞)」 to be complicated.

Can someone explain?

Answer

The 大辞泉 entry for 広がる explains the difference between 広がる and 広まる in the 「用法」 section:

大辞泉：広がる

To paraphrase, 広がる describes something spreading out naturally, like a scenic view or a wildfire, whereas 広まる describes something spreading as the result of an intentional attempt to spread it.

広がる also has the meaning of physically opening up or being unfolded.