What does Buddhism mean by impermanence? Since everything in the world is impermanent, how can there be a cause? Are the two contradictory?

Impermanence is one of the three major dharma seals of Buddhism, and "all actions are impermanent".

Buddhism says that "the origin is empty", because all phenomena in the world are born from the combination of karma, so these phenomena are essentially: no one can produce their own phenomena (all laws have no self), and there is no eternal phenomenon (all actions are impermanent).

It is precisely because all phenomena in the world cannot be "spontaneous" and depend on various conditions of karma and harmony, so once these conditions disappear, these phenomena will disappear. So it's called impermanence.

Karma is actually a philosophical causal relationship, and materialism also recognizes the causal relationship between everything.

Simply put, there is no phenomenon that appears for no reason. Contact the "source of emptiness" and you will understand. It is precisely because of the origin that the combination and combination of these conditions is the cause of a phenomenon. This is the causal link.