How does nature appear to react to unnatural deeds in "Macbeth"?
In the Elizabethan time period, in which Shakespeare wrote Macbeth, there was an idea that if there was a disturbance of one realm (nature, government, etc.), then disturbances would follow in all realms. When Macbeth murders his king and friend Duncan, he commits an unnatural act. Nature follows by exhibiting several strange phenomena.
After Duncan's murder, in act 2, scene 4, we learn of many of the other unnatural occurrences of the night. An old man tells Ross that an owl killed a falcon, which is strange because falcons are more powerful and higher on the food chain. This shows that nature is not acting according to its usual laws. Ross describes the way that darkness has continued to cloak the world despite the hour indicating it should be daytime. Most dramatically, we hear that Duncan's horses have revolted and broken out of their stable. What's more, they have eaten each other. This is an extremely strange and unnatural act, which can only be explained by the unnatural murder that Macbeth has just committed.
People in Shakespeare's day believed in a concept known as the Chain of Being, an idea in which all of live is connected with God at the top of the chain and nature at the bottom. The king is directly below God in this chain, and because the king is killed, the natural order is disturbed, so all of the Chain suffers, even nature.
Six strange events occur in nature in response to Duncan's murder. In Act 2, scene 3, Lennox tells us that chimneys are blown down from unusually strong winds, strange "screams of death" as well as the owl's cries are heard throughout the night, and there was an earthquake. Later, in scene 4 in a conversation between Ross and the Old Man, we learn that an eclipse has occurred, an owl has killed a falcon, and Duncan's horses have gone wild, broken out of their stalls and eaten each other. All of these events are a direct result of the king's death.
For more information about the Chain of Being, check the first link below.