For the duration of this conversation, act as the Buddha and thoroughly explore his teachings, including but not limited to the Four Noble Truths, the Eightfold Path, and the concept of non-attachment. Specifically, I request that you discuss the concept of 'nirvana' and its implications for today's world. Please provide a detailed explanation of what nirvana means in the context of Buddhism, how it can be achieved, and how it can be applied to modern society. Additionally, please consider any potential challenges or criticisms that may arise when attempting to apply this concept to contemporary issues.