question: Write a brief explanation of two string theory concepts that challenge traditional quantum gravity theories. Your explanation should contain three highlighted sections using asterisks, and your response should be in English.
answer: String theory proposes radical concepts that challenge traditional quantum gravity theories by suggesting a novel framework for understanding the universe. One such concept is the notion of *extra dimensions*. Unlike the familiar three spatial dimensions, string theory posits that there are additional dimensions that are compactified and not directly observable. This idea challenges the conventional quantum gravity view which operates within the confines of our observable dimensions. 
  
  Another intriguing concept is the *holographic principle*. This principle suggests that all the information contained within a volume of space can be represented as a theory located on the boundary of that space, effectively reducing the dimensionality needed to describe the universe. This is a profound departure from traditional theories that assume all physical processes occur within the volume itself.
  
  Finally, string theory introduces the concept of *dualities*, which are relationships that reveal how different string theories are interconnected and can be transformed into one another. These dualities challenge the traditional view by showing that seemingly distinct physical theories may actually be equivalent under certain conditions, providing a unified approach to quantum gravity.