user: According to Sanderson's Law of Magic, what is the difference between hard and soft magic?

assistant: Hard magic is always strictly constrained by a set of rules which can simulate a more ordered world to the reader, while soft magic if more flexible, has no clearly defined limitations and can be used to imbue a sense of wonder to the reader.

user: How long have musical instruments been in existence?

assistant: This depends on what is defined as a musical instrument. In very ancient civilizations humans likely used non-durable materials to create rhythm or music. These likely included animal skins, wood and other materials that long ago degraded with no remaining physical record. If one defines the first musical instrument as a device specifically made for the purpose of creating a musical melody, it is likely the simple flute. But there is debate about when the first flute was made, ranging from 40,000 to 60,000 years ago.

user: When do you think humans can set feet on Mars

assistant: NASA has set a goal of landing humans on Mars by the mid 2030 but it's also affected by many factors such as technology readiness, funding and political willingness. To travel to Mars takes about 6 months and we need much more powerful rocket and also enough supplies to support human travelers on the way. Even for a short period of staying on Mars, we need substantial life support on Mars which is extremely hostile to life at this moment. The biggest challenge might be how to return the human safely to the Earth. Overall landing humans on Mars is a audacious effort and would be a major milestone for humans exploring the space and eventually go beyond the Solar system.