What is the difference between dark matter and dark energy?
Dark energy is a placeholder for the unknown physical mechanism by which the expansion of our universe is accelerating. On the other hand, dark matter is the stuff making up most of the mass in our galaxies. So while dark energy is responsible for things moving apart, dark matter holds things together.
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: What is the difference between dark matter and dark energy?
### Input: 
### Response: Dark energy is a placeholder for the unknown physical mechanism by which the expansion of our universe is accelerating. On the other hand, dark matter is the stuff making up most of the mass in our galaxies. So while dark energy is responsible for things moving apart, dark matter holds things together.