The oldest light we can see comes from when the Universe was just 380,000 years old. On its way to us, this light is distorted by things in between, such as hot gas, gravitational fields, magnetic fields etc. If we pin down the nature of these distortions we can do two things:
- Reverse their effect and actually take a look at the very early universe.
- Describe the "stuff in-between" and make predictions about how they have evolved in cosmic time.