Can you call it an observation if the lens you are using may be faulty?
If you use many lenses you can assure yourself that they are not all faulty in the same way. This is why we can safely say that dark matter is observed fact, because we observe it in so many different ways.
If you use many lenses you can assure yourself that they are not all faulty in the same way. This is why we can safely say that dark matter is observed fact, because we observe it in so many different ways.