It is not myself who calls it a science. We have always called yoga a science in India. It is called paravidya(higher science) We called it a science for a very good reason because it produces consistent, objective and replicable results. This is by definition science. If it did not produce consistent, objective and replicable results it would not be a science. This is why I am challenging your statement this is a belief or a religion, especially in light of the fact that I have provided you with the scientific evidence.
We can know not just about the material world with certainty but also the mental world. Why do you factor the mental world out as if it is insigificant? It is far from insigificant it is the most intimate and important world we know. The problem with your thinking is that you have decided to exclude a whole dimension of existence and just look at the material world in isolation as if it exists separately from our mind(big assumption) This is not a scientific attitude at all. The fact of the matter is the world of mind can be studied and investigated just as rigorously as the material world can be, and in India a lot of our research has been in this area. We have proven that it is possible to have certain knowledge of the mind and we have created the science of Yoga in order to do that.
Don’t go around telling us our sciences is not a science and your sciences are sciences. You will not make friends with us by discrediting our thousands of years of research into mind sciences. You are currently using our science and you know yourself the benefits it gives and all of that whether you like it or not is built on Hindu metaphysics. It works because our metaphysics is right.

