When somebody is demanding a proof in support of the yoga teaching, the immediate response is a question what kind of evidence can be presented in the subjective psychological domain where we are dealing with states of consciousness that do not lend themselves to quantification and measurement. If it is a testimony of one’s own personal experience as in autoethnography, which is acceptable now, then there is enough evidence that states of consciousness exist that transcend the normal workings of the human mind. These states of consciousness and their objective effects have been the subject of studies all over the world since the sixties with promising results.
Secondly, there is enough empirical evidence that different forms of yoga help their individual practitioners in ways that we may not fully understand. Yogis speak about subtle laws and transactions of consciousness and energy that takes place behind our tangible observable behaviours observable by the senses as presently organised in the human body. However mysterious it may sound, it is not beyond the scope of logical possibility that there may be other and different types of sense organisation that may glimpse the forces behind the normal sense notations. Just as the animal senses the world differently, just as each human being brings his own perspective that colours the world as it reflects within his own consciousness, so too the yogi climbs beyond the limits of our ordinary perception and discovers realities behind and beyond our normal range.
Are they false evidence just because the average normal humanity does not experience it? Well, he would if he undertook the experiment that the yogi engages in, the experiment of transcending the human formula, of course if he fulfils the conditions of the particular yoga. This is only reasonable since every experiment needs certain conditions and even when all conditions. So, if we take it that direct experience is the only valid evidence in the psychological field then the only way to prove or ‘disprove’ would be to sincerely undertake the experiment and find it out for oneself. That at least is a fair enough requirement from a strictly scientific point of view. The fact that most yoga practitioners who sincerely undertake the yogic journey do experience some change in their consciousness, of varying degrees, which is why they continue to hold on. This is also the reason why yoga has never died unlike religions and belief systems since it is a science that asks us to engage and participate and not accept anything merely as a belief. Though it is unfair to use the methods used in physical sciences to the psychological operations, yet whatever scientific studies have been done till date using different paradigms have shown positive and promising results.
If all this is not evidence enough then I am not sure what exactly is meant by evidence. Yoga, unlike a belief system, is practicable, observable, with its results replicable. But the scientist has to undertake the journey first himself making his own inner field the laboratory of evolution through yoga. Most are not ready to undertake this journey and pass their judgments on a priori denials and ideological beliefs and under the spell of scientific dogmas like the adherents of any religion. Well naturally they do not find any evidence. The blind does not see the sun nor the ape understand the man though the two appear similar in certain ways. But their lack of vision and understanding is not a proof that either does not exist. As to majority, the beliefs of majority has often contradicted scientific evidence and there still people who believe that earth is flat. There are also people who combine an intuitive sense to fill in gaps of understanding and accept evolution as valid though the strictest scientific evidence may be missing like the missing links. Yet we do not discard it as fiction. So too with yoga.
We have the right to ignore the yogic knowledge provided we have put in our efforts in that direction to understand its processes through direct personal application. If not then both science and humility demand that we stay within the boundaries of our ignorance and leave others to follow their faith and see where it leads them. To each his own faith, whether it be a faith in science and its methods, a faith in yoga and its methods, or both.