Introduction to Philosophy/Mystical Experience
Mystical experience as a proof for the existence of God has both a strong element in its favor and a strong weakness against it. Traditionally the mystical experience involves a realization of the One being all, and the All being one. This is a pantheistic view of 'God', i.e. that God is all and all is God. This believe is most common in Eastern religions, such as Hinduism and Taoism, is common among New Age spirituality, and has inconsistently been held by some who claim to be theists.
Mystical expereince as evidence for the existence of God has as its strongest argument in its favor the effects upon the person who claims such things. However, according to atheist Andre Comte-Sponville, the mystical experience as defined above can be experienced without belief in God. Compt-Sponville gave account of his mystical experience of all being one and one being all, himself included i the oneness, while he and his friends were walking the the woods one night. The conversation slowing came to end, his mind became empty, and the happy, peaceful experience overcame him for a short while until he began to think again (The Little Book of Atheist Spirituality,155-159).
There is another religious experience that is different from an ineffable mystical experience. The religious experience that is called conversion. Often more theistic, although not limited to theism, conversion stories are generally remarkable and undeniable. St. Paul's conversion from persecutor to Church proclamator as recorded in the New Testament book of Acts, chapter nine, can be seen as an archetype of other such conversion stories of individuals who have met "God" and had their lives forever changed by such a meeting.
The strongest element against such proof of God's existence is how extremely subjective this type of evidence is. Only Paul saw the vision he claimed he did; but even though the men with him saw no one, they, too, heard the voice (Acts 9:7). Was he delusional? Experiencing a psychotic break brought on by religious zeal? Or did he have an encounter with the Most Divine Being of the Universe?
For the believer, the answer is the former. For the non-convinced skeptic, the answer might be the latter. For both the question is still begged: is there a God, and is there some kind of objective substaniation beyond the mere ancedotal to support such a claim?