Cassius Here's that¹
Godfrey I have taken the easy way out, haven't I.
The place to begin here is in separating the content of the claim from the sensation of the claimant. I am far from denying the mystical experience as a sensation. If you experienced something incredible while you were on acid, my explanation will be simple; that's the sensation the brain experiences while on acid. The sensation is genuine. But the "vision", far from imparting something intelligible, merely reveals the physical nature of the mind (or 'soul', if we prefer). Consciousness emerges from the neurochemistry of the brain. All we had to do to alter the mind, was to alter the neurochemistry.
When neurologists scan the brains of accomplished Buddhist monks in meditation, they see interesting things. Unusual patterns of activity, suggesting that these practitioners are able to exploit neuroplasticity² so that compassion is their native response rather than fear, contempt, ego, etc.
This is good news for the practice of philosophy as a contemplative tradition, But it isn't evidence in support of other Buddhist claims, like karma and rebirth, the six realms, or nirvana.
I hope that clarifies my position somewhat. I have to go work now!
-josh
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¹https://founders.archives.gov/documents/Jefferson/03-10-02-0167