Manifesting has partial origins in the 19th century "New Thought" movement a reaction to Enlightenment "Mind Body" divide. The "New Thought" people thought that disease was a manifestation of problems in thinking and that the body must contain "spiritual" matter. It was one of those tangentially Christian pseudosciences.
The things is... the enlightenment notion of "Mind Body" divide is also tangentially Christian pseudoscience.
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Stay with me here! "Enlightenment thinking" is often used as short hand for "scientific thinking" -- and that it was *in its time*
The ideas of cartesian Dualism are informed by a Christian or at least Christian-Diest perspective, taking their cues from Christian ideas of the spirt/soul which can outlive us to go to Heaven.
From a contemporary scientific perspective we have no evidence of any of this either way and some of it still appears to be non-falsifiable so not really science. 3/
Dualism also causes problems in Computer Science of all places where many ideas about "uploading the mind" and AI consciousness pre-suppose a mind-body dualism.
So what about all the manifesting? Its mostly garbage HOWEVER -- it is possible to make yourself sick by thinking. (but that's not the source of most sickness) Sometimes "thinking positive" is effective. (but it is not magic) The issue is the certainty and hyperbole of these self-help gurus.
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@futurebird I don't think mind-body dualism or lack thereof really affects whether mind uploading is bunk, which it is.
The mind is a separate entity from the matter of the brain. While that means a transfer might be possible in principle, any science/tech-based method can only operate on matter, and thus can't touch the actual mind.
The mind is an emergent property of the brain. It has no existence of its own, so there's nothing for your machine to move from the brain to the computer.
@futurebird Regarding the mind-body kick you've been on: you might want to check out CS Peirce's "Four Incapacitates."