From a psychedelic perspective, that's backwards - if you start, instead, from "what are my perceptions" and try to extrapolate out, you start to find that the default assumptions assume there's a boundary somewhere - "light hits my retina so I see it" "my optic nerve sends a signal so I see it" "certain neurons fire so I see it" but there's no firm place to draw the line "this is where the light stops and where the perception begins", your body and the light are one machine, going from the big bang through the star through space through objects through your eye through your brain - there's no solid boundary between any of those things, it's one long unbroken string of causality.
Or, you're having a conversation with a friend, and you realize that all of the words, all of the concepts, the patterns of your speech, are all things that you got from somewhere else, they flow through you, from person to person, throughout history - you're not having a conversation, the conversation is having _you_
Or, you start thinking about your life and the world and you think about incredible pain you've experienced. And great beauty you've seen. And your greatest fear. And your greatest joy. And you realize - the palette of your experience has _incredible_ dynamic range, like your brain is some kind of magnificent radio and the music it plays is every perception you have - from colors and smells to the most complicated ideas are all things it can receive or transmit or something .... but who is listening?
Or any of thousands of other non-normal schemas. None of these function as scientific knowledge - they're shifts in perspective, but they don't make new predictions (or if they do, those predictions can be re-explaned back into the scientific materialist metaphor!).
And while the goal of science is to see reality as it really is, there's a default perspective to science, which is to isolate components to see how they work in a simplified context, and then to say "the complexity of reality is just like the simplicity of the simplified contexts, only without the simplification" which is a super interesting hallucination but I don't see why it's any more _correct_ than any of the other visions of complexity
That state of direct sense of universal causal connection is achievable sober. Not meditation either (though I hear thats one reliable way too). I accidentally "clicked" into it one day while thinking about the border between my skin and inanimate objects. I thought about the idea of my skin being part of me, my control of this reality, and the objects being somehow just entirely separate. It started to seem to make no sense that I can understand and feel in a deep way that my hand is mine but what it touches is something else. I then started thinking about how the hand seems like its mine, but really only seems like that because of nerves etc. connecting it to my brain. That became a thought about how I can even maintain a coherent mind across the space the brain exists in, and soon enough it clicked and I knew it. It was simultaneously a bit exciting, and profoundly calming.
I don't think I had any direct major life improvement from that realization alone however. It took psychedelics to understand how to use that perspective to snap out of anger or rise above anxious fears.
Foucault, for instance, penned this anecdote about Borges in his introduction to "The Order of Things" five years before he took acid out in death valley:
“This book first arose out of a passage in [Jorge Luis] Borges, out of the laughter that shattered, as I read the passage, all the familiar landmarks of my thought—our thought that bears the stamp of our age and our geography—breaking up all the ordered surfaces and all the planes with which we are accustomed to tame the wild profusion of existing things, and continuing long afterwards to disturb and threaten with collapse our age-old distinction between the Same and the Other. This passage quotes a ‘certain Chinese encyclopaedia’ in which it is written that ‘animals are divided into: (a) belonging to the Emperor, (b) embalmed, (c) tame, (d) suckling pigs, (e) sirens, (f) fabulous, (g) stray dogs, (h) included in the present classification, (i) frenzied, (j) innumerable, (k) drawn with a very fine camelhair brush, (l) et cetera, (m) having just broken the water pitcher, (n) that from a long way off look like flies’. In the wonderment of this taxonomy, the thing we apprehend in one great leap, the thing that, by means of the fable, is demonstrated as the exotic charm of another system of thought, is the limitation of our own, the stark impossibility of thinking that.”
Here is a six hour mathematically rigorous lecture by John Conway in which he argues either everything has free will or nothing has free will. I’m not trying to convince you everything is sentient, but to introduce some doubt in your black & white thinking. https://youtu.be/tmx2tpcdKZY
This assertion is just as unfounded as the opposite.
This is also why, it can be an effective mental health tool, because it rewires inputs and outputs and allows different parts of our brain to experience our feelings or our thoughts. Sometimes profound ideas come from it, sometime it just a bunch of dumb gibberish.
My personal experience was like this: This was nearly 30 years ago, I was 13 and invested some time in 'accidentally' meditating - I just looked at a spot on my roof for a long time. Then suddenly - wham - I literally feel a deep connection between everything I look at. The trees outside my window, the world, everything.
Let me provide an analogue. You can feel pain, yes? You can feel moving your foot? You feel your hands are part of you? Well, it was like that, only, I felt that everything was connected.
Was it just neurons firing in my head, creating a strange mode of sensations for a while? Yes. Was it devoid of deeper scientific significance? Yes. Was it profound? Hell yes.
Deeply spiritual experiences don't need to be mystical or attached to a larger theological context. They can be taken as a non-magical, psychological state of mind just like sleep or orgasm. This does not make them any less profound.
We're experiencing identical perception right now, me in the form of reading the words you wrote, and you in the form of reading these words. The words are just information which is now duplicated in both our minds. When the psychedelic "everything is connected" concept is brought up, this is what is meant. Its not some new magic that has been discovered, its realizing that the mundane everyday mechanics that allow our reality to function, are in fact quite magical, not mundane at all. But anyone can still choose to see it as mundane, its just a choice of lens.
What you're fetishising is called "Scientism". It was pretty en vogue at the end of the 18th century, and arguably led to the rise of both fascism and communism: Both schools of thought, though widely different in almost everything, wanted to rid themselves of all the "feelings" and "sentimentalities" (and jews) that felt superfluous in the coming age of machines and facts and science and progress.
There are a number of common-phrases I'll hear like "everything is connected" or "everything is alive/sentient."
However, not everything is connected, effective thinking is very much about identifying independent problems. Also I certainly don't believe everything is alive, and I certainly don't think this opinion should be held on the basis of chemicals rather than scientific data.
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Edit: And what's most disconcerting is that they seem to think these phrases "mean" something. If they said "Well, there's really no way I can articulate it, but it's changed my emotional outlook on a lot of things" then I'd be much more receptive.