You know, when I was in the Navy, I was a Drug and Alcohol Program Advisor. I was required to know about mind altering substances.
Now, when I retired from the military, I started to look into several things, one of which was shamans and oracles.
One thing that I discovered.....those that were able to "see" into the future were generally those who were astrally projecting themselves there. I started to see what all of them had in common to induce these states.
It was mind altering substances.
The Oracle at Delphi sat in a cave close to a volcanic fissure. They've discovered that those fissures had gases exiting from them that induced a psychotropic state, which is what the Oracle used to generate her prophecies.
I then looked at other places, and remembered something that I'd learned about the founder of AA, Mr. Bill Wilson. It seems that he'd discovered that the only way to cure alcoholism was to induce what he called a "spiritual experience", which resulted in a profound change in attitude and outlook. In the 1960's, he heard of the work being done by Timothy Leary with LSD, as well as the effects, and to him it sounded like what he'd been doing with the 12 Steps.
He (Bill Wilson) dropped acid 3-4 times.
I then started to look at the shaman of various tribes, and found that they did psychotropic substances as well. The Native Americans used peyote, psycilocybin and cannabis, the South American tribes used Salvia Divinorum (diviner's sage), and Ayahusca (a combination of seeds and barks from various plants), African tribes used Dagga and Yopo, and the Siberian shaman used Amantia Muscaria, which is the mushroom referred to in Alice in Wonderland.
Bottom line? All were using some type of substance to induce hallucinations so that they could pass through the barrier between reality (this dimension), and the spirit realm (the other dimension).
Additionally, not all people need to utilize substances to achieve this state. With enough practice at meditation (usually takes years to achieve), you can do the same thing sitting zazen. Incidentally, Native American shaman paid attention to people that they believed were continually in between this realm and the spirit one. It was their insane and crazy people.
Which, is why if anyone is thinking of taking substances that can alter their perception of reality, they should REALLY research things first. They might open up a gateway into a place they don't want to be.
Same thing with astral projection. Incidentally, as a protection device for when you learn to do that? I'd recommend a bracelet made of turquoise, onyx and hematite. Google the myths attached to each of those stones and you'll see why.