I love the title of this blog post, because it is such a damn fine question. During the thirteen years this Church of the Churchless blog has existed, I'd say that this question has been at the root of more posts and comments than any other existential issue.
After all, consider how relatively easy it is to assess the validity of (1) objective experiences of physical reality, and (2) subjective experiences of physical reality.
As an example of (1), if someone claims that they saw a giraffe in their back yard, we've got to consider the circumstances. Perhaps they live in a part of rural Africa where giraffes are common. We'd then give some provisional credence to their claim, though it would be nice to have a photo of the animal, or at least of its footprints (chewed leaves high up on a tree would be additional evidence).
However, if the person lives in New York City, we'd be a lot more skeptical. Sure, it's possible that a giraffe escaped from a zoo or circus. This is very unlikely, though. If a photo of a giraffe in their back yard was provided as proof, we'd want to make sure that it wasn't photoshopped.
My point is that experiences of objective physical reality fall into an intersubjective realm.
Most people have the basic five senses: sight, hearing, taste, touch, smell. Our individual sensory experiences certainly differ -- some can see or hear better than others, and wine tasters are said to be able to distinguish more tastes than the average person -- but by and large, if someone makes a claim about having some sensory experience of the physical world, there are ways to confirm how valid this claim is.
An astronomer who claims to have discovered an unknown planet in the far reaches of our solar system would need to provide some solid objective evidence that the planet actually exists in objective reality.
Moving to (2), on the other hand, purely subjective claims really can't be challenged. If we both see the same movie in a theatre, our experience of the objective images/sounds on the screen will be very similar, but our subjective reaction to the movie may be very different.
"I hated that film." "What? You must be kidding. I loved it!" "No, I really hated it."
Absent some form of sophisticated brain imaging, and maybe not even then, it is usually impossible to know whether someone is truthfully relating a subjective experience. Maybe my movie-watching companion actually liked the film, and is saying she hated it for some unknown reason.
My point here is that usually we take at face value claims about subjective experiences.
If someone tells me they felt at one with the universe after hiking to the top of a coastal mountain and seeing the sun set over the ocean, I'm not going to feel any inclination to challenge that assertion.
Ditto if they went to a Taylor Swift concert and said it was a life-changing experience. "Great," I'd reply, thinking to myself, I doubt this would have been my reaction, but everybody's different.
So now we get to the tricky question.
Objective physical reality really isn't very different for different people. Mostly we experience the objective world in similar ways. If this wasn't the case, intersections with red, green, and yellow lights would be filled with crashes, rather than with drivers almost always reacting to the same sensory inputs in a predictable fashion.
And I think we'd all agree that subjective reality is the opposite -- different people have different subjective experiences of the world. Now, since no one has access to any other person's subjectivity, we have to infer this. However, all of our relationships with people lead us to recognize that they typically view the world much differently than we do.
What's perplexing is when someone claims to have had a subjective experience of an objective supernatural reality. (And believe me, this happens frequently in comments on my blog posts, so I'm almost perpetually perplexed.)
My main reaction to this sort of claim is to echo the oft-heard phrase, "Extraordinary claims demand extraordinary evidence."
Look, if someone says they have discovered some new aspect of physical reality, this is a really big deal. A new subatomic particle. A new planet. A new species. A new tribe (in the 1950s this was common to see in National Geographic; now, very rare).
Solid intersubjective proof would have to be provided of the claim. This is how science works. Also, everyday life. We don't believe that someone saw a space alien, Bigfoot, or the Loch Ness monster just because they said they did.
However, if someone takes LSD, or meditates intensively for years in a dark room, then claims to have had a marvelous epiphany of what the cosmos is all about -- nirvana! enlightenment! satori! -- I'm got no interest in talking them out of that claim.
How could I?
I had many LSD and other psychedelic "trips" in my college years. They basically were indescribable. I can say "walls melted into flowing colors," but those words don't begin to capture my memory of an LSD experience. And here's the important thing:
I'm not claiming that my subjective psychedelic experiences were of some objective reality. I had a unique experience of the world, but this was the same world that a "straight" companion would have experienced -- aside from purely internal non-sensory drug-induced experiences.
So when I hear that a person claims to have subjectively experienced a supernatural level of objective reality, my skeptical sensors go on full alert. I used to believe this was possible, but I've come to recognize the difference between believing and knowing.
Someone may be fully convinced that they've had an experience of a higher non-physical realm of reality. But without intersubjective evidence needed for knowledge, this claim should be viewed skeptically -- even by themselves.
I've meditated almost every day for over 45 years. For a long time I'd meditate for several hours in a dark room or closet. I've seen light. I've heard sounds. I've had profound experiences. But again, I don't claim they were of an objective supernatural reality. All I know is that my subjective self experienced such and such.
Like I said, this is a perpetual theme on this blog: in a comment people will claim to have experienced X, Y, or Z through meditation, the guru's grace, God's power, or whatever.
I rarely respond to these claims.
I'm totally willing to accept that their subjective experience is real. However, this is the same as my being totally willing to believe that someone loved a Taylor Swift concert. A subjective claim doesn't require any validation. It is what it is: someone's inner experience of physical reality.
But when someone claims that they've had an inner, or subjective, experience of an unknown (to the rest of us) bit of supernatural reality, I'm not going to accept that claim without some solid demonstrable evidence.
Objective reality seemingly should come with some objective attributes, even if these are far removed from everyday physical reality. I accept the evidence for a quantum realm, even though quantum phenomena behave very differently from things in everyday reality.
Scientists can show us the effects of the quantum realm, even though it can't be directly experienced by our senses. Most of our modern technology is based on quantum mechanics, so when my iPhone works, that's proof enough for me.
Where, though, is there any solid evidence of a supernatural realm? Short answer: there isn't any.
No one who claims to have experienced such a realm returns with miraculous powers, hitherto unknown knowledge, or anything else that points to a objective realm beyond the physical.
All we have are stories, claims, beliefs, dogmas, and such.
I've got no problem with people who say they've had an experience of divinity. My problem is with people who want me, and others, to accept that their personal experience was of some objective reality.