The subtle bodies reside in astral/mental/causal planes of reality which are in dimensions beyond our familiar three-dimensions (4th, 5th, ?) hence invisible to our physical senses and instruments.
What is an astral/mental/causal plane? How and why are you positing it's existence?
And if such things are
undetectable, then how do we know they are there?
What I had asked was how do we know souls exist, and how can we tell if they go somewhere. I mean, if we can't detect them in the first place, how can we say they're going anywhere or doing anything at all?
Our only way of knowing is by experiencing through the subtle bodies (as in Near Death Experiences and out-of-body experiences). Maybe in the next generation science will be able to peer into other dimensions.
Most of the matter in the universe is not directly detectable at this time.
How have you determined that a "near death experience" involves a soul leaving a body if you can't detect a soul in the first place? In other words, how have you drawn a conclusion about something that you can't detect or demonstrate?
My grandfather's heart stopped on the operating table for a few seconds. So he, "nearly" died. I asked him if he experienced anything and he said it he experienced nothing - it was just like he was sleeping. So, did he not have a soul, or .... ?