The only way we as humans can examine the universe is through our brains.
There’s nothing we can do about it. All senses and experiences are taken in by or bodies and interpreted in our minds. We can not know of anything that our minds can't take in.
For example if we were all blind and no humans had eyes and the part of the brain that interprets vision we would have no concept of seeing or even the existence of light.
This creates a problem, how can we know whether things exist outside of our senses. We are not talking of ultra sonic sound or x-ray vision as we can detect these using instruments than measure them and convert them into properties that we can personally measure so you for example have a display on a screen .
But are there properties of nature that are unknown and cant presently be measured.
So could such things as a spirit world exist and just be outside of our present detection abilities?
How could we establish its existence? Why should we try?
Well significant numbers of people have claimed to have been contacted by the spirit world. By God , angels , spirits , ghosts and other phenomenon.
The number of people involved and it effects on the world (Christianity etc) suggest that we should at least take these claims seriously.( not that we should believe them just at least take them into account)
Can we then establish whether these people are lying or they are misinterpreting normal events.
To know whether they are lying we could subject them to a lie detector test.
I whish this could be arranged but some such as Jesus and Moses are long dead.
To find if they are misinterpreting events we could try to find if whether a certain part of the brain is stimulated a human will experience visions , this would give evidence that a brain malfunction could give rise to visions in normal people and should not be interpreted as anything unusual.
This has been done and a certain part at the front of the Brain can when stimulated give rise to “religious euphoria” (Phantoms in the Brain by V.S.Ramachandran)
The trouble is that even if a part of the brain does this that does not mean a vision had to be a malfunction of the brain. Why?
Well we all dream at night the fact that we can see things in our head does not mean our vision when awake is not real. Also how would we know that visitors from a spirit world do not use this part of the brain in order to communicate?
Perhaps then we should just use or knowledge of how the known universe works and see if we need unknown forces to explain events.
Well this would suggest that a God isn’t needed to make animals and planets as this can be explained by known mechanisms. But it still doesn’t tell us whether any sprit world exists only that we don’t “need” it to explain life on this earth.
Maybe we will never be able to prove or disprove the existences of spirits and ghosts.
Perhaps the only people who know are those that have seen them.
But can we trust them?
So is there a fail safe way of knowing whether people who claim visits from spirits are telling the truth and have understood what has happened to them correctly?