Are you saying if we can't sense something to be able to corroborate its existence through physical scientific means that it does not exist? If so, this was not true in the past and for some things, I expect is not true now, for other things may not be true for thousands and thousands of years to come, until we advance enough to be able to do so.
Almost was saying that, but not exactly. Scientific means are not necessarily needed. I guess I was saying, everything is possible in imagination, not so in the real world, in a round about way.
At it's simplest---
There are two kinds of human thoughts:
Those that handle the physical that does exist and...
those that handle the non-physical that is fiction that doesn't exist.
Here are things that we perceive, along with their description, which are physical or exist in reality:
Because we can touch them, material objects are physical, and exist in reality. In conjunction with that reality that does exist outside our minds, we make crystal clear mental images of material objects within our minds. And in return we can describe them.
In the real world, there is the phenomenon of gravitation; occurring outside our minds, gravitation is a live entity in a manner of speaking; as such gravitation is physical yet unlike material objects gravitation is non-material.
Even though one cannot touch gravitation as one does material objects, and even though gravitation acts out of immaterial space, because gravitation makes objects fall, gravitation is physical. Similarly even though one cannot grab them with one's hands, light rays are physical because they have a physical effect, light rays from the sun heat up our skin.
Both gravitation and light rays, even though non material, are physical and do exist or occur in reality because they act on matter; we clearly perceive their respective effects with our body; and in return we are able to concisely describe these effects. Our perceptions of and then our descriptions of gravitation and light rays corroborate their physical existence.
Even though we have no idea what matter, gravitation and light rays are (in reality), and even though our human interpretations of these things are only ideas (concepts and pictures) we know that these ideas do coincide to real things. We can touch matter, gravitation makes an object fall and light from the sun heats our skin.
This all brings up a story that I love to this day---so will share it as follows:
If you are looking for the key to the universe,
I have good news and bad news.
The bad news is there is no key to the universe.
The good news is it has been left unlocked!