Originally posted by: RichardE
The only ways to measure radiation accurately are with devices we made. So nothing natural. I could receive some radiation and be fine and never have any real issues from it besides perhaps cancer in 30 years.
One of the great pillars of human advancement is the fact we do not just rely on our senses but on our intelligence. We succeeded as a race because our brains are self aware and are intelligent enough to come up with devices to use that our senses or bodies fail in.
I guess where I am going with this, is you don't know. If the theory of time as a dimension is true, it should be possible for some people to be aware of it and perhaps be able to predict the future, it would be the same as a 2D character being self aware of a third dimension that he never experienced. I personally don't believe it exists, but that is not to say it is not possible.
But without devices, then the measurement of the mysterious, invisible "radiation" is that, "Something about this glowing rock kills people in 30 years. We'll say that this rock emits 30 Invisideaths."
There you go, you've got a quantified measurement of radiation.
Right back to inadequacies in a human's natural senses. But if something does affect us, we find a way to measure it, whether it be in "meters" or "invisideaths."
"Psychics" rely on these inadequacies, in accordance with the way people think, to make them see patterns and coincidences where none truly exist. Kind of like how you can see a rabbit in a cloud, or heck,
look at this clustering of dots on your screen.. Just a bunch of dots, right? Not to your brain, because you know to look for a certain pattern.
Psychics, magicians - same thing. A psychic can make a series of vague predictions, and you fill in the missing pieces from your own knowledge, and it is intended that this gives the psychic the appearance of clairvoyance.
And your 2D character - fine, maybe he is aware of this "third dimension." But his world, and his body, are only capable of interacting with a 2 dimensional reality. How would he even describe it to anyone else? There are no words for "up" or "down" in his society, or anywhere in his reality. How would his mind even truly be able to "see" what this place looks like?
In the book Flatland, they described, what was it, a sphere? It was entering through Flatland from "above." To the Flatlanders, it appeared as though a dot appeared in the room, grew to a circle, shrank to a dot, and then vanished.
They couldn't explain how it happened, but they could certainly sense it
somehow, and measure it.
Therein may lie some of the controversy here - the word "sense." Sense need not be one of the 5 you know of. In the example of radiation, and you dying of radiation poisoning (we shall remember your noble sacrifice

), you acted as a sensor, in rather the same way that a fuse acts as a sensor of excessive current through a circuit. You didn't "feel" anything while you were being irradiated, but your death certainly created a data point.
Sure, there are things out there that our technology cannot measure directly yet. For a time, it wasn't possible to directly measure ultraviolet irradiation from sunlight, with say, some kind of spectrograph. But you could measure its effects by how much sunburn you got.
The whole point of this is to say that, if something can affect us (or our surroundings) in any way, that affect in and of itself is a means by which to measure that "something." If something can't affect us, then it can't be measured, and on the same note, if something
can't affect us, does it really matter at all?