We can't see pain, but we can measure it, test it, feel it. Just like oxygen or anything else that we can't see. There is still plenty of evidence of pain, not so much of god
How do you measure pain ? Where is the National Bureau of Standard's pain calibration reference ?
Nope... pain is real, but it is purely subjective. This is why doctors & nurses have to ask patients, "on a scale of 1 to 10, how much pain do you feel ? There is no 'painometer' they can use, like there are thermometers, sphygmomanometers, weightometers (mass scales), pH meters, etc.
As humans, we 'believe' in pain; or better put, we can 'believe' in the pain of others, so we
know pain exists; because we know darn well we have felt it ourselves (on one occasion or another), but yet, there is no physical, objective way to measure pain.
There are physical, objective ways to measure distance, mass and time, and ways to measure all the physical phenomena that can be described by interactions and combination of these 3 fundamentals; but pain ? ... no, it cannot be measured.
Quote from:
https://www.researchgate.net/post/What_is_painA widely accepted scientific definition of pain is that “Pain is an unpleasant sensory and emotional experience that is associated with actual or potential tissue damage or described in such terms.” A key feature of this definition is that it goes on to say, “pain is always subjective.”