To be fair - most people who are agreeing with me don't begin conversations by saying: "I absolutely disagree with you".
I was arguing with you, not with myself.
Cultural concepts are the things that exist. Father Christmas, God & ghosts do not.
Baldrick
You are being a bit silly, you know - quite childish really. I have never measured either black holes or gravity because I'm not a physicist.
Black holes? Very interesting things.
I don't think they can be detected directly yet - but they have an effect that can be measured. On gravity, apart from anything else.
A better example for you to pick would be dark matter.
The most mysterious part of the universe. Completely undetectable & physicists can't say very much about it - but it must be there because the universe couldn't exist if it wasn't.
The thing is - for science to even suspect that something is there, it has to have some kind of measurable effect.
You could prove that invisible unicorns exist, for example, if you could find their footprints. In this instance, you would neither have to see or touch the invisible unicorn, but you would see it's interaction with the ground and make a conclusion from that.
There must be some kind of interaction with something in order for us to suspect that there's something there.