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In the double slit experiment (using single electrons/photons fired one at a time), I wonder what pattern would be displayed on the backboard if it was conducted without any observation at all during or subsequent to the event. Perhaps there is nothing on the backboard at all although we can never know or for that matter nobody can ever know

That's a good question - because it can tip you off to the nature of QM.

If you could somehow manage to detect the fact that the screen was struck by a photon or electron, but kept the location of the strike completely unmeasured and unrecorded, then there would be no precise screen location where the strike occurred.

It can get a lot wilder than that. If you witnessed the pattern on the screen, but then you, the screen, and all recordings of the event then dropped past the event horizon of a black hole, could someone outside the black hole claim that a pattern ever existed? This is why there is such interest in the Black Hole paradox. Allowing information to permanently "leak" from the universe would have truly profound implications.

.Scott said:

That's a good question - because it can tip you off to the nature of QM.

If you could somehow manage to detect the fact that the screen was struck by a photon or electron, but kept the location of the strike completely unmeasured and unrecorded, then there would be no precise screen location where the strike occurred.

It can get a lot wilder than that. If you witnessed the pattern on the screen, but then you, the screen, and all recordings of the event then dropped past the event horizon of a black hole, could someone outside the black hole claim that a pattern ever existed? This is why there is such interest in the Black Hole paradox. Allowing information to permanently "leak" from the universe would have truly profound implications.

I mean ...does the electron/photon exist in our reality if it isn't observed, it only ever potentially exists

ynotpup said:

I mean ...does the electron/photon exist in our reality if it isn't observed, it only ever potentially exists

Can you describe an empirical observation or experiment which would distinguish between an electron that actually "exist(s) in our reality if it isn't observed" versus one that "only ever potentially exists"? If not, you're asking a question about philosophy, not physics.