The largest double-slit projectile I know of is C-60, a soccer-ball shaped molecule of sixty atoms.

https://iopscience.iop.org/article/10.1088/2058-7058/12/11/4

That website's captcha is horrible!

Or amazing.

I got cats with sunglasses

Me too. And I had to click on bird legs to verify o_O

Wiki, citation 19

> The largest entities for which the double-slit experiment has been performed were molecules that each comprised 2000 atoms (whose total mass was 25,000 atomic mass units).[19]

https://en.m.wikipedia.org/wiki/Double-slit_experiment

If the slits are big enough, isn’t that just gravity?

And Why can't gravity serve as an observer?!

The electron/proton entering a slit is affected by gravity!

The entanglement theory would imply that if you build a detector that turns the gravity interaction into a finite piece of data observable by an (amplified) system, then gravity will act as an observer and collapse the waveform when it reaches that point. That's my take on the whole thing... It's almost like information theory. If the information is lost to the sands of time (below noise floor if you will) then the entanglement can continue.

From my recollection of Hawking - it’s the energy of light that disturbs the particle being measured thus confounding the measurement

Presumably a gravity based detector would have similar issues as these particles are affected by gravity (as can be seen around black holes)

I don’t know what it’s called but I read about a proposed experiment to do it in space with macrosized glass beads.