Interesting theory

all of the above & an unimaginable bunch of more on top. i reckon a universe could be folding back on itself, tapering off into the past, splitting into 3 or 100 & moving from a palpable state into an audible entirely. due to the late hour in mine i can't think of other variations atm.

Maybe don't watch Men in Black while your high?

Well there was that entire galaxy inside a trinket on Orion's belt (collar) in the Men in Black movie. Orion was a domestic cat.

Horton hears a Who?

possible, but you have to consider the Plank constant, and the Dunning -Kruger Effect

Objects are always the same size.
It's the view of the observer that makes them differ.

Here's one: whatever is "conceived" exists. Boom.

Perhaps different cosmogical constants apply to different universes, which could affect the scale of particles. Although with nothing within a particular universe to compare to the difference wouldn't be apparent, the fish tanks would be microscopic.
Within the same universe, the bending of spacetime close to a black hole etc would indeed affect scale. Whether the size of an object changed, or if it took a different amount if time for light to travel across that object would depend on the viewpoint of the observer. Though I'm now getting out of my depth!

My instinct here is that since two universes are, quite literally, entirely different universes and exist as completely separate realities, it's impossible - irrelevant, even - to say if scale might vary between them because from within one universe the other doesn't exist. Interesting question, one I'm going to be thinking over.

Ever see the end of MIB?

Yup just marble universes someone is playing with.