thanks friends, and yep, single malt is indeed the water of life. And Evan, consider me as arguing

so make me see what you think yourself seeing. Ah well. might have been a little too hasty, let's call it 'inspired'

. It depends on how you define it, mathematically or, let's call it, astronomically. Would our Omar be that famous Persian poet Bill? Anyway, you can use manifolds, but when I try to translate that into the way I observe dimensions, those we measure normally, a dimension of 2.5 becomes hard to imagine. But it might also be a question of what makes dimensions? I want to define a universe from a local 'point', and it is with that as with a Big Bang, also defined from 'local points' as I read it. You won't find a origin in some singular center, but you do have a accelerating expansion everywhere, which if you turn it around, in my thoughts can be defined as happening in each point, counteracted by gravity (as well as the other four, well three then, forces.)

Doing that the next step then becomes to ask what makes the 'dimensions' we measure. There Pete's definition suits me perfectly. We define those by the amount of coordinates we need to agree on a position, in time and 'space'.

(there is a subtlety to that one, depending on if you want the exact same answer, relatively speaking. Generally speaking though it doesn't matter if our clocks differ for this, as long as we agree on the same amount of coordinates needed.)

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You can think of it this way, as a set of points, each point a center of your locally described universe, meaning all other 'points' you observe. Translated into relativistic terms it's always 'your local clock and ruler' defining it. To that one then need to add some principle allowing points to casually coexist. Maybe that can allow 2.5 dimensions to exist? It depends on what you mean by it, and how you will prove it.