If u were to split a double espresso in 2 cups vs having the same espresso in a single cup. Would it taste the same ??
Just curious as with the double u have a higher layer of crema etc

If you don't stir first, it will likely taste noticeably different.

What extracts changes with time during the shot and doesn't mix well in the cup, leading to sort of a layer cake of flavors. Stirring before sipping, even if you aren't going to split, is essential practice, in my opinion. There are many reasons I prefer stirring over swirling. The lack of coffee stains on your shirt from an oops moment is convincing on its own.

Different strokes. I don't mix the layers. I like to see the evolution of the shot as I drink it, to brighter, more intense bitters and sours at first, too more sweetness at the bottom. There's no one right way to the mountain top

I think so, yes. In addition to the layering Jeff already mentioned, there's also the fact that the single shot gets down to optimal drinking temperature much quicker than the double. So, when comparing the single and the double, you're either comparing (1) two drinks that have spent the same amount of time in the cup but that are at different temperatures, or (2) two drinks at equal temperatures but having spent different amounts of time in the cup. Apples and oranges.

Cup geometry also matters, since "taste" is actually taste and smell combined. As with wine, it is useful to have most of the drinking vessel free of the drink itself. For example, my preference is to have either a single in a demitasse or a double in a cappuccino cup. A double from a demitasse smells, hence tastes, different (and, related to the above point, also gets down to optimal temperature slower).

A split doppio yields two solos that taste the same in my experience. But, the two splits don't taste at all the same as a two individually pulled solos. I nearly always pull two shots, one for my spouse. I used to do two splits into the two cups, yielding two doppios, in the interests of having the two identical and prepared simultaneously. But, that's a PITA when using a scale, so now I pull each cup individually as doppios. Frankly, we don't notice much difference.