The difference is that if the milk is added first, slowly pouring the prepared tea will gradually heat up the milk from its initial temperature to the final combined temperature. If the tea is added first, the milk will start at tea temperature and gradually cool down to the combined temperature.
Imagining a scenario where the milk starts at 0 degrees and the tea at 100 and having a 1:10 milk:tea ratio, the difference is whether the milk gradually heats up 0->90 or gradually cools down 100->90.
Thus, in one scenario the milk will experience more extreme temperatures that can "burn" it whereas in the other scenario it won't.
To me at least I'd say the difference is barely noticeable, if I had to guess I'd say that in a blind tasting I might be able to get 55% of my guesses right.
Without the gravity you don't have the (same) resulting turbulence?
I have no clue how fast the temperature equalizes or how long it takes to scorch milk at different temperatures, but I heard about this as a kid and made the following thought experiment.
If I pour the milk first and then put in a single drop of tea, the milk at the surface of the drop would receive some flash heating, then equalize pretty fast to an average of their temperatures and then as the water turbulences away the resulting temperature would barely be above that of the original milk.
If I pour the tea first and put in a single drop of milk, the relative masses would equalize the temperature of the milk to pretty close to boiling, and it's gonna require a lot of drops before the milk cools down again.
Thus the time spent at higher temperature seems longer in the latter case. Assuming it matters for things like protein breakdown, and that those changes can affect the taste, then the question becomes: how slowly do we have to pour our tea for this to matter? I suspect I don't pour anywhere near slow enough.
Imagining a scenario where the milk starts at 0 degrees and the tea at 100 and having a 1:10 milk:tea ratio, the difference is whether the milk gradually heats up 0->90 or gradually cools down 100->90.
Thus, in one scenario the milk will experience more extreme temperatures that can "burn" it whereas in the other scenario it won't.
To me at least I'd say the difference is barely noticeable, if I had to guess I'd say that in a blind tasting I might be able to get 55% of my guesses right.