Aadi says longitude is counted starting from Greenwich because that is the Earth's "real middle"

Why

Aadi is treating the Prime Meridian like the equator, but the two are not the same kind of line. The equator has a natural, physical definition: it is the circle exactly halfway between the poles, and the Earth's spin decides where the poles are, so nobody could have put the equator somewhere else. Longitude has no such natural starting point — every line from pole to pole is just like every other one, so SOME line had to be picked as '0 degrees' by agreement. In 1884, countries met and chose the line through Greenwich, near London, largely because many ships already used charts based on it. Test it: ask what is physically special about Greenwich itself — nothing; a different meeting could have chosen Paris or Delhi, and all longitudes would simply be counted from there instead. His sister is right: the Prime Meridian's position was a human choice made by international agreement, unlike the equator, which the Earth itself defines.