[nonethewiser]

> Nobody is going to adjust your birthdate when you move abroad.

But that’s just a convention, right? The day you are born is still dependent on the time zone. If you are born in the US at 11pm EST then someone born at that same moment in the UK has a different birthday.

Dates have boundaries. These boundaries are dependent on time zone. We can talk about dates irrespective of time zone but day periods cannot be understood without reference to time zone.

[throwmeaway1212]

You are mixing two things up into one conversation. You are adding time into the conversation, in which case yes you need timezones, but if you don't add time into the conversation and just have dates, then you don't have timezones.

[paulddraper]

> But that’s just a convention, right?

Yes, "just."

Dates are "just" a convention.