Up in the air

If you’re working on resolving an issue but the outcome is still uncertain, you can say it’s up in the air. This means that there are still actions or decisions that need to be made before it is settled.

If you’re planning a meeting or business trip but the exact details are not confirmed, you can say it’s up in the air. This implies that you have a general idea of what you’re going to do, but the details still need to be decided.

That train has left the station.

Have you ever asked to add something to a project that's already finished? You might have heard, "I'm sorry, but that train has left the station." That means you can't change it now because it's been finalized.

Most of the time, this phrase is used in informal conversation.

Here are some examples:

A: She wants to change the date for the office party.
B: Are you kidding me? Everything's set for June 12! That train has left the station.