system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does a conducter do in an orchestra?
gpt
An orchestra can't be a democracy. He is the man in charge. Apart from the leader of the violins, he is the only person who makes decisions. He controls the expression, the rhythm, the dynamics and the speed of the orchestra. He chooses how to interpret the music, and how he wants the audience to experience it, and he controls the orchestra so that the whole group plays all together it that way, and only in that way. 

Or she, of course.

Conductors don't just beat time. They communicate wordlessly with the orchestra with body language, facial expressions and the size and speed of the pattern they're beating with baton or hand. Even the movements of the fingers have meaning. 

Of course, this isn't to imply that all the musicians are looking at the conductor at all times. Far from it. But at any given moment one of them probably will be, and orchestral musicians are adept at seeing the conductor at the edge of their vision while concentrating on their manuscripts too. The conductor is their common frame of reference.

The best way to get a feel for what a conductor can do is to listen to a piece you think you're familiar with, but recordings conducted by different people. I'd recommend Beethoven's fifth symphony (dadadaDAAAA... dadadaDAAAA). You'll be surprised by how many differences are immediately apparent. That's a particularly good symphony for this exercise, as it builds the simple opening motif up and up and up through layers of complexity using every musical trick in the book. Listen to how different conductors achieve that goal.