이미(already) vs 벌써(already)

Q. What's the difference between '이미' and '벌써'? 

A. There are similarities and differences. '벌써' has 2 meanings whereas '이미' has one. 

Let's focus on the difference first. 

You can use only '벌써' when it means "the time is earlier than someone's thought."

So, people use this when they are surprised. 

It is used like this,
"와~ 벌써 10시야. 지하철 끊기기 전에 집에 가야겠다."
"Wow, it's already 10 o'clock.
I have to go before the subway closes."

'벌써' has another meaning which is "a long time ago". '이미' has a similar meaning which is "in the past". 

So, you can say it in two different ways.

For example:
"난 그 사람을 벌써 알고 있었어."
(I already knew him for a long time ago)

"난 그 사람을 이미 알고 있었어."
(I already knew him from the past.)

However there could be a different point of speaking. 

You choose '벌써' if you say focus on time like

" 영화 시간에 벌써 늦었지만 극장에 가 봐야겠다.''
"I'm already late for movie time, but I'll try to go to the theater."

On the other hand, you use '이미' if you want to say about the situations or results that are already over like

"이미 비행기를 놓쳤어. 다음 거 타야겠어."
"I've already missed the plane. So, I should take the next plane." 

'벌써' is more common, though.

https://m.blog.naver.com/uzings/221601310663