"What happens next?" "Only time will tell."

Here's a dialogue:

a. "What happens next?" "Only time will tell."

Both the sentences describe a future event. But the first is in the present tense, whereas the second is expressed with 'will'.

Why the difference?

Solution 1:

"Only time will tell." This can be interpreted as a prediction or a fact about future.

According to "Grammar and Vocabulary for FCE" by Luke Prodromou, "will" can be used for decisions made at the moment of speaking, predictions (often with I believe, expect, etc.), offers or willingness, requests, firm intentions and promises, threats and facts about future.

The present simple tense can also be used to talk about future. It often happens when we talk about timetables, but it's not the case here. The question "what happens next?" sounds like the speaker feels the future is mapped out, if you like. If they don't, why do they ask? After all, no one knows what the future holds. Do you see what I mean?

However, someone may say "what happens next?" asking about events described in a book or a film. The Present Simple is used for that. But the answer "only time will tell" makes it clear we are not talking about this kind of situation.