Dark Netflix series?

I'm at dark now in season one, where Jonas found in Mikkel hospital in 1986.

My question is now why Jonas Mikkel does not respond?

I mean Mikkel is also from 2019 and would have to remember so after all Jonas.

If he addresses Mikkel in this moment or brings back, he will not be born later and he changes the whole future. You will learn more about this later.

So Erik and Yasin are now in 1986?

And Jonas can just go back through the cave in 2019?

He can go back. Mikkel could do that, but he can't remember how or where.