Earlier quoted context omitted.
Just remember under the covers Akka is still using synchronization.
You mean internally? The paradigm they use is immutable-message passing and asynchronous/concurrent processing.
Yes internally. Somewhere deep in the bowels of the akka code, they are communicating state between threads (last I checked they were using a java concurrent queue by default).
At a bare minimum the changes to the location of the head/tail of a queue will need to be visible to multiple threads requiring volatile variables.
The java concurrent queues don't actually use synchronization blocks, they use native CAS operations but thinking that akka removes shared thread state entirely is dangerous.