[Physicist]

Causality is defined in the link---> (d < d_H).

Causality means that causes always precede effects. Do you understand why d < d_H is equivalent?

It is obvious that the horizon expands at the speed of light.

As a matter of fact, during inflation the horizon shrinks.

[AndrewC]

As a matter of fact, during inflation the horizon shrinks.

Isn't that the problem?(things move outside the horizon)