The way things are traditionally presented about time, there is the present, the past is fixed, and the future is open. The second law of thermodynamics is invoked. But how can we be so sure the past is fixed?

Some musings on this topic can be found on [this blog post](http://blogs.discovermagazine.com/cosmicvariance/2008/01/14/boltzmanns-universe/). The past is fixed because there are memories and records of the past. Memories and records are macroscopic averages over microstates. A generic typical state of the universe constrained only by the macroscopic records and memories with the unconstrained microstates varying randomly will increase in entropy in both directions toward the future and past. This is none other than the Boltzmann brain hypothesis. The universe starts off with a random high entropy configuration, accumulates miraculous random fluctuations over time to become more and more ordered, and conspires to a marcostate which apparently tell the story of a past which never happened. How can we know the past is what it is without making the further assumption that the entropy in the past was far lower than what it is now?

An alternative coherent hypothesis is there is a malicious demon who deliberately planted fake memories and records to make it seem as if the past were something it was not. Is there any convincing way of ruling out this hypothesis?