How does the future differ from the past? A new model uses quantum mechanics to postulate a block universe in which the past crystalizes out of a fluid and uncertain future.
Today, Ellis and Rothman introduce a significant new type of block universe. They say the character of the block changes dramatically when quantum mechanics is thrown into the mix. All of a sudden, the past and the future take on entirely different characteristics. The future is dominated by the weird laws of quantum mechanics in which objects can exist in two places at the same time and particles can be so deeply linked that they share the same existence. By contrast, the past is dominated by the unflinching certainty of classical mechanics.
What's interesting is that the transition between these states takes place largely in the present. It's almost as if the past crystallizes out of the future, in the instant we call the present. Ellis and Rothman call this model the "crystallizing block universe" and go on to explore some of its properties.
They point out, for example, that this crystallization process doesn't take place entirely in the present. In quantum mechanics the past can sometimes be delayed, for example in delayed choice experiments. This means the structure of the transition from future to past is more complex than a cursory thought might suggest.
Ellis and Rothman suggest that their model provides a straightforward solution to the problem of the origin of the arrow of time. "The arrow of time arises simply because the future does not yet exist," they say.