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The psychological/perceptual arrow of time

This is the most obvious arrow in human experience: We feel as if we are travelling from the past to the future; we perceive and remember the past and not the future (although sometimes these are treated as two different phenomena). However, because the workings of the mind are so complex and little understood, it is not obvious how the physical arrows of time contribute to this perception. It may be that learning to generate the causes needed to produce desired effects embedded the causal arrow in our perception.

It has also been argued that the arrow of time as we perceive it results from the influence of the second law of thermodynamics on the evolution of the brain, so that the psychological arrow follows from the thermodynamic. To remember something, our memory goes from a disordered state to a more ordered one, or from one ordered state to another. To ensure that the new state is the correct one, energy must be used to perform the work and this increases the disorder in the rest of the universe. There is always a greater increase in disorder than the amount of order gained in our memory, thus the arrow of time in which we remember things is in the same direction as that in which the disorder of the universe increases.

The link between this arrow of time and the thermodynamic arrow of time is best understood if we remember that the Second Law of Thermodynamics dictates that correlations between different parts of a system will be increased towards the future (rather than towards the past). Since memory is correlations between our brain cells (or computer bits) and the outer world, it is obvious why memory should be created as time passes (towards the future) rather than vice versa (towards the past). Additionally, our deeds may affect the future but not the past because affecting the outer world means to create correlations between ourselves (our bodies or brains) and the outer world.