Uncertain times Time is perplexing, or rather, our perception of it is. Why do we remember the past but not the future? Why do we travel inexorably forward in time? Historically physicists from Newton's time onwards have considered the world to be essentially deterministic, i.e. given a sufficiently precise knowledge of the current state of things, and a sufficient grasp of the laws of physics, one could in principle predict the future unfolding of reality indefinitely far into the future with total accuracy. Quantum theory introduces Heisenberg's Uncertainty Principle, which imposes a fundamental limit on the precision with which we can simultaneously gauge the momentum and position of a particle. Consequently the future of things ceases to be predictable (although one can still make probabilistic judgements concerning likely developments). Supposing the universe was deterministic; what would be the implications for our perception of time? Let's consider a computer - a device to which we can attribute an arbitrarily high amount of processing power. Assuming that this device is capable of perceiving the world around it to an arbitrarily high level of precision, it will also be capable of determining the future events that derive from the present state of things. Having a conscious perception of these future events, and a certainty as to their accuracy, is surely not practically distinguishable from having a recollection of past events. In summary then, in a deterministic universe it is possible to create an entity which can effectively 'remember' both past and future events, and therefore has no perception of the 'arrow of time'. I therefore suggest that the Arrow of Time is a consequence of the Uncertainty Principle, and without it, in principle the sense of ‘passage of time’, the past, the present and the future, would have no meaning.