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Friday, December 18, 2015

Is Quantum Weirdness Confined to the Micro Scale?


Physics is very good at producing pristine models clear of noise that perform over time exactly as predicted. This became a world view known as ‘determinism’, that if you knew enough about the initial conditions of a system with sufficient precision you could predict all future events associated with that system.
Whilst precision was never sufficient to predict the state of a system perfectly for long, any deviation was seen as the result of noise, variables not identified or lack of precision of the measuring instruments.
This all changed with the discovery of quantum uncertainty and the probabilistic nature of events at the quantum scale. Even though the macro world is built upon the quantum world, the old world view persists anyway on the macro scale. But are we just choosing not to look at the macro world, the world of the human scale, in a way in which the uncertainty known at the quantum is not in evidence?
Ordinary people believe that the future is uncertain and use language to describe it that is more like scientist’s description of the probabilistic quantum world. The assumption has always been that individuals simply can’t have enough information about current conditions to predict future events. But does predictability have a thermodynamic nature in that only closed systems, those swept of noise, are actually predictable and only when there are large numbers of particles? Are open systems intrinsically unpredictable due to the accumulation of uncertainty?
Let us consider a photon emitted from some point and interacting without being absorbed. The probabilistic nature of the photon’s path spreads from each point of interaction (see the attached illustration). Looking back from the point of interaction we can determine the photon’s path (or confine the probable paths) but looking forward we can only say that the photon will take one of the possible paths but not which path it will take.
If, instead of a single photon we project a laser beam then the majority of photons will follow the shortest path between emitter and absorber, but all other possible paths are still in play. So the beam is more predictable than the single photon.
Now we consider the point of interaction. Let us call the interaction point ‘The Present’, the path followed to that point ‘The Past’ and the field of possible paths to the absorber ‘The Future’. Does this look familiar to us? Of course it does, that is our lives. Looking back from the present we can see the path we took to arrive at where we are today, or limit the possible paths we could have taken, and looking into the future we see the possible paths spread out into a field of possibilities.
In physics we typically have a time line with a future and past and events arrayed quite differently to the above description. Why the big difference? The answer is that we typically map the evolution of interaction points, the present, and never the future and past fields if they can be avoided. Thus we do not identify a fixed point and consider the future and past *relative* to that point but map only the ‘present’ at a future or past time (hence the imagined time travel to ‘the present’ at a different point on a timeline). This is actually very similar to the more deterministic past in the illustration. Shift the observation point to half way between the interaction point and the emission point on the left in the illustration and you have something resembling a standard timeline presentation.
In the quantum world we effectively see ‘chunks’ of time which include the particle’s more deterministic past and indeterminate future. We do not normally see chunks of human time, we never ‘see’ the array of future paths, we tend to see the world from the interaction point, the present, unless we are looking at, for instance, a newborn baby in which case there is so little past that we can only see (in our imagination) the array of possible paths from the present and the probabilistic nature of the baby’s future.
Viewed from a sufficiently objective distance, the human world includes many of the unusual conditions thought to be confined to the quantum world alone smile emoticon