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Determinism

screen on which each of the light particles (photons) leaves a mark. These marks create a pattern which can be very accurately predicted. However, the exact contribution of each particle cannot be calculated beforehand. The behaviour of individual atomic particles appears to be completely indeterministic – all fundamental particles display completely random behaviour that does not appear to be caused by anything. But where does this leave the physical scientists? Indeterminacy – where the future is underdetermined by the current state of affairs – is where the majority of scientists currently stand. They believe that particles don’t have distinct positions and speeds, but can be characterised by a descriptive tool called ‘wave function’. Each point in space possesses a wave function. The probability that a particle will be found in a certain position is given by the size of the wave function at that point. The speed of that particle is given by the rate at which the wave function varies from one point to another. If, at a certain point, you have a wave function that covers a large region and is not strongly peaked then you have a great deal of uncertainty as to the

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position of the particle, but only a very small uncertainty as to the speed of the particle. Conversely, if, at a certain point, you have a wave function that covers a small region and is strongly peaked then you have a very small amount of uncertainty as to the position of the particle, but a very large uncertainty as to the speed of the particle. Above all, it is impossible to know the velocity of the particle – that is to say, the direction in which is travelling. In combination, these uncertainties make even the theoretical prediction of the future quite impossible.

“I at any rate, am convinced that He does not throw dice” The concept of the wave function follows from Heisenberg’s 1926 ‘Uncertainty Principle’. Heisenberg states that the position and speed of a particle can never be measured exactly; the more accurately you know the position of a particle, the less

accurately you know its speed, and vice versa. The inability to ever know the exact position and speed of a particle is related to the ‘observer effect’. Simply put, when attempting to measure the position and speed of a particle, the observer will always have some effect on the outcome, and this can never be eradicated. The best one can hope for is to make the observer effect as small as possible. However, many notable physicists have not and do not hold the indeterminacy view. Einstein, for example, simply could not accept the probabilistic behaviour seen at the atomic level, which led to his infamous statement, “I at any rate, am convinced that He [God] does not throw dice”. Einstein instead subscribed to the notion of ‘hidden variables’. This theory argues that Laplace was correct; the course of the universe is absolutely determined, it’s just that we as humans are unable to see the underlying determinative factors. Hence, it is simply an illusion that everything proceeds in a probabilistic way. If hidden variables exist then many statistical predictions made by quantum mechanics would be rendered completely false. However, experiments conducted over the past four decades have found no evidence for these variables, and Quantum Theory has, as a result, become the model of ‘best fit’. Despite numerous problematic areas, mainstream science has been left with little choice. It must progress on the assumption that quantum theory is correct. However, it is clear, despite popular scientific consensus, that the debate over determinism at the atomic level is still very much open. Although evidence appears to side with quantum mechanics and indeterminacy, there are still many issues to consider. It has taken many, many decades for scientific opinion to shift towards the acceptance of quantum mechanics and the idea of randomness. It would take far less time to swing back to a more Newtonian model if reasonable evidence was presented. The logical and observable will always be easier to accept. Although it might intuitively feel wrong, there is more logical sense in the idea that the future of the universe is predictable than the idea that random activity can exist. Despite science’s ongoing quest for answers, all it is finding in the area of determinism is more questions. V

VIVID 2nd Edition March 2008

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Determinism V The concept of the wave function fol- lows from Heisenberg’s 1926 ‘Uncertainty Principle’. Heisenberg states that the posi- ti...