17 mei 2010

The Twisted Arrow of Time


It's tempting to think of time as a linear sequence of events best captured by a straight line, the x-axis on a graph for example. But physicists have never felt constrained by such a definition, on the contrary they've never hesitated to mould time to their own ends. In thermodynamics, for example, the arrow of time comes about because of irreversible phenomena such as phase transitions, bifurcations and chaos. In relativity, space and time are as one, and Minkowski, in his famous formulation, used the idea of a 'causality cone' to explain the correlation between physical objects. In quantum mechanics, the notion of time becomes even more strange. Time is sometimes two-dimensional, sometimes reversible to maintain CPT (charge, parity, time) symmetry and at other times discontinuous and fractal-like.
In short, physicists reformulate time in whatever suits them, or at least in whatever way provides the best predictive or explanatory power. So why shouldn't biologists try the same trick? Today, they get their chance thanks to some innovative thinking by Giuseppe Longo at the Ecole Normale Superieure in Paris et deux amis.
Longo and co argue that biological entities require a non-linear formulation of time because their existence is characterised by rhythms and cycles rather than linear processes.
So the team has formulated a notion of time which captures the essential rhythms and cycles of biology.

read on...

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