ilya_prigogine_isabelle_stengers_alvin_tofflerbookfi-org

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245 THE CLASH OF DOCTRINES
with disks on lattice sites with an isotropic velocity distribution.
The results follow Boltzmann's predictions.
If, after fifty or a hundred collisions, corresponding to about
I0-6 sec in a dilute gas, the velocities are inverted, a new ensemble
is obtained.15 Now, after the velocity inversion, Boltzmann's
J{ quantity increases instead of decreasing.
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Figure 27. Evolution of :H when velocities are inverted after 50 or 100
collisions. Simulation with 100 "hard spheres."
A similar situation can be produced in spin echo experiments
or plasma echo experiments. There also, over limited
periods of time, an "antithermodynamic" behavior in Boltzmann's
sense may be observed.
But it is important to note that the velocity inversion experiment
becomes increasingly more difficult when the time interval
t0 after which the inversion occurs is increased.
To be able to retrace its past, the gas must remember everything
that happened to it during the time interval from 0 to t0•
There must be "storage" of information. We can express this
storage in terms of correlations between particles. We shall
come back to the question of correlations in Chapter IX. Let
us only mention here that it is precisely this relation between
correlations and collisions that is the element missing from