[Sidenote: Confusion arising from prediction of astronomical phenomena.]
What makes the confusion a natural and almost an unavoidable one is that science seems to point to many cases where we do anticipate the future. Do we not determine beforehand the conjunctions of heavenly bodies, solar and lunar eclipses, in short the greater number of astronomical phenomena? Does not, then, the human intellect embrace in the present moment immense intervals of duration still to come? No doubt it does; but an anticipation of this kind has not the slightest resemblance to the anticipation of a voluntary act. Indeed, as we shall see, the reasons which render it possible to foretell an astronomical phenomenon are the very ones which prevent us from determining in advance an act which springs from our free activity. For the future of the material universe, although contemporaneous with the future of a conscious being, has no analogy to it.
[Sidenote: Illustration from hypothetical acceleration of physical movements.]
In order to put our finger on this vital difference, let us assume for a moment that some mischievous illustration genius, more powerful still than the mischievous genius conjured up by Descartes decreed that all the movements of the universe should go twice as fast. There would be no change in astronomical phenomena, or at any rate in the equations which enable us to foresee them, for in these equations the symbol _t_ does not stand for a duration, but for a relation between two durations, for a certain number of units of time, in short, for a certain number of _simultaneities:_ these simultaneities, these coincidences would still take place in equal number: only the intervals which separate them would have diminished, but these intervals never make their appearance in our calculations. Now these intervals are just duration _lived,_ duration which our consciousness perceives, and our consciousness would soon inform us of a shortening of the day if we had not experienced the usual amount of duration between sunrise and sunset. No doubt it would not measure this shortening, and perhaps it would not even perceive it immediately as a change of quantity; but it would realize in some way or other a decline in the usual storing up of experience, a change in the progress usually accomplished between sunrise and sunset.