Thus, in the infinity of time, the life of the Universe proceeds without real stop.
This conception is, moreover, in accordance with the view certain physicists take of the principle of Carnot.

We shall see, for example, that in the kinetic theory we are led to admit that, after waiting sufficiently long, we can witness the return of the various states through which a mass of gas, for example, has passed in its series of transformations.
If we keep to the present era, evolution has a fixed direction--that which leads to an increase of entropy; and it is possible to enquire, in any given system to what physical manifestations this increase corresponds.

We note that kinetic, potential, electrical, and chemical forms of energy have a great tendency to transform themselves into calorific energy.

A chemical reaction, for example, gives out energy; but if the reaction is not produced under very special conditions, this energy immediately passes into the calorific form.

This is so true, that chemists currently speak of the heat given out by reactions instead of regarding the energy disengaged in general.
In all these transformations the calorific energy obtained has not, from a practical point of view, the same value at which it started.
One cannot, in fact, according to the principle of Carnot, transform it integrally into mechanical energy, since the heat possessed by a body can only yield work on condition that a part of it falls on a body with a lower temperature.