The first subject, that of _Evolution_, will be discussed more fully in the next chapter. All that need be said here is, that the atoms of the universe, with their evolving properties, cannot have existed eternally; for then the course of evolution would have commenced in the eternal past, and would therefore have been finished now. But this is certainly not the case, and evolution is still in progress, or at all events was so a few thousand years ago; and a state of progress cannot be _eternal_. It thus differs from a mere state of _change_ which as we have seen, might be eternal, if the changes were recurring. But a state of _progress_, in which the changes are not recurring, but all tend in one direction, can never be eternal. It must have had a commencement. And this commencement cannot have been a necessity, so it must have been due to some Free Force. In short, evolution requires a previous _Evolver_; since it cannot have been going on for ever, and it cannot have started itself. The other theory, that of the _Degradation of Energy_, is that all energy (motion, etc.) tends to _heat_; the simplest instance being that of two bodies hitting each other when a certain amount of motion is lost, and a corresponding amount of heat is produced. And heat tends to be equally distributed. The heat, for instance, which is now stored up in the sun will in process of time be distributed throughout space, and the same applies to the whole universe; so that everything will eventually have the same temperature. And though this may take millions of years, they are yet nothing to eternity. Therefore, if the universe with all its present forces has existed from eternity, and without any external interference, it must have been reduced to this state long ago. So if this theory is correct (and the only reason for doubting it, is the curious behaviour of _radium_), it seems not only probable, but certain, that the universe had an origin. But an objection has now to be considered. It may be said that the above reasoning is merely another form of the old argument, 'Everything must have a cause, and therefore there must have been a First Cause;' the obvious answer to which is, that then this First Cause must also have had a cause, and so on indefinitely. But this is not the case; for the alleged First Cause is of a different _kind_ from all the others. It is a _Free_ Cause, whereas natural causes are not free, but are themselves effects of other natural causes; and these, again, of previous ones. What we want is a cause which is _not_ also an effect, in other words, a cause which is not moved by anything else, but is moved by itself, or _Free_. When once we get to such a cause as this, there is no need for a previous one.