**Critical Questions:**

- Why can’t we build a machine with 100% efficiency?

After a shamefully long delay, let’s take a look at the consequences of entropy. In the previous section, I described entropy as a measure of the statistical probability of a state.

One of the most significant results of this kind of thinking is that, because high-entropy states are more likely than low-entropy ones, the total entropy of the universe will always tend to increase over time. We have to say “tend to” here because things like all of the air particles in a room jumping to one side can, technically, happen. But if every process obeys this statistical reasoning, then instances of spontaneous entropy decrease are so unlikely that they are essentially impossible, so the total entropy of everything will always be naturally increasing.

Here’s where we can connect things back to energy. First of all, if you want to reduce the amount of entropy in a certain area – like arranging the bricks into a wall – you have to expend some energy.