system
Given the following post, respond as if you're commenting on Reddit:
human
If entropy always increases then why/how did the universe produce complex life?
gpt
The second law of thermodynamics doesn't say entropy always has to increase everywhere all the time, it says than in an isolated system, entropy must increase. 

We'll first look at a simple system, a bunch of blocks in a box. The blocks in a box will never spontaneously stack themselves, but over time, with any vibrations, movements, etc, a stack of blocks will eventually fall over. But, if you reach into the box, you can stack the blocks into a neat stack. Sure, entropy may have decreased in the box, but that's allowed- the box was not isolated. 

So now, looking at the Earth, for example, it is far from isolated. Earth has a bunch of energy coming to it, mainly from the Sun. So, the entropy on Earth is allowed to decrease, because there is energy supplied from the Sun. 

Now, let's go back to the stacking blocks system. If instead of the box being your system, you and the box are the system, you have to look not just at the entropy of the box, but the entropy of you plus the box. That entropy has went up, even if the entropy in the box has went down, because your motion and thinking to stack the box has created waste heat, which is an entropy increase. So, even in an "isolated system" a small part of that system can have a decrease in entropy, as long as the rest of the system has an equal or larger increase in entropy. 

So, going back to to the Earth. If you make the Earth and Sun your "system" then you can't say that energy is supplied to the system from the Sun, but you're still OK. The entropy of the Sun is increasing as it undergoes fusion, so the entropy of the Earth/Sun system is still increasing.