Where Did the Energy Come From? A Physics Puzzle on Entropy and Magnetism

[luthier]

First off, I may or may not know the correct answer to this one...
Here it is..

I have a set of say 100 small perminent magnets which are randomly oriented
in space. I also have an empty burlap sack. I grab each of the magnets one at
a time and throw each one into the bag until all 100 are in the bag.
I then look inside the bag to find that all 100 magnets have attached themselves
to one another to form a single well ordered block of 100.

Remember that there is a law which states that in order to lower entropy you
must add energy in order to "pay" for the decrease in entropy.
The magnets went from a maximum entropy state to one of nearly the most ordered
orientation. Where did the energy come from to lower the entropy ?

Tim

 

[Born2bwire]

The magnetic field stores energy. When two bar magnets come together (or any set of magnetic dipoles) the resulting net magnetic field is weaker in the amount of energy stored than the fields produced when the two magnets are apart. The energy injected or extracted from the fields is the work done on or by the magnets when they are physically moved in the vicinity of each other.

 

[luthier]

Ok, I guess I will have to come up with a better one ! :-)