All I have to say is Yeah Science.
Below you can watch as they shrink a quarter. Even using a proper High Speed camera, they only got 4 frames of the process. That’s freaking fast man. The whole process works by sending tremendous amounts of current through a coil of copper in which the coin is placed. The electricity causes a uniform magnetic field to push the metal together, and evenly shrink the coin. Now, because of the various metals that coins are made of, some work better than others. But all of them are awesome.
It gets better too. If you put 2 coins in at the same time, they get attaracted together and form a crazy Georgia Peach dome like thing.
And if you put square, or other non-round coins in, you get similarly cool shaped novelty items. Take a look at the whole gallery of things, and learn some stuff about science along the way.