Why do prices keep changing

Wrong. Sometimes value changes. In fact, a lot of time value changes.

This is another part of your problem. EMH is more of a way of looking at the world than anything else. It is basically a tautology for most of its proponants. Bob Murphy has covered this quite extensively actually…

My Response to John Cochrane (Who Was Responding to Krugman)

Economists Can Be Hilarious

Ten Things I Hate About the Efficient Markets Hypothesis

Following the Efficient-Markets Hypothesis into Absurdity

Bursting Eugene Fama’s Bubble

And here’s a nice one from Stefan Karlsson:

Of Course Investors Can Beat the Market

Again, prices change many times because underlying factors change. That’s the way markets work. But as for silver, you have to throw in this too.