Science. The universe has no source code for us to read, so we tinker and investigate, take our best guess, see if it holds up under the test cases we're capable of running, and update that guess whenever we encounter edge cases the last guess can't explain. We've gotten quite far without perfect understanding.
I have a feeling that the distribution of complexity in the laws of the universe is likely to be very, very different from the distribution of complexity in code created by an extremely intelligent being (with machinelike memory) that isn't optimizing for simplicity.
