Questions on Laws of Nature

1. Are there really such things as Laws of Nature? If there aren't then what are scientists doing? And if there are, are they discovered by us or invented by us? (This is similar to the question about mathematical Truths: do we discover them or create them?)

2. One of the System Solution criteria for the problem of identifying Laws of Nature was the simplicity of the systems in which they occur (as opposed to the non-simplicity of systems that include 'accidental uniformities.') What makes a system simple - i.e. how would we compare the simplicity of two systems?

3. Could aliens with alien minds have different Laws of Nature in their Science? 

4. Hume thought that experience wasn't able to produce the concept of necessity that we want to have between causes and effects, but I suggested that we could take the concept of necessity that we are familiar with from ethics, maths, etc. to be the right sort of necessity. Do you think that concept is similar enough? Are there in fact several concepts of necessity? Is there a problem with believing that those are justifiable concepts? Where do they come from?