The Watchmaker: my fav argument

[HappySkeptic]

Hawking's point was not that one can arbitrarily chose any theory you like. 

I don't know whether or not Hawking would agree. But as far as his book is concerned, he only favors one theory over the other on the basis of simplicity (which I would argue is equivalent to being arbitrary). And he seems to leave the actual nature of the universe to philosophy. Here's the rest of his quote for reference:

"Despite its role in philosophical debates over the nature of our universe, the real advantage of the Copernican system is simply that the equations of motion are much simpler in the frame of reference in which the sun is at rest."

Hawking was saying that based on the evidence of the time (both theories being workable but not accurate), this is indeed a factor that a scientist may look at.

However, evidence is far more important.

Quantum Theory is one of the most validated theories in science, but solving the mathematics is difficult for most situations.  The mathematics can be stated in a simple manner -- it just can't be solved.  Difficult mathematics does not make a theory wrong -- it would be a factor only if two theories were equal in all other ways.

Einstein said "A theory should be as simple as possible, but no simpler".  This is another way of saying that the most successful theories predict the most with the least assumptions.  However, one cannot know beforehand how simple a theory must be in order to be correct.  It is a relative thing.

As for choosing a simpler theory (all else being equal) being "arbitrary" -- nothing is farther from the truth.  It is based on logic. 

There are an infinite number of ways that a phenomenon can be explained.  One can always add more baseless pieces to a story to make it work.  However, after a while the story gets convoluted.  This is evidence of failure.  There must exist an explanation that maximally explains the phenomenon, with the fewest assumptions.  This explanation is pragmatically better (and one could argue this is the only thing science deals with), but is also preferred on a logical and philosophical basis. 

Something approaching this explanation must be closer to the "truth" than the infinite number of complicated just-so stories that can be spun.  Yes, that is a bit of a Platonic view of "truth", but I argue that science is a mix of Platonism and Pragmatism.