Is Physics the Same Everywhere?
As early as 1916, Eddington proclaimed that the stars obey the same laws of physics as we discover in the laboratory. The known universe was small in those days, but today we can observe much further away and look back many more millions of years in time. The obvious question to ask is: were the laws of physics in general, and spectroscopy in particular, valid, say, 5 billion years ago? How confident can we be in the derived abundances of the elements, in objects that are ten billion light years away, using the physical laws we find today?