What @xraymancs said. The pay is low because employers don’t have to pay more. The market is glutted. This was written in 1999, but things have only gotten worse since.
http://physics.wustl.edu/katz/scientist.html
Sorry - but there isn’t always a correlation between how hard something is and the pay in that field.
This isn’t to discourage you from studying physics if that is what you love. Just that if future earnings is the most important factor in what you choose to study, then physics may not be the right field.