I know that QFT puts in the coupling constants by hand, based on experiment. And many of the coupling constants are suppose to become equal at the grand unification energy. But I wonder if there is any principle that would allow us to calculate the present day coupling constants based the GUT constants (of 1?)? I've seen the graph that shows the coupling constants meeting at high energies. Is that graph based on calculations? Or is it based on data? Or is it just a schematic?