Forgiveness is not a measurable thing. Forgiveness can sometimes seem trivial to the bystander, or forgiver, but priceless to the forgiven. Something may seem unforgiveable to a bystander but not to the forgiver or forgiven. Something might even be trivial to the bystander or the forgiven, but unforgiveable to the forgiver.
For example, a window broken by an errant baseball. To the one who lost the window: trivial. To the bystander: trivial. To the one who broke the window: priceless
Science is built on measured values that don't change with the circumstances. The nature of forgiveness defies this certainty, and makes scientific understanding impossible. Nonetheless, research is ongoing relating to psychological study and genetic study that may make a scientific explanation of forgiveness more clear.