What does Dr. Heidegger discover through his experiment

The lesson that Hawthorne intends to show in his short story "Dr. Heidegger's Experiment" is that if people were ever to be given the opportunity to go back in time, they would also revert back to all the behaviors that characterized them at the time. In essence, people would likely not change. The key reason is simple: people are who they are, no matter in what place or time they exist.

In the story, Dr. Heidegger intends to conduct an experiment where he will give four eccentric old people a youth elixir. He warns them, however, not to allow the feelings of youth to make them go back to committing the same foolish acts that were once dictated by their immaturity and naïveté. They are horrified by their return to old age, particularly the Widow Wycherly, who hides her wrinkling face and wails. Dr. Heidegger delivers the conclusion of his experiment: that the water from the fountain of youth is dangerous and transitory, and their actions have shown it should not be meddled with