By the assistance of Ernest Marsden and Hans Geiger, they performed ​an experiment using alpha particles. His experiment showed that ​atoms were mostly empty space by firing alpha particles to gold foil, if ​the plum pudding model were true, a substantial percentage of them ​would have been deflected back, In fact, most of them went through ​the gold foil, if Thompson's theory was correct all of the alpha ​particles would have been deflected by the foil. This is where ​Rutherford's theory comes in, it's called the nuclear model.