In Walter Isaacson's book "Einstein: His Life and Universe," it is highlighted that Planck's work was pivotal in the advancement of relativity theory. His insights reinforced the idea that physical phenomena, including the behavior of light, should adhere to the principle of least action. This principle suggests that objects like light should take the simplest path when moving between two points.

Planck's contributions not only laid the groundwork for relativity but also played a crucial role in gaining acceptance for these ideas within the scientific community. By validating the principles underlying relativity, Planck helped shift the perspective of physicists towards embracing these revolutionary concepts, thus shaping the landscape of modern physics.