Newtonian mechanics still correctly predicts the behavior of things that are big and slow, e.g. bowling balls. Therefore, in the limit as things become big and slow, any future theory of physics has to reduce to Newtonian mechanics.
Alternatively and more specifically, special relativity is constrained by the fact that it has to reduce to Newtonian mechanics in the limit as the speed of light tends to infinity, and quantum mechanics is constrained by the fact that it has to reduce to Newtonian mechanics in the limit as Planck’s constant tends to zero. Physicists call this idea taking the classical limit.
Newtonian mechanics still correctly predicts the behavior of things that are big and slow, e.g. bowling balls. Therefore, in the limit as things become big and slow, any future theory of physics has to reduce to Newtonian mechanics.
Alternatively and more specifically, special relativity is constrained by the fact that it has to reduce to Newtonian mechanics in the limit as the speed of light tends to infinity, and quantum mechanics is constrained by the fact that it has to reduce to Newtonian mechanics in the limit as Planck’s constant tends to zero. Physicists call this idea taking the classical limit.