For two centuries Newtonian physics had successes unparalleled in the history of science, but toward the end of the 19th century several experiments produced results that had not been anticipated. These results defied explanation with Newtonian physics, and this failure led in the early 20th century to what is called modern physics. Modern physics has two important pillars: quantum mechanics and general relativity. Quantum mechanics is the physics of small systems, such as atoms and subatomic particles. General relativity is the physics of very high speeds or of large concentrations of mass or energy. Both of these realms are beyond the scope of everyday experience, and so quantum mechanical and relativistic effects are not usually noticed. In other words, Newtonian mechanics, which is the physics of everyday experience, is a special case of modern physics.
Some creation scientists view both quantum mechanics and general relativity with suspicion. Part of the suspicion of quantum mechanics stems from the Copenhagen interpretation, a philosophical view of quantum mechanics. In quantum mechanics, the solution that describes location, velocity, and other properties of a particle is a wave function. The wave function amounts to a probability function. Where the value of the wave function is high, there is a high probability of finding the particle, and where the value of the wave function is low, there is a small probability of finding the particle. This result is pretty easy to understand when one considers a large number of particles—where the probability is high there is a greater likelihood of finding more particles.
However, how is one to interpret the result when considering only a single particle? The Copenhagen interpretation states that the particle exists in all possible states simultaneously. The particle exists in this weird state as long as no one observes the particle. Upon observation we say that the wave function collapses and the particle assumes some particular state. If the experiment is conducted often enough, the distribution of outcomes of the experiment matches the predictions of the probability function derived from the wave solution.