Introduction

• Einstein’s most famous challenge to the Copenhagen interpretation
• The prospects of hidden variables
• Quantum entanglement and its meaning
• How quantum physics is at odds with relativity

We will continue to dig deeper into the basic question of what quantum physics actually means. We have become familiar with many ways in which this theory challenges traditional understandings of science, reality, and even common sense. Now we will look at some of the ways quantum physics responds to these challenges.

Along the way, we’ll be forced to question whether our ideas of objective reality are valid in the quantum world, or whether basic rules of logic apply. Disagreements among physicists and philosophers persist even today, and probably will for a long time to come. So we can’t give the final word on this yet. But as we’ll see, experimental evidence might help us decide which common sense ideas we can keep and which we have to let go.