I want to talk a little about the central idea that led Einstein to the concept of General Relativity. To get there, I want you to perform a little experiment.

Take a moment to think carefully about the forces you feel on yourself right now. If you’re sitting, you feel the chair pushing on your back, which pushes on the rest of your body. You feel the floor pushing your feet up. You might feel the muscles and tendons in your shoulder holding your arm up, or strain your neck holding your head up. 

But do you feel the force of gravity?