1. Instead of a clickable text field that says "Simulation is STOPPED" , use something obviously clickable (obvious even when mouse is not hovering over it), like a button, and make it say "Start Simulation" . Likewise, instead of "Simulation is ACTIVE" , make the button say "Stop Simulation" . [more specific version of thehickmans' suggestion]
2. Make active the default state, i.e. the button says "Stop Simulation" by default. [seconding psyklic's suggestion]
1. Instead of a clickable text field that says "Simulation is STOPPED" , use something obviously clickable (obvious even when mouse is not hovering over it), like a button, and make it say "Start Simulation" . Likewise, instead of "Simulation is ACTIVE" , make the button say "Stop Simulation" . [more specific version of thehickmans' suggestion]
2. Make active the default state, i.e. the button says "Stop Simulation" by default. [seconding psyklic's suggestion]