Reaction time is how fast you respond to outside stimuli. Every action you do has to go through your brain to be processed before your body can start moving, sort of like a computer. Whatever the stimulus may be, whether it’s the smell of your neighbor’s grill wafting through the air or the sunshine warming your skin at the beach, your senses are immediately stimulated. The final result is a physical response to the stimulus, a process that happens in just fractions of a second.